Breath-holding time in normal subjects, snorers, and sleep apnea patients

Background: The onset of irregular inspiratory muscle activity has been observed toward the breakpoint of the breath-holding maneuver. We wondered if this was similar to the increased respiratory effort with paradoxical breathing seen during the resolution of an apnea in obstructive sleep apnea syndrome (OSAS). Study objective: To compare the breakpoint of breath holding in normal subjects, OSAS patients, and snorers. Methods: Thirty normal subjects, 30 patients with OSAS, and 16 snorers performed serial breath- holding maneuvers at functional residual capacity (FRC) under standardized pretest conditions using the rebreathing method of Read. Results: Intergroup comparisons were carried out by analysis of variance with post hoc Tukey's Highest Significant Difference tests. Basal end-tidal carbon dioxide (EtCO₂) was significantly higher in OSAS than in normal subjects and snorers. Basal breath-holding time (BHT) was shorter in OSAS as compared with that in normal subjects and snorers (p<0.05). The maximal EtCO₂ level attained was higher in OSAS as compared with normal subjects (p<0.05) and snorers (p=0.052). The maximal BHT in OSAS was shorter than in normal subjects (p<0.05) but not in snorers. The slope of BHT/EtCO₂ differed significantly in OSAS compared with normal subjects and snorers (p<0.05). No significant correlation was found between slope BHT/EtCO₂ and age or body mass index using multiple regression analysis. The FRC of OSAS patients and snorers were similar (p=0.792). Conclusion: We conclude that BHT and slope of BHT/EtCO₂ are different in OSAS subjects as opposed to those in normal subjects and snorers.