Biology ETDs

Publication Date

7-22-1976

Abstract

This study was designed to analyze the effects of heat acclimatization, acute dehydration and physical conditioning on the fluid shifts induced by lower body negative pressure (LBNP). Ten male subjects, five trained runners and five non-runners, were subjected to LBNP before and after nine days of acclimatization to work in the heat and pre- and post-dehydration induced by heat and exercise. During each of the four LBNP runs the subjects were monitored for changes in blood volume and variances in the volume of the left forearm and lower leg at the calf. Each LBNP test consisted of five minute long consecutive stages at 0, -20, -30, -40, -50 and -60 torr. The tests were terminated when syncope was eminent or the full test sequence was completed. Tolerance was expressed as a cumulative stress factor (torr x min). There was an average of 9% loss of plasma volume due to LBNP in the pre-acclimatized, euhydrated state (A-I) and an average of 11% in the same state after acclimatization (B-I). There was an average of 1% loss of plasma volume due to LBNP in the unacclimatized, dehydrated state (A-II) and an average of 4% loss of plasma volume in the acclimatized, dehydrated state (B-II). The non-runners (NR) had a greater plasma volume loss than did runners (R) in most cases. There was a high degree of correlation between the amount of plasma volume lost and LBNP tolerated. With increasing LBNP exposure, the leg volume (LV) increased and arm volume (AV) decreased. After dehydration less volume was shifted to the leg and from the arm. Runners tended to have higher volume shifts to the leg and from the arm in the euhydrated states (A-I and B-I), though they tolerated less LBNP. Acclimatization tended to decrease the amount of volume shifted to and from the limbs in most cases. There was a significant correlation between plasma volume loss and leg volume increases. Limb compliance (Δ% limb volume/Δtorr-min) in both the leg and the arm correlated well with LBNP tolerance. Dehydration tended to increase limb compliance. Acclimatization tended to decrease the leg compliance and increase the arm compliance. Runners had significantly higher levels of limb compliance in all tests than did non-runners. A substantial amount of the total volume shifted to the leg remained there after the release of negative pressure and a recovery period. The volume retained in the leg evidenced a high level of correlation with plasma volume loss. Non-runners had a higher percentage of volume retention than did runners. In conclusion, limb compliance appeared to be a major factor in the LBNP tolerance of a subject, and limb compliance was apparently the underlying influence in variations in total volume shift, plasma volume loss and volume retention. Acclimatization and acute dehydration influenced variations in fluid shift patterns and limb compliance as well as tolerance for LBNP. Physical condition played a role in LBNP tolerance variation by allowing the runners to reach a critical volume shift at a lower level of stress than non-runners. The higher level of limb compliance in the runners appeared to be the major reason for variances in fluid shift patterns and tolerance between runners and non-runners.

Language

English

Document Type

Thesis

Degree Name

Biology

Level of Degree

Masters

Department Name

UNM Biology Department

First Committee Member (Chair)

Ulrich Cameron Luft

Second Committee Member

Marvin LeRoy Riedesel

Third Committee Member

William Raleigh Galey, Jr.

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