Responses of the circulatory system and muscle sympathetic nerve activity to head-down tilt in humans

Nagaya, Ken; Wada, Futoshi; Nakamitsu, Shinichi; Sagawa, Sueko; Shiraki, Keizō

doi:10.1152/ajpregu.1995.268.5.r1289

Cited by 29 publications

(32 citation statements)

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“…In spite of these changes, the arterial blood pressure and f c did not change during HDT in either thermal condition. It has been reported that HDT at an angle of <30°increases central venous pressure and central blood volume without changing the arterial blood pressure and f c under normothermic conditions (Goldsmith et al 1985;London et al 1983;Nagaya et al 1995). The results of the present study suggest that HDT at an angle of 30°or below selectively stimulates cardiopulmonary baroreceptors without additional changes in systemic blood pressure during normothermia and mild hyperthermia.…”

Section: Discussionsupporting

confidence: 60%

“…Therefore, we need to determine the net eect of raised body temperature on the arterial barore¯ex control of f c at a similar loading of the cardiopulmonary baroreceptors between normothermia and hyperthermia. stimulate the cardiopulmonary baroreceptors without changes in systemic arterial pressure and f c (Goldsmith et al 1985;London et al 1983;Nagaya et al 1995). It is therefore thought that the decreased activity of cardiopulmonary baroreceptors during heat stress can recover to the normothermic level with HDT at an angle <30°.…”

Section: Introductionmentioning

confidence: 99%

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Spontaneous arterial baroreflex control of the heart rate during head-down tilt in heat-stressed humans

Yamazaki

Matsumura

Nagata

et al. 2001

European Journal of Applied Physiology

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The purpose of this study was to elucidate the effect of raised body temperature per se during acute heat stress on the spontaneous arterial baroreflex control of heart rate (fc) in humans. To investigate whether unloading of cardiopulmonary baroreceptors during whole-body heating would alter the arterial baroreflex control of fc, we controlled loading of the cardiopulmonary baroreceptors by head-down tilt (HDT) at angles of 5 degrees, 10 degrees, 15 degrees, and 30 degrees during heat stress produced by hot-water-perfused suits. The sensitivity of the arterial baroreceptor-cardiac reflex was calculated from the spontaneous changes in beat-to-beat arterial pressure and fc. As an index of cardiopulmonary baroreceptor loading, the left atrial diameter (LAD) was measured by echocardiography. During whole-body heating, the LAD decreased with the rising body core temperature and increased with the HDT. The decreased LAD during heating almost recovered to the normothermic control level by 10 degrees HDT. In the supine position, cardiac baroreflex sensitivity remained unchanged during heating. Arterial pressure, fc and cardiac baroreflex sensitivity were not changed by HDT ranging from 5 degrees to 30 degrees during heating. These results suggest that cardiac baroreflex sensitivity remain unchanged during graded loading of the cardiopulmonary baroreceptors in heat-stressed humans. Also, we conclude that the sensitivity of the spontaneous arterial baroreflex controlling the fc is not influenced by raised body temperature per se during acute heat stress.

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Section: Discussionsupporting

confidence: 60%

Section: Introductionmentioning

confidence: 99%

Spontaneous arterial baroreflex control of the heart rate during head-down tilt in heat-stressed humans

Yamazaki

Matsumura

Nagata

et al. 2001

European Journal of Applied Physiology

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“…These observations add to evidence that cardiac output and stroke volume of the heart may inXuence cerebral vascular resistance and in turn blood Xow to the brain independently of blood pressure (Ide et al 1998(Ide et al , 1999Immink et al 2006;van Lieshout et al 2001van Lieshout et al , 2003. TPR increased with both upper body elevation and CPAP and was lowest in the headdown position reXecting the level of systemic sympathetic activity (Kardos et al 1997;Nagaya et al 1995). Systemic sympathetic activity may also act on resistance vessels of the brain.…”

Section: Discussionmentioning

confidence: 57%

Influence of upper body position on middle cerebral artery blood velocity during continuous positive airway pressure breathing

et al. 2007

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Continuous positive airway pressure (CPAP) is a treatment modality for pulmonary oxygenation difficulties. CPAP impairs venous return to the heart and, in turn, affects cerebral blood flow (CBF) and augments cerebral blood volume (CBV). We considered that during CPAP, elevation of the upper body would prevent a rise in CBV, while orthostasis would challenge CBF. To determine the body position least affecting indices of CBF and CBV, the middle cerebral artery mean blood velocity (MCA V(mean)) and the near-infrared spectroscopy determined frontal cerebral hemoglobin content (cHbT) were evaluated in 11 healthy subjects during CPAP at different body positions (15 degrees head-down tilt, supine, 15 degrees, 30 degrees and 45 degrees upper body elevation). In the supine position, 10 cmH(2)O of CPAP reduced MCA V(mean) by 9 +/- 3% and increased cHbT by 4 +/- 2 micromol/L (mean +/- SEM); (P < 0.05). In the head-down position, CPAP increased cHbT to 13 +/- 2 micromol/L but left MCA V(mean) unchanged. Upper body elevation by 15 degrees attenuated the CPAP associated reduction in MCA V(mean) (-7 +/- 2%), while cHbT returned to baseline (1 +/- 2 micromol/L). With larger elevation of the upper body MCA V(mean) decreased progressively to -17 +/- 3%, while cHbT remained unchanged from baseline. These results suggest that upper body elevation by approximately 15 degrees during 10 cmH(2)O CPAP prevents an increase in cerebral blood volume with minimal effect on cerebral blood flow.

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“…Recording of MSNA was performed using a tungsten microelectrode (UN (KS1), Frederick Haer, Brunswick, ME, USA) that was manually inserted through intact skin into the right peroneal nerve fascicles without local anesthesia, as previously reported [11][12][13][14]. A reference electrode was placed on the skin near the recording electrode.…”

Section: Measurementsmentioning

confidence: 99%

Changes in Blood Pressure and Muscle Sympathetic Nerve Activity during Water Drinking in Humans.

Endo

Yamauchi²,

Tsutsui³

et al. 2002

JJP

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Water drinking is recognized to be an essential behavior for fluid homeostasis and is frequently and necessarily observed in daily life. Water drinking causes many physiological changes, including fluctuations in endocrine function, cardiovascular system, and fluid balance during or immediately after drinking [1][2][3][4][5][6][7]. Because these changes occur in the early phase of drinking, the contribution of absorbed water from the gastrointestinal tract may be little, if any, but neural factors such as reflex, as with receptors in the oral, pharyngeal, esophageal, or gastric regions, have been suggested. Stimulation of the oropharyngeal region with water results in a decreased release of vasopressin and causes hypotonic diuresis in humans [1]. Recently, we have demonstrated that water drinking caused a biphasic change in blood volume; an initial hemoconcentration followed by hemodilution in humans [2]. The initial hemoconcentration was likely to be induced by a transient rise in blood pressure (BP) immediately after the onset of drinking. The rise in BP following water drinking by animals and humans might be attributed to stimuli from the oropharyngeal region, gastric distension, or other stimuli [3,[8][9][10], however, the mechanism responsible for the drinking- Japanese Journal of Physiology, 52, 421-427, 2002 Key words: pressor response, microneurography, water ingestion, gastric distension, human. Abstract:To investigate the possible involvement of the sympathetic nervous system in pressor response during water drinking, muscle sympathetic nerve activity (MSNA), blood pressure (BP), and heart rate (HR) were continuously measured in healthy young volunteers throughout the experiments of a 5-min control, 2 min of drinking 500 ml water, and a 28-min recovery. To avoid the effects of water passing through the oropharyngeal and esophageal regions and/or effects of swallowing, an equal amount of water was directly infused to the stomach through a stomach tube for 2 min. Water drinking caused a transient increase in mean arterial pressure (MAP) and HR immediately after drinking (⌬MAP, 12.6Ϯ2.1 mmHg; ⌬HR, ϩ19.9Ϯ1.7 beats/min at the peak). An abrupt decrease of MSNA was observed directly during water drinking (⌬burst rate, Ϫ6.9Ϯ1.3 bursts/min; ⌬total activity, Ϫ2,606Ϯ 491 U/min), and it increased to the baseline level thereafter. Gastric infusion had little or no effect on MAP, HR, and MSNA. The present study demonstrated that a pressor response during water drinking was associated with the attenuation of MSNA and not generated by gastric infusion of water at the same rate as in this drinking manner. In conclusion, the rapid rise in BP might be caused through stimulations from the oropharyngeal region, swallowing-induced factors, and/or a feedforward mechanism by a central descending signal from the higher brain centers.

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Responses of the circulatory system and muscle sympathetic nerve activity to head-down tilt in humans

Cited by 29 publications

References 0 publications

Spontaneous arterial baroreflex control of the heart rate during head-down tilt in heat-stressed humans

Spontaneous arterial baroreflex control of the heart rate during head-down tilt in heat-stressed humans

Influence of upper body position on middle cerebral artery blood velocity during continuous positive airway pressure breathing

Changes in Blood Pressure and Muscle Sympathetic Nerve Activity during Water Drinking in Humans.

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