Sleep Quality and Cardiopulmonary Responses During Exercise Testing: Exploring the Chronotropic and Ventilatory Response Relationship with Sleep Quality in Healthy Young Men: A Cross-Sectional Study

<b>Background:</b> Sleep quality is critical to health, and its disturbances may affect multiple systems, including autonomic and respiratory regulation. However, its relationship with chronotropic and ventilatory responses in healthy young men remains underexplored. Thus, the study aimed to investigate the relationship between sleep quality, as measured by the Pittsburgh Sleep Quality Index (PSQI), and chronotropic and ventilatory responses during cardiopulmonary exercise testing (CPET) in a healthy young male population and to explore group differences between good and poor sleepers. <b>Methods:</b> Thirty-three healthy men completed the PSQI and a graded CPET with breath-by-breath gas analysis. Pearson correlation was used to examine relationships between the PSQI and CPET outcomes: chronotropic response (%), tidal volume (VT), minute ventilation (VE), VO₂, VCO₂, expired O₂/CO₂, VE/VO₂, and VE/VCO₂. After accounting for age, height, and weight, the correlation was reassessed. Secondary analyses using a standard cut-off point compared good (PSQI < 5) vs. poor sleepers (PSQI ≥ 5) with Welch's <i>t</i>-tests. Results: Participants were predominantly poor sleepers (84.8%; PSQI 7.3 ± 3.2). A higher PSQI correlated with lower chronotropic response (<i>r</i> = -0.35, <i>p</i> = 0.04), lower VT (<i>r</i> = -0.42, <i>p</i> = 0.02), lower expired O₂ (<i>r</i> = -0.46, <i>p</i> = 0.01), and lower expired CO₂ (<i>r</i> = -0.33, <i>p</i> = 0.05). Associations with VE, VO₂, VCO₂, VE/VO₂, and VE/VCO₂ were small and non-significant (<i>p</i> > 0.05). When age, height, and weight were controlled for, the attenuated chronotropic response association with the PSQI was not significant; however, the PSQI association remained significant for expired O₂ (<i>r</i> = -0.32, <i>p</i> = 0.04), with a trend for VT. In group comparisons, chronotropic response was higher but not significant; good sleepers showed higher VT and greater expired O₂/CO₂ (<i>p</i> < 0.05). <b>Conclusions:</b> Poorer sleep quality was initially associated with multiple cardiopulmonary responses at peak during CPET. However, after controlling for age and anthropometry measures, only expired O₂ remained linked. The findings suggest that routine sleep quality screening may add interpretive value to CPET by flagging individuals with reduced ventilatory depth, warranting prospective studies to test whether improving sleep quality can enhance exercise responses.