✍ Scribed by E. Wolner
No coin nor oath required. For personal study only.
An anesthetized dogs, without opening the thorax, determinations were made of the coronary blood flow, oxygen consumption, cardiac output, cardiac work and the aerobic cardiac efficiency at a slow heart rate (20--100 beats/rain) and constant arterial mean pressure. The retardation of the heart rate was achieved through mechanical irritation of the A-V-node.
The coronary blood flow was within normal limits of 70--100 ml/min/100 g and decreased linearly to 40 ml/min/100 g at a heart rate of 20/min. It was found that there was a direct correlation of the coronary blood flow to the sonare root of the heart rate. The relationship of oxygen consumption to the heart rate was similar to the coronary blood flow because the coronary arterio-coronary venous oxygen difference was constant between 10--14 col-°/0 at all heart rates measured. Thus, at a rate of 20/min the heart used 5 ml/100 g/min oxygen and at a rate of 80/min 10 ml/100 g. Within the limits of normal heart rate, the cardiac output was 4 l/rain and with diminishing rate decrease to 1 1/min whereby there was a simple linear relation between heart rate and cardiac output. The aerobic cardiac efficiency was 20--25°/0 at normal heart rates and it decrease with the square root of the heart rate as the rate diminished. However by rates less than 40/rain a lower cardiac efficiency was found, because in the reckoning of the efficiency only the pressure work was contained.
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