Figure 1.

The effect of sleep stage on pulse transit time (PTT) and heart rate (HR) in control (A), primary snoring (B), mild obstructive sleep apnea (C), and moderate-severe obstructive sleep apnea (D) groups. PTT during sleep was normalized to wake PTT. Wake denotes wake before sleep onset. PTT depicted in solid line; HR, broken line. Stages within each parameter that do not have a letter in common are significantly different (P < 0.001). bpm, beats per minute; NREM, nonrapid eye movement; REM, rapid eye movement.