EFFECTS OF CPAP ON CARDIAC-OUTPUT IN PIGS WITH PACING-INDUCED CONGESTIVE-HEART-FAILURE

Continuous positive airway pressure (CPAP) may improve left ventricula r (LV) function in patients with congestive heart failure (CHF). To un derstand mechanisms involved, in nine sedated, unanesthetized pigs wit h pacing-induced CHF we measured cardiac index (CI), heart rate (HR), LV pressures and volumes, ejection fraction (LVEF), and maximal rate o f LV pressure rise (dp/dtmax). LV end-systolic transmural pressure (af terload) was estimated as LV end-systolic pressure (LVESP)-CPAP. Measu rements were taken at CPAP 0, 5, 10, and 15 cm H2O and during recovery . At CPAP 5 cm H2O, CI increased from 4.23 +/- 1.00 to 4.99 +/- 0.88 L /min/m(2) (p < 0.005), LV end-systolic volume decreased from 82.3 +/- 32.1 to 72.7 +/- 30.3 ml (p < 0.04) and LVEF increased from 0.30 +/- 0 .09 to 0.36 +/- 0.12 (p < 0.02), and dp/dtmax increased. LVESP-CPAP wa s unchanged. After CPAP was discontinued, there was a rise in CI (p < 0.03), HR (p < 0.03), LVESP (p < 0.02), dp/dtmax (p < 0.02) and a decr ease in total peripheral resistance (p < 0.03). We conclude that in CH F, low levels of CPAP improved CI, at least partly by improving contra ctility. Increased CI after discontinuing CPAP may be due to sympathoa drenal stimulation or withdrawal of alpha-adrenergic tone.