Search PubMed⌕ Search

Biomedical subjects

Y T Zhang

Publications and source records attributed to Y T Zhang.

At least 37 records · Page 2Linked to original sources
PubMed1997

Vibromyography as a quantitative measure of muscle force production.

This study was undertaken to investigate the use of vibromyography (VMG) as a tool for quantifying skeletal muscle force production. Fourteen healthy volunteers were pretested using a Cybex isokinetic dynamometer to determine their isometric quadricep maximum voluntary contraction (MVC) values. On the basis of these results, the subjects were separated into two groups: high-force ("HF" MVC mean = 289 ft.lb., range 254-330) and low-force ("LF" MVC mean = 154 ft.lb., range 101-198). A vibromyographic piezoelectric accelerometer (Dytran 3115A) and electromyographic (EMG) surface electrodes were affixed to the rectus femoris muscle and recordings were obtained at 20, 40, 60, 80, and 100% MVC. Root mean squares, median and mean values were computed from digitized data in the time domain while peak values were calculated from a fast Fourier transform for both the VMG and EMG data. A two-way repeated measures MANOVA using relative values and a linear regression model using absolute values were studied using BMDP and MiniTab software. Linear correlations were found between quadricept force and all EMG variables (R2 range 0.71-0.90) except peak (R2 = 0.39). The relationship between VMG and force was less linear (R2 range 0.19-0.69) because VMG values reach a plateau or even drop at 80% and 100% MVC. The HF-LF group differences were significant (p < 0.05), for all VMG values with the exception of root mean squares, but were not significant (p > 0.05) for all four EMG values. This study shows that, while EMG can discriminate force production within a given subject, VMG is a better discriminator of absolute muscle force values between subjects, particularly up to 60% MVC.

Adult↗
PubMed1996

Screening of vibroarthrographic signals via adaptive segmentation and linear prediation modeling.

This paper proposes a noninvasive method to diagnose chondromalacia patella at its early stages by recording knee vibration signals (also known as vibroarthrographic or VAG signals) over the mid-patella during normal movement. An adaptive segmentation method was developed to segment the nonstationary VAG signals. The least squares modeling method was used to reduce the number of data samples to a few model parameters. Model parameters along with a few clinical parameters and a signal variability parameter were then used as discriminant features for screening VAG signals by applying logistic and discriminant algorithms. The system was trained using ten normal and eight abnormal signals. It correctly screened a separate test set of ten normal and eight abnormal signals except for one normal signal. The proposed method should find use as an alternative technique for diagnosis of knee joint pathology or as a test before arthroscopy or major knee surgery.

Algorithms↗
PubMed1996

The behavior of rectus femoris and vastus lateralis during fatigue and recovery: an electromyographic and vibromyographic study.

Eleven subjects performed isometric knee extensor contractions at maximum voluntary contraction (MVC), and at 70% of MVC preceding and following a fatigue test. The fatigue test consisted of a continuous isometric knee extensor contraction at 70% of MVC. The purpose of this study was to describe and compare the behavior of electromyographic (EMG) and vibromyographic (VMG) signals of rectus femoris (RF) and vastus lateralis (VL) muscles during a fatigue-recovery protocol by analyzing the median frequency (MDF) and the root mean square (RMS) values obtained from these signals. EMG and VMG signals of RF and VL muscles were recorded using bipolar surface electrodes and miniature accelerometers, respectively. The MDF of EMG and VMG signals of the two muscles decreased during muscle fatigue and returned to the pre-fatigue values during the fifteen minute recovery period. Assuming a relation between the decrease of the MDF of the EMG signals and a decrease in the conduction velocity of the action potentials in the muscle fibers with fatigue, the subsequent restoration of the MDF indicates that muscle fiber conduction velocity returned to a pre-fatigue state within a short time. The decrease in the MDF of the VMG signals seems to be associated with low-frequency tremor that typically occurs towards the end of exhausting isometric contractions. The RMS of the EMG increased in both RF and VL throughout fatigue and recovery, and may be attributed to increased muscle activation. The RMS values of the VMG do not appear to change in a systematic way during the fatigue and recovery periods.

Adult↗
PubMed1996

Relationships of the vibromyogram to the surface electromyogram of the human rectus femoris muscle during voluntary isometric contraction.

The relationship between vibromyographic (VMG) and electromyographic (EMG) signals during isometric contraction of the human rectus femoris muscles was studied. The method of least squares was used to obtain the best-fitting linear regression model to the root mean squared (RMS) values of the VMG and the EMG. It is shown that for the rectus femoris of four subjects, a linear VMG versus EMG relationship exists during 20-80% of the maximum voluntary contraction (MVC) at 30 degrees, 60 degrees, and 90 degrees of knee joint flexion angles. The relation between the VMG and the EMG may be explained by the order recruitment of motor units and by the "onion-skin" phenomenon of the firing rates of recruited motor units in the regulation of muscle force production as reported in electro-neurophysiologic studies.

Adult↗
PubMed1995

Localization of knee joint cartilage pathology by multichannel vibroarthrography.

This paper proposes non-invasive techniques to localize sound or vibroarthrographic (VAG) signal sources in human knee joints. VAG signals from normal subjects, patients who subsequently underwent arthroscopy, and cadavers with arthroscopically-created lesions, obtained by stimulation with a finger tap over the mid-patella and swinging movement of the leg, were analyzed for time delays using cross-correlation functions for source localization. Correct results were obtained for 13 of the 14 subjects tested by finger stimulation, and for 11 of the 12 subjects whose VAG signals during swinging movement were analyzed. The techniques could be valuable in the diagnosis and treatment of knee pathology before and after joint surgery or drug therapy.

Arthroscopy↗
PubMed1995

The EMG-force relationship of the cat soleus muscle and its association with contractile conditions during locomotion.

The relationship between force and electromyographic (EMG) signals of the cat soleus muscle was obtained for three animals during locomotion at five different speeds (154 steps), using implanted EMG electrodes and a force transducer. Experimentally obtained force-IEMG (= integrated EMG) relationships were compared with theoretically predicted instantaneous activation levels calculated by dividing the measured force by the predicted maximal force that the muscle could possibly generate as a function of its instantaneous contractile conditions. In addition, muscular forces were estimated from the corresponding EMG records exclusively using an adaptive filtering approach. Mean force-IEMG relationships were highly non-linear but similar in shape for different cats and different speeds of locomotion. The theoretically predicted activation-time plots typically showed two peaks, as did the IEMG-time plots. The first IEMG peak tended to be higher than the second one and it appeared to be associated with the initial priming of the muscle for force production at paw contact and the peak force observed early during the stance phase. The second IEMG peak appeared to be a burst of high muscle activation, which might have compensated for the levels of muscle length and shortening velocity that were suboptimal during the latter part of the stance phase. Although it was difficult to explain the soleus forces on the basis of the theoretically predicted instantaneous activation levels, it was straightforward to approximate these forces accurately from EMG data using an adaptive filtering approach.

Animals↗
PubMed1995

Reflex responses associated with manipulative treatments on the thoracic spine: a pilot study.

OBJECTIVE: To test systematically if spinal manipulative treatments (SMT) and the audible release associated with SMT cause activation of spinal muscles. DESIGN: Experimental pilot study. SETTING: Human Performance Laboratory, The University of Calgary. PARTICIPANTS: One male and one female asymptomatic volunteer. INTERVENTION: Slow and fast SMTs to the left transverse process of thoracic vertebrae using a reinforced hypothenar contact. The treatment forces were directed in a posterior-to-anterior direction with the subjects in a prone position. MAIN OUTCOME MEASURES: Forces applied by the chiropractor during SMT. Measurements of the audible release using skin-mounted accelerometers. Electromyographical activity of selected spinal muscles. RESULTS: Electromyographical (EMG) activity was observed consistently 50-100 msec after the onset of each of the fast SMTs, whether the treatment resulted in an audible release or not; for slow SMTs, there was never any visible electromyographical activity of the target muscles, whether the treatment resulted in an audible release or not. CONCLUSION: The results of this study suggest that fast treatment thrusts elicit muscle activation, whereas slow force application does not. The timing of the onset of the EMG response suggests that activation may be produced by a reflex response originating in the muscle spindles. It also appears that the audible release does not (by itself) evoke muscle activation or a joint proprioceptive reflex response as has been speculated in the literature.

Adult↗
PubMed1995

Forces and relative vertebral movements during SMT to unembalmed post-rigor human cadavers: peculiarities associated with joint cavitation.

OBJECTIVE: The purpose of this study was to compare the relative movements between adjacent vertebrae that were accompanied by a cavitation sound to those relative movements wherein no cavitation sound was recorded, during spinal manipulative treatments (SMTs) to T12 of an unembalmed human cadaver. SETTING: The experiment was conducted in the gross anatomy laboratory at the University of Calgary. SUBJECTS: One 77-yr-old male cadaver was used. INTERVENTIONS: High speed cinematography and embedded bone pin markers were used to record the movements of T10, T11, and T12, during the manipulations. A pressure pad was used to measure the posterior-to-anterior (p-to-a) forces exerted by the clinician onto the cadaver. Two uniaxial accelerometers were used to record the p-to-a accelerations of T11 and T12. The clinician delivered five p-to-a thrusts to the right transverse process of T12. P-to-a forces, p-to-a accelerations, and relative (between T10 and T11, and, T11 and T12) p-to-a translations, lateral translations, and axial rotations, were calculated for each thrust. MAIN RESULTS: A cavitation sound was recorded by the T12 accelerometer during the fourth manipulation. The p-to-a force parameters of the fourth trial were not different from those of the other trials. However, the relative lateral translations between the adjacent vertebrae were substantially greater during the fourth manipulation, compared to the other trials. CONCLUSIONS: The characteristics of the relative lateral translations between adjacent vertebrae suggest that the cavitation sound recorded during the fourth manipulation may have been associated with greater laterally applied forces than those during the other manipulations to T12, wherein no cavitation was recorded.

Acceleration↗
PubMed1994

Assessment of muscular fatigue using vibromyography.

The purpose of this study was to investigate the behavior of electromyographical (EMG) and vibromyographical (VMG) signals in the time and frequency domains during a fatigue protocol. EMG and VMG records were obtained from the rectus femoris (RF) and vastus lateralis (VL) muscles of 11 adult male subjects during sustained, isometric knee extensor contractions performed at 70% of maximal voluntary contraction (MVC). The average median frequencies of the power density spectra decreased during the fatigue protocol for the EMG (from 73 to 54 Hz for RF, and from 75 to 57 Hz for VL) and the VMG signals (from 40 to 19 Hz for RF, and from 25 to 12 Hz for VL). Raw EMG signals remained the same qualitatively throughout the fatigue protocol, whereas corresponding VMG records appeared to become "smoother." The results of this study indicate that the pronounced decrease in the high-frequency content of the VMG signal may be observed in the time domain as a "smoothing" of the signal, and thus, that the raw VMG records (which may be displayed readily online) can be used to assess qualitatively the onset and progression of muscular fatigue.

Adult↗
PubMed1994

Adaptive cancellation of muscle contraction interference in vibroarthrographic signals.

Vibroarthrography (VAG) is an innovative, objective, non-invasive technique for obtaining diagnostic information concerning the articular cartilage of a joint. Knee VAG signals can be detected using a contact sensor over the skin surface of the knee joint during knee movement such as flexion and/or extension. These measured signals, however, contain significant interference caused by muscle contraction that is required for knee movement. Quality improvement of VAG signals is an important subject, and crucial in computer-aided diagnosis of cartilage pathology. While simple frequency domain high-pass (or band-pass) filtering could be used for minimizing muscle contraction interference (MCI), it could eliminate possible overlapping spectral components of the VAG signals. In this work, an adaptive MCI cancellation technique is presented as an alternative technique for filtering VAG signals. Methods of measuring the VAG and reference signals (MCI) are described, with details on MCI identification, characterization, and step size optimization for the adaptive filter. The performance of the method is evaluated by simulated signals as well as signals obtained from human subjects under isotonic contraction.

Adult↗
PubMed1994

EMG-force relationship of the cat soleus muscle studied with distributed and non-periodic stimulation of ventral root filaments.

Distributed stimulation of ventral root (VR) filaments and pseudo-random interpulse intervals (based on a Gaussian distribution with a coefficient of variation of 12.5%) were used to modulate electromyographic activity (EMG) and force of the cat soleus muscle to assess the EMG-force relationship. A protocol consisting of addition and rate modulation of ten VR filaments that contain alpha motoneurones to the soleus muscle was adopted. EMG was measured using indwelling electrodes and forces were measured at the distal tendon using a strain transducer. EMG records obtained using this approach were similar in the time and frequency domains to those obtained during voluntary contractions. Force records obtained from stimulation of single VR filaments showed summation effects typical of irregular interpulse intervals. The overall relationship between integrated rectified EMG (IEMG) and mean force was found to be non-linear. At low and high stimulation levels, IEMG tended to increase proportionally more than mean force. In the intermediate stimulation region (i.e. producing forces between approximately 5% and 88% of the maximal tetanic force), the IEMG-mean force relationship was virtually linear. Muscles with a homogeneous fibre type composition, such as the cat soleus muscle, have been reported to have a linear EMG-force relationship.

Animals↗
PubMed1994

Effects of muscle length on the EMG-force relationship of the cat soleus muscle studied using non-periodic stimulation of ventral root filaments.

The effects of changing the length of the cat soleus muscle on electromyographic (EMG) signals, muscle force and the corresponding EMG-force relationship were assessed using distributed stimulation of ten ventral root filaments and irregular interpulse intervals. EMG-force relationships were first determined for four muscle lengths using a protocol of simultaneous addition and rate modulation of ventral root filaments. In the second test, three submaximal levels of stimulation were applied at eight muscle lengths. EMG signals were obtained using surface and wire electrodes, and force was measured using a strain transducer. For most muscle lengths, the relationships between integrated EMG and mean force obtained using wire and surface electrodes were sigmoid with a linear intermediate region. The effects of muscle length on EMG signals were likely to be associated with movement of the recording electrodes relative to each other and to the active motor units. Mean forces increased with increasing muscle length and with increasing levels of stimulation. Mean force-length relationships obtained using submaximal stimulation were not simply scaled down versions of the force-length relationship obtained using supramaximal stimulation of the soleus nerve, but appeared to be shifted towards longer muscle lengths.

Action Potentials↗
PubMed1994

Congenital perforation of the triangular fibrocartilage of the wrist.

The triangular fibrocartilages (TFC) of 136 wrist joints from 48 fetuses and 20 infants fresh cadavers without any evidence of known deformity and injury were studied. Perforations of the TFC were found not only in infants (18.8%), but also in fetuses (25%). The difference between the incidences of the perforations in the two groups is not statistically significant (P > 0.05). Furthermore, we did not find that perforation of the TFC is correlated with either sex or side of wrists (P > 0.05). Histologically, the vascularity and cellularity of the TFC have no significant correlation with the absence or presence of perforation in it. We believe that, besides trauma, inflammation and degeneration, some perforations of the TFCs are congenital in origin, which all take the form of fissure and are located mainly in the radial half of the TFC.

Cartilage, Articular↗
PubMed1994

Distributed random electrical neuromuscular stimulation: effects of the inter-stimulus interval statistics on the EMG spectrum and frequency parameters.

An electrophysiological approach was used to study a distributed random electrical neuromuscular stimulation (ENMS) scheme in which a probability density is assigned to the inter-stimulus intervals (ISI) of the stimuli. One of the objectives of using ENMS techniques in the study of skeletal muscles is to obtain information about the electrical, physiological, and mechanical properties of muscles in a near-physiological situation under a well-controlled experimental design in which problems related to the uncertainty of firing patterns of the central nervous system and physiological interference are avoided. In particular, ISI with a Gaussian density were varied in mean rate, standard deviation (SD), and coefficient of variation. The influence of varying ISI, and the interaction of the ISI statistics with compound motor unit action potentials (CMUAP) on EMG power spectra and their frequency parameters, was assessed theoretically using a mathematical model which is similar to that of EMG signal generation in the electrophysiological case. In order to quantify the effects of ISI statistics on the EMG spectrum, the median frequency was calculated as a function of stimulation rate using analytical expressions for various values of the coefficients of a Gaussian ISI variation. The results obtained suggest that 1) the interaction between ISI statistics and the shape of the CMUAP plays a major role in determining the EMG spectrum; 2) the median frequencies (MF) determined from EMG spectra tend to increase with increasing mean rates of stimulation for a given CMUAP. The rate of increase of the MF depends on the coefficient of the ISI variation; 3) the EMG spectra of random electrically stimulated muscle show peaks at the mean rate of stimulation, and multiples of it, when the coefficient of variation of ISI is small. These peaks decrease in magnitude with increasing coefficients of variation of ISI; and, 4) a variation in the ISI should be introduced in the ENMS, when a reproduction of 'normal' EMG spectra is needed. These results are consistent with those reported for voluntary contraction of skeletal muscles.

Electric Stimulation↗
PubMed1993

Signal-to-noise measures for magnetic resonance imagers.

The signal-to-noise ratio (SNR) in magnetic resonance imaging represents one of the system operating variables that must be determined both for evaluating the performance of different imaging protocols on a particular machine, and for monitoring machine performance as part of a routine quality control (QC) program. Utilizing a phantom and set of automated analysis programs currently under development, this study evaluated several ways of measuring image signal and noise and demonstrated the importance of utilizing measured voxel volumes as opposed to nominal volumes in the calculation of SNR. The NEMA proposed standard for SNR is compared with several other SNR measures and is recommended as the measure to be used in routine SNR reporting. The importance of utilizing other SNR measures in addition to the NEMA proposed standard for routine QC is discussed.

Magnetic Resonance Imaging↗
PubMed1993

Cavitation sounds during spinal manipulative treatments.

OBJECTIVE: The purpose of this study was to confirm a practitioner's perception of cavitation during spinal manipulative therapy in a clinically relevant situation using accelerometer recordings. DESIGN: Experimental study. SETTING: Human Performance Laboratory and Sports Medicine Center, University of Calgary. PARTICIPANTS: Twenty-eight patients from a single practitioner's patient pool who had pain in the area of the thoracic spine. INTERVENTION: Spinal manipulative treatment (SMT) on the transverse process of T4 using a reinforced unilateral contact and delivering a thrust in the posterior to anterior direction. MAIN OUTCOME MEASURES: Instantaneous acceleration signals obtained from the spinous process of T3 during SMT and the practitioner's perception if cavitation had occurred or not at the end of each treatment. CONCLUSIONS: It appears that cavitation may be measured during SMT using accelerometry and that a practitioner's perception of the occurrence of cavitation during SMT is very accurate.

Back Pain↗
PubMed1992

Experimental analysis of T1 imaging with a single-scan, multiple-point, inversion-recovery technique.

Look and Locker's single-scan, multiple-point, T1 determination technique modified for imaging applications was evaluated experimentally for its accuracy and reliability with respect to the pulse sequence parameters, in particular, to the interpulse delay, tD, and the tip angle, alpha. T1 imaging experiments were performed with a 0.5-T imaging system on a phantom which consisted of an array of vials containing 2% agarose gels doped with various amount of Mn2+ using different combinations of the parameter set (tD, alpha). T1 results obtained with this technique were compared with those measured by a conventional inversion-recovery procedure using the same spectrometer. Strategic choice of pulse sequence parameters to minimize experimental errors and the criteria for these choices will be discussed.

Humans↗