Hemodynamic responses of dog lung lobe to lobar venous occlusion

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Abstract
The left lower lobe of the dog lung was perfused with constant flow. When the lobar venous outflow was occluded, the lobar venous pressure rose suddenly to a level below the arterial pressure, and then the arterial and venous pressures rose more slowly. When the outflow was occluded, flow through some downstream segment of the bed ceased. Because flow into the lung continued, the arteriovenous pressure difference after occlusion represents the pressure drop across an upstream segment through which the flow continued. Arteriovenous pressure difference just after outflow occlusion was designated the upstream pressure drop. The arteriovenous pressure difference before occlusion minus the upstream pressure drop was designated the downstream pressure drop. The influence of pulmonary vasoconstriction and flow direction on the size of the upstream and downstream pressure drops was examined. These pressure drops were compared to the pressure drops occurring upstream and downstream from the midpoint of the lobar vascular volume, using the low-viscosity bolus technique. Changes in the upstream and downstream pressure, as evaluated by outflow occlusion, reflect changes in the lobar arterial and venous resistances.