Breath‐Holding: Simple Demonstrations of Complex Physiology

Abstract

The complex interaction of chemical (i.e. chemoreceptors) and mechanical (i.e. lung‐stretch receptors) factors influences breath‐holding (BH). The aim of this project was to develop a simple set of procedures to be used as class‐room demonstrations or laboratory exercises to differentiate the roles of chemical and mechanical mechanisms in regulating BH.The increase in ventilation during rebreathing (plastic bag) was initially used to demonstrate the progressive increase in drive to breathe due to chemical factors. BH time (stopwatch) was also used as a quantifiable and intuitive metric of drive to breathe. Maximal BH's were conducted under the following conditions: 1) end‐expiratory BH (lung stretch receptor unloading), 2) end‐inspiratory BH (lung stretch receptor loading), 3) BH following 30s of hyperventilation (reduces pCO2 & isolates the influence of decreased pO2), and 4) BH following 5 breaths of pure oxygen (elevates pO2 & isolates the influence of increased pCO2). Using the end‐expiratory BH as the standard, students observed the increase in BH time with each of the other 3 maneuvers. An advanced critical thinking procedure was also introduced whereby students rebreathed in and out of a bag twice at the end of a maximal BH before attempting to hold their breath again. This procedure highlights the powerful suppression of drive to breathe by lung‐stretch receptors despite elevated chemical drive to breathe.These procedures represent a simple method to highlight complex physiological mechanisms which contribute to the drive to breathe. Such simple activities are suitable and adaptable for use across a range of physiology curricula and teaching settings.