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Biomedical subjects

S Portnoy

Publications and source records attributed to S Portnoy.

At least 19 recordsLinked to original sources
PubMed2006

Real-time patient-specific finite element analysis of internal stresses in the soft tissues of a residual limb: a new tool for prosthetic fitting.

Fitting of a prosthetic socket is a critical stage in the process of rehabilitation of a trans-tibial amputation (TTA) patient, since a misfit may cause pressure ulcers or a deep tissue injury (DTI: necrosis of the muscle flap under intact skin) in the residual limb. To date, prosthetic fitting typically depends on the subjective skills of the prosthetist, and is not supported by biomedical instrumentation that allows evaluation of the quality of fitting. Specifically, no technology is presently available to provide real-time continuous information on the internal distribution of mechanical stresses in the residual limb during fitting of the prosthesis, or while using it and this severely limits patient evaluations. In this study, a simplified yet clinically oriented patient-specific finite element (FE) model of the residual limb was developed for real-time stress analysis. For this purpose we employed a custom-made FE code that continuously calculates internal stresses in the residual limb, based on boundary conditions acquired in real-time from force sensors, located at the limb-prosthesis interface. Validation of the modeling system was accomplished by means of a synthetic phantom of the residual limb, which allowed simultaneous measurements of interface pressures and internal stresses. Human studies were conducted subsequently in five TTA patients. The dimensions of bones and soft tissues were obtained from X-rays of the residual limb of each patient. An indentation test was performed in order to obtain the effective elastic modulus of the soft tissues of the residual limb. Seven force sensors were placed between the residual limb and the prosthetic liner, and subjects walked on a treadmill during analysis. Generally, stresses under the shinbones were approximately threefold higher than stresses at the soft tissues behind the bones. Usage of a thigh corset decreased the stresses in the residual limb during gait by approximately 80%. Also, the stresses calculated during the trial of a subject who complained about pain and discomfort were the highest, confirming that his socket was not adequately fitted. We conclude that real-time patient-specific FE analysis of internal stresses in deep soft tissues of the residual limb in TTA patients is feasible. This method is promising for improving the fitting of prostheses in the clinical setting and for protecting the residual limb from pressure ulcers and DTI.

Amputees↗
PubMed2005

Psychological profile of children with Noonan syndrome.

A cohort of 48 children with Noonan syndrome, with a mean age of 9 years 10 months (SD 3y 7mo; 28 males, 20 females), was recruited from a national study. Children were assessed using the Wechsler Intelligence Scales and Test of Motor Impairment-Revised (TOMI-R). The Piers-Harris Self-evaluation Questionnaire was also completed in a subgroup of age-appropriate children. Children's parents and teachers completed the Rutter A and B scales to assess of the degree of behavioural and emotional problems respectively. Mean Full-scale IQ score was 84, and one-quarter of the participants had learning disabilities. Verbal IQ tended to be slightly lower than Performance IQ. About half of the group showed evidence of mild to moderate impairment, confirming the impression of 'clumsiness/developmental coordination disorder' on the TOMI-R. Level of self-esteem, as determined by the Piers-Harris Questionnaire, was comparable to that of a standardized population. This research has identified some characteristic psychological features in Noonan syndrome. However, a specific behavioural phenotype could not be identified.

Adolescent↗
PubMed2001

Effectiveness of acupuncture for treatment of childhood constipation.

The aim of the present study was to examine the influence of acupuncture on chronic constipation in children and to investigate their basal plasma panopioid level and the changes of this treatment. Seventeen children constipated for at least six months were treated by five weekly placebo acupuncture sessions, followed by 10 weekly true acupuncture sessions. Their parents filled a bowel habit questionnaire. Panopioid activity was measured at time 0 and after 5, 10, and 15 acupuncture sessions. The frequency of bowel movements in males increased more gradually compared to females and reached a maximal improvement only after 10 true acupuncture sessions, from 1.4 +/- 0.6/week to 4.4 +/- 0.6/week and females from 1.4 +/- 0.3/week up to 5.6 +/- 1.2/week. The basal panopioid activity was lower in constipated children as compared to the control population and increased gradually up to control level after 10 true acupuncture sessions. This study is the first to describe a successful treatment by acupuncture of constipated children.

Acupuncture Therapy↗
PubMed1997

Patient co-operation--how can it be improved?

This paper considers ways of improving patient co-operation. It is divided into two parts. Firstly, communication with the patient (i.e. the child and their parents) and secondly, the use of simple reward charts that are relevant to orthodontics.

Behavior Therapy↗
PubMed1996

Effect of sustained load on dispersion of ventricular repolarization and conduction time in the isolated intact rabbit heart.

INTRODUCTION: It is well known that myocardial stretch can elicit ventricular arrhythmias in experimental models. However, previous reports have predominantly documented stretch-induced arrhythmias during short, pulsatile stretch. The arrhythmogenic mechanism of sustained static stretch is incompletely understood. METHODS AND RESULTS: To examine the influence of sustained load on several electrophysiologic parameters, a latex balloon was placed into the left ventricle of ten isolated Langendorff-perfused rabbit hearts and filled with a neutral volume of fluid. The heart was paced from a catheter inside the right ventricle (apicoseptal endocardial position), and the following parameters were studied during steady-state pacing with a cycle length of 500 msec (S1) and during extrastimulation (S2, base drive of 8 beats): monophasic action potential (MAP) durations at 90% repolarization (APD90) from 5 to 6 epicardial electrodes located on both ventricles and one right ventricular endocardial contact electrode; dispersion of APD90 (range of MAP durations from all electrodes); effective refractory period (ERP) and longest activation time (pacing stimulus to MAP upstroke). After baseline recordings, the balloon inside the left ventricle was filled with a volume of 1.0 mL of fluid by means of a servo-controlled pump. The ERP was significantly shortened from 198 +/- 9 msec at baseline to 183 +/- 8 msec during sustained load (P < 0.03). Similarly, the average APD90 was shortened from 180 +/- 5 msec at baseline to 175 +/- 6 msec during sustained load (P < 0.006) with steady-state pacing and from 178 +/- 6 msec to 170 +/- 8 msec during premature extrastimulation (P < 0.03). At the same time, dispersion of APD90 was increased from 27 +/- 5 msec to 38 +/- 6 msec (P < 0.002) during steady-state pacing and from 28 +/- 4 msec to 38 +/- 6 msec (P = 0.013) during premature extrastimulation. The longest activation time among all MAP recordings was increased from 39 +/- 2 msec to 43 +/- 3 msec (P = 0.003) during steady-state pacing and from 56 +/- 6 msec to 69 +/- 6 msec during premature extrastimulation (P < 0.003). CONCLUSIONS: Sustained load shortens the ERP and the mean APD90, and at the same time increases dispersion of APD90 and prolongs activation times. These findings provide additional insight into the arrhythmogenic mechanisms of sustained mechanical load.

Action Potentials↗
PubMed1995

Electrocardiographic indexes of dispersion of ventricular repolarization: an isolated heart validation study.

OBJECTIVES: This study tested the correlation of QT and JT dispersion and other potentially useful electrocardiographic (ECG) indexes with dispersion of repolarization and recovery time. BACKGROUND: Dispersion of ventricular repolarization is currently being assessed noninvasively from the surface ECG by means of QT and JT dispersion, although their correlation with dispersion of repolarization as measured directly from the myocardium is not well established. METHODS: Multiple monophasic action potentials were recorded simultaneously with a 12-lead ECG from isolated Langendorff-perfused rabbit hearts. The QT and JT dispersion was compared with the dispersion of monophasic action potential duration at 90% repolarization (APD90) and with dispersion of recovery time. As new ECG indexes, total T wave area, T wave area after the peak (late T wave area) and T peak to T end interval were also tested. RESULTS: The QT and JT dispersion showed a significant correlation with the dispersion of APD90 and the dispersion of recovery time (r values between 0.58 and 0.64, respectively, p < 0.001). However, total T wave area showed better correlation, respectively, with dispersion of APD90 and recovery time (r = 0.79 and r = 0.82, p < 0.0001), as did late T wave area (r = 0.81 and r = 0.81, p < 0.0001) and T peak to T end interval (r = 0.81 and r = 0.82, p < 0.0001). CONCLUSIONS: The JT and QT dispersion correlate significantly with dispersion of APD90 and recovery time. The ECG assessment of dispersion of repolarization can be improved by three new ECG dispersion indexes: T peak to T end interval, total T wave area and late T wave area. These new indexes should be tested clinically.

Action Potentials↗
PubMed1995

Outcome at three years of sick neonates involved in a double-blind trial of two parenteral amino acid preparations.

The authors investigated the hypothesis that neonates who received a parenteral amino acid preparation causing high plasma amino acid levels in the first week of life would perform less well at follow-up than those who received a preparation in which the plasma aminogram fell persistently within the normal range. 27 surviving children who had received either preparation as neonates underwent psychometric assessment at three years. Parents completed three questionnaires about temperament, behaviour screening and socio-economic status. Four of 10 patients who had received one preparation and two of 17 infants who had received the other were of below-average intelligence. This may be related to the different amino acids in the mixtures and the hyperamino-acidaemia caused by this.

Amino Acids↗
PubMed1991

Dental status of children in a primary and secondary school in rural Zambia.

This study reports the findings of a survey carried out in Zambia by a UK charity. 'Project Teeth Relief', which aims to provide basic pain relief and dental health education to the rural areas of Zambia. The survey investigated the dental health status of schoolchildren from two rural schools: 354 pupils aged 13-22 years from a secondary school and 121 pupils aged 7-18 years from a primary school. The results show a high level of dental disease in both samples. The results are discussed in relation to the differences between the two schools and to the changes in the social and economic climate in Zambia.

Adolescent↗
PubMed1988

Conduct disorder and cognitive functioning: testing three causal hypotheses.

The sample consisted of black adolescents who were members of the Columbia-Presbyterian chapter of the Collaborative Perinatal Project from birth to age 7. At age 17, subjects and their parents were administered a battery of instruments that included standardized psychiatric diagnostic interviews as part of a call-back study. Results from least-squares and logistic regression analyses were compatible with the hypothesis that deficiencies in cognitive functioning are causally related to adolescent conduct disorder as defined by DSM III. The results suggested that the relation of cognitive functioning to psychiatric status appears to be specific to conduct disorders. The results were incompatible with a "third" variable hypothesis (third factors included neurological status and environmental disadvantage) and the hypothesis that conduct problems lead to deficits in cognitive functioning. The 3 most (and equally) important factors in accounting for age-17 conduct disorder were cognitive functioning, parent psychopathology, and early aggression. A closer look at the data tentatively suggested that a broad deficiency in acculturational learning, rather than narrowly focused social cognitive differences or native endowment, constitutes a key element in the link between cognitive functioning and conduct disorder. Test bias was ruled out as a possible explanation for the results.

Adolescent↗
PubMed1988

Five-year follow-up study of extremely low-birthweight infants.

This study investigated whether extremely low-birthweight (ELBW) babies, who at two years had no major handicaps, were at higher risk for intellectual and socio-emotional problems at five years than a control group of children with normal birthweights. There were statistically significant differences between the two groups. The ELBW children were language-delayed, and more active and more intense in their behaviour. There was a tendency for the ELBW children to be lighter and shorter than the controls, but their mean head-circumference was significantly smaller. In general, however, if no serious neurological, neurosensory or cognitive impairment is found among ELBW children at two years, later cognitive and socio-emotional development is likely to be within the normal range.

Child↗
PubMed1988

The role of play in a pediatric bone marrow transplantation unit.

This article examines the function of play in the care of children who have undergone bone marrow transplantation. The serious nature of the children's illnesses, the rigors of treatment, and the restrictions posed by the environment make the provision of quality play a challenging endeavor. It is clear that the child's play behavior varies with the stage of the transplant procedure. Each phase of the process is a unique condition posing its own set of problems and solutions. Familiarity with these stage-related behaviors may assist health care professionals in working optimally with these patients.

Bone Marrow Transplantation↗
PubMed1987

Studies of dosage, seizure threshold, and seizure duration in ECT.

Seizure threshold, defined as the minimal electrical dosage necessary to elicit adequate generalized seizure, was determined throughout the course of electroconvulsive therapy (ECT) in depressed patients randomly assigned to bilateral and right unilateral treatment, with brief pulse, constant current stimulation. In Study 1, it was found that seizure threshold may be more accurately measured using the unit of charge compared to the traditional unit of watt-second. In Study 2, it was found that seizure threshold was associated with seizure duration. Patients with high thresholds had shorter seizure durations. This indicated that the seizure threshold measure assesses in part functional neural activity. In Study 3, it was found that failure for seizure threshold to increase substantially over the course of ECT was associated with poor clinical outcome. In Study 4, it was found that electrical dosage at threshold was not related to magnitude of acute cognitive impairments. This suggested that the degree to which dosage exceeds threshold may be more strongly tied to adverse effects than the absolute dosage administered to patients. Implications of the data are discussed, particularly in relation to a hypothesized link between the anticonvulsant properties of ECT and its mechanism of therapeutic action.

Cognition Disorders↗
PubMed1986

Effects of depression and ECT on anterograde memory.

This study investigated immediate and delayed recognition memory in depressed patients undergoing electroconvulsive therapy (ECT) and in matched, normal controls. At baseline, patients manifested a marked deficit in immediate memory (acquisition), but showed no deficit in delayed memory (retention). When retested 24-36 hr following the seventh ECT, patients showed reductions in both immediate and delayed memory performance. At retesting 4 days, on average, after the ECT course, immediate memory scores returned to baseline levels, but delayed memory performance remained impaired. The findings supported the classic claims that depression is associated with a deficit in the acquisition of information, whereas ECT has a more profound influence on the retention of information. This dissociative pattern could not be viewed as an artifact of task psychometric properties, nor of practice effects in control subjects.

Bipolar Disorder↗
PubMed1985

Case report of lateralized affective states immediately after ECT.

Dysphoric states were observed in a patient immediately after right unilateral and bilateral ECT, while euphoric states followed left unilateral ECT, suggesting that disruption of lateralized neural mechanisms may have been involved in the pathophysiology of the affective states.

Adult↗