Biomedical subjects

Christa Künemund

Publications and source records attributed to Christa Künemund.

6 recordsLinked to original sources

PubMed2003

Evaluation of performance and load in simulated rescue tasks for a novel design SCBA: effect of weight, volume and weight distribution.

A self-contained breathing apparatus (SCBA) with an innovative rucksack shape that provides a better distribution of its weight over the middle and lower parts of the back (device C: 6l, 13.7 kg) was compared with two conventional SCBA which differed from each other in volume and weight (A: 6l, 15 kg, B: 6.8l, 11.7 kg). Twelve fire-fighters (27-49 yr) performed three exercises while using the three SCBA in a systematically permuted sequence. The exercises consisted of simulated rescue work under natural climatic conditions in a dwelling on the second floor and several typical elements of severe fire-fighting actions. Duration, heart rate, breathing frequency, rectal temperature, and sweat loss were recorded. Perceived exertion was rated and the carrying features of the SCBA were subjectively evaluated. The exercise was executed faster with the rucksack device, heart rates were then lower and the carrying features were evaluated as better. Thus, the weight of the SCBA was shown to be less important than its distribution.

Adult↗

PubMed2002

Evaluation of draught in the workplace.

During 826, 1-h sessions 107 participants (33 women, 74 men, 18-51 years of age) were exposed to defined draughts where air velocity (0.1 < or = V(a) < or = 0.4 m s(-1)), turbulence intensity (< 30, approximately equal to 50, > 70%), draught direction (horizontal, vertical, diagonal), air temperature (11 < or = t(a) < or = 23 degrees C), and metabolic rate ( approximately equal to 60< or = M < or = 156 W m(-2)) were varied but kept constant during single sessions. Perception and evaluation (annoyance due to draught and local cold) were registered using a list of prescribed body parts. Annoyance due to draught increased with the increase in mean air velocity and in turbulence intensity, as well as with the decrease in air temperature and in metabolic rate. The direction of air flow had no influence. As these responses were neither sufficiently predicted by the draught-rating model proposed in ISO 7730 (1994), nor by its extension developed by Toftum (1994a), the latter was modified according to the data registered in this paper. Using the modified model the accordingly predicted percentage of people annoyed by draught agreed highly with the percentage actually observed (r=0.726, p<0.001). As the resulting model covers larger ranges of air temperature and metabolic rate it is suggested that it should substitute the model proposed in ISO 7730 [1994].

Adolescent↗

PubMed2002

Melatonin synthesis: a possible indicator of intolerance to shiftwork.

HYPOTHESIS: Melatonin synthesis, which is directly controlled by the central circadian pacemaker indicates the circadian phase better than rectal temperature. METHODS: Thirty four men (16-32 years, 7 morning, 13 neither, 14 evening types) performed a constant routine (24-26-hr bedrest, < 30 lux, 18-20 degrees C, hourly isocaloric diet). Salivary melatonin level was determined hourly and rectal temperature was continuously recorded. RESULTS: The nadir of rectal temperature occurred 1.5 hr (P = 0.017), the onset of melatonin synthesis 3 hr earlier (P < 0.0001) in morning than in evening types. Morningness was not related to the quantitative but significantly to the temporal parameters, closer to those of melatonin than of rectal temperature. CONCLUSIONS: The melatonin onset is a more reliable indicator of the diurnal type than the nadir of rectal temperature. As morningness has been associated with intolerance to shiftwork, melatonin profiling provides a suitable basis for the establishment of directed preventive measures.

Adaptation, Physiological↗

PubMed2002

Experiments on effects of an intermittent 16.7-Hz magnetic field on salivary melatonin concentrations, rectal temperature, and heart rate in humans.

OBJECTIVES: The present experiments concerned the hypothesis that an intermittent, strong and extremely low frequency magnetic field reduces salivary melatonin levels and delays consecutively the nadirs of rectal temperature and heart rate. METHODS: Twelve healthy young men (18-25 years) participated in three randomly permuted sessions, which were performed as constant routines. The participants kept a strict bed rest over 26 h, air temperature was 20 degrees C, illumination < 30 lx, and sound level < 50 dBA. Salivary melatonin levels were determined hourly, rectal temperature and heart rate were registered continuously throughout. An intermittent magnetic field was administered in one session from 6 p.m. to 2 a.m. at 16.7 Hz, 0.2 mT and alternating on/off-periods of 15 s. This situation was compared with a control session without any additional stress. Another session was performed to determine the participants' ability to respond to a well-known melatonin-suppressing stress, namely bright light (1,500 lx, 10 p.m.-2 a.m.). RESULTS: Bright light inhibited melatonin synthesis in all 12 participants and delayed the nadirs of rectal temperature and heart rate. The only significant alteration that was associated with exposure to the magnetic field was a delay in the heart rate nadir, which was not mediated by an accordingly altered melatonin profile. CONCLUSION: The fact that the circadian rhythm of only the heart rate was altered indicates an internal dissociation which might constitute a health risk in the long run and needs to be investigated more extensively.

Adult↗

PubMed2002

Effects of electromagnetic radiation (bright light, extremely low-frequency magnetic fields, infrared radiation) on the circadian rhythm of melatonin synthesis, rectal temperature, and heart rate.

Electromagnetic spectra reduce melatonin production and delay the nadirs of rectal temperature and heart rate. Seven healthy men (16-22 yrs) completed 4 permuted sessions. The control session consisted of a 24-hours bedrest at < 30 lux, 18 degrees C, and < 50 dBA. In the experimental sessions, either light (1500 lux), magnetic field (16.7 Hz, 0.2 mT), or infrared radiation (65 degrees C) was applied from 5 pm to 1 am. Salivary melatonin level was determined hourly, rectal temperature and heart rate were continuously recorded. Melatonin synthesis was completely suppressed by light but resumed thereafter. The nadirs of rectal temperature and heart rate were delayed. The magnetic field had no effect. Infrared radiation elevated rectal temperature and heart rate. Only bright light affected the circadian rhythms of melatonin synthesis, rectal temperature, and heart rate, however, differently thus causing a dissociation, which might enhance the adverse effects of shiftwork in the long run.

Adolescent↗

PubMed1996

Human Adaptation to Work in Two Different Climates.

The processes of acclimation to hot-dry and to warm-humid climates were studied using two approaches: a quantitative analysis of literature data and an experimental study in the laboratory concerning the physiological parameters of heart rate, rectal temperature, sweat loss, and subjective assessment. Analysis o f literature data: Data from 62 experiments with a total of 813 participants were pooled and recalculated. The experiments ranged from 6 to 24 days, air temperatures from 30.4 to 50.0°C, water vapor pressures from 1.5 to 6.5 kPa, and wet bulb globe temperatures (WBGT) from 27.4 to 38.6°C. Laboratory studies: In the laboratory, 8 participants were acclimated during 15 consecutive days to a hot-dry climate and to a warm-humid climate, which were equivalent in terms of the WBGT (33.5 and 33.6°C, respectively). The participants walked four times for 25 min on a treadmill at a speed of 4 km/h. The hot-dry climate caused somewhat greater strain than the warm-humid condition. In the course of acclimation to the hot-dry climate, heart rate and rectal temperature started at higher levels, decreased slightly steeper but remained on a higher level throughout. Nevertheless, the differences between both thermal conditions were small, and both physiologic functions reached the point of acclimation almost at the same time under warm-humid and under hot-dry exposure. Sweat loss, which is not regarded as a valid predictor for acclimation, was considerably higher but increased less in the hot-dry than in the warm-humid climate.

acclimation↗