Impact of ejection on magnitude and time course of ventricular pressure-generating capacity.

This study focuses on elucidating how ventricular afterloading conditions affect the time course of change of left ventricular pressure (LVP) throughout the cardiac cycle, with particular emphasis on revealing specific limitations in the time-varying elastance model of ventricular dynamics. Studies were performed in eight isolated canine hearts ejecting into a simulated windkessel afterload. LVP waves measured (LVPm) during ejection were compared with those predicted (LVPpred) according to the elastance theory. LVPm exceeded LVPpred from a time point shortly after the onset of ejection to the end of the beat. The instantaneous difference between LVPm and LVPpred increased steadily as ejection proceeded and reached between 45 and 65 mmHg near end ejection. This was in large part due to an average 35-ms prolongation of the time to end systole (tes) in ejecting compared with isovolumic beats. The time constant of relaxation was decreased on ejecting beats so that, despite the marked prolongation of tes, the overall duration of ejecting contractions was not greater than that of isovolumic beats. The results demonstrate a marked ejection-mediated enhancement and prolongation of ventricular pressure-generating capacity during the ejection phase of the cardiac cycle with concomitant acceleration of relaxation. None of these factors are accounted for by the time-varying elastance theory.

[1]  K Sagawa,et al.  Impedance loading servo pump system for excised canine ventricle. , 1982, The American journal of physiology.

[2]  K B Campbell,et al.  Late-systolic pumping properties of the left ventricle. Deviation from elastance-resistance behavior. , 1990, Circulation research.

[3]  A. Pasipoularides,et al.  Clinical assessment of ventricular ejection dynamics with and without outflow obstruction. , 1990, Journal of the American College of Cardiology.

[4]  G Cooper,et al.  Correlation of Force‐Length Area With Oxygen Consumption in Ferret Papillary Muscle , 1987, Circulation research.

[5]  E. Sonnenblick,et al.  Load and time considerations in the force-length relation of cardiac muscle. , 1980, Federation proceedings.

[6]  H B Boom,et al.  Left Ventricular Internal Resistance and Unloaded Ejection Flow Assessed From Pressure‐Flow Relations: A Flow‐Clamp Study on Isolated Rabbit Hearts , 1987, Circulation research.

[7]  S A Glantz,et al.  Volume Loading Slows Left Ventricular Isovolumic Relaxation Rate , 1981, Circulation research.

[8]  H Suga,et al.  Determinants of Instantaneous Pressure in Canine Left Ventricle: Time and Volume Specification , 1980, Circulation research.

[9]  D. Adam,et al.  Myocardial relaxation IV: mechanical determinants of the time course of left ventricular pressure decline during isovolumic relaxation. , 1980, European heart journal.

[10]  Regulation of left ventricular pressure fall. , 1990, European heart journal.

[11]  H. Suga,et al.  Transient vs. steady end-systolic pressure-volume relation in dog left ventricle. , 1987, The American journal of physiology.

[12]  M. Hori,et al.  Ejection Timing as a Major Determinant of Left Ventricular Relaxation Rate in Isolated Perfused Canine Heart , 1984, Circulation research.

[13]  W. Parmley,et al.  Relation between mechanics of contraction and relaxation in mammalian cardiac muscle. , 1969, The American journal of physiology.

[14]  W L Maughan,et al.  Left ventricular interaction with arterial load studied in isolated canine ventricle. , 1983, The American journal of physiology.

[15]  H. T. ter Keurs,et al.  Tension Development and Sarcomere Length in Rat Cardiac Trabeculae: Evidence of Length‐Dependent Activation , 1980, Circulation research.

[16]  R. van Heuningen,et al.  Tension development and sarcomere length in rat cardiac trabeculae. Evidence of length-dependent activation. , 1980 .

[17]  Hiroyukisuga,et al.  Instantaneous Pressure-Volume Relationships and Their Ratio in the Excised, Supported Canine Left Ventricle , 1974 .

[18]  K B Campbell,et al.  Validation of optional elastance-resistance left ventricle pump models. , 1986, The American journal of physiology.

[19]  J. Weiss,et al.  Hemodynamic determinants of the time-course of fall in canine left ventricular pressure. , 1976, The Journal of clinical investigation.

[20]  K. Sagawa,et al.  Long‐term Versus Intrabeat History of Ejection As Determinants of Canine Ventricular End‐Systolic Pressure , 1989, Circulation research.

[21]  Sonnenblick Eh,et al.  Implications of muscle mechanics in the heart. , 1962, Federation proceedings.

[22]  W. E. Craig,et al.  Nonobstructive left ventricular ejection pressure gradients in man. , 1987, Circulation research.

[23]  E. Yellin,et al.  Left ventricular relaxation in the filling and nonfilling intact canine heart. , 1986, The American journal of physiology.

[24]  S. Shroff,et al.  Evidence and quantitation of left ventricular systolic resistance. , 1985, The American journal of physiology.

[25]  N. Westerhof,et al.  “Pressure‐Volume” Relations in Isolated Cat Trabecula , 1981, Circulation research.

[26]  R. O'rourke,et al.  Pharmacologic and hemodynamic influences on the rate of isovolumic left ventricular relaxation in the normal conscious dog. , 1977, The Journal of clinical investigation.

[27]  W. Hunter,et al.  End‐Systolic Pressure As a Balance Between Opposing Effects of Ejection , 1989, Circulation research.

[28]  A Noordergraaf,et al.  Systolic Mechanical Properties of the Left Ventricle: Effects of Volume and Contractile State , 1983, Circulation research.

[29]  IV George Cooper.  Load and length regulation of cardiac energetics. , 1990, Annual review of physiology.

[30]  D. Brutsaert,et al.  Relaxation and diastole of the heart. , 1989, Physiological reviews.

[31]  H. Suga,et al.  Reduction of the duration of isovolumic relaxation in the ejecting left ventricle of the dog: residual volume clamping , 1977, The Journal of physiology.