Clinical evidence for myocardial derecruitment downstream from severe stenosis: pressure-flow control interaction

To verify the interaction between coronary pressure (CP) and blood flow (CB F) control, we studied nine candidates for angioplasty of an isolated lesio n of the left anterior descending coronary artery [i.e., percutaneous trans luminal coronary angioplasty (PTCA)]. CBF (i.e., flow velocity x coronary c ross-sectional area at the Doppler tip) and CP were monitored during washou t of 2-5 mCi of Xe-133 after bolus injection into the left main artery befo re and after PTCA. Xe mean transit time (MTT) was calculated as the area un der the time-activity curve, acquired by a gamma camera, divided by the dos e obtained from a model fit of the Xe curve in the anterior wall. CBF respo nse to intracoronary adenosine (2 mg) was also assessed. PTCA increased bas eline CBF (from 14.5 +/- 9.4 to 20 +/- 8 ml/min, P < 0.01), coronary flow r eserve (from 1.52 +/- 0.24 to 2.33 +/- 0.8, P < 0.01), and CP (from 64 +/- 9 to 100 +/- 10 mmHg, P < 0.05). MTT decreased from 89 +/- 32 to 70 +/- 19 s (P < 0.05) after PTCA; however, MTT and CBF changes were not correlated ( r = -0.09, not significant). Inasmuch as MTT is the ratio of distribution v olume to CBF, MTT x CBF was used as an index of perfused myocardial volume. Volume increased after PTCA from 23 +/- 18 to 56 +/- 30 ml. A direct corre lation was observed between the percent increase in distal CP and percent i ncrease in perfused volume (r = 0.91, P < 0.01). Thus low CP was not associ ated with exhaustion of flow reserve but, rather, with reduction of perfuse d myocardial volume. These data suggest that, in the presence of a severe c oronary stenosis, derecruitment of vascular units occurs that is proportion al to the decrease in driving pressure. Residual perfused units maintain a vasomotor tone, thus explaining the paradoxical persistence of coronary res erve.