ABSTRACT
In health, ventilation is very closely adjusted to metabolic demands and the ventilatory control system has to compensate rapidly for changes such as the increased metabolism of exercise or a reduction in inspired oxygen partial pressure (e.g. at altitude). Ventilatory control is modified in many conditions and it can also be influenced by several drugs. The ‘metabolic’ or reflex system of respiratory control includes receptors that respond to mechanical or chemical stimuli; a central controller with an inherent rhythmicity and output, which are modulated by sensory information; a neural pathway comprising afferent nerves, the brainstem, spinal cord, and intercostal and phrenic nerves; and an effector ‘organ’, the respiratory muscles. The efficiency of the respiratory muscles in adjusting ventilation to meet metabolic requirements is in turn dependent on the mechanical and gas-exchanging properties of the lungs.
