Abstract

The dynamics of transcapillary fluid and protein distribution and endocrine regulation of cardiovascular function were studied in chronically instrumented fetal sheep during the third trimester. Average experimental changes in vascular pressures, blood volume, plasma hormone concentrations, hematocrit and plasma protein concentration were analyzed using mathematical modeling and parameter optimization techniques in order to determine values for the major parameters which regulate fluid, protein and endocrine dynamics and to determine endocrine dose-response relationships to changes in cardiovascular function. The hormones which were considered are arginine vasopressin (AVP), angiotensin II (AII), epinephrine (EPI) and norepinephrine (NE). Vascular disturbances which were considered include intravascular volume loading, hormone infusions, and hypoxic and hemorrhagic stress. Following fetal hemorrhage, interstitial compliance averaged 45 ml/mmHg/kg and vascular compliance averaged 3.0 ml/mmHg/kg while the capillary filtration coefficient averaged 0.40 ml/min/mmHg/kg. For intravascular saline infusions, interstitial compliance averaged 45 ml/mmHg/kg and vascular compliance averaged 3.5 ml/mmHg/kg while the capillary filtration coefficient averaged 0.80 ml/min/ mmHg/kg. The mean fetal reflection coefficient of the capillary membrane for protein was 0.61 following hemorrhage and 0.80 after intravascular saline infusion. Following hormone infusions, plasma half-lives for All, AVP, EPI and NE averaged 0.24, 3.0, 3.8 and 0.60 minutes, respectively, and 1.0, 3.6, 2.7 and 3.6 minutes, following fetal hemorrhage. During fetal hypoxia, half lives for AVP, EPI and NE averaged 9.8, 3.6 and 5.2 minutes, respectively. Production rates of All, AVP, EPI and NE in the plasma appeared to be directly proportional to percent reductions in blood volume during moderate hemorrhage. However, following severe hemorrhage or during fetal hypoxia, increases in production rates were not directly proportional to changes in blood volume or PO2, respectively suggesting that other mechanisms such as PCO2 or pH may also be involved in the release of these hormones. These findings indicate that the fetus has 1) an interstitial compliance approximately 10 times adult values and a capillary filtration coefficient 5 to 10 times adult values, 2) a vascular compliance about one half that of the adult, 3) the ability to increase its vascular resistance and decrease its vascular compliance and capillary surface area through endocrine regulation involving first order dose-response kinetics.

LLU Discipline

Physiology

Department

Physiology

School

Graduate School

First Advisor

John Leonora

Second Advisor

Robert A. Brace

Third Advisor

Kenneth A. Arendt

Fourth Advisor

George Maeda

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

1986

Date (Title Page)

12-1986

Language

English

Library of Congress/MESH Subject Headings

Body Fluids -- physiology; Fetal Heart -- physiology; Endocrine Glands -- physiology

Type

Dissertation

Page Count

xii; 317

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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