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Biomedical subjects

J H Owen

Publications and source records attributed to J H Owen.

At least 19 recordsLinked to original sources
PubMed2005

Participatory rural appraisal to investigate constraints in reporting cattle mortalities in the Odi district of North West Province, south Africa.

Mortalities in cattle can have severe financial implications for small scale and communal farmers in South Africa. They could also be a measurable indicator for surveillance of animal diseases, such as those listed by the Office International des Epizooties (OIE), or diseases included in the regulations of the South African Animal Diseases Act, 1984 (Act 35 of 1984). In order to prevent further mortalities and for accurate surveillance and monitoring of diseases, it is important that farmers participate in the determination of causes of mortality in their cattle. This paper reports on constraints of the reporting diseases to the state veterinary services, the study area being Odi district, in the North West Province. The method that was followed was based on participatory rural appraisal. The selected cattle owners participated in every phase. They were the ones who first spoke to veterinary services about ways to decrease the diseases and mortalities of their cattle. A questionnaire to verify the facts complemented the survey. A total number of 60 farmers were randomly selected from 12 villages. One farmer withdrew, leaving 59 farmers. Most of the farmers in the study were men ( n = 55). The area of study was communal and the farming system traditional and extensive. It was suspected that there was a communication problem and this was proven by the results of the research, as 23 farmers were not even aware that mortalities have to be reported by law. The real problem was that causes of death were not being diagnosed because farmers were not aware that a necropsy could give information on the causes of death. Farmers were keen to receive training in elementary necropsy techniques so as to be able to discuss the cause of death of cattle with the state veterinarian.

Adult↗
PubMed2003

Mathematics at matriculation level as an indicator of success or failure in the 1st year of the Veterinary Nursing Diploma at the Faculty of Veterinary Science, University of Pretoria.

Mathematics at matriculation level (Grade 12) is one of the subjects required for admission to the Veterinary Nursing Diploma in the Faculty at Veterinary Science of the University of Pretoria. The present study shows that there is no statistically significant relationship between the grade of mathematics at matriculation level and the success or failure in the 1st year of study. There is, however, a statistical difference in the adjusted mark obtained for mathematics at matriculation level between the groups that passed and failed the 1st year of the veterinary nursing course. The results of this research are not consistent with other research which showed that secondary school mathematics results are not a significant factor in tertiary education. It is recommended that selection criteria for veterinary nurses should in future still include mathematics, but that cognisance should be taken of the mark obtained and students with higher marks (above 57%) given preference.

Achievement↗
PubMed2000

Relative effectiveness of electrically- vs mechanically-elicited EMGs in detecting pedicle wall perforation and surgically-induced nerve root damage.

Electrical stimulation of a pedicle hole and screw with recording EMGs from the lower extremities has been used as an indicator in detecting perforations of the pedicle. Mechanically-elicited EMGs are reported to be sensitive to mechanical irritation of nerve roots. This study analyzed the sensitivity of the data elicited by two EMG monitoring methods in the presence of a neurologic deficit caused by a malpositioned screw to determine the relative effectiveness of electrically- vs mechanically-elicited EMGs in detecting pedicle wall perforations and nerve root damage in patients undergoing spinal surgery utilizing transpedicular instrumentation. One hundred and four surgeries were monitored using the two EMG methods. Six hundred and fifty-four pedicle holes were prepared and 650 placed pedicle screws were electrically tested. Mechanically-elicited EMGs were monitored from a total of 618 muscles. Electrically-elicited EMGs showed a 62% true-positive rate and a 0.2% false-negative rate in detecting pedicle wall perforations. None of the patients who initially demonstrated abnormal electrically-elicited EMGs demonstrated any post-operative neurologic problems due to an incorrect screw placement. Only one patient who had abnormal mechanically-elicited EMGs during the procedures related to instrumentation developed new L4 radiculopathy immediately post-operatively which was consistent with the level of mechanically-elicited EMGs. Mechanically-elicited EMGs showed a 100% true-positive rate for nerve root irritation and a 3.5% false-negative rate in detecting pedicle wall perforations by malpositioned screw. In conclusion, although mechanically-elicited EMGs were an insensitive technique in detecting a perforation of the pedicle, mechanically-elicited EMGs were more beneficial than electrically-elicited EMGs in detecting the risk of nerve root irritation.

Adult↗
PubMed1998

A comparison of impedance and electromyogram measurements in detecting the presence of pedicle wall breakthrough.

STUDY DESIGN: A prospective comparison of impedance measurements, electrically elicited electromyograms, and mechanically elicited electromyograms to detect pedicle wall breakthrough. OBJECTIVE: To determine whether impedance measurements are as sensitive as electromyogram measurements in evaluating pedicle wall breakthrough. SUMMARY OF BACKGROUND DATA: In a previous animal study, impedance values in pedicle screw placement were tested, to determine a baseline value for an intact pedicle. If pedicle wall breakthrough occurred, it was thought that the impedance values should be significantly lower. METHODS: Impedance measurements, electrically elicited electromyograms and mechanically elicited electromyograms were recorded in 20 patients undergoing surgery for spinal degeneration, using previously described standard protocol. Analysis of variance statistics were used to evaluate the data. RESULTS: Impedance values for the pedicle holes varied from 500 ohms to 31,000 ohms. There was no correlation between these values and those of the two pedicles in which breaches were detected on visual inspection. Electrically elicited electromyograms detected the breakthroughs in both pedicles, whereas mechanically elicited electromyograms detected one of the breakthroughs. CONCLUSIONS: Electrically elicited electromyograms were more sensitive in detecting pedicle wall breakthrough than were impedance measurements. This may be because of the inability to ascribe absolute impedance values to human pedicle bone caused by the wide variability in bone quality.

Adult↗
PubMed1996

Use of spontaneous electromyography during revision and complex total hip arthroplasty.

Intraoperative peripheral nerve injury is a serious potential complication of orthopaedic surgery and various intraoperative neurophysiologic monitoring techniques have been used to avoid this complication. Although somatosensory evoked potentials have been used effectively in spinal surgery, the efficacy of this technique has not been demonstrated in total hip arthroplasty. Spontaneous electromyography is a promising, alternative nerve monitoring technique. This technique was used in 44 consecutive revision and complex hip arthroplasty procedures. Five cases demonstrated sustained electromyography activity during surgery that subsided after retractors were removed and the limb brought into an anatomic position. In none of these five cases was there any evidence of clinical neurologic dysfunction after surgery. One patient developed causalgia without any motor deficit, but had no sustained electromyography activity during surgery. Spontaneous electromyography provides real-time monitoring of nerve function that allows immediate corrective action to be taken before nerve injury occurs.

Adolescent↗
PubMed1996

Evaluation of pedicle screw insertion monitored by intraoperative evoked electromyography.

The insertion of pedicle screws monitored by evoked electromyography (EMG) was prospectively evaluated in the 132 consecutive patients. The technique involved constant-voltage stimulation and was statistically evaluated at both the arbitrary 20- and 40-V settings. The patients were postoperatively evaluated clinically and radiographically. Computed tomography (CT) scanning was performed for new neurologic deficits. Results were divided into three groups: type 1, a negative EMG response; type 2, a positive EMG response, but no corrective action taken; and type 3, a positive EMG response and corrective action undertaken. Nonparametric statistics were used to evaluate the results at both the 20- and 40-V settings. In the type 3 group, in which corrective action was undertaken, there were no neurologic injuries or screw removals, a statistically significant result. Looking at the two intensity levels, at 20- and 40-V settings, there were no statistically significant differences in the three classifications at either intensity level. We concluded the evoked EMG for monitoring pedicle screw insertion is an efficacious adjunct. A positive response at < 20 V with the constant-voltage technique warrants corrective action.

Adult↗
PubMed1996

Neurogenic motor evoked-potential monitoring in anterior cervical surgery.

A prospective evaluation of a consecutive series of patients undergoing anterior cervical surgery monitored by the neurogenic motor evoked-potential technique. To evaluate the efficacy of neurogenic motor evoked-potential (NMEP) monitoring and its ability to predict clinical outcome in anterior cervical surgery. Forty-nine consecutive patients undergoing anterior cervical surgery were monitored using NMEP technique and were followed prospectively. Latency and amplitude data from the median and ulnar nerves were recorded and evaluated at baseline and at closure. Because existing injury or needle placement may affect absolute values, ratios of the data from both sides were used. All patients had their data evaluated for detection of intraoperative neurological injury. Thirty-eight patients had a monoradiculopathy on presentation and were followed for > 1 year and had either a good or excellent clinical result by the Odom criteria. The NMEP data from these patients were evaluated using the paired Student's test, looking for improvement during surgery. No patient had diminution of NMEP data nor a worsening or new neurological deficit. In patients with symptoms < 1 year before surgery, significant improvement was seen in the ipsilateral median nerve ratios (p = 0.05). No statistically significant results were seen in the ulnar nerve latencies or in the amplitude from either nerve. In patients with symptoms > 1 year, no statistically significant improvement was seen in any parameters. NMEP monitoring of anterior cervical surgery is a promising technique, allowing evaluation of the motor tracts. Duration of symptoms affects NMEP results. Intraoperative improvement of NMEP data after decompression may predict improved clinical outcome.

Adult↗
PubMed1995

Efficacy of multimodality spinal cord monitoring during surgery for neuromuscular scoliosis.

STUDY DESIGN: This study determined the relative efficacy of somatosensory-evoked potentials and motor-evoked potentials in monitoring spinal cord function during surgery for patients with idiopathic versus neuromuscular scoliosis. OBJECTIVES: To determine whether patients with idiopathic versus neuromuscular scoliosis demonstrate significantly different somatosensory-evoked potentials and motor-evoked potentials recorded during surgery. SUMMARY OF BACKGROUND DATA: Ashkenaze et al (1993) and others have reported that cortical somatosensory-evoked potentials are unreliable when used to monitor spinal cord function in patients with neuromuscular scoliosis. It was recommended that other neurophysiologic tests be used. METHODS: Somatosensory-evoked potentials and motor-evoked potentials were recorded from two groups of patients: those with idiopathic scoliosis and those with neuromuscular scoliosis. Somatosensory-evoked potentials were obtained before and during surgery. Motor-evoked potentials were obtained during surgery. Normal variability, as indicated from idiopathic scoliotic results, was compared with data obtained from patients with neuromuscular scoliosis. Motor-evoked potentials and somatosensory-evoked potentials were obtained sequentially during the duration of surgery. RESULTS: Single-channel cortical somatosensory-evoked potentials demonstrated a 27% positive rate, which was consistent with results (28%) from Ashkenaze et al. The use of multiple recording sites for the somatosensory-evoked potentials and the addition of motor-evoked potential procedures indicated that a reliable response could be obtained in more than 96% of the patients. It also was found that cortical somatosensory-evoked potentials were more affected by anesthetic agents when recorded from patients with neuromuscular scoliosis compared with patients with idiopathic scoliosis. CONCLUSIONS: Single-channel cortical somatosensory-evoked potentials demonstrated a high level of unreliability, which reduced their clinical effectiveness. However, by using multiple recording sites with the somatosensory-evoked potentials and by administering motor-evoked potential procedures, it was possible to monitor spinal cord function in neuromuscular patients and avoid postoperative neurologic deficits.

Adolescent↗
PubMed1995

Relationship between evoked potentials and clinical status in spinal cord ischemia.

STUDY DESIGN AND METHODS: Sciatic neurogenic motor-evoked potentials, spinal evoked potentials, and somatosensory-evoked potentials were recorded in 12 anesthetized dogs that had arterial ischemia of the lumbar cord produced by ligation of segmental arteries. The presence or absence of the above-mentioned potentials was compared with the clinical status of repeated wake-up tests. RESULTS: Although these results were complicated, sciatic neurogenic motor-evoked potential was more sensitive to the spinal cord ischemia and was a better predictor of clinical outcome than spinal evoked potential and somatosensory-evoked potential. However, the presence was not a guarantee of normal function. The initial morphologic change of these potentials secondary to ischemia consisted of a decrease in amplitude and in the number of peaks without a shift of latency. CONCLUSIONS: The present study suggests that the peripheral neurogenic motor-evoked potential is a better warning system for spinal cord ischemia and that its adoption may contribute to the prevention of cord ischemia during spinal surgery, whereas somatosensory-evoked potential and spinal evoked potential cannot be indices.

Animals↗
PubMed1995

Measurement of pudendal evoked potentials during feminizing genitoplasty: technique and applications.

We report on 6 patients (average age 13 months) with ambiguous genitalia who underwent stimulation of the dorsal neurovascular bundle of the phallus during feminizing genitoplasty. Three patients had the adrenogenital syndrome, 1 underwent removal of a masculinizing adrenal tumor before genital reconstruction, 1 had mixed gonadal dysgenesis and 1 had male pseudohermaphroditism. Stimulation of the dorsal neurovascular bundle with measurement of electromyographic nerve conduction latencies was performed before and after ligation of the corporeal bodies and excision of the erectile tissue. In all 6 cases electromyographic responses were preserved after phallic reduction. Our study clearly shows that modern techniques of genital reconstruction allow for preservation of nerve conduction in the dorsal neurovascular bundle and may permit normal sexual function in adulthood.

Clitoris↗
PubMed1994

Magnetic stimulation of the spine to produce lower extremity EMG responses. Significance of coil position and the presence of bone.

STUDY DESIGN: Magnetic stimulation of the spinal cord in 14 pigs was performed, and compound muscle action potentials (CMAPs) were recorded from lower extremities before and after nerve root and spinal cord lesioning. OBJECTIVES: The authors determined whether magnetic stimulation of the spinal cord produced lower extremity CMAPs. SUMMARY OF BACKGROUND DATA: Previous studies indicated that the magnetic stimulation of the spinal cord would result in lower extremity CMAP if appropriate amounts of spinal bone were removed to expose the spinal cord. RESULTS: Our findings demonstrated that the presence of intervening bone did not affect the reliability or presence of lower extremity CMAPs. Additionally, magnetic stimulation did not result in spinal cord activation but produced activity in nerve roots lateral to nerve root foramen. Lesioning of the spinal cord and complete rhizotomies did not affect magnetically elicited CMAPs. CONCLUSIONS: Magnetic stimulation of the spinal canal does not result in activation of spinal cord motor tracts. Lower extremity CMAPs were elicited by stimulation of nerve roots lateral to nerve root foramen and not of the spinal cord. Magnetic stimulation of the spinal cord is not appropriate for monitoring spinal cord motor tract function.

Animals↗
PubMed1994

The use of mechanically elicited electromyograms to protect nerve roots during surgery for spinal degeneration.

STUDY DESIGN: This study investigated the use of mechanically elicited electromyograms during the placement of pedicle screws in 89 patients undergoing surgery for spinal stenosis. SUMMARY OF BACKGROUND DATA: Several methods for monitoring nerve roots are available. However, mechanically elicited electromyograms may be more sensitive to mechanical irritation of nerve roots by pedicle screws than by other methods. METHODS: Mechanically elicited electromyograms were recorded in muscle groups innervated by cervical or lumbar nerve roots. Confirmation of surgical activity with the level of the electromyogram was correlated. RESULTS: Results indicated that mechanically elicited electromyograms are extremely sensitive to nerve root irritation. Compared to other methods, electromyograms are a viable alternative. CONCLUSIONS: Results from this study indicated that mechanically elicited electromyograms are sensitive and specific to nerve root firings and should be considered for use during the dynamic phases of surgery.

Bone Screws↗
PubMed1994

Relationship between evoked potentials and clinical status in spinal cord ischemia.

STUDY DESIGN: Sciatic neurogenic motor-evoked potentials (sciatic-NMEP), spinal-evoked potentials (spinal-EP), and somatosensory-evoked potentials (SEP) were recorded in the lumbar cord during progressive ligation of segmental arteries. Relationship between electrophysiologic assessment and clinical status was studied. OBJECTIVES: In 12 anesthetized dogs that had arterial ischemia of the lumbar cord produced by ligation of segmental arteries, the aforementioned evoked potentials were recorded, and their presence or absence was compared with the clinical status of repeated wake-up tests. SUMMARY OF BACKGROUND DATA: Both sciatic-NMEP loss and ligation level producing cord ischemia were not associated with severity of wake-up test. Sciatic-NMEPs were lost earlier than spinal-EP and SEPs after progressive ligation. The false-negative rate of sciatic-NMEP, SEP at high spine and at low spine was 12.5%, 20.8%, and 41.7%, respectively. The waveform morphology of potentials by cord ischemia decreased in amplitude and in the number of peaks without a shift of latency. METHODS: First, baseline NMEPs and SEPs were obtained, lumbar arteries were ligated, evoked potentials were recorded continuously, and wake-up test was administered. If sciatic-NMEPs were not lost, intercostal arteries were ligated, and potentials and clinical status were reassessed. RESULTS: Though these results were complicated, sciatic-NMEP was more sensitive to the spinal cord ischemia and a better predictor of clinical outcome than spinal-EP and SEP. However, the presence was not a guarantee of normal function. Somatosensory-evoked potentials are not a good predictor of clinical motor status. The initial morphologic change of these potentials secondary to ischemia consisted of a decrease in amplitude and in the number of peaks without a shift of latency. CONCLUSIONS: The peripheral-NMEP is a better warning system to spinal cord ischemia and its adoption may prevent cord ischemia during surgery, whereas SEP and spinal-EP can not be indicies.

Animals↗
PubMed1994

Post-exercise rehydration in man: effects of electrolyte addition to ingested fluids.

This study examined the effects on water balance of adding electrolytes to fluids ingested after exercise-induced dehydration. Eight healthy male volunteers were dehydrated by approximately 2% of body mass by intermittent cycle exercise. Over a 30-min period after exercise, subjects ingested one of the four test drinks of a volume equivalent to their body mass loss. Drink A was a 90 mmol.l-1 glucose solution; drink B contained 60 mmol.l-1 sodium chloride; drink C contained 25 mmol.l-1 potassium chloride; drink D contained 90 mmol.l-1 glucose, 60 mmol.l-1 sodium chloride and 25 mmol.l-1 potassium chloride. Treatment order was randomised. Blood and urine samples were obtained at intervals throughout the study; subjects remained fasted throughout. Plasma volume increased to the same extent after the rehydration period on all treatments. Serum electrolyte (Na+, K+ and Cl-) concentrations fell initially after rehydration before returning to their pre-exercise levels. Cumulative urine output was greater after ingestion of drink A than after ingestion of any of the other drinks. On the morning following the trial, subjects were in greater net negative fluid balance [mean (SEM); P < 0.02] on trial A [745 (130) ml] than on trials B [405 (51) ml], C [467 (87) ml] or D [407 (34) ml]. There were no differences at any time between the three electrolyte-containing solutions in urine output or net fluid balance. One hour after the end of the rehydration period, urine osmolality had fallen, with a significant treatment effect (P = 0.016); urine osmolality was lowest after ingestion of drink A.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

The effect of nerve root lesioning on various somatosensory evoked potentials in the hog.

Somatosensory evoked potentials (SEPs) were recorded at the lumbar spine following stimulation of the tibial nerve (mixed-nerve SEP; MSEP), the sural nerve (specific nerve SEP; SSEP), and the skin corresponding to the L6 and S1 dermatomes (dermatomal field SEP; DSEP-L and DSEP-S) in the hog. To determine the sensitivity of these three SEPs to the single nerve root (S1 root) function, the effects of nerve roots lesioning were investigated. Cutting S1 nerve root reduced the peak-to-peak amplitude of MSEP by only 28% in comparison with baseline values. The relative amplitudes of SSEP, DSEP-L, and DSEP-S were decreased by 46%, 11% and 51%, respectively. When S1 nerve root was left intact and L5, L6, and S2 nerve roots were cut, the relative amplitudes of MSEP, SSEP, DSEP-L, and DSEP-S were decreased to 68%, 73%, 31%, and 74%, respectively. These results indicate that DSEP-S is as sensitive to the function of S1 nerve root as SSEP but the sensitivities of DSEP-S and SSEP are low in the hog. MSEP is shown unsuitable to monitor the single nerve root dysfunction.

Animals↗
PubMed1993

Innervation pattern of dorsal roots and their effects on the specificity of dermatomal somatosensory evoked potentials.

Dermatomal somatosensory evoked potentials are used to monitor individual nerve root function during degenerative spinal surgery. However, a less than 100% agreement between level(s) of dermatomal somatosensory evoked potentials abnormality and nerve root involvement has been reported. The purpose of this article was to determine the possible cause of this discrepancy. Results from humans suggest that variations in peripheral innervation patterns of the dorsal nerve roots are the main reason for dermatomal somatosensory evoked potentials discrepancy both for cervical and lumbar nerve roots. Because these variations cannot be controlled, the authors recommend that dermatomal somatosensory evoked potentials and additional neurophysiologic methods be used during degenerative surgeries to provide the surgeon with information about individual nerve root function. A patient profile for these methods was provided.

Animals↗