Published Online
on June 27, 2005

A more recent version of this article appeared on August 1, 2005

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Submitted on March 21, 2005
Revised on April 13, 2005

Obstructive Sleep Apnea-Dependent and -Independent Adrenergic Activation in Obesity

Guido Grassi; Anna Facchini; Fosca Quarti Trevano; Raffaella Dell’Oro; Francesca Arenare; Francesco Tana; GianBattista Bolla; Anna Monzani; Maria Robuschi; and Giuseppe Mancia^*

From the Clinica Medica (G.G., A.F., F.Q.T., R.D., F.A., G.M.) and Clinica Pneumologica (F.T., A.M., M.R.), Dipartimento di Medicina Clinica, Prevenzione e Biotecnologie Sanitarie, Università Milano-Bicocca, Ospedale San Gerardo, Monza, Milan, Italy; Centro Interuniversitario di Fisiologia Clinica e Ipertensione (G.G., G.B., G.M.), IRCCS, Milan, Italy; and Istituto Auxologico Italiano IRCCS (G.G., G.M.), Milan, Italy.

^* To whom correspondence should be addressed. E-mail: giuseppe.mancia{at}unimib.it.

Abstract--No agreement exists as to the mechanisms responsible for the sympathetic hyperactivity characterizing human obesity, which has been ascribed recently to a chemoreflex stimulation brought about by obstructive sleep apnea rather than to an increase in body weight, per se. In 86 middle-age normotensive subjects classified according to body mass index, waist-to-hip ratio, and apnea/hypopnea index (overnight polysomnographic evaluation) as lean and obese subjects without or with obstructive sleep apnea, we assessed via microneurography muscle sympathetic nerve traffic. The 4 groups were matched for age, gender, and blood pressure values, the 2 obese groups with and without obstructive sleep apnea showing a similar increase in body mass index (32.4 versus 32.0 kg/m², respectively) and waist-to-hip ratio (0.96 versus 0.95, respectively) compared with the 2 lean groups with or without obstructive sleep apnea (body mass index 24.3 versus 23.8 kg/m² and waist-to-hip ratio 0.77 versus 0.76, respectively; P<0.01). Compared with the nonobstructive sleep apnea lean group, muscle sympathetic nerve activity showed a similar increase in the obstructive sleep apnea lean group and in the nonobstructive sleep apnea obese group (60.4±2.3 and 59.3±2.0 versus 40.9±1.8 bs/100 hb, respectively; P<0.01), a further increase being detected in obstructive sleep apnea subjects (73.1±2.5 bursts/100 heart beats; P<0.01). Our data demonstrate that the sympathetic activation of obesity occurs independently in obstructive sleep apnea. They also show that this condition exerts sympathostimulating effects independent of body weight, and that the obstructive sleep apnea-dependent and -independent sympathostimulation contribute to the overall adrenergic activation of the obese state.

Key words: sleep apnea syndromes • sympathetic nervous system • chemoreceptors • baroreflex

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