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M H Sims

Publications and source records attributed to M H Sims.

31 records · Page 2Linked to original sources
PubMed1982

Recovery cycle of the reflex-evoked muscle potential (H reflex): excitability of spinal motor neurons in the healthy dog.

The recovery cycle for a reflex-evoked muscle potential has been demonstrated in the healthy dog, using the ulnar nerve-interosseous muscle preparation. The amplitude of a test response, at various time intervals (2 to 1,000 ms) after a conditioning response, was compared with the amplitude of the unconditioned response. The resulting ratio was plotted as a function of interstimulus interval. The curve was shown to consist of 3 distinct phases. The 1st phase, called the phase of early responsiveness, lasted from 2 to 20 ms and was characterized by a rapid decrease in amplitude of the test response. The 2nd phase, the phase of unresponsiveness, was characterized by a reduced response, and eventually no response which occurred between 20 and 80 ms. The 3rd phase, the phase of late responsiveness, began with a small test reflex amplitude at 80 ms and increased to 200 ms where it plateaued thereafter. Between 200 and 1,000 ms, there was no significant change in amplitude. Only at 2 ms, where the conditioning and test responses were so close together that they fused, did the mean amplitude of the test response exceed the mean unconditioned response. The reflex-evoked muscle potential recovery curve provides additional proof that the reflex is the equivalent of the H-reflex, and it provides a quantitative measure of spinal cord lower motor neuron excitability in the dog.

Animals↗
PubMed1980

Electrodiagnostic evaluation of hypomagnesemia in sheep.

Experiments were conducted to permit electrophysiological characterization of hypomagnesemia in sheep. For 6 weeks, adult wethers were fed: (1) a diet deficient in magnesium and calcium, (2) a diet deficient in magnesium, (3) a diet deficient in calcium and (4) a control diet. Weekly blood samples were collected to determine plasma concentrations of calcium (CA++), magnesium (Mg++) and potassium (K+). During the 6-week feeding period, electromyography (EMG), nerve conduction velocity (NCV) and strength-duration (S-D) determinations were conducted. At the end of a 6-week period, cerebrospinal fluid (CSF) samples also were taken from the cisterna magna and analyzed for Ca++, Mg++ and K+. The control plasma Mg++ concentration was 2.2 mg/100 ml. There was a depression (P less than .05) in plasma Mg++ in sheep that were fed diets deficient in Mg++ or deficient in Mg++ or Ca++. Plasma Mg++ concentrations in these two groups were .79 and .95 mg/100 ml, respectively, by the last week of diet feeding. EMGs performed during magnesium depletion were normal. In hypomagnesemic sheep, neither motor unit potentials (MUP) resulting from induced voluntary movement nor muscle-evoked potentials (EP) resulting from motor nerve stimulation showed differences (P less than .05) from those in control animals. NCV and muscle excitability (as evaluated by S-D curves) were normal in all sheep. CSF Ca++, Mg++ and K+ were not altered (P less than .05) in sheep fed any of the four diets.

Animals↗
PubMed1980

Maturation of nerve conduction velocity and the evoked muscle potential in the dog.

Maximum nerve conduction velocity (NCV) of motor fibers in the ulnar nerve was measured in dogs ranging in age from 12 hours after birth to 32 weeks and older. The evoked muscle potential (EMP) resulting from ulnar nerve stimulation was recorded from an interosseous muscle and measured for latency, duration, and amplitude. There was a sharp increase in NCV from 6.3 +/- 0.28 m/s (mean +/- SEM) in dogs from 12 hours to 1 week of age to 59.04 +/- 1.41 m/s in dogs 32 weeks and older. The latency of the EMP, resulting from stimulating the ulnar at either a proximal or a distal site, decreased markedly after birth to 4 to 5 weeks and then more gradually until 10 to 12 weeks. In dogs between 10 to 12 weeks and 32 weeks and older, latency increased but was never as high as in the newborn. Duration of the EMP followed a similar pattern. Amplitude increased sharply with age, resulting in a final 14- to 18-fold increase by 32 weeks and older.

Animals↗
PubMed1979

Failure of neuromuscular transmission after complete nerve section in the dog.

After the ulnar nerve was surgically transected, nerve conduction velocity in the distal segment and the evoked motor unit potential (EMUP) from the interosseous muscle were recorded until neuromuscular transmission failed. In five of the six dogs in the experiment, functional conduction ceased by 4.8 days, as determined by failure of both proximal and distal stimulation of the distal segment to evoke a muscle response. From the time of section until neuromuscular failure, the nerve conduction velocity remained unchanged. The amplitude of the EMUP from the interosseous muscle, however, decreased markedly during this time. Changes in other features of the EMUP are also presented. Fibrillation (denervation) potentials did not appear until the first day that muscle response could not be detected by stimulating the nerve. These data present a principle which would enable a determination of relative extent and progression of peripheral nerve damage.

Animals↗
PubMed1979

Porcine mastitis-metritis-agalactia (MMA) syndrome: mammary gland responsiveness to oxytocin given to healthy sows during lactation.

Mammary gland responsiveness to exogenous oxytocin during lactation was assessed by measuring changes in intramammary pressure of healthy sows given (IM injection) synthetic oxytocin (40 U). Response to oxytocin was measured once a week for the first 8 weeks of lactation. Recordings of pressure changes were expressed as mean area (cm2) under the trace at each 10-minute interval over 30 minutes after oxytocin had been given. During the 2nd week of lactation, there was a 55.3% increase (P less than 0.05) in responsiveness to oxytocin (25.1 +/- 4.2 cm2/10 minutes) as compared with the 1st week (13.9 +/- 2.2 cm2/10 minutes). Responsiveness decreased, however, from the 2nd to the 8th week. Since the incidence of mastitis-metritis-agalactia in sows is particularly high during the 1st week of lactation, low responsiveness of the mammary gland to oxytocin may be a contributing factor.

Animals↗
PubMed1977

Depressed thyroid function in two tetraplegic dogs.

Rapidly progressing tetraplegia developed in two 6-year-old dogs, both of which had eaten decayed meat sometime during the 24 hours prior to the onset of paralysis. Both dogs were found to have depressed thyroid function, as indicated by extremely low triiodothyronine (T3) and thyroxine (T4) values. Electromyographic studies revealed some abnormal insertional activity but no abnormal potentials when the fore- and hindlimb muscles were at total rest. Nerve conduction velocity was slightly depressed in 1 of the dogs and severely depressed in the other. Recovery was complete in less than 3 weeks in 1 dog, but the other dog was not completely recovered when placed under the owner's care 2 1/2 months after admission.

Animals↗
PubMedDate not supplied

Urodynamic evaluation of lower urinary tract function in cats after perineal urethrostomy with minimal and extensive dissection.

Perineal urethrostomy was performed in five male cats with minimal, sharp intrapelvic transection of the ischiocavernous and ischiourethralis muscles and ventral penile ligaments, and in five male cats with extensive blunt intrapelvic dissection and sharp muscle transection. Urethral pressure profiles and cystometrograms with simultaneous fine wire electrode sphincter electromyography were performed in sedated cats before surgery and on days 14 and 28. Premicturition pressure, urethral opening pressure, maximum detrusor pressure, total volume infused, and residual volume were measured during cystometry, and maximal urethral closure pressure was measured during profilometry. A grading of (+), (++), or ( ) was used to represent the intensity of electromyographic activity. There was no difference between minimal and extensive dissection for any cystometrogram or profile variable at days 14 or 28. Urethral opening pressure and maximal detrusor pressure during cystometrography were higher in preoperative studies than after minimal or extensive dissection. Sphincter electromyography after surgery was not significantly different from preoperative results in either surgical group. The results of this study indicate that neither sharp nor blunt intrapelvic dissection significantly alters the postoperative urodynamic status in male cats.

Animals↗
PubMedDate not supplied

Partial masking of the canine electroretinogram by oscillatory potentials. The problem of frequency bandwidth.

Recording the electroretinogram (ERG) in dogs has become a standard procedure in clinical ophthalmology. The ERG provides highly objective information about retinal function that is otherwise unobtainable from dogs. However, problems may be encountered in measuring the latencies amplitudes of the a and b waves, depending upon the amplifier bandwidth used to record the potential. Superimposed on the canine ERG are other complex retinal potentials, some of which have higher frequency spectra than those that give rise to a and b waves. Whereas an amplifier bandwidth of 1.0 to 100 Hz or more insures that the slower components of the ERG are recorded, it also allows higher frequency oscillatory potentials (OP) to be recorded on the b wave. The OP cause a notching in the peak of the b wave thus necessitating a decision about how to measure the b wave. Bandwidth characteristics of the ERG and OP are presented and some possible methods for measuring the OP-contaminated ERG are discussed.

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