Effect of stimulation of sublobule IX-b of the cerebellar vermis on cardiac function.

Activation of sublobule IX-b of the cerebellar vermis evokes hypotension, bradycardia and decrease of the phrenic nerve activity in the anesthetized animal. Cardiac performance during the isovolumic phases of systole and relaxation can be evaluated by dP/dtmax, Vpm, dP/dt/DP40 and tau, respectively. In the present study, we evaluated the changes on cardiac function evoked by the stimulation of sublobule IX-b. New Zealand white rabbits were anesthetized, paralyzed and artificially ventilated. A posterior craniotomy was made to reveal and stimulate the cerebellar uvula (4 s train; 50 Hz; 1 ms; 20 microA). The femoral artery and veins were cannulated and a Swan-Ganz catheter was advanced in the upper abdominal aorta to control afterload when inflating the balloon. The left ventricle was catheterized with a Millar catheter. Blood pressure, heart rate, left ventricular pressure were monitored. Results showed a significant decrease on sublobule IX-b stimulation of all the indices of systolic function and an increase of tau indicating a decrease in the speed of the relaxation. These data provide the first evidence of the influence of sublobule IX-b on cardiac function. They may contribute to the understanding of the origin the cardiovascular changes that were observed in two patients with vermian and paravermian hemorrhage.

Normal relationships between cardiovascular variables in active orthostatism and clinostatism in postural change.

OBJECTIVE: Autonomic modulation of hemodynamics, essential for the preservation of homeostasis, is well tested by the abrupt postural change from clinostatism to active orthostatism. The aim of this work was to study normal relationships between the cardiovascular variables in active orthostatism and those in clinostatism. METHODS: Hemodynamic parameters in clinostatism and orthostatism were easily measured in 20 healthy subjects of both sexes, aged between 33 and 78 years, without treatment, using the non-invasive thoracic electric bioimpedance method. RESULTS: Cardiovascular variables values in orthostatism are linearly related with their values in clinostatism. CONCLUSIONS: Results show that cardiovascular variables in active orthostatism are linearly related with their values in clinostatism, each variable being specially regulated. A clinostatism and orthostatism intraindividual correlation was obtained, which provides an easily accessible method of detection and interpretation of autonomic dysfunctions, without deleterious consequences for the subjects, which can be very useful for research on physiopathologic mechanisms.

[Elasticity and viscoelasticity in the circulatory system. IV. Diastolic filling of the left ventricle]. / Elasticidade e viscoelasticidade no aparelho circulatório. IV. Replecção diastólica do ventrículo esquerdo.

This paper studying diastolic left ventricular and myocardial elastic and viscoelastic properties, some of its consequences and its quantification, constitutes the fourth part of a review on circulatory system elasticity and viscoelasticity. The ventricular elastic and viscoelastic properties depend on myocardial ones and on chamber shape and dimensions. Thus it is often necessary to quantify the ventricular and the myocardial properties separately. As an approximation, the viscoelastic effects during diastole can be neglected and the elastic properties deduced from data obtained over the entire filling; however, these properties can be quantified rigorously only when using viscoelastic models. Another method of exact quantification is based on diastatic data alone; the latter do not reflect significant viscoelastic effects because they correspond to a period in which deformation rate is very slow. This study includes several Pathophysiological applications: some alterations in ventricular elastic properties induced by the pericardium are analysed and deviations from normal ventricular and myocardial diastolic properties caused by primary angina pectoris, by effort angina pectoris and by hypertrophy due to volume and pressure overload are examined. The basic Physical and Biophysical concepts essential to the better phenomena understanding are exposed in the first part of this work which constitutes a previous paper component.

[Circulatory system's elasticity and viscoelasticity. III. Isovolumetric relaxation of the left ventricle]. / Elasticidade e viscoelasticidade no aparelho circulatório. III. Relaxamento isovolumétrico do ventrículo esquerdo.

Both in health and in diseases characterized by abnormal diastolic performance in which there is no evidence of strong asynchrony or abnormal myocardium, the ventricular isovolumetric relaxation index more often applied has been the relaxation constant T that assumes a monoexponential pressure decay. Its choice is based on its independence from systolic pressure, mean aortic pressure, telesystolic pressure and volume, auricular pressure and other factors. Nevertheless in patients with gross asynchrony or abnormal myocardium the pressure decay is not exponential and the results obtained with relaxation constant T do not describe adequately the relaxation and are sometimes controversial. Other indexes have been used that do not require a mono-exponential pressure decay. In this paper some models of pressure decay during isovolumetric ventricular relaxation are examined. Some procedures for determination of the relaxation constant T and asymptomatic pressure as well as for other indexes that do not demand pressure decay monoexponentiality (such as the time constants t1/2 and T40 and the dP/dt (20/60) are reviewed. The effects of age and physical exercise on the index T are analyzed. In particular, the suitability of the monoexponential model to ischemic and ventricular hypertrophic states is studied, some results of application of the reported indexes do not requiring pressure isovolumetric decay monoexponentiality are considered and advantages and inconveniences of its use are analysed.

[Cardiovascular physiology. Elasticity and viscoelasticity of the circulatory system. I. Physical basis. II. Arteries]. / Fisiologia cardiovascular. Elasticidade e viscoelasticidade no aparelho circulatório. I. Fundamentos físicos. II. Artérias.

The vascular walls and the myocardium have the mechanical behaviour of viscoelastic materials. This paper consists in the first two parts of a review on elasticity and viscoelasticity in the circulatory system. The main elastic and viscoelastic properties of the arterial walls and some of its consequences are studied and some of its quantification theories are exposed, proceeded by the Physical and Biophysical basis necessary to the understanding of phenomena concerned in the totality of the work. Arterial stress and strain are analysed and the notions of arterial static elastic modulus, stiffness or elastance and compliance or capacitance such as the concepts of dynamic or viscoelastic modulus and stiffness are developed. Creep, stress relaxation, histeresis and pulse waves dispersion and atenuation effects are described.

[Notes on vascular impedance]. / Notas sobre impedância vascular.

The main knowledge on vascular impedance is preceded by the necessary mathematic and biophysic notions to the comprehension of the phenomena which determine the interpretation of the obtained results. Some physiopathologic applications are exemplified.