PubMed Health⌕ Search

Biomedical subjects

L Brundin

Publications and source records attributed to L Brundin.

24 records · Page 2Linked to original sources
PubMed1990

The behaviour of the mean power frequency of the surface electromyogram in biceps brachii with increasing force and during fatigue. With special regard to the electrode distance.

The present study aims to investigate: a) the relationship between force and mean power frequency of the EMG, and b) how the distance between surface electrodes influences the mean power frequency. The study consisted of three parts: 1) a gradually increasing contraction upto 100% MVC, 2) contractions performed at 5 different levels from 20% upto 100% MVC with rest in between, and 3) an endurance test at 30% MVC. Nine healthy women participated. The elbow was flexed 90 degrees and EMG signals were obtained from the biceps brachii. The surface electrodes were placed so that electrode distances of 10 mm, 20 mm and 30 mm were obtained. The mean power frequency increased upto 60% MVC. Above 60% MVC no change in mean power frequency occurred. No differences in the mean power frequency with respect to the electrode distances existed at each force level. No significant differences were found at each contraction level between the gradually increasing contraction and the stepwise increasing contractions. The mean power frequency decreased linearly during the endurance test without any differences with respect to the electrode distances. It is concluded that the different electrode distances do not affect the mean power frequency-force relationship or the decrease in mean power frequency during fatigue. It is proposed that the increase in mean power frequency, on group level, can be used as an indicator of motor unit recruitment. However, this proposal was found to be complicated when individual analyses were made.

Adult↗
PubMed1989

Sound-induced motility of isolated cochlear outer hair cells is frequency-specific.

The inner ear is capable of highly selective frequency discrimination. This is achieved not only by the travelling wave of the basilar membrane in the cochlear partition, but also by the active participation of nonlinear and vulnerable elements that enhance frequency selectivity. It has been shown that isolated mammalian outer hair cells respond with a change in length when subjected to sound stimulation at a fixed frequency. Here we investigate the motile behaviour of isolated cells when the stimulus frequency is varied between 200 and 10,000 Hz. By varying the frequency and the intensity of the tone, it is possible to obtain 'tuning curves' for the motile response. We demonstrate that the cell body of solitary hair cells, free from contact with the basilar membrane, shows a sharply tuned motile behaviour. We suggest that frequency selectivity in the organ of Corti is amplified by the tuned motility of the cell body of outer hair cells.

Acoustic Stimulation↗
PubMed1988

Surface EMG recordings during maximum static shoulder forward flexion in different positions.

This study investigated how position in the range of motion influences the power spectral density function during static shoulder forward flexion. 23 healthy females (20-30 years) volunteered as subjects. They performed maximum static shoulder forward flexions in three positions: 45, 65 and 90 degrees of shoulder flexion. An isokinetic dynamometer was used and the subjects were seated in a specially constructed chair to enable adequate fixation. The elbow was extended and the hand pronated. Electromyographic (EMG) signals (using surface electrodes) were obtained from the descending part of the right trapezius, the anterior portion of the right deltoid, the right infraspinatus and the common belly of the right biceps brachii. The four EMG-signals and the torque and shoulder angle were analyzed by computer. For each 256 ms, mean power frequency, root mean square value and mean torque were calculated. At each of the three positions four 256 ms periods were analyzed and the data are presented as their means. In the trapezius and the biceps brachii the mean power frequency did not change between the three positions. Deltoid and infraspinatus had significantly higher mean power frequencies at 90 degrees than at 45 degrees of flexion. Different factors behind the change in mean power frequency are discussed. The need to standardize the range of motion when studying dynamic fatiguing contractions is emphasised.

Adult↗
PubMed1988

Acoustic stimulation causes tonotopic alterations in the length of isolated outer hair cells from guinea pig hearing organ.

Isolated outer hair cells from the mammalian cochlea exhibit a motile response to electrical or chemical stimulation. Here we show that isolated outer hair cells can also respond to acoustic stimulation, in the form of a tone burst of 200 Hz, by either shortening or lengthening depending on their cochlear location. Cells from the apical region of the cochlea (long cells) responded by increasing their length, whereas those from more basal regions (short cells) responded by decreasing their length. Cells from intermediate positions showed an equal probability for either elongating or shortening. Both the elongating and shortening response was inhibited by 3 microM poly(L-lysine). It is suggested that this tonotopic and bidirectional acoustic response may be one of the active components underlying the specific phase and frequency displacement of the basilar membrane.

Acoustic Stimulation↗
PubMedDate not supplied

Investigating routes to chaos in the guinea-pig cochlea using the continuous wavelet transform and the short-time Fourier transform.

The continuous wavelet transform (CWT) and the short-time Fourier transform (STFT) were used to analyze the time course of cellular motion in the guinea pig inner ear. The velocity responses of individual outer hair cells and Hensen's cells to amplitude modulated (AM) acoustical signals applied to the ear canal displayed characteristics typical of nonlinear systems, such as the generation of spectral components at harmonics of the carrier frequency. Nonlinear effects were particularly pronounced at the highest stimulus levels, where half-harmonic (and sometimes quarter-harmonic) components were also seen. The generation of these components was consistent with the behavior of a dynamical system entering chaos via a period-doubling route. A negative-stiffness Duffing oscillator model yielded period-doubling behavior similar to that of the experimental data. We compared the effectiveness of the CWT and the STFT for analyzing the responses to AM stimuli. The CWT (calculated using a high-Q Morlet-wavelet basis) and the STFT were both useful for identifying the various spectral components present in the AM velocity response of the cell. The high-Q Morlet wavelet CWT was particularly effective in distinguishing the lowest frequency components present in the response, since its frequency resolution is appreciably better than the STFT at low frequencies. Octave-band-based CWTs (using low-Q Morlet, Meyer, and Daubechies 4-tap wavelets) were largely ineffective in analyzing these signals, inasmuch as the frequency spacing between neighboring spectral components was far less than one octave.

Animals↗