Haemodynamic dysfunctions involved in experimental bovine pneumonic pasteurellosis

The present experiments were designed Co challenge, without the bias of anaesthesia, the previously reported statement that intratracheal administration of Pasteurella haemolvtica does not impair haemodynamics in calves. Central venous, pulmonary arterial and capillary wedge and systemic arterial pressures were measured by fluid-filled catheters in 11 calves. Cardiac output was measured by the thermodilution technique, heart rate (HR) was derived from the ECG and stroke volume (SV), pulmonary and systemic vascular resistance were calculated. The haemodynamic values were measured hourly from the first to the tenth hour alter intratracheal inoculation of P. haemolytica. Cardiovascular response was marked and typically consisted of two hypotensive hypodynamic phases. The first, which occurred by the second hour after inoculation, consisted of a transient bradycardia and a systemic vasodilation leading to profound hypotension and reduced venous return. Cardiac performance then recovered, but systemic hypotension persisted and hypoxaemia developed. The second phase occurred by the seventh hour alter inoculation and was associated with a decline in SV, an increase in HR, and pulmonary hypertension. Three different degrees of cardiovascular dysfunctions were found, differing basically in the intensity of the first phase bradycardia and second phase reduction in SV and systemic arterial pressure, suggesting that experimental pneumonia produced by intratracheal instillation of P. haemolytica in calves results in distinct cardiovascular dysfunctions depending on the animal. Ignorance of the underlying haemodynamic status therefore precludes reliable interpretation of physiological as well as pharmacological results using this model of respiratory disease