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Biomedical subjects

J C Dort

Publications and source records attributed to J C Dort.

At least 19 recordsLinked to original sources
PubMed2001

Braking of expiratory airflow in obese pigs during wakefulness and sleep.

Braking of expiratory airflow is a phenomenon prominently seen in neonates where it is thought to defend end-expiratory lung volume. This paper describes pronounced expiratory braking in an adult animal, the obese Vietnamese pot-bellied pig. Three obese pigs were chronically instrumented for recording of intrapleural pressure and bioelectric signals related to sleep. Airflow was measured by a pneumotachograph attached to a facemask. Expiratory airflow resistance was calculated for 10 consecutive expirations during wakefulness, NREM, and REM sleep. All animals demonstrated a biphasic expiratory flow pattern characterized by an initial plateau in flow at a low value followed by a rapid increase later in expiration. Airflow resistance during early expiration was on average four-fold higher than during late expiration. A striking observation was the maintenance of pronounced expiratory braking during NREM and REM sleep. Expiratory braking in these animals is likely due to laryngeal mechanisms and may serve to preserve end-expiratory lung volume or improve hemodynamics.

Airway Resistance↗
PubMed2001

Screening for cerebellopontine angle tumours: conventional MRI vs T2 fast spin echo MRI.

BACKGROUND: Unilateral audiovestibular symptoms are commonly seen in clinical practice and are rarely caused by retrocochlear pathology. However, clinicians are often required to rule out potentially serious causes of these unilateral symptoms. Gadolinium enhanced magnetic resonance imaging (GdMRI) is the most accurate test for detecting small cerebellopontine angle lesions and also screens the adjacent CNS structures. Its main disadvantage is the cost of the procedure. METHODS: We studied 100 consecutive patients with both GdMRI and a newer MRI screening study utilizing unenhanced T2-weighted fast spin echo (fse) MRI. Acquired images were randomly assessed by a panel of three neuro-radiologists. RESULTS: We found that the screening (fse) MRI was as sensitive and specific when detecting cerebellopontine angle tumors. CONCLUSIONS: We conclude that T2-weighted fse MRI is a safe and cost-effective alternative to GdMRI and offers better diagnostic utility when compared to auditory brain stem response (ABR) and CT scans.

Brain Stem↗
PubMed2001

Investigation of skeletal muscle denervation and reinnervation using magnetic resonance spectroscopy.

OBJECTIVE: To determine changes in skeletal muscle metabolism after nerve transection and repair and to correlate metabolic changes with functional recovery. STUDY DESIGN AND SETTING: Male Wistar rats were divided into 6 experimental groups plus a control group. The posterior tibial nerve was transected and reapproximated. At varying times after surgery (1, 2, 4, 6, or 8 weeks) animals were sacrificed, the gastrocnemius muscle was harvested, and proton nuclear magnetic resonance (NMR) spectroscopy was performed. Functional recovery was measured using the sciatic function index. RESULTS: Animals undergoing nerve repair all showed functional recovery whereas the nonrepaired nerve group did not. Concentration of glucose and lactate increased after denervation and then returned toward normal. Choline concentration decreased and then returned toward normal. In animals not undergoing nerve repair, the metabolic abnormalities persisted and showed no sign of recovery over the 8-week observation period. CONCLUSIONS: 1H NMR spectroscopy is a potentially useful tool to study changes in skeletal muscle metabolism after motor nerve injury. SIGNIFICANCE: NMR spectroscopy is rapidly developing into a clinically useful tool. High-field magnets have improved resolution and data acquisition. Basic experiments, such as those described here, will help guide the use of NMR spectroscopy in clinical medicine and will also lead to a better understanding of basic mechanisms of nerve injury and repair.

Action Potentials↗
PubMed2001

Intraoperative magnetic resonance imaging for skull base surgery.

OBJECTIVES/HYPOTHESIS: Skull base surgery has evolved over the past several decades. Major improvements in the imaging of skull base pathology led to better target localization and better surgical planning. The objectives of this study were to assess the use of intraoperative magnetic resonance (MR) imaging in the management of a series of patients with skull base pathology. We hypothesized that high-quality intraoperative MR imaging would have an impact on surgery in this patient group. STUDY DESIGN: Prospective, non-randomized, cohort study. METHODS: Thirty-one patients with skull base lesions underwent surgery in a 1.5-Tesla intraoperative MR suite. The concepts of a moving magnet, high magnetic field strength, and radiofrequency coil design are presented. RESULTS: Eleven of 31 patients had the course of surgery significantly altered by the information acquired from the images obtained during surgery. CONCLUSIONS: Intraoperative MR imaging is a valuable adjunct to skull base surgery. One third of patients had altered surgery as a result of this adjunct. Intraoperative MR imaging is of particular value in the treatment of pituitary adenomas and benign skull base tumors.

Adenoma↗
PubMed2000

Screening strategies for neonatal hearing loss: which test is best?

OBJECTIVE: The objective of this study was to evaluate the accuracy and cost effectiveness of three different methods of hearing screening in newborns. DESIGN: A prospective, randomized cohort design was used. One hundred and five newborns were tested in this preliminary study. SETTING: The study was conducted in a tertiary care hospital setting in both the well baby and special care nurseries. METHODS: Consenting subjects had their hearing tested using automated auditory brainstem response (AABR), distortion-product otoacoustic emissions, and click-evoked otoacoustic emissions. The time to perform the tests was recorded and the cost of each test was calculated. MAIN OUTCOME MEASURES: The main outcomes measured were the time taken to perform each test, the pass/fail rate for each test, and the estimated cost of the tests. RESULTS: In this small cohort of patients, we found that AABR was the most accurate test, but it took longer to perform and was more expensive than either of the otoacoustic emission tests. However, the sensitivity and specificity of otoacoustic emissions were less than that of AABR. Test time decreased as the examiner gained experience, and we anticipate that experience will also result in better accuracy for the otoacoustic emission tests. CONCLUSIONS: Hearing screening in a hospital-based newborn population is both feasible and cost effective. Although AABR was more expensive, its better accuracy must be considered. As technology improves, the cost of all three tests will diminish. More robust conclusions cannot be made based on this small patient population.

Canada↗
PubMed1999

Monitoring respiratory function and sleep in the obese Vietnamese pot-bellied pig.

Development of drug treatments for obstructive sleep-disordered breathing has been impeded by the lack of animal models. The obese pig may be a suitable animal model, as it has been reported to experience sleep-disordered breathing resembling human obstructive sleep apnea. The purpose of this paper is to describe in detail techniques for chronic instrumentation of the obese Vietnamese pot-bellied pig and to study respiratory function during sleep. Under general anesthesia, four obese pigs were instrumented for long-term recording of intrapleural and tracheal pressures, genioglossal EMG, and bioelectric signals related to sleep. A custom-fitted face mask was used to record respiratory variables including airflow, snoring, and expired CO(2). Most chronic instrumentation provided robust signals for up to 6 wk after installation. All pigs displayed sleep-disordered breathing characterized by increased resistance to airflow, snoring, inspiratory flow limitation, and possible sleep disruption. Apneas and hypopneas were not a feature of breathing during sleep in these animals. Nonetheless, this animal preparation may be useful for exploring possible drug treatments for obstructive sleep-disordered breathing.

Animals↗
PubMed1997

Asymmetric hearing loss: toward cost-effective diagnosis.

OBJECTIVE: Unilateral audiovestibular symptoms are commonly seen in clinical practice, and the treating physician frequently considers retrocochlear disease in the differential diagnosis. These considerations often precipitate a lengthy and expensive battery of tests. This study was conducted to evaluate the diagnostic yield of the various tests available in the investigation of these symptoms and to recommend changes to practice patterns, if appropriate. METHODS: We examined a cohort of 310 patients with unilateral audiovestibular symptoms who were referred to our radiology department for investigation. All patients had complete auditory assessments, and 144 underwent auditory evoked potential testing (ABR). There were 258 contrast-enhanced CT (CECT) scans and 86 gadolinium-enhanced MRI (Gd-MRI) scans performed. RESULTS: A total of 12 cerebellopontine angle (CPA) tumours were diagnosed. CONCLUSIONS: MRI is the diagnostic tool of choice in patients with asymmetric sensory neural hearing loss (ASHL), but it is expensive and not always easily available. Analysis of diagnostic accuracy of CECT and ABR, both used as screening tests, demonstrate their limitations and reveals that CECT is no more accurate than ABR, although it is three times more costly. Based on these data, we have changed our diagnostic approach to patients with unilateral audiovestibular symptoms. Patients are either evaluated with MRI or are screened initially with ABR based on clinical suspicion. CECT is no longer routinely included in the evaluation of patients with ASHL. Finally, newer emerging MRI techniques promise faster and less expensive examinations with increased diagnostic accuracy.

Algorithms↗
PubMed1997

Magnetic resonance imaging of the extratemporal facial nerve of the rat.

OBJECTIVE: Magnetic resonance imaging (MRI) is an evolving technology that is being investigated for application in the study of the facial nerve. At the present time the majority of investigators use paramagnetic contrast agents, and the clinical utility of MRI for evaluation of facial paralysis is unproved. This study investigated both normal and injured rat facial nerves without contrast enhancement. METHOD: Anatomic dissection and histologic studies were performed to better define the location of the facial nerve. A surface coil was used to improve image resolution. RESULTS: Proton-weighted images showed that the normal facial nerve was a solid structure while the injured facial nerve was bright on T2-weighted images. CONCLUSION: MRI is a potentially useful method of investigating patients with facial nerve dysfunction. Further research is needed to clarify its role.

Animals↗
PubMed1997

Biochemical changes in denervated muscle identified by magnetic resonance spectroscopy.

OBJECTIVE: Magnetic resonance spectroscopy (MRS) has the potential to noninvasively delineate early biochemical changes in denervated muscle. In this study, we examine metabolic changes in denervated rat facial muscles using quantitative invitro 1H and 31P MRS. METHODS: Forty male Wistar rats were subjected to transection of the facial nerve trunk on the left and sham exposure on the right, and allowed to recover. The animals were then reoperated at 1, 2, 4, or 8 weeks after the initial procedure. EMG of the facial muscles and facial nerve conduction studies were performed at both time points, and facial muscles were harvested from normal and control sides at the second procedure. Perchloric acid extracts of facial muscles were then prepared for analysis using MRS. RESULTS: The results showed a progressive time-dependent decrease in Cr, PCr, Pi, ATP, and ADP all on the transected side. CONCLUSION: This study is an important step in the development of clinically relevant noninvasive methods of assessing and quantifying degeneration in nerve-muscle systems.

Adenosine Diphosphate↗
PubMed1996

Posttraumatic macroglossia complicated by hyaluronidase injection.

A patient with posttraumatic macroglossia has been presented. A literature review reveals that this is a rare sequela of tongue injury and is usually of acute onset. The delayed symptom of swelling in this patient and the exacerbation of swelling in association with hyaluronidase suggest a causal relationship between the two events. Macroglossia has not been reported in association with hyaluronidase injection, and it is recommended that the drug not be used to treat swelling after tongue injury.

Adult↗
PubMed1995

Nonmetallic foreign bodies of the skull base: a diagnostic challenge.

Cases of physical trauma have become more common in emergency departments, since life in modern society has become increasingly dangerous. Foreign bodies in the head and neck region are more common, therefore, and management principles are well-defined. Typically, these foreign bodies are metal, plastic, or glass and often easily diagnosed; however, wooden foreign bodies pose special problems for the physician and, therefore, warrant separate consideration. We present the case of a 21-year-old male who was stabbed in the submental region with a large wooden stake and discuss the surgical and follow-up treatment of this interesting case, including the roles and limitations of angiography, computerized tomography, and magnetic resonance imaging.

Adult↗
PubMed1994

CO2 laser repair of the facial nerve: an experimental study in the rat.

The facial nerve is often injured by trauma, infection or during the course of tumour resection. Many techniques of nerve anastomosis have been described with the current standard nerve repair using the microscope and monofilament suture. The purpose of this study was to evaluate the CO2 surgical laser as a tool for facial nerve anastomosis. Following preliminary electrical measurements 36 nerves were anastomosed using either laser or conventional monofilament suture. Laser anastomosis had neither beneficial nor detrimental effects on nerve regeneration. This method of anastomosis may be advantageous when surgical access is limited. In addition this study found that the use of CO2 laser as a dissecting or vapourizing tool in proximity to intact facial nerves results in degenerative changes.

Anastomosis, Surgical↗
PubMed1994

Unilateral vestibular deafferentation: a model of adaptation.

After acute loss of peripheral vestibular function, a centrally adaptive process takes place. Clinical measurements of vestibular adaptation are useful, both diagnostically and as a means of following patients after acute vestibular deficits. Ocular torsion is one measurement that can be used to follow these acutely disabled patients. The measurement is made from fundus photographs and is technically easy to perform and interpret. We present a pilot study from our Vestibular Disorders Clinic using fundus photography to measure the optic nerve head-foveal angle in six patients undergoing unilateral vestibular neurectomy, with subsequent analysis resulting in a speculative mathematical model of vestibular compensation in the roll plane. While the identification or selection of patients with significant ocular torsions from the vestibular population remains ill-defined, fundus photography remains an easy and useful method of following compensation in postoperative patients.

Adaptation, Physiological↗
PubMed1994

Acute epiglottitis in adults: diagnosis and treatment in 43 patients.

Epiglottitis (supraglottitis) is an acute infection involving the supraglottic larynx that usually occurs in children, but can also affect adult patients. The purpose of this study was to retrospectively analyze diagnostic and treatment methods in adults with epiglottitis seen over a 10-year period at the Winnipeg Health Sciences Centre. Forty-three epiglottitis patients over the age of 16 were treated between 1982 and 1992. Treatment was individualized according to airway status at presentation, and not based on clinical staging protocols. A total of 29 patients were treated conservatively, whereas 14 patients were intubated immediately. One expectantly managed patient had to be intubated on the ward, and one patient died from septicemia. No presenting symptom or sign reliably predicted the need for intubation. Epiglottitis is seen in adults and can be easily and safely diagnosed by either indirect or flexible laryngoscopy. Endotracheal intubation is the safest and most direct means of securing the airway in severely affected patients. Staging systems are useful for retrospective data analysis, but should not be relied on to predict the course of patients with an inherently unpredictable disease.

Acute Disease↗