Physical training and the dynamics of the cardiac baroreflex: a comparison when blood pressure rises and falls.

In the analysis of baroreceptor reflex sensitivity (BRS) through the sequence method, spontaneous cardiac sequences are sought in which systolic blood pressure (SBP) increases are accompanied by an increase in inter-beat interval (IBI) ("up" sequences), or in which a decrease in SBP is accompanied by a decrease in IBI ("down" sequences). The regression line between the SBP and the IBI values produces an estimate of BRS in ms/mm Hg. The "up" sequences are mainly associated with vagal activation and the "down" sequences with vagal inhibition. This study evaluated the effect of regular exercise on BRS assessed differentially for the "up" and "down" sequences. Thirty two regular exercisers and 27 sedentary students performed a serial arithmetic task after a baseline period. Results show that BRS in the "up" sequences was greater for the physically active group than for the sedentary group. For the physically active group, BRS in the "up" sequences was higher than BRS in the "down" sequences. The arithmetic task produced a significant BRS decrease in the "up" sequences for the physically active group but not for the sedentary group. These results show that regular exercise modulates the dynamics of the cardiac baroreflex. The differences between the "up" and "down" sequences suggest that the physically active group displays high parasympathetic cardiac control and autonomic cardiac adjustment to stressful conditions in which vagal withdrawal plays a key role in the cardiac response.