Dj. Duncker et al., EFFECT OF EXERCISE ON CORONARY PRESSURE-FLOW RELATIONSHIP IN HYPERTROPHIED LEFT-VENTRICLE, American journal of physiology. Heart and circulatory physiology, 38(1), 1995, pp. 271-281
Left ventricular (LV) hypertrophy (LVH) secondary to chronic pressure
overload is associated with increased susceptibility to myocardial hyp
operfusion and ischemia during exercise. The present study was perform
ed to determine whether exercise causes alterations in minimum coronar
y resistance or effective back pressure [coronary pressure at zero flo
w (P-zf)] that limit maximum myocardial perfusion in the hypertrophied
heart. Ascending aortic banding in 7 dogs increased the LV weight-to-
body weight ratio to 7.7 +/- 0.3 g/kg compared with 4.6 +/- 0.2 g/kg i
n 11 normal dogs (P < 0.01). Maximum coronary vasodilation was produce
d by intracoronary infusion of adenosine. Under resting conditions, th
e slope of the pressure-flow relationship (conductance) was significan
tly lower in the LVH animals than in the normal dogs (7.2 +/- 0.8 vs.
11.9 +/- 0.8 x 10(-2) ml . min(-1). g(-1). mmHg(-1); P < 0.01); the sl
ope correlated with the degree of hypertrophy (r = 0.74; P < 0.001). T
he P-zf measured during total coronary artery occlusion (P-zf,P-measur
ed) was significantly elevated in LVH compared with normal dogs (25.6
+/- 2.2 vs. 13.0 +/- 1.2 mmHg; P < 0.01); P-zf,P-measured was positive
ly correlated (r = 0.78, P < 0.0005) with LV end-diastolic pressure me
asured during total coronary artery occlusion (9.0 +/- 1.1 mmHg in nor
mal dogs and 22.2 +/- 3.2 mmHg in LVH dogs; P < 0.01). Graded treadmil
l exercise to maximum heart rates of 210 +/- 9 and 201 +/- 8 beats/min
in normal and LVH animals, respectively, caused similar decreases in
the slope of the pressure-flow relationship in LVH (from 7.7 +/- 0.9 t
o 6.1 +/- 0.8 x 10(-2) ml . min(-1). g(-1). mmHg(-1); P < 0.01) and no
rmal dogs (from 11.9 +/- 0.8 to 10.0 +/- 0.7 x 10(-2) ml . min(-1). g(
-1). mmHg(-1); P < 0.01). However, exercise-induced increases in P-zf,
P-measured were significantly greater in the LVH animals (from 25.6 +/
- 2.2 to 40.8 +/- 2.1 mmHg; P < 0.01) than in normal animals (from 13.
0 +/- 1.2 to 24 +/- 2.1 mmHg; P < 0.01) (P < 0.01 LVH vs. normal). The
greater increase in P-zf paralleled a more pronounced increase in LV
end-diastolic pressure in the LVH dogs (from 22.2 +/- 3.2 to 39.1 +/-
2.7 mmHg) than in normal dogs (from 9.0 +/- 1.1 to 14.2 +/- 2.0 mmHg).
The results suggest that exaggerated increases in filling pressure du
ring exercise in the hypertrophied left ventricles contributed to impa
irment of myocardial perfusion during exercise by augmenting the back
pressure, which opposes coronary flow. This could be of particular imp
ortance because of the limited vasodilator reserve available to compen
sate for increased effective back pressure in the hypertrophied heart
and might contribute to increased vulnerability to ischemia during the
high metabolic demands of exercise.