Pulse transit time-derived respiratory parameters and their variability across sleep stages.

We considered the capability of pulse transit time (PTT) to provide respiratory information in obstructive sleep apnea (OSA) patients. PTT-derived respiratory frequency was quite well correlated with that derived from inductance plethysmography, with amplitude slightly less so. The PTT-derived respiratory estimates were also used to distinguish sleep stage. In some subjects, statistically significant differences in respiratory parameters were observed between Wake, REM, and Stage 2 sleep, but this effect was highly subject dependent.