A study was conducted to clarify the effect of hyperoxia (HO) on exercise tolerance andhemodynamics in patients with ischemic heart disease (IHD) . The subjects were 10 patients with serious IHD who showed ischemic ST depression during low-intensity exercise testing. In all subjects, cardiopulmonary exercise testing (CPX) was performed using two types of inhalation : normoxia (NO) and HO (O₂: 60%, N₂: 40%) . Heart rate (HR), blood pressure (BP), rating of perceived exertion (RPE), elapsed exercise duration and pressure rate product (PRP) were measured, and ECG was recorded during CPX according to the Bruce protocol. The peak oxygen uptake (VO₂peak) was calculated using the appropriate formula. These data were compared between the NO and HO groups, and the following results were obtained.
ST depressions on ECG, BP, HR and PRP after 20 min of rest showed no changes under NO. The other hand, only ST depression was improved after 20 min of rest under HO. The exercise duration in HO group was longer than in the NO group, and the VO₂peak in the HO group was higher than in the NO group. However, peak RPE showed no significant difference between the HO and NO groups. The incidence of ST depression as an endpoint of CPX showed no significant difference between the two groups. BP, HR and PRP at the CPX endpoint showed no significant differences between the HO and NO groups. In patients whose exercise duration was prolonged beyond the mean value by HO, peak HR and PRP were increased significantly. However, this tendency was not seen in patients whose exercise was prolonged for less than the mean value.
In conclusion, these results suggest that an increase in the oxygen supply to peripheral working muscles may play an important role in increasing exercise tolerance under HO in IHD patients.