Systems and methods for determining when to measure a physiological parameter

1. A method for monitoring blood pressure (BP), the method comprising:

(a) determining, by a processor, a current BP measurement using a non-invasive blood pressure (NIBP) device;

(b) associating, by the processor, a first reference metric value and a second reference metric value with the current BP measurement, wherein the first reference metric value is based at least in part on a reference pulse rate, and wherein the second reference metric value is at least one of a reference differential pulse transit time (DPTT), a reference pulse moment, and a reference photoplethysmograph (PPG) baseline offset;

(c) monitoring, by the processor, a first metric value and a second metric value based at least in part on a continuous non-invasive technique, wherein the first monitored metric value is based at least in part on pulse rate, and wherein the second monitored metric value is at least one of DPTT, pulse moment and PPG baseline offset;

(d) computing, by the processor, a first difference based at least in part on the first monitored metric value and the first reference metric value;

(e) computing, by the processor, a second difference based at least in part on the second monitored metric value and the second reference metric value;

(f) computing, by the processor, a composite metric based on the first difference and the second difference;

(g) updating, by the processor, the current BP measurement using the NIBP device when the composite metric exceeds a threshold;

(h) determining, by the processor, at least one calibration coefficient of a photoplethysmography based non-invasive blood pressure (PNIBP) calculation formula when the composite metric exceeds the threshold; and

(i) determining, by the processor, a physiological parameter using a device that is calibrated using the at least one calibration coefficient.

2. The method of claim 1 , wherein the first metric value is based at least in part on pulse rate, DPTT, and one or more of pulse wave area, pulse statistical moment, pulse wave centroid, rotational moments, pulse wave fiducial positions, and DC offset.

3. The method of claim 1 , wherein the threshold is based at least in part on the current blood pressure measurement.

4. The method of claim 1 , wherein the threshold is based on the first monitored metric value.

5. The method of claim 1 , wherein the threshold value is based at least in part on the relative magnitudes of the first monitored metric value and the first reference metric value.

6. The method of claim 1 , wherein the threshold is based at least in part on user input.

7. The method of claim 1 , wherein the first monitored metric value is based at least in part on a photoplethysmograph (PPG) signal.

8. The method of claim 1 , wherein computing the first difference further comprises computing a difference based at least in part on pulse rate, and two or more of DPPT, signal derivative, pulse wave area, notch position, pulse moment, and PPG baseline offset.

9. The method of claim 1 , further comprising measuring a change in the first monitored metric value, wherein computing the first difference based at least in part on the first monitored metric value and the first reference metric value is further based at least in part on the change in the first monitored metric value.

10. The method of claim 1 , further comprising repeating steps (a) through (i) at least once upon completing step (i).

11. A system for monitoring blood pressure (BP), the system comprising:

at least one sensing device;

a signal input configured to receive at least one physiological signal of a subject from the at least one sensing device;

a non-invasive blood pressure (NIBP) device; and

a processor coupled to the signal input and to the NIBP device and configured to:

(a) determine a current BP measurement using the NIBP device;

(b) associate a first reference metric value and a second reference metric value with the current BP measurement based at least in part on the at least one physiological signal, wherein the first reference metric value is based at least in part on a reference pulse rate and the second reference metric value is at least one of a reference differential pulse transit time (DPTT), a reference pulse moment, and a reference photoplethysmograph (PPG) baseline offset;

c) monitor a first metric value and a second metric value based at least in part on a continuous noninvasive technique and on the at least one physiological signal, wherein the first monitored metric value is based at least in part on pulse rate and the second monitored metric value is at least one of DPTT, pulse moment, and PPG baseline offset;

(d) compute a first difference based at least in part on the first monitored metric value and the first reference metric value;

(e) compute a second difference based at least in part on the second monitored metric value and the second reference metric value;

(f) compute a composite metric based on the first difference and the second difference;

(g) update the current BP measurement using the NIBP device when the composite metric exceeds a threshold;

(h) determine at least one calibration coefficient of a photoplethysmography based non-invasive blood pressure (PNIBP) calculation formula when the composite metric exceeds the threshold; and

(i) determine a physiological parameter using a device that is calibrated using the at least one calibration coefficient.

12. The system of claim 11 , wherein the processor is further configured to compute the threshold value.

13. The system of claim 11 , wherein the processors is further configured to receive user input, wherein the threshold value is determined based at least in part on user input.

14. The system of claim 11 , wherein the threshold is based on the first monitored metric value.

15. The system of claim 11 , wherein the threshold value is based at least in part on the relative magnitudes of the first monitored metric value and the first reference metric value.

16. The system of claim 11 , wherein the processor is further configured to compute the first difference based at least in part on pulse rate, and two or more of DPPT, signal derivative, pulse wave area, notch position, pulse moment, and PPG baseline offset.

17. The system of claim 11 , wherein the processor is further configured to measure a change in the first monitored metric value, wherein the first difference is further based at least in part on the change in the first monitored metric value.

18. The system of claim 11 , wherein the at least one sensing device comprises a photoplethysmograph (PPG) sensor.

19. The system of claim 11 , wherein the processor is further configured to repeat steps (a) through (i) at least once upon completing step (i).

20. The system of claim 11 , wherein the at least one sensing device comprises two PPG sensors.