Systemic and pulmonary haemodynamics in normal neonatal foals

Cardiopulmonary function was studied in 10 full-term healthy foals from birth to 14 days of age. Systemic and pulmonary haemodynamics were recorded in lateral recumbency via indwelling aortic and pulmonary artery catheters. Mean body weight increased from 45.4 +/- 2.4 kg on Day 1 to 70.6 +/- 6.1 kg on Day 14. All foals had a continuous murmur of patent ductus arteriosus for 3-6 days. From Day 1 (12 h old) to Day 14, heart rate increased (89 +/- 4 to 95 +/- 5/min), mean aortic pressure increased (87.7 +/- 1.9 to 100.3 +/- 3.2 mmHg), mean pulmonary artery pressure decreased (38.6 +/- 4.6 to 27.4 +/- 3.0 mmHg), mean right atrial pressure was unchanged (4.5 +/- 0.5 to 4.6 +/- 0.9 mmHg), mean pulmonary artery wedge pressure was unchanged (7.6 +/- 0.9 mmHg to 8.1 +/- 0.7 mmHg), cardiac output increased (8.03 +/- 0.59 to 15.88 +/- 1.90 l/min), cardiac index increased (180.5 +/- 10.3 to 222.1 +/- 21.6 ml/kg/min), stroke volume increased (90.4 +/- 5.7 to 164.2 +/- 25.9 ml), stroke volume index was unchanged (2.04 +/- 0.10 to 2.30 +/- 0.35 ml/kg), pulmonary vascular resistance decreased (314 +/- 39 to 104 +/- 21 aru), systemic vascular resistance decreased (858 +/- 70 to 497 +/- 87 aru), and pulmonary/systemic resistance ratio decreased (38 +/- 6 to 21 +/- 5%). All changes were gradual, although pulmonary artery pressure and pulmonary vascular resistance decreased rapidly in the first 24 h. Catheters were well tolerated over several days, indicating their feasibility for studying cardiovascular function in full-term or premature equine neonates.