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Biomedical subjects

M K White

Publications and source records attributed to M K White.

At least 19 recordsLinked to original sources
PubMed1991

Effects of thermal environment and chemical protective clothing on work tolerance, physiological responses, and subjective ratings.

This study examined the physiological and subjective responses of nine healthy men who performed work while wearing two types of protective ensembles in each of three thermal environments. The subjects, all experienced with the use of protective ensembles, each performed low intensity treadmill exercise (23% of VO2 max while not wearing a Self-Contained Breathing Apparatus [SCBA] or protective clothing) under six experimental conditions: two ensembles (SCBA--light work clothing and SCBA; and CHEM--a two-piece chemical protective ensemble with SCBA) during exposure to 'cool' (10.6 degrees C/water vapour pressure [Pw] 0.76 kPa), 'neutral' (22.6 degrees C/Pw 1.52 kPa), and 'hot' (34 degrees C/Pw 2.90 kPa) environments. Each test was intended to continue for 120 min; however the duration and number of work/rest periods within the testing session varied according to the specific responses of each individual. At the completion of each test seven subjective responses were recorded. Physiological data, collected every minute during each test, included heart rate, and skin and rectal temperature. The total worktime was significantly shorter in the hot environment while wearing the CHEM ensemble (53.4 min) compared to all the other conditions (103-105 min). The mean maximum physiological values also indicated significant differences due to thermal environment and/or ensemble. Work performance did not appear to be limited in a cold environment with either ensemble tested. The physiological responses to working in the CHEM/neutral condition were very similar to those occurring in a hot environment wearing the SCBA ensemble. The subjective responses also indicated significant differences due to thermal environment and ensemble, with subjects perceiving the CHEM ensemble as less favourable than the SCBA ensemble. The results suggested that, even at a low work intensity, individuals wearing chemical protective clothing in the heat will require progressively shorter work periods, and more frequent and longer rest periods.

Adult↗
PubMed1991

The effectiveness of ice- and Freon-based personal cooling systems during work in fully encapsulating suits in the heat.

The use of cooling garments in conjunction with fully encapsulating suits offers the potential for reducing the heat strain for workers at hazardous waste sites and chemical emergencies. This study examined the use of ice- and Freon-based cooling garments during exercise in the heat while wearing a U.S. Coast Guard chemical response suit (CRS), a fully encapsulating, Teflon-coated, Nomex suit. Responses of nine healthy men (mean age 28.8 yr) were measured during moderate exercise at 30% of their maximal oxygen consumption in an environmental chamber maintained at 33.9 degrees C (93 degrees F) and 82% relative humidity. The four randomly assigned experimental conditions were (1) the CONTROL, consisting of a self-contained breathing apparatus (SCBA) worn in conjunction with shorts, shirt, helmet, and shoes; (2) the CRS, consisting of the Coast Guard CRS worn with shorts, shirt, SCBA, helmet, gloves, and boots; (3) the ICE, which was identical to the CRS ensemble, with the addition of an ice and water cooling system; and (4) the FREON, which was also identical to the CRS ensemble, with the addition of a Freon-based cooling system. To the author's knowledge, this paper is the first to quantify and compare a Freon-based system with a circulating ice water system. The subjects performed repeated rest/work intervals for 45 min, followed by a 10-min recovery period. Measured physiological responses, including heart rate, skin, rectal, and axillary temperatures, were recorded at 1-min intervals during the tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Differential regulation of glucose transporter isoforms by the src oncogene in chicken embryo fibroblasts.

The increase in glucose transport that occurs when chicken embryo fibroblasts (CEFs) are transformed by src is associated with an increase in the amount of type 1 glucose transporter protein, and we have previously shown that this effect is due to a decrease in the degradation rate of this protein. The rate of CEF type 1 glucose transporter biosynthesis and the level of its mRNA are unaffected by src transformation. To study the molecular basis of this phenomenon, we have been isolating chicken glucose transporter cDNAs by hybridization to a rat type 1 glucose transporter probe at low stringency. Surprisingly, these clones corresponded to a message encoding a protein which has most sequence similarity to the human type 3 glucose transporter and which we refer to as CEF-GT3. CEF-GT3 is clearly distinct from the CEF type 1 transporter that we have previously described. Northern (RNA) analysis of CEF RNA with CEF-GT3 cDNA revealed two messages of 1.7 and 3.3 kb which were both greatly induced by src transformation. When the CEF-GT3 cDNA was expressed in rat fibroblasts, a three-to fourfold enhancement of 2-deoxyglucose uptake was observed, indicating that CEF-GT3 is a functional glucose transporter. Northern analyses using a CEF-GT3 and a rat type 1 probe demonstrated that there is no hybridization between different isoforms but that there is cross-species hybridization between the rat type 1 probe and the chicken homolog. Southern blot analyses confirmed that the chicken genomic type 1 and type 3 transporters are encoded by distinct genes. We conclude that CEFs express two types of transporter, type 1 (which we have previously reported to be regulated posttranslationally by src) and a novel type 3 isoform which, unlike type 1, shows mRNA induction upon src transformation. We conclude that src regulates glucose transport in CEFs simultaneously by two different mechanisms.

Amino Acid Sequence↗
PubMed1990

The src oncogene can regulate a human glucose transporter expressed in chicken embryo fibroblasts.

When fibroblasts are transformed by the src oncogene, there is a two- to fivefold increase in glucose transport and in the level of immunoprecipitable glucose transporter protein. In chicken embryo fibroblasts (CEFs), this increase is correlated with a comparable reduction in the rate at which the glucose transporter protein is turned over. In contrast, in mammalian fibroblasts glucose transporter biosynthesis is increased by src, but there is little or no change in its turnover. To further understand the action of src on transporter turnover, we investigated whether a mammalian transporter can be stabilized by src in a chicken cell environment. The human type 1 glucose transporter protein (hGT), originally cloned from HepG2 cells, was expressed in CEFs or Rat-1 fibroblasts by using a retroviral vector. In CEFs transformed by a temperature-sensitive src mutant, tsNY68, turnover of hGT was lower at the permissive temperature (36 degrees C) than at the nonpermissive temperature (42 degrees C). When this protein was expressed in CEFs transformed by wild-type src, no difference in turnover was observed at the two temperatures. In the case of Rat-1 cells transformed by the temperature-sensitive src mutant tsLA29, turnover of hGT was the same at the permissive temperature (35 degrees C) as at the nonpermissive temperature (39.5 degrees C). These data demonstrate that a heterologous glucose transporter behaves in the same way in chicken and rat cells as the respective endogenous transporter, i.e., when src is active, the protein is stablilized against turnover in chicken cells but not in rat cells.

Animals↗
PubMed1989

Work tolerance and subjective responses to wearing protective clothing and respirators during physical work.

This study examined work tolerance and subjective responses while performing two levels of work and wearing four types of protective ensembles. Nine males (mean age = 24.8 years, weight = 75.3 kg, VO2 max = 44.6 ml/kg min) each performed a series of eight experimental tests in random order, each lasting up to 180 min in duration. Work was performed on a motor-driven treadmill at a set walking speed and elevation which produced work intensities of either 30% or 60% of each subject's maximum aerobic capacity. Work/rest intervals were established based on anticipated SCBA refill requirements. Environmental temperature averaged 22.6 degrees C and average relative humidity was 55%. The four protective ensembles were: a control ensemble consisting of light work clothing (CONTROL); light work clothing with an open circuit self-contained breathing apparatus (SCBA); firefighter's turnout gear with SCBA (FF); and chemical protective clothing with SCBA (CHEM). Test duration (tolerance time) was determined by physiological responses reaching a predetermined indicator of high stress or by a 180-min limit. Physiological and subjective measurements obtained every 2.5 min included: heart rate, skin temperature, rectal temperature, and subjective ratings of perceived exertion, thermal sensation, and perspiration. The mean tolerance times were 155, 130, 26, and 73 min, respectively, for the CONTROL, SCBA, FF, and CHEM conditions during low intensity work; and 91, 23, 4, and 13 min, respectively, during high intensity work. Differences between ensemble and work intensity were significant. FF and CHEM heart rate responses did not reach a steady state, and rose rapidly compared to CONTROL and SCBA values. SCBA heart rates remained approximately 15 beats higher than the CONTROL ensemble during the tests. At the low work intensity, mean skin temperatures at the end of the test were 32.7, 33.1, 36.7, and 36.3 degrees C, while mean core temperatures were 37.6, 37.9, 37.9, and 38.5 degrees C, respectively. The subjective data indicated that, in general, subjects were able to perceive relative degrees of physiologic strain under laboratory conditions. Wearing protective clothing and respirators results in significant and potentially dangerous thermoregulatory and cardiovascular stress to the wearer even at low work intensities in a neutral environment. Physiologically and subjectively, firefighter's turnout gear (the heaviest ensemble) produced the most stress, followed by the CHEM, SCBA, and CONTROL protective ensembles.

Body Temperature↗
PubMed1989

Physiological and subjective responses to working in disposable protective coveralls and respirators commonly used by the asbestos abatement industry.

The physiological and subjective effects of working with different respirators while wearing lightweight disposable (Tyvek 1412 polyolefin) coveralls commonly used by the asbestos abatement industry were studied. Nine healthy men (mean age = 27.3 yr, weight = 76.9 kg) each performed a series of four exercise tests with four different respirator ensembles in counterbalanced order. Treadmill work was performed at a set walking speed of 4 kph (2.5 mph), 0 percent elevation (220 kcal/hr), a controlled environmental temperature of 33.9 degrees C, and 50% relative humidity. Each test continued up to 120 min, with repeated work/rest intervals of 26 min of work and 4 min of rest. Tyvek disposable coveralls and hoods were worn with each of these four different respirator ensembles: (1) control--a lightweight, low resistance mask; (2) HEPA--an air purifying, full facepiece respirator with dual high efficiency filters; (3) SAR--a supplied-air, pressure-demand respirator with escape filter; (4) SCBA--an open circuit, pressure-demand, self-contained breathing apparatus. Physiological measurements obtained every minute during each test included heart rate and skin and rectal temperatures. Subjective evaluations of clothing, respirator, and facepiece comfort, ease of breathing, temperature and perspiration in the mask and clothing, and respirator load also were measured at the end of the test. Data were analyzed using an analysis of variance. Results indicated that heart rate at the end of the test differed by less than 8 BPM between the control condition and the SCBA (heaviest) condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Physiological responses to the wearing of fire fighter's turnout gear with neoprene and GORE-TEX barrier liners.

This study examined the physiological effects of performing moderate and high intensity work while wearing fire fighter's turnout gear with either a neoprene or GORE-TEX barrier liner. Eight healthy men, experienced with the use of respirators and protective clothing, each performed moderate and high intensity treadmill exercise (44% and 71% of maximum work capacity) in a double-blind study at 27.6 degrees C (50% RH) while wearing complete fire fighter's turnout gear (weighing 23 kg) with either a neoprene or GORE-TEX barrier liner. Physiological measurements obtained included minute ventilation, heart rate, skin temperature, rectal temperature and sweat rate. Subjective evaluations of perceived exertion, comfort, clothing breathability, temperature and perspiration also were obtained. Tests were terminated (tolerance time) when objective or subjective signs of near maximal stress were observed (i.e., 90% of the maximum heart rate, rectal temperature of 39 degrees C, dizziness, etc.). Mean tolerance times for the moderate intensity exercise were 27.4 (+/- 7.3 S.D.) and 30.9 (+/- 7.9) min, respectively, for the neoprene and GORE-TEX barrier liners and at the high intensity were 7.2 (+/- 2.1) and 7.5 (+/- 2.3) min, respectively. Analysis of variance indicated that significant differences caused by liner were observed in skin temperature (0.6 degrees C higher with the neoprene ensemble). No significant differences caused by liner were seen in tolerance time, heart rate, sweat rate or subjective ratings.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Transformation by the src oncogene alters glucose transport into rat and chicken cells by different mechanisms.

Transformation of both rat and chicken fibroblasts by the src oncogene leads to a four- to fivefold increase in the rate of glucose transport and in the level of the glucose transporter protein. We have previously shown that, with chicken embryo fibroblasts, transformation leads to a reduction in the rate of degradation of the transporter, with little or no increase in the rate of its biosynthesis. We now show that, with the rat-1 cell line, the opposite result was obtained. src-induced transformation led to an increase in transporter biosynthesis, with little effect on turnover. A src-induced increase in transporter mRNA entirely accounted for the increase in biosynthesis of the protein. By contrast, in chicken embryo fibroblasts, the level of transporter mRNA was low and was not induced to rise by src transformation. Thus, src induced an increase in the level of the glucose transport protein by fundamentally different mechanisms in chicken embryo fibroblasts and rat-1 cells. To test whether this difference was due to rat-1 cells being an immortalized cell line, we measured transporter mRNA levels in primary fibroblast cultures from rat embryos and in parallel cultures transformed by src. Transporter mRNA was inducible by src in these cells. Thus, the difference in mRNA inducibility between chicken and rat cells is not due to immortalization.

Animals↗
PubMed1988

Optimal positive end-expiratory pressure therapy in infants and children with acute respiratory failure.

Positive end-expiratory pressure (PEEP) has become a mainstay in the treatment of hypoxemic acute respiratory failure (ARF). Whereas PEEP improves arterial oxygen tension by decreasing intrapulmonary shunting, it may also impair cardiac output and hence decrease systemic oxygen transport. Inasmuch as optimizing oxygen transport is a goal of therapy in ARF, we sought to determine if the level of PEEP that results in maximal oxygen transport could be estimated from measurements of compliance of the respiratory system (Crs) or PaO2. We studied the effects of PEEP application on cardiorespiratory parameters in 15 children who required mechanical ventilation for ARF. Static Crs, PaO2, central venous and arterial blood pressures, indicator dilution cardiac index (CI), and oxygen transport were determined at 0, 3, 6, 9, 12, and 15 cm H2O PEEP. PaO2 increased significantly at PEEP levels greater than or equal to 9 cm H2O (p less than 0.001), while CI fell by 15% between 0 and 15 cm end-expiratory pressure (p less than 0.02). Crs and oxygen transport did not change significantly with increasing levels of PEEP. The level of PEEP resulting in maximal oxygen transport ranged from 0 to 15 cm H2O, and in all patients it corresponded to PEEP of best CI. At levels of PEEP above that associated with maximal oxygen transport, CI and oxygen transport fell significantly, while PaO2 continued to rise. No relationship between Crs and oxygen transport was observed. In our normovolemic patients with ARF, neither PaO2 nor Crs predicted PEEP of maximal oxygen transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1987

Degradation and biosynthesis of the glucose transporter protein in chicken embryo fibroblasts transformed by the src oncogene.

The rate of glucose transport in cultured fibroblasts is regulated to a number of physiological variables, including malignant transformation by src, glucose starvation, and stimulation with mitogens. Much of this transport regulation can be accounted for by variations in the amount of transporter protein in the cells. To determine the mechanisms by which levels of the transporter are regulated, we measured the rates of synthesis and degradation of the transporter by pulse-chase experiments and immunoprecipitation of the transporter. We found that transformation by the src oncogene results in a large decrease in the rate at which the transporter protein is degraded but that it does not appreciably increase the rate of transporter biosynthesis. On the other hand, glucose starvation and mitogen stimulation increase the rate of transporter biosynthesis, although a role for control of degradation is possible in these circumstances also. Variations in the rate of glucose transport or the amount of the transporter are not associated with phosphorylation of the transporter protein.

Animals↗
PubMed1987

Reduced work tolerance associated with wearing protective clothing and respirators.

This study examined worker tolerance and physiological responses to two levels of work while subjects wore various types of protective clothing and respirators. Nine healthy men (mean age = 24.8 years, weight = 75.3 kg, max VO2 = 44.6 mL/kg/min), experienced with the use of respirators, each performed a randomized series of eight experimental tests, each test scheduled to last 180 min. Work was performed on a motor-driven treadmill at a set walking speed and elevation indicative of either 30% (low work intensity) or 60% (high work intensity) of maximum work capacity for each individual. Four protective clothing ensembles were examined: light work clothing (LIGHT), light work clothing with SCBA (SCBA), firefighter's turnout gear with SCBA (FF) and chemical protective clothing with SCBA (CHEM). Physiological measurements included heart rate, skin and rectal temperature, and minute ventilation. Measurements were obtained every 2.5 min until test termination (tolerance time). If less than 180 min, tolerance time was defined by subjective or objective signs of near maximal stress. Mean tolerance times at the low work intensity were 167, 130, 26 and 73 min, respectively, for the LIGHT, SCBA, FF and CHEM ensembles. At the high intensity, mean tolerance times were 91, 23, 4 and 13 min, respectively. At the low work intensity, heart rate with SCBA rose very slowly during the tests and remained approximately 15 beats/min higher than the heart rate for subjects wearing the LIGHT ensemble. In contrast, heart rate with the FF and CHEM ensembles rose sharply and did not approach steady-state values.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1985

Hydrogen sulfide and the probabilities of 'inhalation' through a tympanic membrane defect.

We conclude that workers with tympanic membrane defects (perforated eardrums) should not be excluded from working in atmospheres containing concentrations of hydrogen sulfide (H2S). Several existing requirements and recommendations exclude workers with perforated eardrums from working in or around H2S. Such protective measures stem from the belief that H2S can enter the body through the perforation in sufficient measure to compromise the wearer's respiratory protection. However, based on calculations of anticipated leakage of H2S for a variety of eustachian tube conditions and in the absence of either medical literature or personal reports documenting H2S poisoning due to eardrum perforation, the recommendation for excluding workers with such a condition from working in or around H2S is not supported. The anatomy, physiology, and pathology of the eustachian tube are discussed, including the effects such devices as tympanomaxillary shunts might have on contaminant leakage. The National Institute for Occupational Safety and Health (NIOSH) criteria for respirator tests and sources of respirator leakage are examined and NIOSH recommendations for respiratory protection against H2S are outlined.

Ear Deformities, Acquired↗
PubMed1984

Alterations induced by glucose deprivation and tunicamycin in the kinetic parameters of hexose transport in hybrid cells.

Matched pairs of malignant and non-malignant hybrid cells were compared in their response to glucose deprivation and to tunicamycin. Glucose deprivation induced an increase in the maximum velocity in the malignant cells, but not in the non-malignant cells. The Michaelis constant of hexose uptake was largely unchanged by glucose deprivation except in the case of one melanoma derivative, PG19 G-, which showed a large increase in Michaelis constant when deprived of glucose. Tunicamycin increased the Michaelis constant of hexose uptake in both malignant and non-malignant cell lines. It is therefore possible that the Michaelis constant of hexose uptake is affected by the extent of glycosylation of one or more of the cell membrane glycoproteins.

Animals↗
PubMed1979

Complementation analysis of eleven tryptophanase mutations in Escherichia coli.

Nine independent mutants deficient in tryptophanase activity were isolated. Each mutation was transferred to a specialized transducing phage that carries the tryptophanase region of the Escherichia coli chromosome. The nine phages thus produced, and a tenth carrying a previously characterized tryptophanase mutation, were used to lysogenize a bacterial strain harbouring a mutation in the tryptophanase structural gene and also a suppressor of polarity. In no case was complementation observed; we conclude that there is no closely linked positive regulatory gene for tryptophanase.

Bacteriophage lambda↗
PubMed1977

A case-control study of uterine perforations documented at laparoscopy.

A case-control analysis was done of 19 cases of uterine perforations which occurred during laparoscopic sterilization at Gardy Memorial Hospital in Atlanta, between February 1, 1974, and January 31, 1976. The over-all perforation rate, 30.4 per 1,000 procedures, is three to 30 times that commonly reported for dilatation and suction or sharp curettage (D&C) of the uterus. Case women were 10.4 times more likely than control women to combine two of the following three characteristics: age greater than 34, parity greater than 4, and obesity greater than 20 per cent above the ideal body weight for height. Surgeons with fewer months of formal Ob/Gyn training were no more likely than their relatively more experienced colleagues to perforate the uterus. No other risk factors were delineated. It is believed that the perforation rate, higher in this study than in earlier ones, reflects better ascertainment of perforations. The bleeding site was always visualized with the laparoscope in this series.

Adult↗