Pulse transit time and blood pressure changes following auditory-evoked subcortical arousal and waking of infants

Abstract

Study objectives: To establish a normal range of data in 3-month-old infants in relation to changes in cardiovascular measurements, with particular reference to pulse transit time (PTT), following subcortical arousals and awakenings from sleep. Design: Prospective study. Setting: Sleep laboratory, Dunedin Hospital Participants: Twenty healthy infants aged 9-12 weeks. Methods: Nap studies were performed using a standard polysomnographic setup with the addition of a Portapres blood pressure (BP) cuff (wrist application) and a piezoelectric sensor on the foot. PTT was measured from the ECG-R waveform to the arrival of the pulse peripherally. Infants were exposed to white noise from 50 to 100 dB at 10 dB intervals within REM and NREM sleep. Results: Awakening thresholds were higher (P = 0.01) in NREM (>90 dB) than REM sleep (mean ± SD; 74.3 ± 9.4dB). Subcortical thresholds were always 10 dB below waking thresholds. Following awakening, there was an immediate increase in HR, SBP, and DBP of 21%, 14%, and 17%, respectively, and a 13% decrease in PTT returning to baseline within 25-30 seconds. PTT at baseline measured 140 ± 11 and 139 ± 9 msec in NREM and REM sleep, respectively, and decreased approximately 20 msec with waking. PTT changes were negatively correlated with heart rate (HR) but not BP, although a trend was evident. Conclusions: At 3 months of age, infants provoked to arouse from sleep showed PTT changes that inversely mimicked BP trends, suggesting that PTT could be useful in infant studies as a marker for autonomic perturbations that occur during sleep in both clinical and research settings.