• Gwirtz, Patricia (PI)

Project Details


The heart and coronary blood vessels receive constant sympathetic neural
activity, referred to as tone, which modulates heart rate, contractile
strength and coronary vascular resistance. Studies have indicated that
there is a potential alteration in the sympathetic nervous system control,
or the amount of sympathetic activity to the heart and blood vessels with
exercise training. The proposed study was designed to investigate the
relationship between the neural and metabolic regulation of coronary blood
flow during an exercise training program. The hypothesis tested is:
exercise training enhances the autonomic sympathetic tone on coronary
vessels at rest and during physiological stress states, such as treadmill
exercise. The sensitivity to adrenergic receptor agonists and antagonists
will be studied in the chronically instrumented, conscious dog. Left
circumflex coronary blood flow will be measured simultaneously with
regional myocardial segment length using a range gated, pulsed Doppler
flowmeter and ultrasonic dimension gages. Regional coronary blood flow
distribution will be determined by the microsphere technique. Diastolic
coronary vascular resistance will be calculated using diastolic aortic
pressure and left circumflex coronary artery blood flow. Myocardial
reactive hyperemia will be produced by occlusion and release of an
externally controlled hydraulic occluder implanted around the circumflex
coronary artery. Changes in coronary blood flow, diastolic coronary
vascular resistance, myocardial segment length and heart rate to adrenergic
stimulation of alpha- and beta-receptor agonists and to 15 sec coronary
artery occlusions will be compared before, during and after a 10-week
exercise training program. Drugs will be administered using an implanted
coronary artery catheter, avoiding systemic drug effects. Using these
techniques it is possible to perturb only the coronary vascular bed and
measure both total and regional coronary blood flow in conscious dogs. We
can also determine whether a modification in the sympathetic nervous system
is real or if changes are metabolic in origin by simultaneously measuring
regional myocardial function. The long term goal of these studies is to
describe changes in the control of coronary blood flow due to daily
exercise in normal individuals and to then apply this knowledge in the
future to individuals with cardiovascular disease.
Effective start/end date31/12/8931/12/89


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