Change in diffusing capacity with blood flow in an improved isolated lung preparation

¹ Department of Physiology, Université de Montréal, Montreal, Canada

The isolated blood-perfused cat lung preparation has been improved by using large cannulas placed so as to minimize kinking of large vessels and by reducing the pressure produced by the perfusing pump by placing resistances between it and the lung. This improved preparation was capable of accepting blood flows up to 500 ml/min for 5–10 min and could be studied for 3–5 hr before deteriorating. The diffusing capacity for carbon monoxide, Dl, was measured at various blood flows up to 500 ml/min in seven isolated lung preparations improved as indicated. A breath-holding method using a gas mixture containing 2% SF₆ and 0.3% CO was employed for measuring Dl. The test gas was analyzed on a gas chromatograph. Dl increased with blood flow in all the lungs studied. In four of them which were studied at constant left atrial pressure, Dl increased steadily by 10%/100 ml increase in blood flow throughout the range studied. Pulmonary vascular resistance decreased as Dl increased.