Sleep as a tool for evaluating autonomic drive to the heart in cardiac transplant patients.

Abstract

The aim of this study was to investigate the autonomic drive to the heart in cardiac transplant patients (CTP) using heart rate (HR) and HR variability (HRV) analysis during non-rapid eye movement (NREM)-rapid eye movement (REM) sleep cycles, in particular during arousal associated with the emergence from slow wave sleep (SWS). In healthy subjects, this arousal is characterized by a pronounced HR surge, and HRV is lower during SWS than during the subsequent "active" sleep stage 2 and REM sleep. The participants were 24 adults, 14 CTP (men, n = 11; women, n = 3; mean age, 62.2 +/- 2.2 years; time after transplantation, 4-14 years) and 10 control subjects (men, n = 7; women, n = 3; mean age, 61.0 +/- 1.8 years). The subjects underwent polygraphic sleep, cardiac, and respiratory recordings during an experimental night. HR was measured during the arousal. HRV was estimated from the R-R intervals in 5-minute stationary segments preceding and following arousal, ie, during SWS and active sleep stage 2 from the first 2 complete NREM-REM sleep cycles. In controls, HR increased during arousal associated with the emergence from SWS during the 2 sleep cycles (P < .05). Sleep-stage-dependent increases of all HRV indexes were observed in the 2 sleep cycles. Concerning CTP, 5 of them displayed a smaller HR increase at arousal, whereas 9 other patients had no HR variation. This distinction between the 2 groups of CTP was confirmed by HRV analysis. The patients with HR reactivity to arousal presented significant sleep-stage-dependent increases in global HRV and sympathetic HRV indexes, whereas the nonreactive group was characterized by an inability of HRV to change with sleep-stage alternation. Sympathetic HRV indexes were significantly higher in the reactive patients than in nonreactive patients, but high frequency power reflecting parasympathetic activity did not differ. However, the absolute HRV indexes were greatly decreased in both groups of patients compared to controls. HR reactivity during arousal associated with the emergence from SWS, corroborated by HRV surrounding arousal, may suggest a partial improvement of the sympathetic drive to the heart in some CTP, with no indication of increased parasympathetic activity. Other signs of reinnervation have to be identified to validate this hypothesis.