Influence of state of inflation of the lung on pulmonary vascular resistance

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Abstract
The relationship between the degree of pulmonary inflation and the pulmonary vascular resistance was studied in an open-chested dog preparation. It was possible to control the state of inflation and the blood flow to the lung under study. Vascular resistance could then be observed under controlled conditions. In most cases the resistance at complete collapse was very slightly higher than at moderate levels of inflation. In a few instances collapse was associated with a more marked elevation of resistance. Higher levels of inflation resulted in elevation of vascular resistance. At high levels of pulmonary blood flow and pulmonary arterial pressure, the flow resistance curve is lower than at low levels of blood flow. The resistance values obtained during deflation of the lung were consistently different at equal transpulmonary pressures from those obtained during inflation. The possible reasons for this hysteresis are discussed. Evidence is presented that the increased resistance at high levels of lung inflation is due to the effect of transpulmonary pressure on the vessels surrounding the alveoli. Submitted on January 11, 1960