In order to study hemodynamic ch -nges in gestational period, 15 cases of pregnant rabbits in various gestational period, in ranging from 49gm to 260gm in pregnant uterine, weight by measure, were used in this experiments.
Following hemodynamic analysis were done in every run of experiments. Cardiac output was determined by the dye dilution method with T-1814, and mean circulation time and central blood volume were calculated from the dye dilution curve, meanwhile total peripheral resistance was calculated from mean arterial blood pressure and cardiac output and also plasma volume and blood volume by the dye dilution method.
The data obtained were, compared to mean values of control group which was obtained from 10 cases of non-pregnant rabbits. Data obtained in the pregnant rabbits were analysed for their weight of pregnant uterus.
1. The rate of increase in plasma and blood volume were not obvious in the pregnant rabbits containing about 50gm of uterine weight, and proportionately abruptly increased with uterine weight in the pregnant rabbits whose uterine weight were more than 50gm, thereafter remained maximum plateau value whose uterine weight were more than 200gm.
The maximum plateau values of plasma and blood volume averaged 94m1 and 140ml, showed-,19%. and 12% increase with control value of .76±6.4m1 and 125±8.5ml. While, the bood volume per body weight was slightly decreased to about 3.3%.
Decrease in blood volume per body weight, higher rate of increase in plasma volume than, blood volume and:, decrease in hematocrit during gestation seems to induce the pregnant anemia in rabbits.
2.. Cardiac output, plasma flow and cardiac output per body weight were increased proportionately as the uterus gains its weight. Cardiac output ,& plasma (flow were increased to the maximum level of 262ml/min and 178m1/min which showed about 32.1% and 48.2% increase compare with control value of 197±10.3m1/min and 120±7.2mg%min. Also cardiac output per body weight was increased.12.9% at the maximum level.
The facts that cardiac output per body weight increased in spite of decrease in . blood volume per body weight might be a compensatory mechanism in the anemic tissues of pregnant rabbits.
3. There was little difference in heart rate in the pregnant rabbits whose uterine weight grew to 50gm., thereafter, begin to increase, showing maximum plateau value at uterine weight of more than 100gm., mean of the maximum value was 200 beats/min. which showed 12% increase compared to the control value, Since increasing rate of heart rate is lower than that of cardiac output, stroke volume also increase in pregnant rabbit.
4. Central blood volume showed a slight increasing tendency and was almost identical to control level up to 200gm of uterine weight. However, it was markedly increased in more than 200gm of uterine weight.
5. Total peripheral resistance was descent inversely as the uterus gains its weight. Minimum value of total peripheral resistance in the late gestational period was 2.41X104 dyne. sec/cm´, about 36.2% decreased compared with control value of 3.78X-10^4´ dyne. sec/cm^5.
From the above data, according to the growth of fetus of rabbits, cardiac output is expected to increase as the result of increasing in heart rate and stroke volume.
From these effects, the possibility is expected to give excessive cardiac load. However, the decrease in total peripheral resistance might be compensating efficiently to minimize the cardiac load. Mechanism of lowering the total peripheral resistance during gestation were briefly discussed.
|