Biomedical subjects

J Heller

Publications and source records attributed to J Heller.

At least 127 records · Page 7Linked to original sources

PubMed1994

Ventilatory threshold and work efficiency during exercise on cycle and paddling ergometers in young female kayakists.

The aim of this study was to assess the effects of increasing specific (paddling ergometer) and non-specific (cycle ergometer) exercise on parameters relating to the ventilatory threshold (Th(vent)) and work efficiency in 11 young female flat-water kayakists. When these trained subjects were tested using non-specific workloads, their oxygen uptake (VO2) values at Th(vent), as a percentage of VO2max (%VO2max), were close to those of untrained subjects [74.2 (5.6) % VO2max, mean (SD)]. However, when we tested the same subjects using specific exercise, we recorded values typical of highly trained athletes [84.8 (4.7) % VO2max). For the non-specific exercise on the cycle ergometer, we recorded work efficiency values close to those of untrained subjects [22.3 (2.5) %]; however, for the specific exercise on the paddling ergometer, we recorded much lower values [13.4 (3.0) %] both at the level of Th(vent). The work efficiency at two warm-up submaximal exercise loads on the paddling ergometer was non-significantly lower than values at Th(vent) [12.3 (2.8) % and 12.9 (2.9) % respectively]. Significant correlations were found between maximal-performance VO2 (ml.kg-1.min-1) and performance at Th(vent) during paddling and race performance (0.623, 0.630 and 0.648 respectively, all P < 0.05). Because the results of both specific and non-specific submaximal exercise tests are different, we suggest caution in the interpretation of physiological variables that may be sensitive to training status. The evaluation of Th(vent) and work efficiency as supplementary parameters during laboratory studies enables the determination of the effectiveness of the training process and the specific adaptation of the subjects.

Adaptation, Physiological↗

PubMed1994

Gamma sterilization of a semi-solid poly(ortho ester) designed for controlled drug delivery--validation and radiation effects.

Radiation sterilization is becoming increasingly popular for the sterilization of many pharmaceutical products. Although this technique is not limited to the sterilization of polymers, it is probably the most suitable method for such materials. This method however suffers several drawbacks. The sterilization of a product must lead to a safety level of 10(-6), i.e. one chance in a million to find a contaminated sample. In many cases, this assurance of sterility can be achieved by using a uniform treatment dose of 2.5 Mrad, recommended by the pharmacopeia. We investigated the possibility of using doses of radiation inferior to 2.5 Mrad to sterilize a semi-solid poly(ortho ester) (POE) developed for use as carrier in controlled drug delivery. After determination of the initial bioburden, the polymer was intentionally contaminated with the bioindicator Bacillus pumilus E 601. Following exposure to gamma irradiation, the D10 value of the radio resistant bioindicator was determined. Using the initial contamination value, the reduction factor D10 and the safety level, it is possible to calculate an optimal sterilizing dose for POE. All polymers are affected by ionizing radiation and the amount of radiation which produces a significant change in properties may vary from one polymer to the other. A molecular weight and dynamic viscosity decrease resulting from backbone cleavage was observed for this POE at a dose lower than 2.0 Mrad. Evaluation of the structure using 1H-NMR, 13C-NMR and IR analysis shows that for doses higher than 2.0 Mrad, another degredation process takes place.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗

PubMed1994

Energy cost of running in young and adult female athletes.

Maximal oxygen uptake (VO2 max.kg-1) and energy cost of running were determined on the treadmill in groups of differently trained young and adult athletes. The VO2 max.kg-1 was in all cases higher in adults than in young athletes. These differences were significant (p < 0.05) in long-distance runners (n = 12, mean age = 24.2 +/- 2.2 vs 17.3 +/- 0.9 yrs, mean VO2 max.kg-1 = 66.9 +/- 4.2 vs 58.2 +/- 4.3 ml.min-1.kg-1), and in middle-distance runners (10, 22.9 +/- 2.8 vs 16, 16.6 +/- 0.8, 62.3 +/- 3.7 vs 56.1 +/- 2.8); in canoeists these differences were non-significant (7, 21.1 +/- 2.1 vs 16.0 +/- 2.3 vs 8, 48.2 +/- 2.6). Values of energy cost of running--coefficients of energy demand of running c, which indicates how much energy is required to transfer 1 kg of body mass on a distance of 1 m--were lower in adult athletes than in young athletes. These differences were significant (p < 0.05) only in long-distance runners (3.69 +/- 0.15 vs 3.84 +/- 0.14 J.kg-1.m-1). In middle-distance runners (3.67 +/- 0.19 vs 3.76 +/- 0.18), and in canoeists (3.84 +/- 0.14 vs 3.86 +/- 0.18) these differences were non-significant. It is concluded that the differences in energy cost of running between trained adult and young female athletes are probably associated with differences in adaptation to the running, and with the technique of movement. Differences in running speed (sports performance) between adult and young athletes are associated with differences in VO2 max.kg-1 and c.

Adolescent↗

PubMed1993

Visual evoked potentials in adrenoleukodystrophy: a trial with glycerol trioleate and Lorenzo oil.

Adrenoleukodystrophy is an X-linked metabolic disorder with very-long-chain fatty acid (VLCFA) accumulation and multifocal nervous system demyelination, often with early involvement of visual pathways. Dietary therapy with glycerol trioleate and glycerol trierucate (Lorenzo oil) diminishes VLCFA levels. In a study of patients with the adrenomyeloneuropathy phenotype of adrenoleukodystrophy, we used pattern-reversal visual evoked potentials to evaluate visual pathways before and after treatment. Of 108 patients tested, all 26 women and 68 of the 82 men had normal potentials at baseline. Seventy patients were retested at 1 year, at which time VLCFA levels were markedly diminished. Of them, the responses in the 10 men who showed abnormalities at baseline remained abnormal; the latencies in 4 men with initially normal responses became abnormal. No patients improved. There were no correlations between disease duration prior to treatment, baseline P100 latencies, VLCFA levels, or the change in P100 latencies and VLCFA levels after dietary treatment for 1 year. Pattern-reversal visual evoked potentials were abnormal in 17% of the men with adrenoleukodystrophy, and there was no evidence that reduction of VLCFA levels improved or retarded visual pathway demyelination.

Adolescent↗

PubMed1993

Biotolerance of a semisolid hydrophobic biodegradable poly(ortho ester) for controlled drug delivery.

We evaluated the biotolerance of a new semisolid poly(ortho ester) (POE) intended for controlled drug delivery. Two different investigations were carried out in rats: subcutaneous injections and the cage-implant system. Sodium hyaluronate (SH), 1%, in phosphate buffer was used as a noninflammatory control. When injected subcutaneously in rats, the POE induced a mild and local inflammation at 3 and 7 days followed by a minimal chronic inflammation at 14 and 21 days. When using the cage-implant system, we quantified the inflammatory components of the exudate surrounding the implanted material within the cage system at 3, 7, 14, and 21 days. The total leukocyte and macrophage concentrations were higher only at 7 days for both SH and POE compared to the control (empty cage). The other parameters were not significantly different from the control. These results show that POE is well-tolerated by rats when used subcutaneously.

Animals↗

PubMed1993

Relative utilization of reptiles and rodents as hosts by immature Ixodes scapularis (Acari: Ixodidae) in the coastal plain of North Carolina, USA.

The interaction of immature black-legged ticks, Ixodes scapularis, with reptiles and rodents was investigated in various woodland habitats in the coastal plain of North Carolina. Reptiles were sampled from April 1 to September 30, 1991. No ticks were found on 95 specimens representing 16 species of snakes. Ticks were found on 54 (36.7%) of 147 lizards. I. scapularis was the only tick recovered from lizards. Some lizards were collected in drift fence traps each month of the study except August. Capture rates averaged one lizard per 16 trap-days. Larvae and nymphs of I. scapularis were removed from the southeastern five-lined skink (Eumeces inexpectatus), the ground skink (Scincella lateralis), the broad-headed skink (E. laticeps) and the eastern glass lizard (Ophisaurus ventralis), but ticks were not found on three other lizard species. Tick infestation rates and loads for parasitized species are presented. Ticks were almost exclusively attached at the base or in the axils of forelimbs of skinks and in the lateral grooves of eastern glass lizards. Rodents were live-trapped at sites where lizards were sampled and at other sites from 1 July, 1990 to 30 January, 1992. Capture rates averaged one rodent per 47 trap-nights. Ticks were found on 23 (17.8%) of 129 animals inspected. Five species of rodents were examined but only four species were found to be tick-infested. In contrast to lizards, few I. scapularis were collected. Rodents, principally the white-footed mouse (Peromyscus leucopus) and cotton mouse (P. gossypinus) were most frequently infested with immature American dog ticks, Dermacentor variabilis, during winter and early spring months. Burdens of D. variabilis on these rodents averaged 0.3 ticks per rodent. Effects of the diversion of ticks from feeding on Peromyscus mice on the transmission of the Lyme disease spirochete are discussed.

Animals↗

PubMed1993

The role of the kidney in the development of hypertension: a transplantation study in the Prague hypertensive rat.

It has been shown that genetic hypertension in rats usually "travels with the kidney". To elucidate the mechanism of this phenomenon further, experiments were carried out in the Prague hypertensive (PH) rat, a model of genetic hypertension derived from the Wistar strain, in which a normotensive parallel, the Prague normotensive (PN) rat, was also bred from the same parent pair. Thus, it is possible to transfer organs between both parallels without substantial signs of rejection and without the use of immunosuppressive drugs. Unilateral nephrectomy and transplantation of one kidney between PH and PN rats, did not affect the arterial blood pressure (BP). Transplantation of one kidney from PN rats to bilaterally nephrectomised PH rats normalised the high BP. If a PH rat was left with one original kidney in situ after the transplantation of a "normotensive" kidney, the high BP persisted until the original "hypertensive" kidney was removed. This removal resulted in sustained normalisation of BP. When the development of high BP in the PH rats was prevented for 2 months after weaning by antihypertensive drugs, transplantation of kidneys from these rats to bilaterally nephrectomised PN rats always induced a sustained hypertension in the recipient. These results argue against a role of high-BP-induced damage to the kidney and against an intrinsic increase in the salt-reabsorptive capacity of the tubular epithelium in PH rats. The data support the view that the kidney from PH rats produces a "hypertensinogenic" substance, the secretion of which is genetically determined and is not influenced by the magnitude of the BP.

Animals↗

PubMed1993

A morphine-triggered delivery system useful in the treatment of heroin addiction.

The ultimate objective of this work is to develop a device that can be triggered by morphine to release naltrexone. Two device configurations are described. In one configuration, naltrexone is dispersed in cellulose acetate phthalate microspheres which are then spray-coated with trilaurin. In the other configuration, naltrexone is dispersed in an n-octyl half ester of methyl vinyl ether and maleic anhydride copolymer and the mixture fabricated into a disk which is then coated with trilaurin. The microspheres are designed to release naltrexone abruptly while the disks are designed to release naltrexone at a constant rate over a two week period. The microspheres, or the disk along with a reversibly inactivated lipase are placed inside a semipermeable membrane that allows free passage of morphine and naltrexone but excludes the higher molecular weight components of the device. Reversible inactivation of lipase is achieved by covalent attachment of morphine and complexing with morphine antibody. Activation of the device occurs by diffusion of morphine into the device and displacing the lipase-morphine conjugate from the antibody. The activated lipase then removes the trilaurin protective coating, thus triggering naltrexone release.

Biodegradation, Environmental↗

PubMed1993

Age-dependent differences in the effect of ischaemia on the rat kidney: prevention of the postischaemic damage by different drugs.

The acute and subchronic effects of temporary renal ischaemia (45 min) were investigated in one- and two-month old rats. During bilaterial occlusion of renal arteries, the systemic blood pressure (BP) decreased from 90 to 55 and from 100 to 75 mmHg in one- and two-month old rats, respectively. Immediately after reperfusion, BP returned to the baseline level. This temporary drop in BP was prevented by continuous infusion of normal saline, dopamine, or mannitol. However, postischaemic lethality was very similar in all groups (45% in young and 28% in adult rats). An increase in blood urea concentration was observed only 24 hours after the ligation procedure. However, the rats died within 4 postischaemic days often without an elevation in blood urea. Different treatment schedules (infusion of normal saline, dopamine, and mannitol, bolus injection of dimethyl sulfoxide /DMSO/, mannitol, or furosemide, 7-day treatment with thiamazole) were compared. Lethality was reduced only by thiamazole in young rats (45% vs 11%, p < or = 0.01). No ammelioration was seen in adult rats; the lethality was increased in these rats after furosemide (28% vs 73%, p < or = 0.01). The increase in blood urea concentration regularly observed in all rats 24 hours after ischaemia, was lower in all treated groups of young rats except dopamine. In adults, only saline infusion ammeliorated this increase; on the other hand furosemide led to a higher increase than in untreated controls. Saline infusion, DMSO, mannitol, furosemide, and thiamazole treatment are all partially protective in young rats.

Aging↗

PubMed1993

Synthesis and characterization of a new biodegradable semi-solid poly(ortho ester) for drug delivery systems.

Since the late 1970s, three families of poly(ortho esters) (POE) were synthesized to provide bioerodible carriers for drug delivery devices. The most recent POE is a semi-solid polymer with a viscous behavior at room temperature. Polymer synthesis by a transesterification reaction between a triol and a trialkyl ortho ester is described. The structure of the polymer was confirmed by conventional methods such as 1H-NMR, 13C-NMR and FT-IR. Information concerning average molecular weight and intrinsic viscosity was obtained respectively by GPC and viscosimetry. Residual solvents in the polymer were determined using gas chromatography. The chromatographic conditions were optimized to enable the quantification of the solvents in concentrations of a few percent. The mechanical behavior of the semi-solid POE was determined by rheometric measurements. Hydrolysis of the polymer leads to the formation of the original triol and the carboxylic acid derived from the trialkyl ortho ester used in the transesterification step. No toxicological problems associated with these compounds are anticipated.

Biodegradation, Environmental↗

PubMed1993

The Prague Hypertensive Rat: a new model of genetic hypertension.

Several animal models of genetic hypertension have been developed but not all of them possess a closely related control strain. Therefore, a new model based on Wistar rats is described in which both hypertensive and normotensive lines were bred from a single parental pair. Several basic data on the two lines (called the Prague Hypertensive Rat, PHR, and the Prague Normotensive Rat, PNR) are given. PNR had a longer survival compared with PHR. At the age of 7 weeks, systolic blood pressure was 161 +/- 14 mmHg in PHR males and 109 +/- 9 mmHg in PNR males. Its further increase with age was very slow in PNR but very steep in PHR. Typical left ventricular cardiac hypertrophy developed in PHR in which cardiac output was not significantly different from that of PNR but total peripheral resistance was higher. Kidney weight was also greater in PHR than in PNR. There was no difference in basic renal functions except of proteinuria which was higher in PHR than in PNR. No differences were observed in extracellular and interstitial fluid volumes whereas plasma and blood volumes were slightly but significantly greater in PHR than in PNR suggesting a shift of extracellular fluid towards the intravascular compartment. This hypertensive model the parameters of which resemble to those of human essential hypertension should be especially suitable for cross-transplantation studies.

Animals↗

PubMed1993

Ventilatory threshold in young and adult female athletes.

We determined in a laboratory on the treadmill the ventilatory threshold in relatively similarly trained groups of young and adult female athletes (14 adult long-distance runners mean age = 24.3 +/- 2.3 yrs; mean VO2max.kg-1 = 66.9 +/- 4.2 ml.kg-1.min-1; 11 adolescents 16.3 +/- 0.9; 58.4 +/- 4.4; 10 adult middle distance runners mean age = 22.9 +/- 2.9 yrs and VO2max.kg-1 = 62.3 +/- 3.7 ml/kg-1/min-1; 16 juniors 16.6 +/- 0.8 and 15.1 +/- 2.8; 7 adult canoeists 21.1 +/- 2.1 and 50.0 +/- 2.9; 8 adolescents 16.0 +/- 0.9 and 48.2 +/- 2.6). Maximal blood lactate concentration was found in all groups slightly lower in young athletes than in adults (in long-distance runners 10.9 +/- 2.6 vs 11.4 +/- 3.2 mmol.l-1; in middle-distance runners 12.4 +/- 2.3 vs 12.7 +/- 2.9; in canoeists 11.8 +/- 3.3 vs 12.1 +/- 3.6). The differences in maximal blood lactate concentration were nonsignificant in all groups. We did not find any significant differences in percentage of maximal aerobic power on the ventilatory threshold level. In long-distance runners the mean value of % VO2max at AT was 85.1 +/- 3.8% for adults and 84.9 +/- 2.7% for adolescents, in middle-distance runners 82.9 +/- 2.1% and 82.6 +/- 3.2%, respectively, and in adult canoeists 79.9 +/- 2.6%, and in juniors 79.4 +/- 3.0%. According to these results we can conclude that the physical activity and/or level of physical fitness seem to be main factors which may influence the values of % VO2max at VT during the growth.

Adolescent↗

PubMed1993

Modulated release from drug delivery devices.

Modulated drug release devices are devices that are capable of adjusting drug output to meet a physiological need. Such devices can be broadly grouped as externally modulated and self-modulated. In the former case, an externally generated signal is applied to the device, which then adjusts drug output in response to the intensity of the signal. In the latter case, the changes in drug release are caused by changes in the environment surrounding the polymer and no external signal is necessary. Because of the real need for an improved treatment of diabetes, a significant portion of the research currently under way deals with the modulated release of insulin.

Administration, Cutaneous↗

PubMed1992

The influence of weight reduction and exercise regimes upon the personality profiles of overweight males.

In the present study, the MMPI was used to detect personality changes in 53 overweight, yet otherwise healthy, males who were participating in either a weight reduction or an aerobic exercise conditioning program. Analysis of pre- and post-intervention scores revealed that only the participants in the aerobic conditioning group demonstrated the predicted desirable psychological changes. More specifically, this group displayed significant clinically desirable changes on the Hs, PD, and HEA scores. Similar to the weight loss participants, a demographically matched nonintervention comparison group showed none of these desirable changes and actually yielded a significant increase on the D scale. However, when compared to this "normal" group, both intervention programs showed statistically significant differences on at least two MMPI scales.

Age Factors↗

PubMed1992

Biocompatibility and mechanical properties of a totally absorbable composite material for orthopaedic fixation devices.

Bioabsorbable polymer/inorganic phosphate fiber composites are prone to rapid degradation due to water sensitivity of the interface between the degradable polymer and the degradable fiber. This article describes successful fabrication and laboratory evaluation of a candidate bioabsorbable composite implant material with mechanical properties similar to bone. The composite studied was poly(ortho ester) reinforced with randomly-oriented, crystalline microfibers of calcium-sodium-metaphosphate. The component materials showed no acute cytotoxicity as determined by tissue culture agar overlay. Treating the microfibers with a diamine-silane coupling agent improved mechanical properties and slowed degradation in saline, but strength still decreased 50% in 1 week. When the composite material was then coated with a layer of matrix polymer alone it retained 70% of its strength and 70% of its stiffness after 4 weeks exposure to 7.4 pH Tris-buffered saline at body temperature. The marked improvement with the coating can be attributed to the hydrophobicity of poly(ortho esters).

Biodegradation, Environmental↗

PubMed1992

The effect of lipase on the release of naltrexone from triglyceride-coated cellulose acetate phthalate microspheres.

The ultimate objective of this work is to develop a device that can be triggered by morphine to release naltrexone. In this device, naltrexone is dispersed in cellulose acetate phthalate microspheres which are then spray-coated with a trilaurin protective coating. The microspheres are contained within a macroporous cylinder which also contains a reversibly inactivated lipase. This enzyme in its inactive state is unable to remove the protective coating but in its active state is able to do so. Inactivation is achieved by the covalent attachment of morphine followed by complexation with a morphine antibody. Triggering is accomplished by the displacement of the lipase-morphine conjugate from the antibody. In this phase we have investigated the effect of lipase on the release of naltrexone from trilaurin-coated microspheres and found that the coated microspheres are stable in a pH 7.4 phosphate buffer at 37 degrees C for at least 1 month, but release 80% of the incorporated naltrexone in one hour when 100 mg of capsules in 5 mL buffer are exposed to 25 micrograms of lipase.

Biocompatible Materials↗

PubMed1991

[Conversion of the intensity of loading from the bicycle ergometer to a treadmill and to field training in women].

When evaluating the standard of functional fitness, state of training or work capacity of subjects, when diagnosing loads, when assessing training of healthy subjects and sportsmen and locomotor rehabilitation of patients usually two types of ergometers are used--a pedalling ergometer and a treadmill. Each of these ergometers has its specific properties, advantages and shortcomings. For the practical use of results of functional examination in the laboratory, where the majority of our diagnostic departments possesses only a pedalling ergometer it is necessary to convert the load intensity from the bicycle to a treadmill and to the field where physical training is usually implemented. Based on our measurements in groups women with different grades of training, differing as to age, it is possible to elaborate a general equation which relates the load intensity on the pedalling ergometer P/W.kg-1 and the speed of running on the treadmill with a zero gradient v/km.h-1 in the form v = 3,695.P-1,419. This relationship can be used with an error of cca 12% in the zone of submaximal load intensities (up to 90% of the maximal load intensity). For P lower than 3.9 W.kg-1 this equation can be used for direct conversion to flat ground. For higher load intensities there is the relationship v = 3,156.P + 0.446 which has the same error of 12% as for even ground.

Adolescent↗

PubMed1991

[Energy requirements in women during pedalling on a bicycle ergometer].

The bicycle ergometer is the most frequently used equipment for loading tests for the purpose of functional diagnosis and for the purpose of locomotor rehabilitation. The energy required to meet this locomotor activity is within a wide range of load intensities which depends linearily on the intensity of pedalling. The steepness of this linear relationship which characterizes the degree of adaptation of the organism to this type of locomotor activity is the smaller the more the investigated subjects are adapted to the load. In general it depends on the degree of training, age, sex, strength, pedalling frequency, on the load protocol and on the biomechanical conditions during pedalling (e.g. the height of the saddle). Based on our measurements in a group of untrained women of different age and in trained women of different age it can be demonstrated that all individual relations between energy characterized by means of VO2 and the intensity of the load - P is within the zone where the upper borderline is formed by the equation VO2(ml) = 11.00.P (W) + 403 and the lower borderline by VO2(ml) = 9.90.P (W) + 252. The basic relationship, independent on the degree of training, age and strength, valid in the zone of pedalling frequencies of 60-80 rot. min-1 and in the zone of load intensities of 75-325 W has the shape of VO2(ml) = 10.60.P(W) + 269. The maximum error of assessment of VO2 by means of the load intensity is 9% or less.

Adolescent↗