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Biomedical subjects

David Howard

Publications and source records attributed to David Howard.

At least 19 recordsLinked to original sources
PubMed2006

Laryngocele: a rare complication of surgical tracheostomy.

BACKGROUND: A laryngocele is usually a cystic dilatation of the laryngeal saccule. The etiology behind its occurrence is still unclear, but congenital and acquired factors have been implicated in its development. CASE PRESENTATION: We present a rare case of laryngocele occurring in a 77-year-old Caucasian woman. The patient presented with one month history of altered voice, no other associated symptoms were reported. The medical history of the patient included respiratory failure secondary to childhood polio at the age of ten; the airway management included a surgical tracheostomy. Flexible naso-laryngoscopy revealed a soft mass arising from the posterior pharyngeal wall obscuring the view of the posterior commissure and vocal folds. The shape of the mass altered with respiration and on performing valsalva maneuver. A plain lateral neck radiograph revealed a large air filled sac originating from the laryngeal cartilages and extending along the posterior pharyngeal wall. The patient was then treated by endoscopic laser marsupialization and reviewed annually.We discuss the complications of tracheostomy and the pathophysiology of laryngoceles and in particular the likely aetiological factors in this case. CONCLUSION: A laryngocele presenting in a female patient with tracheostomy is extremely rare and has not been to date reported in the world literature. A local mechanical condition may be the determinant factor in the pathogenesis of the disease.

Aged↗
PubMed2006

Predictive modelling of human walking over a complete gait cycle.

An inverse dynamics multi-segment model of the body was combined with optimisation techniques to simulate normal walking in the sagittal plane on level ground. Walking is formulated as an optimal motor task subject to multiple constraints with minimisation of mechanical energy expenditure over a complete gait cycle being the performance criterion. All segmental motions and ground reactions were predicted from only three simple gait descriptors (inputs): walking velocity, cycle period and double stance duration. Quantitative comparisons of the model predictions with gait measurements show that the model reproduced the significant characteristics of normal gait in the sagittal plane. The simulation results suggest that minimising energy expenditure is a primary control objective in normal walking. However, there is also some evidence for the existence of multiple concurrent performance objectives.

Biomechanical Phenomena↗
PubMed2006

Cumulative semantic inhibition in picture naming: experimental and computational studies.

We report an experiment in which subjects named 120 pictures, consisting of series of five pictures drawn from each of 24 semantic categories (and intermixed with 45 fillers). The number of intervening trials (lag) between successive presentations of members of the same category varied from two to eight. Subjects' naming latencies were slowed by 30 ms for each preceding member of the category. This effect was both cumulative and linear, and unrelated to the lag elapsing since the previous presentation of a category member. These results definitively demonstrate the occurrence of cumulative interference for word retrieval by prior retrieval of other exemplars of the same semantic category-cumulative semantic inhibition. We claim that this inhibition effect could only occur if the spoken word production system possesses three specific properties (competition, priming, and sharing of semantic activation). We provide computational-modelling evidence in support of this claim. We show that no current theory of spoken word production has all of these properties. In their current form, all these theories are falsified by these results. We briefly discuss the obstacles that may be encountered by current models were they modified to account for our findings.

Adolescent↗
PubMed2006

Re-visiting "semantic facilitation" of word retrieval for people with aphasia: facilitation yes but semantic no.

Previous research has shown that word-to-picture matching for targets that cannot be named at pre-test results in improved naming relative to untreated control items for people with aphasia. This paper replicates and extends this finding and investigates its source. Is the effect a result of priming of semantic representations, or of post-semantic mechanisms in word retrieval? The first experiment shows that word-to-picture matching with unrelated distractors improves naming at short (2-3 minutes) and long (up to 25 minute) lags. There was no effect of being made aware of the relationship between word-to-picture matching and picture naming. People who have a semantic impairment improve only with a short lag between word-to-picture matching and naming. Participants with less semantic impairment show larger priming effects that are equal at short and long lags between word-to-picture matching and naming. The second experiment shows that the facilitation effect is just as large for word-to-picture matching with unrelated distractors as with semantically-related distractors. Furthermore, overall there was no difference between matching with coordinate items and with associated items. The results of these experiments show that facilitation of naming by word-to-picture matching in people with aphasia cannot be a result of the priming of semantic representations. Instead they are consistent with two effects: word-to-picture matching results in priming at a lemma level for aphasic people with a semantic impairment that is only found with a short lag between word-to-picture matching and naming. Word-to-picture matching causes priming of the lemma to output lexicon entry mapping that benefits participants with less semantic impairment that is evident at both a short and long lag between word-to-picture matching and naming. These findings fit well with previous research on repetition priming of naming with normal subjects.

Aphasia↗
PubMed2005

Listening to narrative speech after aphasic stroke: the role of the left anterior temporal lobe.

The dorsal bank of the primate superior temporal sulcus (STS) is a polysensory area with rich connections to unimodal sensory association cortices. These include auditory projections that process complex acoustic information, including conspecific vocalizations. We investigated whether an extensive left posterior temporal (Wernicke's area) lesion, which included destruction of early auditory cortex, may contribute to impaired spoken narrative comprehension as a consequence of reduced function in the anterior STS, a region not included within the boundary of infarction. Listening to narratives in normal subjects activated the posterior-anterior extent of the left STS, as far forward as the temporal pole. The presence of a Wernicke's area lesion was associated with both impaired sentence comprehension and a reduced physiological response to heard narratives in the intact anterior left STS when compared to aphasic patients without temporal lobe damage and normal controls. Thus, in addition to the loss of language function in left posterior temporal cortex as the direct result of infarction, posterior ablation that includes primary and early association auditory cortex impairs language function in the intact anterior left temporal lobe. The implication is that clinical studies of language on stroke patients have underestimated the role of left anterior temporal cortex in comprehension of narrative speech.

Adult↗
PubMed2005

"The W and M are mixing me up": use of a visual code in verbal short-term memory tasks.

When normal participants are presented with written verbal short-term memory tasks (e.g., remembering a set of letters for immediate spoken recall) there is evidence to suggest that the information is re-coded into phonological form. This paper presents a single case study of MJK whose reading follows the pattern of phonological dyslexia. In short-term memory tasks MJK does not phonologically re-code written materials but, it is argued, uses a visual code. There are three main lines of evidence for this, (a) MJK tends to substitute visually similar items for one another, (b) her performance is better with visual than auditory stimuli, and (c) she is able to remember numbers (e.g., 8) better than written words (e.g., eight). Investigation of short-term memory in others with phonological dyslexia is warranted.

Acoustic Stimulation↗
PubMed2005

Dynamic analysis of load carriage biomechanics during level walking.

This paper describes an investigation into the biomechanical effects of load carriage dynamics on human locomotion performance. A whole body, inverse dynamics gait model has been developed which uses only kinematic input data to define the gait cycle. To provide input data, three-dimensional gait measurements have been conducted to capture whole body motion while carrying a backpack. A nonlinear suspension model is employed to describe the backpack dynamics. The model parameters for a particular backpack system can be identified using a dynamic load carriage test-rig. Biomechanical assessments have been conducted based on combined gait and pack simulations. It was found that the backpack suspension stiffness and damping have little effect on human locomotion energetics. However, decreasing suspension stiffness offers important biomechanical advantages. The peak values of vertical pack force, acting on the trunk, and lower limb joint loads are all moderated. This would reduce shoulder strap pressures and the risk of injury when heavy loads are carried.

Biomechanical Phenomena↗
PubMed2005

Automated design of robust discriminant analysis classifier for foot pressure lesions using kinematic data.

In the recent years, the use of motion tracking systems for acquisition of functional biomechanical gait data, has received increasing interest due to the richness and accuracy of the measured kinematic information. However, costs frequently restrict the number of subjects employed, and this makes the dimensionality of the collected data far higher than the available samples. This paper applies discriminant analysis algorithms to the classification of patients with different types of foot lesions, in order to establish an association between foot motion and lesion formation. With primary attention to small sample size situations, we compare different types of Bayesian classifiers and evaluate their performance with various dimensionality reduction techniques for feature extraction, as well as search methods for selection of raw kinematic variables. Finally, we propose a novel integrated method which fine-tunes the classifier parameters and selects the most relevant kinematic variables simultaneously. Performance comparisons are using robust resampling techniques such as Bootstrap 632+ and k-fold cross-validation. Results from experimentations with lesion subjects suffering from pathological plantar hyperkeratosis, show that the proposed method can lead to approximately 96% correct classification rates with less than 10% of the original features.

Adult↗
PubMed2005

Securing tracheal stents: a new and simple method.

Indwelling silastic stents have been used in the subglottis and upper trachea to manage laryngotracheal abnormalities. A number of methods of fixation have been described. The authors describe a quick and simple method of fixing endoluminal tracheal stents using a single suture.

Humans↗
PubMed2004

Endomyocardial biopsy plays a role in diagnosing patients with unexplained cardiomyopathy.

BACKGROUND: The etiology of cardiomyopathy is usually inferred from clinical information and preliminary laboratory studies. Patients with unexplained cardiomyopathy may be referred for endomyocardial biopsy (EMBx). It is unknown whether pathological information obtained from EMBx is beneficial or alters the diagnosis established clinically. This study was undertaken to evaluate the utility of EMBx in confirming or excluding a clinically suspected diagnosis. METHODS: We evaluated 845 patients with initially unexplained cardiomyopathy who underwent EMBx between 1982 and 1997 at The Johns Hopkins Hospital. For each patient, an initial clinical diagnosis, an EMBx diagnosis, and a final diagnosis prior to discharge based on all available data were established. RESULTS: The final diagnosis differed from the initial clinical diagnosis in 264 (31%) of these patients; EMBx made the diagnosis in 196 (75%) of these cases. Initial diagnoses most frequently altered were myocarditis (34%) and idiopathic cardiomyopathy (25%). Initial diagnoses least likely to be altered were those in which biopsy was used to confirm or grade a previously documented illness, such as hemochromatosis (11%), amyloidosis (18%), or cardiomyopathy secondary to doxorubicin toxicity (0%). EMBx was more sensitive than clinical diagnosis in detecting myocarditis and amyloidosis, and proved to be very specific in detecting ischemic cardiomyopathy, myocarditis, amyloidosis, and hemochromatosis. CONCLUSIONS: In patients with unexplained cardiomyopathy after a standard evaluation, the clinical assessment of the etiology is inaccurate in 31% of patients. EMBx establishes the final diagnosis in 75% of these patients with a high degree of specificity.

Amyloidosis↗
PubMed2004

Consumptive coagulopathy complicating juvenile angiofibroma.

OBJECTIVE: To investigate the incidence and clinical significance of deranged clotting results among patients with juvenile (nasopharyngeal) angiofibroma. METHODS: Twenty consecutive patients treated for juvenile angiofibroma between March 1998 and July 2002 in whom preoperative coagulation tests were performed were selected. Results were compared with normal laboratory values, and clinical and histological records were retrospectively analysed. RESULTS: Four out of 20 patients were found to have abnormal tests, consistent with concurrent consumptive coagulopathies. One patient was found to have a raised D-dimer level. This resolved following removal of the lesion. CONCLUSIONS: The association between larger arterio-venous malformations and disseminated intravascular coagulopathy is well described (Kasabach-Merritt syndrome). Our findings suggest that low-grade consumptive coagulopathies may also complicate smaller juvenile angiofibromas, implying that preoperative coagulation screening tests may have a role in ensuring optimal perioperative haemostasis.

Adolescent↗
PubMed2003

Temporal lobe regions engaged during normal speech comprehension.

Processing of speech is obligatory. Thus, during normal speech comprehension, the listener is aware of the overall meaning of the speaker's utterance without the need to direct attention to individual linguistic and paralinguistic (intonational, prosodic, etc.) features contained within the speech signal. However, most functional neuroimaging studies of speech perception have used metalinguistic tasks that required the subjects to attend to specific features of the stimuli. Such tasks have demanded a forced-choice decision and a motor response from the subjects, which will engage frontal systems and may include unpredictable top-down modulation of the signals observed in one or more of the temporal lobe neural systems engaged during speech perception. This study contrasted the implicit comprehension of simple narrative speech with listening to reversed versions of the narratives: the latter are as acoustically complex as speech but are unintelligible in terms of both linguistic and paralinguistic information. The result demonstrated that normal comprehension, free of task demands that do not form part of everyday discourse, engages regions distributed between the two temporal lobes, more widely on the left. In particular, comprehension is dependent on anterolateral and ventral left temporal regions, as suggested by observations on patients with semantic dementia, as well as posterior regions described in studies on aphasic stroke patients. The only frontal contribution was confined to the ventrolateral left prefrontal cortex, compatible with observations that comprehension of simple speech is preserved in patients with left posterior frontal infarction.

Adult↗
PubMed2003

Olfactory neuroblastoma: past, present, and future?

OBJECTIVE: To consider the long-term survival and outcomes in patients with olfactory neuroblastoma undergoing craniofacial resection. STUDY DESIGN: A single-center prospective cohort study. METHODS: All patients with olfactory neuroblastoma treated in a 23-year period with craniofacial resection (with or without radiotherapy) were analyzed; a multivariate analysis was included. RESULTS: Forty-two patients aged 12 to 70 years were assessed, 83% of whom had received no preceding treatment. Craniofacial resection was used in all cases, combined with radiotherapy in 24 patients (57%). Duration of follow-up ranged from 2 to 206 months (mean follow-up period, 57 mo). The disease-free actuarial survival and overall survival were 77% and 61% at 5 years and 53% and 42% at 10 years, respectively. A Cox regression analysis identified intracranial extension and orbital involvement as independent factors affecting outcome. CONCLUSION: Craniofacial resection combined with radiotherapy offers the gold standard of care against which other approaches such as endoscopic resection must be judged.

Adolescent↗
PubMed2002

A physiological change in the homotopic cortex following left posterior temporal lobe infarction.

We investigated the relationship between cerebral activity (measured with positron emission tomography) and word rate in normal subjects and aphasic patients listening to monosyllabic words at rates up to those encountered in normal speech. By measuring the slope of the regression of the individual activity-word rate responses in the temporal cortex in normal subjects, we identified a functional asymmetry in the posterior superior temporal sulcus. The response was greater (steeper) on the left. Using the same study design, we identified a steeper activity-word rate response in the right posterior superior temporal sulcus of patients who had recovered single-word auditory comprehension after infarction of the left posterior temporal cortex. This response was significantly different from that observed in both normal subjects and a group of patients with left hemisphere infarcts that spared the posterior temporal cortex. The results demonstrated a change in physiological responsiveness in the contralateral homotopic cortex after posterior temporal infarction.

Adult↗
PubMed2002

Traumatic retrobulbar hemorrhage: emergent decompression by lateral canthotomy and cantholysis.

Traumatic retrobulbar hemorrhage may result in acute loss of vision that is reversible when recognized and treated promptly. A case of traumatic retrobulbar hemorrhage is presented. The technique of emergent orbital decompression by lateral canthotomy and cantholysis is described. The anatomy of the lateral canthus and the surgical procedure are illustrated by gross dissection.

Aged↗
PubMed2002

Endoscopic CO2 laser management of laryngocele.

OBJECTIVE: To report on the management of laryngoceles by CO2 laser-assisted endoscopic excision. STUDY DESIGN: A 15-year retrospective study of 12 adult patients (7 men and 5 women) who presented with a laryngocele. Nine patients had an internal laryngocele, one patient had an external laryngocele, and two patients had combined internal-external components. Two laryngoceles were right-sided, six were left-sided, and four were bilateral. METHODS: An endoscopic examination of the laryngocele was carried out for both diagnostic and therapeutic purposes. Once identified the air- or mucus-filled cyst (extending from the laryngeal ventricle into the paraglottic space and beyond the thyrohyoid membrane in some cases), the laryngocele was excised in toto, with its surrounding capsule, via endoscopic approach using the CO2 laser. RESULTS: The main presenting symptom was dysphonia in seven patients, visible or palpable mass in the neck in three, and upper airway obstruction in the remaining two. All laryngoceles were treated with endoscopic laser excision of the internal and external components when required. The average postoperative stay in hospital was 1.8 days. Only two of the patients treated had a tracheotomy; both cases presented elsewhere with an emergency airway obstruction, which necessitated tracheotomy. In these two cases, decannulation was subsequently performed. There were no significant complications. The follow-up ranged from 6 months to 5 years. CONCLUSION: CO2 laser-assisted endoscopic excision of a laryngocele is a quick, precise, and safe alternative to an external approach excision (lateral thyroidotomy, laryngofissure) with fewer complications than its external counterparts, resulting in speedier rehabilitation of both the patient and his or her voice.

Adult↗
PubMed2002

Rhinologic changes in Wegener's granulomatosis.

Twenty-eight patients with a clinical diagnosis of sinonasal Wegener's granulomatosis were referred for imaging during the period 1990-2001. Of these, 10 had clinical symptoms and signs confined to the nose and sinuses and 18 had classical systemic Wegener's. The computed tomography (CT) and magnetic resonance (MRI) scans of the series were reviewed by a panel of one otolaryngologist and two radiologists. From the total of 28 patients, 85.7 per cent showed non-specific mucosal thickening in the nasal cavity or paranasal sinuses, 75 per cent showed evidence of bone destruction, and 50 per cent new bone formation in the walls of the sinus cavities. In addition the orbit was affected in 30 per cent of patients. The diagnosis of systemic Wegener's granulomatosis is made clinically but the condition may present characteristic features on imaging by CT and MRI. In a patient without a history of previous sinonasal surgery, a combination of bone destruction and new bone formation on CT is virtually diagnostic of Wegener's especially when accompanied on MRI by a fat signal from the sclerotic sinus wall. These changes are important diagnostically in localized sinonasal Wegener's granulomatosis where the clinical diagnosis may be uncertain and the cANCA test can be negative.

Adolescent↗