RESUMO
Resumo Fundamento A ecocardiografia tridimensional (ECO 3D) permite a geração de uma curva volume-tempo representativa das alterações no volume ventricular esquerdo (VE) ao longo de todo o ciclo cardíaco. Objetivo O presente estudo tem como objetivo demonstrar as adaptações hemodinâmicas presentes na cardiomiopatia chagásica (CC) por meio das medidas de volume e fluxo obtidas pela curva volume-tempo por ECO 3D. Métodos Vinte pacientes com CC e 15 indivíduos saudáveis foram incluídos prospectivamente em um estudo de desenho transversal. Realizou-se ECO 3D em todos os indivíduos e as curvas volume-tempo do VE foram geradas. O fluxo foi obtido pela primeira derivada da curva volume-tempo por meio do software MATLAB. A significância estatística foi definida com p<0,05. Resultados Embora os pacientes com CC tivessem menor fração de ejeção do VE em comparação com o grupo controle (29,8±7,5 vs. 57,7±6,1, p<0,001), o volume (61,5±25,2 vs. 53,8±21,0, p=0,364) e o fluxo de ejeção máximo durante a sístole (-360,3±147,5 vs. -305,6±126,0, p = 0,231) mostraram-se semelhantes entre os grupos. Da mesma forma, o fluxo máximo na fase de enchimento inicial e durante a contração atrial mostrou-se semelhante entre os grupos. Um aumento na pré-carga expressa pelo volume diastólico final do VE (204,8±79,4 vs. 93,0±32,6), p<0,001) pode manter o fluxo e o volume ejetado semelhantes aos dos controles. Conclusão Com uma ferramenta não invasiva, demonstramos que o aumento no volume diastólico final do VE pode ser o principal mecanismo de adaptação que mantém o fluxo e o volume ejetado no cenário de disfunção sistólica ventricular esquerda severa.
Abstract Background Three-dimensional echocardiography (3D ECHO) allows the generation of a volume-time curve representative of changes in the left ventricular (LV) volume throughout the entire cardiac cycle. Objective This study aims to demonstrate the hemodynamic adaptations present in Chagas cardiomyopathy (CC) by means of the volume and flow measurements obtained by the volume-time curve by 3D ECHO. Methods Twenty patients with CC and 15 healthy subjects were prospectively enrolled in a cross-sectional design study. 3D ECHO was performed in all subjects and the volume over time curves of the LV was generated. The flow was obtained by the first derivative of the volume-time curve using the software MATLAB. Statistical significance was set at p<0.05. Results Although CC patients had lower LV ejection fraction compared to the control group (29.8±7.5 vs. 57.7±6.1, p<0.001), stroke volume (61.5±25.2 vs. 53.8±21.0, p=0.364) and maximum ejection flow during systole (-360.3±147.5 vs. -305.6±126.0, p=0.231) were similar between the groups. Likewise, the maximum flow in the early diastolic filling phase and during atrial contraction was similar between groups. An increase in preload expressed by LV end diastolic volume (204.8±79.4 vs. 93.0±32.6), p<0.001) may maintain the flow and stroke volumes similar to the controls. Conclusion Using a non-invasive tool, we demonstrated that an increase in LV end-diastolic volume may be the main adaptation mechanism that maintains the flow and stroke volumes in the setting of severe LV systolic dysfunction.
RESUMO
Resumen La ley o mecanismo de Frank-Starling describe la relación entre la longitud inicial de las fibras miocárdicas y la fuerza generada por su poder de contracción. Aunque ni Otto Frank (1895) como tampoco Ernest Starling (1915) fueron los primeros en descubrir que el volumen diastólico final regula el trabajo del corazón, su participación para este famoso epónimo fisiológico es indiscutible, y de ahí que sus nombres perduraran por más de un siglo en el ambiente de la fisiología, la cardiología y los cuidados intensivos, entre otras disciplinas. Se revisa la biografía de Otto Frank (1865-1944), un excepcional fisiólogo alemán con un amplio conocimiento en física, matemáticas y ciencias naturales, que formuló principios teóricos para la fisiología muscular y cardiovascular, además de muchas otras contribuciones metodológicas e instrumentales. También se examina la vida del gran médico y fisiólogo inglés Ernest Henry Starling (1866-1927), quien elaboró diversos y relevantes aportes científicos, más allá de sus afamadas publicaciones sobre la función circulatoria. Finalmente, el presente artículo comenta en forma breve sus principales y más importantes contribuciones, así como también aspectos menos conocidos de sus logros científicos.
Abstract Frank-Starling's law or mechanism describes the relationship between the initial length of myocardial fibers and the force generated by their contraction power. Although neither Otto Frank (1895) nor Ernest Starling (1915) were the first to discover that the final diastolic volume regulates the work of the heart, their participation for this famous physiological eponym is indisputable, enduring their names for more than a century in the environment of physiology, cardiology and intensive care, among other disciplines. The biography of Otto Frank (1865-1944) is reviewed, who was an exceptional German physiologist with extensive knowledge in physics, mathematics and natural sciences who formulated theoretical principles for muscular and cardiovascular physiology, in addition to many other methodological contributions in instrumentals. Also examined the life of the great English physician and physiologist Ernest Henry Starling (1866-1927), who produced various and relevant scientific contributions, beyond his famous publications on circulatory function. Finally, this article briefly comments on its main and most important contributions, as well as less known aspects of its scientific achievements.
RESUMO
The Frank-Starling law of the heart is a filling-force mechanism (FFm), a positive relationship between the distension of a ventricular chamber and its force of ejection, and such a mechanism is found across all the studied vertebrate lineages. The functioning of the cardiovascular system is usually described by means of the cardiac and vascular functions, the former related to the contractility of the heart and the latter related to the afterload imposed on the ventricle. The crossing of these functions is the so-called 'operation point', and the FFm is supposed to play a stabilizing role for the short-term variations in the working of the system. In the present study, we analyze whether the FFm is truly responsible for such a stability within two different settings: one-ventricle and two-ventricle hearts. To approach the query, we linearized the region around an arbitrary operation point and put forward a dynamical system of differential equations to describe the relationship among volumes in face of blood flows governed by pressure differences between compartments. Our results show that the FFm is not necessary to give stability to an operation point. Thus, which forces selected and maintained such a mechanism in all vertebrates? The present results indicate three different and complementary roles for the FFm: (1) it decreases the demands of a central controlling system over the circulatory system; (2) it smooths out perturbations in volumes; and (3) it guarantees faster transitions between operation points, i.e. it allows for rapid changes in cardiac output.