Cardio-respiratory effects of change of body position

The erect "active" position is man's normal or "physiological" state. Gravitational stresses, acting directly on the arterial and venous circulations, and indirectly through diaphragmatic mechanics and intra-abdominal transmitted pressures on the lung, are important in determining the net cardiorespiratory response to change in body position. In normal active man, homeostatic compensatory responses maintain physiological normal ranges. In disease states, after immobility or prolonged bed rest, and in the presence of pharmacological agents, these compensatory responses may be attenuated. Under anaesthesia, the degree of compromise which will occur will be determined in part by the baseline against which the anaesthesia is induced. Consideration of all of these factors is thus important in anticipating or predicting the effects of changes in body position during anaesthesia,