Graduate Thesis Or Dissertation
 

Cardiovascular changes during pregnancy in the ewe

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  • In order to study maternal cardiovascular adjustments to pregnancy, serial determinations were carried out on five pregnant and lour nonpregnant ewes. Measurements were made at approximately two to three week intervals, and continued for nine weeks after delivery. Cardiac output was measured with the dye dilution technique using Evans blue dye and a continuously recording densitometer. Plasma volume was simultaneously estimated. Intra-arterial blood pressure was measured with a strain gauge transducer. All measurements were made on the sheep while they stood quietly in a stanchion, only local anesthesia being used at the sites of vessel puncture. Carotid loops were constructed to facilitate arterial catheterization. Statistical analysis was carried out by subtracting the average value of each function in each sheep for 30 days after delivery from the average value of the same function for 30 days before delivery. The differences obtained in the pregnant sheep were compared with figures similarly obtained in the nonpregnant sheep by means of the t-test. The average values of the measurements in the pregnant ewes in the last three weeks of pregnancy were as follows: a. Cardiac output, 10.3 lit/min. This was 41% greater than the average postpartum value, and the difference was statistically significant (P <0.01). Cardiac output per unit of body weight, 157 m /kg/min. This was 31% greater than the postpartum average (P <0.02). c. Heart rate, 109 beats per minute. This was 30% greater than the postpartum average (P <0.02). d. Arterial systolic blood pressure, 88 mm Hg. This was 18% less than the postpartum average (P <0.1). e. Arterial diastolic blood pressure, 74 mm Hg. This was 15% less than the postpartum average (N.S.). f. Peripheral resistance, 616 dyne sec cm⁻⁵. This was 42% less than the postpartum average (P <0.01). g. Blood volume, 4.9 liters. This was 9% greater than the postpartum average (P <0.05). h. Blood volume per unit of body weight, 74 ml/kg. This was 1% greater than the postpartum average (N.S.). i. Plasma volume, 3.4 liters. This was 10% greater than the postpartum average (P <0.05). j. Hematocrit, 31 %. This was the same as the postpartum average (N.S.). k. Body weight, 66.8 kg. This was 8% greater than the postpartum average (P <0.01). The changes accompanying pregnancy in the ewes were similar in many respects to those reported for the human. The main differences noted were the smaller increase in blood volume and absence of "anemia of pregnancy" in the sheep. The possible distribution of the increased blood flow and mechanisms involved in the circulatory adjustments to pregnancy are discussed.
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