Читать книгу Respiratory Medicine - Stephen J. Bourke - Страница 31

Blood will carry different quantities of a gas when it is at different partial pressures, as described by a dissociation curve. The dissociation curves for oxygen and carbon dioxide are very different (they are shown together on the same scale in Fig. 1.9). The amount of carbon dioxide carried by the blood is roughly proportional to the P_aCO₂ over the whole range normally encountered, whereas the quantity of oxygen carried is only proportional to the P_aO₂ over a very limited range of about 3–7 kPa (22–52 mmHg). Above 13.3 kPa (100 mmHg), the haemoglobin is fully saturated. Further increases in partial pressure result in hardly any additional oxygen being carried.