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Biomedical subjects

I H Muir

Publications and source records attributed to I H Muir.

15 recordsLinked to original sources
PubMed2001

Micro-environment changes inside impermeable protective clothing during a continuous work exposure.

Protective clothing (PC) results in a micro-environment between itself and the body. Workers are then exposed to a heat stress greater than the ambient environment alone, which is a reflection of micro-environment, metabolic rate and time. Adjustments to the ambient environment to account for the micro-environment have been formulated as a means to predict heat strain for safety and productivity purposes. Measurement of the actual micro-environment was made for a mean of 63.1 +/- 7.9 min using a remote sensor at the shoulder, hip and thigh levels on 15 subjects during a continuous work protocol (300 kcal/h) in impermeable PC at an ambient temperature of 30.1 degrees C wet bulb globe temperature (WBGT) (32 degrees C dry, 29 degrees C wet, 33 degrees C globe). Micro-environment temperature increased over the duration of the work period. There was no statistically significant difference (p>0.05) between the measurements made at the three different body sites for temperature or humidity. The mean micro-environmental WBGT at the end of work was 34.6 degrees C WBGT. Micro-environment WBGT increased rapidly in the first 20 min of work then slowed, rising only 0.5 degrees C WBGT from 40 to 60 min. These results suggest that at this particular high ambient temperature (30.1 degrees C WBGT) an adjustment factor of 5 degrees C WBGT would give a more accurate indication of thermal stress for up to 1 h of continuous moderate work within PC. For shorter work durations, an even smaller adjustment would be appropriate.

Adult↗
PubMed2001

Prediction of rectal temperature from ear canal temperature.

Personal heat strain monitoring provides the best means for maximizing worker safety and productivity in hot jobs. The present study compared methods for reducing the environmental effect on aural canal temperature in an attempt to reduce the predictive error of a personal heat stress monitor (QST) and a simple ear thermistor (EAR). Subjects underwent three exposures in impermeable protective clothing (PC) in an environment of 30.1 degrees C wet bulb globe temperature (WBGT) wearing either ear plugs (PLG), ear moulds (MLD) or ear moulds and earmuffs (MFS). Mean work time across all trials was 63.1 +/- 7.9 min, with a mean rectal temperature at 60 min of 38.5 +/- 0.1 degrees C and a sweat production rate of 29.7 +/- 8.6 g/min. Rectal temperature was used as the criterion measure of core temperature. Although group mean predictions were satisfactory, large SD of mean differences (+/- 0.36) meant that predictive ability of QST for individuals was greatly impaired. A simple well-insulated ear thermistor showed slightly better accuracy (+/- 0.28) as a predictor of rectal temperature across time, particularly at peak temperatures. Incorporating the predictive error of aural temperature still extended the duration of safe work times relative to ACGIH guidelines. Further investigation is still necessary to ensure that predictions based on aural temperature are accurate and safe for the worker population across varying conditions.

Adult↗
PubMed2000

Gender differences in sweat lactate.

Sweat rate may affect sweat lactate concentration. The current study examined potential gender differences in sweat lactate concentrations because of varying sweat rates. Males (n = 6) and females (n = 6) of similar age, percentage body fat, and maximal oxygen consumption (VO2max) completed constant load (CON) cycling (30 min--approximately 40% VO2max) and interval cycling (INT) (15 1-min intervals each separated by 1 min of rest) trials at 32 (1) degrees C wet bulb globe temperature (WBGT). Trials were preceded by 15 min of warm-up (0.5 kp, 60 rpms) and followed by 15 min of rest. Blood and sweat samples were collected at 15, 25, 35, 45, and 60 min during each trial. Total body water loss was used to calculate sweat rate. Blood lactate concentrations (CON approximately equal to 2 mmol.l-1, INT approximately equal to 6 mmol.l-1) and sweat lactate concentrations (CON and INT approximately equal to 12 mmol.l-1) were not significantly different (P > 0.05) at any time between genders for CON or INT. Overall sweat rates (ml.h-1) were not significantly different (P > 0.05) between trials but were significantly greater (P < or = 0.05) for males than for females for CON [779.7 (292.6) versus 450.3 (84.6) ml.h-1] and INT [798.0 (268.3) versus 503.0 (41.4) ml.h-1]. However, correcting for surface area diminished the difference [CON: 390.7 (134.4) versus 277.7 (44.4) ml.h-1, INT: 401.5 (124.1) versus 310.6 (23.4) ml.h-1 (P < or = 0.07)]. Estimated total lactate secretion was significantly greater (P < or = 0.05) in males for CON and INT. Results suggest that sweat rate differences do not affect sweat lactate concentrations between genders.

Adult↗
PubMed2000

Effects of high and low blood lactate concentrations on sweat lactate response.

Sweat lactate results from eccrine gland metabolism, however, the possible clearance of blood lactate through sweat has not been resolved. On separate days in an environmental chamber (32 +/- 1 C) 12 subjects completed a constant load (CON) (30 min at 40% VO2 max) and an interval cycling trial (INT) (15 one-min intervals at 80% VO2 max, each separated by one min rest) each designed to elicit different blood lactate responses. Each 30 min cycling trial was preceded by 15 min warm-up (30 watts) and followed by 15 min passive rest. Sweat and blood were analyzed for lactate concentration at 15, 25, 35, 45, and 60 min during CON and INT. Total body water loss was used to calculate sweat rate (ml/hr). Blood lactate was significantly greater (p < or = 0.05) at 25, 35, 45, and 60 min during INT compared to CON (approximately 5 mmol/L vs 1.5 mmol/L). Sweat lactate was not significantly different (p>0.05) between trials at any time (approximately 10 mmol/L). Sweat rates (approximately 600ml/hr) and estimated total lactate secretion were not significantly different (CON vs. INT) (p > 0.05). Elevated blood lactate was not associated with changes in sweat lactate concentration. Sweat lactate seems to originate in eccrine glands independent of blood lactate.

Adult↗
PubMed1992

Neutron and X-ray solution-scattering studies of the ternary complex between proteoglycan-binding region, link protein and hyaluronan.

Proteoglycan aggregates of cartilage are stabilized by the formation of a ternary complex between the G1 domain at the N-terminus of the proteoglycan monomer (aggrecan), link protein and hyaluronan polysaccharide. Both the G1 domain and link protein contain similar three-domain structures formed from an immunoglobulin fold and two proteoglycan tandem repeats, the arrangement of which had been investigated by neutron and synchrotron X-ray scattering [Perkins, Nealis, Dunham, Hardingham & Muir (1991) Biochemistry 30, 10708-10716]. Here, solution scattering was used to investigate the ternary complexes formed between a proteolytic fragment of proteoglycan monomer containing G1 (termed binding region), link protein and hyaluronan oligosaccharides containing either 34 or 450 saccharide units (HA34 and HA450). The ternary complex with HA34 had a neutron radius of gyration, RG, at infinite contrast not exceeding 5.5 nm. The ternary complex with HA34 had an X-ray cross-sectional radius of gyration Rxs of 2.4 nm and a neutron Rxs at infinite contrast of 2.00 nm. Since both were similar or larger than the Rxs for binding region (X-rays, 2.04 nm; neutrons, 1.84 nm) and link protein (neutrons, 0.8 nm), analyses showed that the cross-sectional mean width of the ternary complex is greater than those in each of the free proteins, i.e. the two proteins associated side-by-side. Similar results were obtained with HA450 complexed with binding region and with both binding region and link protein. This structural model was verified by hydrodynamic simulations of the experimental sedimentation coefficient of 5.5 S, which showed that a compact ternary-complex structure was formed. Although scattering curve simulations using small spheres were limited for the ternary complex with HA34 because of its approximate RG value, the scattering data were compatible with the formation of a compact complex formed by side-by-side contacts between G1 and link protein.

Extracellular Matrix Proteins↗
PubMed1991

Molecular modeling of the multidomain structures of the proteoglycan binding region and the link protein of cartilage by neutron and synchrotron X-ray scattering.

The interaction of proteoglycan monomers with hyaluronate in cartilage is mediated by a globular binding region at the N-terminus of the proteoglycan monomer; this interaction is stabilized by link protein. Sequences show that both the binding region (27% carbohydrate) and the link protein (6% carbohydrate) contain an immunoglobulin (Ig) fold domain and two proteoglycan tandem repeat (PTR) domains. Both proteins were investigated by neutron and synchrotron X-ray solution scattering, in which nonspecific aggregate formation was reduced by the use of citraconylation to modify surface lysine residues. The neutron and X-ray radius of gyration RG of native and citraconylated binding region is 5.1 nm, and the cross-sectional RG (RXS) is 1.9-2.0 nm. No neutron contrast dependence of the RG values was observed; however, a large contrast dependence was seen for the RXS values which is attributed to the high carbohydrate content of the binding region. The neutron RG for citraconylated link protein is 2.9 nm, its RXS is 0.8 nm, and these data are also independent of the neutron contrast. The scattering curves of binding region and link protein were modeled using small spheres. Both protein structures were defined initially by the representation of one domain by a crystal structure for a variable Ig fold and a fixed volume for the two PTR domains calculated from sequence data. The final models showed that the different dimensions and neutron contrast properties of binding region compared to link protein could be attributed to an extended glycosylated C-terminal peptide with extended carbohydrate structures in the binding region.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1990

T-cell mediated cytolysis: evidence for target-cell suicide.

The mechanism by which cytotoxic T-lymphocytes (Tc) induce the death of specific target cells is still controversial. We have used quantitative cytochemical methods to distinguish the metabolic activities of the target cells from those of the Tc, even when they are attached to each other. Early events following Tc-P8(15) target cell interaction were first, increased glucose 6-phosphate dehydrogenase activity and second, labilization of the lysosomes within the target cell: these changes could be mimicked, in part, by polyamines and could be inhibited by inhibiting ornithine decarboxylase (ODC) activity. The crucial role of ODC in the chain of events that led to cytolysis in this particular experimental system was shown first, by measuring ODC activity directly and secondly, by the inhibition of cytolysis by the presence of a selective inhibitor of ODC activity.

Animals↗
PubMed1988

Rapid changes in target cell lysosomes induced by cytotoxic T cells: indication of target suicide?

Although many studies have attempted to elucidate how cytotoxic T (Tc) lymphocytes cause the death of target cells, the mechanism is still controversial. In the present study the effect on the integrity of the lysosomes of the target cell has been investigated. We show here that the specific recognition and attachment of cloned type A influenza-specific Tc cells to A/X31 influenza virus-infected target cells caused rapid change in the amount of lysosomal naphthylamidase activity that was bound within the lysosomes, indicating that the lysosomal membranes in the target cells had been totally labilized. Target cells infected with type B influenza virus served as controls. We therefore suggest that the viral specificity of Tc lymphocytes allows for recognition and intimate membrane contact with suitably infected targets. This intimate contact induces sufficient perturbation of the target cell plasma membrane so as to cause total labilization of the target cell lysosomes which could account for intracellular lysis.

Animals↗
PubMed1988

A reappraisal of the structure of normal canine articular cartilage.

It has been shown that some of the controversy over the structure of articular cartilage may be due to slight differences in the orientation of the sample that has been studied. As our decisive criterion we have used the simple physical fact that elongate proteins, such as collagen micelles, that can exhibit form-birefringence, had to show virtually straight extinction when viewed under crossed polars. The use of a variably adjustable microtome chuck facilitated small adjustments in the orientation of the cartilage to meet this criterion. Under these conditions, the collagen of the matrix has been shown to be aligned mainly perpendicularly to the surface which was bounded by a thin lamina in which the collagen showed birefringence at 90 degrees to that of the matrix. The conventionally described zonation of articular cartilage has been shown to be inadequate for that of the dog tibial plateau. The conventional Zone 2 has been shown to consist of two zones, Zones 2a and 2b, with different cell sizes, cell concentrations, and concentration of matrix components.

Animals↗
PubMed1986

Enzymic heterogeneity of normal canine articular cartilage.

Articular cartilage is generally considered to be an homogeneous tissue. It has now been shown that, although different regions of the medial tibial cartilage of the dog have very similar oxidative enzymic activities, each region is heterogeneous with respect to these activities. The conventional histological delineation of this cartilage has been modified, to take into account a narrow band (designated zone 2a), just below the most superficial spindle-shaped cells, that has higher oxidative enzymic activity than any other. Changes in the activity in this zone might be diluted by the lack of change in other zones if measured by conventional biochemical procedures which could not measure the activities of the different zones separately.

Alcohol Oxidoreductases↗
PubMed1985

Altered orientation of glycosaminoglycans and cellular changes in the tibial cartilage in the first two weeks of experimental canine osteoarthritis.

Changes in the cellularity and in the nature of the matrix were studied in the cartilages of the tibial plateau in experimentally induced arthritis in the dog, 7 and 14 days after section of the anterior cruciate ligament. Samples from the different regions of these cartilages were chilled and sectioned in a cryostat, with a variable microtome chuck to allow precise orientation of the specimens. The samples were examined by normal light microscopy, by microscopic interferometry, and by quantitative polarized light microscopy. The orientation of the glycosaminoglycans was assessed by the new "induced birefringence" method. The results indicated that only the region of the medial tibial cartilage that was unprotected by the meniscus was affected, showing increased water content, loss of superficial cells, and a decrease in orientation of the glycosaminoglycans. Whereas the birefringence of the collagen was unaffected, the superficial area that lacked oriented glycosaminoglycans was markedly increased; this may be a useful indicator of early osteoarthritic changes.

Alcian Blue↗
PubMed1984

Possible mechanism for target cell lysis by cytotoxic T-cells.

The mechanism of the lysis of target cells by cytotoxic T-cells (Tc) is still obscure; there is no evidence for transfer of material from the Tc and prior to lysis, despite intimate contact, the plasma membranes of both types of cell appear to remain intact. The effects on the target cell lysosomes of brief contact between anti-viral Tc and targets bearing both the appropriate histocompatibility and viral antigens, have been examined cytochemically. Both the distribution of acid phosphatase activity and the percentage bound lysosomal naphthylamidase activity indicated that, in virus-infected target cells exposed to Tc, the lysosomal membranes became totally labilized. Thus the contact between Tc and targets appears to cause sufficient perturbation of the target plasma membrane as to cause the intracellular release of some agent that activates 'suicide capsule' lysosomes.

Acid Phosphatase↗
PubMedDate not supplied

Effects of a novel ice-cooling technique on work in protective clothing at 28 degrees C, 23 degrees C, and 18 degrees C WBGTs.

This study tested a new ice cooling system that permits ice cooling system recharge without personal protective clothing removal. Six male volunteers (22.1 +/- 1.2 years) underwent tests with the new ice cooling system (COOL) and without (NOCL) at a moderate work rate (450 W) in three environments of 28, 23, and 18 +/- 1 degrees C wet bulb globe temperature. Walks at 28 degrees C were carried out first with NOCL and COOL counterbalanced, then test order and environment were counterbalanced. At 28 degrees C, mean work time in COOL significantly increased by 37.5 min (188%) over NOCL (p < 0.05). At 23 degrees C mean work time in COOL was significantly increased by 44.3 min (171%) compared with NOCL (p < 0.05). Mean work times at 18 degrees C were not significantly different, although all subjects completed the 120 minutes of work in COOL compared with a mean work time of 109 +/- 20 min for NOCL. During rest, mean reductions in rectal temperature were significantly greater in COOL than NOCL (p < 0.05) at 28 and 23 degrees C. Mean heart rate calculated for the same point in both treatments was significantly lower for COOL at 28, 23, and 18 degrees C (p < 0.05). Thermal comfort rating was significantly different at 18 and 23 degrees C (p < 0.05). This new design seemed to provide comparable cooling to conventional vests and also provides greater practicality for field use. Even in experimental form the suit demonstrated increased productivity due to extended tolerance time.

Adult↗