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Biomedical subjects

R Hardt

Publications and source records attributed to R Hardt.

13 recordsLinked to original sources
PubMed2002

Cardiovascular function of workers exposed to carbon disulphide.

OBJECTIVES: The aim of the study was to verify that exposure to carbon disulphide (CS(2)) up to 10 ppm results in a negative inotropic effect on cardiovascular function. METHODS: In a cross-sectional study a total of 325 workers exposed to CS(2) in the rayon-producing industry and 179 controls from the same plants were examined. The exposure assessment was based on personal air sampling and biological monitoring (2-thiothiazolidine-4-carboxylic acid (TTCA) in urine) for all persons. The examination consisted of a standardised questionnaire, physical examination, assessment of body fat mass, ergometric test with the determination of work capacity at heart rates of 100, 130, 150 and 170 beats/min, and electrocardiography. RESULTS: The mean external exposure was 6.04 ppm CS(2) (range: 0.03-91.08); the mean internal exposure was 1.14 mg TTCA/g creatinine (range: 0.02-11.50). The workers exposed to CS(2) showed better physical fitness. The diameters of the left heart chamber of the exposed persons were not significantly different when compared with occupationally non-exposed workers, but there was a tendency of increasing diameters for the exposed employees. In the multiple linear regression the diameters showed physiologically plausible correlations with the body mass index, body fat mass, alcohol consumption, and physical fitness, but not, however, with the exposure, neither with the exposure group in all persons nor with the internal or external exposure within the exposed workers. CONCLUSIONS: In this study, differences in the heart chamber diameters between exposed persons and controls could not be confirmed. Differences in physical fitness and constitution can explain differences in heart chamber diameters.

Adult↗
PubMed1996

Carbon disulphide. IV. Cardiovascular function in workers in the viscose industry.

OBJECTIVE: The aim of the study was to examine whether an increase can be detected in the prevalence of coronary heart disease or a higher prevalence of unusual cardiological findings in workers with occupational exposure to carbon disulphide (CS2) at the level of the threshold limit value of 10 ppm currently valid in occupational medicine. METHODS: In a cross-sectional study we investigated 247 men occupationally exposed to CS2 and a comparable control group (n = 222). The current exposure to CS2 was measured using personal air monitoring and biological monitoring of all test persons. A cumulative exposure index (median of CS2 exposure in the past multiplied by the duration of employment) was calculated. In addition to collecting comprehensive anamnestic data on all persons, we carried out a physical examination, an ultrasound examination of the large arteries, a resting and exercise ECG and an echocardiographic examination. RESULTS: No increase could be found in the prevalence of coronary heart disease or of arteriosclerotic findings in the exposed subjects. There was no difference in the distribution of the performance of the two groups in the ergometric tests. The echocardiogram showed a median increase in the diameter of the left atrium and left ventricle of 1-2 mm in the exposed subjects. These differences could also be confirmed statistically after multiple linear regression analysis. The left ventricular, telesystolic diameter was positively associated (P < 0.05) with internal exposure (CS2 metabolite in urine), and fractional shortening revealed a plausible negative trend (P = 0.0755). Current external exposure (CS2 in air) and cumulative exposure did not influence any of the parameters investigated. CONCLUSION: The findings may indicate a negatively inotropic effect of CS2 so far unknown in man. However, no clinical relevance for this effect was apparent.

Carbon Disulfide↗
PubMed1995

Carbon disulphide. III. Risk factors for coronary heart diseases in workers in the viscose industry.

To evaluate risk factors for coronary heart disease and factors which can influence the course of acute myocardial infarction in workers exposed to CS2 we performed a cross-sectional study of 247 workers in the viscose industry. The control group of 222 men from the same plant was comparable for age, social status and physical work. The CS2 exposure determined by personal air sampling ranged from < 0.2 ppm to 65.7 ppm (median: 4.0 ppm) and the duration of exposure ranged from 4 to 220 (median: 66) months. Using a multiple linear regression model we found neither higher blood pressure at rest or after exercise, nor hyperlipoproteinaemia in a higher degree, nor lower high-density lipoprotein (HDL) or lower apolipoprotein A-I levels, nor higher blood glucose values, nor indicators of direct cardiotoxic effects or signs of disturbances in blood coagulation in the exposed group in comparison to controls. Regarding the influence of chronic exposure on the investigated parameters, we found an inverse correlation of the cumulative exposure (mean CS2 exposure in the department multiplied by the duration of work in this department) with the HDL concentration. The HDL levels correlated with the duration but not with the intensity of exposure. In the same way the apolipoprotein A-I levels showed a negative association with the duration of exposure in the exposed group as well as in the control group. The HDL concentrations showed the same trend for the controls. It therefore seems that this finding is more likely due to confounding factors than to the CS2 exposure. As all subjects (exposed and controls) have done shift work, in some cases for a long time, this kind of work could be responsible for the negative relationship between the duration of employment as a shift worker and the apolipoprotein A-I and HDL levels. At the current air-borne levels no significant differences were found between the exposed persons and the controls in the distribution frequency for blood pressure values, lipoproteins, blood glucose, blood coagulation and indicators of direct cardiotoxic effects.

Adult↗
PubMed1993

Low polarization pacing lead for detecting the ventricular-evoked response.

The cardiac response to a pacing pulse is potentially useful for rate adaptive pacemakers and threshold tracking systems. However, until now capture recognition of the ventricular-evoked response by the use of a single electrode for stimulation as well as detection was limited by the electrode polarization. Electronic measures against the stimulus polarization artifact have not been successful due to the variability of the after potential or the requirement of additional battery power. Following the idea of Lewin, Myers and Parsonnet, who introduced the idea of a non-polarizable porous electrode for physiological stimulation, titanium nitride (TiN) and iridium (Ir) coatings with fractal surface structure have been developed with high electro-chemical active surface areas and Helmholtz double-layer capacities of up to 50,000 microF/cm2, thus reducing the polarization artifact significantly. Two types of endocardial leads (10 with a fractal TiN coating and 5 with a fractal Ir coating) were implanted in the apex of the right ventricle and the polarization artifact, as well as the evoked response, was measured. Both types of pacing leads show a 90% reduction in the polarization artifact in comparison to conventional leads. If an autoshort of approximately 20 to 50 ms is applied after the pacing pulse, the polarization artifact of these leads is negligible, thus enabling reliable detection of at least the repolarization phase of the ventricular-evoked response, which is fully sufficient for capture recognition. Additionally, due to their low polarization losses, TiN- or Ir-coated electrodes with fractal surface structure have a unique stimulation and detection performance.

Aged↗
PubMed1990

Sputter-deposited TiN electrode coatings for superior sensing and pacing performance.

The sensing and pacing performance of pacemaker electrodes is characterized by the electrochemical properties of the electrode/tissue interface affecting tissue reactions and the kinetics of the ionic exchange. The usually smooth metallic electrode surface results in a high pass filter characteristic. To better match the electrode's filter characteristic to the spectral content of the depolarization signal, various combinations of electrode shape, material and surface structure have been researched. The electrode with sputter-deposited TiN coating presented in this report has been designed to meet the demand for low acute as well as chronic thresholds and superior sensing performance not only with respect to spontaneous activity but also regarding the detection of the evoked response. The clinical results obtained with this electrode prove the excellent pacing and sensing properties resulting from minimized polarization losses and optimized filtering of the signal to be detected, respectively. The acute and chronic clinical advantages over previous concepts are attributed mainly to the biocompatibility of the material used and the microcrystalline surface structure achieved by the coating process. The design concept of the new electrode is presented together with the clinical results obtained. While the advancements in microelectronics and battery technology have certainly formed the basis for the development of pulse generators featuring an ever increasing versatility of functions at the same or even smaller pacemaker dimensions, from a point of view of pacing system performance the development of improved electrode concepts as the one presented must be regarded as equally indispensable.

Biocompatible Materials↗
PubMed1987

[The analysis of caramel colors. 1. Differentiation of classes of caramel coloring agents with Curie-point pyrolysis-capillary gas chromatography-mass spectrometry].

After an introduction on the production, classification, legislative regulations, toxicology, and analysis of caramel colours, a report is given on the examination of these colourings by Curie-point pyrolysis-capillary gas chromatography-mass spectrometry. This method enables the differentiation between the four classes of caramel colours on the basis of the most concentrated of more than 100 identified pyrolysis products, which requires small quantities of substance (100 micrograms) and short periods of time (1 h).

Carbohydrates↗
PubMed1987

Responsiveness of microcirculation and local cold vasodilation to capsaicin in the intact and chronically denervated canine tongue.

Lingual blood flow and its distribution were determined at rest and in response to local cooling of the tongue (32 degrees C) in 6 anaesthetized, paralyzed and artificially ventilated dogs before and after two intraarterial (i.a.) injections of capsaicin (2.5 mg) at an interval of about 40 min. In 3 dogs, the same protocol was performed after degeneration of the chorda-lingual and glossopharyngeal nerves due to prior transection. In general the first i.a. injection of capsaicin resulted in a marked and the second injection in a smaller decrease of lingual blood flow. Local cooling of the tongue induced significant increases in lingual blood flow before as well as after capsaicin treatment, regardless of whether sensory innervation was intact or degenerated. In both the untreated and capsaicin treated dogs the increase in lingual blood flow during local cooling of the tongue was solely due to an increase in blood flow through the arteriovenous anastomoses, while blood flow through the capillaries of the mucosa and muscles even decreased. The findings suggest that capsaicin-induced vasoconstriction of the tongue vessels is due to a direct effect on vascular receptors. It is further suggested that cold vasodilatation of the canine tongue is not mediated by axon collaterals releasing substance P. Direct thermal effects on the intramural ganglia and the postganglionic vasomotor efferents innervating the AVAs, or on AVAs basal tone itself are suggested as the underlying mechanism.

Animals↗
PubMedDate not supplied

[Titanium nitride cardiac pacemaker electrodes].

The sensing and pacing performance of pacemaker electrodes is characterized by the electrochemical properties of the electrodes/tissue layer; the usually smooth metallic electrode surface results in a high pass filter characteristic. Consequently, the detected intracardiac signals, which control the implantable systems, are not optimally matched to the spectral contents of the depolarisation signal. To avoid interference caused by noise (EMI, muscle potentials, etc.) a shift of the frequency of the band pass towards the lower frequency spectrum is required. As previously reported, the electrochemical properties of sintered and surface-treated electrodes prove the predicted improvement of sensing performance if titanium-nitride coated electrodes are used. Our results demonstrate their superiority above all the other electrodes presently known. The advantages can be referred to the micro-crystalline surface structure achieved by sputter-deposited electrode coatings and the kinetics of the ionic exchange. Furthermore, the acute thresholds achieved with the TiN-systems were significantly better than those of the smooth metallic surface. These results were also confirmed for chronic implants and are attributable to the known biocompatibility of titanium and its alloys.

Electrocardiography↗
PubMedDate not supplied

[Motion energy as a control variable for adapting stimulation frequency].

An activity sensing rate-responsive pacing system is presented which adaptively controls heart rate to adjust cardiac output in response to increased metabolic demand, and more optimally restore homeostasis of the intact cardiovascular system. The current use of ventricular demand and DDD universal pacing systems, although rate and multi-parameter and multi-function programmable, are fixed at these programmed settings. These devices are adequate for patients at rest or during moderate exertion, but are suboptimal for physically active patients whose physiology requires increased oxygen supply to meet an increased cardiac demand. In the past, these patients may have experienced fatigue or dyspnea out of proportion to their cardiovascular disease. The Ergos rate-adaptive single- and dual-chamber pacing system is a second generation pulse generator which is rate responsive to a patient's increased physiologic demand by sensing a motion signal which reflects increased work load and the need for a compensating increase in heart rate. Ergos offers increased assistance to patients with sinus bradycardia who may require the rate-responsiveness with the additional advantage of AV synchrony. Clinical results show the effectiveness of the presented sensor control by motion energy for rate adaptive pacing therapy.

Cardiac Output↗
PubMedDate not supplied

[Analysis of myocardial evoked potentials in relation to ergometric load and heart rate for use in frequency-adaptive cardiac pacemakers].

The aim of this study was to evaluate the ventricular evoked response (VER) measured with unipolar fractally coated pacing leads for use with rate-responsive pacemakers. To this end, the morphology of the VER, its variation with pacing rate and various levels of physical loading, and the long-term stability of the signal were studied using the telemetric features of implantable pacemakers. Fractally coated electrodes were used in order to minimize the stimulation artefact, thus enabling a reliable unipolar measurement of the VER. The VER shows uniform basic morphology, and remains virtually unchanged after 3 months; moreover, frequency and load-dependent changes of VER morphology were identical for all patients. A special programming device has been developed to evaluate a rate adaptive algorithm for optimizing the pacing rate to the current loading situation, and was successfully tested in two patients. The algorithm was shown to be capable of calculating a heart rate adequate for haemodynamic demand.

Aged↗