Effect of simulated microgravity on cardiopulmonary baroreflex control of forearm vascular resistance

1994 ◽  
Vol 266 (6) ◽  
pp. R1962-R1969 ◽  
Author(s):  
V. A. Convertino ◽  
D. F. Doerr ◽  
D. A. Ludwig ◽  
J. Vernikos
Keyword(s):  
Vascular Resistance ◽  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Reflex Response ◽  
Baroreflex Control ◽  
Circulating Blood Volume ◽  
Response Characteristics ◽  
Cardiopulmonary Baroreflex ◽  
Cardiopulmonary Baroreceptors ◽  
Forearm Vascular Resistance

The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) were studied in 11 healthy men before and after 7 days of 6 degrees head-down bedrest to test the hypothesis that microgravity alters this reflex response. We assessed the relationship between stimulus [changes in central venous pressure (delta CVP)] and reflex response (delta FVR) during unloading of cardiopulmonary baroreceptors with lower body negative pressure (LBNP; 0 to -20 mmHg). delta CVP during bedrest and LBNP was estimated from peripheral vein pressures in the dependent right arm. Compared with prebedrest baseline, plasma volume and estimated CVP were decreased by 13 and 33%, respectively, at 7 days of bedrest. Progressive reflex forearm vasoconstriction occurred in response to graded reductions in estimated CVP during LBNP, and delta FVR per unit delta CVP was doubled after bedrest. The increase in sensitivity of the cardiopulmonary baroreflex control of FVR was related to reduced circulating blood volume, suggesting that enhanced peripheral vasoconstriction in individuals adapted to microgravity can be attributed, in part, to hypovolemia. In addition, microgravity appears to alter the stimulus for cardiopulmonary baroreceptors to a lower operational range of CVP, suggesting the possibility of chronic resetting.

Diminished baroreflex control of forearm vascular resistance in physically fit humans

1987 ◽  
Vol 63 (1) ◽  
pp. 105-110 ◽  
Author(s):  
G. W. Mack ◽  
X. G. Shi ◽  
H. Nose ◽  
A. Tripathi ◽  
E. R. Nadel
Keyword(s):  
Linear Relationship ◽  
Blood Volume ◽  
Vascular Resistance ◽  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Vo2 Max ◽  
Total Blood ◽  
Baroreflex Control ◽  
Stimulus Response ◽  
Forearm Vascular Resistance

The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) were studied in five unfit [UF, maximal O2 consumption (VO2 max) = 38.5 ml X min-1 X kg-1] and six fit (F, VO2 max = 57.0 ml X min-1 X kg-1) subjects. We assessed the relationship between reflex stimulus, i.e., changes in central venous pressure (CVP) and response, i.e., FVR, during selective unloading of the cardiopulmonary mechanoreceptors with lower body negative pressure (0 to -20 mmHg). The linear relationship between FVR and CVP, the gain of this baroreflex, was significantly diminished in the F subjects, -2.42 +/- 0.57 U/mmHg, compared with the UF, -5.15 +/- 0.58 U/mmHg. Both groups, F and UF, had similar resting values for CVP and FVR; thus the diminished gain in F subjects was not simply an artifact resulting from a shift of the set point along the baroreflex stimulus-response curve. We also found a linear relationship between baroreflex gain and total blood volume (r = 0.59, P less than 0.05). We conclude that the gain of this vascular reflex is attenuated in trained individuals and is related to cardiovascular adaptations, such as an increased blood volume, associated with exercise training.

Baroreflex responses to acute changes in blood volume in humans

1990 ◽  
Vol 259 (4) ◽  
pp. R792-R798 ◽  
Author(s):  
C. A. Thompson ◽  
D. L. Tatro ◽  
D. A. Ludwig ◽  
V. A. Convertino
Keyword(s):  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Peripheral Resistance ◽  
Cardiac Response ◽  
Stimulus Response ◽  
Cardiopulmonary Baroreflex ◽  
Low Levels ◽  
Acute Changes ◽  
Pressure Changes ◽  
Forearm Vascular Resistance

To test the hypothesis that acute changes in plasma volume affect the stimulus-response relations of high- and low-pressure baroreflexes, eight men (27-44 yr old) underwent measurements for carotid-cardiac and cardiopulmonary baroreflex responses under the following three volemic conditions: hypovolemic, normovolemic, and hypervolemic. The stimulus-response relation of the carotid-cardiac response curve was generated using a neck cuff device, which delivered pressure changes between +40 and -65 mmHg in continuous steps of 15 mmHg. The stimulus-response relationships of the cardiopulmonary baroreflex were studied by measurements of forearm vascular resistance (FVR) and peripheral venous pressure (PVP) during low levels of lower body negative pressure (0 to -20 mmHg). Altered vascular volume had no effect on response relations of the carotid-cardiac baroreflex but did alter the gain of the cardiopulmonary baroreflex (-7.93 +/- 1.73, -4.36 +/- 1.38, and -2.56 +/- 1.59 peripheral resistance units/mmHg for hypovolemic, normovolemic, and hypervolemic, respectively) independent of shifts in baseline FVR and PVP. These results indicate greater demand for vasoconstriction for equal reductions in venous pressure during progressive hypovolemia; this condition may compromise the capacity to provide adequate peripheral resistance during severe orthostatic stress. Fluid loading before reentry after spaceflight may act to restore vasoconstrictive capacity of the cardiopulmonary baroreflex but may not be an effective countermeasure against potential post-flight impairment of the carotid-cardiac baroreflex.

Baroreflex regulation of hindquarter vascular resistance during acute blood volume expansion

1984 ◽  
Vol 246 (1) ◽  
pp. H74-H79 ◽  
Author(s):  
G. B. Guo ◽  
D. R. Richardson
Keyword(s):  
Blood Volume ◽  
Vascular Resistance ◽  
Volume Expansion ◽  
Time Course ◽  
Venous Pressure ◽  
Systemic Arterial Pressure ◽  
Baroreflex Control ◽  
Blood Volume Expansion ◽  
Cardiopulmonary Receptors ◽  
Cardiopulmonary Baroreceptors

The baroreflex control of hindquarter vascular resistance in response to a 30% blood volume expansion (BVE) was examined in constant-flow perfused hindlimbs of chloralose-urethan-anesthetized rats. Volume expansion initially increased both systemic arterial pressure (SAP) and central venous pressure (CVP) while decreasing hindquarter vascular resistance. After these initial changes, there was a parallel return of hindquarter-vascular resistance and CVP to pre-expansion levels, suggesting that cardiopulmonary afferents play a major role in the vascular resistance adjustments to volume expansion. This notion was supported in a separate set of experiments in which CVP was elevated selectively while SAP was held constant. This manipulation elicited a decrease in hindquarter vascular resistance, which was significantly attenuated following vagal cardiopulmonary denervation. The return of hindquarter vascular resistance following BVE also occurred in the presence of elevated SAP in rats with vagotomy and aortic nerve denervation, i.e., only the carotid sinus baroreflexes intact, but the time course was much faster compared with preparations with cardiopulmonary receptors intact. No response of hindquarter vascular resistance to BVE was observed in rats with both sinoaortic and cardiopulmonary baroreceptors denervated. These findings suggest that the return of hindquarter vascular resistance following BVE involves a gradual increase in sympathetic outflow to the hindquarters resulting from both a decrease in cardiopulmonary afferent activity and a rapid adaptation of arterial baroreflexes.

Cardiopulmonary baroreceptors modulate carotid baroreflex control of heart rate during dynamic exercise in humans

1995 ◽  
Vol 268 (4) ◽  
pp. H1567-H1576 ◽  
Author(s):  
J. T. Potts ◽  
X. Shi ◽  
P. B. Raven
Keyword(s):  
Heart Rate ◽  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Dynamic Exercise ◽  
Inhibitory Interaction ◽  
Baroreflex Control ◽  
Carotid Baroreflex ◽  
Maximal Gain ◽  
High Level ◽  
Cardiopulmonary Baroreceptors

Numerous studies have reported that, at rest, maximal carotid baroreflex gain is modulated by cardiopulmonary baroreceptors. The purpose of this study was to measure the maximal gain for carotid baroreflex control of heart rate (HR) and blood pressure [mean arterial pressure (MAP)] during dynamic exercise alone and when exercise was accompanied by two levels of cardiopulmonary baroreceptor unloading. Lower body negative pressure (LBNP) produced similar reductions in central venous pressure (CVP) at rest and during exercise. Baroreflex gain for HR at rest was not affected by low-level LBNP but was significantly increased by high-level LBNP [-0.31 +/- 0.05 to -0.57 +/- 0.23 beats.min-1.mmHg-1 carotid sinus pressure (CSP), no LBNP vs. high-level LBNP, P < 0.05]. Exercise combined with low- and high-level LBNP resulted in reflex HR gains (-0.83 +/- 0.44 and -0.83 +/- 0.17 beats.min-1.mmHg-1 CSP, low- vs. high-level LBNP, P < 0.05) that were significantly greater than the algebraic sum of the HR gain measured during exercise and LBNP alone. Neither exercise nor the two levels of LBNP significantly altered baroreflex gain for MAP. The slope relating HR gain to CVP at rest was significant (0.07 +/- 0.02 beats.min-1.mmHg CSP-1.mmHg CVP-1, P < 0.01) and increased 114% during exercise (P < 0.05). A similar analysis of MAP gain found no difference in slope between rest and exercise (P > 0.05). Together these data indicate 1) a tonic inhibitory interaction between cardiopulmonary baroreceptors and carotid baroreflex control of HR during exercise, and 2) a nonlinear relationship between deactivation of cardiopulmonary baroreceptors and changes in carotid baroreflex gain. This interaction may improve overall cardiovascular regulation when central blood volume and/or CVP is reduced, as has been reported during prolonged exercise in the heat.

Modeling of arterial and cardiopulmonary baroreflex control of heart rate

1997 ◽  
Vol 272 (5) ◽  
pp. H2343-H2352 ◽  
Author(s):  
T. H. Desai ◽  
J. C. Collins ◽  
M. Snell ◽  
R. Mosqueda-Garcia
Keyword(s):  
Aortic Arch ◽  
Carotid Sinus ◽  
Lower Body Negative Pressure ◽  
Venous Pressure ◽  
Chamber Pressure ◽  
Baroreflex Control ◽  
Cardiopulmonary Baroreflex ◽  
Phenylephrine Infusion ◽  
Cardiopulmonary Receptors ◽  
Pressure Changes

We evaluated R-R interval changes (delta R-R interval) in 13 subjects (27 +/- 6 yr; 7 men and 6 women) as a function of blood pressure changes at the carotid sinus and aortic arch and central venous pressure changes at the cardiopulmonary receptors. Neck chamber pressure and suction were used to change pressure at the carotid sinus while lower body negative pressure, phenylephrine infusion, and nitroprusside infusion were used to change pressure at the carotid sinus (delta CSP), aortic arch (delta AAP), and cardiopulmonary receptors (delta CPP). Random effects regression analysis showed a significant linear relationship for delta R-R interval (-1.75 + 1.64 delta CSP + 15.40 delta AAP + 29.02 delta CPP + error), and the correlation (r) between the observed and predicted delta R-R interval was 0.82 (P < 0.00001). Sixty-seven percent of the delta R-R interval variability observed in the study is explained by the model. delta AAP accounts for approximately 63%, delta CSP for 14%, and delta CPP for 23% of the explained delta R-R interval.

scholarly journals Digitalis-induced augmentation of cardiopulmonary baroreflex control of forearm vascular resistance.

Circulation ◽  
1985 ◽  
Vol 71 (1) ◽  
pp. 11-16 ◽  
Author(s):  
T Imamura ◽  
A Takeshita ◽  
T Ashihara ◽  
K Yamamoto ◽  
S Hoka ◽  
...  
Keyword(s):  
Vascular Resistance ◽  
Baroreflex Control ◽  
Cardiopulmonary Baroreflex ◽  
Forearm Vascular Resistance

CARDIOPULMONARY BAROREFLEX CONTROL OF FOREARM VASCULAR RESISTANCE AFTER TRAINING IN OLDER ADULTS

1995 ◽  
Vol 27 (Supplement) ◽  
pp. S31
Author(s):  
N. S. Stachenfeld ◽  
G. W. Mack ◽  
A. C. Jozsi ◽  
L. DiPietro ◽  
E. R. Nadel
Keyword(s):  
Older Adults ◽  
Vascular Resistance ◽  
Baroreflex Control ◽  
Cardiopulmonary Baroreflex ◽  
Forearm Vascular Resistance
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