High resolution mechanical function in the intact porcine heart: mechanical effects of pacemaker location

The necessity to quantify the mechanical function with high spatial resolution stemmed from the advancement of myocardial salvaging techniques. Since these therapies are localized interventions, a whole field technique with high spatial resolution was needed to differentiate the normal, diseased, and treated myocardium. We developed a phase correlation algorithm for measuring myocardial displacement at high spatial resolution and to determine the regional mechanical function in the intact heart. Porcine hearts were exposed and high contrast microparticles were placed on the myocardium. A pressure transducer, inserted into the left ventricle, synchronized the pressure (LVP) with image acquisition using a charge-coupled device camera. The deformation of the myocardium was measured with a resolution of 0.58+/-0.04 mm. Within the region of interest (ROI), regional stroke work (RSW), defined as the integral of LVP with respect to regional area, was determined on average at 21 locations with a resolution of 27.1+/-2.7 mm2. To alter regional mechanical function, the heart was paced at three different locations around the ROI. Independent of the pacemaker location, RSW decreased in the ROI. In addition, a gradient of increasing RSW in the outward direction radiating from the pacemaker was observed in all pacing protocols. These data demonstrated the ability to determine regional whole field mechanical function with high spatial resolution, and the significant alterations induced by electrical pacing.     

Selective battering of the family pet

Abstract

We examined the attitudes, perceptions and behaviors of both pet-abusing and non-pet-abusing perpetrators of family violence. Using data collected from victims residing at domestic violence shelters, results indicated that relative to their non-pet-abusing counterparts, pet-abusing batterers tend to less often show affection toward their pets, more often communicate with their pets only through commands and threats, more often view companion animals as property, are more likely to scapegoat their pets, and are more likely to have unrealistic expectations about their pets, more frequently punish their pets, and are more sensitive to stressful life events—particularly those perceived to be caused by the pet. We also queried respondents about batterers' past history with pets, the frequency and type of abuse inflicted on animals, the number of batterers who hunt, the frequency with which children witnessed abuse of the family pet, the impact of animal guardianship on decisions to remain with or return to the batterer, and where companion animals ended up when victims fled the batterer.     

Physiological basis for mechanical time-variance in the heart: special consideration of non-linear function

A relationship between ventricular pressure and volume is developed starting from basic cardiac muscle mechanics. The known and measurable properties of myocardium, such as the Hill law, the periodic excitation-contraction mechanism, and non-linear elasticity of the surrounding elastin and collagen structure, are formulated into a myofibril unit. A cylindrical geometry is chosen to represent the structure of the ventricle, using the myofibril unit as the basic building block. Pressure-volume isochrones computed from this model illustrate non-linear function in the heart which arises from both geometric effects and muscle effects. The above theory and model is linearized to provide a special study case. The behavior that resulted is that of a time-varying elastance, E(t), and, hence, can help in the interpretation of its meaning. It is found that the minimum in E(t) is the consequence of the stiffness of the myocardial fibrous network, adjusted by a geometric factor. In addition, the magnitude of E(t) is governed by myocardial contractility, a geometric factor, and the excitation-contraction mechanism, where time-dependency is imparted by periodic excitation. Since the elastic fibers are the only true elastic elements, the quantity of elastance is determined by controlled volume feedback. A circuit model is provided to illustrate this concept. The non-linear active and passive heart function curves are specified independently. These curves are required to intersect below the resting volume and result in a negative pressure at the intersection. This is found to explain the phenomenon of ventricular suction. In addition, they lead to a time-varying dead volume by virtue of time-dependent isochronal slope. Non-linear function is introduced to the model and is found to explain the variation in curvature of the ventricular isochrones.     

The effect of lanthanum on the mechanical function of the isolated perfused rat heart at different extracellular calcium concentrations.

The effects of 50 microM lanthanum (La3+) on the contractile force, rate and coronary flow of rat hearts perfused with solutions containing 2.5, 5, 7.5 mM calcium (Ca2+) have been investigated. La3+ produced a rapid and marked decrease in contractile force within 1-3 min ("early La(3+)-effect"). The inhibition of contractility by La3+ was reduced progressively when the Ca2+ ion concentration in the perfusion fluid was raised from 2.5 to 7.5 mM. However, after 10-80 min of La3+ perfusion the contractile force was increased significantly ("late La(3+)-effect"). Elevation of Ca2+ during exposure to La3+ increased its effect. During the late La(3+)-effect, a marked decrease in heart rate and a significant increase in time to reach peak tension, time for half relaxation and twitch duration was observed. High concentrations of perfusate Ca2+ decreased the chronotropic response to La3+, in contrast, elevated Ca2+ potentiated La(3+)-induced increase in time to reach peak tension, time for half relaxation and twitch duration. La3+ produced a significant decrease in coronary flow. High Ca2+ augmented the decrease coronary flow. The findings indicate that La3+ may produce marked effects on myocardial function. High extracellular Ca2+ reduces the La(3+)-induced initial decrease in force of contraction, but potentiates the late increase in contractile force by La3+. Elevated external Ca2+ also increases the effects of La3+ on twitch parameters, heart rate and coronary flow.     

Effect of heterogeneity of the myocardium on its mechanical function

The influence of the mechanical heterogeneity on the myocardium contractility was evaluated. The heterogeneity was imitated by parallel connection of two papillar muscles with different mechanical properties. The rate of muscle shortening was controlled by a feed-back from tension of each of the muscles or both muscles simultaneously in the precision ergometer. The "force-velocity" and "length-force" relations were registered for each muscle independently, and in case of parallel connection of two muscles. It was shown that connection of two muscles in parallel influenced significantly the distribution of load in the muscles, maximal and mean velocity of their shortening. It is stated that the key phenomenon controlling the value and the heterogeneity influence sign is mechano-chemical uncoupling (inactivation).     

Definitive assumption of heart function by the artificial heart

Reproducing the function of the natural heart with an artificial heart requires a multi-disciplinary approach. Problems to be solved are anatomical, physiological, biological and technical ones. Moreover, clinical use of the artificial heart on a large scale in the near future may involve economical, ethical and legal issues. These several aspects are reviewed, and the State of the Art in 1981 is established.     

Effects of octylguanidine on the electrical and mechanical events of xenopus heart

The effects of octylguanide on the electrical and mechanical events of Xenopus heart perfused at the rate of 5 ml/m with oxigenated Ringer of ph 7,4 at 24 degrees C were studied. The early effects on the action potential resemble those of the tetrodotoxina, the later effects looks like instead as those observed with metabolic poisons. The cardiac preparations poisoned by octylguanidine still have a metabolic reserve available to furnish energy for the contractile process.     

新型机械心脏瓣膜的研究

目前临床使用的各种机械心脏瓣膜的主要问题是血栓栓塞和与抗凝治疗有关的出血,其缺陷在于瓣膜开启时,碟片和支架将瓣膜的整个血流通道分隔成三至四个较小的血流通道。在这种受阻隔的血流通宫,形成容易诱发血栓的高剪应力区、紊流和滞流区。我们研制的两种机械心脏瓣膜在瓣膜开启时,没有任何支架和碟片分隔瓣膜的血流通道,使血流与天然心脏瓣膜中的相类似,可减少对血液的危害,从而可减少换瓣病人对抗凝治疗的依赖程度。     

Effects of caffeine on the mechanical properties of developing rat heart ventricles

The effects of caffeine on isometric contractions of right-ventricular strips during the postnatal development of the rat heart were studied. Caffeine (2-10 mM) had a positive inotropic effect on ventricular strips of 3-15-days-old rats but a negative inotropic effect on the muscles of rats older than 22 days. Rest-twitch potentiation was most prominent in the muscles of 3-15-days-old rats but weakened clearly after that age. The potentiation was eliminated by 5 and 10 mM caffeine. An abrupt increase in frequency from 0.2 to 2 Hz caused a positive tension-staircase in 3-15-days-old rats but a negative staircase in older rats, the latter effect being eliminated by caffeine. It is suggested that the observed changes during the third postnatal week are due to a shift from extracellular to intracellular Ca2+ as the main source of this cation.