Left ventricular isovolumetric pressure-volume relations, “diastolic tone”, and contractility in the rat heart after physical training

Abstract

An intermittent swimming training of 40 rats for eight weeks resulted in an increase of 17% in heart weight, which is regarded as an index for the degree of hypertrophy.Measurement of left ventricular pressure and volume in the isovoIumetrically beating and the arrested heart of open chest rats gave the following results of the trained rats, as compared with controls of the same age and body weight:1. Due to the increased ventricular capacity, the diastolic and systolic pressurevolume curves are shifted to higher volumes. 2. In spite of the enlarged radius the diastolic wall stress is only slightly increased for a given diastolic pressure. Thus diastolic load of left ventricular myocardium should not be essentially increased in the intact animal. 3. The passive elastic wall properties are practically unaltered in this type of hypertrophy. The elastic stiffness (tangent modulus) as a function of wall stress is not decreased. The "regulative Dilatation" is not to be attributed to a functional decrease of "diastolic tone", but is sufficiently explained by muscle fibre growth. 4. Under the condition that the same diastolic wall stress corresponds with practically the same length of sarcomeres, the correlation between isovolumetric systolic wall stress as well as velocity of wall stress development and the corresponding diastolic wall stress reveals a slight increase in contractile capability. 5. In the isovolumetric mechanograrn the point of inflexion is reached later, but at higher pressures. The slight decrease of the quotient (dp/dtmax)/P i cannot be interpreted as decreased contractily.These findings are in agreement with former findings in our laboratory on the linear cardiac muscle strip (Goltz et al., 1972, Kiimmereit, 1973.Upon critical evaluation of the results and their meaning in relation to the cardiac performance, it can be confirmed that the performance of the total i) Supported by the Deutsche Forschungsgemeinschaft. ~) Herrn Prof. Dr. K. Spang, Stuttgart, zum 65. Geburtstag.

The influence of endurance training on mechanical catecholamine responsiveness, β-adrenoceptor density and myosin isoenzyme pattern of rat ventricular myocardium

“…It is generally accepted that endurance physical training increases the work and power capacity of the whole heart (12) and may also influence the contractile capability of cardiac muscle (11,16), although the latter effect is denied by some authors (23). Nevertheless, adaptive changes at the myocardial level due to long term swimming training of the rat are unequivocal (25,26,32).…”

Myocardial elasticity and left ventricular distensibility as related to oxygen deficiency and right ventricular filling. Analysis in a rat heart model

“…Assuming a thick-walled spherical shell, midwall circumferential stress oR was calculated according to Giilch in (18).and to (30,39 where the ratio of ventricular inner volume V and wall volume W represents a standardization factor in order to obtain valid interindividual comparisons. Considering the midwall region as representative for the other wall regions, the midwall differential elastic modulus ER was evaluated using the following equation:…”

Effects of physical training on the myocardium of streptozotocin-induced diabetic rats

“…These changes might be due to an enhanced insulin sensitivity in tisssues brought about by exercise-training (1,12,13). According to previous literature, swimming enhances myocardial contractility (2,5,6,10,12,16). In the present study, however, the isometric developed tension of isolated left ventricular papillary muscles was not altered by swimming in diabetic rats, although dT/dtmax was increased.…”