Mechanical and Chemical Control of Breath Holding

Abstract

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.MOST of the factors of importance in determining the breaking point of breath holding have been known for many years. Hill and Flack [1908] noted that if oxygen was breathed beforehand rather than air, the breath holding time was longer. They also noted that the alveolar pCO2 (hereafter referred to as pCO2) was higher at breaking point after breath holding on oxygen; this was presumably due to the longer duration of breath holding.In the same paper they reported that their subjects could rebreathe expired air from a bag for some two to four times as long as their maximum breath holding time on air. They thus demonstrated that ventilation of the lungs allowed the subject to tolerate a greater hypoxia and greater hypercapnia than occurred at the breaking point of breath holding. This finding, now some sixty years old, suggests that some form of interaction of chemicall and mechanical stimuli occurs during breath holding. Subsequent studies defined the roles of oxygen, CO2 and lung volume more clearly [Douglas and Haldane, 1909;Klocke and Rahn, 1959;Muxworthy, 1951] and the whole subject has been reviewed by Mithoefer [1964]. The relationship between rebreathing and breath holding was further explored by Fowler [1954]. He found that after subjects had reached the breaking point of a breath hold, a few breaths of a gas mixture which did not improve their blood gases allowed them to perform a second, shorter breath hold, and subsequently a third. He did not attempt to determine the number of breaths necessary to allow the second (or third) breath hold of the series.

The Influence of Lung Shrinkage on Breath Holding Time

“…Although we only used three subjects, each served as his own control, and each breath holding-CO2 response curve was based on three or more breath holds. We have found that the relationship between breath holding time and initial PCO2 remains very constant for any one subject, with a coefficient of variation for the slope of 8-6 per cent and for the intercept of 2-8 per cent [Godfrey and Campbell, 1969]. The data on which these calculations were based, were obtained on one of the subjects (D.W.) of the present study.…”

“…The experiments described here, in the previous paper [Godfrey and Campbell, 1969] and by Fowler [1954] all argue against specific chemical or lung volume thresholds for the breaking point of breath holding, or any constant relationship between final pCO2 and volume. The earlier finding of such a relationship [Mithoefer, 1959] can be explained by the fact that all his breath holds were begun at approximately the same pCO2 and with a larger lung volume the breath holding time increased and hence the final pCO2 was higher.…”

“…was that described in the previous paper [Godfrey and Campbell, 1969]. The subject rebreathed a C02/02 mixture from a 6 1. bag and the initial gas composition was adjusted to have a PCO2 of approximately 54 mm Hg and a P02 of 290 mm Hg, irrespective of ambient pressure.…”

“…At a lower ambient pressure gas density is reduced so that a given number of 02 molecules absorbed occupies a larger volume; CO2 excretion is blocked as before and therefore the lungs shrink faster. We have then used the rebreathing-breath holding method described in the previous paper [Godfrey and Campbell 1969], to define the relationships between breath holding time and pCO2 under conditions of normal or increased rate of shrinkage. …”

The effect of CO2 on ventilation and breath‐holding during exercise and while breathing through an added resistance

“…These are based on rebreathing C02:02 mixtures from a small bag (Read, 1967; Godfrey & Campbell, 1969 …”