Dissecting Cardiovascular Responses to a Fixed-Interval Volitional Sighing Protocol Using a Mixed Modeling Approach.

Sighing generates a reliable sympathetic cardiovascular response that, like exercise, could be leveraged in a graded "stress test" to reveal preclinical changes in cardiovascular health and stress reactivity. This study presents the fixed-interval volitional sighing (FIVS) protocol, which rhythmically paces sighs at different frequencies to systematically load the cardiovascular system. Cardiovascular and autonomic responses during the FIVS protocol were statistically dissected to independently characterize physiological responses. Sex differences were explored as a preliminary step toward characterizing factors that affect sigh reactivity. Healthy college students (n = 250, 65% female) completed a baseline task and two sighing tasks: a longer inter-sigh interval task (1 sigh per 30 s, long interval), followed by a shorter inter-sigh interval task (1 sigh per 15 s, short interval). Heart rate (HR), blood pressure, and respiration were continuously measured. Mixed models with a priori cardiorespiratory assumptions isolated HR, low-frequency heart rate variability (LF-HRV), high-frequency HRV (HF-HRV), pulse transit time variability (PTTv), mean arterial pressure (MAP), low-frequency blood pressure variability (LF-BPV), and high-frequency BPV (HF-BPV) responses to the sighing tasks. HR, LF-HRV, PTTv, MAP, and LF-BPV increased significantly from baseline to both sighing tasks, with greater changes observed during short-interval sighing. HF-BPV increased similarly from baseline to both sighing tasks. HF-HRV decreased only during the short-interval sighing task. Males exhibited greater increases than females in HR, LF-HRV, LF-BPV, HF-BPV, and PTTv but smaller decreases in HF-HRV in response to sighing. Volitional sighing elicits cardiac, vascular, and autonomic responses consistent with sympathetic activation. As time under load and loading intensity increased, greater responses were observed in several vascular and sympathetic indices. Sex differences suggest that the FIVS protocol can detect person-specific differences in cardiovascular responding. Sighing is physically accessible for most people, and the FIVS protocol may be useful as a stress test to detect early-stage cardiovascular or autonomic dysfunction.