PULMONARY VASCULAR-RESISTANCE DISTRIBUTION AND RECRUITMENT OF MICROVASCULAR SURFACE-AREA

To test the hypothesis that the distribution of hemodynamic resistance is involved in the control of pulmonary capillary surface area, we me asured permeability-surface area product (PS) and longitudinal resista nce distribution (LRD) as functions of perfusion rate in isolated rabb it lungs under zone II conditions (n = 10) and through the zone II-III transition (n = 4). PS, considered to be indicative of functioning ca pillary surface area, was measured with the aid of the diffusion-limit ed tracer [C-14]propanediol, whereas LRD was determined using a viscou s bolus technique. LRD was seen to change character with increasing fl ow and increasing PS/surface area, becoming bimodal with low central r esistance as full capillary recruitment was approached in zone III. Ef fects of hypoxic ventilation were studied in zone II in five lungs; it was found that hypoxia altered the LRD and eradicated the normoxic de pendence of PS/surface area on perfusion rate. It was concluded that L RD is involved in the determination of functioning capillary surface a rea.