HEMODYNAMIC EFFECTS OF CONTINUOUS POSITIVE AND NEGATIVE PRESSURE BREATHING IN NEWBORN PIGS

Abstract

It has been assumed that the hemodynamic effects of continuous positive airway pressure(CPAP) and continuous negative pressure(CNP) are similar. Cardiac output(CO) utilizing dye dilution curves, heart rate(HR), arterial blood pressure(BP) and central venous pressure(CVP) were measured in 5 normal newborn pigs subjected to different levels of CPAP and CNP. CPAP was supplied with a head box whereas CNP was applied with a box enclosing the chest and upper abdomen. No significant differences were found in HR and BP between CPAP and CNP. Results of CVP and CO were:CVP increased as CPAP increased while the opposite occurred on CNP. CO decreased in 4/5 animals with +10CPAP and in all animals with +15CPAP. With CNP results were less consistent. CO increased on -5CNP but showed an overall tendency to decrease on -10 and -15CNP. However, this drop was smaller than the decrease which occurred on CPAP. The better CO during CNP compared to CPAP can be due in part to the decrease in CVP improving venous return from the body portions not subjected to CNP. The fall in CO above -5CNP may be due to either pooling of blood in body portions subjected to CNP or to increased pulmonary vascular resistance due to alveolar overdistension.