Development Of A Cold Pressor Test Protocol To Evaluate Cardiac Autonomic Function

PURPOSE This study tested the reliability and reproducibility of a cold pressor test protocol for the evaluation of cardiac autonomic function. Secondary goals were to investigate the effects of gender and posture on cardiac autonomic function. METHODS Twenty-four normotensive men (n = 12) and women (n = 12) completed 3 trials of the study protocol that included heart rate, blood pressure and ventilatory data collection during 3 postures (left lateral lying, standing and seated for 15 minutes each) and during the cold pressor test (hand immersed in 5°Celsius water for 6 minutes). Spectral analysis of heart rate variability and spontaneous baroreflex sensitivity were used to identify variables indicative of of cardiac autonomic function. RESULTS Betwen trials 1 and 2, there were no significant differences in variables indicative of cardiac autonomic function during the cold pressor test and postural changes. Significant correlations were observed in all heart rate variability and spontaneous baroreflex sensitivity variables, except for low frequency power in the lying posture and during the cold pressor test. Bland-Altman plots constructed for heart rate variability and spontaneous baroreflex variables in trials 1 versus 2 revealed no significant systematic biases. Heart rate and blood pressure were significantly higher and total power, high frequency power, and low frequency power were significantly lower during the cold pressor test compared to the seated posture. The sympathetic nervous system (SNS) indicator increased significantly from a baseline value of 0.45±0.06 to 0.82±0.2 during the cold pressor test. Significant changes were also observed in the parasympathetic nervous system (PNS) indicator, which decreased from a baseline value of 0.87±0.10 to 0.45±0.30 in response to the cold pressor test. In comparison to the left lateral lying posture, both genders showed a significant increase in the SNS indicator and decreases in the R-R interval and spontaneous baroreflex slope when standing. The only significant gender difference was in the PNS indicator during the left lateral lying posture, with women having a higher value than men (0.50±0.05 vs. 0.29±0.04). CONCLUSIONS Findings support the hypothesis that the cold pressor test is a reliable and reproducible method for testing cardiac autonomic function. Cardiac autonomic function exhibits gender and postural differences in humans. Supported by The Physicians' Services Incorporated Foundation (Canada), the Garfield Kelly Cardiovascular Research and Development Fund, and Advisory Research Committee (Queen's University)