Autonomic Activity and Water Immersion
Abstract
The autonomic nervous system reflexively controls many physiological systems, including the cardiovascular and ventilatory systems." Water immersion causes fluid shifts within the body thatincrease central blood volume and intravascular fluid volume. These increa"ses are thought to cause changes in autonomic activity, however it is not known if sympathetic nerve activity is reduced during wate""r immersion. Because the autonomic nervous system controls the cardiovascular and ventilatory systems, it is imperative to understan"d changes in autonomic activity during water immersion in order to develop countermeasures to protect Navy and recreational divers f"rom potentially adverse physiological responses to the environmental conditions that they are exposed to. In this context, Navy and"" recreational divers routinelybreathe 100% oxygen, which lowers sympathetic activity, heart rate, and blood pressure. A further dec""rease in sympathetic drive could increase the risk of water immersion-induced pathophysiology, such as carbon dioxide retention. Alo""ng these lines, it is not known how autonomic activity is affected by an increase in arterial carbon dioxide (which is a sympathetic""stimulus) during water immersion. Furthermore, it is not known how autonomic activity is affected by these breathing conditions dur""ing cold water immersion. Therefore, our specific aims are to: 1) determine if sympathetic nerve activity is altered by breathing 1""00% oxygen air compared to air breathing during both thermoneutral and cold water immersion conditions, and2) determine if sympathe"tic nerve activity is altered by breathing hypercapnic air compared to air breathing during both thermoneutral and cold water immersion conditions. We hypothesize that 1) cold water immersion will increase sympathetic nerve activity compared to thermoneutral wat"er immersion during air breathing, 2) breathing 100% oxygen air during thermoneutral andcold water immersion will reduce sympathet""ic nerve activity compared to the air breathing conditions, and 3) breathing hypercapnic air during thermoneutral and cold water im"mersion will increase sympathetic nerve activity compared to the air breathing conditions. We will use microneurography to directly" measure multi-unit postganglionic muscle sympathetic nerve burstactivity in humans, along with continuously measuring cardiovascul""ar and ventilatory variables, during these water immersion conditions to address our hypotheses.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Sep 01, 2017
- Source ID
- N000141712665
Entities
People
- Blair D Johnson
Organizations
- Office of Naval Research
- Research Foundation for the State University of New York
- United States Navy