Regulation of arterial blood pressure in humans during isometric muscle contraction and lower body negative pressure

1. Lower-body subatmospheric (negative) pressure led to a prompt reduction in central venous pressure and arterial blood pressure. Arterial blood pressure was then restored within 30 s and there was a tachycardia. These reflex responses have been used to investigate the role angiotensin plays in blood pressure control. 2. The initial plasma renin activity (2.9 ng of angiotensin I h−1 ml−1) did not change during the brief lowering of pressure. Before pressure was lowered neither the angiotensin-converting enzyme inhibitor nor a competitive antagonist, [Sar1,Ala8]-angiotensin II, lowered arterial pressure. 3. Nevertheless, after inhibition of the renin-angiotensin system by these agents, the reduction in blood pressure induced by lower-body negative pressure became greater and the blood pressure recovery was impaired. 4. The findings suggest that angiotensin, at a blood concentration which has no direct effect on blood pressure, interacts with the sympathetic nervous system to maintain arterial blood pressure.

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Angiotensin II does not contribute to rapid reflex control of arterial pressure

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1991.261.2.r473 ◽

1991 ◽

Vol 261 (2) ◽

pp. R473-R477 ◽

Cited By ~ 1

Author(s):

D. R. Brown ◽

J. D. Yingling ◽

D. C. Randall ◽

H. M. Aral ◽

J. M. Evans ◽

...

Keyword(s):

Blood Pressure ◽

Power Spectrum ◽

Arterial Pressure ◽

Negative Pressure ◽

Lower Body Negative Pressure ◽

Lower Body ◽

Converting Enzyme ◽

Salt Diet ◽

Arterial Blood ◽

Before And After

Pharmacological blockade of the renin-angiotensin converting enzyme reportedly alters the heart rate (HR) power spectrum in conscious dogs, suggesting that these hormones contribute to the short-term regulation of arterial blood pressure. We tested this possibility using four independent procedures. First, HR power spectrum was determined in seven awake dogs before and after administration of enalaprilat (300 ng/kg), a converting-enzyme inhibitor. There were no significant changes in the average amplitude for the spectral peak between 0.003 and 0.1 Hz (i.e., the "low-frequency peak"). Second, the HR power spectrum was measured in 11 awake rabbits before and after treatment with deoxycorticosterone acetate (1 mg.kg-1.day-1) and salt (0.9% saline ad libitum) for 7 days to depress plasma renin levels. There were no significant changes in the amplitude of the HR power spectrum, although mean HR decreased from 206 +/- 3 to 184 +/- 4 beats/min after treatment. In the third experiment, another group of rabbits (n = 8) was tested after 2 wk on a low-salt diet to elevate plasma angiotensin levels and then after 2 wk on a normal salt diet. Once again there were no significant effects on the HR power spectrum. Finally, tranquilized dogs (n = 9) were subjected to sinusoidally varying lower body negative pressure at selected frequencies of 0.008-0.12 Hz. Tests were conducted in the control state and after administration of an angiotensin receptor antagonist (saralasin, 1 microgram.kg-1.min-1). Lower body negative pressure-induced fluctuations in arterial blood pressure were similar in both states. We find no evidence for the role of the renin-angiotensin system in the moment-to-moment regulation of arterial pressure and HR.

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Reduced spontaneous baroreflex response slope during lower body negative pressure after 28 days of head-down bed rest

Journal of Applied Physiology ◽

10.1152/jappl.1994.77.1.69 ◽

1994 ◽

Vol 77 (1) ◽

pp. 69-77 ◽

Cited By ~ 62

Author(s):

R. L. Hughson ◽

A. Maillet ◽

C. Gharib ◽

J. O. Fortrat ◽

Y. Yamamoto ◽

...

Keyword(s):

Blood Pressure ◽

Negative Pressure ◽

Lower Body Negative Pressure ◽

Bed Rest ◽

Lower Body ◽

Short Term ◽

Arterial Blood ◽

Response Slope ◽

Systolic Arterial Blood Pressure ◽

Spontaneous Baroreflex

Effects of 28 days of continuous 6 degrees head-down tilt bed rest on spontaneous vagally mediated baroreflex response slope were evaluated from beat-by-beat relationships between R-R interval and systolic arterial blood pressure. Twelve healthy men (age 27–42 yr) were assigned to either countermeasure (CM) or no-countermeasure (no-CM) groups. CM consisted of strenuous short-term exercise once per day 6 days/wk from days 7 to 28 and lower body negative pressure (LBNP) for 15 min on days 16, 18, 20, and 22–28. Spontaneous baroreflex slope was evaluated by application of linear regression to sequences of at least three beats in which systolic blood pressure and R-R interval changed in the same direction. Measurements were made pre-, mid- (day 15), and post-bed rest at rest and during progressive LBNP tests (3 min at each of -20, -30, -40, and -50 mmHg). R-R interval decreased progressively and significantly (P < 0.0001) over duration of bed rest. Spontaneous baroreflex slope at rest in pre-bed rest was 18.5 +/- 2.1 ms/mm Hg for CM and 14.9 +/- 1.6 ms/mmHg for no-CM. There was a significant reduction in baroreflex slope as a function of bed rest, and it was further reduced during LBNP (P < 0.0001). Between CM and no-CM groups differences existed, but these were present pre-bed rest and appeared unaffected by countermeasures.(ABSTRACT TRUNCATED AT 250 WORDS)

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Factors mediating the pressor response to isometric muscle contraction: An experimental study in healthy volunteers during lower body negative pressure

PLoS ONE ◽

10.1371/journal.pone.0243627 ◽

2020 ◽

Vol 15 (12) ◽

pp. e0243627

Author(s):

Niels A. Stens ◽

Jonny Hisdal ◽

Espen F. Bakke ◽

Narinder Kaur ◽

Archana Sharma ◽

...

Keyword(s):

Blood Pressure ◽

Negative Pressure ◽

Lower Body Negative Pressure ◽

Blood Pressure Response ◽

Pressor Response ◽

Isometric Exercise ◽

Peripheral Resistance ◽

Relative Importance ◽

Lower Body ◽

Arterial Blood

Whilst both cardiac output (CO) and total peripheral resistance (TPR) determine mean arterial blood pressure (MAP), their relative importance in the pressor response to isometric exercise remains unclear. This study aimed to elucidate the relative importance of these two different factors by examining pressor responses during cardiopulmonary unloading leading to step-wise reductions in CO. Hemodynamics were investigated in 11 healthy individuals before, during and after two-minute isometric exercise during lower body negative pressure (LBNP; -20mmHg and -40mmHg). The blood pressure response to isometric exercise was similar during normal and reduced preload, despite a step-wise reduction in CO during LBNP (-20mmHg and -40mmHg). During -20mmHg LBNP, the decreased stroke volume, and consequently CO, was counteracted by an increased TPR, while heart rate (HR) was unaffected. HR was increased during -40 mmHg LBNP, although insufficient to maintain CO; the drop in CO was perfectly compensated by an increased TPR to maintain MAP. Likewise, transient application of LBNP (-20mmHg and -40mmHg) resulted in a short transient drop in MAP, caused by a decrease in CO, which was compensated by an increase in TPR. This study suggests that, in case of reductions of CO, changes in TPR are primarily responsible for maintaining the pressor response during isometric exercise. This highlights the relative importance of TPR compared to CO in mediating the pressor response during isometric exercise.

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Effects of Facial Cooling on Elderly and Young Subjects: Interactions with Breath-Holding and Lower Body Negative Pressure

Clinical Science ◽

10.1042/cs0900485 ◽

1996 ◽

Vol 90 (6) ◽

pp. 485-492 ◽

Cited By ~ 19

Author(s):

K. J. Collins ◽

T. A. Abdel-Rahman ◽

J. C. Easton ◽

P. Sacco ◽

J. Ison ◽

...

Keyword(s):

Blood Pressure ◽

Negative Pressure ◽

Lower Body Negative Pressure ◽

The Elderly ◽

Elderly Subjects ◽

Breath Holding ◽

Lower Body ◽

Arterial Blood ◽

Facial Cooling ◽

Young Subjects

1. The effects of convective facial cooling by cold air on arterial blood pressure, heart rate and finger blood flow and on the reflex interactions between facial cooling and respiratory and orthostatic cardiac reflexes have been examined in 28 young adults (20–39 years) and 17 elderly (66–78 years) volunteer subjects. 2. During 2 min facial cooling alone, bradycardia was smaller (P < 0.001) and reduction in finger blood flow smaller (P < 0.001) in elderly subjects than in young subjects. Increases in systolic blood pressure and mean arterial pressure were similar and diastolic pressure increased only in the young subjects. Systolic blood pressure and mean arterial pressure remained elevated in the elderly 1 min after facial cooling, but subsided in the young. 3. Arterial blood pressure increased more during a 30-s breath-hold in expiration than in inspiration (P < 0.001) in both groups, and this was exaggerated by breath-hold in expiration combined with facial cooling. The bradycardia produced by facial cooling and breath-holding in expiration was more pronounced in the young subjects than in the elderly (P < 0.002). 4. Interactions between facial cooling and orthostatic reflexes induced by lower-body negative pressure showed significantly different age-related linear trends. Facial cooling diminished the hypotension induced by lower-body negative pressure in both groups. Facial cooling had a greater effect in diminishing the lower-body negative pressure-induced tachycardia in the young than in the elderly. 5. The mechanism of alteration of the facial cooling response in elderly subjects could be largely impairment of arterial baroreflexes, particularly as a result of reduced cardiac vagal activity as well as impairment of cardiopulmonary reflexes with ageing.

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Noise-Enhanced Heart Rate and Sympathetic Nerve Responses to Oscillatory Lower Body Negative Pressure in Humans

Journal of Neurophysiology ◽

10.1152/jn.2001.86.2.559 ◽

2001 ◽

Vol 86 (2) ◽

pp. 559-564 ◽

Cited By ~ 21

Author(s):

Ichiro Hidaka ◽

Shin-Ichi Ando ◽

Hideaki Shigematsu ◽

Koji Sakai ◽

Soko Setoguchi ◽

...

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Stochastic Resonance ◽

Negative Pressure ◽

Sympathetic Nerve ◽

Carotid Sinus ◽

Lower Body Negative Pressure ◽

Arterial System ◽

Lower Body ◽

Cardiopulmonary Baroreceptors

By injecting noise into the carotid sinus baroreceptors, we previously showed that heart rate (HR) responses to weak oscillatory tilt were enhanced via a mechanism known as “stochastic resonance.” It remains unclear, however, whether the same responses would be observed when using oscillatory lower body negative pressure (LBNP), which would unload the cardiopulmonary baroreceptors with physically negligible effects on the arterial system. Also, the vasomotor sympathetic activity directly controlling peripheral resistance against hypotensive stimuli was not observed. We therefore investigated the effects of weak (0 to approximately −10 mmHg) oscillatory (0.03 Hz) LBNP on HR and muscle sympathetic nerve activity (MSNA) while adding incremental noise to the carotid sinus baroreceptors via a pneumatic neck chamber. The signal-to-noise ratio of HR, cardiac interbeat interval, and total MSNA were all significantly improved by increasing noise intensity, while there was no significant change in the arterial blood pressure in synchronized with the oscillatory LBNP. We conclude that the stochastic resonance, affecting both HR and MSNA, results from the interaction of noise with the signal in the brain stem, where the neuronal inputs from the arterial and cardiopulmonary baroreceptors first come together in the nucleus tractus solitarius. Also, these results indicate that the noise could induce functional improvement in human blood pressure regulatory system in overcoming given hypotensive stimuli.

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Sustained increases in sympathetic outflow during prolonged lower body negative pressure in humans

Journal of Applied Physiology ◽

10.1152/jappl.1990.68.3.1004 ◽

1990 ◽

Vol 68 (3) ◽

pp. 1004-1009 ◽

Cited By ~ 41

Author(s):

M. J. Joyner ◽

J. T. Shepherd ◽

D. R. Seals

Keyword(s):

Blood Flow ◽

Negative Pressure ◽

Lower Body Negative Pressure ◽

Partial Recovery ◽

Sympathetic Outflow ◽

Lower Body ◽

Control Value ◽

Arterial Blood ◽

Change In Mean ◽

Cardiopulmonary Baroreceptors

The purpose of this study was to determine whether prolonged unloading of cardiopulmonary baroreceptors with lower body negative pressure (LBNP) causes constant increases in sympathetic outflow to skeletal muscles. Eight healthy subjects underwent a 20-min control period followed by 20 min of 15-mmHg LBNP. This pressure was selected because it did not cause any significant change in mean arterial blood pressure (sphygmomanometry) or heart rate, suggesting that the cardiopulmonary baroreceptors were selectively unloaded and the activity of the arterial baroreceptors was unchanged. Muscle sympathetic nerve activity in the peroneal nerve (MSNA, microneurography) increased from an average of 21.8 +/- 1.7 bursts/min over the last 5 min of control to 29.0 +/- 2.9 bursts/min during the 1st min of LBNP (P less than 0.05 LBNP vs. control). The increase in MSNA observed during the 1st min was sustained throughout LBNP. Forelimb blood flow (plethysmography) decreased abruptly at the onset of the LBNP from a control value of 4.3 +/- 0.5 ml.min-1.100 ml-1 to 2.5 +/- 0.2 at the 1st min; the flow then increased and remained significantly above this value, but below the control value, throughout LBNP. Similar blood flow findings were obtained in additional studies, when the hand circulation was excluded during the flow measurements. Forearm skin blood flow (laser Doppler) also decreased abruptly at the onset of LBNP and was followed by partial recovery, but these changes were too small to account for all the increases in limb blood flow over the course of LBNP.(ABSTRACT TRUNCATED AT 250 WORDS)

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Differential sympathetic nerve and heart rate spectral effects of nonhypotensive lower body negative pressure

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.2001.281.2.r468 ◽

2001 ◽

Vol 281 (2) ◽

pp. R468-R475 ◽

Cited By ~ 31

Author(s):

John S. Floras ◽

Gary C. Butler ◽

Shin-Ichi Ando ◽

Steven C. Brooks ◽

Michael J. Pollard ◽

...

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Stroke Volume ◽

Negative Pressure ◽

Sympathetic Nerve ◽

Lower Body Negative Pressure ◽

Muscle Sympathetic Nerve Activity ◽

Venous Pressure ◽

Harmonic Component ◽

Lower Body

Lower body negative pressure (LBNP; −5 and −15 mmHg) was applied to 14 men (mean age 44 yr) to test the hypothesis that reductions in preload without effect on stroke volume or blood pressure increase selectively muscle sympathetic nerve activity (MSNA), but not the ratio of low- to high-frequency harmonic component of spectral power (PL/PH), a coarse-graining power spectral estimate of sympathetic heart rate (HR) modulation. LBNP at −5 mmHg lowered central venous pressure and had no effect on stroke volume (Doppler) or systolic blood pressure but reduced vagal HR modulation. This latter finding, a manifestation of arterial baroreceptor unloading, refutes the concept that low levels of LBNP interrogate, selectively, cardiopulmonary reflexes. MSNA increased, whereas PL/PH and HR were unchanged. This discordance is consistent with selectivity of efferent sympathetic responses to nonhypotensive LBNP and with unloading of tonically active sympathoexcitatory atrial reflexes in some subjects. Hypotensive LBNP (−15 mmHg) increased MSNA and PL/PH, but there was no correlation between these changes within subjects. Therefore, HR variability has limited utility as an estimate of the magnitude of orthostatic changes in sympathetic discharge to muscle.

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Effects of chronic tobacco smoke exposure on arterial blood pressure regulation

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1984.247.4.h556 ◽

1984 ◽

Vol 247 (4) ◽

pp. H556-H562

Author(s):

C. H. Bennett ◽

D. R. Richardson

Keyword(s):

Blood Pressure ◽

Cardiovascular System ◽

Arterial Blood Pressure ◽

Tobacco Smoke ◽

Sham Group ◽

Lower Body ◽

Pressure Regulation ◽

Arterial Blood ◽

Group A ◽

Group B

The purpose of this study was to determine the effects of long-term consumption of tobacco smoke on arterial blood pressure regulation. Male Sprague-Dawley rats were administered tobacco smoke for 6-8 mo. Two groups of animals (A and B) received tobacco smoke containing different levels of nicotine (group A: high nicotine, 4 mg/cigarette; group B: low nicotine, 1 mg/cigarette), while a third group (C) served as a sham control by receiving only puffs of room air. Reflex adjustments in mean arterial blood pressure (MAP), heart rate (HR), lower body blood flow, and lower body vascular resistance were compared between the three groups. In the anesthetized control state, no significant difference existed for the cardiovascular parameters measured in the three groups. However, perturbating the cardiovascular system by reducing central blood volume via a 60 degrees head-up tilt elicited less of a fall in MAP in the two smoke groups compared with the sham group. Percent decreases in MAP follow: group A, 23%; group B, 22%; and group C, 48%. Increasing MAP with phenylephrine elicited a significantly greater (P less than 0.05) reduction in HR in groups A and B (smoke treated) compared with group C (sham treated). Finally, varying carotid sinus pressure elicited significantly greater (P less than 0.01) changes in MAP in the smoke-treated animals (A and B) compared with the sham group (C). It is concluded that chronic tobacco smoke administration to laboratory rats increases the sensitivity of the reflex control of the cardiovascular system.

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