RESTRICTION OF REGIONAL BLOOD-FLOW AND DIAPHRAGMATIC CONTRACTILITY

We have tested the hypothesis that the diaphragmatic head-to-head arterial anastomosis system should maintain adequate diaphragmatic function even during occlusion of some of its arteries. In six anesthetized open-chest dogs, left phrenic vein blood flow (Qphv) was measured by pulsed Doppler flowmetry. Contractility was measured by sonomicrometry in the left costal and crural diaphragm. The diaphragm was paced for 15 min by continuous bilateral supramaximal phrenic nerve stimulation. In five separate runs the following arteries were occluded at minute 5: 1) left phrenic artery, 2) internal mammary artery (IMA), 3) left phrenic artery and IMA, 4) descending aorta, and 5) descending aorta and IMA. Occlusion was then released at minute 10 of the run. In runs 1-3 there were no changes in contractility in costal or crural diaphragm and no changes in Qphv. However, in runs 4 and 5, Qphv decreased to 55.2 +/- 7.4 and 24.0 +/- 6.5% of control values, respectively. In run 4, percent maximum shortening from functional residual capacity (%L(FRC)) of the crural diaphragm decreased by 39.1%, while %L(FRC) of the costal diaphragm increased by 41.4% and abdominal pressure decreased by 47.0%. In run 5, abdominal pressure decreased by 53.5% and %L(FRC) of the crural and costal diaphragm decreased by 45.5 and 5.8%, respectively. Also relative postocclusion hyperemia was greater in run 5 (64.8%) than in run 4 (40.2%). We conclude that 1) the blood supply by intercostal arteries is sufficient to maintain normal costal and crural contractility in a diaphragm developing mild level of work (tension-time index of < 0.20) and 2) IMA perfusion alone can sustain normal contractility of the costal but not of the crural diaphragm.