Breaking Point of Two Breath Holds Separated by a Single Inspiration

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

Alveolar gas tensions were measured during six trials for each of three men at normal resting level, at the end of a maximum inspiration, at the breaking point of a first breath hold, at the end of a single gasp and at the breaking point of a second breath hold. The volume of the inspirations preceding each breath hold, as well as the breath holding times, was also measured. The first breath holding time was substantially longer than the second. When Gray's chemical ventilation equation was used, the equivalent ventilation ratio at the first breaking point was significantly lower than that of the second breaking point. Other factors in addition to the chemical stimuli may affect the breaking point of breath holding and the longer time of the first breath hold may allow these additional factors to lower tolerance to chemical stimuli at the first breaking point.