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Biomedical subjects

R Cihák

Publications and source records attributed to R Cihák.

At least 19 recordsLinked to original sources
PubMed1994

Modelling tissue behaviour based on hyperelasticity theory.

The tissues are during their physiological function, e.g., in the course of growth, adolescence, and aging, subjected to a cyclic mechanical loading and to large displacements and rotations as well. A tissue free of all external tractions is in a state that minimizes its internal power. In the course of aging of the tissues, for instance in the wall of the aorta, the vein, and also in the myocardium or heart valves, the decrease of the water content and increase of the collagen content occurs; while in compact and trabecular bone the contents of both mineral substances and collagen, undergo reduction. In accordance with it, the strain energy function and the constitutive equations of living tissue based on the hyperelasticity theory using rotationless strain were studied. On the base of the proposed eigenvalue decomposition of the rotationless strain tensor and hyperelasticity the strain energy function was formulated as depending on biological time of tissue. The quantity of strain energy function per unit of the biological time, which essentially characterizes the velocity of change of mechanical response of tissue in the course of its aging, was also defined. The coefficient of tissue aging is the further diagnostic parameter, which is independent of the rotationless strain tensor and expresses the relative change of mechanical response of tissue during the biological time. The corresponding constitutive equation of tissue depending on the biological time is also determined. On the base of the regression analysis the theoretical stress-strain curves for myocardium and blood vessels were determined. The numerical results reveal that the coefficient of aging progressively increases in hardening tissues (coronary artery, vena cava inferior) whereas at the softening tissues it has a relatively slow increase at the dependence on tissue aging.

Adolescent↗
PubMed1992

Functional changes in the right and left ventricle during development of cardiac hypertrophy and after its regression.

OBJECTIVE: The aim was to determine left and right ventricular functional reserves and collagen concentration during the development of cardiac hypertrophy and after its regression. METHODS: Two experimental models of cardiac hypertrophy (chronic thyroxine or isoprenaline treatment of adult rats) were compared 24 h and five weeks after the agent was last given. Pressure changes in the left (right) ventricle before and after acute aortic (pulmonary artery) ligation were recorded in open chest anaesthetised animals. The difference in dP/dtmax after and before ligation was regarded as the functional reserve. The total collagen concentration was determined in both ventricles separately by means of hydroxyproline. RESULTS: Left and right ventricular weight increased by 20% and 30% respectively in the two models employed. In the thyroxine treated group, the functional reserve of the left ventricle rose very noticeably, whereas in the isoprenaline treated group it decreased. The right ventricular functional reserve did not differ from that in the controls in either of the two groups. The collagen concentration rose in the left ventricle in the isoprenaline group only. Five weeks after the last administration of the agent, cardiac mass and ventricular function did not differ from the control values in either of the models studied; the only exception was the incomplete regression of left ventricular hypertrophy and persistent structural and functional impairment of the left ventricle in the isoprenaline treated group. CONCLUSIONS: Our results indicate that hearts undergoing a comparable degree of experimental hypertrophy may have different functional and structural properties; significant differences were found between the right and left ventricular response. Regression of hypertrophy together with a reversal of ventricular function usually occurs unless the myocardium has received severe structural damage.

Animals↗
PubMed1992

Changes in ventricular effective refractory periods after two extrastimuli and ventricular electrical instability.

Using programmed stimulation with one and three extrastimuli delivered in the right ventricular apex, we compared the effective refractory period (ERP) during sinus rhythm (ERP-SR) and during the third extrastimulus (ERP-S3) in patients without ventricular tachycardias (control group, n = 87) and in patients with documented ventricular tachycardia (VT group, n = 76). The protocol was not completed to determine ERP-S3 in one patient in the control group and in 15 patients in the VT group. We observed a significantly greater change (i.e., shortening) in ERP after two extrastimuli in the VT group compared with patients without VT (delta ERP = 45 +/- 20 msec in the control group and 70 +/- 16 msec in the VT group, P < 0.001). This electrophysiological phenomenon, along with conduction delay, may play an important role in VT induction.

Cardiac Pacing, Artificial↗
PubMed1992

[24-hour effect and tolerance for perindopril (Prestarium) in mild and moderate essential hypertension].

A multicentre investigation of antihypertensive treatment by perindopril was conducted in three centres of Czechoslovakia. The investigation comprised 51 patients with mild to moderate essential hypertension (diastolic pressure 95-115 mmHg) who were taking perindopril for a period of three months, the initial dose being 4 mg (1 tablet per day). If the blood pressure did not drop to normal levels (dBP < 90 mmHg), the dose was increased to 8 mg after 1 month and if after 2 months of treatment the blood pressure did not reach normal levels, a thiazide diuretic was added. The antihypertensive effectiveness was assessed 24 hours after ingestion of the drug. The blood pressure declined significantly already after the first month of monotherapy with perindopril. It declined then significantly up to the end of the 3rd month of treatment. The systolic blood pressure declined by 9.4 mmHg after the first month of monotherapy with perindopril and by 15.9 mmHg after 3 months of treatment. The diastolic blood pressure declined by 8.1 mmHg after one month of monotherapy and by 12.4 mmHg at the end of three-month treatment. The clinical and biological tolerance was excellent and only one patient discontinued treatment for reasons not related to the administered drug. Twenty-four hour monitoring of the blood pressure also proved the favourable effect of perindopril.

Adolescent↗
PubMed1992

[Can pharmacotherapy in heart failure affect mortality?].

The prognosis of patients with advanced chronic cardiac failure is very poor. Only investigations made in recent years provided evidence that this adverse prognosis can be influenced by conservative pharmacological treatment. Among many tested vasodilating substances positive data were obtained only with high doses of nitrates with hydralazine and in particular with inhibitors of the angiotensin converting enzyme which are the greatest advance in the treatment of chronic cardiac failure. Preparations of this group mitigate the symptomatology, increase load tolerance and improve the prognosis. So far they are indicated above all in severe forms of cardiac failure, however, the possibility to use them also in milder forms and in patients with myocardial infarction is intensively investigated. The basis of pharmacological treatment remain diuretics. The position of digitalis in the treatment of cardiac failure is revised at present; in a major proportion of patients, in particular those with a preserved sinus rhythm, its administration is useless. A number of other positively inotropic substances was tested, catecholamines as well as phosphodiesterase inhibitors (amrinone, milrinone, xamoterol, enoximone). Contrary to acute failure, their effect in chronic failure is controversial, data on an improved prognosis are lacking and some investigations reveal an adverse trend. Almost half the patients with cardiac failure die from a sudden death and it would thus be logical to use antiarrhythmic drugs. Here, too, however, data on an improved diagnosis are lacking. The results of hitherto accomplished studies were rather disappointing, the investigation with the most promising antiarrhythmic agent--amiodarone--is still under way.

Heart Failure↗
PubMed1991

Effect of isradipine on 24-h blood pressure profile demonstrated by repeated monitoring.

The antihypertensive effect of isradipine was assessed by repeated 24-h ambulatory blood pressure monitoring. Using an SPS device (Sandoz Pharma, Basel, Switzerland), monitoring was carried out in 10 male patients with mild essential hypertension (1) after a placebo period, (2) after six months, and (3) after 12 to 13 months of treatment with isradipine (average dose 2.5 mg twice daily). Mean 24-h blood pressure decreased significantly after both periods 2 and 3 (from 148/93 mm Hg to 137/87 and 130/85 mm Hg, respectively). The total number of hypertensive systolic and diastolic blood pressure values also decreased. The normal circadian blood pressure curve was preserved, showing the reduction throughout the 24-h period, and the early morning rise in blood pressure was markedly blunted. These results indicate that isradipine has a favorable effect on the 24-h blood pressure profile that persisted throughout six and 12 months of antihypertensive therapy.

Adult↗
PubMed1990

24-hour ambulatory blood pressure monitoring in the treatment of mild hypertension with isradipine.

Twenty-four-hour ambulatory blood pressure (BP) monitoring allows the physician to follow the course of blood pressure of a patient at the worksite, at home, and during sleep. All these undisputed advantages made the technique an important part of studies designed to assess the effect of new antihypertensive drugs. In a study involving 14 patients with mild hypertension. 24-hour BP levels were monitored before and after treatment with isradipine (Lomir, Sandoz), a new calcium antagonist. A marked decrease in mean systolic BP (146.8 +/- 4.1 vs. 133.8 +/- 3.3 mmHg, p less than 0.01) as well as diastolic pressure (92.4 +/- 1.4 vs. 86.0 +/- 1.1 mmHg, p less than 0.01) was found after 6-month therapy compared with the values determined in the placebo period. The incidence of hypertensive BP values during the day was likewise reduced. The circadian rhythm of BP was retained. The nocturnal decrease in BP was less prominent than during the day, and there was a marked reduction in the rapid morning rise in BP. Overall, 24-hour BP monitoring demonstrated a favourable effect of isradipine on the diurnal profile of BP.

Antihypertensive Agents↗
PubMed1990

Current status of 24-hour ambulatory blood pressure monitoring in clinical practice.

Twenty-four-hour monitoring of blood pressure (BP) is a new non-invasive technique of examination which, apart from becoming a useful research tool, has found widespread use in clinical practice. Monitoring detects BP fluctuations due to changes in physical and mental activities throughout the day and to physiological circadian rhythms, especially the nocturnal BP decrease. Monitored BP shows a better correlation with the degree of target organ damage than casual BP. In patients with increased BP values persisting despite therapy, BP monitoring makes it possible to differentiate hypertensives with truly resistant or inadequately treated hypertension from those showing substantially higher BP values in the doctor's office than their normal daytime levels are. BP monitoring may improve the accuracy of prediction of cardiovascular complications. This fact, however, has to be verified by other prospective studies which may expand the range of potential applications of this new method.

Arousal↗
PubMed1989

[24-hour ambulatory monitoring of blood pressure and the diagnosis of resistant hypertension].

Twenty-four hour ambulatory monitoring of the blood pressure (BP) is a new non-invasive examination method which makes it possible to follow up the BP in the patients' environment--at work, at home during sleep. Casual assessment of BP in the surgery causes in some patients an alarm reaction to the assessment, the so-called "white coat phenomenon", and thus frequently does not reflect the considerable variability of BP associated with physical activity and changes of the psychic state in the course of the day. Monitoring of the BP is an important part of investigations comparing the action of different antihypertensive drugs, it is, however, also helpful in clinical practice. It makes possible a more satisfactory evaluation, in particular in patients with mild hypertension, and frequently also more accurate assessment of the diagnosis. In some patients where despite treatment higher BP readings persist, monitoring of the BP makes it possible to differentiate patients with truly resistant or inadequately treated hypertension from those who have substantially higher BP readings in the surgery than in the course of the day.

Adult↗
PubMed1989

Morphological research of the locomotor apparatus.

This paper presents the results of a study focussed on the locomotor apparatus and on the biological systems integrated in it. This study was carried out by a large group of workers in the Institute of Anatomy in Prague, with close and mutual interweaving of their contributed works. The review demonstrates the ontological advancement achieved in the fields of morphology and development of these locomotor structures. From descriptive studies it proceeds towards experimental works specially oriented to understand developmental mechanisms and the causality of their origin, within the context of the most recent advancements in developmental morphology. Even individual applications in clinical practice, which might arise, have been pointed out. The whole set of works having been referred to, from which only a fraction necessarily limited due to the length of this publication could be cited, also demonstrated here the possibilities of employing knowledge obtained about the locomotor apparatus of the limbs in further research concerning the more generalized aspects of the mechanisms of development and their regulations, down to their molecular biological level.

Adult↗
PubMed1987

Benzidine and 3,3'-dichlorobenzidine (DCB) induce micronuclei in the bone marrow and the fetal liver of mice after gavage.

Single oral dose of benzidine (300 mg/kg) and DCB (1000 mg/kg) to male ICR mice elicited positive response in the bone marrow micronucleus test. In the transplacental micronucleus test, the compounds were administered to pregnant females in the same manner. A significant increase in the frequency of micronuclei occurred in the fetal liver, but not in the bone marrow of mothers. The relative values of bone marrow and transplacental micronucleus tests for the prediction of carcinogenicity of these compounds is discussed.

3,3'-Dichlorobenzidine↗
PubMed1985

Cytogenetic effects of quinoxaline-1,4-dioxide-type growth-promoting agents. III. Transplacental micronucleus test in mice.

The growth-promoting agents carbadox and olaquindox were active in the mouse transplacental micronucleus test, whereas cyadox was ineffective. Chemicals were administered p.o. and i.p. at a dose of 100 mg/kg and the effect was observed 18 h after treatment. The effects observed in fetal liver were parallel to those in maternal bone marrow, but fetal tissue was approximately 2-3 times more sensitive.

Administration, Oral↗
PubMed1983

Cytogenetic effects of quinoxaline-1,4-dioxide-type growth-promoting agents. I. Micronucleus test in rats.

The cytogenetic activities of 3 growth-promoting agents carbadox, olaquindox and cyadox were examined by the micronucleus test. These chemicals were administered i.p. to male Wistar rats 30 and 6 h before they were killed. Single-dose levels were 5, 10, 15, 30, 60, 90, 120 and 240 mg/kg for carbadox; 30, 60, 90, 120 and 240 mg/kg for olaquindox; and for cyadox 30, 60, 120 and 240 mg/kg. Over the entire dose range tested, carbadox induced a statistically significant increase in the number of micronucleated polychromatic erythrocytes in the rat bone marrow, whereas similar activity of olaquindox started at a dose of 2 X 60 mg/kg. The effect of cyadox was very low even at the highest dosage tested. Further testing of the genotoxicity of this class of chemicals is required. The genetic activity of the solvent used (dimethyl sulfoxide) is briefly discussed.

Animals↗