睡眠時無呼吸症候群の夜間心拍数変動

Heart Rate Variation during Sleep in Obstructive Sleep Apnea Syndrome:A case report

　睡眠時無呼吸症候群の1例で睡眠時の心拍数変動を観察した．症例は34歳，男性．主訴は呼吸困難と傾眠傾向．著明な肥満体であり，入院時には著明な低酸素血症（PaO₂　38.0Torr）および高炭酸ガス血症（PaCO₂　69.5 Torr）を呈していた．治療前の無呼吸指数は41.1と重症の睡眠時無呼吸症候群であった．入眠とともに洞性頻脈が出現し持続したが，心拍数は無呼吸時に低下し，呼吸再開時に反射的に上昇した．減量および口蓋垂口蓋咽頭形成術にて無呼吸指数は13.5と軽快し，低酸素血症および高炭酸ガス血症も改善した．その結果，睡眠中に認められた持続性の洞性頻脈は劇的に消失した．夜間睡眠中の心拍数変動の周波数解析では，LF／HFは治療前後で2.22から1.61まで低下した．長時間の無呼吸による低酸素・高炭酸ガス血症により惹起された交感神経活動の亢進により，夜間の洞性頻脈は生じていたと考えられた．

We analyzed the heart rate variation (HRV) during sleep in a case of sleep apnea syndrome. A 34-year-old man was admitted because of dyspnea and somnolence. He was markedly obese. During sleep he showed sinus tachycardia and cyclic variation of heart rate associat-ed with apnea. With weight reduction and uvlopalato-pharyngoplasty, his symptoms and arterial blood gas were improved,: apnea index 41.1 → 13.5, PaO₂ 38.0 → 76.3 Torr, and PaCO₂ 69.5 → 42.0 Torr. Sinus ta-chycardia observed during sleep diminished dramati-cally. HRV was evaluated using spectral variables of low frequency (LF) and high frequency (HR) components, and the LF/HF ratio was determined from Holter recordings. After treatment, the HF component was increased from 30 to 415 msec² and the LF/HF ratio was decreased from 2.22 to 1.61. Thus, accelerated sympa-thetic activation, triggered by hypoxia and hypercapnia, may result in an unusual sinus tachycardia during sleep.