Direct and indirect measurement of the effects of halothane and isoflurane on arterial wall mechanics
Although the detrimental effects of anesthetic agents on ventricular function have been quantified, their corresponding impact on arterial system mechanics remains less well studied. The goal of this dissertation was to quantify the effects of halothane and isoflurane on arterial mechanical properties. The three element Windkessel model of the arterial afterload system was employed to estimate characteristic impedance, total arterial compliance, and total arterial resistance from aortic input impedance spectra obtained in both chronically and acutely instrumented dogs in the presence of both halothane and isoflurane. Impedance spectra were obtained via spectral analysis of aortic blood pressure and flow waves. In addition, the conductance catheter technique for chamber volume measurement was examined as a potential tool for quantifying arterial mechanical properties. In the acute preparation, simultaneous measurements of aortic pressure and diameter, by both conductance and sonomicrometry were made. From these measurements, characteristic impedance and distensibility were calculated. An in vitro isolated aorta model and corresponding finite element model were constructed to determine the accuracy of the conductance technique and to examine the electric field distribution under a variety of experimental conditions. The results showed that both halothane and isoflurane caused similar increases in aortic characteristic impedance, total arterial compliance, and aortic distensibility. Isoflurane but not halothane decreased total arterial resistance. Windkessel parameters determined by direct sonomicronometric measurement of aortic diameter were more sensitive to anesthetic-induced changes than those determined indirectly from aortic input impedance spectra. The conductance catheter technique showed good agreement with sonomicrometry for measurement of aortic segmental volume if corrections were introduced for the non homogeneity of the electric field. It was concluded that the differential effects of halothane and isoflurane on the arterial system are confined to the steady-state and not the oscillatory components of afterload. The conductance catheter technique has the potential to provide accurate real-time estimation of absolute aortic segmental volume if the non homogeneity of the electric field can be determined. The finite element model developed to examine this field may, in the future, provide a means of precisely estimating the effects of non homogeneity on conductance volume measurements.
Douglas Anthony Hettrick,
"Direct and indirect measurement of the effects of halothane and isoflurane on arterial wall mechanics"
(January 1, 1995).
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