Basic respiratory physiology

The primary function of the respiratory system is to deliver oxygen to the bloodstream and to remove carbon dioxide as a waste gas from the body. This involves moving volumes of gas into and out of the lungs – ventilation – and diffusion of oxygen and carbon dioxide between the lungs and the bloodstream – gas exchange. As one of the main functions of the respiratory system is to deliver oxygen into the bloodstream, respiratory disease commonly manifests with hypoxaemia, and in special circumstances such as at altitude, hypoxaemia occurs in health. There are five main mechanisms by which hypoxaemia can occur: impaired ventilation: hypoventilation; diffusion limitation; ventilation/perfusion mismatch; right-to-left shunt; and a reduction in the inspired oxygen fraction.