Ka. Overholser et al., PULMONARY VASCULAR-RESISTANCE DISTRIBUTION AND RECRUITMENT OF MICROVASCULAR SURFACE-AREA, Journal of applied physiology, 77(2), 1994, pp. 845-855
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.