Patent Application
20150065830
The subject matter disclosed herein generally relates to operating a sensor for determining blood characteristics of a subject. More specifically, the subject matter relates to systems and methods for switching the operation of a pulse oximeter sensor for determining blood characteristics of a subject based on the quality of the subject's plethysmographic data.
Doctors, primary physicians, and the like, often use sensors (e.g., pulse oximeter sensor) to monitor blood characteristics, for example, oxygen saturation level, heart rate, and the like, of their patients. Existing pulse oximeter sensors have numerous problems. For example, the pulse oximeter sensors that continuously operate during a cardiac cycle of a patient consume significant amounts of power to pulse the light emitting diodes of the pulse oximeter sensor. In another example, the pulse oximeter sensors that operate during only the systolic phase of a cardiac cycle face challenges in synchronizing the pulsing of LEDs with the heart rate of the subject.
Thus, there is a need for an enhanced system and method for operating a sensor for determining blood characteristics of a subject.
In accordance with one aspect of the present technique, a method includes receiving continuous photoplethysmographic (PPG) data of a subject from a sensor and calculating a continuous blood characteristic (BC) based on the continuous PPG data. The method also includes calculating a first quality metric of the continuous PPG data based on a sequence of the continuous BC. The method further includes determining whether the first quality metric satisfies a stability criterion and sending a first notification to the sensor in response to determining that the first quality metric satisfies the stability criterion. The first notification instructs the sensor to collect compressed PPG data of the subject.
In accordance with one aspect of the present systems, a system includes a calculation module configured to receive continuous PPG data of a subject from a sensor, calculate a continuous BC based on the continuous PPG data, and calculate a first quality metric of the continuous PPG data based on a sequence of the continuous BC. The system also includes a determination module configured to determine whether the first quality metric satisfies a stability criterion and send a first notification to the sensor in response to determining that the first quality metric satisfies the stability criterion. The first notification instructs the sensor to collect compressed PPG data of the subject.
In accordance with one aspect of the present technique, a computer program product encoding instructions is disclosed. The instructions when executed by a processor, causes the processor to receive continuous PPG data of a subject from a sensor and calculate a continuous BC based on the continuous PPG data. The instructions further cause the processor to calculate a first quality metric of the continuous PPG data based on a sequence of the continuous BC. The instructions further cause the processor to determine whether the first quality metric satisfies a stability criterion and send a first notification to the sensor in response to determining that the first quality metric satisfies the stability criterion. The first notification instructs the sensor to collect compressed PPG data of the subject.
These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings.
The singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise.
As used herein, the term “non-transitory computer-readable media” is intended to be representative of any tangible computer-based device implemented in any method or technology for short-term and long-term storage of information, such as computer-readable instructions, data structures, program modules and sub-modules, or other data in any device. Therefore, the methods described herein may be encoded as executable instructions embodied in a tangible, non-transitory, computer readable medium, including, without limitation, a storage device and/or a memory device. Such instructions, when executed by a processor, cause the processor to perform at least a portion of the methods described herein. Moreover, as used herein, the term “non-transitory computer-readable media” includes all tangible, computer-readable media, including, without limitation, non-transitory computer storage devices, including, without limitation, volatile and nonvolatile media, and removable and non-removable media such as a firmware, physical and virtual storage, CD-ROMs, DVDs, and any other digital source such as a network or the Internet, as well as yet to be developed digital means, with the sole exception being a transitory, propagating signal.
As used herein, the terms “software” and “firmware” are interchangeable, and may include any computer program stored in memory for execution by devices that include, without limitation, mobile devices, clusters, personal computers, workstations, clients, and servers.
As used herein, the term “computer” and related terms, e.g., “computing device”, are not limited to integrated circuits referred to in the art as a computer, but broadly refers to at least one microcontroller, microcomputer, programmable logic controller (PLC), application specific integrated circuit, and other programmable circuits, and these terms are used interchangeably herein.
Approximating language, as used herein throughout the description and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about” and “substantially”, are not limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or inter-changed, such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise.
A system and method for operating a sensor for determining blood characteristics (e.g., oxygen saturation, heart rate, and the like) of a subject (e.g., a patient in a hospital and the like) is described herein.
The network 140 may be a wired or wireless communication type, and may have any number of configurations such as a star configuration, token ring configuration, or other known configurations. Furthermore, the network 140 may include a local area network (LAN), a wide area network (WAN) (e.g., the Internet), and/or any other interconnected data path across which multiple devices may communicate. In one embodiment, the network 140 may be a peer-to-peer network. The network 140 may also be coupled to or include portions of a telecommunication network for transmitting data in a variety of different communication protocols. In another embodiment, the network 140 includes Bluetooth communication networks or a cellular communications network for transmitting and receiving data such as via a short messaging service (SMS), a multimedia messaging service (MMS), a hypertext transfer protocol (HTTP), a direct data connection, WAP, email, and the like. While only one network 140 is shown coupled to the sensor 105 and the switching unit 150, multiple networks 140 may be coupled to the entities.
The sensor 105 may be any type of device for collecting PPG data of a subject. Typically, the PPG data indicates the change in volume within a body part of the subject due to fluctuations in the amount of blood, air, and the like, within the body part. In the illustrated embodiment, the sensor 105 is a pulse oximeter sensor including an optoelectronic unit 110 and a control unit 115 configured to collect photoplethysmographic (PPG) data of the subject. The sensor 105 is further configured to send the collected PPG data of the subject to the switching unit 150 via the network 140. The sensor 105 is coupled to the network 140 via a signal line 135. The signal line 135 is provided for illustrative purposes and represents the sensor 105 communicating by wires or wirelessly over the network 140.
The optoelectronic unit 110 includes a plurality of light emitting elements (not shown), for example, light emitting diodes (LED) for emitting light through a body part (e.g., finger, ear lobe, and the like) of a subject. In one embodiment, the optoelectronic unit 110 includes two LEDs for emitting light at wavelengths of 660 nm (red) and 940 nm (infrared). Although, the optoelectronic unit 110 is described herein as including two LEDs emitting red light and infrared light, in other embodiments, the optoelectronic unit 110 may include LEDs emitting light at any wavelength. The optoelectronic unit 110 further includes at least one photo detector (not shown) for receiving the light emitted by the LEDs after passing through a body part of the subject and converting them into electrical signals, i.e., PPG data.
The control unit 115 includes a continuous module 120 and a compressed module 130 configured to control the operation of the optoelectronic unit 110 (i.e., switching on and switching off of the plurality of LEDs) to collect the PPG data during one or more cardiac cycles of a subject. A cardiac cycle refers to a sequence of events related to the flow of blood that occurs from the beginning of one heartbeat to the beginning of the next heartbeat of a subject. The cardiac cycle includes a systolic phase and a subsequent diastolic phase. During the systolic phase, the heart ventricles contract and pump blood into the arteries of the subject. During the diastolic phase, the ventricles of the heart relax and get filled with blood. In one embodiment, the control unit 115 may include a memory (not shown) and a processor (not shown) for storing and executing the codes and routines of the continuous module 120 and the compressed module 130. Although, the control unit 115 is described above according to one embodiment as a part of the sensor 105, in other embodiments, the control unit 105 may be included in the switching unit 150.
The continuous module 120 includes codes and routines to operate the optoelectronic unit 110 to collect PPG data throughout one or more cardiac cycles, i.e., during the systolic and the diastolic phases. The continuous module 120 periodically switches on and switches off the plurality of LEDs and receives corresponding PPG waveforms (i.e., PPG data) recorded by the photo detector.
Referring now to
The graph 240 illustrates the time instants at which the continuous module switches on (T-on) and switches off (T-off) the LED to record the PPG waveform 225. In the illustrated embodiment, the continuous module switches on the LED during both systolic and diastolic phases of each cardiac cycle for recording the PPG waveform 225. Although,
Referring back to
Referring again to
The processor 185 may include at least one arithmetic logic unit, microprocessor, general purpose controller or other processor arrays to perform computations, and/or retrieve data stored on the memory 190. In another embodiment, the processor 185 is a multiple core processor. The processor 185 processes data signals and may include various computing architectures including a complex instruction set computer (CISC) architecture, a reduced instruction set computer (RISC) architecture, or an architecture implementing a combination of instruction sets. The processing capability of the processor 185 in one embodiment may be limited to supporting the retrieval of data and transmission of data. The processing capability of the processor 185 in another embodiment may also perform more complex tasks, including various types of feature extraction, modulating, encoding, multiplexing, and the like. In other embodiments, other type of processors, operating systems, and physical configurations are also envisioned.
The memory 190 may be a non-transitory storage medium. For example, the memory 190 may be a dynamic random access memory (DRAM) device, a static random access memory (SRAM) device, flash memory or other memory devices. In one embodiment, the memory 190 also includes a non-volatile memory or similar permanent storage device, and media such as a hard disk drive, a floppy disk drive, a compact disc read only memory (CD-ROM) device, a digital versatile disc read only memory (DVD-ROM) device, a digital versatile disc random access memory (DVD-RAM) device, a digital versatile disc rewritable (DVD-RW) device, a flash memory device, or other non-volatile storage devices.
The memory 190 stores data that is required for the switching application 160 to perform associated functions. In one embodiment, the memory 190 stores the modules (e.g., communication module 170, calculation module 175, and the like) of the switching application 160. In another embodiment, the memory 190 stores stability criteria (e.g., standard deviation threshold value, environmental threshold value, time threshold value, and the like) that are defined, for example, by an administrator of the switching unit 150. The stability criteria are described below in further detail with reference to the determination module 180.
The communication module 170 includes codes and routines configured to handle communications between the sensor 105 and other modules of the switching application 160. In one embodiment, the communication module 170 includes a set of instructions executable by the processor 185 to provide the functionality for handling communications between the sensor 105 and other modules of the switching application 160. In another embodiment, the communication module 170 is stored in the memory 190 and is accessible and executable by the processor 185. In either embodiment, the communication module 170 is adapted for communication and cooperation with the processor 185 and other modules of the switching application 160.
In one embodiment, the communication module 170 receives PPG data from the control unit 115 of the sensor 105 via the network 140. For example, the communication module 170 receives the PPG data in real-time corresponding to each cardiac cycle of the subject. The received PPG data includes either continuous PPG data recorded by the continuous module 120 or compressed PPG data recorded by the compressed module 130. In such an embodiment, the communication module 170 sends the PPG data to the calculation module 175. In another embodiment, the communication module 170 receives a notification instruction for switching the operation of the sensor 105 from the determination module 180. In such an embodiment, the communication module 170 sends the notification to the control unit 115 of the sensor 105 via the network 140.
The calculation module 175 includes codes and routines configured to calculate one or more blood characteristics (BCs) and calculating one or more quality metrics of the PPG data. In one embodiment, the calculation module 175 includes a set of instructions executable by the processor 185 to provide the functionality for calculating one or more BCs and one or more quality metrics of the PPG data. In another embodiment, the calculation module 175 is stored in the memory 190 and accessible and executable by the processor 185. In either embodiment, the calculation module 175 is adapted for communication and cooperation with the processor 185 and other modules of the switching application 160.
The calculation module 175 receives PPG data from the communication module 170 and calculates one or more BCs (e.g., percentage modulation, oxygen saturation, heart rate, and the like) from the received PPG data. In one embodiment, the calculation module 175 receives continuous PPG data that includes a continuous PPG waveform recorded by operating an LED emitting red light and another continuous PPG waveform recorded by operating an LED emitting infrared light. For the purpose of clarity and convenience, a BC calculated from the continuous PPG data is referred to herein as a continuous BC.
In one embodiment, the calculation module 175 calculates a percentage modulation (i.e., a perfusion index) of each continuous PPG waveform for each cardiac cycle as a continuous BC. The calculation module 175 calculates a percentage modulation based on the equation:
% mod is the percentage modulation of the continuous PPG waveform;
ACmax is the maximum value of the continuous PPG waveform;
ACmin is the minimum value of the continuous PPG waveform; and
DC is the offset level of the continuous PPG waveform.
Referring again to
In another embodiment, the calculation module 175 calculates a ratio between the % modR and the % modIR for each cardiac cycle as a continuous BC. In a further embodiment, the calculation module 175 calculates an oxygen saturation (Spo2 value) of a subject based on the ratio between % modR and the % modIR using a calibration function.
Referring again to
In one embodiment, the calculation module 175 receives compressed PPG data from the communication module 170. The calculation module 175 calculates one or more BCs from the compressed PPG data similar to the aforementioned calculation of the one or more continuous BCs. For the purpose of clarity and convenience, a BC calculated from the compressed PPG data is referred to herein as a “compressed BC”. For example, the calculation module 175 calculates the % modR as a compressed BC based on the compressed PPG waveform 325 (See
The calculation module 175 further calculates one or more quality metrics of the received PPG data. In one embodiment, the calculation module 175 calculates a quality metric of the continuous PPG data based on a sequence of continuous BCs corresponding to a sequence of cardiac cycles of the subject. In such an embodiment, the calculation module 175 determines an average BC (e.g., arithmetic mean, a weighted arithmetic mean, geometric mean, median, mode, etc.) of the sequence of continuous BCs. The calculation module 175 then calculates a standard deviation of each continuous BC in the sequence using the average BC as the quality metric. For example, the calculation module 175 determines an average Spo2 value for a sequence of three Spo2 values. The calculation module 175 then calculates a standard deviation of each of the three Spo2 values as the quality metric of the received continuous PPG data. Although, the quality metric based on the sequence of continuous BCs is described above using Spo2 values according to one example, in other examples, the calculation module 175 can calculate the quality metric using % mod values, ratio between % modR and the % modIR, heart rate, and the like.
In another embodiment, the calculation module 175 calculates a quality metric of the continuous PPG data by determining a presence of environmental signals in the received continuous PPG data. The environmental signals include, for example, noise signals caused due to electrical circuitry of the optoelectronic unit 110, motion artifacts caused due to the movement of the subject, and the like. In such an embodiment, the calculation module 175 transforms the two continuous PPG waveforms (i.e., continuous PPG data) into a Fourier domain to determine the presence of the environmental signals. The calculation module 175 calculates the amplitude of the environmental signal as a quality metric of the received continuous PPG data.
In one embodiment, the calculation module 175 receives compressed PPG data from the communication module 170. In such an embodiment, the calculation module 175 calculates one or more quality metrics for the compressed PPG data similar to the aforementioned calculation of one or more quality metrics for the continuous PPG data. For example, the calculation module 175 determines an average heart rate value (i.e., compressed BC) for a sequence of five heart rate values. The calculation module 175 then calculates a standard deviation of each of the five heart rate values as the quality metric of the received compressed PPG data. In another example, the calculation module 175 determines a presence of an environmental signal in the compressed PPG data and calculates the amplitude of the environmental signal as a quality metric of the compressed PPG data.
The calculation module 175 sends the one or more quality metrics of the PPG data to the determination module 180. In one embodiment, the calculation module 175 generates graphical data for displaying the one or more BCs to, for example, a doctor. In such an embodiment, the calculation module 175 sends the graphical data to a display device (not shown) coupled to either the switching unit 150 or the sensor 105.
The determination module 180 includes codes and routines configured to determine whether one or more quality metrics of the PPG data satisfies a stability criteria and switch the operation of the sensor 105. In one embodiment, the determination module 180 includes a set of instructions executable by the processor 185 to provide the functionality for determining whether one or more quality metrics of the received PPG data satisfies a stability criteria and for switching the operation of the sensor 105. In another embodiment, the determination module 180 is stored in the memory 190 and accessible and executable by the processor 185. In either embodiment, the determination module 180 is adapted for communication and cooperation with the processor 185 and other modules of the switching application 160.
In one embodiment, the determination module 180 receives one or more quality metrics of continuous PPG data. The determination module 180 determines whether the one or more quality metrics of the continuous PPG data satisfy one or more stability criteria. The stability criteria (e.g., standard deviation threshold value, environmental threshold value, time threshold value, and the like) are defined by, for example, an administrator of the switching unit 160. The determination module 180 sends a first notification to the sensor 105 in response to determining that the one or more quality metrics satisfy the stability criteria. In such an embodiment, the first notification instructs the sensor 105 to operate the compressed module of the optoelectronic unit 115 and collect compressed PPG data of the subject.
For example, the determination module 180 receives the standard deviations of the heart rate of a subject over three cardiac cycles as 1, 0, and 1. In such an example, the determination module 180 determines that the standard deviation of each heart rate is within the standard deviation threshold value of 3. The determination module 180 then sends the first notification to the sensor 105 to stop the collection of continuous PPG data and start the collection of compressed PPG data. In another example, the determination module 180 receives the amplitude of an environmental signal present in the received continuous PPG data. If the determination module 180 determines that the amplitude of the environmental signal is lesser than the environmental threshold value, the determination module 180 sends the first notification to the sensor 105.
In another embodiment, the determination module 180 receives one or more quality metrics of compressed PPG data. The determination module 180 determines whether the one or more quality metrics of the compressed PPG data satisfy one or more stability criteria. The determination module 180 sends a second notification to the sensor 105 in response to determining that the one or more quality metrics fail to satisfy the stability criteria. In such an embodiment, the second notification instructs the sensor 105 to operate the continuous module 120 of the optoelectronic unit 115 and collect continuous PPG data of the subject.
For example, the determination module 180 receives the standard deviations of the heart rate of a subject over four cardiac cycles as 1, 0, 1 and 5. In such an example, the determination module 180 determines that the standard deviation of the heart rate during the fourth cardiac cycle exceeds the standard deviation threshold value of 3. The determination module 180 then sends the second notification to the sensor 105 to stop the collection of compressed PPG data and start the collection of continuous PPG data. In another example, the determination module 180 receives the amplitude of an environmental signal present in the received compressed PPG data. If the determination module 180 determines that the amplitude of the environmental signal exceeds the environmental threshold value, the determination module 180 sends the second notification to the sensor 105.
In one embodiment, the determination module 180 sends the second notification to the sensor 105 based on an elapsed time. The elapsed time indicates the time duration for which the sensor 105 has been collecting compressed PPG data of the subject. The determination module 180 calculates the elapsed time in response to sending the first notification to the sensor 105. In such an embodiment, the determination module 180 determines whether the elapsed time is within a time threshold value. The determination module 180 sends the second notification to the sensor 105 in response to determining that the elapsed time has exceeded the time duration value. In another embodiment, the determination module 180 receives a user input, for example, from a doctor, for collecting continuous PPG of a subject. In such an embodiment, the determination module 180 sends the second notification to the sensor 105.
In yet another embodiment, the determination module 180 determines whether the switching unit 150 receives the PPG data continuously from the sensor 105. For example, the determination module 180 determines whether the communication module 170 receives PPG data in real-time corresponding to every cardiac cycle of the subject. The determination module 180 sends the first notification in response to determining that that the communication module 170 fails to receive the PPG data in real-time. The communication module 170 may fail to receive the PPG data continuously due to, for example, a failure in the functioning of the network 140, signal lines, 135, 145 and the like. The first notification instructs the sensor 105 to collect compressed PPG data of the subject. Such an embodiment is advantageous as temporarily storing compressed PPG data in the memory (not shown) of the sensor 105 requires lesser storage space than storing continuous PPG data.
If the first quality metric fails to satisfy the stability criterion, the communication module continues to receive continuous PPG data of the subject from the sensor 502. If the first quality metric satisfies the stability criterion, the determination module sends a first notification instructing the sensor to collect compressed PPG data of the subject 510. The communication module then receives compressed PPG data of the subject from the sensor 512. The calculation module calculates a compressed BC based on the compressed PPG data 514. For example, the calculation module calculates the Spo2 value from the compressed PPG data as the compressed BC. The calculation module further calculates a second quality metric of the compressed PPG data based on a sequence of the compressed BCs 516. In the above example, calculation module calculates the standard deviation for a sequence of five compressed Spo2 values as the second quality metric.
The determination module then determines whether the second quality metric satisfies a stability criterion 518. In the above example, the determination module determines whether the standard deviation of each compressed Spo2 value is within the standard deviation threshold value. If the second quality metric satisfies the stability criterion, the communication module continues to receive compressed PPG data of the subject from the sensor 512. If the second quality metric fails to satisfy the stability criterion, the determination module sends a second notification instructing the sensor to collect continuous PPG data of the subject 520.
Although the method 500 is described as switching the operation of the sensor based on single type of quality metric (i.e., standard deviation of continuous Spo2 and compressed Spo2) according to one embodiment, in other embodiments, the sensor operation may be switched based on a combination of multiple quality metrics. For example, the calculation module calculates the Spo2 value and the heart rate value from the received continuous PPG data as continuous BCs. The calculation module then calculates the standard deviation for a sequence of Spo2 and heart rate values as the first quality metric. In such an example, the determination module sends the first notification if the standard deviation of each Spo2 value and each heart rate value is within the standard deviation threshold value. Although, in this example, determination module compares the standard deviation of the Spo2 values and the heart rate values with the same standard deviation threshold value, in other examples, the determination module may compare them with different standard deviation threshold values.
In another example, the calculation module calculates the Spo2 value from the received compressed PPG data as a compressed BC. The calculation module calculates the standard deviation for a sequence of Spo2 values and the amplitude of an environmental signal in the compressed PPG data as the second quality metric. In such an example, the determination module sends the second notification if either the standard deviations of the Spo2 values exceed the standard deviation threshold value or if the amplitude of the environmental signal exceeds the environmental threshold value.
Referring now to
The graph 650 illustrates the compressed PPG waveform 665 received by the switching unit over three successive cardiac cycles of the subject (i.e., cardiac cycles 4-6). The compressed PPG waveform 665 is recorded by operating the LED emitting infrared light using the compressed module. The control unit of the sensor switches the operation of the LED from the continuous module to the compressed module in response to receiving the first notification from the switching unit. The calculation module then calculates % modIR of the compressed PPG waveform 665 as the compressed BC. The table 670 illustrates the sequence of % modIR values of the compressed PPG waveform 665. The calculation module further calculates the standard deviation for each of the % modIR values shown in the table 670, as the second quality metric. The determination module determines that the standard deviation of the % modIR value during the sixth cardiac cycle exceeds the standard deviation threshold value and hence fails to satisfy the stability criterion. The determination module then sends a second notification instructing the sensor to collect continuous PPG data of the subject.
The above described method for switching the operation of a sensor based on the quality of the PPG data is advantageous compared to existing methods for determining BCs due to lesser power consumption by the LEDs and higher reliability and accuracy of the determined BCs.
It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
While the subject matter has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the inventions are not limited to such disclosed embodiments. Rather, the subject matter can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the inventions. Additionally, while various embodiments of the subject matter have been described, it is to be understood that aspects of the inventions may include only some of the described embodiments. Accordingly, the inventions are not to be seen as limited by the foregoing description, but are only limited by the scope of the appended claims.
This invention was made with partial Government support under contract number W81XWH1110833 awarded by U.S. Department of the Army. The Government has certain rights in the invention.
