There are still a significant number of astronauts at Johnson Space Center who suffer from postflight orthostatic hypotension and presyncope. The mandatory use of fluid loading with salt tablets and water, anti-gravity suits, and the liquid cooling garment has not eliminated the problem. A growing body of evidence suggests that there are major physiological systems that become dysfunctional as a result of space flight. The degree of dysfunction varies from minimal to severe. Several studies have provided evidence that autonomic function is impaired during and after space flight. Additional factors, such as local factors, could also be involved. An area that has not been studied in humans is the effects of space flight on nitric oxide physiology and its modulation of blood pressure. The study proposed in this application will continue the pursuit of mechanisms of autonomic dysfunction in presyncopal astronauts. In addition, it will begin to elucidate changes in nitric oxide production and the resulting effects of the cardiovascular system.
The study has two specific aims: 1) to compare preflight to postflight changes in responses of veins to adrenergic agonists between presyncopal and nonpresyncopal astronauts; 2) to compare preflight to postflight changes in nitric oxide levels, inducible nitric oxide synthase messenger RNA and protein, cell adhesion molecules associated with endothelial activation, responses to acetylcholine with and without nitric oxide synthase inhibition, and reactive hyperemia responses in the brachial artery in the arm and the popliteal artery in the leg, between presyncopal and nonpresyncopal astronauts. Presyncopal and nonpresyncopal astronauts will be defined by their ability to complete a 10-minute upright tilt test on landing day.
By determining the mechanisms of orthostatic hypotension in astronauts, new light may be shed on the underlying causes of the clinical situations. An additional benefit is that these studies will add important new knowledge about nitric oxide and blood pressure control before and after space flight. These findings also will provide new information regarding the inter-relationships among nitric oxide physiology, autonomic function and volume regulation in the same subjects.
APPROACH
This investigation has been deselected; therefore, the approach is not available at this time.
RESULTS
This investigation has been deselected; therefore, results are not available at this time.