PHYSIOLOGY OF DIASTOLIC FUNCTION AND TRANSMITRAL PRESSURE-FLOW RELATIONS - 05/09/11
Résumé |
The discovery of the circulation by Harvey placed the pumping function of the heart at the focal point of most subsequent studies dealing with cardiac function, thereby emphasizing the importance of systole and minimizing the role of diastole. Heart failure was thus seen to be a consequence of systolic dysfunction and not diastolic dysfunction. Within the last few decades there has been a growing realization that heart failure can occur in the presence of normal systolic function, which has served to place the study of diastolic function on an equal footing with that of systolic function. An explosion of studies dealing with diastolic function has been spawned by the development of sophisticated echocardiographic techniques, particularly pulsed Doppler flowmetry.41, 52 Using echocardiography, it is now possible to noninvasively measure: chamber dimensions; motion of the mitral annulus and valve; motion of the chamber walls; transmitral and pulmonary vein flows; and intracardiac flow.93 Also, because of the MR imaging techniques of tagging the myocardium11, 53 and blood,95 and the development of three-dimensional (3D) echocardiography,59 it is now possible to examine the fine details of intramyocardial stress-strain relations and intraventricular and transmitral blood motion. Ultrasophisticated 3D computer modeling of the cardiac chambers and blood flow will complement these modalities in the near future.54, 72
The functional behavior of the normal and pathologic cardiac chamber can now be assessed noninvasively. Full confidence in our analyses requires an understanding and appreciation of the basic physiology of diastolic function. This article focuses on providing the physiological basis for many of the indices used to describe normal and abnormal diastolic function. Most of the modalities available for the study of diastole are covered in subsequent articles. We focus on the relationship between the indices derived from the transmitral filling patterns and the passive and active properties of the cardiac chambers that create those filling patterns. Toward this end, we rely primarily on those studies that used simultaneous measurements of pressures and flows in their investigations.* These studies deserve our attention because they offer the most physiological insight into the relationship between Doppler indices and diastolic function and dysfunction. Based on the same reasoning, we have selected the following review papers for the readers' consideration.†
Following the clinical approach used by most cardiologists, we define diastole as starting with the onset of isovolumic relaxation (IVR) and ending with the closure of the mitral valve. We stress that this is an operational definition designed to elucidate mechanical function at the macro level; it should not be applied to function at the micro level. Diastole thus includes the isovolumic relaxation period (IVRP) and the diastolic filling period (DFP). This approach is functionally reasonable because the contribution to measured ventricular pressure by the active property of myocardial relaxation sets up the conditions for the onset of mitral flow; pressure due to the passive properties then dominates; and finally, flow ends with the closure of the mitral valve following the atrial contraction. Perhaps, muscle mechanics and pump function may be best studied by limiting the definition of diastole to only the passive phase,10 but we think that diastolic function is best studied by including relaxation in the analysis.81
Like most other investigators, we relate early and late diastolic flow patterns to ventricular relaxation and chamber compliance, respectively, but unlike most, we do not ascribe changes in early flow solely to relaxation, nor do we relate late events solely to compliance. We show that this simplification fails to consider the interaction between early and late properties,82 and it also fails to recognize the dynamic interaction between blood flow and chamber properties. We show that the pressure measured during isovolumic relaxation is influenced by properties in addition to deactivation; and that diastolic suction, when produced by elastic recoil, is a consequence of chamber properties64 including compliance and is not, as often stated, a property of relaxation. When we analyze ventricular compliance we depart from the ubiquitous exponential and use a logarithmic approach64 that proves to be more physiologically based. The current approach to diastolic function tends to be related to the study of isolated diastolic dysfunction and relies on indices that are relevant only when systolic function is presumed normal, usually based on the criterion of ejection fraction (EF) greater than 50%. Because this article is concerned with all of the physiological determinants of left ventricular filling, it covers both systolic and diastolic conditions. This article is designed to enhance and clarify the reader's understanding of the study of diastole and to encourage an ongoing discussion of this complex subject.
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| Address reprint requests to Edward L. Yellin, PhD, Department of Physiology and Biophysics, Albert Einstein College of Medicine, Room M208, 1300 Morris Park Avenue, Bronx, NY 10461, e-mail: yellin@aecom.yu.edu |
Vol 18 - N° 3
P. 411-433 - août 2000 Retour au numéro
Article précédent
- PREFACE
- SÁNDOR J. KOVÁCS
- CONNECTIVE TISSUE AND THE HEART : Functional Significance and Regulatory Mechanisms
- Brad S. Burlew, Karl T. Weber
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