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Biomedical subjects

J Radvan

Publications and source records attributed to J Radvan.

12 recordsLinked to original sources
PubMed1998

Isolated kidney controlled perfusion with true physiological pulsatile waveform.

A computer controlled perfusion system has been developed to study the behavior of perfused kidneys in several conditions. The system is designed to perform kidney perfusions at constant pressure and low temperature (about 4 degrees C). We compared 2 types of perfusion pumps, a classical roller pump widely used in hemodialysis circuits and a vacuum powered tubular pump with active valves developed by our group and able to produce a flow pattern very similar to the pulse wave in the human circulatory system. In this preliminary study, we show the hydrodynamics obtained with both pumps in isolated hypothermic kidneys perfused with this system. The different flow patterns with both pumps seem to determine differences in the preservation conditions of the kidney.

Animals↗
PubMed1996

Clamping stiffness and its influence on load distribution between paired internal spinal fixation devices.

The load distribution between two internal spinal fixation devices depends, besides other factors, on their stiffness. The stiffness ranges were determined experimentally for the clamps of the AO internal fixator with lateral nut and with posterior nut as well as for the clamps of the SOCON fixator. The stiffness of eight devices each differed by a factor of 3.1 for the clamp with lateral nut, by a factor of 1.5 for the clamp with posterior nut, and by a factor of 1.4 for the clamp of the SOCON fixator. For the AO clamp with lateral nut, the influence of the nut-tightening torque on the stiffness was determined. Using instrumented internal spinal fixation devices mounted to plastic vertebrae and simulating a corpectomy, the load distribution between the implants was measured for different tightening torques. It could be shown that, for the AO internal fixator whose clamps have a lateral nut, a nut-tightening torque > 5 Nm has only a negligible influence on load-sharing between the implants. Tooth damage occurs when the teeth of the clamp body and clamping jaw of the clamp with lateral nut do not gear together exactly, which leads to changes in the clamping stiffness and load-sharing between the two implants.

Humans↗
PubMed1995

Effect of aging on myocardial perfusion reserve.

UNLABELLED: Myocardial perfusion reserve (hyperemic divided by basal myocardial blood flow) describes vasodilator responsiveness of coronary-resistive vessels. The effect of aging and gender on myocardial perfusion reserve remains controversial. METHODS: We studied 56 normal volunteers (21 women, 35 men; aged 50 +/- 20 yr, range 21-86 yr) with 15O-water PET to measure myocardial blood flow during basal and hyperemic states with intravenous dipyridamole (0.56 mg/kg, n = 46) or adenosine (140 micrograms/kg/min, n = 10). For comparative analysis, patients were grouped according to age: < 30 yr (n = 11), 30-49 yr (n = 18), 50-69 yr (n = 15) and > or = 70 yr (n = 12). RESULTS: Overall, basal flow was 1.00 +/- 0.26 ml/min/g and hyperemic flow was 3.31 +/- 1.38 ml/min/g, resulting in a myocardial perfusion reserve of 3.38 +/- 1.35. There was an increase in basal flow with age (r = 0.45, p < 0.025), although hyperemic flow was only lower in patients > or = 70 yr, causing a significant reduction in myocardial perfusion reserve: 3.54 +/- 0.96 in < 30 yr, 4.23 +/- 1.35 in 30-49 yr, 3.51 +/- 1.21 in 50-69 yr and 1.94 +/- 0.46 in > or = 70 yr (p < 0.05 versus all groups < 70 yr). CONCLUSION: Myocardial blood flow during basal and hyperemia conditions are roughly comparable up to 60 yr of age. Above this age, there is significant increase in basal flow associated with an increase in systolic blood pressure. Above 70 yr, there is a significant reduction in hyperemic flow, and thus myocardial perfusion reserve independent of hemodynamic response to vasodilator stress.

Adenosine↗
PubMed1992

Defecation frequency and timing, and stool form in the general population: a prospective study.

Because the range of bowel habits and stool types in the community is unknown we questioned 838 men and 1059 women, comprising 72.2% of a random stratified sample of the East Bristol population. Most of them kept records of three consecutive defecations, including stool form on a validated six point scale ranging from hard, round lumps to mushy. Questionnaire responses agreed moderately well with recorded data. Although the most common bowel habit was once daily this was a minority practice in both sexes; a regular 24 hour cycle was apparent in only 40% of men and 33% of women. Another 7% of men and 4% of women seemed to have a regular twice or thrice daily bowel habit. Thus most people had irregular bowels. A third of women defecated less often than daily and 1% once a week or less. Stools at the constipated end of the scale were passed more often by women than men. In women of child bearing age bowel habit and the spectrum of stool types were shifted towards constipation and irregularity compared with older women and three cases of severe slow transit constipation were discovered in young women. Otherwise age had little effect on bowel habit or stool type. Normal stool types, defined as those least likely to evoke symptoms, accounted for only 56% of all stools in women and 61% in men. Most defecations occurred in the early morning and earlier in men than in women. We conclude that conventionally normal bowel function is enjoyed by less than half the population and that, in this aspect of human physiology, younger women are especially disadvantaged.

Adult↗
PubMed1987

Adult community-acquired staphylococcal pneumonia in the antibiotic era: a review of 61 cases.

We have reviewed the clinical and laboratory features of 61 cases of adult community-acquired staphylococcal pneumonia. A seasonal incidence was found and most cases occurred in April. Clinical and laboratory features were similar to those found in other forms of community-acquired pneumonia. Sputum Gram-stain was positive for staphylococci in 69 per cent of cases and blood cultures were positive in 20 per cent. Evidence of Influenza virus infection was found in 52 per cent of cases. Eighteen patients died (30 per cent). Age greater than 45 years, confusion, reduced conscious level, raised blood urea, acidosis, bacteraemia and admission to the intensive care unit were associated significantly with death. Despite appropriate antibiotic treatment mortality in staphylococcal pneumonia remains high.

Adolescent↗
PubMedDate not supplied

Evaluation of the extent and timing of the coronary hyperemic response to dipyridamole: a study with transesophageal echocardiography and positron emission tomography with oxygen 15 water.

Coronary flow reserve may be measured with Doppler-derived coronary blood-flow velocity or scintigraphic assessment of myocardial perfusion. The purpose of this study was to compare coronary flow velocity and perfusion measures of flow reserve with respect to their extent and time course. Coronary flow velocity reserve in the proximal left anterior descending coronary artery measured by pulsed-wave Doppler at transesophageal echocardiography, with measures of perfusion reserve obtained in the corresponding territory, were measured by a standard O15 water technique at positron emission tomography. Eighteen male volunteers underwent both tests on different days in random order, with dipyridamole stress (0.56 mg/kg). After correction of resting flow and perfusion measurements to a standard cardiac workload (to compensate for heterogeneity in hemodynamics between the two studies), coronary flow reserve was calculated as the ratio between dipyridamoleand corrected resting flow. The uncorrected perfusion reserve measured by positron emission tomography was 3.7 +/- 1.2, compared with a corrected perfusion reserve of 2.3 +/- 0.7. This correlated with a corrected flow velocity reserve of 2.9 +/- 1.0 at transesophageal echocardiography (R = 0.92; p < 0.001). The mean difference between these results was 0.58 +/- 0.41; discrepant results occurred at higher flows, in the presence of discordant blood pressure responses to stress, and because of intersubject variations in the timing of the peak coronary flow response, which were detected by continuous monitoring at transesophageal echocardiography. Measurement of coronary flow reserve at transesophageal echocardiography correlates well with measurements at positron emission tomography, and discrepancies are minimized if measurements are taken at the same time after dipyridamole.

Adult↗