Comparison of slow-paced breathing interventions with and without an inhalation-hold on physiological outcomes: A randomized cross-over pilot study.

Slow-paced breathing (SPB) interventions have shown promise for modulating physiological regulation and enhancing cognitive performance. However, few studies have empirically examined how specific components of the breathing structure, particularly inhalation-holds during SPB, influence autonomic and endocrine responses. Thus, the present pilot study sought to address this gap by comparing the physiological and psychological outcomes of SPB with and without a 4-s post-inhalation breath hold using a within-subjects design. Participants (n = 32; 37% female) completed two SPB conditions in a randomized order: a prolonged-exhalation pattern (4-6) without a breath hold and a matched pattern with an inhalation-hold (4-4-6). Measures of hypothalamic-pituitary-adrenal (HPA) axis activity (salivary cortisol), cardiac autonomic regulation (RMSSD), sympathetic activation (skin conductance), and self-reported stress, arousal, and mood were collected. Results indicated that the inhalation-hold condition produced significantly greater decreases in cortisol and RMSSD than the no-hold SPB condition, although supplementary HF power analyses did not replicate the RMSSD interaction effect. Measures of tonic skin conductance increased over time in both conditions, and no differences between conditions were observed. Neither breathing pattern significantly impacted self-reported stress, arousal, or mood. These findings suggest that a four-second inhalation-hold can modulate HPA activity during SPB with a prolonged exhalation, but the respiratory mechanics of the hold may alter short-term respiratory-cardiac dynamics reflected in RMSSD.