Mechanical and Chemical Control of Breath Holding

A method is described for the study of breath holding in which the breath holds are separated by rebreathing to enable accurate control of pCO2; its theoretical basis is discussed. At the end of a breath hold, rebreathing a mixture such that the pCO2 continues to rise, nevertheless permits the breath hold to be resumed. The number of breaths during the rebreathing is unimportant and a single breath permits as long a resumed breath hold as five breaths. Healthy adult males held their breath at residual volume. The relationship between breath holding time and pCO2 at the start or end of a breath hold was found to be linear; the higher the pCO2 the shorter the breath holding time. The relationship was unaffected by ten minutes of isocapnic hyperventilation. These findings imply that the duration of breath holding is directly related to pCO2 but is unaffected by the previous mechanical pattern of breathing.