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 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.

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.

Hemodynamic Strategies in Blood Pressure Regulation During Orthostatic Challenge in Women

1997 ◽  
Vol 22 (4) ◽  
pp. 351-367
Author(s):  
Tania L. Culham ◽  
Gabrielle K. Savard
Keyword(s):  
Blood Pressure ◽  
Arterial Pressure ◽  
Stroke Volume ◽  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Peripheral Resistance ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
Orthostatic Challenge ◽  
Carotid Baroreflex

Several studies indicate that carotid baroreflex responsiveness is a good predictor of orthostatic tolerance. Two groups of healthy women with high (HI) and low (LO) carotid baroreflex responsiveness were studied (a) to determine any differences in the level of orthostatic tolerance of the two groups, and (b) to study the hemodynamic strategies used by HI and LO responders to regulate arterial pressure during the orthostatic challenge of lower body negative pressure (LBNP). Orthostatic tolerance was similar between the two groups, whereas the hemodynamic strategies recruited to maintain blood pressure at −40 mmHg LBNP differed: HI responders exhibited greater LBNP-induced decreases in stroke volume and cardiac output, as well as a greater increase in peripheral resistance compared to LO responders (p < .05). In addition, a significant increase in plasma renin activity during LBNP was found in the HI responders only. No significant between-group differences were found in arterial and cardiopulmonary control of vascular resistance or arterial haroreflex control of heart rate during LBNP. Key words: arterial pressure, carotid baroreceptor, lower body negative pressure, orthostatic tolerance, stroke volume

Water drinking improves orthostatic tolerance in patients with posturally related syncope

2006 ◽  
Vol 110 (3) ◽  
pp. 343-352 ◽  
Author(s):  
Victoria E. Claydon ◽  
Christoph Schroeder ◽  
Lucy J. Norcliffe ◽  
Jens Jordan ◽  
Roger Hainsworth
Keyword(s):  
Blood Pressure ◽  
Cerebral Blood Flow Velocity ◽  
Peripheral Resistance ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
Water Drinking ◽  
Randomized Controlled ◽  
Combined Test ◽  
Time Required ◽  
The Relationship

Water drinking improves OT (orthostatic tolerance) in healthy volunteers; however, responses to water in patients with PRS (posturally related syncope) are unknown. Therefore the aim of the present study was to examine whether water would improve OT in patients with PRS. In a randomized controlled cross-over fashion, nine patients with PRS ingested 500 ml and 50 ml (control) of water 15 min before tilting on two separate days. OT was determined using a combined test of head-up tilting and lower body suction and expressed as the time required to induce presyncope. We measured blood pressure and heart rate (using Portapres®) and middle cerebral artery velocity (using transcranial Doppler). SV (stroke volume) and TPR (total peripheral resistance) were calculated using the Modelflow® method. OT was significantly (P<0.02) greater after drinking 500 ml of water than after 50 ml (25.4±1.5 compared with 19.8±2.3 min respectively). After ingestion of 500 ml of water, blood pressure during tilting was higher, the tiltinduced reduction in SV was smaller and the increase in TPR was greater (all P<0.05). The correlation coefficient of the relationship between cerebral blood flow velocity and pressure was lower after 500 ml of water (0.43±0.1 compared with 0.73±0.1; P<0.05), indicating better autoregulation. In conclusion, drinking 500 ml of water increased OT and improved cardiovascular and cerebrovascular control during orthostasis. Patients with PRS should be encouraged to drink water before situations likely to precipitate a syncopal attack.

Gender affects calf venous compliance at rest and during baroreceptor unloading in humans

2004 ◽  
Vol 286 (3) ◽  
pp. H895-H901 ◽  
Author(s):  
Kevin D. Monahan ◽  
Chester A. Ray
Keyword(s):  
Lower Body Negative Pressure ◽  
Cuff Pressure ◽  
Cold Pressor ◽  
Orthostatic Tolerance ◽  
Sympathetic Outflow ◽  
Lower Body ◽  
Venous Compliance ◽  
Supine Posture ◽  
Volume Relation ◽  
Cold Pressor Testing

Leg venous compliance is a determinant of peripheral venous pooling during orthostatic stress such that high venous compliance could contribute to reduced orthostatic tolerance. We tested the hypotheses that 1) calf venous compliance is reduced during baroreceptor unloading, and 2) calf venous compliance is greater in women than men. Twelve men (27 ± 2 yr) and 12 women (25 ± 2 yr) were studied in the supine posture. Calf venous compliance was determined by inflating a thigh venous collecting cuff to 60 mmHg for 8 min and then decreasing cuff pressure at a rate of 1 mmHg/s to 0 mmHg. The slope of the pressure-compliance relation (compliance = β1 + 2·β2·cuff pressure), which is the first derivative of the quadratic pressure-volume relation [(Δlimb volume) = β0 + β1·(cuff pressure) + β2·(cuff pressure)2] during the reduction in collecting cuff pressure, was used to assess venous compliance at baseline and during one-legged lower body negative pressure (LBNP; —50 mmHg). At baseline, calf venous compliance was 48% lower ( P < 0.001) in women than men and decreased in men (Δ—25 ± 8%; P < 0.05) but not women (Δ1 ± 11%) during LBNP. Rhythmic ischemic handgrip (Δ6 ± 9%) and cold pressor testing (Δ—9 ± 7%) did not alter calf venous compliance in a subgroup of men ( n = 6). These data indicate gender-dependent effects on calf venous compliance under conditions associated with low sympathetic outflow (i.e., rest) and high sympathetic outflow (i.e., LBNP). However, they cannot explain gender-associated differences in orthostatic tolerance.

Carotid arterial haemodynamics after mild degrees of lower-body negative pressure in man

1992 ◽  
Vol 83 (5) ◽  
pp. 535-540 ◽  
Author(s):  
P. J. Lacolley ◽  
B. M. Pannier ◽  
M. A. Slama ◽  
J. L. Cuche ◽  
A. P. G. Hoeks ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Weight Bearing ◽  
Normal Subjects ◽  
Lower Body ◽  
Head Up Tilt ◽  
Cardiopulmonary Receptors ◽  
Carotid Arterial

1. Pulsatile changes in the diameter of the common carotid artery were studied transcutaneously using an echo-tracking technique in 15 normal subjects: eight subjects before and during application of graded lower-body negative pressure from −5 to −15 mmHg, and seven subjects before and during weight-bearing head-up tilt at 30 and 60 degrees. 2. In concomitant studies of changes in forearm vascular resistance, it was seen that mild lower-body negative pressure produced deactivation of cardiopulmonary receptors without changes in systemic blood pressure or heart rate. 3. After lower-body negative pressure, a significant decrease in carotid arterial diastolic diameter [from 0.662 ± 0.028 to 0.624 ± 0.033 cm (lower-body negative pressure −10 mmHg) and 0.640 ± 0.030 cm lower-body negative pressure −15 mmHg), P<0.001 and <0.05] was observed. 4. After head-up tilt, carotid arterial diameter was also significantly decreased at 30 and 60 degrees, whereas a significant increase in heart rate occurred only at 60 degrees and mean blood pressure did not change. 5. The study provides evidence that the geometry of the arterial wall is substantially modified by noninvasive manoeuvres such as head-up tilting and lower-body negative pressure. The latter is assumed to selectively deactivate human cardiopulmonary receptors, but the present data suggest that local changes may also influence carotid baroreceptors.

Cardiovascular Models of Simulated Moon and Mars Gravities: Head-Up Tilt vs. Lower Body Unweighting

2014 ◽  
Vol 85 (4) ◽  
pp. 414-419 ◽  
Author(s):  
Vladimir I. Kostas ◽  
Michael B. Stenger ◽  
Charles F. Knapp ◽  
Robert Shapiro ◽  
Siqi Wang ◽  
...  
Keyword(s):  
Lower Body ◽  
Head Up Tilt ◽  
Cardiovascular Models

Volume regulating hormone responses to repeated head-up tilt and lower body negative pressure

2011 ◽  
Vol 41 (8) ◽  
pp. 863-869 ◽  
Author(s):  
Andreas Roessler ◽  
Nandu Goswami ◽  
Bernd Haditsch ◽  
Jack A. Loeppky ◽  
Friedrich C. Luft ◽  
...  
Keyword(s):  
Negative Pressure ◽  
Lower Body Negative Pressure ◽  
Lower Body ◽  
Head Up Tilt ◽  
Hormone Responses

Construction of a lower body negative pressure chamber

2007 ◽  
Vol 31 (1) ◽  
pp. 76-81 ◽  
Author(s):  
Ben T. A. Esch ◽  
Jessica M. Scott ◽  
Darren E. R. Warburton
Keyword(s):  
Negative Pressure ◽  
Atmospheric Pressure ◽  
Lower Body Negative Pressure ◽  
Physiological Responses ◽  
Pressure Chamber ◽  
Orthostatic Tolerance ◽  
Lower Body ◽  
Important Research ◽  
Gravitational Stress ◽  
Design Plan

Lower body negative pressure (LBNP) is an established and important technique used to physiologically stress the human body, particularly the cardiovascular system. LBNP is most often used to simulate gravitational stress, but it has also been used to simulate hemorrhage, alter preload, and manipulate baroreceptors. During experimentation, the consequences of LBNP and the reflex increases in heart rate and blood pressure can be manipulated and observed in a well-controlled manner, thus making LBNP an important research tool. Numerous laboratories have developed LBNP devices for use in research settings, and a few devices are commercially available. However, it is often difficult for new users to find adequately described design plans. Furthermore, many available plans require sophisticated and expensive materials and/or technical support. Therefore, we have created an affordable design plan for a LBNP chamber. The purpose of this article was to share our design template with others. In particular, we hope that this information will be of use in academic and research settings. Our pressure chamber has been stress tested to 100 mmHg below atmospheric pressure and has been used successfully to test orthostatic tolerance and physiological responses to −50 mmHg.

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