Carotid–cardiac baroreflex and training status: significance of initial responsiveness

The aim of this study was to demonstrate that within a population of healthy men (n = 15) of varying levels of aerobic fitness Formula: see text, (i) there are high and low responders with respect to carotid–cardiac baroreflex responsiveness, despite similar baseline heart rates (HRs) both at rest and during dynamic exercise, and (ii) there is a weak association between this responsiveness and training status Formula: see text because of a large overlap in the responses between trained (endurance, ET) and untrained (UT) individuals. Baroreflex function curves were derived during supine rest for each subject by applying varying pressures around the neck in a beat-to-beat ramp (for 12 beats) of +40 to −60 mmHg (1 mmHg = 133.3 Pa). Subjects were divided into low (n = 8) and high (n = 7) responders on the basis of the magnitude of the maximal dynamic R–R interval (RRI) range of the baroreflex curve. Both bradycardic (percent slowing) and tachycardic (percent acceleration) components of the baroreflex curve, and peak sinus node responses (HR, RRI) to continuous neck suction (−60 mmHg) at rest and during exercise (cycling, 45% Formula: see text) were greater in high compared with low responders (p < 0.05), as assessed using both HR and RRI scales. When subjects were divided into ET and UT groups, both RRI range and maximal gain at rest were the only indices of baroreflex responsiveness that were different (p < 0.05) between the two groups, and a significant correlation was found between Formula: see text and RRI range (r 2 = 0.497, p < 0.01); a lower resting HR in ET and mathematical skewing with the RRI scale could in part explain these findings. Taken together, these results emphasize that initial carotid–cardiac baroreflex responsiveness must be considered when assessing the effect of exercise training on baroreflex function.Key words: arterial baroreflex, bradycardia, parasympathetic, endurance training.