Figure 1

Schema of factors involved in increased ventilatory drive. Cytokines, endotoxin (LPS) and acidaemia produce an initial increase in the drive to breathe. Demands on the ventilatory muscles (especially the diaphgram) are also increased by a decrease in dynamic compliance of the lungs and chest wall. Increased metabolic activity in ventilatory muscles activates type III and IV afferents, which further increase the drive to breathe. Lung injury activates vagal afferents that also increase respiratory drive. Efferent activity from the brain increases sympathetic activity, which can lead to vasoconstriction and increased heart rate. See text for further details. LPS, lipopolysaccharide.