Micropipette and vascular occlusion pressures in isolated lungs of newborn lambs

We compared measurements made by vascular occlusion, double occlusion, and micropuncture techniques in isolated perfused lungs of 3- to 10-day-old lambs. After adding indomethacin to the perfusate of 16 lungs, we used the micropuncture technique to measure pressures in 20- to 80-microns-diam arterioles (Pa80), 20- to 50-microns-diam venules (Pv20), and 50- to 150-microns-diam venules (Pv150). The vascular occlusion and double occlusion techniques were used in these same lungs to measure inflow occlusion (Pao), outflow occlusion (Pvo), and double occlusion pressures (Pdo). In 14 other lungs without indomethacin added to the perfusate, we measured Pv20 and Pvo before and during alveolar hypoxia and/or before and after the addition of papaverine to the perfusate. In indomethacin-treated lungs, Pao was greater than Pa80, Pvo equaled Pv20 and Pv150, and Pdo was the same as Pa80, Pv20, and Pv150. In lungs without indomethacin treatment, Pvo was less than Pv20 both before and during hypoxia but Pvo equaled Pv20 after papaverine was added to the perfusate. Thus, in indomethacin-treated lungs of newborn lambs, Pao reflected pressure in arteries > 80 microns diam, Pdo reflected pressure between 80-microns-diam arteries and 150-microns-diam veins, and Pvo was similar to pressure in veins both as small as 20 microns diam and as large as 150 microns diam. However, without indomethacin there was a gradient between Pvo and Pv20 both before and during hypoxia but not after vasomotor tone was reduced with papaverine. Thus, the correlation between Pvo and micropuncture pressure in Pv20 and Pv150 was not constant and appeared related to vasomotor tone.