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- Spaak, J, et al.
(författare)
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Human carotid baroreflex during isometric lower arm contraction and ischemia.
- 1998
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 275:3 Pt 2, s. H940-945
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Tidskriftsartikel (refereegranskat)abstract
- Our aim was to determine the roles of somatomotor activation and muscle ischemia for the tachycardia and hypertension of isometric arm contraction. Carotid-cardiac and carotid-mean arterial pressure (MAP) baroreflex response curves were determined in 10 men during rest, during isometric arm contraction at 30% of maximum, and during postcontraction ischemia. Carotid distending pressure (CDP) was changed by applying pressure and suction in a neck chamber. Pressures ranged from +40 to -80 mmHg and were applied repeatedly for 15 s during the three conditions. Maximum slopes and ranges of the response curves did not differ among conditions. The heart rate (HR) curve was shifted to a 14 +/- 1.8 (mean +/- SE) beats/min higher HR and a 9 +/- 5.7 mmHg higher CDP during contraction and to a 14 +/- 5.9 mmHg higher CDP during postcontraction ischemia with no change of HR compared with rest. The MAP curve was shifted to a 20 +/- 2.8 mmHg higher MAP and to a 18 +/- 5.4 mmHg higher CDP during contraction, and the same shifts were recorded during postcontraction ischemia. We conclude that neither somatomotor activation nor muscle ischemia changes the sensitivity of arterial baroreflexes. The upward shift of the MAP response curve, with no shift of the HR response curve during postexercise ischemia, supports the notion of parallel pathways for MAP and HR regulation in which HR responses are entirely caused by somatomotor activation and the pressor response is mainly caused by muscle ischemia.
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- Sundblad, Patrik, et al.
(författare)
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Influence of apnea on cardiovascular responses to neck suction during exercise.
- 1996
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 271:4 Pt 2, s. H1370-1374
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Tidskriftsartikel (refereegranskat)abstract
- Short-lasting neck suction (NS) is a common method to assess the carotid-cardiac baroreflex, and NS is usually applied during apnea to avoid breath-synchronous variations of heart rate (HR) and blood pressure. We hypothesized that the apnea might provoke cardiovascular effects that could confound the HR and blood pressure responses to NS. HR and blood pressure responses to 10-s trains of 50-mmHg pulses of NS were studied in six male subjects during supine rest, upright rest, isometric arm exercise at 30% of maximal voluntary contraction, and dynamic leg exercise at 100 W in the sitting position. Repeated NS sequences were performed during apnea preceded by a relaxed expiration to functional residual capacity and during eupnea. Initial HR responses to NS were similar during eupnea and apnea in all conditions. However, during isometric and dynamic exercise, recordings made under eupneic and apneic conditions differed during the second half of the NS period. During apneic isometric arm contraction, the elevation of mean carotid distending pressure (MCDP) (arterial pressure at carotid level minus NS pressure) was maintained at a 25-35% higher level than during eupneic isometric exercise over the last half of the NS period. In dynamic exercise, mean arterial pressure and MCDP started to increase after 3-5 s of apneic NS, whereas they were maintained during eupnea. One to three seconds later, HR started to drop markedly in apneic subjects, reaching values 20 beats/min lower than those in eupneic subjects at the end of the NS. We conclude that cardiovascular effects of apnea may appear after only 8 s of apnea in dynamic exercise and therefore could confound responses to NS.
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- Sundblad, Patrik, et al.
(författare)
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Slowing of carotid-cardiac baroreflex with standing and with isometric and dynamic muscle activity.
- 1996
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Ingår i: American Journal of Physiology. - 0002-9513 .- 2163-5773. ; 271:4 Pt 2, s. H1363-1369
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Tidskriftsartikel (refereegranskat)abstract
- 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 of neck suction (NS) were studied in six male subjects during supine rest, upright rest, isometric arm exercise at 30% of maximum voluntary contraction, and dynamic leg exercise at 100 W in the sitting position. Estimated mean carotid distending pressure increased by approximately 20 mmHg with 50-mmHg, QRS-triggered, pulsatile NS. Repeated NS sequences were performed in each condition. The amplitude of the bradycardic response was highly variable among the subjects and did not differ significantly between conditions, mean values ranging from 0.3 to 0.6 beats.min-1.mmHg-1. In supine rest, the full bradycardic response appeared 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 responses to develop. Our results support the notion that the carotid-cardiac baroreflex in humans becomes slowed under conditions of concurrent sympathetic stimulation.
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