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Continuous Positive Airway Pressure Treatment Improves Baroreflex Control of Heart Rate during Sleep in Severe Obstructive Sleep Apnea Syndrome

Istituto di Fisiopatologia Respiratoria, Italian National Research Council, Palermo; Clinica Medica 1, Milano-Bicocca University, Istituto Auxologico Italiano; Centro di Bioingegneria, Fondazione Don Carlo Gnocchi ONLUS, Milano and Politecnico di Milano, Milan; and Clinica Medica, Milano University, Ospedale San Gerardo, Monza, Italy

Correspondence and requests for reprints should be addressed to Maria R. Bonsignore, M.D., Istituto di Fisiopatologia Respiratoria, Italian National Research Council, Via Ugo La Malfa, 153–90146 Palermo, Italy. E-mail: marisa{at}ifr.pa.cnr.it

The role of the arterial baroreflex in the cardiovascular changes associated with the obstructive sleep apnea syndrome (OSAS), and the effect of nasal continuous positive airway pressure (CPAP) treatment on baroreflex function during sleep are unknown. Baroreflex control of heart rate was studied in 29 normotensive patients with OSAS under no treatment, in 11 age-matched control subjects, and in 10 patients at CPAP withdrawal after 5.5 ± 3.7 (range 3–14) months of treatment. Baroreflex control of heart rate was assessed by "sequence method" analysis of continuous blood pressure recordings (Finapres) obtained during nocturnal polysomnography. In untreated OSAS, baroreflex sensitivity (BRS) was low during wakefulness and non–rapid eye movement (REM) stage 2 sleep compared with control subjects, and correlated inversely with mean lowest Sa_O2 and the blood pressure increase after apneas. After CPAP treatment, the apnea-hypopnea index was lower, and mean lowest Sa_O2 higher than before treatment. After CPAP, patients were more bradycardic, blood pressure and its standard deviation decreased as Sa_O2 improved in non-REM stage 2 sleep, and BRS increased (nocturnal wakefulness: +59%; non-REM stage 2 sleep: +68% over pretreatment values). Our data suggest that baroreflex dysfunction in OSAS may be at least partly accounted for by nocturnal intermittent hypoxemia, and can be reversed by long-term CPAP treatment.

Key Words: sleep-disordered breathing • hypertension • autonomic nervous system

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