Pulmonary hydraulic impedance response to cromakalim (BRL 34915) in newborn pigs

Cromakalim (BRL 34915), a novel vasodilator, is used clinically to manage systemic hypertension. Its effects on the intact newborn pulmonary circulation remain unclear. The purpose of this study was to determine the response of both the mean and pulsatile pulmonary hemodynamic parameters to intravenous infusion of BRL 34915 (0.1 mg/kg/min for 10 min) in 48-hr-old open-chest Yorkshire pigs. Animals were divided into two groups: Group I pigs had a high mean baseline pulmonary artery pressure (PAP) (> 17 mm Hg), while Group II pigs had a low to normal baseline mean PAP (< 17 mm Hg). Following instrumentation for high-fidelity recordings of PAP and flow, baseline data were acquired. Employing Fourier analysis, characteristic impedance (Zo), input mean impedance (Zm), impedance harmonic moduli (units in dyn sec cm-5), and phase angles (radians) were determined. Pulmonary vascular resistance (PVR) was calculated and aortic pressure (AP, mm Hg) was also measured. All values = mean +/- SEM. Group I animals ("high tone") underwent a decrease in PAP (17.9 +/- 1.6 mm Hg vs 13.6 +/- 1.9 mm Hg, P = 0.008) and PVR (4310 +/- 816 dyn sec cm-5 vs 3713 +/- 687 dyn sec cm-5, P = 0.04). Group II animals ("low tone") responded with an increase in PAP (11.5 +/- 0.4 mm Hg vs 16.6 +/- 1.8 mm Hg, P = 0.029). AP decreased in Group I (40 +/- 3.8 mm Hg vs 21.5 +/- 2.8 mm Hg, P = 0.008) and Group II (51.2 +/- 10.8 mm Hg vs 31.2 +/- 10.9 mm Hg, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)