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Biomedical subjects

N Tiedt

Publications and source records attributed to N Tiedt.

At least 37 records · Page 2Linked to original sources
PubMed1979

[Time parameters of the retinal control of light intensity and influencing parameters].

The variability of the pupillomotoric control of light intensity was analysed in response to changes in the duration of the light flash, the respiratory phase during stimulation and the age of the subjects. The method of infrared pupillography was used to determine dynamic time parameters. With increasing duration of the light flash from 8 to 125, 250 and 500 ms we observed an acceleration of the latencies whilst the other time parameters were prolonged. There was no significant influence of the time of stimulation during the respiratory cycle. With growing age increased latencies and reduced time parameters of the pupillomotoric transient response were found. The possible reason and importance of the observed changes are discussed.

Adolescent↗
PubMed1978

[A new dynamic test with optimal multifrequent binary work-load patterns on the bicycle ergometer].

A new dynamic test with work-load changes on the bicycle ergometer is described using optimal multifrequent binary test signals, which are based on the theory of an active design of experiments. In comparison to step, impulse, ramp and sinusoidal work-load changes this new test includes the advantage that it provides good accuracy within a short time for measurement and evaluation. First results indicate the possibility of a good analysis of the dynamics of the heart rate response using linear models. Statements for approximation of the system in the frequency range lead to the estimation of time constant models, which allow a good estimation of the behaviour of the regulation of the heart rate.

Exercise Test↗
PubMed1975

Dynamic characteristics of heart-rate responses to sine-function work-load patterns in man.

Dynamic characteristics of heart rate in response to sinusoidal variations of work load were analysed in 8 male and 3 female untrained students exercising in a sitting position on a bicycle ergometer. The mean work load was 90 watt in men and 60 watt in women, the amplitudes being 50 and 30 watt respectively. Nine different frequencies were used, the periods varying from 0.5 to 15.0 min. By means of harmonic analysis, the fundamental components in the response of the heart rate have been shown to prevail over the 2nd and 3rd harmonics, indicating a mainly linear behaviour of the control system in the work-load range studied. A comparison of the frequency response of untrained males and females observed in this study and of trained sportsmen, investigated by wigertz (1970), reveals differences between the groups. The individual and ensemble mean frequency responses have been described by several transfer functions, the best fit having been obtained with functions containing two time constants including one with a highly damped oscillating element. The dominating dynamic parameter is a time constant of about 20 to 30 sec. This time constant tends to be shorter and its portion of the frequency response diminishes in order from the untrained females and males to the trained sportsmen. The individual time constant decreases as the PWC170 increases, and is therefore a suitable criterion for estimating the physical performance of individuals under dynamic conditions.

Adult↗
PubMed1975

[Dynamics of the human heart rate during changes of posture under various climatic conditions].

The time course of the heart rate (15-sec-periods) during active orthostasis (10 min) was investigated according to types found by Drischel et al. under different climatic conditions in 51 female and 50 male subjects. Constant types were observed in each subject in 3 repeated tests on different days at 20 degrees C and 55% R.H., the types remaining constant even at 25 and 90% R.H. The increase in environmental temperature from 15 to 30 and 45 degrees C showed a significant alteration from type A via different transitional types to type B. At 45 degrees C, an additional type was observed called superhigh type B, functionally being a precollapse type. The variation in typology includes the dynamics of the initial process of the active orthostasis as well as the deviation between the steady-state of the heart rate in erect and in supine position. The physiological mechanisms eliciting the changes in the dynamic behaviour and the correlations with the effective temperature are discussed.

Climate↗
PubMedDate not supplied

Is there an abluminal release of endothelium-derived relaxing factor (EDRF)?

In superfusion bioassay systems of rabbit thoracic aorta and femoral artery ring segments as well as canine femoral artery and coronary ring segments the release of endothelium-derived relaxing factor (EDRF) was stimulated by acetylcholine in donor segments with intact endothelium. The transition of EDRF through the vessel wall ("abluminal release") was not revealed in both bioassay systems. Externally applied acetylcholine did not reach the luminal surface of rabbit thoracic aorta but induced EDRF release in canine femoral artery segments.

Acetylcholine↗
PubMedDate not supplied

Heterogeneity of the response of venous smooth muscle to arterial endothelium-derived relaxing factor (EDRF) in respect of the role of nitric oxide.

In bioassay and organ bath experiments, the responses of different canine venous preparations to arterial and their own EDRF were studied. Vena jugularis, vena femoralis and vena mesenterica relaxed on both EDRFs released by acetylcholine. Vena saphena, venae cordis and vena portae did not show endothelium-dependent dilation, either under bioassay or in organ bath experiments. All the veins tested relaxed completely after sodium nitroprusside administration. The identity of EDRF and nitric oxide is not confirmed by this study.

Animals↗