過換気により誘発された神経調節性失神の1例

A Case of Neurally Mediated Syncope Induced by Hyperventilation

　患者は37歳，女性．学童期から年に4〜5回の頻度で，立位にて意識消失感，動悸発作を経験し，過換気症候群と診断されていた．諸検査にて発作の原因は認められず，神経調節性失神を疑い，頭位挙上試験（HUT）を施行した．初回のHUTでは起立直後から過換気状態になり，血圧低下に引き続き失神が誘発された．失神時には血漿エピネフリン濃度（PE）および血漿ノルエピネフリン濃度（PNE）の著明な上昇を認めた．Paper bag法併用により失神は予防し得た．Paper bag法併用下のPEは失神時と比し低値であったが，PNEの上昇は失神時と比し高率であった．Paper bag法非併用下では再度血圧低下，失神が誘発され，再現性が確認された．本症例は過換気により神経調節性失神が誘発され，失神出現時と非出現時の血中カテコラミンに特徴的な変化が認められたため報告した．

Hyperventilation-induced neurally mediated syncope (NMS) is described in a 37-year-old woman. The patient had been ambulanced to the emergency room several times a year because of syncopal symptom and had been diagnosed as hyperventilation syndrome since she started attending elementary school. She visited our hospital and examinations to clarify the cause of symp-toms were carried out. Head up tilt test (HUT : 80') was performed and NMS (vasodepressor type) was induced at 17 minutes of HUT. NMS was preceded by hyperventilation. This was proved by blood gas analy-sis. Paper bag therapy prevented development of NMS during 30 minutes of HUT. Hyperventilation progress-ing to NMS was reproducible by HUT without paper bag therapy. Without paper bag therapy, the increase in plasma epinephrine level (PE) was larger and the increase in the plasma norepinephrine level (PNE) was smaller than with paper bag therapy. Imbalance of increase in PE and PNE due to hyperventilation is a possible mechanism inducing neurally mediated syncope in this patient.