Methodological Aspects of Slow-Paced Breathing in Healthy Young Individuals with Optimal and Suboptimal Spirometric Indices

Background: The methodology of slow-paced breathing (SPB) to optimize cardiorespiratory function requires further refinement. The aim of this study was to identify the methodological ranges of resonance breathing frequencies during SPB in healthy young adults with optimal and suboptimal spirometric indices. Methods: Twenty-eight healthy Indian students living in the Arctic Russian region (age 21–24 years; 20 males, 8 females) underwent spirometry and 2 min HRV recordings at 6 time points: baseline (spontaneous breathing) and SPB periods of 9–13 s with biofeedback. Results: Participants were divided into Group 1 (FEV1 ≥ 80% predicted, n = 13) and Group 2 (FEV1 < 80% predicted, n = 15). At baseline, Group 2 showed reduced overall HRV, lower vagal activity, a higher stress index and lower baroreflex power (by LFmx) vs. Group 1. During SPB, Group 1 exhibited more significant vagal enhancement, peaking at 9–10 s breathing periods. Group 2 showed delayed, wave-like responses with peak effects at 9 s and/or 12–13 s. Conclusions: SPB frequency depends on the level of FEV1: 9–10 s periods in individuals with FEV1 ≥ 80% predicted, and 9 s and/or 12–13 s periods (delayed effect) in those with FEV1 < 80% predicted, which may be due to cardiorespiratory strain under uncomfortable climatic conditions.