Critical level of cerebral oxygenation during exercise in patients with left ventricular dysfunction

In a recent study the indexes of cerebral oxygenation decreased during maximal exercise in nearly half of all patients with left ventricular dysfunction. Whether these levels decrease severely enough to influence mental status or level of consciousness was evaluated in the present study.

Forty-two patients with idiopathic dilated cardiomyopathy (IDC) and 29 healthy subjects underwent a symptom-limited maximal exercise test. The cerebral oxyhemoglobin (O(2)Hb) and tissue oxygenation index (TOI) were continuously monitored using near-infrared spectroscopy. The changes in O(2)Hb and TOI were also measured in 7 subjects: 2 who experienced episodes of reduced consciousness caused by sudden decreases in blood pressure during exercise recovery and 5 who exhibited sustained ventricular tachycardia during an electrophysiological study. The change in cerebral O(2)Hb during exercise in patients with IDC averaged 0.38+/-3.39 micromol/L, significantly lower than in the normal subjects (4.30+/-4.47 micromol/L, p<0.0001). The cerebral O(2)Hb decreased during exercise in 18 of 42 patients with IDC. The change in cerebral TOI in the IDC patients during exercise was significantly less than that in the normal subjects (-2.0+/-4.7 vs 2.1+/-5.8%, p=0.002). The mean decreases in cerebral O(2)Hb and TOI were -5.34 micromol/L and -9.7%, respectively, in the patients with reduced consciousness during exercise recovery, and -2.52 micromol/L and -16.5%, respectively, in those with ventricular tachycardia.

The indexes of cerebral oxygenation may drop severely enough during maximal exercise in some patients with severe IDC that consciousness is affected.