Microvascular pressure profile of serosal vessels of rat trachea

The distribution of intravascular pressures within the pulmonary airway microcirculation is an important determinant of transvascular liquid balance. Intravascular pressures were measured in the serosal vessels of the trachea in anesthetized, ventilated rats. The ventral portion of the trachea was surgically exposed and suffused with warm (37 degrees C) Krebs-Ringer bicarbonate. The serosal microvasculature was observed with a video microscope, and microvessel pressures and diameters were measured using the servo-null technique and video calipers, respectively. Mean arterial pressure (MAP) was monitored from the left femoral artery and averaged 106.1 +/- 5.2 mmHg (n = 14). The highest pressure (77% of MAP) was measured in a large (95-microns diam) transverse arteriole. As arteriolar diameter decreased from 39 to 11 microns, pressures fell from 62 to 18% of MAP. Capillaries drained into venular networks that formed extensive arcades. Pressures in these postcapillary venules (20-75 microns diam) were 7.7 +/- 5.5% of MAP (n = 9). These vessels in turn drained into large venous sinuses (120-425 microns diam) where pressures averaged 5.7 +/- 2.3% of MAP (n = 7). A four-parameter logistical model of these data predicts that capillary pressures range from 27 to 15% of MAP. We conclude that 1) a substantial resistance exists across precapillary arterioles less than 40 microns diam and 2) a small pressure drop occurs between systemic arteries and primary feed arterioles in this tissue.