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 that increase central blood volume and intravascular fluid volume. These increases are thought to cause changes in autonomic activity, however it is not known if sympathetic nerve activity is reduced during water immersion. Because the autonomic nervous system controls the cardiovascular and ventilatory systems, it is imperative to understand changes in autonomic activity during water immersion in order to develop countermeasures to protect Navy and recreational divers from potentially adverse physiological responses to the environmental conditions that they are exposed to. In this context, Navy and recreational divers routinely breathe 100% oxygen, which lowers sympathetic activity, heart rate, and blood pressure. A further decrease in sympathetic drive could increase the risk of water immersion-induced pathophysiology, such as carbon dioxide retention. Along 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 during cold water immersion. Therefore, our specific aims are to: 1) determine if sympathetic nerve activity is altered by breathing 100% oxygen air compared to air breathing during both thermoneutral and cold water immersion conditions, and 2) determine if sympathetic 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 water immersion during air breathing, 2) breathing 100% oxygen air during thermoneutral and cold water immersion will reduce sympathetic nerve activity compared to the air breathing conditions, and 3) breathing hypercapnic air during thermoneutral and cold water immersion will increase sympathetic nerve activity compared to the air breathing conditions. We will use microneurography to directly measure multi-unit postganglionic muscle sympathetic nerve burst activity in humans, along with continuously measuring cardiovascular and ventilatory variables, during these water immersion conditions to address our hypotheses.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 19, 2020
- Source ID
- N000142012878
Entities
People
- Blair D Johnson
Organizations
- Indiana University
- Office of Naval Research
- United States Navy