Mechanism of functional residual capacity increase in haemorrhagic shock.

Shock was elicited in anaesthetized dogs by maintaining a haemorrhagic hypotension of 4 kPa until 30 per cent spontaneous refusion, followed by total reinfusion. Functional residual capacity (FRC) and minute ventilation increased considerably similarly to our previous experiments. Lactate content in both the external intercostal and the biceps femoris muscles increased significantly in advanced shock. The expiratory external abdominal oblique muscle showed electromyographic signs of fatigue. At the height of the FRC changes tonic contraction of the external intercostal muscle could be demonstrated electron microscopically. This tonic contraction is the main factor in the large FRC rise in late shock forming the basis of a hitherto unknown vicious circle.