Evaluating changes in pulse transit time drop index in patients with obstructive sleep apnea before and during CPAP therapy

Airflow limitation in patients with obstructive sleep apnea (OSA) leads to arousal, increased sympathetic nervous system activity, and elevated blood pressure, which causes a decrease in pulse transit time (PTT). The present study aims to evaluate the effect of CPAP therapy on PTT in patients with moderate to severe OSA. This was a cross-sectional study. Split-night polysomnography (PSG) study was performed for each participant with apnea-hypopnea index (AHI) ≥ 15 before and during CPAP therapy. The PTT was calculated as the time interval between the R wave of the electrocardiogram and the following arrival point in fingertip photoplethysmography. PTT drop was defined as a fall in the PTT curve of ≥15 ms lasting at least for 3 s and at most for 30 s. PTT drop index was defined as the number of drops in PTT that occur per hour of sleep. A total of 30 patients were included. PTT significantly increased, and PTT drop index significantly decreased during CPAP therapy (P < 0.001). PTT was significantly correlated to sleep efficiency (r_s = -0.376, P = 0.049) and oxygen desaturation index (ODI) (r_s = -0.428, P = 0.018). PTT drop index was strongly correlated to AHI (r_s = 0.802, P < 0.001), respiratory disturbance index (RDI) (r_s = 0.807, P < 0.001), ODI (r_s = 0.693, P < 0.001), arousal index (r_s = 0.807, P < 0.001), and periodic leg movement (PLM) index (r_s = 0.400, P = 0.035). Overall, the findings from this study indicated that the PTT drop index is a non-invasive and useful marker for evaluating the severity of OSA and the effectiveness of treatment in patients with moderate to severe OSA.