Pulmonary dysfunction in neonatal calves after intratracheal inoculation of small volumes of fluid.

Intratracheal instillation of 20 ml of room temperature (21 to 24 C) fluid in anesthetized neonatal calves resulted in rapid onset of reversible pulmonary dysfunction. Arterial O2 tension and dynamic compliance decreased, whereas pulmonary arterial pressure, pulmonary vascular resistance, alveolar arterial O2 difference, and total pulmonary resistance increased from base-line values. Abnormalities of gas exchange and pulmonary mechanics were induced by intratracheal fluid instillation whether or not Pasteurella haemolytica was in the inoculum. Physical manipulation of the calf without intratracheal fluid instillation (sham inoculation) did not influence pulmonary function. Bilateral vagotomy eliminated the increase in pulmonary resistance and the decrease in dynamic compliance, but did not eliminate hypoxemia, increased alveolar arterial O2 difference, or pulmonary hypertension recorded after intratracheal fluid instillation. Seemingly, changes in pulmonary mechanics are mediated via the vagus nerve. However, one or more additional mechanisms must be responsible for the hypoxemia and pulmonary hypertension.

Hemodynamic effects of acute pneumonia experimentally induced in newborn calves inoculated with Pasteurella haemolytica.

Hemodynamic responses to acute pneumonia and to hypoxia were investigated in 10 newborn calves. Experiments were performed on heparinized, anesthesized and ventilated calves. Control calves were inoculated intratracheally with bovine fetal serum. Pneumonia was induced in treated calves by intratracheal inoculation with P haemolytica suspended in bovine fetal serum. Before inoculation (base line), at the time of inoculation (T = 0), and at 30-minute intervals for 3 hours, pulmonary arterial pressure (Ppa), systemic arterial pressure, cardiac output (CO), arterial blood gases, pulmonary vascular resistance (PVR), and systemic vascular resistance were determined. At T = 0, calves in both groups became hypoxemic, alveolar-arterial O2 difference, PVR, and Ppa increased, and CO and systemic vascular resistance remained unchanged. At subsequent measurement intervals, all values returned to base-line in control calves, whereas treated calves had progressive hypoxemia associated with a decrease in Ppa and PVR, with no change in CO. Three hours after inoculation and after inhalation of 10% O2 in N2, PVR increased significantly in the control calves. In the treated group, hypoxia did not increase the resistance, compared with base-line and 3-hour values. The data indicate decreased Ppa during pneumonic pasteurellosis is because of a decrease in PVR and that pneumonia may attenuate the normal pulmonary hypoxic vasoconstrictor response.