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Evidence for increased cardiac compliance during exposure to simulated microgravity
S C Koenig1, V A Convertino, J W Fanton
1Physiology Research Branch, Clinical Sciences Division, Brooks Air Force Base, Texas 78235, USA.
The American Journal of Physiology
|October 2, 1998
Summary
Simulated microgravity from head-down tilt increases cardiac compliance and reduces orthostatic tolerance. This is linked to lower stroke volume, cardiac output, and peak cardiac contractility.
Area of Science:
- Cardiovascular Physiology
- Space Physiology
Background:
- Simulated microgravity alters fluid distribution and cardiovascular function.
- Understanding cardiac adaptations to microgravity is crucial for astronaut health.
Purpose of the Study:
- To investigate if simulated microgravity increases cardiac compliance.
- To determine if reduced orthostatic tolerance is linked to decreased cardiac contractility.
Main Methods:
- Invasively instrumented rhesus monkeys were exposed to 4 days of head-down tilt (HDT) and lower body negative pressure (LBNP).
- Measurements included central venous pressure, left ventricular pressures, stroke volume, and adrenergic responsiveness.
Main Results:
- Head-down tilt induced a hypovolemic and hypoadrenergic state, reducing tolerance to LBNP.
- Reduced LBNP tolerance correlated with decreased stroke volume, cardiac output, and left ventricular peak dP/dt.
- Head-down tilt increased cardiac compliance, evidenced by reduced central venous pressure without changes in left ventricular end-diastolic area.
Conclusions:
- Increased cardiac compliance is associated with headward fluid shifts, mimicking spaceflight conditions.
- Reduced orthostatic tolerance during simulated microgravity is linked to diminished cardiac contractility.