Evidence for Increased Cardiac Compliance During Exposure to Simulated Microgravity.
Abstract
We measured specific hemodynamic responses during 4 days (96 hours) of head-down tilt (HDT) in invasively- instrumented rhesus monkeys to test the hypothesis that exposure to simulated microgravity causes increased cardiac compliance. Six rhesus monkeys underwent the following two 5-day experimental conditions (days 0-4) separated by 9 days of ambulatory activities in a cross-over counterbalance design: 1) continuous exposure to l0% HDT; and 2)16 hours per day of 80% head-up tilt and 8 hours supine (control). Each animal underwent daily measurements of central venous pressure (CVP), left ventricular (LVP) and aortic (AoP) pressures, stroke volume (SV), and esophageal pressure (EsP). Additionally, each animal underwent measurement of plasma volume (day 2) and provocative tests which included graded dose administration of phenylepluine (al-adrenergic responsiveness) and isoproterenol (bl-adrenergic responsiveness) (day 3), and application of lower body negative pressure (day 4). Compared to the control condition, a 34% reduction in CVP (-1.6 mmHg, P = 0.010) and no change in left ventricular end-diastolic volume during HDT was associated with increased mean left ventricular end-diastolic compliance from 0.894 n 0.143 m1/mmllg compared to 1.111 fi 0.170 m1/mmHg (P = 0.0053). Increased cardiac compliance could not be explained by reduced thoracic transmural pressure since EsP was unaltered by HDT. Our data provide the fffst direct evidence that increased cardiac compliance is associated with headward fluid shifts similar to those induced by exposure to spaceflight.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 1998
- Accession Number
- ADA353948
Entities
People
- Craig A. Reister
- F. A. Gaffeney
- John W. Fanton
- Steven C. Koenig
- Víctor A. Convertino
Organizations
- United States Air Force School of Aerospace Medicine