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Coronary pressure-flow relation in left ventricular hypertrophy. Importance of changes in back pressure versus
D J Duncker1, J Zhang, R J Bache
1Department of Medicine, University of Minnesota Medical School, Minneapolis 55455.
Insights
Left ventricular hypertrophy (LVH) in dogs reduces coronary flow capacity due to increased coronary resistance and back pressure. This study investigated the coronary pressure-flow relationship in hypertrophied ventricles.
Area of Science:
- Cardiovascular Physiology
- Cardiac Hypertrophy Research
Background:
- Pressure-overloaded hypertrophied left ventricle (LVH) exhibits perfusion abnormalities.
- These abnormalities may stem from increased minimum coronary resistance or elevated back pressure due to extravascular forces.
Purpose of the Study:
- To investigate the coronary pressure-flow relationship in canine left ventricular hypertrophy (LVH).
- To differentiate between changes in minimum coronary resistance and back pressure in LVH.
Main Methods:
- Induction of LVH in dogs via ascending aortic banding.
- Maximal coronary vasodilation achieved using intravenous adenosine infusion.
- Analysis of the coronary pressure-flow relation, including slope (1/alpha PF) and pressure at zero flow (Pf=0).
Main Results:
- LVH group showed a significantly decreased slope (alpha PF) compared to normal dogs (5.8 vs. 9.3 x 10^-2 (ml/min/g)/mmHg, p < 0.05).
- The slope (alpha PF) correlated with the left ventricular to body weight ratio, indicating hypertrophy's role.
- Elevated pressure at zero flow (Pf=0) was observed in the LVH group (24.1 vs. 11.7 mmHg, p < 0.05).
Conclusions:
- LVH significantly impairs coronary flow capacity.
- Increased coronary resistance, not just high pressure, contributes to reduced flow in LVH.
- Elevated extravascular compressive forces likely increase back pressure in LVH.
Abstract:
Perfusion abnormalities in the pressure-overloaded hypertrophied left ventricle could result from an increase in minimum coronary resistance or an increase in effective back pressure due to increased extravascular compressive forces. Since the pressure-flow relation of the maximally vasodilated coronary bed allows dissociation of minimum resistance (inverse slope [1/alpha PF]) and back pressure (pressure at zero flow [Pf = 0]), the present study was undertaken to examine the coronary pressure-flow relation in left ventricular hypertrophy (LVH). Ascending aortic banding in eight dogs at 6-8 weeks of age (LVH group) increased the left ventricular to body weight ratio to 8.7 +/- 0.6 g/kg as compared with 4.8 +/- 0.2 g/kg in nine normal dogs (p < 0.05). Maximum coronary vasodilation was produced by infusion of adenosine (1 mg/kg per minute i.v.). The slope of the coronary pressure-flow relation (alpha PF) was 5.8 +/- 0.5 10(-2) (ml/min per gram)/mm Hg in the LVH group and 9.3 +/- 0.6 10(-2) (ml/min per gram)/mm Hg in the normal group (p < 0.05). alpha PF was significantly correlated with the left ventricular to body weight ratio but not with coronary pressure, suggesting that the degree of hypertrophy and not exposure to high coronary pressure was responsible for the observed decrease in alpha PF. Pf = 0 was 24.1 +/- 2.6 mm Hg in the LVH group and 11.7 +/- 1.2 mm Hg in the normal group (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)