Optical-based oscillometry blood pressure measurement device
An optical-based oscillometric blood pressure measurement device includes a cuff, which is pneumatically connected to an inflation/deflation unit and electronically connected to a pressure detection unit. It also includes light emission diode and photodiode pairs, and a volume detection unit that converts the plethysmogram received by the photodiode to the optical oscilloetrygram as the artery volume signal. Its control unit determines inflation/deflation slopes and the start/stop pressures and accurately traces the prescribed controller set point. Its extraction unit measures the systolic, diastolic, and mean arterial pressure accurately.
1. An optical-based oscillometric blood pressure measurement device for measuring arterial blood pressure, comprising: a cuff that is configured to fit on a blood pressure measurement site to compress an artery of the measurement site; an inflation/deflation unit that consists of a piezoelectric pump and a valve, to increase and decrease a pressure inside the cuff; a pressure detection unit that detects a cuff pressure, which is the pressure inside the cuff; one or more light-emitting diode and photodiode pairs, to generate plethysmogram; a volume detection unit that detects an arterial volume signal indicating a volume of the artery per unit length; a control unit that sets the cuff pressure by controlling the inflation/deflation unit; and an extraction unit that extracts the relationship of the arterial volume with a transmural pressure as defined by the difference between the arterial pressure and the cuff pressure, wherein the extraction unit measures the volume and pressure waveforms to detect systolic, diastolic, and the mean arterial pressure for each heartbeat of a subject, wherein the pressure waveforms are derived from a starting point, a flat phase, a ramp up phase, and a stop point; and wherein the extraction unit is configured to utilize a curve fitting method for performing a breathing noise removal process for eliminating noises introduced by breathing by the subject, wherein the breathing noise removal process is performed by a sinusoidal function Fb=k×sin(2π(α xi+β)), wherein k, α, and β are parameters required to define the sinusoidal function, and xi is a time series at systolic or diastolic peaks.
2. The optical-based oscillometric blood pressure measurement device of claim 1 , wherein the measurement site includes at least one of the subjects' fingers, wrist, arm, or ankle.
3. The optical-based oscillometric blood pressure measurement device of claim 1 , wherein the valve comprises at least one of a piezoelectric valve, a solenoid valve, an electromechanical valve, or a fixed orifice to release pneumatic pressure in an air bag of the cuff, and wherein pneumatic pressure is modulated by the pump.
4. The optical-based oscillometric blood pressure measurement device of claim 1 , wherein the light-emitting diode and photodiode pairs can be single or plural, and the total numbers of the light-emitting diode and the total numbers of the photodiodes can be unequal.
5. The optical-based oscillometric blood pressure measurement device of claim 1 , wherein the volume detection unit, control unit, and extraction unit operate in the CPU of a microcontroller, whose input channels comprises of digit input channels and/or analog to digital (ADC) input channels, and whose output channels of comprises analog output channels and/or digital to analog (DAC) output channels.
6. A volume detection method of detecting the volume signal for an optical-based oscillometric blood pressure measurement device for measuring blood pressure, comprising: a cuff that is configured to fit on a blood pressure measurement site to compress an artery of the measurement site; an inflation/deflation unit that consists of a piezoelectric pump and a valve, to increase and decrease a pressure inside the cuff; a pressure detection unit that detects a cuff pressure, which is the pressure inside the cuff; one or more light-emitting diode and photodiode pairs, to generate plethysmogram; volume detection unit that detects an arterial volume signal indicating a volume of the artery per unit length, where the volume detection method further comprises providing a negative logarithm method, a LED/photodiode driver adjusting method, and a heartbeat detection method; a control unit that set the cuff pressure by controlling the inflation/deflation unit; and providing an extraction unit that extracts the relationship of the arterial volume with a transmural pressure as defined by the difference between the arterial pressure and the cuff pressure, wherein the extraction unit measures the volume and pressure waveforms to detect systolic, diastolic, and the mean arterial pressure of each heartbeat of a subject; wherein the pressure waveforms are derived from a starting point, a flat phase, a ramp up phase, and a stop point; and wherein the extraction unit is configured to utilize a curve fitting method for performing a breathing noise removal process for eliminating noises introduced by breathing by the subject, wherein the breathing noise removal process is performed by a sinusoidal function Fb=k×sin(2π(α xi+β)), wherein k, α, and β are parameters required to define the sinusoidal function, and xi is a time series at systolic or diastolic peaks.
7. The volume detection method of claim 6 , wherein the negative logarithm method converts the plethysmogram into an arterial volume signal per unit length by subtracting from a system constant and logarithm conversion.
8. The volume detection method of claim 6 , wherein the LED/photodiode driver adjusting method adjusts the LED driver constants whether they are gains or ADCs, or Photodiode driver constants whether they are gains or DACs, to achieve the maximum signal to noise ratio of volume signal.
9. The volume detection method of claim 6 , wherein the heartbeat detection method identifies each heartbeat real-time in the volume waveform, with its systolic peak value and time, diastolic valley value and time, and the heartbeat rate.
10. A control method of controlling of an optical-based oscillometric blood pressure measurement device for measuring blood pressure, comprising: a cuff that is configured to fit on a blood pressure measurement site to compress an artery of the measurement site; an inflation/deflation unit that consists of a piezoelectric pump and a valve, to increase and decrease a pressure inside the cuff; a pressure detection unit that detects a cuff pressure, which is the pressure inside the cuff; one or more light emitting diode and photodiode pairs, to generate plethysmogram; a volume detection unit that detects an arterial volume signal indicating a volume of the artery per unit length; the method comprising providing a control unit that sets the cuff pressure by controlling the inflation/deflation unit, with a model-based predictive controller, a two-degree of freedom Proportional integral, and differential (PID) controller, a ramp up controller, and ramp down controller; and an extraction unit that extracts the relationship of the arterial volume with a transmural pressure as defined by the difference between the arterial pressure and the cuff pressure, wherein the extraction unit measures the volume and pressure waveforms to detect systolic, diastolic, and the mean arterial pressure of a each heartbeat of a subject; wherein the pressure waveforms are derived from a starting point, a flat phase, a ramp up phase, and a stop point; and wherein the extraction unit is configured to utilize a curve fitting method for performing a breathing noise removal process for eliminating noises introduced by breathing by the subject, wherein the breathing noise removal process is performed by a sinusoidal function Fb=k×sin(2π(α xi+B)), wherein k, α, and β are parameters required to define the sinusoidal function, and xi is a time series at systolic or diastolic peaks.
11. The control method of claim 10 , wherein the model-based predictive controller includes pump and valve models, which are nonlinear, and describes the relationship between the required cuff pressure and the pump/valve driver parameters wherein, for any cuff pressure, the model outputs the estimated pump DAC and valve DAC or their gains.
12. The control method of claim 10 , wherein the two-degree of freedom Proportional, integral, and differential (PID) controller provides the final control outputs to eliminate the linear portion of the control errors.
13. The control method of claim 10 , wherein the ramp-up controller calculates the inflation pressure slope and start/stop pressures.
14. The control method of claim 10 , wherein the ramp-down controller calculates the deflation pressure slope and start/stop pressures.
15. An extraction method of measuring the arterial pressures of a subject for an optical-based oscillometric blood pressure measurement device for measuring blood pressure, comprising: a cuff that is configured to fit on a blood pressure measurement site to compress an artery of the measurement site; an inflation/deflation unit that consists of a piezoelectric pump and a valve, to increase and decrease a pressure inside the cuff; a pressure detection unit that detects a cuff pressure, which is the pressure inside the cuff; one or more light emitting diode and photodiode pairs, to generate plethysmogram; volume detection unit that detects an arterial volume signal indicating a volume of the artery per unit length; a control unit that set the cuff pressure by controlling the inflation/deflation unit; and extraction unit that extracts the relationship of the arterial volume with a transmural pressure as defined by the difference between the arterial pressure and the cuff pressure, wherein the extraction unit measures the volume and pressure waveforms to detect systolic, diastolic, and the mean arterial pressure of a subject; wherein the pressure waveforms are derived from a starting point, a flat phase, a ramp up phase, and a stop point; and wherein the extraction unit is configured to utilize a curve fitting method for performing a breathing noise removal process for eliminating noises introduced by breathing by the subject, wherein the breathing noise removal process is performed by a sinusoidal function Fb=k×sin(2π(α xi+B)), wherein k, α, and β are parameters required to define the sinusoidal function, and xi is a time series at systolic or diastolic peaks, the method comprising providing a pressure-volume curve building method, a curve fitting method, a mean arterial pressure (MAP) computation method, a systolic/diastolic extraction method, and an arterial unloading value calculation method.
16. The extraction method of claim 15 , wherein the pressure-volume curve building method uses the volume waveform and the deflation pressure, to derive the pressure and arterial volume relationship.
17. The extraction method of claim 15 , wherein the curve fitting method eliminates the noises introduced by breathing by removing breathing effects from the systolic volume contour measured by the extraction unit.
18. The extraction method of claim 15 , wherein the mean arterial pressure computation method derives the mean arterial pressure using the volume change due to systolic and diastolic pressure and eliminates the noise using a quadratic curve fitting wherein finding the location of the maximum of the curve gives the MAP.
19. The extraction method of claim 15 , wherein the systolic/diastolic extraction method uses the finite-difference of the pressure and arterial volume relationship to identify their maximums, and thus to find the systolic and diastolic pressures of a subject.
20. The extraction method of claim 15 , wherein the arterial unloading value calculation method calculates the unloading point of volume, where the transmural pressure equals zero.