Selective photoacoustic sampling for blood pressure prediction

1 . A biometric system, comprising:

a heart rate waveform analyzer configured to:

monitor a heart rate waveform associated with a subject to detect cardiac cycle markers; and

determine one or more cardiac phase transition windows based on the cardiac cycle markers;

a photoacoustic sampling system, including:

a piezoelectric receiver; and

a light source system; and

a control system configured to:

activate the photoacoustic sampling system at a start of a first cardiac phase transition window of the one or more cardiac phase transition windows, the first cardiac phase transition window corresponding to a systolic-to-diastolic transition;

during the first cardiac phase transition window:

control the light source system to emit a first plurality of light pulses into biological tissue of the subject, the biological tissue including blood and blood vessels at depths within the biological tissue;

receive, from the piezoelectric receiver, first signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the first plurality of light pulses; and

obtain first plethysmography data based on the first signals; and

deactivate the photoacoustic sampling system by an end of the first cardiac phase transition window,

wherein the control system is further configured to:

activate the photoacoustic sampling system at a start of a second cardiac phase transition window of the one or more cardiac phase transition windows, the second cardiac phase transition window corresponding to a diastolic-to-systolic transition;

during the second cardiac phase transition window:

control the light source system to emit a second plurality of light pulses into the biological tissue of the subject;

receive, from the piezoelectric receiver, second signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the second plurality of light pulses; and

obtain second plethysmography data based on the second signals; and

deactivate the photoacoustic sampling system by an end of the second cardiac phase transition window;

wherein the heart rate waveform analyzer and the control system include one or more general purpose single- or multi-chip processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs) or other programmable logic devices, discrete gates or transistor logic, discrete hardware components, or combinations thereof.

2 . The biometric system of claim 1 , wherein the control system is further configured to deactivate the photoacoustic sampling system prior to the end of the first cardiac phase transition window responsive to a determination that the first plethysmography data includes at least a threshold number of samples.

3 . The biometric system of claim 1 , wherein the heart rate waveform analyzer is further configured to obtain the heart rate waveform based on a data stream received from a heart activity sensor.

4 . The biometric system of claim 1 , wherein the control system is further configured to: determine a blood pressure based on the first plethysmography data and the second plethysmography data; and display the blood pressure on a display.

5 . The biometric system of claim 4 , wherein the control system is further configured to determine the blood pressure based on systolic phase data comprised in the first plethysmography data, without reference to diastolic phase data comprised in the second plethysmography data.

6 . The biometric system of claim 1 , wherein the first plethysmography data and the second plethysmography data are photoacoustic plethysmography (PAPG) data.

7 . The biometric system of claim 6 , wherein the control system is further configured to generate a two-dimensional (2D) PAPG image based on the PAPG data.

8 . The biometric system of claim 7 , wherein the 2D PAPG image comprises a depth time dimension and a pulse time dimension.

9 . A biometric method, comprising:

monitoring a heart rate waveform associated with a subject to detect cardiac cycle markers;

determining one or more cardiac phase transition windows based on the cardiac cycle markers;

activating a photoacoustic sampling system at a start of a first cardiac phase transition window of the one or more cardiac phase transition windows, the first cardiac phase transition window corresponding to a systolic-to-diastolic transition, the photoacoustic sampling system including a piezoelectric receiver and a light source system;

during the first cardiac phase transition window:

controlling the light source system to emit a first plurality of light pulses into biological tissue of the subject, the biological tissue including blood and blood vessels at depths within the biological tissue;

receiving, from the piezoelectric receiver, first signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the first plurality of light pulses; and

obtaining first plethysmography data based on the first signals; and

deactivating the photoacoustic sampling system by an end of the first cardiac phase transition window;

activating the photoacoustic sampling system at a start of a second cardiac phase transition window of the one or more cardiac phase transition windows, the second cardiac phase transition window corresponding to a diastolic-to-systolic transition;

during the second cardiac phase transition window:

controlling the light source system to emit a second plurality of light pulses into biological tissue of the subject;

receiving, from the piezoelectric receiver, second signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the second plurality of light pulses; and

obtaining second plethysmography data based on the second signals; and

deactivating the photoacoustic sampling system by an end of the second cardiac phase transition window.

10 . The biometric method of claim 9 , further comprising deactivating the photoacoustic sampling system prior to the end of the first cardiac phase transition window responsive to a determination, that the first plethysmography data includes at least a threshold number of samples.

11 . The biometric method of claim 9 , further comprising obtaining the heart rate waveform based on a data stream received from a heart activity sensor.

12 . The biometric method of claim 9 , further comprising: determining a blood pressure based on the first plethysmography data and the second plethysmography data; and displaying the blood pressure on a display.

13 . The biometric method of claim 12 , further comprising determining the blood pressure based on systolic phase data comprised in the first plethysmography data, without reference to diastolic phase data comprised in the second plethysmography data.

14 . The biometric method of claim 9 , wherein the first plethysmography data and the second plethysmography data are photoacoustic plethysmography (PAPG) data.

15 . The biometric method of claim 14 , further comprising generating a two-dimensional (2D) PAPG image based on the PAPG data.

16 . The biometric method of claim 15 , wherein the 2D PAPG image comprises a depth time dimension and a pulse time dimension.

17 . One or more non-transitory media having software stored thereon, the software including instructions for controlling one or more devices to perform a biometric method, the biometric method comprising:

monitoring a heart rate waveform associated with a subject to detect cardiac cycle markers;

determining one or more cardiac phase transition windows based on the cardiac cycle markers;

activating a photoacoustic sampling system at a start of a first cardiac phase transition window of the one or more cardiac phase transition windows, the first cardiac phase transition window corresponding to a systolic-to-diastolic transition, the photoacoustic sampling system including a piezoelectric receiver and a light source system;

during the first cardiac phase transition window:

controlling the light source system to emit a first plurality of light pulses into biological tissue of the subject, the biological tissue including blood and blood vessels at depths within the biological tissue;

receiving, from the piezoelectric receiver, first signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the first plurality of light pulses; and

obtaining first plethysmography data based on the first signals; and

deactivating the photoacoustic sampling system by an end of the first cardiac phase transition window;

activating the photoacoustic sampling system at a start of a second cardiac phase transition window of the one or more cardiac phase transition windows, the second cardiac phase transition window corresponding to a diastolic-to-systolic transition;

during the second cardiac phase transition window:

controlling the light source system to emit a second plurality of light pulses into biological tissue of the subject;

receiving, from the piezoelectric receiver, second signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the second plurality of light pulses; and

obtaining second plethysmography data based on the second signals; and

deactivating the photoacoustic sampling system by an end of the second cardiac phase transition window.

18 . The one or more non-transitory media of claim 17 , wherein the biometric method further comprises deactivating the photoacoustic sampling system prior to the end of the first cardiac phase transition window responsive to a determination that the first plethysmography data includes at least a threshold number of samples.

19 . The one or more non-transitory media of claim 17 , wherein the biometric method further comprises obtaining the heart rate waveform based on a data stream received from a heart activity sensor.

20 . The one or more non-transitory media of claim 17 , wherein the biometric method further comprises: determining a blood pressure based on the first plethysmography data and the second plethysmography data; and displaying the blood pressure on a display.

21 . The one or more non-transitory media of claim 20 , wherein the biometric method further comprises determining the blood pressure based on systolic phase data comprised in the first plethysmography data, without reference to diastolic phase data comprised in the second plethysmography data.

22 . The one or more non-transitory media of claim 17 , wherein the first plethysmography data and the second plethysmography data are photoacoustic plethysmography (PAPG) data.

23 . An apparatus comprising:

a photoacoustic system, including:

a piezoelectric receiver; and

a light source system; and

a control system configured to:

receive heart rate waveform data, the heart rate waveform data indicating one or more cardiac phase transition windows based on cardiac cycle markers, from a heart rate waveform analyzer;

activate the photoacoustic sampling system at a start of a first cardiac phase transition window indicated by the heart rate waveform data, the first cardiac phase transition window corresponding to a systolic-to-diastolic transition;

during the first cardiac phase transition window:

control the light source system to emit a first plurality of light pulses into biological tissue of a subject, the biological tissue including blood and blood vessels at depths within the biological tissue;

receive, from the piezoelectric receiver, first signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the first plurality of light pulses; and

obtain first plethysmography data based on the first signals; and

deactivate the photoacoustic sampling system by an end of the first cardiac phase transition window;

wherein the control system is further configured to:

activate the photoacoustic sampling system at a start of a second cardiac phase transition window of the one or more cardiac phase transition windows, the second cardiac phase transition window corresponding to a diastolic-to-systolic transition;

during the second cardiac phase transition window:

control the light source system to emit a second plurality of light pulses into the biological tissue of the subject;

receive, from the piezoelectric receiver, second signals corresponding to acoustic waves emitted from the biological tissue and corresponding to photoacoustic emissions from the blood and the blood vessels caused by the second plurality of light pulses; and

obtain second plethysmography data based on the second signals; and

deactivate the photoacoustic sampling system by an end of the second cardiac phase transition window.

24 . The apparatus of claim 23 , wherein the control system is further configured to deactivate the photoacoustic sampling system prior to the end of the first cardiac phase transition window responsive to a determination that the first plethysmography data includes at least a threshold number of samples.