Impedance cardiography in the elderly

Williams, Brian Owen (1983) Impedance cardiography in the elderly. MD thesis, University of Glasgow.

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Abstract

Experience gained by performing 1250 impedance cardiograms in 362 elderly subjects has shown that the technique is simple, noninvasive and highly reproducible; it lends itself to the investigation of cardiovascular problems in the elderly. Minor modifications to the method, as applied to the elderly, may improve the validity of stroke volume estimation. Cyclical, small changes in thoracic impedance do occur and are related to the cardiac cycle but from the evidence available it is not clear whether the change is solely related to left ventricular stroke volume or a combination of left and right ventricular stroke volumes. The Kubicek stroke volume formula is clearly empirical but it provides an accurate though not precise estimate of the stroke volume and cardiac output. Poor accuracy is obtained in the presence of valvular regurgitation and right bundle branch block due to characteristic first derivative impedance waveform abnormalities and in atrial fibrillation because of a natural wide variation of the stroke volume on a beat to beat basis. Poor accuracy occurs in patients with chronic lung disease due to systematic effects on the basal thoracic impedance. The impedance method tends to overestimate larger cardiac outputs and underestimate smaller cardiac output values. Absolute values for the cardiac output are, however, rarely required in medicine and despite some doubts about the validity of impedance absolute values it does provide an accurate reflection of expected relative changes. The method is a useful non-invasive technique for the haemodynamic investigation of elderly patients with symptomatic postural hypotension where the essential problem appears to be due to a failure of the peripheral vascular system to respond to the effects of orthostatic stress. The impedance cardiogram is useful for the measurement of systolic time intervals, changes in thoracic fluid content, assessment of myocardial contractility and the eludication of beat to beat haemodynamic changes in individual patients in atrial fibrillation. The waveform gives useful information about left atrial function, the bundle branch blocks, and it is helpful in the assessment of aortic valve regurgitation.

Item Type: Thesis (MD)
Qualification Level: Doctoral
Additional Information: Adviser: Francis I Caird
Keywords: Medicine, Medical imaging
Date of Award: 1983
Depositing User: Enlighten Team
Unique ID: glathesis:1983-72918
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 11 Jun 2019 11:06
Last Modified: 11 Jun 2019 11:06
URI: http://theses.gla.ac.uk/id/eprint/72918

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