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Biomedical subjects

D Howard

Publications and source records attributed to D Howard.

At least 55 records · Page 3Linked to original sources
PubMed2000

Optimum imaging for sinonasal malignancy.

A combination of computed tomography (CT) and magnetic resonance imaging (MRI) is now established as the optimum assessment of sinonasal malignancy. CT and MRI are of particular value in assessing the skull base, orbit and pteryo-palatine and infratemporal fossae. Although MRI offers better differentiation of tumour from surrounding tissue and fluid, coronal CT is still required for the demonstration of bone erosion particularly in the region of the cribriform plate. Thus the extent of local tumour spread may be determined with a degree of accuracy in excess of 98 per cent. However, the final determinant of penetration of the dura and orbital periosteum requires per-operative frozen section assessment. A knowledge of the tissue characteristics and site of origin can be of value in distinguishing some of the commoner sinonasal malignancies such as squamous cell carcinoma, adenocarcinoma, adenoid cystic carcinoma, olfactory neuroblastoma and chondrosarcoma. Imaging, particularly MRI also plays an important role in the post-therapeutic follow-up of patients, indicating areas of residual or recurrent disease, defining suspicious areas for biopsy. Post-operative surveillance is best achieved with three planar T1-weighted MRI, with, and without, gadolinium and axial T2-weighted sequences. The subtraction of the T1 pre- and post gadolinium T1 sequences can be of particular value in delineating recurrence.

Chondrosarcoma↗
PubMed2000

Imaging for juvenile angiofibroma.

Juvenile angiofibroma presents characteristic imaging signs, may of which allow diagnosis and accurate estimation of extent without recourse to the dangers of biopsy. The diagnosis by computed tomography (CT) is based upon the site of origin of the lesion in the pterygopalatine fossa. There are two constant features: (1) a mass in the posterior nasal cavity and pterygopalatine fossa; (2) erosion of bone behind the sphenopalatine foramen with extension to the upper medial pterygoid plate. Good bone imaging on CT is essential to show invasion of the cancellous bone of the sphenoid. This is the main predictor of recurrence: the deeper the extension, the larger the potential tumour remnant likely to be left following surgery. The characteristic features on magnetic resonance imaging (MRI) are due to the high vascularity of the tumour causing signal voids and strong post-contrast enhancement. MRI shows the pre-operative soft tissue extent of angiofibroma optimally, but its more important application is to provide post-operative surveillance: to show any residual or recurrent tumour, record tumour growth or natural involution and monitor the effects of radiotherapy.

Adolescent↗
PubMed2000

Impaired reading in patients with right hemianopia.

A left occipital stroke may result in alexia for two reasons, which may coexist depending on the distribution of the lesion. A lesion of the left lateroventral prestriate cortex or its afferents impairs word recognition ("pure" alexia). If the left primary visual cortex or its afferents are destroyed, resulting in a complete right homonymous hemianopia, rightward saccades during text reading are disrupted ("hemianopic" alexia). By using functional imaging, we showed two separate but interdependent systems involved in reading. The first, subserving word recognition, involved the representation of foveal vision in the left and right primary visual cortex and the ventral prestriate cortex. The second system, responsible for the planning and execution of reading saccades, consisted of the representation of right parafoveal vision in the left visual cortex, the bilateral posterior parietal cortex (left > right), and the frontal eye fields (right > left). Disruption of this distributed neural system was demonstrated in patients with severe right homonymous hemianopia, commensurate with their inability to perform normal reading eye movements. Text reading, before processes involved in comprehension, requires the integration of perceptual and motor processes. We have demonstrated these distributed neural systems in normal readers and have shown how a right homonymous hemianopia disrupts the motor preparation of reading saccades during text reading.

Adult↗
PubMed2000

Prospective allometric scaling: does the emperor have clothes?

We are not suggesting that an allometric relationship between pharmacokinetic parameters in animals and humans does not exist; we believe that it does. We are suggesting that using prospective AS to select doses in an FTIM study may lead to a false sense of security given the large publication bias in the literature. There are a number of unrecognized pitfalls to this approach, including (1) prediction intervals so wide as to be of limited use, (2) prediction error is often no better than arbitrarily chosen constants, and (3) it is not possible to determine which drugs will fail a priori. We encourage journals to publish studies in which prospective AS has failed so as scientists we may begin to see what makes these compounds different, with a goal toward better prediction of human pharmacokinetics.

Animals↗
PubMed2000

An acute stroke service: potential to improve patient outcome without increasing length of stay.

Acute stroke is associated with a high morbidity and mortality: up to 24% of patients may not survive their hospital admission. Stroke unit care has been shown in a meta-analysis to reduce this morbidity and mortality. We present a three-year audit of the first acute stroke service in an Irish teaching hospital. The audit was carried out prospectively on 193 patients admitted to the acute stroke service, from July 1996 to end of June 1999. Details regarding patients, type and severity of stroke, length of stay and outcome were collected prospectively on a standard pro-forma. We observed a reduction in mortality from 19% to 15% to 9%, and an increasing percentage of patients discharged home from 55% to 64% to 68%, in year 1, year 2 and year 3 respectively. A trend towards a greater number of patients, younger age and improved outcome with lower mortality was observed from year to year, without significant change in length of stay. This study confirms the value to patients of organised stroke care in terms of reduction in mortality and morbidity without increasing length of stay or disability. We suggest that every acute hospital should have organised stroke care.

Acute Disease↗
PubMed2000

The impact of waiting time on liver transplant outcomes.

OBJECTIVE: To measure the impact of patient waiting time on the probability of graft failure following liver transplantation. DATA SOURCES: Observations on all patients receiving transplants between 1995 and 1997 collected by the United Network for Organ Sharing. STUDY DESIGN: This study uses a two-stage probit algorithm. The first stage is an ordinary least squares regression of controls and indicators of patient blood type (the instrument set) on waiting time. The second uses the predicted value from the first regression in a probit analysis where the dependent variable is graft failure. PRINCIPAL FINDINGS: Waiting time has a statistically and clinically significant effect on the probability of graft failure following transplantation. Waiting 50 additional days for a transplant increases the probability of graft failure at one year by between one and two percentage points. CONCLUSIONS: Policies to reduce waiting times will yield clinical benefits beyond decreasing the length of time patients spend in poor health.

Algorithms↗
PubMed1999

The War Events Questionnaire.

BACKGROUND: The measurement of exposure to war in large epidemiological studies necessitates the use of easily administered and reliable questionnaires that cover a range of war events. The War Event Questionnaire (WEQ) was designed by our group to address these issues and has proved to be quite easy to administer. The aim of this study is to establish the inter-rater reliability of the WEQ. METHOD: Two trained interviewers alternated in administering parts I and II of the WEQ. RESULTS: The Kappa statistics used to calculate the degree of agreement between the two raters ranged from 0.281 to 0.774 for part I events and from 0.189 to 1.000 for part II events. CONCLUSION: The WEQ has proved to be a useful instrument that addresses both objective and the subjective war experiences; it is a fairly reliable instrument and has helped us avoid tautological assessment of the mental health effects of war.

Adolescent↗
PubMed1999

MR imaging of levator ani muscle recovery following vaginal delivery.

Our aim was to quantify the changes that occur in the levator ani muscles (LA) after vaginal delivery using magnetic resonance imaging. Fourteen women underwent MRI 1 day postpartum. Six of them were also scanned 1, 2, 6 weeks and 6 months after delivery. LA signal intensities and thickness, in areas of the urogenital and the levator hiatus were assessed in the transverse plane. Perineal body position was measured in the sagittal plane. One day postpartum a higher T2-signal intensity of the LA compared to the obturator internus muscle was found in all women and a lower T1-signal intensity in 8 of 12 women. By 6 months these differences were present in only 1 woman in the left LA. An elevation in perineal body position of 13.4 +/- 7.3 mm (P < 0.05), as well as a decrease in the area of the urogenital hiatus by 27% (P<0.05) and of the levator hiatus by 22% (P < 0.05) by 2 weeks postpartum suggest a return of normal LA geometry. LA thickness showed interindividual variations, and a complete loss of LA tissue was found in 1 woman. Changes in LA signal intensity, topography and thickness during the puerperium can be documented using MR imaging.

Adult↗
PubMed1999

Fistula-in-ano after episiotomy.

BACKGROUND: In the past 2 years, we treated three women with fourth-degree lacerations or episiotomy infections presenting with persistent pain and drainage not responding to standard treatment. CASES: These women were referred for evaluation 5 weeks, 3.5 months, and 2 years postpartum. After diagnosing fistula-in-ano, we treated them with fistulotomy and curettage, which resolved the problem. CONCLUSION: When a patient presents with pain or drainage at her episiotomy site, fistula-in-ano should be considered.

Adult↗
PubMed1999

Complement depletion does not reduce brain injury in a rabbit model of thromboembolic stroke.

The contribution of the complement system to cerebral ischemic and ischemia/reperfusion injury was examined in a rabbit model of thromboembolic stroke by delivery of an autologous clot embolus to the intracranial circulation via the internal carotid artery. A two-by-two factorial design was employed to study the impact of complement depletion via pretreatment with cobra venom factor (CVF, 100 U/kg i.v.) in the setting of permanent (without tissue plasminogen activator; t-PA) and transient (with t-PA) cerebral ischemia. Thirty-two New Zealand white rabbits were assigned to one of four groups (n=8, each group): control without t-PA, control with t-PA, CVF without t-PA and CVF with t-PA. In the complement intact animals, t-PA administration resulted in an approximate 30% reduction in infarct size when compared to the group not receiving t-PA (20.4+/-6.6% of hemisphere area vs. 30.1+/-7.2%; mean+/-SEM). However, infarct sizes in the complement depleted rabbits, with (30.7+/-8.2%) or without (30.2+/-7.9%) t-PA, were no different from the control group receiving no therapy. Similarly, no difference in regional cerebral blood flow or final intracranial pressure values was noted between any of the four groups. Complement activation does not appear to be a primary contributor to brain injury in acute thromboembolic stroke.

Animals↗
PubMed1999

Dynamic contrast-enhanced MRI of Implanted VX2 tumors in rabbit muscle: comparison of Gd-DTPA and NMS60.

We studied the dynamics of injected contrast enhancement in implanted VX2 tumors in rabbit thigh muscle. We compared two contrast agents Gd-DTPA and NMS60, a novel gadolinium containing trimer of molecular weight 2.1 kd. T1-weighted spin echo images were acquired preinjection and at 5-60 min after i.v. injection of 0.1 mmol/kg of agent. Dynamic T1-weighted SPGR images (1.9 s/image) were acquired during the bolus injection. Male NZW rabbits (n = 13) were implanted with approximately 2 x 10(6) VX2 tumor cells and grew tumors of 28+/-27 mL over 12 to 21 days. NMS60 showed significantly greater peak enhancement in muscle, tumor rim, and core compared to DTPA in both T1-weighted and SPGR images. NMS60 also showed delayed peak enhancement in the dynamic scans (compared to Gd-DTPA) and significantly reduced leakage rate constant into the extravascular space for tumor rim (K21 = 5.1 min(-1) vs. 11.5 min(-1) based on a 2 compartment kinetic model). The intermediate weight contrast agent NMS60 offers greater tumor enhancement than Gd-DTPA and may offer improved regional differentiation on the basis of vascular permeability in tumors.

Animals↗
PubMed1999

Dimensional change in muscle as a control signal for powered upper limb prostheses: a pilot study.

The vast majority of externally powered prostheses are controlled from the myoelectric signal, measured at the skin surface using socket-located electrodes. This signal has been well researched and sophisticated signal processing methods developed. Nevertheless, the inherent properties of the signal, such as its broad bandwidth and low voltage amplitude, make its use less than straightforward in the control of low frequency activity such as powered prosthetic hand movement. This paper reports on a pilot study of an alternative, a signal derived from dimensional change in muscle. A new socket-located sensor was designed to measure dimensional change in muscle, the linearised output of which is termed the myokinemetric (MK) signal. This was used in a series of tasks aimed at investigating the potential for its use in upper-limb prosthesis control. Six amputee subjects were tested, of whom one was a regular user of the myoelectric hand, one had some experience, and four had little or no previous experience of controlling devices using their residual limb. Data is presented on the problems of shift in signal range with time and socket donning and doffing and on the ability of subjects to control the amplitude of the signal. The results show that subjects were able to control the magnitude of the MK signal to a significant degree, with typical errors averaging 0.1-0.3 mm, around 10% of the signal range. The principal problem encountered was the shift in signal with time and socket donning and doffing.

Adult↗
PubMed1999

Juvenile angiofibroma: the lessons of 20 years of modern imaging.

Seventy-two patients with juvenile angiofibroma have been investigated by computerized tomography (CT) and/or magnetic resonance imaging (MRI) over a period of 20 years. The evidence from these studies indicates that angiofibroma takes origin in the pterygo-palatine fossa at the aperture of the pterygoid (vidian) canal. An important extension of the tumour is posteriorly along the pterygoid canal with invasion of the cancellous bone of the pterygoid base, and greater wing of the sphenoid (60 per cent of patients). Distinctive features of angiofibroma are the high recurrence rate, and the rapidity with which many tumours recur. It is postulated that the principal determinant of recurrence is a high tumour growth rate at the time of surgery coupled with incomplete surgical excision. The inability to remove the tumour in toto is principally due to deep invasion of the sphenoid, as described above. In this series 93 per cent of recurrences occurred with this type of tumour extension. A contributory cause in these patients is the use of pre-operative embolization. The treatment implications of these findings are examined.

Adolescent↗
PubMed1998

Distress symptoms among urban African American children and adolescents: a psychometric evaluation of the Checklist of Children's Distress Symptoms.

OBJECTIVES: To explore the factor structure of the Checklist of Children's Distress Symptoms (CCDS); to examine whether there is a higher-order single construct underlying the CCDS measure; and, to assess the association between children's distress symptoms, as reflected by the CCDS factors, and children's self-reported exposure to community violence (both victimization and witness events). DESIGNS: Community-based cross-sectional survey. SETTINGS: Ten public housing developments in an eastern metropolis. PARTICIPANTS: A total of 349 low-income urban African American children and adolescents (198 males; 151 females), 9 through 15 years of age. MEASURES: Children's distress symptoms, exposure to community violence, and selected demographic information including parental education, parental employment status, perceived health status, and school performance. ANALYSIS: Exploratory factor analysis was performed to determine the factorial structure of the CCDS measure. Second-order confirmatory factor analysis was performed to determine if there is a higher-order single underlying construct among CCDS factors. Pearson correlation coefficients were computed to assess the relationship between exposure to violence and CCDS factors. MAJOR FINDINGS: The exploratory factor analysis yielded a 6-factor solution for the CCDS measure with satisfactory internal consistency. The confirmatory factor model with a single second-order construct yielded a good fit to the data. In general, youth who experienced violent victimization or witnessed violent events reported higher levels of distress symptoms than those who did not. Distress symptoms labeled as "intrusive thoughts," "distraction," and "lack of belongingness" were most frequently associated with exposure to violence. Distress symptoms did not differ on the basis of sex or age. CONCLUSIONS: The CCDS has utility as a measure of distress symptoms among urban African American children and adolescents. Whereas analysis provided support for a single higher-order construct, using the proposed 6-factor structure should enhance our understanding of the psychological impact of exposure to violence on youth and contribute to more effective intervention efforts.

Adolescent↗