AJP - Heart and Circulatory Physiology, Vol 256, Issue 6 1645-H1650, Copyright © 1989 by American Physiological Society
Hyperemic response to coronary occlusion during a single diastole in conscious dog
N. Sadick, G. P. Dube, P. A. McHale and J. C. Greenfield Jr
Department of Medicine, Duke University Medical Center, Durham 27710.
This study determined whether the reactive hyperemic response to a 400-ms
diastolic coronary occlusion is dependent on ventricular systole. Studies
were obtained on 11 conscious dogs with complete heart block paced at 60
beats/min. A pressure catheter was chronically implanted in the aorta. An
electromagnetic flow probe and pneumatic occluder were implanted on the
circumflex coronary artery. Three interventions were employed: 1)
interruption of pacing for a single beat generating a long diastolic period
of 2,000 ms in duration (LDC); 2) introduction of a 400-ms diastolic
coronary occlusion early in a long diastole (LD4); and 3) a 400-ms
diastolic occlusion during uninterrupted pacing (400R). The rise in
diastolic coronary vascular resistance index noted during LDC was inhibited
significantly in the last 600 ms of diastole during LD4. Thus an
intervening systole is not required for a reactive hyperemic response to a
diastolic coronary occlusion. During 400R, the resistance index was lower
than that found during LD4. The reactive hyperemic response may be caused
by either a myogenic or metabolic mechanism or by both. The greater
vasodilatation observed after the postocclusion systole in 400R probably
reflects metabolic influences.
