Hemodynamic effects of continuous negative extrathoracic pressure and continuous positive airway pressure in piglets with normal lungs

The hemodynamic effects produced by continuous positive airway pressure (CPAP) and continuous negative extrathoracic pressure (CNEP) of 4 and 8 cm H₂O were compared in 8 normal, spontaneously breathing piglets. Arterial blood gases and hemodynamic measurements were obtained before and during CPAP and CNEP of 4 and 8 cm H₂O. CPAP 8 cm H₂O and CNEP 8 cm H₂O produced significant increases (p < 0.01) in PaO₂ from baselines 76 ± 3 to 85 ± 3 and 77 ± 4 to 85 ± 3 mmHg,respectively. No significant changes occurred in PaCo₂ or cardiac index, except during CPAP 8 cm H₂O [38 ± 1 to 44 ± 2 mmHg (p < 0.05) and 376 ± 30 to 330 ± 30 ml/kg/min (p < 0.05), respectively]. During CPAP of 4 cm H₂O, significant increases occurred in mean right atrial pressure (P̄ra) (2.1 ± 0.3 to 3.3 ± 0.4 mmHg; p < 0.01), left ventricular end-diastolic pressure (LVEDP) (2.8 ± 0.4 to 3.7 ± 0.3 mmHg; p < 0.01), and mean pulmonary artery pressure (P̄pa) (12.9 ± 0.8 to 15.1 ± 0.8 mmHg; p < 0.01). CPAP of 8 cm H₂O produced marked increases in P̄ra (2.1 ± 0.2 to 4.9 ± 0.7 mmHg: p < 0.01), LVEDP (2.7 ± 0.5 to 4.5 ± 0.4 mmHg; p < 0.01) and P̄pa (12.8 ± 0.8 to 17.7 ± 0.6 mmHg, p < 0.01). In contrast, CNEP of 8 cm H₂O produced decreases in P̄ra (2.1 ± 0.2 to 1.3 ± 0.3 mmHgHg; p < 0.01), LVEDP (2.6 ± 0.5 to 1.7 ± 0.4mmHg; p < 0.01), and P̄pa (12.9 ± 1.0 to 11.4 ± 1.0 mmHg; p < 0.01). CNEP in contrast to CPAP produced an improvement in oxygenation while decreasing vascular pressures and maintaining cardiac output near basal levels. These data support clinical experience which suggests a beneficial effect of CNEP in the treatment of patients with increased pulmonary vascular resistance and pulmonary hypertension.