OBJECTIVES: To test the efficacy of a bicarbonate-containing artificial physiologic tear solution (solution PT) in providing an environment in which the damaged corneal epithelium can recover its normal barrier function and to compare this solution with other available artificial tears. Also, to investigate the effects on the corneal mucin layer and epithelial ultrastructure. METHODS: The corneal epithelial permeability of anesthetized rabbits was increased by exposure to 0.1% benzalkonium chloride. The corneas were then exposed to solution PT, with or without bicarbonate, or one of four commercially available artificial tear solutions for 1.5 hours, followed by a 5-minute exposure to 5(6)-carboxyfluorescein. Frozen sections of the corneas were examined by fluorescence microscopy. The fluorescence intensity (FI) of the epithelium was measured by image analysis. Undamaged corneas exposed to tear solutions were examined by transmission electron microscopy after fixation of the mucin layer with cetylpyridinium chloride. RESULTS: The FI of corneas damaged by benzalkonium chloride was increased threefold above those of undamaged controls. Damaged corneas treated with either of two commercial isotonic tear solutions partially recovered their barrier function, but the FI did not reach control levels. Corneas treated with hypotonic solutions containing ethylenediaminetetraacetic acid (EDTA) did not recover. In contrast, the FI of corneas treated with solution PT returned to control levels. This effect was lost in the absence of bicarbonate. Solution PT and the two isotonic solutions maintained normal corneal ultrastructure and mucin layer. Lack of bicarbonate in solution PT resulted in focal damage to superficial epithelial cells, whereas the EDTA-containing solutions destroyed the first two cell layers and reduced the mucin thickness. CONCLUSIONS: Bicarbonate-containing solution PT is superior to the other tear solutions tested in promoting recovery of the damaged corneal epithelial barrier and maintaining normal ultrastructure. The presence of bicarbonate appears to be essential to this process.

Bicarbonates↗

PubMed1994

Empirical prediction of physiological response to prolonged work in encapsulating protective clothing.

Work in moderate or hotter environments while wearing encapsulating protective clothing (PC) results in heat storage and substantial diminution of work productivity, as well as being a potential health risk. An ability to predict the responses of workers using PC would be very useful. Predictions were made of work times at 21 degrees C of 15 subjects performing prolonged hard work (450 W gross) while wearing PC, based upon prior measures of short-duration bench stepping in PC and heart rate responses. A simple model was derived that shows good potential for predicting work time in moderate temperatures in PC; Total Time = 7.2 (bench step duration) - 34 (bench comfort) + 4 (height); R2 = 0.83, C.V. = 13. Unexpectedly, models that incorporated recovery heart rate as a variable were not as effective. With further refinement, the prediction approach tested in this study would be immediately useful for managing military and civilian personnel working in PC. Additionally, it could be utilized at minimal cost during routine training.

Adult↗

PubMed1994

Responses to repeated days of light work at moderate temperatures in protective clothing.

This study assessed workers' ability to sustain work output over four consecutive workdays in encapsulating protective clothing (PC). Six subjects wearing a two-piece PC ensemble cycled at a work rate of 38 W in a 29/22 degrees C (dry/wet bulb) ambient temperature. Work continued until rectal temperature (Tre) reached 38.3 degrees C, or volitional fatigue. Subjects then rested without PC in a 21 degrees C room until Tre reached 38.0 degrees C to simulate micro- or macro-environmental cooling during rest. Work was alternated with rest for four hours total. Contrary to expectations, mean work time did not diminish on succeeding days. Subject responses to the repeated exposures was highly variable and in no case changed significantly (p > .05) from day one to day four. Subjects tolerated well repeated four-hour exposures with controlled elevations in Tre. There was no clear evidence of either increased or decreased tolerance of this work-rest paradigm across days.

Adaptation, Physiological↗

PubMed1986

Outcome after prenatal detection of a sporadic, unstable translocation t(5;21).

Amniotic fluid cultures from a 37 year old woman showed a sporadic 46,XX,t(5;21)(5qter----5p13 or p14::5pter----5p13 or p14::21p12----21qter) complement. In the majority of metaphases the 5p fragment was attached to the stalks of chromosome 21; however, in 9% of metaphases, the fragment was loosely attached by a 'thread' and in 6% it was completely detached. Silver staining and in situ hybridisation with a homologous ribosomal gene probe, which localises to stalk regions (nucleolar organisers, NOR) of human acrocentric chromosomes, failed to show a reciprocal exchange. Prognosis was uncertain because the possibility that the 5p fragment might have been lost in some cell lines could not be excluded. Nonetheless, the parents elected to continue the pregnancy. The translocation was confirmed in blood specimens obtained both at birth and at 1 year of age and showed similar instability. However, the proband shows no anomalies and is developing normally at 1 year.

Adult↗