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erebral blood flow in the resting state is regulated adequately by complex compensatory mechanisms. 1,2 During exercise, however, the O2 demand of exercising muscles surges to levels 10-15-fold higher than that in the resting state. The blood flow to the exercising muscles increases tremendously to meet this sudden surge in O2 demand. As the blood flow to each organ is determined by cardiac output, an increased distribution of blood flow to the muscle may deprive other organs of blood, especially in patients with an impaired increase in cardiac output during exercise.We recently studied cerebral oxygenation during exercise in patients with left ventricular (LV) dysfunction by measuring cerebral oxyhemoglobin (O2Hb) with a near infrared spectroscopy (NIRS) system. 3 The results indicated that the cerebral O2Hb fell during exercise in nearly half of the patients, and that the decrease was more prominent in the patients with lower LV function. These findings suggest that the decrease in cerebral O2Hb during exercise in patients with LV dysfunction reflects a cerebral hypoxemia caused by an impaired O2 transport to the brain. However, Circulation Journal Vol. 70, November 2006 no earlier studies have investigated whether the decrease in cerebral O2Hb during exercise in these patients is potentially severe enough to affect their mental status.In the present study, we sought to clarify whether the decreased levels of the cerebral oxygenation indexes during exercise posed such a threat in patients with LV dysfunction. We attempted to accomplish this by comparing the decreased levels of the indexes during exercise in these patients with those in subjects who had experienced reduced consciousness because of either of 2 reasons, that is, a sudden drop in blood pressure induced by a parasympathetic reflex or sustained ventricular tachycardia. MethodsThis research consisted of 3 parts: (1) an initial study to evaluate the indexes of cerebral oxygenation during exercise in patients with idiopathic dilated cardiomyopathy (IDC) and in healthy subjects; (2) a second study to evaluate the decreased levels of cerebral oxygenation indexes in subjects who experienced reduced consciousness during exercise recovery; and (3) a third study to measure the levels of cerebral oxygenation indexes in subjects who experienced reduced consciousness as a result of sustained ventricular tachycardia during an electrophysiological study.The committee on the ethical use of human subjects of our institution approved the protocol and procedures for all the studies. The purposes and risks of the studies were explained to the subjects, and written informed consent was Critical Level of Cerebral Oxygenation During Exercise in Patients With Left Ventricular DysfunctionAkira Koike, MD*; Masayo Hoshimoto* , **; Akihiko Tajima, BS*; Osamu Nagayama, BS*; Kaori Yamaguchi, BS*; Ayumi Goda, MD* , † ; Takeshi Yamashita, MD*; Koichi Sagara, MD*; Haruki Itoh, MD † † ; Tadanori Aizawa, MD* Background In a recent study the indexes of cerebral oxygenation decrea...

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