Breath Holding During Exercise

¹ From the Applied Physiology Branch, Directorate of Medical Research, U.S. Army Chemical Warfare Laboratories, Army Chemical Center, Maryland

The duration of maximum voluntary apnea (B) with fully inflated lungs in one experienced subject was determined during and immediately after treadmill exercise, with oxygen uptake (M) ranging up to 2.8 liters/min. The product MB was constant during exercise over the range of 0.5–2.3 liters/min. of oxygen uptake; above and below this range of oxygen uptake, MB was less. The constant had the dimensions of an oxygen debt of 0.44 liters. The carbon dioxide tension in gas expelled at the end of the holds during exercise decreased in linear fashion as breath holding time increased. Although the changes in MB at the transitions from rest to moderate work and from moderate to hard work are unexplained, they may be accounted for by the factors that are responsible for the changes in a) frequency of breathing, b) the ratio of ventilation to oxygen uptake and c) the end-tidal carbon dioxide tension, at the same transition points. In continuous recordings the concentration of the end-tidal carbon dioxide at the two highest rates of oxygen uptake never reached as high as the concentrations found at more moderate rates.