Abstract
Rapid infusion of i.v. saline, a model of pulmonary interstitial edema, alters the distribution of pulmonary perfusion, raises pulmonary capillary blood volume, and increases bronchial wall thickness in humans. We hypothesized infusion would disrupt pulmonary gas exchange by altering VA/Q matching. Seven males (26±3 years, FEV1 110±16% pred.) performed spirometry and had the distribution of VA/Q measured using MIGET, before and after 20ml/kg i.v. of normal saline delivered in ~30 minutes. Infusion increased thoracic fluid content by 12% (P < 0.0001), left FVC unchanged, but reduced expiratory flows (e.g. FEF25–75 fell from 5.1±0.4 to 4.1±0.4 l/sec, P < 0.05). However, infusion left the distribution of VA/Q unchanged; log SDV 0.40±0.03 pre, 0.38±0.04 post, NS; logSDQ, 0.38±0.03 pre, 0.37±0.03 post, NS. There was no significant change in arterial PO2 (99.2±2.5 pre, 99.5±2.9 mmHg post, NS) but arterial PCO2 was decreased (38.7±0.6 pre, 37.1±1.1 mmHg post, P<0.05). Thus, infusion compressed small airways, and caused a mild degree of hyperventilation, but the matching of ventilation to perfusion was maintained, suggesting active control of blood flow to minimize the gas exchange consequences.
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