Effects of static and fluctuating airway pressure on intact pulmonary circulation

The direct effects on the pulmonary circulation of static and fluctuating airway pressure were compared in intact close-chest infant lambs with reactive pulmonary vasculature under α-chloralose anesthesia. A preparation developed to permit independent ventilation of right and left lungs and independent measurement of right and left lung blood flow was employed to separate direct from indirect effects of unilateral airway pressure changes on pulmonary vascular resistance (PVR). Both static and fluctuating unilateral airway pressure interventions directly elevated ipsilateral PVR. For purposes of comparison mean alveolar pressure (P̄(A)) was estimated for both static and fluctuating trials. Fluctuating interventions increased PVR more than did static trials at comparable levels of P̄(A). Substantially less P̄(A) was needed to double ipsilateral PVR by fluctuating than by static interventions (16 vs. 26 mmHg, respectively). These data indicate that, in the intact animal with reactive pulmonary vasculature, both P̄(A) and the waveform of airway pressure applied can influence PVR.