Left Ventricular Performance at High End-Diastolic Pressures in Isolated, Perfused Dog Hearts

Abstract

In the isolated, blood-perfused heart of the dog, left ventricular developed pressure and developed mean wall stress were observed while the ventricle contracted at a constant, nearly isovolumic afterload and while end-diastolic pressure was raised to levels exceeding 100 mm Hg. Coronary perfusion pressure was maintained at the level of the peak systolic pressure. Dilatation of die mitral ring and consequent mitral regurgitation were avoided by left atrial plication. Normalized graphs of percent of peak developed pressure against end-diastolic pressure showed that developed pressure rose abruptly with diastolic pressure, peaked at a diastolic pressure of approximately 30 mm Hg, and declined 14.7% (±0.9 SE) at an end-diastolic pressure of 100 mm Hg. Likewise, developed mean wall stress rose abruptly with diastolic pressure, peaked at a higher diastolic pressure of approximately 50 mm Hg, and declined only 7.5% (±0.8 SE) from this peak at an end-diastolic pressure of 100 mm Hg. Similar findings were observed in hearts acutely depressed with propranolol. Electron micrographs showed sarcomere length to average 2.275fi and 2.300/A in ventricles fixed in diastole while subjected to pressures of 61 and 100 mm Hg, respectively, after potassium arrest, confirming the findings illustrated by the normalized graphs. These observations imply that in the isolated heart of the dog there is no loss of ventricular performance attributable to a descending limb of the Frank-Starling mechanism until the end-diastolic pressure exceeds 60 mm Hg and that this loss is minimal at diastolic pressures as high as 100 mm Hg. ADDITIONAL KEY WORDSsarcomere length supported heart propranolol Frank-Starling developed pressure descending limb isovolumic contraction mean wall stress ventricular circumference developed tension • It is generally accepted that the tension developed by striated muscle during the active state is a direct function of its resting length up to a point at which a further increase in resting length is accompanied by a decrease in developed tension. Recent observers have shown both for cardiac and skeletal muscle strips that an increase in resting length is accompanied by a decrease in developed tension when the sarcomere is stretched beyond 2.2/J L and the H band appears (1-4).In contrast to muscle strips, evidence for a descending limb of ventricular performance in the intact ventricle has been less consistent. Some observers have not been able to find a descending limb at left ventricular enddiastolic pressures far exceeding the physiological range (5-7). In addition, arguments have been presented which imply that the cardiovascular system can support the instability inherent* in a descending limb for only a very short period of time and that such a

Left Ventricular Performance and Coronary Flow after Coronary Embolization with Plastic Microspheres

“…Second, in a previous report from this laboratory, only a slight descending limb of ventricular function was noted at high end-diastolic pressures in the healthy left ventricle (11). As others have reported pronounced descending limbs of ventricular performance when the coronary circulation was compromised (12), the question was raised as to what extent coronary embolization might have the same effect, or at least provide a model to study the extent to which such a descending limb might develop in a specifically diseased heart.…”

“…The preparation. The preparation used has been described previously in detail and will be described only briefly herein (11). Slight modifications of the original preparation were made to permit a continuous and accurate recording of coronary flow.…”

The Anrep Effect Reconsidered

“…The basic preparation has been described previously in detail (15,16). Only slight modifications of the original design were made to permit rapid stabilization of systolic pressure.…”

“…As previously described (15,16), hearts with lungs attached were excised as quickly as possible from heparinized healthy mongrel dogs weighing 11-25 kg under chloralose (60 mg/kg) and urethane (900 mg/kg) anesthesia. After excision, the hearts were immediately perfused with blood from the femoral artery of a healthy, similarly anesthetized and heparinized, donor dog.…”

“…1). It was assumed that in this plane the ventricle could be treated as a thickwalled sphere (15 where R, = internal radius in centimeters, Cd = external circumference of the distended ventricle in centimeters, and Ce = external circumference of the ventricle in centimeters after being emptied by suction (15).…”