Análise das propriedades mecânicas do miocárdio através do plano de fase
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Data
2008-05-09
Autores
Camilo, Luciana Moisés
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Editor
Universidade Federal do Espírito Santo
Resumo
The phase plane (PP) is a plot of the ventricular pressure in the X-axis and its time derivative in the Y-axis. One of the PP properties is that the final portion is a straight line segment and its slope (Ө) is a time constant that might represent a viscoelastic constant of the muscle. We aimed to compare the behavior of Ө among normal, hypertensives and hypertrophied rat hearts and to evaluate the influences of inotropic interventions on Ө. According an ideal mathematical model of approach of the isovolumic pressure curve, is given that PPA = P x dP/dt. As know that the external cardiac work (Wext) is the time rate of change of work, PdV, the equation can be rewrite in the following way: Text = P. dV . dP dP dt Since in this experimental model the volume is constant, the PPA is proportional to the Wext. The objective of this work was to compare the behavior of Ө and PPA among normal, hypertensives and hypertrophied rats heart and to evaluate the influences of the inotropics interventions on these variables. We used isolated hearts perfused by the Langendorff technique (male Wistar and spontaneously hypertensive rats- SHR), weighing between 210 and 280g, divided in 4 groups: (C) Wistar Control (n=7); SHR (n=7); (ISO,) rats with Isoproterenol-induced hypertrophy (0.3mg/Kg/day, n=9); and (V) rats treated only with vehicle (soyan bean oil, n=6). The experimental protocol consisted of performing ventricular function curves, changes in stimulation frequency and external Ca+2 (0.5, 1.25 and 2.5 mM) and β-adrenergic stimulation (0.1mL; 10- 5M). Left ventricle isovolumic pressure curve and its first derivative (dP/dt) were registered for the construction of the PP. The measures of Ө and PPA were obtained by using the Autocad 2004 software. Results are expressed as mean ± SEM. Statistical analysis: ANOVA 1 and/or 2 way; Fisher post-hoc test, significant for p<0,05. Slopes obtained after stabilization at DP of 10mmHg and during the performance of ventricular function curves were larger in the SHR and ISO groups. 26 The increase of the stimulation frequency significantly increased θ in all groups, as well as the increase of [Ca+2 ex] and the administration of isoproterenol. PPA was higher in SHR group than others. Positive inotropics interventions had provoked proportional increase of PPA in all groups. The increase of the stimulation frequency and the lower [Ca+2 ex] resulted in reduction of the PPA. Myocardial left ventricular hypertrophy in SHR and the chronic treatment with ISO modify the speed of isovolumic pressure decay increasing the slope. Regarding the inotropic interventions the increase of the slope might be linked to the increase of speed of isovolumic pressure decay, due to inotropic action in the helical ventricular myocardial band (HVMB) segments, specifically the ascending segment that operates on diastolic phase. PPA behavior contextualized the situations where the hearts had been submitted, in respect to the Wext.
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Palavras-chave
Plano de fase , Hipertrofia cardíaca , Banda ventricular helicoidal , Trabalho sistólico