Heart Rate Variability During Sleep in Snorers With and Without Obstructive Sleep Apnea

Abstract

To the Editor: We have read with interest the article by Ferini-Strambi et al1Ferini-Strambi L Zucconi M Oldani A Smirne S Heart rate variability during sleep in snorers with and without obstructive sleep apnea.Chest. 1992; 102: 1023-1027Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar examining heart rate variability in obstructive sleep apnea syndrome (OSAS), which appeared in the October 1992 issue of Chest. In patients with OSAS there are repetitive heart rate (HR) changes with bradycardia occurring during apnea followed by a tachycardia at the resumption of ventilation generally concomitant with a microarousal. These changes in HR are mediated by the autonomic nervous system (ANS).2Zwillich C Devlin T White D Douglas N Weil J Martin R Bradycardia during sleep apnea, characteristics and mechanisms.J Clin Invest. 1982; 69: 1286-1292Crossref PubMed Scopus (266) Google Scholar Ferini- Strambi et al1Ferini-Strambi L Zucconi M Oldani A Smirne S Heart rate variability during sleep in snorers with and without obstructive sleep apnea.Chest. 1992; 102: 1023-1027Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar have studied the HR variability during apnea in nonrapid eye movement (NREM) and rapid eye movement (REM) sleep using the ratio of the longest R-R interval during the apneic event to the shortest R-R interval after the end of the apneic event. In patients with respiratory disturbance index (RDI) >10, they found a reduced HR variability related to a reduced sympathetic tone in the postapneic phase (only in NREM). The autonomic nervous system (ANS) can also be studied during daytime using autonomic stress tests (AST) (ie, Valsalva maneuver, respiratory sinus arrhythmia and BP response to sustained handgrip and postural response). In contrast to what Ferini-Strambi et al1Ferini-Strambi L Zucconi M Oldani A Smirne S Heart rate variability during sleep in snorers with and without obstructive sleep apnea.Chest. 1992; 102: 1023-1027Abstract Full Text Full Text PDF PubMed Scopus (48) Google Scholar have mentioned in their introduction, these tests are not only commonly used but also validated by using a strict methodology and have established age-related normal values.3Ewing DJ Campbell IW Clarke BF Assessment of cardiovascular effects in diabetic autonomic neuropathy and prognostic implications.Ann Int Med. 1980; 92: 308-311Crossref PubMed Scopus (400) Google Scholar, 4Ingall TJ McLeod JG O'Brien PC The effect of aging on autonomic nervous system function.Aust N Z J Med. 1990; 20: 570-577Crossref PubMed Scopus (90) Google Scholar These tests have been extensively used to study ANS dysfunction in diabetes.4Ingall TJ McLeod JG O'Brien PC The effect of aging on autonomic nervous system function.Aust N Z J Med. 1990; 20: 570-577Crossref PubMed Scopus (90) Google Scholar With attention to methodologie requirements and excluding patients at risk of autonomic dysfunction or taking drugs that might influence the results of AST, we have performed AST in snorers (RDI <10), moderate OSAS (10>RDI<30) and severe OSAS (RDI >30).5Veale D Pépin JL Lévy PA Autonomic stress tests in obstructive sleep apnea syndrome and snoring.Sleep. 1992; 15: 505-513PubMed Google Scholar We have found concordant results to those of Ferini-Strambi et al. In particular, AST abnormalities were predominant in severe OSAS. Moreover, there were significant differences between normal and abnormal AST groups in nocturnal SaO2 cumulative time spent under 90 percent SaO2 (48 vs 162 min, p=0.004) and minimal SaÛ2 (80 percent vs 64 percent, p=0.011). Our study, therefore, suggests ANS dysfunction in OSAS. Some of the subjects studied had normal AST, so it is probably a secondary defect. The evolution of these tests under CPAP, however, remains to be studied. Therefore, an alteration of ANS function has now been shown in OSAS using two different approaches. Moreover, while Ferini-Strambi et al have shown acute consequences of OSA on the ANS, we have demonstrated chronic changes in ANS function. These findings both contribute to a better understanding of OSAS pathophysiology. The study of ANS function during sleep is, in any case, practical in subjects who routinely undergo nocturnal polysomnography, like patients with OSAS. Heart Rate Variability During Sleep in Snorers With and Without Obstructive Sleep ApneaCHESTVol. 105Issue 4PreviewTo the Editor: Full-Text PDF