Increased release of alpha-atrial natriuretic peptide during controlled mechanical ventilation with positive end-expiratory pressure in humans.

The objective of this study was to test the hypothesis that a release of alpha-artrial natriuretic peptide (ANP) is depressed resulting in the reduction of urinary output in patients receiving controlled mechanical ventilation (CMV) with positive end-expiratory pressure (PEEP). Five normovolemic patients with no apparent cardiac, renal, endocrine, or pulmonary dysfunctions were included in this study. After the patients were mechanically ventilated using a volume-cycled ventilator with zero cmH(2)O PEEP for one hour, hemodynamic variables were measured. Urine and blood samples were collected after the measurements. Plasma alpha-ANP levels were determined on blood samples taken from radial artery using specific radioimmunoassay. Then PEEP levels were changed to 5, 10, 15 and, finally, 0 cmH(2)O in four consecutive one-hour periods. At the end of each period, the measurements and collection of the samples were repeated. With increasing levels of PEEP, central venous pressure (CVP), pulmonary artery wedge pressure (PAWP), and heart rate were pressure-dependently increased. On the other hand, cardiac output and urinary output were decreased. Plasma levels of alpha-ANP were also increased by the institution of PEEP. These changes occurred in a pressure-dependent fashion. Urinary sodium excretion, potassium excretion, fractional excretion of sodium and free water clearance remained unchanged. It is concluded that a release of alpha-ANP was augmented rather than depressed with PEEP. This suggests that a decrease in urinary excretion in patients with PEEP may not be due to a reduced release of alpha-ANP.