PRESSURE-DIAMETER RELATIONS OF CAPILLARIES AND SMALL BLOOD VESSELS IN FROG LUNG

Static pressure-diameter measurements were made on the small pulmonary blood vessels of the frog lung and the change in the septal area occupied by capillaries was investigated between intravascular pressures of 1-27 cm H2O. Over this pressure range the smallest arteries (30μ-50μ) increased their radius by 27% while the change for veins of the same size was 6%. Medium size arteries and veins (50-150μ) showed a similar pattern of increase in radius by 30% while the largest arteries (150μ-400μ) increased their radius by 50% over the complete pressure range. Between 1 and 22 cm H2O the mean increase in arterial radius was 1 cm H2O (30-50μ) to 2 cm H20 (300μ-400μ). Capillaries occupied 79% of the alveolar septum at low intracapillary (1 cm H2O) pressures and less than 80.5% at higher intracapillary pressures (27 cm H2O). The average capillary length in the frog lung was 644μ ± 39μ (S.E.M.). These results indicate that the small arterial blood vessels of the lung are highly compliant and capable of large alterations in blood volume and resistance with changes in intravascular pressure. © 1969.