Prolonged lung-to-finger circulation time indicates an increased risk of intermittent hypoxemia in sleep apnea patients

Intermittent hypoxemia is closely associated with cardiovascular dysfunction and may be a more accurate indicator of OSA severity than conventional metrics. Another key factor is the lung-to-finger circulation time (LFCt), defined as the duration from the cessation of a respiratory event to the lowest point of oxygen desaturation. LFCt serves as a surrogate marker for circulatory delay and is linked with cardiovascular function. Yet, the specific associations between respiratory and hypoxemia characteristics and LFCt in OSA patients remain unclear. This study aims to investigate these associations, ultimately contributing to a more nuanced understanding of OSA severity.The study comprised 878 in-lab polysomnographies of patients with suspected OSA. The conventional OSA metrics were computed along with nine hypoxemia metrics and then divided into quartiles (Q1-Q4) based on respiratory event duration. In addition, these were further divided into sub-quartiles based on LFCt. The empirical cumulative distribution functions (CDFs) and linear regression models were used to investigate the association between desaturation metrics and LFCt.The results showed that prolonged LFCt was associated with increased hypoxic severity. Based on CDFs, the hypoxic severity significantly increased with longer LFCt despite the duration of respiratory events. Furthermore, fall duration was elevated in patients with longer LFCt (Q1-FallDur:14.6 s; Q4-FallDur:29.8 s;p<0.0001). The regression models also showed significant association between hypoxic severity and LFCt (Q1-FallSlope: β=−3.224; Q4-FallSlope: β=−6.178;p<0.0001).Considering LFCt along with desaturation metrics might be useful in estimating the association between the severity of OSA, physiological consequences of respiratory events, and cardiac health.