A myocardial blood flow (MBF) in the inner and outer layer of the left ventricle was measured in thoracotomized anesthetized dogs by means of hydrogen clearance method. A recessed type platinum electrode was designed in order to insert easily into the myocardium and to maintain constantly the sensitivity to H
2 partial pressure in the myocardium. It was constructed from the platinum wire, 100μ in diameter, covered with a glass which was further enveloped by an injection needle. MBF was calculated from the wash-out curves of hydrogen currents in the platinum electrode tip placed in the left ventricular wall.
The values measured by this method were in good agreement with those of coronary sinus blood flow obtained by means of coronary sinus catheter electrode.
Hydrogen currents in the inner and outer layer of the left ventricle via a pair of the electrodes and also in the aorta via catheter electrode were simultaneously recorded on the muti-channel recorder.
Using this method, the regional MBF during hypoxia, tachycardia or pressure-rise and following the administration of β-stimulating, β-blocking agent or noradrenaline was measured, and the following results were obtained.
1) The average MBF in the inner and outer layer was 112.4 and 98.7m
l/100m
l/min respectively. Thus, MBF in the former is higher by 21%.
2) Following 6.7% O
2 breathing, MBF in the inner layer increased from 106.7 to 175.0m
l/100m
l /min and that in the outer layer from 72.2 to 145.5m
l/ 100m
l/min on average. Accordingly I:O ratio (blood flow ratio of inner to outer layer) decreased from 1.48 to 1.25. Under this condition, heart rate and mean aortic blood pressure increased from 127.8 to 142.2 beats/min and 126.6 to 156.4mmHg, respectively.
3) Tachycardia induced by atrial pacing produced a significant augmentation of MBF and I:O ratio was reduced. Aortic pressure-rise produced by angiotensin II (0.2μg/kg/min) did not significantly change the MBF.
4) Isoproterenol (0.3μg/kg/min) produced an increase of the outer layer blood flow without significant change in the inner layer and I:O ratio reduced from 1.31 to 1.00 on average. Propranolol (0.3mg/kg) did not change the MBF in the inner layer but that in the outer reduced by 23.6%, and I:O ratio increased from 1.03 to 1.25. Noradrenaline (1μg/kg/min) produced a remarkable increment of MBF in the inner from 89.1 to 129.3m
l/100m
l/min, and I:O ratio increased from 1.22 to 1.43.
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