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|Title: ||Haemodynamic changes during human pregnancy|
|Authors: ||Robson, Stephen Courtenay|
|Issue Date: ||1992 |
|Publisher: ||Newcastle University|
|Abstract: ||The aim of this work was to investigate the physiological adaptations that occur in the
maternal cardiovascular system during singleton and twin pregnancy. The cardiovascular
system has been shown to undergo major adaptations during human pregnancy. Most
investigators agreed that cardiac output increased during pregnancy however there was no
unanimity regarding the extent and timing of this increase nor about the physiological
mechanisms underlying it. Even less was known about the haemodynamic readjustments
following delivery and about the alterations in multiple pregnancy.
Further study has been limited by the lack of an accurate noninvasive technique which is
applicable and reproducible during pregnancy. Cross-sectional echocardiography combined
with Doppler ultrasound measurement of blood velocity provides a noninvasive method for
measuring cardiac output at a number of locations within the heart and great vessels.
Preliminary investigations revealed that cardiac outputs determined by this method
correlated closely with those measured by the direct Fick technique in non-pregnant
subjects. In addition the method was highly reproducible in both pregnant and nonpregnant
subjects. M-mode echocardiography allows accurate and noninvasive
measurements of cardiac chamber size and ventricular function. These measurements were
also found to be highly reproducible in pregnant and non-pregnant subjects. Using these
techniques the aims of this thesis were to investigate the extent, timing and mechanisms of
the changes in cardiac output during singleton and twin pregnancy.
Echocardiographic investigations were performed prior to and during singleton pregnancy,
during the first 6 months after singleton pregnancy, and during and 6 months after twin
pregnancy. All subjects were studied in the left semi-lateral position. The results suggested
(1) During singleton pregnancy cardiac output was increased early in the first trimester and
continued to rise until 24 weeks gestation when values were 43-49% above pre-pregnant
control values. Thereafter there was no further change. Heart rate and left ventricular
function increased during the first trimester. Left atrial and left ventricular end-diastolic
dimensions increased during the second trimester suggesting an increase in venous return.
Cardiac valve cross-sectional areas and left ventricular wall thickness also increased during
pregnancy. After delivery cardiac output had fallen to non-pregnant values by 2 weeks.
This was associated with reductions in left ventricular performance and left atrial and left
ventricular end-diastolic dimensions. The decrease in valve cross-sectional areas and left
ventricular wall thickness was not evident until later in the puerperium. (2) During twin pregnancy cardiac output was increased by 20 weeks gestation and
thereafter showed no further change. Maximum cardiac output was 59-62% above
postnatal control values. This increase was greater than that recorded during singleton
pregnancy due to a relatively greater increase in heart rate. Twin pregnancy was also
associated with a greater increase in left atrial dimension.
The results of these studies shed light on some of the the unanswered questions in the field
of maternal haemodynamics. The noninvasive Doppler techniques used allowed accurate
and reproducible measurements of cardiac output in pregnant subjects. This work has
important implications for the future investigation of cardiac and hypertensive disorders
|Description: ||MD Thesis|
|Appears in Collections:||School of Medical Sciences Education Development|
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