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Biomedical subjects

S G Thomas

Publications and source records attributed to S G Thomas.

At least 37 records · Page 2Linked to original sources
PubMed1996

Irreversible silicone oil adhesion to silicone intraocular lenses. A clinicopathologic analysis.

PURPOSE: To report a newly defined complication of foldable intraocular lenses (IOLs), namely silicone oil-silicone IOL interaction. This is a complication not generally seen by the implanting cataract surgeon but, rather, at a later stage in a patient's postoperative course, by a vitreoretinal surgeon. METHODS: Three clinical case histories, including two explanted silicone IOLs, were submitted for analysis. The submitted silicone lenses were photographed under water, and the nature of the silicone oil coating was documented. RESULTS: In each instance, the silicone coating was manifest as a thick coating with droplet formation on the lens surface that was tenaciously adherent and could not be dislodged by instruments or injection of viscoelastics. CONCLUSION: The use of silicone IOLs in patients with current vitreoretinal disease or those who are at high risk for future vitreoretinal disease that may require silicone oil as part of the therapy should be reconsidered. The authors recommend that information regarding the existence and significance of this complication be printed on all silicone oil and silicone IOL packages and inserts (if not as a warning, at least as an informative comment regarding the existence of this condition). This is a rare but clinically significant complication that will affect the occasional patient treated with both of these modalities.

Adult↗
PubMed1995

A study to validate the modified Canadian Aerobic Fitness Test.

This study evaluated the predictive ability of the modified Canadian Aerobic Fitness Test (mCAFT) on an independent sample of subjects and compared it to the original Canadian Aerobic Fitness Test (CAFT). Male and female subjects (n = 154), 15-69 yrs of age, performed the mCAFT and a maximal treadmill test. VO2max scores predicted from the mCAFT equation did not differ significantly from those measured during the treadmill test, whether the sample was analysed overall or categorized by sex, whereas the CAFT (Jetté) equation resulted in VO2max scores that were significantly lower than either the measured values or those predicted using the mCAFT. The strength of the linear relationship between predicted and measured VO2max scores is the same for both the mCAFT (r = 0.88) and CAFT (r = 0.89). However, the mCAFT results in a lower mean square error (37.0 for mCAFT vs. 63.3 for CAFT) and thus is an improvement over the CAFT prediction.

Adolescent↗
PubMed1994

Traumatic thoracic aortic rupture: investigation determines outcome.

Blunt thoracic aortic rupture (TAR) initially presents with subtle signs but is usually fatal if not diagnosed and treated early. Does the diagnostic process affect outcome? The definitive test most widely promoted is thoracic (arch) aortography but is usually only available in major teaching hospitals. Thoracic computerized tomography (CT) scanning is more readily available but its role in diagnosis of TAR is unproven. A retrospective review of trauma databases and medical record indexes over a 7 year period identified 38 patients presenting with TAR at Westmead and Royal North Shore Hospitals in the period 1984-91. Thirteen patients (34%) were dead on arrival or died within 15 min of arrival at either hospital. Five patients (13%) who arrived in cardiac arrest (with suspected TAR) died after immediate thoracotomy (two in the Emergency Department and three in the operating room). Two patients (5%) died from severe head injuries and were not investigated for TAR. Eighteen patients (47%) remained alive long enough for investigation and were considered potentially salvageable. Nine of these survived. Only 13 patients had arch aortography. No patient survived without an aortogram. Five patients had a chest CT scan; aortography followed in four patients. Computerized tomography scans delayed aortography or were misinterpreted. Review of all trauma thoracic (arch) aortograms for the same period at Westmead Hospital revealed a diagnosis of TAR in 7.4%. Blind thoracotomy did not result in survival. Computerized tomography scanning of the chest was of no value in the management of this injury. Early suspicion of possible thoracic aortic rupture demands urgent arch aortography and this remains the diagnostic 'gold standard'.

Adolescent↗
PubMed1993

The novel marine natural product plocamadiene A causes histamine release from mast cells of the guinea-pig and rat in vitro.

1. Plocamadiene A is a polyhalogenated monoterpene, (1R, 2S, 4S, 1'E)-2-bromo-1-chloro-4-(2'-chloroethenyl)-1-methyl-5- methylenecyclohexane, isolated from red marine algae of the Plocamium genus. 2. This study examined the activity of plocamadiene A on guinea-pig isolated ileum (GPI) and subsequently on rat isolated peritoneal mast cells. 3. Plocamadiene A (1 micrograms/mL) produced a slow onset, sustained contraction of the GPI. This was insensitive to atropine (1 mumol/L) and tetrodotoxin (1 mumol/L), but was significantly reduced by H1-histamine receptor antagonists including mepyramine (10 nmol/L), chlorcyclizine (10 nmol/L) and diphenhydramine (0.1 mumol/L). The H2-histamine receptor antagonists cimetidine (0.1 mumol/L) and ranitidine (10 nmol/L) potentiated the response to plocamadiene A (1 micrograms/mL). 4. The amplitude of contraction caused by plocamadiene A (1 micrograms/mL) gradually decreased when the compound was applied repeatedly to the GPI for 5 min every 10 min for 150 min. 5. Contractions to plocamadiene A (1 micrograms/mL) were reduced to approximately 66% of the time control in ovalbumin-sensitized GPI challenged with ovalbumin to release endogenous contractile agents. 6. Cromolyn (0.1 mmol/L) inhibited (by 40%) the response in the GPI caused by plocamadiene A (1 micrograms/mL) as compared with time controls. 7. Spectrofluorometric assay suggested that both plocamadiene A (10 micrograms/mL) and compound 48/80 (10 micrograms/mL) caused histamine release from rat peritoneal mast cells in vitro. This release of histamine was reduced by cromolyn (100 micrograms/mL). 8. This study concluded that plocamadiene A releases histamine from mast cells of the GPI and peritoneal mast cells in the rat.

Animals↗
PubMed1993

Prediction of maximal oxygen uptake from a modified Canadian aerobic fitness test.

The purpose of the present study was to increase the accuracy of prediction of VO2max from the Canadian Aerobic Fitness Test (CAFT) by modifying the protocol and developing a new equation. Males and females between the ages of 15 and 69 years (n = 129) were tested on four occasions. Each subject performed four submaximal step tests (modified CAFT protocol) and a maximal treadmill test. The modification of the protocol consisted of allowing each subject to complete the number of stages needed to reach a target heart rate of 85% of age-predicted maximum. This required adding a new Stage 8 for men and Stages 7 and 8 for women. The prediction equation resulting from regression analysis was, VO2max (ml.kg-1 x min-1) = 32.0 + 16.0 VO2 - 0.24 Age - 0.17 Wt (R2 - 0.77; delta 2 - 26.6), where VO2 = oxygen cost of stepping at the final level (L.min-1), Age = age (yrs), and Wt = body mass (kg).

Adaptation, Physiological↗
PubMed1993

Cardiac output and left ventricular function in response to exercise in older men.

Studies of the cardiovascular response to exercise in older subjects have presented conflicting data regarding left ventricular function, the cardiac output-oxygen consumption (Q-VO2) relationship, and the pattern of change in Q, stroke volume (SV), and arteriovenous O2 difference. We have examined the cardiovascular response to submaximal and strenuous exercise in 96 men of mean age 63 years during an incremental treadmill test with Q determined by CO2 rebreathing, and in 12 subjects studied during incremental supine exercise with left ventricular volumes evaluated by radionuclide angiocardiography. During treadmill exercise the Q was approximately 10% lower than reported for younger samples, with a lower intercept of the Q-VO2 relationship. During near-maximal exercise Q was approximately 15 L.min-1, with SV of 95 mL plateauing or showing a small decline in heavy work. Peak arteriovenous O2 difference (150 + mL.L-1) approached values of the young. During the supine exercise SV increased from rest to exercise, with a consistent increase in ejection fraction (rest, 66%, to peak exercise, 76%). In contrast to a prior report, the end-diastolic volume was constant, with the increase of SV attributable to a reduced end-systolic volume. Also, in contrast to a number of reports in older subjects, our findings show only small losses in cardiovascular response, and in left ventricular performance during light through strenuous exercise.

Aged↗
PubMed1993

Sources of variation in oxygen consumption during a stepping task.

Factors that determine oxygen uptake during stepping exercise (modified Canadian Aerobic Fitness Test, CAFT) were examined in 66 women and 55 men. Subjects ranged in age from 15 to 67 yr, VO2max from 22.5 to 76.9, leg length from 75.0 to 101.0 cm, and body mass from 48.4 to 107.7 kg. In accordance with the modified CAFT protocol, subjects stepped at cadences determined by their age and heart rate response. The oxygen demand of stepping at each cadence was measured on two occasions. A paired t-test revealed no significant (P > 0.05) difference in oxygen demand between the repeats and the intraclass correlation coefficient was 0.51. The coefficient of variation of oxygen uptake (ml O2.kg-1.min-1) at a given stepping cadence averaged 10.4%. Regression analysis indicated that little variation in oxygen demand could be explained by simple descriptors of the subjects. Age was weakly related to oxygen demand at a given level (males r = 0.26, females r = 0.58). Stepwise multiple regression of the oxygen uptake at selected stepping cadences on possible independent variables confirmed that little of the variation could be explained by age, aerobic fitness, leg length, or adiposity (maximum R2 = 0.34). We conclude that variation in the oxygen demand of a stepping task can account for a large portion of the error in predicting VO2max from a submaximal stepping test. Our ability to predict the oxygen demand of stepping from subject characteristics is limited.

Adolescent↗
PubMed1992

Repeated measurements of pulmonary function following spinal cord injury.

Twelve subjects (11 males, 1 female) with complete spinal cord lesion (level of lesion ranging from C4 to T10), with a mean age of 23.5 years participated in pulmonary function testing (PFT). Inspiratory and expiratory flow measurements were made at 2-month intervals from 25 to 351 days post injury. The values were interpolated and extrapolated to common dates to facilitate comparison. The effect of time on pulmonary function was determined by a repeated measures ANOVA. Forced expiratory volume in 1 second (FEV1.0) significantly increased during the course of the study (40%, p < 0.05), but increases in forced vital capacity (FVC) (32.5%) and maximal voluntary ventilation (MVV) (16%) were not statistically significant. Lesion level was found to be correlated (Spearman Product Moment Correlation) with pulmonary function if a single measure was made (r = 0.55 to 0.73), but emerged as a stronger predictor if the average of several repeated PFTs was correlated with lesion level (r = 0.74 to 0.84). In addition, lesion level was not correlated with the amount of improvement attained during the time period studied. We conclude that the time course of recovery of pulmonary function is variable between individuals with spinal cord injuries and can only be weakly predicted by knowledge of the initial value and the lesion level.

Adolescent↗
PubMed1992

Immune responses and increased training of the elite athlete.

Ten elite male runners (age, 29.8 +/- 1.7 yr; maximum oxygen consumption, 65.3 +/- 4.9 ml.kg-1.min-1; 10-km times, 31 min 43 s +/- 1 min 46 s) deliberately increased training schedules by an average of 38% for 3 wk. Resting heart rate and maximal oxygen intake were unchanged, but the heart rate response to acute exercise was decreased. Following heavy training, blood samples taken at rest showed trends to a decreased helper/suppressor cell ratio, an increased phytohemagglutinin (PHA)- and concanavalin (ConA)-stimulated lymphocyte proliferation, and a decreased production of immunoglobulins IgG and IgM. Whereas PHA-stimulated lymphocyte proliferation was initially unchanged by acute exercise, after 3 wk of heavy training the same acute exercise caused an 18% suppression of proliferation. Acute exercise following heavy training did not alter pokeweed-stimulated IgG or IgM synthesis. There was no correlation between changes in lymphocyte subpopulations, helper/suppressor ratios, and mitogen-induced cellular proliferation. The immune system of endurance-trained athletes at rest seemed to tolerate the stress of heavy training, but superimposition of a bout of acute exercise on the chronic stress of heavy training resulted in immunosuppression, which was transient and most likely not of clinical significance.

Adult↗
PubMed1992

Reliability and validity of a fitness assessment for epidemiological studies.

A pilot study was conducted to investigate the applicability of the Canadian Aerobic Fitness Test (CAFT) for use in epidemiological studies. Thirty subjects ranging in age from 18 to 65 were evaluated for cardiorespiratory fitness on four separate visits. Protocols used included maximal treadmill testing, maximal step testing, and the CAFT. Results from these evaluations suggested that (a) habituation to the CAFT was negligible; (b) prediction of VO2max from the CAFT in fit subjects remains a problem and further equation development for this group may be necessary; (c) maximal step-test protocols do not result in unequivocal VO2max determinations and may lead to misclassification of fitness level; and (d) although the CAFT correlates highly to treadmill VO2max (r = 0.90), a relatively large standard error may result in as high as a 13% error in estimating VO2max and may lead to problems in classifying fitness in some populations (e.g., older unfit).

Adolescent↗
PubMed1992

Selection of a maximal test protocol to validate the Canadian Aerobic Fitness Test.

The purpose of this study was to select a maximal aerobic power test protocol with which to validate a submaximal step test prediction equation. Subjects (N = 129), males and females 15 to 69 years of age, performed one maximal step test and one maximal treadmill test. The maximal treadmill protocol yielded higher peak VO2, ventilation, heart rate, and RER values. An age-predicted maximum heart rate was achieved by 35% of subjects on the step test and 55% on the treadmill. An RER of 1.15 was attained by 22% of the subjects on the step test and 53% on the treadmill. Regression analysis indicated that the submaximal test was more predictive of VO2max when the maximum was attained using the treadmill rather than the maximal step protocol. Peak VO2 values obtained from subjects tested on the treadmill will be used to develop a new prediction equation for the Canadian Aerobic Fitness Test.

Adolescent↗
PubMed1991

Physical activity and the immune system.

Methods of examining immune function include a charting of susceptibility to infections, differential blood counts or lymphocyte counts, and measures of cell proliferation and immunoglobulin synthesis in response to external mitogens. The reported acute response to exercise is transient and quite variable, depending upon the type of exercise, the immunological methodology used, the intensity of effort relative to the fitness of the individual, and the timing of observation. A leucocytosis, a granulocytosis, a small lymphocytosis, and a decrease in the proportion of T to B cells reflect mainly changes of blood volume, demargination, and migration of cells. Lymphocyte subsets show a decreased helper/suppressor cell ratio and an increase of natural killer cells. Because of the lymphocytosis, mitogens induce an increased overall cell proliferation, but proliferation for a given number of cells is decreased. Prolonged exercise leads to a decrease of serum and salivary immunoglobulin levels. Soluble factors such as interleukin-1 and interferon are increased by a bout of exercise. Cross-sectional comparisons and training experiments suggest that under resting conditions well-conditioned individuals show some lymphocytosis, increased natural killer cell activity, higher levels of interleukin-1, and possibly an enhanced reaction to mitogens. Moderate training does not greatly change exercise responses at a given fraction of maximal effort. Excessive training suppresses immune function, but the changes are small, variable, and thus difficult to relate to overtraining. Moreover, because of their transient nature, they have only a limited influence upon the risks of infection or cancer.

Exercise↗
PubMed1991

Physiological characteristics of elite female basketball players.

Successful performance in international basketball competition requires an appreciation of the physical demands of the sport and the capacities of the team to respond to those demands. Optimal performance now requires a combination of technical and tactical abilities as well as a high degree of physical fitness. The objectives of this study were to assess physiological components considered important to game performance in players selected to the national team roster in 1988 or 1989, and to use this information to describe the team and positional profiles. Data obtained from maximal treadmill tests, anthropometry, sprints, isokinetic dynamometry, and other tasks reflected those qualities required of elite players. In relation to previously reported data, the athletes were generally taller and heavier and had higher maximal aerobic power than international and college players of 7 to 10 years ago. The data can also be used to identify target standards for current and prospective team members.

Adult↗
PubMed1989

Physiological profiles of the Canadian National Judo Team.

The physiology of Canadian National Judo Team members is described. These athletes differed widely in body size (height 157.4-187.7 cm; mass 56.5-100.8 kg). Aerobic fitness (treadmill) was high (VO2max = 4.49 I.min-1; 59.2 mL.kg-I.min-I), but relative VO2max decreased with increasing body mass. Elite judoka of other nations (Australia, 53.2; Poland, 59.0; Norway, 58.5) had comparable aerobic fitness. Significant (p less than 0.05) correlations between upper- (arm cranking, PWC170) versus lower-body aerobic fitness (r = 0.48), and upper- versus lower-body anaerobic power (r = 0.89) and capacity (r = 0.88) (Wingate) were observed. Peak power output (AnPP = 9.3 W.kg-I) and anaerobic capacity (AnCap = 260 J.kg-I) during arm cranking averaged 80% of leg-cranking values (AnPP = 13.7 W.kg-I; AnCap = 320 J.kg-I). Upper-body strength (bench press, one repetition, maximum = 100 kg) was also associated with upper-body anaerobic power (r = 0.72). Judoka exhibit a high degree of aerobic and anaerobic conditioning, and a pattern of total body fitness that is specifically required for their sport.

Adolescent↗
PubMed1986

Resistive breathing training in patients with chronic obstructive pulmonary disease.

In order to investigate the effect of resistive breathing training on ventilatory muscular endurance, we examined the maximal sustained ventilatory capacity in ten patients with chronic obstructive pulmonary disease (COPD) before and after a six-week program of resistive breathing training. In addition, we investigated the effect of altered breathing strategy on resistive breathing performance. The patients performed two 15-minute sessions of resistive breathing daily for six weeks using an inspiratory resistive device (Pflex). Before and after the training, we found no significant change in spirometric data, pulmonary volumes, maximal inspiratory pressure, and maximal expiratory pressure. Of the ten patients, seven failed to show an improvement in their performance of resistive breathing. Furthermore, the maximal sustained ventilatory capacity was unchanged after the resistive breathing training. After the completion of the training program, seven of the patients participated in an additional experiment in which they were instructed to take long slow inspirations while breathing through the resistive device. With this change in breathing pattern, five of the seven were able to improve their performance of resistive breathing. Analysis of the breathing strategy showed that a reduction in the peak mouth pressure, breathing frequency, and external resistive work with a longer inspiratory time was beneficial. We conclude that neither resistive breathing performance nor ventilatory muscular endurance, as measured by sustained hyperpnea, is improved by resistive breathing training performed according to the current instructions with the resistive device, and alterations in breathing strategy have a profound effect on the performance of resistive breathing. The lack of details of breathing strategy in previous studies of resistive breathing makes it difficult to determine if previously demonstrated improvements were due to a real enhancement of ventilatory muscular performance or merely secondary to a different strategy.

Aged↗