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Biomedical subjects

S G Thomas

Publications and source records attributed to S G Thomas.

At least 19 recordsLinked to original sources
PubMed1998

Physical impairments and functional limitations: a comparison of individuals 1 year after total knee arthroplasty with control subjects.

BACKGROUND AND PURPOSE: The purpose of this study was to examine the physical impairments and functional limitations of individuals with total knee arthroplasty (TKA), as compared with individuals with no diagnosed knee disease (control subjects). SUBJECTS: Twenty-nine individuals 1 year following TKA (13 women, 16 men) and 40 age- and gender-matched control subjects (18 women, 22 men) were assessed. METHODS: Walking speed, stair-climbing ability, knee torque (in newton-meters), and total work performed during 15 repeated contractions were evaluated. RESULTS: Walking speeds for men with TKA were 13% and 17% slower at normal and fast speeds, respectively. Their stair-climbing ability was even more compromised (51% slower). Walking speeds for women with TKA were 17% and 18% slower at normal and fast speeds, respectively. Similarly, their stair-climbing time was more compromised (43% slower). Men with TKA were 37% to 39% weaker and performed 36% to 37% less total work of their knee extensors compared with the control subjects. Similarly, women with TKA had knee extensor strength deficits of 28% to 29% and performed 24% less total work. CONCLUSION AND DISCUSSION: One year after TKA, marked physical impairments and functional limitations persisted. [Walsh M, Woodhouse LJ, Thomas SG, Finch E. Physical impairments and functional limitations: a comparison of individuals 1 year after total knee arthroplasty with control subjects.

Arthroplasty, Replacement, Knee↗
PubMed1998

Edema, oncotic pressure, and free entropy: novel considerations for the treatment of edema through attention to thermodynamics.

Over 170 years after Richard Bright and a century after Ernest H. Starling, the development, location, and severity of edema in patients with renal impairment continue to baffle the predictions of most nephrologists. While much of the phenomenon can be explained by levels of serum proteins, or hydrostatic pressures, there are stunning exceptions well known to any practicing nephrologist. Some of the derangement is undoubtedly due to unmeasured but well-known variables, such as membrane permeability; however, other factors such as free entropy of plasma are also clearly involved. The study of other polyelectrolyte colloids, similar to plasma proteins, for industrial purposes has led to the identification of various phenomena such as counterion condensation that can result in loss of entropy and consequently osmotic pressure. Variables known to result in a loss of free entropy, such as pH, oxidation products and ligand binding, are discussed. Older equations developed by van't Hoff and Donnan might require replacement by newer mathematical models such as the nonlinear Poisson-Boltzmann equation or the Monte Carlo simulator. Attempts to restore free entropy to plasma would be a more physiological treatment of edema than diuretic use. Implications are noted for future drug development to treat edema.

Blood Proteins↗
PubMed1998

Components of the neuronal exocytotic machinery in the anterior pituitary of the ovariectomised ewe and the effects of oestrogen in gonadotropes as studied with confocal microscopy.

We have investigated exocytotic proteins in ovine pituitary cells and sought to identify changes in expression of these proteins related to the effects of estrogen on luteinising hormone (LH) secretion in the ovariectomised ewe. Sheep were treated with either oestradiol benzoate, or oil (i.m.) and blood samples collected for LH assay. Pituitaries were perfusion-fixed and dual-label immunohistochemistry was performed to identify hormone-secreting cells, and colocalise synaptic proteins within different cell types. Synaptophysin, SNAP-25, VAMP-2, rab3A, Munc-18-1, alpha/beta-SNAP, csp, and secretogranin II were detected in gonadotropes and somatotropes. Lactotropes were positive for SNAP-25 and synaptophysin (other synaptic proteins not investigated). Synaptotagmin I was detected in gonadotropes and lactotropes, but not somatotropes. Synaptophysin, SNAP-25, synaptotagmins I, II and III, VAMP-2, rab3A, Munc-18-1, alpha/beta-SNAP, csp, and secretogranin II were detected in nerve fibres of the posterior lobe. Membrane staining for SNAP-25 and weak cytoplasmic labelling for both synaptotagmin I and secretogranin II were detected in the intermediate lobe. Syntaxin and complexin II antibodies did not label any region of the ovine pituitary. Oestrogen treatment, to induce a pre-ovulatory-like LH surge, caused migration of LH-containing secretory granules toward the plasma membrane of gonadotropes, but did not alter the percentage of gonadotropes expressing each exocytotic protein. Oestrogen treatment caused a similar redistribution of csp and secretogranin II staining in gonadotropes. We conclude that synaptic protein expression is not altered in the anterior pituitary at the time when LH secretion is maximal. The ubiquitous distribution of many exocytotic proteins suggests that all hormone-secreting cells of the pituitary gland contain the same, or similar exocytotic machinery, but distinct 'activating factors' are required to selectively trigger the secretion of individual hormones.

Animals↗
PubMed1998

Functional ability perceived by individuals following total knee arthroplasty compared to age-matched individuals without knee disability.

A comparison of function of individuals 1 year after total knee arthroplasty (TKA) with healthy control subjects (controls) meaningfully describes outcome in these patients. Perception of function measured by two questionnaires, the Lower Extremity Activity Profile (LEAP) and the Western Ontario McMaster Osteoarthritis Index (WOMAC), and walking and stair performance was compared between 29 patients, 1 year after TKA, and 40 controls. There was significantly greater perceived difficulty with function in patients with TKA than in controls. In TKA men, LEAP and WOMAC scores correlated respectively with self-paced walk speed (r = -.71 and -.55) and stair performance time (r = 0.70 and 0.68). In TKA women, LEAP difficulty score correlated with self-paced walk speed (r = -.41) and stair performance time (r = -0.71). By 1 year, TKA subjects regained 80% of the function of controls. Perception of function after TKA can be measured by either questionnaire in men; however, the LEAP is the preferable questionnaire with women.

Aged↗
PubMed1997

Quantitating the capillary supply and the response to resistance training in older men.

Resistance training (RT) has been shown to increase aerobic power in older humans. To determine the effects of RT on the capillary supply in this population, nine older men (65-74 y) engaged in 9 weeks RT of the lower body. Following RT, peak O2 uptake (V.O2,peak) increased by 7% (P<.01). Needle biopsies (vastus lateralis muscle) revealed significant increases (mean +/- SE) in fibre area (3,874 +/- 314 microm2 to 4,778 +/- 309 microm2), fibre perimeter (P, 262 +/- 11 microm to 296 +/- 11 microm), capillary contacts (3.7 +/- .2 to 4.3 +/- .3) and the individual capillary-to-fibre ratio (C:Fi, 1. 33 +/- .32 to 1.61 +/- .37, P<.005). To evaluate the potential for blood-tissue exchange, both fibre area-based and perimeter-based measures of the capillary supply were compared. While the area-based measures were maintained, C:Fi/P was increased, consistent with an increase in the size of the fibre-capillary interface and thus, an increased potential for oxygen flux following RT. Of the measurements of capillary supply, V.O2,peak correlated best with C:Fi/P (r = 0.69, P<.005). These results indicate a significant increase in the capillary supply relative to the perimeter, but not the cross-sectional area, of the muscle fibres following RT in older men, and that C:Fi/P is strongly correlated to the V.O2,peak in this population.

Aged↗
PubMed1997

Silicone oil adhesion to intraocular lenses: an experimental study comparing various biomaterials.

PURPOSE: To perform an in vitro experimental study comparing the degree of adherence of silicone oil to various rigid and foldable intraocular lens (IOL) designs and to the human lens capsule. SETTING: Center for Research on Ocular Therapeutics and Biodevices, Department of Ophthalmology, Storm Eye Institute, Medical University of South Carolina, Charleston, South Carolina, USA. METHODS: Seven IOL styles comprising various biomaterials were studied: fluorine-treated (Fluorlens), heparin-surface-modified (HSM), hydrogel, Memory-Lens, Poly(methyl methacrylate) (PMMA), soft acrylic, and silicone lenses; the human crystalline lens was also studied. Each lens was immersed in silicone oil for 12 hours, than photographed, studied by scanning electron microscopy (except the crystalline lens), and subjected to computer-generated image analysis to determine the silicone oil coverage. RESULTS: Silicone oil coverage of dry silicone lenses was 100% and of lenses immersed in normal saline, 82.5%. The least coverage was on the heparin-surface-modified lens (mean score 9.4%). Coverage of the other four lenses ranged from approximately 15.1% to 33.7%. Mean coverage of the human lens capsule was 10.9%. CONCLUSION: Although a silicone IOL shows maximal adherence to silicone oil, other lens biomaterials are not immune to this complication. Silicone oil coverage was related to the dispersive energy component of the surface charge of the IOL biomaterial. Low dispersive energy materials had less silicone oil coverage, while those with higher dispersive energy had more oil coverage.

Adhesiveness↗
PubMed1997

Resistance and aerobic training in older men: effects on VO2peak and the capillary supply to skeletal muscle.

Both aerobic training (AT) and resistance training (RT) may increase aerobic power (VO2peak) in the older population; however, the role of changes in the capillary supply in this response has not been evaluated. Twenty healthy men (age 65-74 yr) engaged in either 9 wk of lower body RT followed by 9 wk of AT on a cycle ergometer (RT-->AT group) or 18 wk of AT on a cycle ergometer (AT-->AT group). RT was performed three times per week and consisted of three sets of four exercises at 6-12 repetitions maximum. AT was performed three times per week for 30 min at 60-70% heart rate reserve. VO2peak was increased after both RT and AT (P < 0.05). Biopsies (vastus lateralis) revealed that the number of capillaries per fiber perimeter length was increased after both AT and RT (P < 0.05), paralleling the changes in VO2peak, whereas capillary density was increased only after AT (P < 0.01). These results, and the finding of a significant correlation between the change in capillary supply and VO2peak (r = 0.52), suggest the possibility that similar mechanisms may be involved in the increase of VO2peak after high-intensity RT and AT in the older population.

Aged↗
PubMed1997

The positive feedback action of estrogen mobilizes LH-containing, but not FSH-containing secretory granules in ovine gonadotropes.

It has previously been shown in the ewe that luteinizing hormone (LH)-containing secretory granules become polarized to the side of the gonadotrope nearest to a vascular sinusoid during the preovulatory period. We have used laser scanning confocal microscopy to monitor the migration of LH and follicle stimulating hormone (FSH)-containing secretory granules in the gonadotrope of the ewe. Ovariectomized (OVX) ewes (n = 4/group) were given either 50 micrograms of estradiol benzoate (EB) or oil and were killed 16 h later for collection of the pituitary glands for immunohistochemistry and confocal microscopy. Pituitary sections were simultaneously immunolabelled for LH and FSH and were visualized on the same sections using fluorescent markers. All cells that contained LH also contained FSH and vice versa. The results showed that LH-containing granules were uniformly distributed throughout the cytoplasm in 83% of gonadotropes from controls, while in the remaining 17% the granules were predominantly located adjacent to the plasma membrane. Following EB treatment, LH-containing secretory granules were distributed around the plasma membrane in 84% of immunopositive gonadotropes; FSH remained uniformly distributed throughout the cytoplasm. We conclude that estrogen causes the movement of LH-containing granules to the plasma membrane in gonadotropes but does not influence the distribution of FSH-containing granules. Rather than being polarized to one side of the cell, the LH-containing granules were distributed around the periphery of the cell.

Animals↗
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↗