Leg mass and lower body negative pressure tolerance  in men and women

Lawler, Lori A.; Halliwill, John R.; Summer, Jolene M.; Joyner, Michael J.; Mulvagh, Sharon L.

doi:10.1152/jappl.1998.85.4.1471

Cited by 15 publications

(12 citation statements)

References 12 publications

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“…Another factor that might make the women in the present study more susceptible is their smaller body size and muscle mass (19,30,37). The influence of muscle mass on orthostatic tolerance is controversial: one report indicated that greater muscle mass may be associated with greater orthostatic tolerance (25), whereas another did not (23). Difference in size is probably not the primary reason for the intergroup differences in the present study for two reasons.…”

Section: Discussionmentioning

confidence: 74%

Postspaceflight orthostatic hypotension occurs mostly in women and is predicted by low vascular resistance

Waters

Ziegler

Meck

2002

Journal of Applied Physiology

189

178

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About 20% of astronauts suffer postspaceflight presyncope. We studied pre- to postflight (5- to 16-day missions) cardiovascular responses to standing in 35 astronauts to determine differences between 1) men and women and 2) presyncopal and nonpresyncopal groups. The groups were presyncopal women, presyncopal men, and nonpresyncopal men based on their ability to stand for 10 min postflight. Preflight, women and presyncopal men had low vascular resistance, with the women having the lowest. Postflight, women experienced higher rates of presyncope (100 vs. 20%; P = 0.001) and greater losses of plasma volume (20 vs. 7%; P < 0.05) than men. Also, presyncopal subjects had lower standing mean arterial pressure (P < or = 0.001) and vascular resistance (P < 0.05), smaller increases in norepinephrine (P < or = 0.058) and greater increases in epinephrine (P < or = 0.058) than nonpresyncopal subjects. Presyncopal subjects had a strong dependence on plasma volume to maintain standing stroke volume. These findings suggest that postflight presyncope is greatest in women, and this can be ascribed to a combination of inherently low-resistance responses, a strong dependence on volume status, and relative hypoadrenergic responses. Conversely, high vascular resistance and postflight hyperadrenergic responses prevent presyncope.

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Section: Discussionmentioning

confidence: 74%

Postspaceflight orthostatic hypotension occurs mostly in women and is predicted by low vascular resistance

Waters

Ziegler

Meck

2002

Journal of Applied Physiology

189

178

View full text Add to dashboard Cite

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“…On the other hand, calf skeletal muscle hypertrophy from chronic resistance exercise training has been reported to reduce leg compliance (23,32). Lawler et al (22) tested the hypothesis that subjects with less leg muscle (dual energy X-ray absorptiometry) would have increased venous blood pooling during lower body negative pressure (LBNP) and an increased propensity toward orthostatic intolerance (22). These authors reported no association between lower extremity lean tissue and orthostatic tolerance and concluded that alterations in muscle mass that were not associated with specific interventions, such as bed rest or resistance training, did not predict a response to LBNP (22).…”

Section: Discussionmentioning

confidence: 99%

“…Lawler et al (22) tested the hypothesis that subjects with less leg muscle (dual energy X-ray absorptiometry) would have increased venous blood pooling during lower body negative pressure (LBNP) and an increased propensity toward orthostatic intolerance (22). These authors reported no association between lower extremity lean tissue and orthostatic tolerance and concluded that alterations in muscle mass that were not associated with specific interventions, such as bed rest or resistance training, did not predict a response to LBNP (22). The specific effect of chronic spinal cord injury on the relationship among lower extremity muscle, leg compliance, and orthostatic tolerance has not been thoroughly investigated, and the report herein is a preliminary view of these complex associations.…”

Section: Discussionmentioning

confidence: 99%

Cardiac homeostasis is independent of calf venous compliance in subjects with paraplegia

Wecht

Meersman

Weir

et al. 2003

American Journal of Physiology-Heart and Circulatory Physiology

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The purpose of this study was to examine cardiac hemodynamics during acute head-up tilt (HUT) and calf venous function during acute head-down tilt (HDT) in subjects with paraplegia compared with sedentary nondisabled controls. Nineteen paraplegic males (below T6) and nine age-, height-, and weight-matched control subjects participated. Heart rate, stroke volume, and cardiac output were assessed using the noninvasive acetylene uptake method. Venous vascular function of the calf was assessed using venous occlusion plethysmography. After supine measurements were collected, the table was moved to 10 degrees HDT followed by the three levels of HUT (10, 35, and 75 degrees ) in random order. Cardiac hemodynamics were similar between the groups at all positions. Calf circumference was significantly reduced in the paraplegic group compared with the control group (P < 0.001). Venous capacitance and compliance were significantly reduced in the paraplegic compared with control group at supine and HDT. Neither venous capacitance (P = 0.37) nor compliance (P = 0.19) increased from supine with 10 degrees HDT in the paraplegic group. A significant linear relationship was established between supine venous compliance and supine cardiac output in the control group (r = 0.80, P < 0.02) but not in the paraplegic group. The findings of reduced calf circumference and similar venous capacitance at supine rest and 10 degrees HDT in the paraplegic group imply that structural changes may have limited venous dispensability in individuals with chronic paraplegia. Furthermore, the lack of a relationship between supine venous compliance and supine cardiac output suggests that cardiac homeostasis does not rely on venous compliance in subjects with paraplegia.

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“…In that study, the subjects were very well-trained divers and a great increase in compliance of 108% after bed rest was reported. In prior studies, increased compliance has been shown to be correlated to reduction in calf muscle volume (10,12), and muscle atrophy has been postulated as an explanation for increased compliance, resulting in orthostatic intolerance in some (5, 6, 10-12, 33), but not all (27), studies. However, in the present study no leg or arm volume changes were observed during the bed rest period, indicating only minor muscle atrophy.…”

Section: Comparison With Previous Bed Rest and Spaceflight Studiesmentioning

confidence: 98%

Effects of 18 days of bed rest on leg and arm venous properties

Bleeker¹,

Groot²,

Pawelczyk³

et al. 2004

Journal of Applied Physiology

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Venous function may be altered by bed rest deconditioning. Yet the contribution of altered venous compliance to the orthostatic intolerance observed after bed rest is uncertain. The purpose of this study was to assess the effect of 18 days of bed rest on leg and arm (respectively large and small change in gravitational gradients and use patterns) venous properties. We hypothesized that the magnitude of these venous changes would be related to orthostatic intolerance. Eleven healthy subjects (10 men, 1 woman) participated in the study. Before (pre) and after (post) 18 days of 6 degrees head-down tilt bed rest, strain gauge venous occlusion plethysmography was used to assess limb venous vascular characteristics. Leg venous compliance was significantly decreased after bed rest (pre: 0.048 +/- 0.007 ml x 100 ml(-1) x mmHg(-1), post: 0.033 +/- 0.007 ml x 100 ml(-1) x mmHg(-1); P < 0.01), whereas arm compliance did not change. Leg venous flow resistance increased significantly after bed rest (pre: 1.73 +/- 1.08 mmHg x ml(-1) x 100 ml x min, post: 3.10 +/- 1.00 mmHg x ml(-1) x 100 ml x min; P < 0.05). Maximal lower body negative pressure tolerance, which was expressed as cumulative stress index (pressure x time), decreased in all subjects after bed rest (pre: 932 mmHg x min, post: 747 mmHg x min). The decrease in orthostatic tolerance was not related to changes in leg venous compliance. In conclusion, this study demonstrates that after bed rest, leg venous compliance is reduced and leg venous outflow resistance is enhanced. However, these changes are not related to measures of orthostatic tolerance; therefore, alterations in venous compliance do not to play a major role in orthostatic intolerance after 18 days of head-down tilt bed rest.

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Leg mass and lower body negative pressure tolerance in men and women

Cited by 15 publications

References 12 publications

Postspaceflight orthostatic hypotension occurs mostly in women and is predicted by low vascular resistance

Postspaceflight orthostatic hypotension occurs mostly in women and is predicted by low vascular resistance

Cardiac homeostasis is independent of calf venous compliance in subjects with paraplegia

Effects of 18 days of bed rest on leg and arm venous properties

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