Dissociation of diastolic pressure-segment length and pressure-wall thickness relations during vasodilation in the conscious dog.

The effects of pharmacologic vasodilation and reductions in circumflex coronary artery pressure on the ventricular diastolic pressure-segment length and pressure-wall thickness relations were studied in nine conscious dogs equipped with an inflatable cuff on the proximal circumflex artery, a micromanometer in the left ventricle and four sets of piezoelectric crystals to measure wall thickness and endocardial segment length in the left circumflex and left anterior descending artery territories. Adenosine infusion into the circumflex coronary artery increased endocardial and transmural blood flow to that territory (measured by microspheres) by 436% and 487%, respectively (both p less than 0.05), and shifted the left circumflex artery territory pressure-wall thickness curve upward (p less than 0.05) without affecting the circumflex pressure-segment length, the left anterior descending artery territory pressure-segment length or pressure-wall thickness curves significantly; papaverine also shifted the circumflex region pressure-wall thickness curve upward (p less than 0.05). Both with and without vasodilation, moderate reductions in circumflex artery perfusion pressure did not affect the position of the ventricular pressure-wall thickness or the pressure-segment length curve (although during adenosine infusion endocardial blood flow decreased from 436% to approximately 100% of control values). More severe reductions in perfusion pressure (less than 45 mm Hg under control conditions and less than 30 mm Hg during adenosine infusion) decreased coronary blood flow below control values and caused a marked downward shift of the circumflex region pressure-segment length curve without affecting the position of the pressure-wall thickness curve.(ABSTRACT TRUNCATED AT 250 WORDS)