Biomedical subjects

U Shahani

Publications and source records attributed to U Shahani.

7 recordsLinked to original sources

PubMed1998

Neuromagnetic recordings of the human peripheral nerve with planar SQUID gradiometers.

Magnetic fields produced by a travelling volley in the human ulnar nerve have been successfully measured in a lightly shielded environment. Recordings of the tangential component of the magnetic field were made using a planar second-order gradiometer integrated with a first-order gradiometric superconducting quantum interference device (SQUID). Devices were fabricated in our clean-room facility at the University of Strathclyde and measurements taken in an eddy-current shielded room at the Wellcome Biomagnetism Unit. We use no additional shielding and no electronic differencing or field-nulling techniques. Evoked magnetic fields of 60 fT peak-to-peak were obtained after 1536 averages but they could be seen easily as early as 512 averages. Measurements were made over four points above the ulnar nerve on the upper arm and from these the conduction velocity was calculated as 60 m s(-1).

Equipment Design↗

PubMed1997

Habituation-like effects cause a significant decrease in response in MRI neuroactivation during visual stimulation.

A wide range of rest/stimulus cycle durations (40-360 sec) is reported to have been used by various groups for MRI neuroactivation studies of the visual cortex. In this paper we demonstrate a clear habituation-like response for longer cycle durations which results in a halving of apparent activation between cycle durations of 138 and 276 sec. This has important implications, not only in terms of optimizing the technique, but also in providing an insight into the underlying physiological mechanisms.

Adult↗

PubMed1995

Synchronization between motor cortex and spinal motoneuronal pool during the performance of a maintained motor task in man.

1. Simultaneous recordings of cortical activity, recorded as the magnetoencephalogram (MEG), and the electromyogram (EMG) of the ipsilateral and contralateral first dorsal interosseous muscles (1DI) were made during maintained voluntary contractions. 2. The MEG recorded from a localized region of the sensorimotor cortex of the dominant hemisphere was coherent with the EMG from the contralateral 1DI muscle over a limited band of frequencies. The peak coherence was confined largely within the beta range of cortical activity (13-35 Hz). Significant cortical activity at 10 Hz and 40-50 Hz was not correlated with motor output. The MEG and EMG from the ipsilateral 1DI muscle were uncorrelated at all frequencies. 3. Significant coherence between the MEG and the EMG was associated with synchronous behaviour between the MEG and EMG in the time domain. 4. The results demonstrate that synchronized cortical activity contributing to MEG activity within the beta range of frequencies during maintained voluntary contractions is coupled to motor output at frequencies of motor-unit activity associated with motor-unit synchronization. This observation provides further evidence for the involvement of cortical neurones in the generation of motor-unit synchronization. 5. We suggest that the coherence between MEG and contralateral EMG observed during maintained isometric contractions may provide an example of binding within the motor system.

Adult↗

PubMed1994

Antenatal fetal magnetocardiography: a new method for fetal surveillance?

OBJECTIVE: To establish the reliability of fetal magnetocardiography as a method of measuring the time intervals of the fetal heart during the antenatal period. DESIGN: A prospective study. SETTING: Wellcome Biomagnetism Unit, Southern General Hospital. SUBJECTS: One hundred and six low risk pregnant women at 20 to 42 weeks gestation. MAIN OUTCOME MEASURES: Success in obtaining QRS complexes, P waves and T waves. Correlation of time intervals with fetal outcome. RESULTS: The technique was acceptable to pregnant women. A QRS complex was successfully demonstrated in 68 (67%) of the unaveraged traces. Using off-line averaging techniques on these 68 cases, P waves were obtained in 75% and T waves in 72%. Although good quality traces were obtained throughout the range of gestational ages, in general it was more difficult below 28 weeks. QRS duration (R2 = 7%, P = 0.02) demonstrated a positive linear correlation with increasing gestation. Of the 35 (51%) cases with umbilical vein pH analysis available, only one result was less than 7.2. No significant relation was found between measurements of the fetal waveforms and the pH results. CONCLUSION: The technique of fetal magnetocardiography provides a significant advance in the technological field for the demonstration of QRS complexes and the full PQRST waveforms in gestations from 20 weeks onwards. With further technical improvements the clinical impact of this technique can be assessed more fully.

Adolescent↗

PubMed1990

Long-lasting modification of reflexes after neonatal nerve injury in the rat.

The reflex activity of motoneurones to the extensor digitorum longus (EDL) muscle following sciatic nerve crush during the first 5 days after birth (neonatal crush) or in the adult (adult crush) was studied 3-6 months later, when the axons had reinnervated their target muscles. Electromyograms (EMG) and muscle tension were recorded from the EDL muscle (a physiological flexor) on the injured and uninjured sides. Reflex responses were evoked by stimulation of the common peroneal (CP), the tibial (T) and the sural (S) nerves, ipsilateral and contralateral to the side of injury. In animals which had sustained a neonatal crush, stimulation of branches of the injured sciatic nerve elicited ipsilateral reflex responses that were about 3 times larger than those recorded from the uninjured side or in normal animals. Stimulation of the CP nerve on the uninjured side invariably elicited a contralateral reflex response from the reinnervated muscles, while stimulation of the CP nerve on the injured side either failed to produce a response or produced a very weak reflex response from the control muscles. Reflexes recorded from the reinnervated muscles by stimulation of the tibial and sural branches of the uninjured sciatic nerve were 3-7 times greater than those recorded from the uninjured side or in normal animals. The reflex responses obtained from reinnervated muscles of animals with nerve injury in adulthood were similar to those obtained from control, unoperated adult rats. These results indicate that sciatic nerve injury during a critical development period leads to a permanent enhancement of reflex responses from reinnervated fast flexor muscles not seen after similar injury in adults.

Adaptation, Physiological↗

PubMed1990

Impairment of developing fast muscles after nerve injury in the rat depends upon the period of denervation.

After injury to the peripheral nerve in rat pups at 5 days of age the development of the fast muscles tibialis anterior and extensor digitorum longus is impaired. Whether the length of time during which the muscles are denervated affects the degree of impairment was studied here. In one group of animals the peroneal nerve was crushed near to the muscles in one leg and further away from the muscles in the other leg. In another group of animals the sciatic nerve was crushed in one leg at 5 days and in some of these animals the nerve was crushed again 5-7 days later. The recovery of TA and EDL was measured by recording the weight and tension developed once reinnervation was complete. When the nerve was crushed close to the muscles, the muscles recovered significantly better than when the site of injury was further away, while delaying reinnervation by crushing the sciatic nerve a second time, impaired recovery of the muscles. It is concluded that the permanent impairment of fast muscles seen after neonatal nerve injury depends upon the length of time that the muscles are separated from their motoneurones.

Animals↗

PubMed1985

Long-latency spinal reflexes in humans.

Stretching human muscles with a mechanical device gave rise to multiple peaks in the rectified and averaged electromyogram. In the first dorsal interosseous the latency of the first peak (M1) was 32.4 +/- 2.4 ms (SD) and the latency of the second peak (M2) was 55.1 +/- 11.3 ms, in both cases measured from the time of the stimulus to the take-off point of the peak. Often a third peak (M3) was seen, having a considerably longer latency. The origin of peak M1 was considered to be in the stretch reflex arc because of its latency and its invariable association with muscle movement. Peak M2 was due to stimulation of afferent terminals in the skin and/or subcutaneous tissues by the mechanical device producing the muscle stretch. The conduction velocity of the pathway involved in the generation of the M1 component is the same as that for M2. This implies that central processing in the spinal cord delays the M2 response. The M2 mechanism does not involve a transcortical (long-loop) pathway because in foot muscles the M1-M2 delay remains the same as is found for hand muscles, although M1 latency is prolonged (to 39.4 +/- 6.2 ms for extensor digitorum longus). This indicates that there is not time for M2 impulses to traverse a pathway any longer than that passing to and from the spinal cord.

Afferent Pathways↗