Value of beat-to-beat blood pressure changes, detected by pulse transit time, in the management of the obstructive sleep apnoea/hypopnoea syndrome

Abstract

Two important aspects of a respiratory sleep study are a measure of inspiratory effort and an estimate of the number of arousals. These can be derived from an indirect estimate of beat-to-beat blood pressure (BP), pulse transit time (PTT). This study investigated the reproducibility of inspiratory BP falls (reflecting inspiratory effort), and BP arousals derived from PTT, and the contribution they could make to the management of the obstructive sleep apnoea/hypopnoea syndrome (OSAHS). Overnight PTT was recorded at home in 40 patients being investigated for OSAHS, and a second PTT recording was made in the sleep laboratory with full polysomnography. Patients were divided into three groups according to the severity of their sleep disorder, and a third PTT recording was made at home in 13 patients subsequently established on nasal continuous positive airway pressure (CPAP). The reproducibility between the home and laboratory studies was reasonable (r=0.87 for inspiratory BP falls, r=0.81 for BP arousals). Both derivatives showed a clear progression through the three patient groups, which returned to normal on treatment. The differences between the groups were significant (p<0.001 for inspiratory BP falls, p=0.0014 for BP arousals). Receiver operator characteristic curves, used to compare polysomnography variables and PTT variables, confirmed that the PTT variables were as good as apnoea-hypopnoea index (AHI), >4% arterial oxygen saturation dip rate and electroencephalography micro-arousals at dividing patients into two groups, either requiring nasal CPAP or not requiring CPAP. Pulse transit time can provide a noninvasive estimate of inspiratory effort and a measure of arousals that together documented disease severity and response to treatment and may be useful in managing obstructive sleep apnoea/hypopnoea syndrome.