Monitoring of Cardiovascular Reactivity During Cold Pressor Test Using Photoplethysmography

Cold pressor test (CPT) is a standard autonomic function test to assess the sympathetic activity. The rise in diastolic blood pressure, secondary to the vasoconstriction in the peripheral vessels has been traditionally used to quantify the sympathetic reactivity to cold stimulus. In the present study, the ongoing short-term changes in vascular condition during CPT have been directly studied using waveform analysis of infrared finger-tip photoplethysmogram (PPG). Electrocardiogram (ECG) and PPG were simultaneously recorded from 11 healthy volunteers in resting condition (1 min), during (1 min) and after (5 min) the test. The PPG characteristics such as peak-to-peak interval (PPI), peak amplitude, slope, crest time and decay time were computed for every PPG pulse. In addition, the beat-to-beat changes of pulse wave transit time (PTT) representing the vascular compliance were also computed. The results depicted that the mean PPI, decay time and PTT were significantly different (respectively p≪0.01, p≪0.05 and p≪0.01) during CPT compared to rest. A sharp significant change was noticed in the amplitude (3.77±1.50 to 0.90±0.41 V) and slope (48.39±23.86 to 12.33±6.05 V/s) in response to the cold stimulus followed by a slow recovery phase. These results suggest that PPG based objectively derived parameters can be used for quantification of sympathetic reactivity and for continuous monitoring of vascular reactivity.