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Biomedical subjects

R J Hamilton

Publications and source records attributed to R J Hamilton.

At least 37 records · Page 2Linked to original sources
PubMed1997

The case of Baby M: nursing care in an ethical wilderness.

This is a reflective case study of an infant with Down Syndrome and a potentially fatal cardiac defect. It is a story of hope and loss, of silence and learning to speak, and of relinquishing space and standing ground. The purpose of this article is to explore the conflicting claims a neonatal intensive care (NICU) nurse faces in caring for critically ill infants. The questions of "Who speaks?" and "Who listens?" are addressed. The concepts of women's moral development and a nursing definition of voice are included. It is proposed that the conventional feminine voice and the embodied knowledge so integral to expert nursing actually draw strength away from the voice that needs to be permitted into the circle of decision makers when ethical issues are raised in the NICU.

Down Syndrome↗
PubMed1996

Near infrared spectroscopy applied to intrapartum fetal monitoring.

NIRS as a technique for intrapartum fetal monitoring is at present only able to be used as an investigative research tool. We feel that it has enormous potential to give access to previously inaccessible information about fetal cerebral haemodynamic and oxygenation changes in labour. The major limitations at present are technological, and the problems addressed in this review need to be resolved before clinicians can advance the technique. In the future, standardized measurement parameters that truly reflect cerebral oxygenation, along with a range of normality need to be established. This would require the study of very large numbers of uncomplicated labours. Comparison with data from labours complicated by what we currently call 'fetal distress' and correlation with outcome measures in the neonate would then be needed to determine abnormal patterns of change related to intracerebral hypoxia-ischaemia. This is severely limited by the current inability to measure absolute levels of oxygenation necessary to validate the method. To use the technique for routine surveillance in labour would require considerable refinement of both the equipment and the data analysis systems to improve the acceptability of the technique. It is not possible to envisage a role for NIRS in routine surveillance of low-risk pregnancies, but it may in future prove to have a role in the management of high-risk pregnancies and may well improve our understanding of intracerebral pathology.

Bias↗
PubMed1996

Rapid improvement of acute pulmonary edema with sublingual captopril.

OBJECTIVE: To test the hypothesis that sublingual captopril produces a more rapid improvement of acute pulmonary edema (APE) than does placebo, when added to a standard regimen of O2, nitrates, morphine, and furosemide. METHODS: Prospective, randomized, double-blind, placebo-controlled clinical trial in an urban teaching hospital ED. Adults brought to the ED with APE were given captopril or placebo sublingually. Every 5 minutes a clinical APE distress score (APEX) was obtained. RESULTS: Over the first 40 minutes of treatment, the mean APEXs were significantly better for the patients given captopril [p < 0.001, F = 14.5, one-way (repeated-measures) analysis of variance (ANOVA)]. At 30 minutes, the patients given captopril had a mean APEX improvement of 43% (i.e., to 57% of initial distress); the group given the current standard regimen plus placebo improved only 25% (i.e., to 75% of initial distress; p = 0.03, multiway ANOVA). In addition, there was less respiratory failure necessitating mechanical ventilation in the captopril patients (9%) vs the placebo patients (20%), which did not achieve significance (p = 0.10, Fisher's exact test). CONCLUSION: In APE, the addition of sublingual captopril to the standard regimen of O2, nitrates, morphine, and furosemide produces more rapid clinical improvement than does the standard regimen alone.

Acute Disease↗
PubMed1996

The omni wedge: a method to produce wedged fields at arbitrary orientations.

A method to produce wedged fields at any orientation relative to the collimator is described. The wedged field is generated by combining two appropriately weighted orthogonal wedged field segments at fixed collimator and gantry positions. The method requires only that wedged fields can be produced in orthogonal directions without rotating the collimator, such as is commonly provided on most radiation therapy accelerators by sets of standard and rotated wedges. Expressions are derived relating the effective wedge angle and orientation to the weighting and wedge angles of the orthogonal wedged field segments. This technique will be important when using multileaf collimator field shaping for which collimator rotation is dictated by target or critical structure shape and orientation. The term omni wedge is introduced to describe this technique.

Biophysical Phenomena↗
PubMed1996

Repositioning accuracy of a noninvasive head fixation system for stereotactic radiotherapy.

We report on the repositioning accuracy of patient setup achieved with a noninvasive head fixation device for stereotactic radiotherapy. A custom head mask which attaches to our stereotactic radiosurgery head ring assembly is fabricated for each patient. The position and orientation of a patient in the stereotatic space at the time of treatment are determined from analyzing portal films containing images of radio-opaque spheres embedded in a custom mouthpiece. From analysis of 104 setups of 12 patients, we find that the average distance between the treated isocenter and its mean position is 1.8 mm, and that the standard deviations of the position of the treated isocenter in stereotactic coordinate space about its mean position are less than 1.4 mm in translation in any direction and less than 1 degree of rotation about any axis.

Equipment Design↗
PubMed1995

Comparison of static conformal field with multiple noncoplanar arc techniques for stereotactic radiosurgery or stereotactic radiotherapy.

PURPOSE: Compare the use of static conformal fields with the use of multiple noncoplanar arcs for stereotactic radiosurgery or stereotactic radiotherapy treatment of intracranial lesions. Evaluate the efficacy of these treatment techniques to deliver dose distributions comparable to those considered acceptable in current radiotherapy practice. METHODS AND MATERIALS: A previously treated radiosurgery case of a patient presenting with an irregularly shaped intracranial lesion was selected. Using a three-dimensional (3D) treatment-planning system, treatment plans using a single isocenter multiple noncoplanar arc technique and multiple noncoplanar conformal static fields were generated. Isodose distributions and dose volume histograms (DVHs) were computed for each treatment plan. We required that the 80% (of maximum dose) isodose surface enclose the target volume for all treatment plans. The prescription isodose was set equal to the minimum target isodose. The DVHs were analyzed to evaluate and compare the different treatment plans. RESULTS: The dose distribution in the target volume becomes more uniform as the number of conformal fields increases. The volume of normal tissue receiving low doses (> 10% of prescription isodose) increases as the number of static fields increases. The single isocenter multiple arc plan treats the greatest volume of normal tissue to low doses, approximately 1.6 times more volume than that treated by four static fields. The volume of normal tissue receiving high (> 90% of prescription isodose) and intermediate (> 50% of prescription isodose) doses decreases by 29 and 22%, respectively, as the number of static fields is increased from four to eight. Increasing the number of static fields to 12 only further reduces the high and intermediate dose volumes by 10 and 6%, respectively. The volume receiving the prescription dose is more than 3.5 times larger than the target volume for all treatment plans. CONCLUSIONS: Use of a multiple noncoplanar conformal static field treatment technique can significantly reduce the volume of normal tissue receiving high and intermediate doses compared with a single isocenter multiple arc treatment technique, while providing a more uniform dose in the target volume. Close conformation of the prescription isodose to the target volume is not possible using static uniform conformal fields for target shapes lacking an axis of rotational symmetry or plane of mirror symmetry.

Brain Neoplasms↗
PubMed1995

The potential for normal tissue dose reduction with neoadjuvant hormonal therapy in conformal treatment planning for stage C prostate cancer.

PURPOSE: Preirradiation hormonal cytoreduction of prostate cancer has been proven to reduce exposure of normal structures by decreasing the size of the target volume. Dose-volume histogram (DVH) analysis, however, does not always appear to demonstrate a strong positive benefit with the use of neoadjuvant hormone therapy. This study analyzes various other factors influencing dose to normal organs, which may determine the success or failure of neoadjuvant hormonal therapy in achieving its goals. METHODS AND MATERIALS: Patients with bulky clinical Stage C adenocarcinoma of the prostate were given 3 months of hormone treatment consisting of oral Flutamide and monthly Zoladex injections prior to irradiation. Computerized tomography (CT) scans of the pelvis were obtained both prior to and following hormonal treatment. Treatment plans were generated by three-dimensional (3D) conformal treatment planning. The change in the volume of the prostate was assessed along with the percentage of prescribed dose delivered to the rectum and bladder. Various factors such as prostate size, bladder/rectum size, and organ shape were studied. Both dose-volume histograms (DVH) and dose-surface area histograms (DSH) were used for analysis. RESULTS: Six of seven patients had reduction in the size of their prostates. The mean volumes of the prostate before and after hormonal manipulation were 129.1 +/- 32.9 standard deviation (SD) cm3 and 73.0 +/- 29.5 SD cm3, respectively (p = 0.0059). The volume of rectum receiving 80% of the prescribed dose was reduced in five of seven patients from a mean of 83.2 to 59.9 cm3 (p = 0.045). The volume of bladder receiving 80% of the prescribed dose was also reduced in five out of seven patients from a mean of 74.5 to 40.2 cm3 (p = 0.098). Correlation between the size of the prostate and volume of rectum and bladder treated was not always consistent: greater reduction in prostate size did not necessarily result in large decreases in dose to bladder or rectum. The total size of the bladder and rectum were found to be important factors in normal tissue radiation exposure; the benefits of hormone therapy may be lost if the bladder and rectum are allowed to decrease in size. Also, the bladder may be prone to sagging into the pelvis of some patients following hormone therapy, resulting in a less optimal therapeutic ratio. CONCLUSION: Reduction in prostate size by neoadjuvant hormonal manipulation does decrease the amount of normal tissue irradiated in most patients. However, the correlation between the reduction in prostate size and amount of rectum or bladder treated is not linear if other variables are not controlled. Factors such as the shape of the organs, as well as the distensible nature of the bladder and rectum, play major roles in dose to normal tissues. These facts may mask the benefits of cytoreduction and could be obstacles in realizing consistent benefits from preirradiation hormonal treatment in the clinical setting if they are ignored.

Adenocarcinoma↗
PubMed1995

Mobitz type I heart block after pokeweed ingestion.

The leaves of Phytolacca americana (pokeweed), when ingested, typically produce a self-limited but severe gastroenteritis characterized by intense vomiting and frothy diarrhea. Although cardiac effects have been reported in previous cases of pokeweed ingestion, no cardiac toxin has ever been identified in pokeweed. We report the case of a family who ingested raw and/or cooked pokeweed leaves, and 1 member who developed a Mobitz type I heart block associated with vomiting which resolved after i.v. promethazine. This suggests the possibility that some cardiac effects of pokeweed are secondary to the increased vagal tone seen with severe gastrointestinal colic.

Adult↗
PubMed1991

An operationally oriented approach to medical care in space.

As plans to bring the United States into the realm of continuously manned space operations are written, questions concerning the medical support of those operations have been raised. A review of the simple, time-tested principles that guide military operational medicine can be applied to medical care in space. Based on this operational approach, I conclude that a successful medical team must understand the mission, identify medical resources, define medical evacuation capabilities, anticipate medical issues and plan solutions, and develop facility requirements. Once all this has been accomplished, appropriate selection and training of medical personnel completes the preparation.

Aerospace Medicine↗
PubMed1991

Techniques to enhance safety in acceleration research and fighter aircrew training.

Acceleration (+Gz) research and aircrew training using human centrifuges involves considerable stress that can alter normal cardiovascular and neurologic function even in completely healthy individuals. It is clear that electrocardiographic rate, rhythm, and conduction disturbances are frequently associated with +Gz exposures. These cardiac changes can result in altered perfusion of the central nervous system (CNS) to an extent which exceeds that induced by the +Gz stress alone. Although centrifuge-based research and training have a proven record of overall safety, there is finite risk associated with such stressful exposures, and adverse events have been observed. It is, therefore, extremely important to continually develop improved avenues to enhance human safety during centrifuge exposure. We have implemented techniques that can be immediately employed by centrifuge medical personnel to reduce the potential for significant CNS embarrassment and possible injury. These include techniques to 1) reduce excessive parasympathetic tone that may result in marked bradycardia and transient asystole post +Gz stress, and 2) manually controlled inflation and pulsation of the anti-G suit to enhance CNS perfusion post +Gz stress.

Aerospace Medicine↗
PubMed1987

A critique of the concept of MRI centers.

A significant proportion of MRI units are being installed in MRI Centers that are free standing enterprises offering outpatient diagnoses separate from hospitals. The development of such Centers represents a challenge to more traditional arrangements and may have serious implications for physician responsibility that depend on their management and administration. In this review several legal and ethical issues arising from the proliferation of such Centers are analyzed and it is argued that regulatory attitudes may need to be altered to avoid major shifts of emphasis in the pattern of use of high cost imaging equipment.

Community Health Centers↗