Acute and persistent effects of a 46-kilometre wilderness trail run at altitude: Cardiovascular autonomic modulation and baroreflexes

Objective: To test the hypothesis that prolonged physical exercise induces long-lasting effects on blood pressure and heart rate we studied 17 endurance runners before and after the 1995 Sandia Wilderness Crossing Research Run (46 km of rocky trails, average altitude 2500 m). Methods: We evaluated the response of the cardiovascular system to sympathetic stimulation by orthostatism and to sympathetic and parasympathetic carotid baroreceptor stimulations by sinusoidal neck suction at different frequencies (sympathetic activity on blood pressure by low-frequency stimulation, parasympathetic activity on RR interval by high-frequency stimulation). We used power spectral analysis of beat-to-beat RR interval, systolic and diastolic non-invasive blood pressure, in order to quantify the respiratory fluctuations (depending on vagal activity on the RR interval) and the slower non-respiratory fluctuations, depending on sympathetic activity on the blood pressure. Recordings were performed 24 h before, and 30 min, 24 h and 48 h after the run. Results: Thirty minutes after the race we found reduced blood pressure, signs of relative sympathetic predominance (increased RR interval low-frequency/high-frequency ratio from 0.65 +/- 0.15 to 1.63 +/- 0.37, P < 0.05), reduced effect of parasympathetic baroreceptor stimulation (decrease in RR interval high-frequency neck-suction synchronous oscillations, from 5.33 +/- 0.34 to 3.55 +/- 0.37 ln-ms(2), P < 0.005), unchanged blood pressure responses to sympathetic stimulations; 24 h after the race, the response to parasympathetic stimulation was increased (to 6.44 +/- 0.32 ln-ms(2), P < 0.0005) compared ro baseline (24 h before the race), whereas sympathetic stimulation by neck suction had no longer an effect on blood pressure. Conclusion: The acute effects of prolonged exertion are associated with a relative increase in sympathetic activity. Twenty-four hours after this race an increased sensitivity to vagal and reduced sensitivity to sympathetic baroreflex stimulations was found. In this field study at altitude we found long-lasting effects on cardiovascular autonomic modulation after physical exertion.