Fourteen sheep fetuses in the third trimester of gestation were surgically prepared with intravascular catheters and 5 were nephrectomized. All experiments were done on unanaesthetized fetuses in utero, 3 to 9 days after surgery. Mean arterial blood pressure was recorded while fetal blood volume was changed by injection or withdrawal of blood, or infusion of Ringer's or dextran solutions. Fetal arterial blood gases and pH changed little during the experiments and were shown not to have affected the results. Arterial blood pressure was strongly influenced by changes in fetal blood volume and was also found to depend on haematocrit. There were no detectable differences between the responses of normal and nephrectomized fetuses or between normal fetuses and fetuses treated with hexamethonium. In all preparations central venous pressure depended on blood volume. Heart rate did not depend on blood volume in normal fetuses, but an increase in heart rate with an increase in blood volume was seen after hexamethonium. The open loop gain of baroceptor control of arterial blood pressure could not be proved to differ significantly from zero. Venoconstrictor responses and heart rate responses of reflex origin did not occur when arterial blood pressure was changed. The absence of detectable baroceptor control appears to explain the great sensitivity of arterial blood pressure to blood volume in the unanaesthetized fetal lamb.
|Original language||English (US)|
|Number of pages||15|
|Journal||Quarterly Journal of Experimental Physiology|
|Publication status||Published - 1974|
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