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Biomedical subjects

J Rittweger

Publications and source records attributed to J Rittweger.

9 recordsLinked to original sources
PubMed2000

Identification of nonstationary dynamics in physiological recordings.

We present a novel framework for the analysis of time series from dynamical systems that alternate between different operating modes. The method simultaneously segments and identifies the dynamical modes by using predictive models. In extension to previous approaches, it allows an identification of smooth transition between successive modes. The method can be used for analysis, diagnosis, prediction, and control. In an application to EEG and respiratory data recorded from humans during afternoon naps, the obtained segmentations of the data agree with the sleep stage segmentation of a medical expert to a large extent. However, in contrast to the manual segmentation, our method does not require a priori knowledge about physiology. Moreover, it has a high temporal resolution and reveals previously unclassified details of the transitions. In particular, a parameter is found that is potentially helpful for vigilance monitoring. We expect that the method will generally be useful for the analysis of nonstationary dynamical systems, which are abundant in medicine, chemistry, biology and engineering.

Electroencephalography↗
PubMed2000

Bone-muscle strength indices for the human lower leg.

This cross-sectional study is based on images from the lower leg as assessed by peripheral quantitative computer tomography (pQCT). Measurements were performed in 39 female and 38 male control subjects and 15 female professional volleyball players, all between 18 and 30 years of age. The images were obtained at shank levels of 4%, 14%, 33%, and 66% from the distal end. Bone and muscle cross-sectional areas, and the bones' density-weighted area moment of resistance and of inertia were assessed. From these, muscle-bone strength indices (MBSIs) were developed for compression (CI = 100. bone area/muscle area) and bending (BI = 100. bone area moment of resistance/muscle area/tibia length). Significant correlations between muscle cross-sectional area and bone were found at all section levels investigated. The strongest correlation for compression was observed in the sections at 14% (correlation coefficient r = 0.74), where 4.10 +/- 0.46 cm(2) bone, on average, was related to 100 cm(2) muscle. The compression index (CI) at the 14% level was independent of the tibia length. Interestingly, the 15 athletes had significantly greater CIs than the control subjects. This is most probably due to the greater tension development in the athletes. The highest correlation for bending was for anteroposterior bending at 33% of tibia length (r = 0.81), where the area moment of resistance, R, was on, average, 4.21 +/- 0.54 cm(3)/100 cm(2) muscle/m tibia length. Analysis of the bones' area moment of inertia showed that buckling is a possible cause of bending at the 33% and 66% levels, but not at the 14% level. No gender differences in MBSI were found. Likewise, age was without significant effect. The data show that bone architecture depends critically on muscle cross section and tension development. Moreover, bone geometry (e.g., the tibia length) influences the geometrical distribution of bone mineral, as it was found that long bones adapted to the same compressive strength are wider than short ones. We conclude that MBSIs offer a powerful diagnostic tool for bone disorders and may contribute to improving the treatment of bone metabolic and other diseases.

Absorptiometry, Photon↗
PubMed2000

Acute physiological effects of exhaustive whole-body vibration exercise in man.

Vibration exercise (VE) is a new neuromuscular training method which is applied in athletes as well as in prevention and therapy of osteoporosis. The present study explored the physiological mechanisms of fatigue by VE in 37 young healthy subjects. Exercise and cardiovascular data were compared to progressive bicycle ergometry until exhaustion. VE was performed in two sessions, with a 26 Hz vibration on a ground plate, in combination with squatting plus additional load (40% of body weight). After VE, subjectively perceived exertion on Borg's scale was 18, and thus as high as after bicycle ergometry. Heart rate after VE increased to 128 min-1, blood pressure to 132/52 mmHg, and lactate to 3.5 mM. Oxygen uptake in VE was 48.8% of VO2max in bicycle ergometry. After VE, voluntary force in knee extension was reduced by 9.2%, jump height by 9.1%, and the decrease of EMG median frequency during maximal voluntary contraction was attenuated. The reproducibility in the two VE sessions was quite good: for heart rate, oxygen uptake and reduction in jump height, correlation coefficients of values from session 1 and from session 2 were between 0.67 and 0.7. Thus, VE can be well controlled in terms of these parameters. Surprisingly, an itching erythema was found in about half of the individuals, and an increase in cutaneous blood flow. It follows that exhaustive whole-body VE elicits a mild cardiovascular exertion, and that neural as well as muscular mechanisms of fatigue may play a role.

Adult↗
PubMed1999

Common slow modulation of respiration, arterial blood pressure and cortical activity during sleep onset while napping.

Using healthy subjects, concomitant 30- to 60-s modulations of respiration, arterial blood pressure and EEG activity were found in 21 experiments about napping. Although mean arterial pressure (MAP) modulations above and below 1/30 Hz increased, in respiratory amplitude (RA) only the lower frequency components augmented significantly. This slow modulation of RA was found to be asymmetrical in time, the duration of RA decreasing parts in the modulation waves being 42% longer than the duration of RA increasing parts. The concomitance of the slow modulations in the different organ systems is accounted for by the influence of the common brainstem system (CBS), which regulates and integrates respiratory, cardiovascular and somatomotor systems and the adjustment of central nervous activity (vigilance). The described common, slow modulations outline the importance of dampening influences during sleep onset. They may provide an important tool for the investigation of the regulatory systems during sleep onset, as well as for investigations about sleep apnoea syndrome and Cheyne-Stokes breathing.

Adult↗
PubMed1998

Respiratory-like periodicities in slow eye movements during sleep onset.

Slow eye movements (SEMs) during sleep onset and their relationship to vegetative rhythms were investigated in six healthy, sleep-deprived subjects, yielding 143-289 SEMs in an epoch of 31.5-56 min per experiment. Exclusively, sleep in stages I and II was recorded. From the bandpass-filtered electro-oculogram (EOG) signal (cut-off frequencies 0.05 and 1 Hz), turning points of the gaze were detected and compared with the start of inspiration, which was discriminated from the abdominal respiratory excursions. SEM cycle times varied considerably more than respiratory cycle times (P < 0.05 in Levene's test). Both were preferentially of equal length, or, in some subjects, in 2:1 co-ordination. Cross-correlation histograms yielded that inspiration and SEMs were also temporally co-ordinated. Thus, there is a temporal coherence regarding the occurrence, the cycle time and the phase between SEMs and a respiratory-like rhythm. Our findings show that it is not exactly the respiratory rhythm that is mirrored in the SEMs. Rather, we favour the interpretation of an autorhythmicity that is temporarily connected to the common brainstem system in the reticular formation of the brainstem.

Adult↗
PubMed1997

Influences of mandatory breathing on rhythmical components of electrodermal activity.

We investigated whether rhythmical components of electrodermal activity (EDA) can be influenced by voluntary modification of the respiratory frequency. Fifty-five volunteers participated in an experiment with nine mandatory sections of cycle times between 3.1 s and 12.2 s. The cycle time of the rhythmical EDA components often differed considerably from respiratory cycle time. ANOVA yielded that both cycle time and position within the section had an effect on the EDA power of the mandatory cycles (P < 0.05). No significant interaction between effects of section and of position was discovered (P > 0.1). A separate analysis of the cycle times of the rhythmical EDA components revealed integer relationship with the respiratory cycle times. Thus, voluntary changes in the respiratory frequency can influence occurrence and cycle time of rhythmical EDA components in a way similar to sliding coordination in the sense of E. von Holst.

Adult↗
PubMed1996

Electrodermal activity reveals respiratory and slower rhythms of the autonomic nervous system.

Electrodermal Activity (EDA) was measured in 55 subjects during (1) an alarm reaction, (2) mental load, and (3) physical load. In 34 subjects, not only was a transient response observed, but also, oscillatory patterns characterizing short term variations of EDA. The durations of these oscillations varied between 3-16 s. Most commonly, they were approximately within the frequency range of respiration, or lower, at about 0.1 Hz. The EDA-rhythms were also related to the arterial blood pressure. They were, however, not strictly synchronized with respiration or with the blood pressure waves. We conclude that assessment of EDA in combination with fluctuations of the heart rate, and also, if possible, arterial blood pressure, may turn out to be a useful tool in the evaluation of the interaction between different regulatory processes that are realized by the common brainstem system.

Acoustic Stimulation↗
PubMed1992

Different modes of dampening influence from baroreceptors are determined by the functional organization of the NTS neuronal network.

Simultaneous recordings of several neurones of the first relay station of baroreceptor afferents show that its general activity-dampening influence is realized via the common brainstem system (CBS) which itself controls the processing on the neurones of the nucleus of the solitary tract (NTS). This feedback system maintains the degree of activity which is necessary for the ongoing behaviour as long as it fits to the environmental situation. The output of the NTS is determined partly by the CBS, partly by the properties of the peripheral afferent input, partly by the dynamic functional organization of the local circuits and partly by influences from other brain areas.

Action Potentials↗