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Biomedical subjects

S J Thomas

Publications and source records attributed to S J Thomas.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1985

Sustained release systems for ethinylestrogens.

The immunoreactive serum concentration of ethinylestradiol (EE) was measured by a specific radioimmunoassay after a single intramuscular administration of a combined preparation of Norethindrone (NET) and Mestranol (ME). The mean peak serum value for the 6 women studied was 278.5 pm/m1/m2 of body surface area (BSA), and was reached 11.17 days after dosing, with a half-life of absorption (T1/2 abs) of 9.37 days. In 5 out of 6 subjects EE was detectable in the circulaton for 21 days after injection. The mean serum concentration time curve was calculated in 2720.67 pg/day/m1/m2. The shape of the 1-21 day concentration-time curve shows a sustained release pattern, suitable for a long acting fertility regulation method.

Biology↗
PubMed1984

Spatial organization of axonal microtubules.

Several workers have found that axonal microtubules have a uniform polarity orientation. It is the "+" end of the polymer that is distal to the cell body. The experiments reported here investigate whether this high degree of organization can be accounted for on the basis of structures or mechanisms within the axon. Substantial depolymerization of axonal microtubules was observed in isolated, postganglionic sympathetic nerve fibers of the cat subjected to cold treatment; generally less than 10% of the original number of microtubules/micron 2 remained in cross section. The number of cold stable MTs that remained was not correlated with axonal area and they were also found within Schwann cells. Microtubules were allowed to repolymerize and the polarity orientation of the reassembled microtubules was determined. In fibers from four cats, a majority of reassembled microtubules returned with the original polarity orientation. However, in no case was the polarity orientation as uniform as the original organization. The degree to which the original orientation returned in a fiber was correlated with the number of cold-stable microtubules in the fiber. We suggest that stable microtubule fragments serve as nucleating elements for microtubule assembly and play a role in the spatial organization of neuronal microtubules. The extremely rapid reassembly of microtubules that we observed, returning to near control levels within the first 5 min, supports microtubule elongation from a nucleus. However, in three of four fibers examined this initial assembly was followed by an equally rapid, but transient decline in microtubule number to a value that was significantly different than the initial peak. This observation is difficult to interpret; however, a similar transient peak has been reported upon repolymerization of spindle microtubules after pressure induced depolymerization.

Animals↗
PubMed1984

Corneal damage induced by pulsed CO2 laser radiation.

Corneal damage thresholds were determined in Dutch Belted rabbits following CO2 laser radiation with pulse widths of 1.7, 25 and 250 ns. The threshold values for corneal clouding found for the 3 cases were 0.33, 0.54 and 0.18 J/cm2, respectively. These results are in accord with expectations based on a thermal-damage mechanism, with no evidence of acoustic shock or other mechanisms contributing to the observed damage for the exposure parameters used in this study. The data support the suggested maximum permissible exposure levels for short-pulse far-infrared laser radiation as quoted in current laser safety standards.

Animals↗
PubMed1984

Massive hemorrhage in an ileal duplication cyst.

We have described massive intermittent intestinal hemorrhage due to a vascular anomaly in an ileal duplication cyst in a 30-year-old man. This unusual case illustrates that these lesions disguise themselves symptomatically and must be considered in the differential diagnosis of gastrointestinal bleeding.

Adult↗