Atrial natriuretic peptide decrease during spontaneous breathing with continuous positive airway pressure in volume-expanded healthy volunteers

We examined the effect of spontaneous breathing with continuous positive airway pressure (CPAP) on the plasma concentrations of immunoreactive (ir) alpha-atrial natriuretic peptide (ANP). In three experiments, each of 11 healthy male volunteers performed CPAP at 20, 10 and 0 cm H2O for 2 h during continuous volume loading. Samples were drawn from a peripheral vein. Plasma concentrations of irANP were determined by a sensitive radioimmunoassay. Significantly lower concentrations of irANP were observed during 20 cm H2O CPAP than at 10 and 0 cm H2O. The concentrations of irANP did not differ significantly when individuals breathing with CPAP at 10 and at 0 cm H2O were compared. Our data suggest that CPAP at 20 cm H2O lowers the release of ANP in volume-expanded subjects. We hypothesize that this phenomenon may contribute to the fluid retention and renal dysfunction observed frequently during high CPAP levels. The decline in plasma concentrations of irANP may be the result of atrial compression by the distended lungs and of reduced venous return to the heart during CPAP.