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dc.contributor.authorYoung, Lesley Elissaen
dc.date.accessioned2018-05-14T10:17:07Z
dc.date.available2018-05-14T10:17:07Z
dc.date.issued1996
dc.identifier.urihttp://hdl.handle.net/1842/30053
dc.description.abstracten
dc.description.abstractStudies were undertaken using transesophageal Doppler echocardiography to monitor left ventricular systolic function in anaesthetised horses. A 3.5 MHz transoesophageal probe was specifically developed in collaboration with Vingmed Sound for equine use. The indices of systolic function investigated were maximum acceleration of aortic blood flow (dv/dt^J, maximum blood flow velocity, (V^J, cardiac output (CO), left ventricular pre-ejection period (PEP) and left ventricular ejection time (ET).en
dc.description.abstractThe feasibility of the technique was demonstrated in a group of 8 healthy Thoroughbred horses anaesthetised using a standard protocol. It was established that two dimensional transoesophageal echocardiography provided a reference view of the left ventricular outflow tract and aorta that consistently allowed high quality Doppler echocardiographic measurement of aortic blood flow velocity. The flow envelopes obtained were suitable for measurement of indices of left ventricular systolic function. The repeatability of the measured indices was similar to that of the maximum rate of rise of left ventricular pressure (LVdp/dtmax), obtained simultaneously by cardiac catheterisation.en
dc.description.abstractCardiac output estimations made using transoesophageal Doppler echocardiography were compared with those obtained by thermodilution in the same group of horses under general anaesthesia. Cardiac output was altered by infusions of the sympathomimetic amine, dobutamine. Aortic velocity spectra obtained both by high pulse repetition frequency and continuous wave insonation modes were used to obtain the velocity time integral for calculation of cardiac output. The measurements derived from transoesophageal echocardiography agreed well with those obtained by thermodilution. Both correlation coefficients and limits of agreement between the two techniques were better than those obtained from similar studies in standing horses using transthoracic echocardiography.en
dc.description.abstractThe sensitivity of the Doppler derived indices of left ventricular function to inotropic intervention was assessed in the final sequence of studies. As these indices are derived during the ejection period they are load dependent, so their response to changes in ventricular loading was also assessed and compared with the most commonly used index of myocardial contractility in horses, LVdp/dtmax. Three drugs were administered to the anaesthetised horses in a randomised sequence during three separate anaesthetic episodes. The drugs, dobutamine, dopamine and dopexamine were selected because of their relatively different effects on afterload, preload and contractility. Maximum acceleration of aortic blood flow was as sensitive to the changes in ventricular performance as LVdp/dtmax. Maximum aortic blood velocity showed the same qualitative response to infusion of the drugs but the changes were quantitatively less than in dv/dtmax and LVdp/dtmax. The systolic time intervals, PEP and ET, were also responsive to drug infusion; pre-ejection period shortened with each drug, whilst ET increased after dopamine and dopexamine, but was reduced by dobutamine.en
dc.description.abstractThese studies have shown that dv/dtmax is as sensitive as the invasive index LVdp/dtmax for detecting changes in left ventricular performance. In addition dv/dtmax and Vmax appear to be no more affected by changes in ventricular loading conditions than the isovolumic index LVdp/dtmax. It is concluded that transoesophageal Doppler echocardiography provides a minimally invasive technique for assessment of left ventricular systolic function in anaesthetised horses.en
dc.publisherThe University of Edinburghen
dc.relation.ispartofAnnexe Thesis Digitisation Project 2018 Block 18en
dc.relation.isreferencedbyAlready catalogueden
dc.titleMeasurement of left ventricular function in anaesthetised horses using transoesophageal doppler echocardiographyen
dc.typeThesis or Dissertationen
dc.type.qualificationlevelDoctoralen
dc.type.qualificationnamePhD Doctor of Philosophyen


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