Key points Immersion in thermoneutral water activates protective airway reflexes, and aspiration does not occur until lung oxygen stores have been used up and hypoxia causes the airway to open. In cold water, the cold shock reflex causes gasping and…
Key points Environments in which a closed atmosphere suitable for breathing is maintained include closed-circuit anaesthesia, submarines and space vehicles. Problems of maintaining acceptably low carbon dioxide concentrations and low levels of inhaled contaminants are common to all these environments.…
Key points When diving in water the increased density of inhaled gases and immersion in water cause an increase in the work of breathing, which can impair gas exchange during exercise. At greater than about 4 atmospheres absolute pressure nitrogen…
Key points Low inspired oxygen partial pressure at altitude causes immediate hyperventilation, which increases further with acclimatization to produce hypocapnia and improve oxygen levels. The rate of ascent and altitude achieved are determinants of altitude-related illnesses, which vary from mild…
Key points Obese subjects have reduced static and dynamic lung volumes because of compression of the chest cavity by the mass of the chest wall and abdominal contents. Chest wall compliance is reduced by obesity, and the lower lung volume…
Key points During normal sleep tidal volume is reduced, with maximal reduction in ventilation occurring during rapid eye movement sleep when breathing also becomes irregular. Reduction in the speed and strength of pharyngeal muscle reflexes causes increased airways resistance, leading…
Key points Oxygen consumption increases linearly with the power expended during exercise. The extra tissue oxygen requirement is provided by increases in cardiac output and blood oxygen extraction. To accommodate these changes ventilation also increases linearly with exercise—this response occurs…
Key points Hormonal changes of pregnancy stimulate breathing, causing an increase in tidal volume and hypocapnia. In late pregnancy the enlarged uterus reduces lung volume, particularly in the supine position. Human lung development is incomplete at birth, with new alveoli…
Key points The entire cardiac output passes through the pulmonary circulation, so the lungs act as a filter, preventing emboli from passing to the left side of the circulation. The lungs constitute a huge interface between the outside environment and…
Key points Oxygen moves down a partial pressure gradient between the inspired gas and its point of use in the mitochondria, where the oxygen partial pressure may be only 0.13 kPa (1 mmHg). Significant barriers to oxygen transfer are between…