P. Sundblad et D. Linnarsson, SLOWING OF CAROTID-CARDIAC BAROREFLEX WITH STANDING AND WITH ISOMETRIC AND DYNAMIC MUSCLE-ACTIVITY, American journal of physiology. Heart and circulatory physiology, 40(4), 1996, pp. 1363-1369
We hypothesized that the carotid-cardiac baroreflex becomes slowed in
conditions with increased sympathetic activity. Changes in heart rate
(HR) and blood pressure in response to 10-s trains of 50-mmHg pulses o
f neck suction (NS) were studied in six male subjects during supine re
st, upright rest, isometric arm exercise at 30% of maximum voluntary c
ontraction, and dynamic leg exercise at 100 W in the sitting position.
Estimated mean carotid distending pressure increased by similar to 20
mmHg with 50-mmHg, QRS-triggered, pulsatile NS. Repeated NS sequences
were performed in each condition. The amplitude of the bradycardic re
sponse was highly variable among the subjects and did not differ signi
ficantly between conditions, mean values ranging from 0.3 to 0.6 beats
. min(-1). mmHg(-1). In supine rest, the full bradycardic response ap
peared within <1 s, i.e., during or immediately after the R-R interval
of the first NS pulse. In the other conditions it took significantly
longer, 2-3 s or three to seven R-R intervals, for the full HR respons
es to develop. Our results support the notion that the carotid-cardiac
baroreflex in humans becomes slowed under conditions of concurrent sy
mpathetic stimulation.