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Biomedical subjects

S J Thomas

Publications and source records attributed to S J Thomas.

At least 19 recordsLinked to original sources
PubMed1992

Slaked lime and betel nut cancer in Papua New Guinea.

Oral squamous cell cancer is the most common malignant tumour in Papua New Guinea. We have found that oral cancer in this region is concentrated at the corner of the mouth and cheek, by striking contrast with western populations, and corresponds precisely with the site of application of lime in 77% of 169 cases. Powdered slaked lime applied to the chewed Areca nut with Piper betle inflorescence at the corner of the mouth causes the mean pH to rise to 10, at which reactive oxygen species are generated from betel quid ingredients in vitro. Reactive oxygen species, together with sustained lime-induced cell proliferation, suggest a possible mechanism of carcinogenesis for this tumour.

Areca↗
PubMed1991

Induction of apoptosis during normal and neoplastic B-cell development in the bursa of Fabricius.

The lymphoid cells of embryonic bursal follicles are engaged in rapid growth and preimmune diversification of immunoglobulin genes. Disruption of follicular architecture by mechanical dispersion of these cells in short-term tissue culture was accompanied by continued cell division and extensive cell death by apoptosis. Apoptosis was suppressed in parallel cultures of intact follicles. gamma Radiation also triggered extensive apoptosis in embryonic bursal follicles within a few hours. Preneoplastic bursal stem cell populations induced by a v-myc oncogene were hypersensitive to induction of apoptosis by follicular dispersion and radiation. In contrast, tumor progression in v-myc- and v-rel-initiated bursal neoplasms was accompanied by development of resistance to induction of apoptosis. A programmed cell death pathway can be activated during normal B-cell development in the bursa, and alterations in the expression of this pathway accompany neoplastic change in this system.

Animals↗
PubMed1990

Parotid gland malignancy presenting as temporomandibular joint pain or dysfunction.

Temporomandibular joint pain and dysfunction is a common complaint and a frequent cause of referral to oral and maxillofacial surgeons. The importance of considering malignant disease in the differential diagnosis is illustrated by the following cases of parotid gland neoplasia which were referred as temporomandibular joint dysfunction.

Aged↗
PubMed1990

Vaginal birth after cesarean delivery: results of a 5-year multicenter collaborative study.

Cesarean delivery has become the most frequently performed major operation in the United States. Widespread use of vaginal birth after previous cesarean delivery could potentially eliminate up to one-third of cesareans. However, many physicians have been reluctant to adopt this policy without large studies conclusively demonstrating its safety. This study evaluated the maternal and perinatal outcomes of over 5000 cases of labor after previous cesarean delivery. This multicenter study began in 1984 and initially included nine California hospitals. During the first 2 years, there were 1776 trials of labor resulting in 1314 vaginal births. In January 1986 two additional hospitals joined the collaborative project. Over the next 3 years, there were 3957 trials of labor resulting in 2977 vaginal births at the 11 participating hospitals. During the entire study period, 5733 patients opted for a trial of labor and 4291 (75%) delivered vaginally. There were no maternal deaths in the trial-of-labor group, and perinatal mortality was not significantly different from that of the general obstetric population. These results support the findings of numerous smaller studies that have concluded that the policy of routine repeat cesarean delivery should be abandoned.

California↗
PubMed1989

The effect of ventilation on aortic blood gases during left ventricular ejection before separation from cardiopulmonary bypass.

The time to begin ventilating a cardiac surgical patient recovering from hyperkalemic arrest is controversial. Those who advocate ventilating as soon as the left ventricle begins to eject believe that blood ejected from the left ventricle is likely to be hypoxic since it perfuses collapsed, nonventilated alveoli and that this may be the major blood supply perfusing the coronary arteries. The present study attempts to answer this question by sampling blood gases from the aorta in proximity to the coronary ostia in patients both before and after ventilation. Ten patients undergoing coronary artery bypass grafting using the left internal mammary artery were studied. Each patient served as his own control. Distal anastomoses were placed under hyperkalemic, hypothermic cardiac arrest. The aorta was unclamped, and an intrinsic or paced heart rate of 70 beats per minute was achieved. The heart was allowed to eject to a pulse pressure of 20 to 40 mmHg. Rectal temperatures were between 32 degrees C and 34 degrees C. Blood gases were drawn simultaneously from the proximal aortic root, radial artery, pulmonary artery, and the venous circuit of the cardiopulmonary bypass (CPB) machine. The lungs were then twice inflated with a sustained positive pressure of 30 cm H2O, and the patient was ventilated (10 mL/kg tidal volume, FIO2 1.0, 10 breaths per minute) for two minutes. Another set of blood gases was then obtained. Filling pressures, aortic systolic and diastolic pressures, and CPB flows were kept constant for both sets of samples. There was no significant difference in aortic root PaO2 attributable to ventilation. PCO2 was significantly lower, and pH was significantly higher in the ventilated group.(ABSTRACT TRUNCATED AT 250 WORDS)

Aorta↗
PubMed1989

Papillary carcinoma of the thyroid: additional evidence in support of a familial component.

Although a higher incidence of medullary carcinoma of the thyroid is well known to occur in families with syndromes of multiple endocrine neoplasia (MEN II and III), an epidemiologic familial component has only very rarely been ascribed to papillary carcinoma. In this report we describe a mother and daughter presenting with neck masses at an early age and subsequently found to have metastatic papillary thyroid carcinoma documented on pathology following thyroidectomy. The occurrence of the neoplasm at an advanced stage in closely related individuals early in life suggests that underlying genetic factors may predispose to this malignancy. Familial papillary carcinoma of the thyroid may have a hereditary basis independent of its association with the syndromes of multiple polyposis and of multiple hamartomas, and thus may represent a new entity with characteristics which distinguish it as a distinct subset of the more common disease.

Adolescent↗
PubMed1988

Skin dose near compensating filters in radiotherapy.

In radiotherapy treatments with MV beams, the use of tissue compensators affects the dose to the skin. Methods of calculating the relative skin dose (RSD) are described and a formula is derived to predict the contribution of a tissue compensator to the RSD. Measurements of RSD for various field sizes and distances from the compensator are presented.

Filtration↗
PubMed1988

Sigmoidovaginal fistula secondary to diverticular disease. A report of three cases.

Colovaginal fistula from any cause is rare. Diverticular disease is the most common cause. We treated three women for sigmoidovaginal fistulae secondary to diverticular disease. These 3 cases bring the total number reported to 49. Diagnosis of these fistulae may be difficult, and controversy exists over which form of surgical management should be employed. Since more women are living to an age at which diverticular disease is common, colovaginal fistulae probably will be encountered by the gynecologist with increasing frequency. Colovaginal fistula secondary to diverticular disease should be considered in the differential diagnosis when an elderly women complains of flatus vaginalis.

Aged↗
PubMed1987

C5a and thromboxane generation associated with pulmonary vaso- and broncho-constriction during protamine reversal of heparin.

The authors conducted a study in humans to determine the mediators associated with acute pulmonary vaso- and broncho-constriction occurring episodically with protamine reversal of heparin anticoagulation. Of 48 adult patients investigated prospectively after termination of cardiopulmonary bypass, two presented a sudden increase of airway pressure, acute pulmonary hypertension, and systemic hypotension 1-3 min after right atrial protamine injection. In these two subjects, plasma levels of C5a increased from 0.7 and 2.2 to 9.8 and 9.9 ng/ml, respectively, and thromboxane B2 increased from 0.26 and 0.34 to 7.5 and 16.2 ng/ml 1 minute after drug injection. A third subject not identified prospectively had an identical reaction and mediator profile (C5a, 10.2 ng/ml; TxB2, 18.6 ng/ml at 1 min). The plasma levels of these mediators were unchanged in the remaining patients (C5a, 0.7 +/- 1.1 [x +/- S.D.] to 0.6 +/- 0.9 ng/ml; TxB2, 0.16 +/- 0.12 to 0.15 +/- 0.07 ng/ml). Plasma histamine was not involved in this type of reaction, but increased from 0.7-10.4 ng/ml in a fourth patient who became hypotensive without acute pulmonary hypertension, bronchoconstriction, or elevation of C5a or TxB2. The authors' data indicate that the generation of high plasma levels of C5a anaphylatoxins and thromboxane is associated with pulmonary vaso- and broncho-constriction induced by protamine reversal of heparin in humans.

Adult↗
PubMed1987

Birthweight-specific risk factors for necrotising enterocolitis.

In a multicentre case-control study of necrotising enterocolitis risk factors were found to vary with birthweight of cases. In very low birthweight cases the risk factors identified were those associated with prolonged or recurrent hypoxia (recurrent apnoea, respiratory distress, assisted ventilation, and umbilical artery catheterisation). In heavier birthweight infants the risk factors were, in contrast, related to hypoxia at birth (low 1 minute Apgar score and endotracheal intubation at birth) and umbilical vessel catheterisation used in exchange transfusions. Contradictory findings in published case-control studies carried out in the USA may be due to differences in patient populations and management policies. Hypoxia and umbilical vessel catheterisation should still be considered as risk factors for necrotising enterocolitis.

Apgar Score↗
PubMed1986

The pattern evoked electroretinogram in optic neuritis. A combined psychophysical and electrophysiological study.

The electroretinogram (ERG) and the occipital visual evoked potential (VEP) evoked by sinusoidal grating stimuli have been recorded in cases with a past history of optic neuritis. Although a significant reduction in pattern ERG amplitude was found in the patient group there was considerable overlap between the patient and the control populations. The pattern ERG was not found to be a sensitive test in providing evidence of a previous attack of optic neuritis. Reduction in VEP amplitude was considerably greater than was the reduction in ERG amplitude. The residual visual deficit in the patients was quantified by measuring contrast sensitivity. Overall, the greater the residual deficit the greater was the ERG abnormality, but in some individual patients it was found that the contrast sensitivity loss and the ERG amplitude reduction were not well correlated. No evidence was found for a latency change peripheral to the generators of the pattern ERG which might contribute to the VEP latency changes which occur following an attack of optic neuritis.

Electroretinography↗
PubMed1986

Retinal hemorrhage thresholds for Q-switched neodymium-Yag laser exposures.

Thresholds for retinal vitreal and contained hemorrhages were determined for 1064 nm laser light at 30-nsec and 4-nsec pulsewidths. Rhesus monkeys received graded exposures from a neodymium-yag laser onto either the macular or extramacular region of the retina. Contained hemorrhages appeared as concentric ring structures with white punctate centers. The vitreal hemorrhage was characterized by the presence of choroidal blood in the vitreal chamber at the exposure site. The 30-nsec contained hemorrhage threshold (ED50) was 1.7 mJ on the macula and 2.1 mJ for an extramacular exposure. The 30-nsec vitreal hemorrhage macular threshold was 2.3 mJ, and the extramacular threshold was 6.6 mJ. The threshold for the 4-nsec pulsewidths to produce a hemorrhage (vitreal or contained) on the retina (macula or extramacular) was 340 microJ.

Animals↗
PubMed1985

Ocular effects of pulsed Nd laser radiation: variation of threshold with pulsewidth.

This study of retinal damage thresholds in the rhesus monkey eye investigated the effects of Nd:YAG laser radiation at four pulsewidths; 4, 30, and 200 ns, and 10 microseconds. The thresholds for induction of minimal ophthalmoscopically visible lesions for the four pulsewidths were 158, 326, 170, and 425 microJ, respectively, incident at the eye in single-pulse exposures. The data are interpreted to imply a flat trend of threshold with pulsewidth over the range of pulsewidths examined, in agreement with maximum permissible exposures quoted in existing laser safety standards. This finding is in contrast with the hypothesis of an anomalous trend of increasing threshold with decreasing pulsewidth which was suggested for the nanosec-microsec pulsewidth range based on the sparse data base previously available.

Animals↗