Autonomic Responses to Acute Hyperoxia are Impaired in Patients with Peripheral Artery Disease

Abstract

Prior reports suggest that oxidative stress plays an important role in the development of atherosclerotic diseases such as peripheral artery disease (PAD). The effects of acute hyperoxia, an important acute oxidative stressor, on autonomic function have not been well studied in PAD. We hypothesized that the autonomic responses to acute hyperoxia would be impaired in PAD. We studied 17 patients with PAD (12M, 5F, 67 ± 2 yrs) and 15 healthy controls (10M, 5F, 65 ± 2 yrs). The ankle‐brachial indexes in the patients were 0.57 ± 0.03 in the most affected leg and 0.77 ± 0.04 in the less affected leg, respectively. Beat‐by‐beat heart rate (HR, from ECG) and blood pressure (BP, with Finometer) were recorded for 10 min under normoxic resting conditions and during 5‐min hyperoxia (100% oxygen) as an acute oxidative stress test. HR variability (HRV) was calculated and cardiac baroreflex sensitivity (BRS) was estimated with the sequence technique. Under resting conditions, mean HR and mean arterial pressure (MAP) were not significantly different between the groups. Resting values of the root mean square of successive differences between normal heartbeats (RMSSD, a HRV index for parasympathetic activity; 14.1 ± 1.0 vs. 19.8 ± 2.2 ms, P = 0.032) and cardiac BRS (6.43 ± 0.78 vs. 14.86 ± 2.56 ms/mmHg, P = 0.001) were significantly lower in PAD than in healthy controls. Hyperoxia lowered HR in both groups and raised MAP only in patients with PAD. During hyperoxia both HR and MAP were significantly higher in PAD than in controls. Hyperoxia induced an increase in RMSSD and the high frequency (HF) component of HRV (another index for parasympathetic activity) in healthy subjects. However, during hyperoxia no increase in parasympathetic activity was observed in PAD. Both RMSSD and the HF component of the whole trial (i.e. baseline and hyperoxia) in PAD were lower than those in healthy control subjects. Hyperoxia did not induce changes in cardiac BRS in either group, while cardiac BRS of the whole trial in PAD was lower than that in healthy controls. These data suggest that resting parasympathetic activity and cardiac baroreflex function are impaired in PAD. Moreover, the autonomic response to acute oxidative stress (i.e. an increase in parasympathetic activity) is also impaired in PAD. Further studies are needed to examine if antioxidant agents can improve autonomic function in PAD.