Critical Level of Cerebral Oxygenation During Exercise in Patients With Left Ventricular Dysfunction

Abstract

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...

Effects of Supplemental O2 Inhalation on Cerebral Oxygenation During Exercise in Patients With Left Ventricular Dysfunction

“…3 We recently compared the decreased levels of O2Hb and TOI at the forehead during exercise in patients with LV dysfunction with those in subjects who had experienced reduced consciousness because of a sudden drop in blood pressure induced by a parasympathetic reflex or sustained ventricular tachycardia. 22 We found that the decreases in these indexes during exercise in some patients were comparable to those in subjects who experienced reduced consciousness, which suggests that the indexes of cerebral oxygenation may drop to levels low enough to affect the level of consciousness during maximal exercise in patients with severe LV dysfunction. 22 Based on these findings, we hypothesized that breathing high O2 would raise the PaO2 and subsequently improve cerebral oxygenation in patients with LV dysfunction.…”

“…22 We found that the decreases in these indexes during exercise in some patients were comparable to those in subjects who experienced reduced consciousness, which suggests that the indexes of cerebral oxygenation may drop to levels low enough to affect the level of consciousness during maximal exercise in patients with severe LV dysfunction. 22 Based on these findings, we hypothesized that breathing high O2 would raise the PaO2 and subsequently improve cerebral oxygenation in patients with LV dysfunction. As expected, in the present study we found that breathing 50% O2 diminished the decrease in cerebral O2Hb in patients with reduced LVEF who had clearly demonstrated it during moderate to high intensity exercise while breathing room air.…”

Clinical Significance of Cerebral Oxygenation During Exercise in Patients With Coronary Artery Disease

“…19 We found that the decreases in cerebral O2Hb during exercise in some patients were comparable to those in subjects who experienced reduced consciousness. This finding suggests that the index of cerebral oxygenation might drop to levels low enough during maximal exercise to affect the level of consciousness in some cardiac patients, especially those with severe left ventricular dysfunction.…”

“…From the results of the previous investigations, 1,2,7,19 we assumed that the decrease in O2Hb during exercise would be an abnormal phenomenon. Thus, we used the ΔO2Hb level of "0" as a cut-off point for the Kaplan -Meier method without using a receiver operating characteristics (ROC) curve analysis.…”

Letter to the Editor, "Clinical Significance of Cerebral Oxygenation During Exercise in Patients With Coronary Artery Disease"

“…Considering the potential clinical relevance of their findings, 1 we would suggest they expand the results to include the TOI data as correctly done in their other recent interesting clinical studies. 10,11 …”