Relationship between Plasma Volume, Carotid Baroreceptor Sensitivity and Orthostatic Tolerance

1995 ◽  
Vol 88 (4) ◽  
pp. 463-470 ◽  
Author(s):  
H. El-Sayed ◽  
R. Hainsworth
Keyword(s):  
Plasma Volume ◽  
Pulse Interval ◽  
Blue Dye ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
Baroreceptor Sensitivity ◽  
Carotid Baroreceptor ◽  
Asymptomatic Volunteers ◽  
Head Up Tilt ◽  
Blood Volumes

1. Studies were carried out on 43 otherwise healthy patients referred for investigation for attacks of syncope of unknown cause and on six healthy volunteers. 2. Plasma volume was determined by Evans Blue dye dilution and blood volume was estimated using haematocrit. Carotid baroreceptor sensitivity was determined from the changes in pulse interval in response to subatmospheric pressures applied to the neck overlying the carotid sinuses, and orthostatic tolerance was assessed as the time to presyncope in a test of head-up tilt, followed by the addition of graded lower body suction. 3. Eight patients and one volunteer fainted during head-up tilt alone, 23 patients and two volunteers fainted during tilt with lower body suction at −20 mmHg and 12 patients and three volunteers either fainted during suction at −40 mmHg or tolerated the entire procedure. 4. Although plasma and blood volumes were higher in males than females, the values normalized for either body weight or for calculated lean body mass were not different between male and female patients and asymptomatic volunteers. The subjects showing the greatest resistance to syncope were found to have significantly larger plasma and blood volumes (P < 0.0001) and significantly smaller baroreceptor sensitivities (P < 0.0002) than those who fainted earlier. 5. There was a highly significant positive correlation in all subjects between orthostatic tolerance (time to onset of syncope) and plasma and blood volumes (r = 0.60, P < 0.0001; r = 0.53, P < 0.0002), and highly significant negative correlations between time to syncope and baroreceptor sensitivity (r = −0.61, P < 0.0001) and between baroreceptor sensitivity and plasma and blood volumes (r = −0.54, P < 0.0001; r = −0.31, P < 0.03). 6. These results show that tolerance to orthostatic stress is favoured by large plasma and blood volumes and a low sensitivity of the carotid baroreceptor—heart rate reflex.

Lower body negative pressure exercise plus brief postexercise lower body negative pressure improve post-bed rest orthostatic tolerance

2007 ◽  
Vol 103 (6) ◽  
pp. 1964-1972 ◽  
Author(s):  
Donald E. Watenpaugh ◽  
Deborah D. O'Leary ◽  
Suzanne M. Schneider ◽  
Stuart M. C. Lee ◽  
Brandon R. Macias ◽  
...  
Keyword(s):  
Negative Pressure ◽  
Acute Exercise ◽  
Treadmill Exercise ◽  
Orthostatic Intolerance ◽  
Lower Body Negative Pressure ◽  
Bed Rest ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
Before And After ◽  
Head Up Tilt

Orthostatic intolerance follows actual weightlessness and weightlessness simulated by bed rest. Orthostasis immediately after acute exercise imposes greater cardiovascular stress than orthostasis without prior exercise. We hypothesized that 5 min/day of simulated orthostasis [supine lower body negative pressure (LBNP)] immediately following LBNP exercise maintains orthostatic tolerance during bed rest. Identical twins (14 women, 16 men) underwent 30 days of 6° head-down tilt bed rest. One of each pair was randomly selected as a control, and their sibling performed 40 min/day of treadmill exercise while supine in 53 mmHg (SD 4) [7.05 kPa (SD 0.50)] LBNP. LBNP continued for 5 min after exercise stopped. Head-up tilt at 60° plus graded LBNP assessed orthostatic tolerance before and after bed rest. Hemodynamic measurements accompanied these tests. Bed rest decreased orthostatic tolerance time to a greater extent in control [34% (SD 10)] than in countermeasure subjects [13% (SD 20); P < 0.004]. Controls exhibited cardiac stroke volume reduction and relative cardioacceleration typically seen after bed rest, yet no such changes occurred in the countermeasure group. These findings demonstrate that 40 min/day of supine LBNP treadmill exercise followed immediately by 5 min of resting LBNP attenuates, but does not fully prevent, the orthostatic intolerance associated with 30 days of bed rest. We speculate that longer postexercise LBNP may improve results. Together with our earlier related studies, these ground-based results support spaceflight evaluation of postexercise orthostatic stress as a time-efficient countermeasure against postflight orthostatic intolerance.

Effects of head-up tilting on baroreceptor control in subjects with different tolerances to orthostatic stress

2002 ◽  
Vol 103 (3) ◽  
pp. 221-226 ◽  
Author(s):  
V.L. COOPER ◽  
R. HAINSWORTH
Keyword(s):  
Blood Pressure ◽  
Vascular Resistance ◽  
Stress Test ◽  
Orthostatic Stress ◽  
Orthostatic Tolerance ◽  
Arterial Blood ◽  
Carotid Baroreceptor ◽  
Head Up Tilt ◽  
Orthostatic Stress Test ◽  
Neck Pressure

During orthostatic stress, an increase in peripheral vascular resistance normally results in arterial blood pressure being well maintained, despite a decrease in cardiac output. The present study was undertaken to determine whether the sensitivity of the carotid baroreceptor reflex was increased during orthostatic stress and whether failure to develop this increase was associated with poor orthostatic tolerance. Three groups of subjects were studied: asymptomatic controls; patients investigated for suspected posturally related syncope but who had normal responses to an orthostatic stress test (normal patients); and patients who were shown to have low orthostatic tolerance (early fainters). We determined responses of R–R interval and forearm vascular resistance (mean arterial pressure/brachial artery velocity by Doppler ultrasonography) to the loading and unloading of carotid baroreceptors by application of pressures of -30 and +30mmHg to a chamber fitted over the neck. Responses were determined after 20min of supine rest and after 10min of head-up tilt at 60°. Responses of cardiac interval were not significantly different between the three groups, and they were not altered by the postural change. Vascular responses also did not differ between the groups during supine rest. However, in healthy volunteers and in normal patients, responses to both neck suction and pressure were significantly enhanced during head-up tilt. In controls, responses to suction were increased by tilt from 0.04±0.1 to -1.01±0.2%·mmHg-1 (means±S.E.M.; P<0.001) and those to neck pressure from -0.6±0.3 to -3.1±1.1%·mmHg-1 (P<0.05). In the normal patients, the corresponding changes were: during suction, from -0.2±0.1 to -0.7±0.1%·mmHg-1 (P<0.05); during pressure, from -0.7±0.1 to -1.5±0.3%·mmHg-1 (P<0.05). In contrast, in patients with low orthostatic tolerance, posture had no effect on the reflex (neck suction, from -0.3±0.1 to -0.3±0.1%·mmHg-1; neck pressure, from -1.0±0.3 to -0.9±0.2%·mmHg-1). We suggest that an increase in the sensitivity of the carotid baroreceptor/vascular resistance reflex may be important in the maintenance of blood pressure during orthostatic stress, and that failure of this to occur in patients with posturally related syncope may go some way towards explaining their poor orthostatic tolerance.

Combined head-up tilt and lower body suction: A test of orthostatic tolerance

1994 ◽  
Vol 4 (1-2) ◽  
pp. 41-47 ◽  
Author(s):  
K. M. EI-Bedawi ◽  
R. Hainsworth
Keyword(s):  
Orthostatic Tolerance ◽  
Lower Body ◽  
Head Up Tilt

Lower vascular tone and larger plasma volume in Parkinson's disease with orthostatic hypotension

2011 ◽  
Vol 111 (2) ◽  
pp. 443-448 ◽  
Author(s):  
J. T. Groothuis ◽  
R. A. J. Esselink ◽  
J. P. H. Seeger ◽  
M. J. H. van Aalst ◽  
M. T. E. Hopman ◽  
...  
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Blood Flow ◽  
Orthostatic Hypotension ◽  
Vascular Resistance ◽  
Plasma Volume ◽  
Venous Pressure ◽  
Dilution Method ◽  
Significant Difference ◽  
Head Up Tilt

The pathophysiology of orthostatic hypotension in Parkinson's disease (PD) is incompletely understood. The primary focus has thus far been on failure of the baroreflex, a central mediated vasoconstrictor mechanism. Here, we test the role of two other possible factors: 1) a reduced peripheral vasoconstriction (which may contribute because PD includes a generalized sympathetic denervation); and 2) an inadequate plasma volume (which may explain why plasma volume expansion can manage orthostatic hypotension in PD). We included 11 PD patients with orthostatic hypotension (PD + OH), 14 PD patients without orthostatic hypotension (PD − OH), and 15 age-matched healthy controls. Leg blood flow was examined using duplex ultrasound during 60° head-up tilt. Leg vascular resistance was calculated as the arterial-venous pressure gradient divided by blood flow. In a subset of 9 PD + OH, 9 PD − OH, and 8 controls, plasma volume was determined by indicator dilution method with radiolabeled albumin (125I-HSA). The basal leg vascular resistance was significantly lower in PD + OH (0.7 ± 0.3 mmHg·ml−1·min) compared with PD − OH (1.3 ± 0.6 mmHg·ml−1·min, P < 0.01) and controls (1.3 ± 0.5 mmHg·ml−1·min, P < 0.01). Leg vascular resistance increased significantly during 60° head-up tilt with no significant difference between the groups. Plasma volume was significantly larger in PD + OH (3,869 ± 265 ml) compared with PD − OH (3,123 ± 377 ml, P < 0.01) and controls (3,204 ± 537 ml, P < 0.01). These results indicate that PD + OH have a lower basal leg vascular resistance in combination with a larger plasma volume compared with PD − OH and controls. Despite the increase in leg vascular resistance during 60° head-up tilt, PD + OH are unable to maintain their blood pressure.

Blood and plasma volume in adult males

1962 ◽  
Vol 17 (2) ◽  
pp. 195-198 ◽  
Author(s):  
Marvin J. Yiengst ◽  
Nathan W. Shock
Keyword(s):  
Plasma Volume ◽  
Age Groups ◽  
Dilution Method ◽  
Total Blood Volume ◽  
Adult Males ◽  
Age Changes ◽  
Total Blood ◽  
Mean Values ◽  
The Mean ◽  
Blood Volumes

Total blood volumes were estimated in 94 normal ambulatory males, aged 19–95 years, by the T-1824 dye dilution method. There were no significant age changes when results were expressed in terms of either body weight or surface area. The mean values for individual age groups between 40'49 and 80'95 years varied between 46.7 ± 1.5 and 51.5 ± 1.5 ml/kg body wt. for plasma volume and between 75.1 ± 2.0 and 82.3 ± 2.0 ml/kg body wt. for total blood volume. Submitted on October 16, 1961

A CONSTANT-RATE INDICATOR-INFUSION TECHNIC FOR THE MEASUREMENT OF CENTRAL VASCULAR VOLUME IN MAN

1955 ◽  
Vol 33 (3) ◽  
pp. 340-348 ◽  
Author(s):  
Dorrance Bowers ◽  
John T. Shepherd ◽  
Earl H. Wood
Keyword(s):  
Pulmonary Artery ◽  
Right Ventricle ◽  
Radial Artery ◽  
Evans Blue ◽  
Equilibrium Concentration ◽  
Blue Dye ◽  
Vascular Volume ◽  
Constant Rate ◽  
The Right ◽  
Blood Volumes

Evans blue dye was injected at a constant rate into the right ventricle or pulmonary artery of 17 subjects in 21 experiments. The consequent arterial dilution patterns were recorded continuously by a cuvette oximeter connected to an indwelling needle in the radial artery. From these dilution patterns the amount and concentration of dye in the intravascular space between the injecting and sampling sites were determined when an equilibrium concentration was attained. From these dimensions the "central vascular volume" was calculated. The values for the central vascular volume thus derived showed agreement with those determined in near-simultaneous estimations by Hamilton's modification of Stewart's method. The values for the "lung blood volumes" by the Newman method in these subjects were systematically smaller than the values for the central vascular volume.

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