Static and dynamic changes in carotid artery diameter in humans during and after strenuous exercise

Abstract

Arterial baroreflex function is altered by dynamic exercise, but it is not clear to what extent baroreflex changes are due to altered transduction of pressure into deformation of the barosensory vessel wall. In this study we measured changes in mean common carotid artery diameter and the pulsatile pressure : diameter ratio (PDR) during and after dynamic exercise. Ten young, healthy subjects performed a graded exercise protocol to exhaustion on a bicycle ergometer. Carotid dimensions were measured with an ultrasound wall-tracking system; central arterial pressure was measured with the use of radial tonometry and the generalized transfer function; baroreflex sensitivity (BRS) was assessed in the post-exercise period by spectral analysis and the sequence method. Data are given as means +/- S.E.M. Mean carotid artery diameter increased during exercise as compared with control levels, but carotid distension amplitude did not change. PDR was reduced from 27.3+/-2.7 to 13.7+/-1.0 microm mmHg(-1). Immediately after stopping exercise, the carotid artery constricted and PDR remained reduced. At 60 min post-exercise, the carotid artery dilated and the PDR increased above control levels (33.9+/-1.4 microm mmHg(-1)). The post-exercise changes in PDR were closely paralleled by those in BRS (0.74< or = r < or =0.83, P<0.05). These changes in mean carotid diameter and PDR suggest that the mean baroreceptor activity level increases during exercise, with reduced dynamic sensitivity; at the end of exercise baroreceptors are suddenly unloaded, then at 1 h post-exercise, baroreceptor activity increases again with increasing dynamic sensitivity. The close correlation between PDR and BRS observed at post-exercise underlies the significance of mechanical factors in arterial baroreflex control.

Figure 1. Carotid artery distension wave and blood pressure recordings before, during and after dynamic exercise

Carotid artery distension wave recordings and corresponding blood pressure values in one representative subject during the control period, at peak-exercise, and at 5 and 55 min post-exercise. SBP, systolic blood pressure; DBP, diastolic blood pressure. Time scale = 1 s.

Figure 2. Effect of dynamic exercise on systolic and diastolic carotid diameter

Changes in averaged systolic and diastolic carotid diameter (A) and arterial pressure (B) values at rest (control, C), during the early, middle and late phase of dynamic exercise (E₁, E₂ and E₃, respectively) and at 10 min intervals during the post-exercise period. Subjects took part in two trials, one involving the exercise bout (•), the other involving supine rest for the same period of time and requiring the same measurements (○). Data are given as means ± s.e.m. *Significantly different from control at P < 0.05.

Figure 3. Effect of dynamic exercise on mean carotid diameter, carotid distension, arterial pressure and pulse pressure

Changes in averaged mean carotid diameter (A, ○), mean arterial pressure (A, •), carotid distension (B, ○) and pulse pressure (B, •) during the early, middle and late phase of dynamic exercise, and at 10 min intervals during the post-exercise period, as a percentage of the control period (C = 100 %). Data are given as means ± s.e.m. *Significantly different from control at P < 0.05.

Figure 4. Effect of dynamic exercise on the PDR and BRS

Changes from baseline (means ± s.e.m) in the PDR (•) and BRS, as assessed by spectral analysis (LF_α, ○). *Significantly different from control at P < 0.05.