Search

Myocardial DNA concentration and ventricular weight were measured in the hearts of normal and spontaneously hypertensive rats varying in age from 1 day to 1 year and the ventricular DNA content calculated. A linear relation between ventricular DNA content and ventricular weight was observed in both rat strains. This linear relation was deduced theoretically, assuming that the number of ventricular non-myocytes per heart was proportional to ventricular weight and that the number of ventricular myocytes per heart was constant after the first postnatal week. The fit with experimental data produced values of the number of ventricular myocytes (42.5 X 10(6] and non-myocytes (199 X 10(6) per gram of ventricular tissue) in normal rat heart. Using published data on ventricular volume occupied by myocytes (80%) and myocardial specific density (1.06 g X ml-1), the mean(SD) volume of individual myocytes could be calculated (17758(2632) multiplied by ventricular weight, expressed in micron 3 X g). The values obtained compared well with experimental observations reported in the present study (18504(131) micron 3 X g) and in other studies. Hearts from spontaneously hypertensive rats had lower numbers of myocytes (37.4 X 10(6] and non-myocytes (180 X 10(6) per gram) per heart than normal hearts with identical ventricular weights. Hearts of normal 2 month old rats that were made hypertrophic by various means were identical to non-hypertrophic hearts of normal older rats with identical ventricular weights in relation to the number of ventricular myocytes and non-myocytes per heart. It is concluded that ventricular hypertrophy induced in young adult rats might be regarded as normal growth occurring at an accelerated rate.

The peripheral factor (PF), i.e. the ratio: artero-venous oxygen extraction to total peripheral resistences, has been studied in a total of 8 professional basket players under controlled work-load conditions. The results obtained by continuous monitoring heart rate, oxygen consumption, pulmonary ventilation, arterial blood pressure etc, have shown that from 0 to 150 watt work-load, the PF increases linearly showing a slope of 83 degrees, whereas from 150 to 200 watt the pendence reduces up to 45 degrees. The absolute value of PF from a resting value of 3.83 mlo2 X min-1 X mmHg-1 increases up to 21,64 (at 150 watt) and to a maximum of 23.45 mlo2 X min-1 X mmHg-1 at 200 watt. The slope of the first range of load (83 degrees) is quite similar to what previously observed in endurance athletes (cyclists) whereas the 45 degrees angular coefficient indicates that the increased energy demand in basket-players can be obtained only with a large cardiac load.

The author presents 2 cases of genu varum due to Blount's disease, one in an infant and the other in an adolescent. Both were successfully corrected by monolateral medial epiphyseal distraction using Hoffmann's external fixator.

The authors carried out an experimental study to quantify the stability of monolateral fixation devices of the Hoffmann type. The technical tests indicated that changes were needed in the geometry of the devices; these were achieved by designing a junction piece which enables the transfixion pins and the smooth stabilization rod to remain in the same plane, while leaving the rest of the instrumentation unchanged. The use of this component makes the fixation device more stable and lighter than the classic monolateral devices commonly used. It also prevents the separation and rotation of the fragments that can occur when rods not in the same plane are subjected to compression.

The load sensitivity of the relaxation phase was studied in rat papillary muscle, with isotonic afterloaded contractions and stretches applied after the peak of isometric twitches. The tension decay occurred earlier in isotonic than in isometric contractions. When a central region of the preparation was marked with small stainless steel pins, a lengthening of this region could be shown during relaxation of isometric (fixed end) contractions. This lengthening was earlier and faster in isotonic afterloaded contractions. Therefore the sensitivity of relaxation to load or length changes could be described in the context of the general mechanism of relaxation which takes into account the non uniform behaviour of the muscle and the internal movement during contractions. Interventions which decelerate the activation decay rate had different effects on the load dependence of relaxation. Caffeine addition and substitution of strontium for calcium abolished the load sensitivity while a temperature reduction had no influence on it.

The effect of stretch on the time-course of relaxation has been investigated in rat papillary muscle. In control conditions, a quick stretch carried out at or after the peak of an isometric twitch promotes an earlier and faster relaxation. Following inotropic interventions which decelerate the activation decay rate (caffeine addition and Ca2+ replacement with Sr2+) the onset and time-course of relaxation are unaffected by the stretch.

When caffeine plus calcium is added to the perfusing medium, isometric relaxation of rat myocardium is no longer affected by length changes occurring during the twitch. The dependence of isometric relaxation on the initial muscle length is still present and more pronounced after caffeine addition.

Equilibration and washout curves of inulin were determined in isolated rat papillary muscles. Inulin uptake did not reach a steady-state value even after a long equilibration time. The effects of contractile activity were investigated. Isometric contractions increased the rate of inulin uptake and washout. In isotonic conditions, a smaller increase in the uptake and washout was observed. These changes could be attributed to an actual increase of inulin distribution space and/or to an accelerated diffusion kinetics.

In order to estimate wave propagation "in vitro", aortic compliance has been studied by means of rings and stripes from 6 adult male Wistar rats. Lengthening and shortening maneuvres have been performed; the pulse transmission rate was evaluated by calculating the elastic modulus during the maneuvres. A Norepinephrine infusion has been done. Results obtained show that transmission rate is higher in shortening than in lengthening phases. Norepinephrine did not significantly affect the values. The rate values were not greatly different whether "in vitro" or "in vivo". By increasing specimen stress, the rate too was increased, but the amount was lower than "in vivo" values. Hence it was assumable that rate variations "in vivo", should be partially influenced by elastic modulus, and a vegetative intervention should be implied.

Pulse wave transmission rate has been measured "in vivo" in 6 male anaesthetized Wistar rats, by means of cannulae, inserted both in carotid and femoral arteries. The measure has been done by calculating the time delay of several corresponding levels in the two pressure pulses: at the foot, during the ascending phase, at the peak. Three different intervention have been carried out: Ach, NA, blood transfusion. The transmission rate outcame higher at the pulse foot than at the peak, in control animals and in Ach and blood transfusion interventions. The NA intervention inverted this behaviour, where the increase in transmission rate did not correspond to the rate of pressure growing. The possible influences of a vegetative component on arterial viscoelastic behaviour are discussed.

In order to investigate internal shortening effects upon time course of active state, a study on rat papillary muscle has been carried out. Internal (or CE) shortening was evaluated according to a mechanical muscle model in which parallel elastic (PE), series elastic (SE), contractile (CE) elements are represented. CE force-velocity-shortening-time relationships have been used to describe time course of muscle active state in isometric, completely isotonic, afterloaded, and stopped isotonic contractions. The results obtained suggest that, regardless of type of contraction utilized, the parameters of muscle active state are strongly influenced by the amount of CE shortening.