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Biomedical subjects

C Stick

Publications and source records attributed to C Stick.

At least 19 recordsLinked to original sources
PubMed2000

Monitoring of environmental UV radiation by biological dosimeters.

As a consequence of the stratospheric ozone layer depletion biological systems can be damaged due to increased UV-B radiation. The aim of biological dosimetry is to establish a quantitative basis for the risk assessment of the biosphere. DNA is the most important target molecule of biological systems having special sensitivity against short wavelength components of the environmental radiation. Biological dosimeters are usually simple organisms, or components of them, modeling the cellular DNA. Phage T7 and polycrystalline uracil biological dosimeters have been developed and used in our laboratory for monitoring the environmental radiation in different radiation conditions (from the polar to equatorial regions). Comparisons with Robertson-Berger (RB) meter data, as well as with model calculation data weighted by the corresponding spectral sensitivities of the dosimeters are presented. Suggestion is given how to determine the trend of the increase in the biological risk due to ozone depletion.

Bacteriophage T7↗
PubMed1993

Volume changes in the lower leg during quiet standing and cycling exercise at different ambient temperatures.

The purpose of this study was to investigate whether ambient temperature influences both the rate of leg swelling during orthostasis and the oedema-preventing effect of the skeletal muscle pump. Using mercury-in-rubber strain gauges, volume changes were measured in the calf (n = 34) and near the ankle (n = 24) in healthy volunteers aged 19-33 years. Measurements were performed during 12 min of motionless standing in an upright posture and during 17 min of cycle exercise at intensities of 50 W and a pedalling rate of 50 rpm. The experiments were done in an air-conditioned chamber at temperatures of 20, 28 and 36 degrees C and 50% relative humidity. The rate of leg swelling, which occurred while standing, did not differ significantly among the three temperatures. The mean increases in calf volume during 10 min (min 2-12) orthostasis were 1.6 (SEM 0.1)%, 1.9 (SEM 0.2)% and 2.0 (SEM 0.2)% at 20, 28 and 36 degrees C respectively. In the ankle region the mean values were 0.9 (SEM 0.1)%, 1.0 (SEM 0.1)%, and 1.0 (SEM 0.1)% at the three temperatures, respectively. Exercising at low temperatures continuously reduced the volume of the leg, but at 36 degrees C the leg volume did not change significantly either at the calf or near the ankle. The mean volume changes measured between min 2 and min 15 were, at the calf, -1.1 (SEM 0.1)%, -0.8 (SEM 0.2)%, and -0.02 (SEM 0.1)% at 20, 28 and 36 degrees C, respectively. Near the ankle the mean changes were -0.7 (SEM 0.1)%, -0.3 (SEM 0.1)%, and +0.2 (SEM 0.1)%.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Venous pressure in the saphenous vein near the ankle during changes in posture and exercise at different ambient temperatures.

The venous pressure in the saphenous vein at the ankle was measured in ten healthy subjects (5 men, 5 women) aged 19-33 years during supine posture, orthostasis and cycle ergometer exercise (50 W, 50 rpm). Measurements were made at 20, 28 and 36 degrees C at 50% relative humidity. A custom-built setup consisting of two pressure transducers and a differential amplifier was used to compensate for the hydrostatic effects, temperature influences and movement artefacts that disturbed the pressure measurements. Pressure was lowest in the supine position and varied only slightly with the ambient temperature. The mean pressures were 7 (SEM 1) mmHg [0.9 (SEM 0.13) kPa], 7 (SEM 1) mmHg [0.9 (SEM 0.13) kPa], 4 (SEM 1) mmHg [0.5 (SEM 0.13) kPa] at 20, 28 and 36 degrees C. The venous pressure increased when the subjects were passively tilted from a supine to an upright posture. The rate of the increase was smaller at 20 degrees C than at 28 degrees and 36 degrees C. The final level the pressure reached during motionless standing differed slightly. The mean pressures were 76 (SEM 2) mmHg [10.1 (SEM 0.27) kPa], 79 (SEM 7) mmHg [10.5 (SEM 0.93) kPa] and 75 (SEM 3) mmHg [10.0 (SEM 0.40)] at the three temperatures. When starting exercising, venous pressure decreased within the 1st min to a level which remained virtually constant until the end of exercise. However, this level was found to be temperature dependent. It was lowest at 20 degrees C (26 (SEM 3) mmHg [3.5 (SEM 0.40) kPa]) and increased with temperature.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Measurements of volume changes and venous pressure in the human lower leg during walking and running.

This study investigates whether walking or running prevents the formation of edema in the lower leg. In 18 volunteers changes in calf volume were measured using strain gauge plethysmography during slow (3 km/h) and fast (6 km/h) walking or running (10 km/h) on a treadmill for 20 min each. Venous pressure was measured in a superficial vein near the ankle. Low-pass filtering removed motion artifacts from the signals. Slow walking reduced the calf volume in a biphasic manner: a rapid decrease was followed by a slow decline, lasting from about minute 2 to minute 20, its mean rate being -0.073%/min. Besides a rapid initial decrease, no significant change was observed during fast walking. During running, the calf volume first increased within 7 min to a maximum of 2.5% and subsequently decreased with a mean rate of -0.096%/min. The medians of venous pressure were 84.0, 23.5, 30.4, and 29.5 mmHg during quiet standing, slow and fast walking, and running, respectively. The experimental results prove the hypothesis that walking prevents dependent edema formation. This effect, however, cannot be fully explained by the lowered venous pressures.

Adult↗
PubMed1991

[Do strong static magnetic fields in NMR tomography modify tissue perfusion?].

Findings obtained in humans and test animals raised the question whether strong static magnetic fields as used in NMR-tomography may affect tissue perfusion. In two test series including 20 subjects, each skin blood flow at the thumb was determined by heat clearance, and forearm blood flow was measured by venous occlusion plethysmography. For comparative purposes, measurements were carried out bilaterally at both extremities. The experiments consisted of three sections that lasted 10 min each. During the second section the thumb or the forearm were unilaterally exposed to magnetic fields of 0.9 to 1 T and 0.4 to 0.5 T, respectively. The results of this section were compared with the values obtained during the experimental sections prior to and after the exposure to the magnetic field. The results were also compared with the blood flow measured at the contralateral extremity. Neither at the skin of the thumb nor at the forearm were there changes in local blood flow attributable to the magnetic fields applied.

Adult↗
PubMed1990

Slow volume changes in calf and thigh during cycle ergometer exercise.

To study the transcapillary fluid movements in the human lower limb in the upright body position and during muscle exercise, the slow changes in thigh and calf volumes were measured by mercury-in-rubber-strain gauge plethysmography. Measurements were carried out on 20 healthy volunteers while sitting, standing and doing cycle ergometer exercise at intensities of 50 and 100-W. A plethysmographic recording of slow extravascular volume changes during muscle exercise was possible because movement artefacts were eliminated by low-pass filtering. While standing and sitting the volumes of both thigh and calf increased due to enhanced transcapillary filtration. While standing the mean rate of increase was 0.13%.min-1 in the calf and 0.09%.min-1 in the thigh. During cycle ergometer exercise at 50 and 100 W, the calf volume decreased with a mean rate of -0.09.min-1. In contrast, the thigh volume did not change significantly during exercise at 50 W and increased at 100 W. Most of the increase occurred during the first half of the experimental period i.e. between min 2 and 12, amounting to +0.6%. Thus, simultaneous measurements revealed opposite changes in the thigh and calf. This demonstrates that the conflicting findings reported in the literature may have occurred because opposite changes can occur in different muscle groups of the working limb at the same time. Lowered venous pressure, increased lymph flow and increased tissue pressure in the contracting muscle are considered to have caused the reduction in calf volume during exercise.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

On the edema-preventing effect of the calf muscle pump.

During motionless standing an increased hydrostatic pressure leads to increased transcapillary fluid filtration into the interstitial space of the tissues of the lower extremities. The resulting changes in calf volume were measured using a mercury-in-silastic strain gauge. Following a change in body posture from lying to standing or sitting a two-stage change in calf volume was observed. A fast initial filling of the capacitance vessels was followed by a slow but continuous increase in calf volume during motionless standing and sitting with the legs dependent passively. The mean rates of this slow increase were about 0.17%.min-1 during standing and 0.12%.min-1 during sitting, respectively. During cycle ergometer exercise the plethysmographic recordings were highly influenced by movement artifacts. These artifacts, however, were removed from the recordings by low-pass filtering. As a result the slow volume changes, i.e. changes of the extravascular fluid were selected from the recorded signal. Contrary to the increases during standing and sitting the calf volumes of all 30 subjects decreased during cycle ergometer exercise. The mean decrease during 18 min of cycling (2-20 min) was -1.6% at 50 W work load and -1.9% at 100 W, respectively. This difference was statistically significant (p less than or equal to 0.01). The factors which may counteract the development of an interstitial edema, even during quiet standing and sitting, are discussed in detail. During cycling, however, three factors are most likely to contribute to the observed reduction in calf volume: (1) The decrease in venous pressure, which in turn reduces the effective filtration pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1988

On the efficacy of various irradiation regimens in phototherapy of neonatal hyperbilirubinaemia.

The efficacy of various irradiation regimens in phototherapy of neonatal hyperbilirubinaemia was analysed. One hundred and one newborns were assigned to three groups at random. The best results were achieved when six special blue fluorescent lamps were used and the sides of the incubator were draped with white cloth to reflect the light diffusely. This simple measure increased the therapeutic effect by approx. 35%. Compared to standard phototherapy units equipped with fluorescent lights, a halide lamp was no more effective. The results of the clinical trial confirm the conclusions drawn from measurements, published previously. According to those findings, irradiating large areas of skin as homogeneously as possible should produce optimum results. Using a lamp with a large surface in combination with diffusely reflecting areas should best meet this requirement.

Bilirubin↗
PubMed1986

[Dermatitis solaris in newborn infants following phototherapy with a halogenide radiation unit].

Two cases of dermatitis solaris in newborns after phototherapy with a halide burner gave reason to measure the UV-B radiation emitted by the instrument used. Values between 0.8 microW/cm2 and 1.8 microW/cm2 were found. In small areas under the lamp housing the intensities of the UV-B radiation reached up to 10 microW/cm2. These high intensities are caused by the design of the lamp housing. Especially in connection with aluminium foil used to increase the efficacy of the therapy skin leasons as described may be produced.

Bilirubin↗
PubMed1985

The distribution of radiant power in a phototherapy unit equipped with a metal halide lamp.

The effective radiant power of a metal halide lamp for phototherapy of neonatal jaundice was measured in an incubator. This new lamp is characterised by an extremely heterogeneous field of irradiance with a high intensity in the centre and a marked decrease towards the sides. The mean radiant intensity in a central area (20 X 40 cm) of the incubator can be compared with the values achieved with standard fluorescent lamps in an incubator lined with white cloth. As the field of irradiance is more homogeneous in the latter case, advances in therapy are not to be expected from the use of metal halide lamps in their present form.

Humans↗
PubMed1985

On physiological edema in man's lower extremity.

To examine whether the so-called musculovenous pump counteracts the development of interstitial edema in the lower extremities of man in the upright position, the volume changes in the calf which occurred during twenty minutes of rhythmic muscular exercise were measured in twenty-three subjects by impedance-plethysmography. The results were compared with the volume increase found during quiet relaxed standing for the same length of time. Contrary to the hypothesis, and edema-protective effect of the musculovenous pump could only be shown in about half the number of the subjects. In the others, muscular exercise led to increases in calf volume which were higher than those measured in the normal upright position. These results show that the calf muscle pump does not generally have a edema-protective effect but rather that muscle contractions also activate mechanisms which stimulate the extravasation of fluid. In a second test-series with twenty subjects, changes in calf volume were measured during the course of the day. In nearly all cases, the calf volume was greater in the evening than in the morning. It could be shown that the volume increases in the evening are caused by an increase in extravascular fluid. Compared to the increase in extravascular volume occurring during twenty minutes, in a normal upright position, the accumulation of extravascular fluid during the day is, however, remarkably low. Although it is still unknown how interstitial edema in man's lower extremities is prevented during the day, these findings lead to the hypothesis that the edema-preventing mechanisms, for instance the muscle-lymphpump, do not become maximally effective until a certain volume has accumulated in the interstitial space.

Adult↗
PubMed1984

On the distribution of irradiation intensity in phototherapy. Measurements of effective irradiance in an incubator.

Knowledge of the effective irradiation dose is a prerequisite to predicting the efficacy of phototherapy. To gain this information, the field of irradiation of a phototherapy lamp was measured in an incubator. It became apparent that the radiant power is extremely heterogeneously distributed in the incubator. By decreasing the distance from the lamps, the radiant power is increased, with the heterogeneity of irradiation growing considerably at the same time. Lining the incubator with reflecting cloth results in a greater homogeneity of the field of irradiance and an increase in radiant power. Moreover, the lining causes a doubling of the indirect reflected radiance. The findings presented here are discussed in view of their importance for doses in phototherapy. It can be concluded that to increase the efficacy of phototherapy, lining the incubator with reflecting cloths is a more effective measure than moving the patient closer to the lamp.

Dose-Response Relationship, Radiation↗
PubMed1984

[A simple measuring device for monitoring radiation in phototherapy].

A simple low cost device is described for measuring the irradiation intensity used in phototherapy of hyperbilirubinemia in newborns. The spectral selectivity of the sensor is adapted to the most effective wavelength for phototherapy. The device can be calibrated in W/m2. A description of calibration is given. When fluorescent lamps adapted to phototherapy are used, the accuracy of the device can be compared to that of commercially manufactured units. The sensitivity is sufficient to measure differences of irradiance significant for the therapy. The device is suitable to quantify phototherapy of the newborn infant suffering from hyperbilirubinemia.

Humans↗
PubMed1981

[Transthoracic electrical impedance (author's transl)].

The measurement of transthoracic impedance is used by many authors to determine tidal volume and changes of intrathoracic fluid volume. In clinical diagnostics, too, this method has been introduced. Furthermore, the stroke volume of the heart is often said to be calculable from changes in impedance synchronous with the cardiac cycle. This paper investigates the theoretical foundations, and tries to estimate the extent by which the various measuring errors inherent in this method may falsify the results obtained. Measurements of the phase angle show that the errors occurring when using impedance instead of resistance are negligible. The determination of impedance is considerably influenced by breathing and body position. An analysis of these normally superimposing effects demonstrates the problematic nature of this method. It is shown that changes in intrathoracic fluid volume can be determined only with unchanged positioning of the electrodes, constant body position and elimination of the influence of breathing. Respiratory movements can be registered, whereas the influence of changes in the basic impedance on determining the stroke volume by impedance cardiography has not been fully researched.

Adult↗