Integrated Diaphragmatic Function, Chemosensitivity, Erythrocyte Gas Transport and Endurance in Exercising Divers
Abstract
During underwater exercise, personal endurance capacity and elevated blood carbon dioxide (hypercapnia) are key parameters that affect a divers safety and performance. Unlike exercise on dry land, hypercapnia often occurs during dives and can impair cognitive function and predispose the diver to central nervous system (CNS) oxygen toxicity and convulsions underwater. Carbon dioxide is a byproduct of metabolism and is carried from body tissues via the bloodstream to the lungs, where it is exhaled. Under normal conditions, on dry land, carbon dioxide levels in the blood are tightly controlled by three cooperating structures: a system of sensors in the arteries and brain, controllers in the brain, and the respiratory muscles. Elevation of carbon dioxide levels in the blood normally causes an increase in breathing, which then acts to reduce carbon dioxide level, and the degree to which this increase in ventilation occurs (ventilatory chemosensitivity) varies among individuals. Some people intrinsically have low ventilatory chemosensitivity, and these people are more likely to develop hypercssion-critical variable, and both endurance and the ability to control blood carbon dioxide depend on the muscles that perform breathing (respiratory muscles, mainly the diaphragm). Endurance of a muscle is dependent on structures within the cell (mitochondria) that convert oxygen and fuel into energy, and muscle function, including the number of mitochondria, can be enhanced by specific training. Therefore, it may be possible to use training to improve the endurance capabilities of a divers respiratory muscles, and reduce their risk of hypercapnia. Respiratory muscle training (RMT) can be performed by breathing through a resistance several times per week for 30-60 minutes. In divers RMT has several beneficial effects, such as enhancing underwater endurance and increasing ventilatory chemosensitivity. Based on previous studies from our lab that showed enhanced mitochondrial numbers, we plan to test an augmented method of RMT that includes breathing a low, sub-toxic level of carbon monoxide during training. In this study we will test the effect of daily respiratory muscle training with and without added carbon monoxide on respiratory muscle power, diaphragm thickness measured with ultrasound, respiratory muscle endurance and, during a dive to 50 feet underwater, exercise endurance. Arterial blood carbon dioxide and lactic acid levels will be measured during exercise tests before and after training. All measurements will be obtained before and after one month of RMT, performed either with or without added low-dose carbon monoxide. Movement of carbon dioxide (and oxygen) through cell membranes into and out of the blood occurs mostly through channels. It is possible that in some individuals carbon dioxide transport may be limited by low numbers of gas channels, especially during exercise, but most studies of gas channels thus far have been performed in animals, with little information from humans. We plan to obtain red blood cells from the volunteers in this study to test permeability to oxygen and carbon dioxide, and to correlate exercise performance and blood carbon dioxide levels with lab-based analysis of the efficiency with which oxygen and carbon dioxide move into and out of red blood cell membranes. The aims of this project are: (1) understand the mechanisms by which red blood cells transport oxygen and carbon dioxide and their possible effects on exercise capacity; and (2) test a method that could increase personal endurance and reduce excessive rise in blood carbon dioxide during underwater exercise.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2021
- Source ID
- N000142112366
Entities
People
- Richard E Moon
Organizations
- Duke University
- Office of Naval Research
- United States Navy