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1 Consiglio Nazionale delle Ricerche Institute of Clinical Physiology, Pisa 56100; and 2 Institute of Systems Science and Biomedical Engineering, Padua 35100, Italy
To verify the
interaction between coronary pressure (CP) and blood flow (CBF)
control, we studied nine candidates for angioplasty of an isolated
lesion of the left anterior descending coronary artery [i.e.,
percutaneous transluminal coronary angioplasty (PTCA)]. CBF (i.e.,
flow velocity × coronary cross-sectional area at the Doppler tip)
and CP were monitored during washout of 2-5 mCi of 133Xe after bolus injection into the left main artery
before and after PTCA. Xe mean transit time (MTT) was calculated as the
area under the time-activity curve, acquired by a gamma camera, divided by the dose obtained from a model fit of the Xe curve in the anterior wall. CBF response to intracoronary adenosine (2 mg) was also assessed.
PTCA increased baseline CBF (from 14.5 ± 9.4 to 20 ± 8 ml/min, P < 0.01), coronary flow reserve (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 volume to CBF, MTT × CBF was used as an index of perfused myocardial volume. Volume
increased after PTCA from 23 ± 18 to 56 ± 30 ml. A direct
correlation was observed between the percent increase in distal CP and
percent increase in perfused volume (r = 0.91, P < 0.01). Thus low CP was not associated with
exhaustion of flow reserve but, rather, with reduction of perfused
myocardial volume. These data suggest that, in the presence of a severe
coronary stenosis, derecruitment of vascular units occurs that is
proportional to the decrease in driving pressure. Residual perfused
units maintain a vasomotor tone, thus explaining the paradoxical
persistence of coronary reserve.
coronary circulation; microcirculation; coronary angioplasty; autoregulation; coronary artery disease
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