Analysis of the double occlusion which provides four pressure gradients.

The arterial, double and venous occlusions are used to partition pulmonary vascular resistance into four segments. In this study, we tested whether the same can be accomplished from one double occlusion. In an isolated canine lung left lower lobe perfused with blood (flow rate = 500 mL.min-1), the pulmonary arterial and venous pressures (Pa and Pv, respectively) were measured directly. Arterial, double, and venous occlusions were performed and analysed as usual (Method 1) to measure pressures in small arteries and small veins (Pa' and Pv', respectively) and capillary pressure (Pc). Alternatively, one double occlusion was analysed (Method 2), not only for Pa, Pv and Pc, but also as independent arterial and venous occlusions to measure Pa' and Pv'. Method 1 yielded Pa, Pa', Pc, Pv', and Pv (Baseline) of 14.2 +/- 1.7, 10.8 +/- 1.6, 8.9 +/- 1.9, 7.3 +/- 1.5 and 1.3 +/- 0.6 mmHg, respectively (1 mmHg = 0.133 kPa). Method 2 yielded values for the same five pressures equal to 14.7 +/- 2.1, 11.0 +/- 2.2, 8.9 +/- 1.9, 7.3 +/- 1.3 and 1.3 +/- 0.6 mmHg, respectively. There was no significant difference in the pressure profile obtained using the two methods, nor were there differences during hypoxia and angiotensin infusion. These results suggest that a more thorough analysis of the double occlusion can provide the same information about distribution of vascular resistance as provided by a combination of the three occlusions. The advantage of the new approach is that fewer occlusions are needed and resistance distribution can be assessed during a transient response. Because all pressures are derived from one occlusion, the pressures would be more accurate relative to each other.