Patent Application
20190104946
Embodiments of the invention relate to a method, apparatus, and system for measuring blood pressure.
There are presently many different types of pressure sensor configurations for measuring blood pressure and blood pressure waveforms of a patient.
As one example, a Disposable Pressure Transducer (DPT) may be used with arterial and other catheters. It is a low fidelity, low cost, disposable pressure sensor. The DPT housing mounts on an IV pole and connects to the catheter through long tubing. The housing is a flow through device that keeps the pressure sensor patent by maintaining a constant pressure upstream of the sensor. Additionally, fluid can be added or withdrawn from the patient through the sensor. The DPT is a differential pressure sensor that measures relative to the atmospheric pressure in the room. To compensate for pressures generated by height differences (gravity) between the catheter and the patient's heart, the DPT is positioned on the IV pole at the patient's heart level.
As another example, a finger cuff pressure sensor may be used to measure the pressure generated with an air system in a volume clamp cuff. This is a common air pressure sensor that measures the air pressure in the volume clamp cuff relative to atmospheric pressure in the room. The sensor may be located within a wrist unit.
A second pressure sensor, a Heart Reference Sensor (HRS), may be utilized with the finger cuff system to compensate for pressures generated by height differences between the patient's finger and heart. The HRS connects an oil filled bladder located at the patient's heart level to a pressure sensor located at the patient's finger or wrist unit through an oil filled tube. The gravity generated pressures between the patient's heart level and finger level are measured by the HRS and subtracted from the cuff pressure sensor in the system's data processing software/algorithms
The DPT's strengths are its low cost and its high modularity—it can easily be connected to a wide variety of catheters through the long tubing and a luer fitting. The two primary shortcomings of the DPT are the data losses due to the tubing and the process of leveling the DPT with the patient's heart on the IV pole. The long tubing introduces noise and artifacts due to mechanical resonances. To remove these effects, the sensor's data may be filtered, but this also removes significant higher frequency information from the data signal. Blood pressure waveforms are often processed in real-time with algorithms that calculate hemodynamic and physiological parameters such as Stroke Volume Variation and Cardiac Output. The loss of information slows algorithm convergence, and leaves the algorithm unable to track patients with arrhythmias and other effects. Further, the heart level system adds work to the clinician's workflow and doesn't track the patient's movements.
On the other hand, the finger cuff system uses two pressure sensors and combines the results in order to measure blood pressure that is compensated for by the patient's heart level and atmospheric pressure. Using two sensors is expensive and complicates manufacturing.
Therefore, there is a need for improved blood pressure measurement devices.
Embodiments of the invention may relate to a blood pressure measurement device for a patient at a patient measurement site, comprising: a housing; and a pressure sensing chip mounted in the housing that is attachable to the patient measurement site. The pressure sensing chip may include a pressure transducing member. The pressure sensing chip may be configured to measure the patient's blood pressure based upon: 1) pressure applied by the patient's blood against the pressure transducing member at a first side of the pressure transducing member; and 2) gravity generated pressures over a height difference between the patient's heart level and a point of blood pressure measurement applied against the pressure transducing member at a second side of the pressure transducing member.
Embodiments of the invention may relate to a blood pressure measurement device for a patient at a patient measurement site, comprising: a housing; and a pressure sensing chip mounted in the housing that is attachable to the patient measurement site. The pressure sensing chip may include a pressure transducing member. The pressure sensing chip may be configured to measure the patient's blood pressure based upon 1) pressure applied by the patient's blood against the pressure transducing member at a first side of the pressure transducing member and 2) gravity generated pressures over a height difference between the patient's heart level and a point of blood pressure measurement applied against the pressure transducing member at a second side of the pressure transducing member.
The pressure transducing member may include a membrane that includes a piezo resistive strain sensor such that a patient's blood abutting against the membrane results in a deformation of the membrane which is measured as a change in resistance in the piezo resistive strain sensor and is measured by the pressure sensing chip for measuring the patient's blood pressure. Any liquid with the same density as blood, typically around 1060 kg/m3, may be used as a measuring liquid abutting against the second side of the pressure transducing member to compensate for gravity generated pressures over a height difference between the patient's heart level and the point of blood pressure measurement. While any liquid with the same density as blood will correctly transfer gravity generated pressures to the pressure transducing member, it is generally preferred that the liquid be inert and biocompatible. It should be appreciated that oil or any suitable liquid may be utilized.
Referring to
The resistance in the piezo resistive strain sensor 110 is a function of membrane deformation. Thus, the patient's blood pressure may be measured indirectly through the measurement of the resistance in the piezo resistive strain sensor 110. A resistance measuring circuit 120 may be utilized to measure the resistance in the piezo resistive strain sensor. In one embodiment, the resistance measuring circuit 120 may comprise a Wheatstone bridge circuit. The output signal of the resistance measuring circuit 120 may be fed into a pressure sensing and data processing monitor that processes the output signal, determines the patient's blood pressure, and displays the patient's blood pressure to clinicians.
In one embodiment, pressure transducing member—piezo resistive strain sensor 110 and the resistance measuring circuit 120 may be incorporated into a silicon pressure sensing chip.
Referring to
In particular, the pressure sensing chip 210 includes the pressure transducing membrane 205 (e.g., the deformable membrane 205 utilizing piezo resistive strain sensors) and the pressure sensing chip 210 measures the membrane deflection. The pressure sensing chip 210 may be packaged into a plastic housing 215 that allows the blood pressure bearing media 220—e.g., blood or air—access to a first side of the pressure transducing membrane 205 and the heart level and ambient pressure bearing media 225 access to a second side (opposite the first side) of the membrane 205.
In one embodiment, the housing 215 may be made of two pieces that are attached together and sealed with silicone gaskets 230 around the pressure sensing chip 210. The blood pressure side (e.g., the first side) may include a silicone plug or seal 235 (e.g., silicone gasket, air vent, and wire strain relief) that allows air to escape from the pressure sensing region through perforations 255 in the housing once the pressure measurement device 200 is attached to a catheter and exposed to the patient's blood pressure. Thus, in one embodiment, the blood pressure measurement device 200 may be attached to a catheter or another suitable measurement site. The heart level side (e.g., the second side) may include a connection for a liquid filled tube 240 and a sealing port 245 (e.g., a silicone or viton plug) to close the liquid filled tube. As has been described, it should be appreciated that oil or any suitable liquid may be utilized. Electrical connections may be made directly to the pressure sensing chip 210 via a wire 250. The wire 250 may be connected to the pressure sensing chip 210 at a connector outside the pressure sensing region and may enable direct electrical connections from the pressure sensing chip 210 to a pressure sensing and data processing monitor (e.g., via a cable).
Therefore, the pressure sensing chip 210 may be configured to measure the patient's blood pressure based upon: 1) pressure applied by the patient's blood against the membrane 205 at a first side of the membrane 205 and 2) gravity generated pressures over a height difference between the patient's heart level and a point of blood pressure measurement applied against the membrane 205 at a second side of the membrane 205.
Referring to
Referring to
Therefore, embodiments of the invention eliminate the need for long tubing that degrades the DPT pressure signal in DPT systems. This enables faster algorithm convergence and other high resolution data benefits. Further, it simplifies the operating room (OR) environment by eliminating cables and simplifying clinician setup. Further, embodiments of the invention reduce cost associated with finger cuff systems by reducing the number of required pressure sensors from two to one.
It should be appreciated that aspects of the invention previously described may be implemented in conjunction with the execution of instructions by processors, circuitry, controllers, control circuitry, etc. As an example, control circuity may operate under the control of a program, algorithm, routine, or the execution of instructions to execute methods or processes (e.g., method 400 of
The various illustrative logical blocks, processors, modules, and circuitry described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a specialized processor, circuitry, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A processor may be a microprocessor or any conventional processor, controller, microcontroller, circuitry, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module/firmware executed by a processor, or any combination thereof. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
This application claims priority to U.S. Provisional Application Ser. No. 62/571,120, filed Oct. 11, 2017, the contents of which are incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62571120 | Oct 2017 | US |
