Patent Application
20230414888
The present disclosure relates generally to respiratory assist devices. More specifically, the disclosure relates to a respiratory fluid control device or adapter for delivering and calculating a total volume of gas delivered to a patient.
Positive airway pressure therapies are used for the treatment of various respiratory conditions including both central apnea and obstructive apnea. During sleep or sedation, it is common in patients for the muscles that normally hold the upper airway open to relax so that airway tissues partially occlude or obstruct the airway, preventing adequate gas flow to the lungs. In many patients that are in a relaxed state such as sleeping or who have received sedative drugs, the muscles of the upper airways are relaxed to such an extent that any effort to inhale by the patient collapses the airway and obstructs gas flow restricting ability to draw in breathable gas. The negative pressure created as the patient tries to draw gas into the lungs pulls the airway closed even more, exacerbating the problem.
Positive airway pressure (PAP) therapies use a breathing mask and a source of flowing breathable gas to create positive pressure in the airway. This positive pressure supports the airway opening such that it does not collapse as the patient inhales. The flow generator used for PAP must have sufficient flow to supply patient inhalation volume and compensate for any mask leak. The flow generator must also have sufficient positive pressure to counterbalance any negative pressures created by the patient during inhalation. Continuous positive airway pressure, or CPAP, is a specific PAP therapy that continuously applies a specific prescribed pressure to the airways. CPAP forces the airway to stay open during inhalation so that breathable gas can pass freely into the lungs on demand even when the airway opening is relaxed.
According to the present disclosure, a system for determining total flow output from a flow generator can include: the flow generator for connection to a patient interface; the patient interface in communication with a patient interface pressure sensor to measure a patient interface pressure at the patient interface; an oxygen input line for conveying oxygen from a source of oxygen to the flow generator, the oxygen input line comprising an oxygen flow valve for controlling a flow of oxygen from an oxygen source to the flow generator, and an oxygen input line sensor for determining oxygen input line flow; and wherein the patient interface pressure sensor and the oxygen input line sensor are in communication with a controller, the controller programmed to receive the patient interface pressure and the oxygen input line flow and determine the total flow output from the flow generator based on the patient interface pressure at the patient interface and the oxygen input line flow.
In some configurations, the oxygen input line sensor comprises a pressure sensor for measuring oxygen input line pressure and wherein the oxygen input line flow is determined by the oxygen input line pressure. In other examples, the oxygen input line sensor comprises an oxygen flowmeter for measuring an oxygen input line flow. The controller can be programmed to determine the total gas flow output from the flow generator based on the patient pressure at the patient interface and the oxygen input line flow. In some examples the controller is programmed with at least one algorithm to calculate total flow output based on known patient pressure at the patient interface and known oxygen input line flow.
In some examples, a method for determining total flow generator flow output can include the following steps: obtaining, by a processor, information relating to a patient interface pressure and an oxygen input line flow; and determining, by the processor, a total flow generator flow output based on the patient interface pressure and the oxygen input line flow. The method can also include the step of obtaining, by a processor, information relating to a flow generator type; and wherein the step of determining, by the processor, a total flow generator flow output comprises determining, by the processor, the total flow generator flow output based on the patient interface pressure, the oxygen input line flow, and the flow generator type. The controller may be programmed with at least one algorithm to calculate the total flow generator flow output based on known patient interface pressure at the patient interface and known oxygen input line flow.
According to another aspect, a system is described for determining an amount of gas inhaled by a patient. The system can include: a flow generator for connection to a patient interface; the patient interface in communication with a patient interface pressure sensor to measure patient interface pressure at the patient interface; an oxygen input line for conveying oxygen from a source of oxygen to the flow generator, the oxygen input line comprising an oxygen flow valve for controlling a flow of oxygen from the source of oxygen to the flow generator, and an oxygen input line sensor for determining an oxygen input line flow; wherein the patient interface pressure sensor and the oxygen input line sensor are in communication with a processor, and wherein the processor is programmed to receive, during a pause between a patient exhalation and a patient inhalation, the patient pressure at the patient interface and the oxygen input line flow and determine a leak flow output from the flow generator based on the patient pressure at the patient interface and the oxygen input line flow during the pause between the patient exhalation and the patient inhalation; wherein the processor is further programmed to receive, during the patient inhalation, the patient pressure at the patient interface and the oxygen input line flow and determine a total flow output from the flow generator based on the patient pressure at the patient interface and the oxygen input line flow during a patient inhalation; and wherein the processor is further programmed to calculate a patient flow by subtracting the leak flow output from the total flow output.
The processor can be programmed to calculate a tidal volume of gas by integrating the patient flow over a single breath. The controller can be programmed with at least one algorithm to calculate total flow output based on known patient pressure at the patient interface and known oxygen input line flow. The controller can further be programmed to calculate a concentration of oxygen in the patient flow to determine a fraction of inhaled oxygen.
According to another aspect, the system further comprises a housing, the controller, the oxygen flow valve, and the patient interface pressure sensor located within the housing, the housing having a coupler to couple to the source of oxygen to the housing, and the housing have a receptacle; and wherein the flow generator is coupled to a proximal end of the oxygen input line, and wherein a distal end of the oxygen input line comprises a connector to connect to the receptacle of the housing, the connector comprising a type-identifier, and the receptacle comprising a reader in communication with the controller, the reader to read the type-identifier and convey the type-identifier to the controller.
In yet another aspect, a method for calculating patient tidal volume of gas inhaled includes: obtaining, by a processor, information relating to a patient interface pressure and an oxygen input line flow, determining, by the processor, a total flow generator flow output based on the patient interface pressure and the oxygen input line flow, obtaining, by the processor, a leak flow, calculating, by the processor, patient flow by subtracting the leak flow from the total flow generator flow output; calculating, by the processor, patient tidal volume of gas inhaled by integrating the patient flow over a single breath. The step of determining, by the processor, a flow generator total flow output based on the patient interface pressure and the oxygen input line flow, can include the processor determining the flow generator total flow output based on at least one of: a pre-defined mathematical function stored in a memory accessible by the processor, a lookup table stored in a memory accessible by the processor, and a trained artificial neural network stored in a memory accessible by the processor. In some examples, the method further comprises the step of calculating a concentration of oxygen in the patient flow to determine a fraction of inhaled oxygen.
According to another aspect, a method for calculating a percentage of oxygen in a volume of gas inhaled during an inhalation can include the steps of: obtaining, by a processor, information relating to a flow generator input; obtaining, by a processor, information relating to a flow generator output; determining, by the processor, an oxygen leak flow, calculating, by the processor, a percentage of oxygen in a volume of gas inhaled by: adding 21% of a difference between a total oxygen flow generator flow output and a total oxygen flow generator flow input over a time of the inhalation to the total oxygen flow generator flow input over the time of the inhalation, subtracting the oxygen leak flow over the time of the inhalation to determine a volume of oxygen inhaled; and dividing the volume of oxygen inhaled by a total volume of gas inhaled. The step of determining, by the processor, the oxygen leak flow, comprises determining, by the processor, a pause period between a patient exhalation and a patient inhalation, and wherein the method further comprises the steps of: obtaining, by a processor, the flow generator output during the pause period between the patient exhalation and the patient inhalation; and determining, by the processor, a flow generator leak flow based on the flow generator output during the pause period.
The drawings are illustrative and not limiting of the scope of the invention which is defined by the appended claims. Not every element of the disclosure can be clearly displayed in a single drawing, and as such not every drawing shows each element of the disclosure. The components in the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding parts throughout the several views.
The present disclosure relates generally to a system and device for improved oxygen delivery to a patient as well as a method of measuring volume of gas inhaled by the patient. As used herein, “proximal” refers to a portion of the system or device that is closer to the patient when in use, and “distal” refers to a portion of the system or device that is farther from the patient when in use. For example, the system described herein may be used in conjunction with a patient's mask and the proximal end of the mask is the end closer to the patient and the distal end is the end farther from the patient. The system described herein may include a CPAP adapter or flow generator, and as used herein, “flow generator” means any type of fluid flow control apparatus, such as an adapter, a flow generator, a Venturi adapter, or any other device that can be connected to a patient interface (such as a mask) to input a high pressure oxygen flow into the adapter and output from the adapter a low pressure of oxygen and/or a low pressure of oxygen blended with ambient air. The patient interface could be a mask, an endotracheal tube, a supraglottic airway device (a laryngeal mask airway is common), etc.
Referring to
Flow generator 14 can be any suitable flow generator known in the art. Flow generator 14 can have known characteristics that are pre-determined or pre-measured. For example, a flow generator with a particular nozzle configuration and dimensions, can have a known or pre-determined oxygen flow output at various oxygen input line pressures and patient interface pressures as described in more detail below. The flow generator 14 takes an input of low-flow, high-pressure compressed oxygen and outputs a high-flow, low-pressure gas source suitable to provide CPAP therapy even in the presence of mask leak.
Flow generators 14 generally use a high velocity jet of oxygen inside of the body of the flow generator to draw in ambient air, thereby creating a higher flow oxygen/air gas blend. The high velocity jet of gas is created by passing high-pressure oxygen through a small-orifice nozzle in the adapter. Because air and oxygen are viscous gases, the jet of oxygen that exits through the small-orifice nozzle pulls ambient air into the flow generator 14 through ports such that when flow is unobstructed, the total flow at the outlet (on the proximal mask/patient side) of the flow generator 14 is much greater than the flow of oxygen input through the small-orifice nozzle. Efficient flow generators 14 generate an output flow that is many times greater than the input flow of oxygen through the small-orifice nozzle, where efficiency is calculated as the quotient of output flow over input flow. The efficiency of the flow generator can be raised by, among other things, increasing the velocity of oxygen as it exits the small-orifice nozzle. Several variations of nozzles are possible, and U.S. patent application Ser. No. 17/737,829, which is incorporated herein by reference in its entirety, describes some exemplary flow generators 14 which can be used in system described herein. Other flow generators known in the art can also be used.
In some configurations the flow generator 14 includes one or more unique identification markers. This unique identification marker can include details relating to the flow generator 14, such as the dimensions of the flow generator and the configuration of the nozzle(s). The controller 40 may be able to automatically determine what type of flow generator 14 is being used by reading or receiving the data from the unique identification marker. For example, near-field communication, RFID, Bluetooth, or other wireless protocols can communicate the data associated with the unique identification marker of the flow generator 14 to the controller 40. Or wired communications can also be used. In other configurations described below, the unique identification marker is included on a connector which is connected to a housing that houses the controller 40.
The flow generator 14 is used to generate a flow into the patient interface 18. Patient interface 18 can include any suitable interface. Masks that cover the nose and mouth are common, and endotracheal tubes, supraglottic airway devices, etc., are also possible. In configurations where the patient interface 18 is an endotracheal tube, the system can include software for controlling the oxygen valve to turn the oxygen flow on and off for a certain duration and at a certain frequency for moving gas in and out of the lungs.
While in use, the patient interface 18 has a pressure which is caused by several different factors. For example, as the patient breathes in, it causes a negative pressure in the patient interface 18. Similarly, the pressure exerted on the patient interface 18 by the flow generator 14 causes a negative pressure. As the patient breaths out, it causes a positive pressure in the patient interface.
The pressure in the patient interface 18 is measured by a patient interface pressure sensor 22. The patient interface pressure sensor 22 can be located on the patient interface 18, or the patient interface pressure sensor 22 can be in fluid communication with the patient interface 18. The patient interface pressure sensor 22 can be in communication with one or more processor(s) 40. The processor(s) 40 can receive data, either directly or indirectly, from the patient interface pressure sensor. The communication can be either wired or wireless depending on the desired configuration.
Oxygen from oxygen source 44 is delivered to the patient interface 18 through oxygen input line 27. In the exemplary configuration shown in
Oxygen control valve 31 can be in communication with controller 40 to control the oxygen control valve 31. The controller 40 may be used to control the oxygen control valve 31 to deliver a specific flow rate of oxygen to a patient. For example, the controller may set a flow rate that changes up to 100 times per second according to variables such as the desired oxygen delivery for the particular patient. The variable-type of flow control valve 31 may be, for example, those known in the art such as the EVP Series Proportional Control Valves manufactured by Clippard Instrument Laboratory, Inc. In other configurations, a separate oxygen control valve 31 may not be provided.
The oxygen flow from the oxygen source 44, when connected to the flow generator 14, converts high pressure oxygen (which is typically around 55 pounds per square inch) into a low pressure oxygen/air blend suitable for CPAP therapy (typically less than 0.35 pounds per square inch or 25 cm H2O). The flow generator 14 is capable of supplying gas to the patient at high flow rates so that it can maintain patient interface pressure even when the patient is inhaling or when the patient interface 18 leaks. The patient interface pressure sensor 22 can be connected to the patient interface 18 so that controller(s) 40 can receive the patient interface pressure and automatically adjust oxygen flow by adjusting oxygen control valve 31 to maintain the patient interface pressure at the prescribed CPAP pressure.
In the exemplary configuration shown in
In some configurations, an oxygen input line sensor 35 comprises a pressure sensor 37 (
Because the pressure in the oxygen input line 27 is much higher than the pressure in the patient interface 18 and because the resistance to gas flow through the nozzle of the flow generator has been characterized, the oxygen flow rate can be effectively calculated by using a pressure sensor as the oxygen input line sensor 35. The oxygen input line pressure as measured by the pressure sensor 37 can be substituted for the oxygen flow measurement or can be considered as an oxygen flow measurement. The measured oxygen flow signal can either be taken as the directly measured oxygen flow rate as measured by an oxygen flowmeter 39 (
In the exemplary configuration shown in
An exemplary configuration of a controller 40 which can be used in an oxygen delivery and/or measurement system is shown in the block diagram of
The functions of the various elements shown in the figures, including any functional blocks labeled as “controller(s)” and/or “processor(s)”, may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared. Moreover, explicit use of the term “processor” should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, network processor, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), flash memory, and/or non-volatile storage. Other hardware, conventional and/or custom, may also be included within the controller 40 and/or oxygen delivery system 10.
In some configurations, the controller 40 may be programmed, through one or more processor(s) 49 and memory 55, to determine the oxygen flow output from the flow generator 14. The controller 40 can determine total flow output from the flow generator 14 in several different ways. The flow generator 14 includes air input ports that are open to ambient air such that there is no direct measurement of air flow into or out of the flow generator. Additionally, when the flow exiting the flow generator 14 at its exit port is blocked (such as when a patient breathes out), oxygen flow entering the flow generator 14 from the oxygen input line 27 can escape from the flow generator 14 through the air input port(s) of the flow generator 14 rather than through the exit port of the flow generator into the patient mask. So instead of directly measuring the output flow of the flow generator 14 and the input flow of the flow generator 14, patient interface pressure and oxygen input line pressure sensor can be measured directly and provided to the controller 40, and an algorithm can be applied to calculate the output flow of the flow generator 14 for each possible combination of output pressure and oxygen flow.
As discussed above, characteristics and parameters of a particular flow generator 14 can be known or predetermined. For example, for a given flow generator 14 having predetermined dimensions and a predetermined configuration of nozzle(s), the output flow can be known by prior measurement for a given patient interface pressure and an oxygen input line pressure sensor. CPAP flow generators are designed to increase volume of inhaled oxygen, and the concentration of oxygen in the gas exiting the flow generator (i.e., the flow generator flow output) changes as a function of the oxygen input line flow rate and the patient interface pressure. By mapping this function of measured flow output at various known oxygen input line flow rates and patient interface pressure, an algorithm unique to a particular flow generator can be created.
Algorithm parameters are unique for each flow generator design and dimensions. In other words, algorithm parameters are specific for the unique design of a particular type of flow generator. The algorithm can be as simple as a pre-stored lookup table, a polynomial curve fit or other method of reporting a pre-determined output value for a given combination of mask (output) pressure and oxygen flow rate. The parameters of the algorithm are predetermined. This can typically be done on the test bench by generating multiple combinations of oxygen input line 27 flow and patient interface pressure and measuring corresponding output flow using calibrated equipment. Flow generator characterization data can also be collected while directly controlling the patient interface pressure or while applying a flow restrictor, or a range of flow restrictions, to the output of the flow generator and recording the output flow corresponding to applied oxygen flow rates.
After enough data points are collected, they can be input into a controller 40. For example the data points can be stored in memory 55, and an algorithm (shown as the curve 64 fit to the data points 59 in
By measuring the flow generator 14 output flow for many possible combinations of measured oxygen flow rates through oxygen input line 27 and measured patient interface pressure for a specific flow generator 14, the flow generator 14 can be functionally characterized. This oxygen flow and patient interface characterization data can be used to generate data tables and/or algorithm parameters that are used to determine what output flow to report for a given combination of oxygen flow and patient interface pressure. This allows the output flow rate for a particular flow generator 14 to be determined for any given combination of input oxygen flow and measured patient interface pressure.
An algorithm and pre-collected data or algorithm parameters can be applied which use directly measured oxygen flow and patient interface pressure as inputs to determine the concentration of oxygen in the gas exiting the flow generator (i.e., the patient flow). Any suitable algorithm can be used to convert a known patient interface pressure and oxygen input line flow to an estimated flow generator output. By way of example and not limitation, this can be done by using a pre-defined mathematical function, a polynomial, or other, curve fit, a lookup table, an artificial neural network trained using the characterization data, a nearest neighbor search algorithm or other numerical method used to define an output value given two or more input values.
While the description above refers to determining the output flow of the flow generator 14, flow can also be calculated as pressure divided by resistance. By determining the resistance observed at the patient interface 18, the flow becomes trivial. Therefore, instead of calculating the flow output of the flow generator 14, the output resistance of the flow generator 14 can be calculated.
With a knowledge of the output flow of the flow generator 14, the flow into the patient interface 18 can be integrated over the breath to calculate the patient's inspiratory tidal volume or the volume inhaled during each single breath. Breath volume in turn can be used to determine the volume of gas inhaled by the patient each minute. This parameter is often used by clinicians to determine patient status. Without this method of determining the output flow from the flow generator 14, a direct flow measurement device between the patient interface 18 and the flow generator 14 would be needed. This could be costly and can also interfere with patient care if the direct flow measurement device is not properly positioned within the system.
In some configurations, the system further comprises a method of determining the tidal volume for the patient. Tidal volume is the amount of air that moves in or out of the lungs with each respiratory cycle. The inspired breath volume, or tidal volume, is calculated as the sum (or integral of) flow over the course of the inspiratory phase of the breath with leak volume subtracted over this same phase. To determine tidal volume, the method can include the step of calculating or determining patient interface 18 leak. When there is leak around the patient interface (such as leak around a mask seal), all of the flow exiting the flow generator 14 is not inhaled by the patient. That is, some of the flow output by the flow generator 14 is lost to leakage.
By subtracting the amount of leakage from the total output flow of the flow generator 14, the method can more accurately determine the output flow that is delivered or inhaled by the patient. To determine the leak rate, the method includes the step of determining the flow rate from the flow generator during the period of the end-expiratory pause at the end of each exhalation. During this pause at the end of exhalation, the patient is resting and there is no movement of gas into or out of the patient. Because there is no movement of gas into or out of the patient, during this time all output flow from the flow generator 14 is attributed to leak flow. This leak flow rate can be measured breath by breath, and on the subsequent breath(s) that leak flow is subtracted from the total flow generator output flow to calculate the flow that is inhaled by the patient during that particular breath. This sum of the flow inhaled by the patient during the breath can be used to determine tidal volume.
With a calculated mask leak rate, which is subtracted from the determined total flow generator flow output, a volume of gas inhaled by a patient can be calculated.
The method can include the step 100 of obtaining, by a processor, information relating to a patient interface pressure and an oxygen input line flow. This includes the patient interface pressure, which can be measured, for example, by patient interface pressure sensor 22. This also includes the oxygen input line flow, which can be measured, for example, by a flowmeter and/or an oxygen input line pressure sensor. The processor then determines (step 105) a total flow generator flow output based on the patient interface pressure and the oxygen input line flow. This can be done in any suitable manner, such as through an algorithm, lookup tables, etc.
After the total flow generator flow output is determined, the processor can then determine a leak flow (step 110). Leak flow is determined by first identifying the period of the end-expiratory pause at the end of an exhalation. This can be done, for example, by the processor/controller 40 tracking a breath over time by measuring the patient interface pressure over time to determine when there is a pause in breathing. The pause is detected as a period of unchanging mask pressure and oxygen flow. Inhalation is detected as the period when added oxygen flow is needed to maintain mask pressure. Exhalation is the period when less oxygen flow into the flow generator is needed to maintain set mask pressure. The pause is the time between these two conditions.
At the pause before the patient begins their next inhalation (in which there is no movement of gas into or out of the patient), the processor can measure the patient interface pressure and the oxygen input line flow and determine the output flow from the flow generator 14. At this pause, all output flow from the flow generator 14 is attributed to leak flow.
After the processor determines leak flow, the processor can calculate the patient flow (step 115) by subtracting the leak flow from the total flow generator flow output. Once the patient flow is known, the processor can calculate the patient tidal volume of gas inhaled by integrating the patient flow over a predetermined time period. For example, the patient tidal volume of gas for a single breath can be determined by integrating the patient flow over the time period of an inhalation. In some examples, the patient tidal volume of gas inhaled for a given time period (for example, for one minute) can be determined by integrating the patient flow for each of the inhalations during that time period (step 120).
In addition to determining the patient tidal volume of oxygen inhaled, the controller 40 can further output these details to a display (see
Another feature of the system 10 can include the ability of the controller 40 to automatically determine what type of flow generator 14 is being used. The controller 40 can have memory 55 that is programmed with algorithms and look-up tables for several different types of flow generators. The controller 40 can automatically determine what type of flow generator 14 is being used and apply the appropriate algorithm for that particular flow generator 14. This can be accomplished in several ways. For example, the flow generator 14 can have a unique identifier located on the flow generator (such as a QR code, an alpha-numeric code, etc.). In some configurations, the clinician inputs this unique code into the system to inform the controller. In other configurations, the controller 40 detects this unique code automatically through the use of wired or wireless technology.
An exemplary configuration of a housing 70 to house controller 40 and other input/output devices is shown in
A connector 74 is inserted into a receptacle 78 on the housing 70. Connector 74 can have a unique, readable code or type-identifier thereon and receptacle 78 can have a reader to read the code. Many configurations are possible to achieve this result, and several are discussed in U.S. Pat. No. 10,737,049, which is incorporated herein in its entirety. By way of example and not limitation, one or more of the following can be used: a code printed on the connector 74, a gradient printed on the connector 74, an angled cut-away formed in the connector 74, and/or a reflective pad on the connector 74.
Connector 74 includes an oxygen input line 27 which is connected to flow generator 14. The distal end 27b of the oxygen input line is attached to the connector 74. In some configurations, the distal end 27b of the oxygen input line 27 is non-removably attached to the connector 74. The proximal end 27a of the oxygen input line is attached to a flow generator 14. The unique, readable code on the connector 74 is specific to the type of flow generator 14 which is connected to the connector 74. Different flow generators have different readable codes on their specific connectors 74. This readable code is read by one or more input/output devices in communication with the controller 40. The controller 40, in turn, applies the algorithm that is appropriate for the unique flow generator that is detected.
In yet another example, the current system can also be used to calculate the fraction of inspired oxygen (FiO2). FiO2 is the percent of the percent of the total volume of gas entering the patient's lung that is comprised of oxygen. Since the total gas volume is a mix of oxygen and entrained ambient air, it can be useful to clinicians to know how much of the patient's breath is oxygen. Determining the FiO2 can be accomplished according to different methods.
The system described above measures the flow of gas that exits the flow generator and the portion of gas that is inhaled by the patient. Because the flow generator uses compressed oxygen as its input gas, the gas entering the mask has a higher fraction of oxygen than ambient room air. The concentration of oxygen in the gas exiting the flow generator is a function of the oxygen flow and the mask pressure. In the same way that the flow generator can be characterized to measure the total gas flow at its output, the flow generator can also be characterized to measure the concentration of oxygen in the gas that exits the flow generator. This is done by measuring the oxygen concentration at the output of the flow generator while creating all possible combinations of oxygen flow and mask pressure. These measurements are then used to calculate oxygen fraction (concentration) in the gas exiting the flow generator using a method similar to that described above.
After the total flow generator oxygen flow output is determined, the processor can then determine an oxygen leak flow (step 210). Oxygen leak flow is determined by first identifying the period of the end-expiratory pause at the end of an exhalation. This can be done, for example, by the processor/controller 40 tracking a breath over time by measuring the patient interface pressure over time to determine when there is a pause in breathing. The pause is detected as a period of unchanging mask pressure and oxygen flow. Inhalation is detected as the period when added oxygen flow is needed to maintain mask pressure. Exhalation is the period when less oxygen flow into the flow generator is needed to maintain set mask pressure. The pause is the time between these two conditions. At this pause, all output flow from the flow generator 14 is attributed to leak flow.
After the processor determines oxygen leak flow, the processor can calculate the patient oxygen flow (step 215) by subtracting the oxygen leak flow from the total flow generator oxygen flow output. Once the patient oxygen flow is known, the processor can calculate the patient tidal volume of oxygen inhaled by integrating the patient oxygen flow over a predetermined time period. For example, the patient tidal volume of oxygen for a single breath can be determined by integrating the patient flow over the time period of an inhalation. And the total patient tidal volume of gas inhaled for a given time period (for example, for the last breath, for the last one minute, etc.) can be determined by integrating the patient flow for each of the inhalations during that time period (step 220).
Another method of determining FiO2 is determining the percentage of oxygen in the total volume of gas output by the flow generator. The percentage of oxygen can be determined by computing the volume of pure oxygen included in the total volume inhaled by the patient and dividing by the total volume of gas inhaled. To determine the volume of pure oxygen inhaled, two flow measurements are considered: the input flow into the flow generator (which is pure oxygen from oxygen source 44) and the output flow from the flow generator (which is a mix of the pure oxygen from the oxygen source 44 and entrained ambient air which is 21% oxygen).
During exhalation, some amount of gas is pushed out of the patient's lungs. After the patient is done exhaling, lung re-pressurization occurs, and the flow generator pushes some amount of gas into the lungs in order to raise the patient's airway pressure back up to the set CPAP pressure. Thus some amount of gas (mix of oxygen and ambient air) enters the patient even before inhalation. Then during EEP there is no gas movement in or out of the patient until inhalation, when a larger amount of oxygen and ambient air mixture is brought into the patient's lungs.
As discussed above, leak flow can be determined by the output of the flow generator during EEP (see
The volume of gas and oxygen output by the flow generator during inhalation (from Tk to Tl) is computed by integrating the input flow, indicated at 74, and output flow 78, see
In some configurations, the amount of oxygen delivered to a patient during lung re-pressurization can also be calculated.
After the patient is done exhaling, lung re-pressurization occurs, and the flow generator pushes some amount of gas into the lungs to raise the patient's airway pressure back up to the set CPAP pressure. Thus some amount of gas (mix of oxygen and ambient air) enters the patient even before inhalation. There is also a certain amount of space in the patient's trachea as well as space in the patient's mask at the patient interface that impacts the FiO2. The volume of the mask can be approximately measured, but the volume of the patient's trachea is typically estimated by one or more known estimation methods. The combination of these two spaces is referred to as “dead space.”
After exhalation, the dead space is filled with exhaled gas that has been expelled from the lungs, which is comprised of some amount of oxygen (typically about 5-6% less than whatever the previous amount of inhaled oxygen was). During lung re-pressurization, this gas in the trachea and mask is the first to get pushed into the lungs followed the gas output by the flow generator that is needed to get the patient's airway up to the set CPAP pressure.
After the gas from the trachea and mask are pushed into the lungs, the trachea and mask space are filled with gas with an oxygen concentration which was output by the flow generator during the lung re-pressurization. This concentration is computed similar to the method of computing the oxygen concentration that was output by the flow generator during inhalation. Both the input flow 81 (assumed to be 100% oxygen) and output flow 85 (assumed to be 21% for the amount that is greater than the input flow, or the difference between the output flow and the input flow) are integrated over the duration of lung re-pressurization (with the leak flow volume subtracted from each). The difference between the volumes from output flow and input flow account for the entrained air, which is comprised of approximately 21% oxygen. Adding that 21% to the input volume and dividing it by the output volume from this phase of the breath gives the concentration of oxygen output by the flow generator during lung re-pressurization.
The total amount of oxygen that enters the lungs during the lung re-pressurization phase is the sum of the product of the dead space volume and the previous FiO2 percentage and the product of the lung re-pressurization oxygen concentration and the difference between the total lung re-pressurization volume and the dead space volume. In other examples, the total amount of oxygen that enters the lungs during the lung re-pressurization phase can be calculated as the sum of the product of the dead space volume and a percentage slightly less than the previous FiO2 percentage and the product of the lung re-pressurization oxygen concentration and the difference between the total lung re-pressurization volume and the dead space volume. Mathematically this can be represented as: lung_re-pressurization_oxygen_volume=dead_space_volume*previous_FiO2+lung_re-pressurization_oxygen_concentration*(lung_re-pressurization_total_volume−dead_space_volume).
During EEP, no gas is entering the patient, but the flow that is being output by the flow generator pushes out the volume of the mask and replaces it with gas of a new concentration of oxygen. This oxygen concentration is characteristic of the design of the flow generator along with the amount of leak present. This EEP oxygen concentration is a value that can be mathematically characterized for a given adapter design based on the amount of leak flow present. By the end of EEP, at time Tk, the trachea volume is filled with gas with the lung re-pressurization oxygen concentration, and the mask is filled with gas with the oxygen concentration that has been characterized from the adapter and leak flow present.
Consideration of the oxygen concentration of the dead space can also be made when calculating the concentration of oxygen inhaled during inhalation. During inhalation, the first gas to enter the patient's lung is the gas in the dead space, and then the volume that is output by the flow generator. Therefore, assuming the volume inhaled by the patient is greater than the volume of the dead space, the total volume of oxygen in the lungs is the sum of the oxygen from the lung re-pressurization, the dead space oxygen, and the concentration of oxygen from inhalation times the total inhaled volume subtract the dead space.
In the case where the total volume inhaled is less than the dead space volume but greater than the tracheal volume, the total volume of oxygen inhaled is the sum of the oxygen from lung re-pressurization, the lung re-pressurization oxygen concentration times the tracheal volume, and the characterized EEP concentration times the difference between total inhaled volume and tracheal volume (to account for oxygen in the mask).
In the case where the total volume inhaled is less than the tracheal volume, the total volume of oxygen in the lung is the sum of the oxygen from lung re-pressurization and the lung re-pressurization oxygen concentration times the total inhaled volume.
The following is an exemplary calculation of the fraction of inspired oxygen during an exemplary patient breath. The specific numbers provided are given by way of example and not limitation, and the principals of the calculations set forth below can be applied to other breaths with different numerical data measurements and assumptions. For this exemplary calculation, input flow and output flow have been measured over the time of a breath. The following assumed values are used: previous breath has FiO2 of 80%; volume of the patient's trachea volume is 150 mL; and volume of the mask is 100 mL. The dead space volume is the sum of the trachea and mask volumes. These assumptions are shown as:
0
mask_vol
trach_col
_
0.
F
2
indicates data missing or illegible when filed
The leak flow is found by examining the flow generator output flow during EEP. Since this may be a noisy signal, averaging or filtering can be applied to obtain the approximately constant leak flow during EEP, which can be used to find the leak volume during lung re-pressurization as well as inhalation. This can be done a number of ways, and in this specific example a recursive median filter is used to reduce noise spikes, and sort the samples into a histogram. The histogram bin with the highest occurrence is used as constant flow value during EEP:
output and input
during
breath_output_flow[EEP_start:insp_start]
breath_input_flow[EEP_start:insp_start]
lineFlowFilter = histogramFilter
bucketWidth=0.25, buck
Min
bucketsMax
100)
recursiveMedianFilter(n=11, initialVal
output_flow_EEP[0]
through samples and filters the signal
range(0,
(output_flow_EEP))
runFilter
output_flow_EEP[
])
addSample(flowSample)
baselineFlowFilter.getMax( )
highest occuring flow,
from the histogram
input
steps as the output flow
, bucketsMin=
bucketsMax=100)
=11, initialVal
input_flow_EEP[0])
in range(0,
(input_flow_EEP))
runFilter(input_flow_EEP[
])
addSample(flowSample)
output leak flow)
str(baselineFLow_adap)
L/min
)
input leak flow)
str(baselineFlow_prox)
L/min
)
indicates data missing or illegible when filed
The oxygen concentration of the leak flow is an intrinsic characteristic of the adapter design and the amount of leak flow present. For this particular flow generator with the given leak flow, the oxygen concentration has been determined by characterizing this behavior through sampling the oxygen concentration given different leak flows. This was fit to two linear equations where the input is the ratio of the baseline flow (or leak flow) for the output flow over the baseline flow (or leak flow) for the input flow:
baselineFlow_adap/baselineFlow_prox
the ratio of
flow to input leak
for
the
flow
[−0.202, 1.
1
]
[−0.
52
3, 0.
242]
computing the oxygen concentration
Leak
lower
[0]
flowRatio
lowerCoeff[
]
Leak
upperCoeff[0]
flowRatio
upperCoeff[
]
(
Leak flow oxygen concentration
str(
Leak))
7317073170
indicates data missing or illegible when filed
To find the volume of oxygen and the volume of total gas during lung re-pressurization that contribute to the patient's FiO2, both the input and output flows are integrated over the course of the re-pressurization:
over the duration of lung re-pressurization. Dividing by 60 converts th
value to mL.
break_t[LRP_start:EEP_start])/60
breath_t[LRP_start:EEP_start])/60
Integrated output flow
str(LRP_integrated_output_flow)
mL
)
Integrated input flow
str(LRP_integrated_input_flow)
mL
)
indicates data missing or illegible when filed
Output leak flow is integrated over this same duration to get the volume of gas lost to leak during lung re-pressurization:
(breath_t[EEP_start)
breath_t[LAP_start])/60.0
Output Leak Volume:
str(LRP_output_flow_leak_vol)
mL
)
indicates data missing or illegible when filed
The amount of this leak volume that is credited to oxygen can be computed by multiplying the oxygen leak concentration by the leak volume. Additionally, to account for the 21% oxygen contained in the entrained air portion, 21% of the difference between the total leak volume and the pure oxygen leak volume can be added to get the total volume of oxygen from leak flow:
2_leak_vol
2Leak
LRP_output_flow_leak_vol
0.21
(LRP_output_flow_leak_vol
2Leak
LRP_output_flow_leak_vol)
Output Flow Oxygen Leak Volume:
str(LRP_
2_leak_vol)
mL
)
indicates data missing or illegible when filed
With the leak volumes for lung re-pressurization known, the total amount of oxygen and total amount of gas that is output by the flow generator that is not lost to leak during this phase of the breath can be computed. Leak flows are subtracted from the integrated values calculated above, and then as done previously, oxygen content in the entrained air is accounted for by adding 21% of the difference to the oxygen volume:
re-pressurization output volume
2_prox = LRP_integrated_input_flow − LRP_
2_leak_vol #lung
re-pressurization input volume
2_vol = LRP_
2_prox + 0.21
(LRP_vol − LRP_
2_prox) #lung re-pressurization
total oxygen volume
Oxygen volume
+ str(LRP_
2_vol) +
mL
)
Total volume
+ str(LRP_vol) +
mL
)
indicates data missing or illegible when filed
Because of the dead space, not all of this volume reaches the patient's lungs at this time. The volume of the dead space (with an oxygen concentration of the previous FiO2) gets pushed into the lungs first, and the dead space is then left being filled with the concentration of oxygen that is output by the flow generator. However, if the total lung re-pressurization volume is smaller than the dead space, then the entire volume entering the lung is derived from the dead space. This is the case with this exemplary breath, so the volume of gas entering the lung has an oxygen concentration of the previous breath's FiO2. The total volume of oxygen entering the patient's lung is computed as:
2LRP = LAP_
2_vol/LAP_vol #oxygen concentration output by flow generator
2 = LAP_vol * Fi
2_d
2 = dead space_vol > Fi
2_d
2LRP
(LAP_vol − dead_space_vol)
Flow Generator Oxygen Concentration:
+ str(
2LRP))
Total volume of oxygen entering the lung during re-pressurization
+
str(VLung
2) +
mL
)
indicates data missing or illegible when filed
The dead space is now filled with gas from lung re-pressurization at that same oxygen concentration (unless the dead space is larger than the total volume from this phase of the breath, in which case it is some mix of the previous FiO2 and the lung re-pressurization concentration). However, during EEP, the mask portion fills with the characterized leak concentration from earlier. Thus the dead space oxygen content is computed as follows:
2_vol = track_vol *
2LRP + mask_vol *
2Leak
2_vol = LRP_vol
Fi
2_d
+ (trach_vol − LRP_vol)*
2LRP +
mask_vol *
2Leak
2_vol = trach_vol * Fi
2_d
mask_vol *
2Leak
Dead space oxygen volume:
+ str(dead_space_
2_vol) +
mL
)
indicates data missing or illegible when filed
Next, for the inhalation portion of the breath, the input flow and output flow during inhalation are integrated:
exp_start], breath_t[insp_start:exp_start])/60
breath_t[insp_start:exp_start])/60
Integrated output flow:
+ str(insp_integrated_output_flow) +
mL
)
Integrated input flow:
+ str(insp_integrated_input_flow) +
mL
)
indicates data missing or illegible when filed
Leak volume is obtained by integrating the leak flow over this same period:
breath_t[insp_start])/60.0
Output Flow Leak Volume:
+ str(insp_output_flow_leak_vol) +
mL
)
indicates data missing or illegible when filed
The amount of this leak volume that can be accounted for by oxygen is computed the same was as during lung re-pressurization:
2_leak_vol =
2Leak*insp_output_flow_leak_vol + 0.21 *
(insp_output_flow_leak_vol −
2Leak*insp_output_flow_leak_vol)
Output Flow Oxygen Leak Volume:
+ str(insp_
2_leak_vol) +
mL
)
indicates data missing or illegible when filed
The tidal volume can be computed as the total output volume subtract the leak volume. The amount of this volume that is oxygen is computed the same way as for the calculation of the volume that is oxygen for the lung re-pressurization phase of the breath described above:
2_prox = insp_integrated_input_flow − insp_
2_leak_vol #input oxygen
volume
2 = insp_
2_prox + 0.21*(VTI − insp_
2_prox) #total oxygen volume is the
tidal volume output by the adapter
2 = VTI_
2/VTI #oxygen concentration in the tidal volume output by the
adapter
Oxygen volume:
+ str(VTI_
2) +
mL
)
Tidal volume:
+ str(VTI) +
mL
)
Oxygen concentration:
+ str(insp_02) +
mL
)
indicates data missing or illegible when filed
The total volume of oxygen that enters the patient's lung can now be computed. It is dependent on the tidal volume in comparison to the dead space volume as outlined below:
2 = VLong
2 +
2LRP
VTI
2 = VLung
2 +
2LRP*trach_vol +
2Leak * (VTI − trach_vol)
2 = VLung
2 + dead_space_
2_vol + insp_
2 * (VTI − dead_space_vol)
volume of oxygen entering lung:
+ str(V_
2) +
mL
)
Total volume of gas entering the lung:
+ str(V) +
mL
)
indicates data missing or illegible when filed
Finally, the fraction of inspired oxygen can be computed as the volume of oxygen entering the lung divided by the total volume of gas entering the lung during the entire breath:
2 = V_
2/V
Fi
2
+ str(Fi
2))
2: 0.7337675632477664
indicates data missing or illegible when filed
Other calculations can also be made based on the patient interface pressures and corresponding oxygen input line flow taken over time. For example, breath timing (such as breath rate, time since start of inhalation, expiratory pause duration, etc.) can be determined from the data collected. These additional calculations can be taken into consideration for the controller to determine the tidal volume of oxygen. Additionally, other input parameters can be measured and added as part of the algorithm to further improve accuracy. Examples of additional input parameters that can be applied to improve the accuracy of flow measurements might include the setting of the oxygen control valve, barometric pressure, size of the patient and other related information.
Aspect 1: A system for determining total flow output from a flow generator, the system comprising:
Aspect 2: The system of Aspect 1, wherein the oxygen input line sensor comprises a pressure sensor for measuring oxygen input line pressure and wherein the oxygen input line flow is determined by the oxygen input line pressure.
Aspect 3: The system of Aspect 1 wherein the oxygen input line sensor comprises an oxygen flowmeter for measuring an oxygen input line flow.
Aspect 4: The system of Aspect 1, 2, or 3, The system of claim 1, wherein the controller is programmed to determine the total flow output from the flow generator based on the patient interface pressure at the patient interface and the oxygen input line flow.
Aspect 5: The system of Aspect 4, wherein the controller is programmed with at least one algorithm to calculate total flow output based on known patient pressure at the patient interface and known oxygen input line flow
Aspect 6: The system of any of Aspects 1-5, wherein the system further comprises a housing, the controller, the oxygen flow valve, and the patient interface pressure sensor located within the housing, the housing having a coupler to couple to the oxygen source to the housing, and the housing have a receptacle; and
Aspect 7: A method for determining total flow generator flow output, the method comprising:
Aspect 8: The method according to Aspect 7, wherein the method further comprises the step of obtaining, by a processor, information relating to a flow generator type; and
Aspect 9: The method of Aspect 7 or 8, wherein the controller is programmed with at least one algorithm to calculate the total flow generator flow output based on known patient interface pressure at the patient interface and known oxygen input line flow.
Aspect 10: A system for determining an amount of gas inhaled by a patient, the system comprising:
Aspect 11: The system of Aspect 10, wherein the processor is further programmed to calculate a tidal volume of gas by integrating the patient flow over a single breath.
Aspect 12: The system of Aspect 10 or Aspect 11, wherein the oxygen input line sensor for measuring oxygen input line flow is a flow sensor.
Aspect 13: The system of any Aspect 10 or Aspect 11, wherein the oxygen input line sensor for measuring oxygen input line flow is an oxygen input line pressure sensor.
Aspect 14: The system of any one of Aspects 10-13, wherein the controller is programmed with at least one algorithm to calculate total flow output based on known patient pressure at the patient interface and known oxygen input line flow.
Aspect 15: The system of any one of Aspects 10-14, wherein the controller is further programmed to calculate a concentration of oxygen in the patient flow to determine a fraction of inhaled oxygen.
Aspect 16: The system of any one of Aspects 10-15, wherein the system further comprises a housing, the controller, the oxygen flow valve, and the patient interface pressure sensor located within the housing, the housing having a coupler to couple to the source of oxygen to the housing, and the housing have a receptacle; and
Aspect 17: The system of any one of Aspects 10-16, wherein the flow generator comprises a type-identifier, and wherein the controller is programmed to receive data relating to the type-identifier of the flow generator.
Aspect 18: A method for calculating patient tidal volume of gas inhaled, the method comprising:
Aspect 19: The method of Aspect 18, wherein the step of determining, by the processor, a flow generator total flow output based on the patient interface pressure and the oxygen input line flow, comprises the processor determining the flow generator total flow output based on at least one of: a pre-defined mathematical function stored in a memory accessible by the processor, a lookup table stored in a memory accessible by the processor, and a trained artificial neural network stored in a memory accessible by the processor.
Aspect 20: The method of Aspect 18 or Aspect 19, wherein the step of obtaining, by the processor, a leak flow, comprises determining, by the processor, a pause period between a patient exhalation and a patient inhalation, and wherein the method further comprises the steps of:
Aspect 21: The method of any one of Aspects 18-20, wherein the method further comprises the step of calculating a concentration of oxygen in the patient flow to determine a fraction of inhaled oxygen.
Aspect 22: A method for calculating a percentage of oxygen in a volume of gas inhaled during an inhalation, the method comprising:
Aspect 23: The method for calculating the percentage of oxygen in a volume of gas inhaled during an inhalation of Aspect 22, wherein the step of determining, by the processor, the oxygen leak flow, comprises determining, by the processor, a pause period between a patient exhalation and a patient inhalation, and wherein the method further comprises the steps of:
The description is only exemplary of the principles of the disclosure, and should not be viewed as narrowing the scope of the claims which follow, which claims define the full scope of the invention. Various aspects discussed in one drawing may be present and/or used in conjunction with the embodiment shown in another drawing, and each element shown in multiple drawings may be discussed only once. The described features, structures, or characteristics of configurations of the disclosure may be combined in any suitable manner in one or more configurations. In some cases, detailed description of well-known items or repeated description of substantially the same configurations may be omitted to facilitate the understanding of those skilled in the art by avoiding an unnecessarily redundant description. All statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.
Reference in the specification to “one configuration” “one embodiment,” “a configuration” “an example,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the configuration is included in at least one configuration, but is not a requirement that such feature, structure or characteristic be present in any particular configuration unless expressly set forth in the claims as being present. The appearances of the phrase “in one configuration” or “in one example” in various places may not necessarily limit the inclusion of a particular element of the disclosure to a single configuration, rather the element may be included in other or all configurations discussed herein.
As used in this specification and the appended claims, singular forms such as “a,” “an,” and “the” may include the plural unless the context clearly dictates otherwise. Thus, for example, reference to “a processor” may include one or more of such processors, and reference to “the sensor” may include reference to one or more of such sensors.
As used herein, the term “generally” refers to something that is more of the designated adjective than not, or the converse if used in the negative. As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be “a little above” or “a little below” the endpoint while still accomplishing the function associated with the range, for example, “about” may be within 10% of the given number or given range. As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member.
Numerical data may be expressed in a range format. This range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. For example, a numerical range of “about 5 to about 60” should be interpreted to include not only the explicitly recited values of about 5 to about 60, but also include individual values and sub-ranges within the indicated range. Thus, included in this numerical range are individual values such as 6, 7, 8, 9, etc., through 60, and sub-ranges such as from 10-20, from 30-40, and from 50-60, etc., as well as each number individually. This same principle applies to ranges reciting only one numerical value as a minimum or a maximum. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.
While methods are described herein in discrete steps in a particular order for the sake of clarity, the steps do not require a particular order and more than one step may be performed at the same time. For example, a later step may begin before earlier step completes. Or, a later step may be completed before an earlier step is started. For example, the processor and/or controller can simultaneously determine the flow generator flow output based on patient interface pressure and oxygen input line flow and the leak flow. Additionally, the word “connected” and “coupled” is used throughout for clarity of the description and can include either a direct connection or an indirect connection.
Other embodiments and configurations may be devised which do not depart from the scopes of the claims. Features from different embodiments and configurations may be employed separately or in combination. Accordingly, all additions, deletions and modifications to the disclosed subject matter that fall within the scopes of the claims are to be embraced thereby. The scope of each claim is indicated and limited only by its plain language and the full scope of available legal equivalents to its elements. Furthermore, if any references have been made to patents and printed publications throughout this disclosure, each of these references and printed publications are individually incorporated herein by reference in their entirety.
