Spontaneous baroreflex modulation of heart rate during incremental exercise test in humans

In this study we investigated the integrated arterial baroreflex control of HR during upright incremental (20 W/2 min) exercise test to exhaustion in 6 healthy males (25-40 yrs). Arterial blood pressure (BP) and HR were measured by Finapres and an ECG lead. Baroreflex sensitivity (BRS) was assessed by quantifying the slope of the regression line between systolic arterial pressure and HR (or RRint) changes over spontaneously occurring hypertension-bradycardia or hypotension-tachycardia sequences. This method is based on the analysis of the ongoing, reciprocal, changes in BP and HR and, as such, it does not require steady-state circulatory conditions. MAP HR VO₂ BRS BRS (mmHg) (b/min) (ml/Kg/min) (b/min/mmHg) (ms/mmHg) REST 102.4±3 76.8±4 3.3±0.2 -1.07±0.12 11.8±2.1 EXE 130.8±4* 166.3±5* 31.0±1.4* -0.53±0.15* 1.3±0.4* A progressive decrease in spontaneous BRS occurred during exercise, such that the baroreflex buffering of BP changes by means of fast changes in HR appeared almost abolished at the higher workloads. The results indicate that the integrated baroreceptor-cardiac reflex sensitivity is reduced during heavy exercise, and this independently on the use of RRint or HR to calculate BRS.