Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Exhalation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,297 records · Page 72Linked to original sources
PubMedDate not supplied

Work performance when breathing through different respirator exhalation resistances.

This study evaluated performance of individuals exercising at a fixed workload and wearing full-facepiece respirators modified to provide expiratory resistances of 0.27, 0.47, 1.81, 4.43, and 12.27 cmH20 x s x L(-1). On five separate occasions, 15 volunteers exercised to voluntary endpoint on a treadmill at fixed speeds and grades chosen to elicit 85% of maximal aerobic capacity for an unencumbered condition. Exercise performance time was recorded at the cessation of each test. Results showed that performance time decreased linearly (R2 = 0.79; p<0.001) with increased resistances, and no threshold value below which expiratory resistance has no impact on performance was found. Average oxygen consumption rates and minute ventilation also decreased linearly with increased expiratory resistances, indicating that increases in expiratory resistance result in a considerable level of hypoventilation. From the perspective of respirator design, the results of this study suggest that the only practical expiratory resistance level limitation is the reduction in performance that will be acceptable to the end users.

Adolescent↗
PubMed1996

Prototype instrument employing a microsensor array for the analysis of organic vapors in exhaled breath.

A prototype portable instrument capable of selectively measuring organic vapors in breath at low- and sub-ppm concentrations was tested. The instrument employs an array of four polymer-coated surface-acoustic-wave (SAW) resonators and microprocessor-controlled pumps, valves, and heating elements for preconcentration and thermal desorption of breath samples. Response data are passed to an external personal computer for processing. Sensor responses are based on the reversible changes in the mass and viscoelasticity of the polymeric coatings accompanying vapor sorption. Calibrations were performed for perchloroethylene, trichloroethylene, and methoxyflurane at 100% relative humidity using 15 mg of TenaxTA as the preconcentrator adsorbent. Analyses were then conducted of 250-mL breath samples prepared in Tedlar bags spiked with one of the three solvents within the range of 2 to 18 ppm. Differences between concentrations measured using the prototype instrument and those measured by gas chromatography ranged from -6 to 17% for perchloroethylene. Similar results were obtained for trichloroethylene and methoxyflurane with larger differences occurring at lower concentrations. Estimated limits of detection of 0.7, 0.6, and 4 ppm were achieved for perchloroethylene, trichloroethylene, and methoxyflurane, respectively. These preliminary results demonstrate the feasibility of using SAW sensor technology for field breath analysis.

Breath Tests↗
PubMed1996

Investigation of organic vapor losses to condensed water vapor in Tedlar bags used for exhaled-breath sampling.

This study evaluated the potential loss of organic vapors to condensed water in bags used for breath sampling. "Wet" test atmospheres were prepared by transferring nitrogen into 1-L Tedlar bags and spiking with water and each of several organic solvents (methanol, acetone, 2-butanone,m-xylene, 1,1,1 trichloroethane, and perchloroethylene) to yield atmospheres representative of a 500-mL breath sample collected at 37 degrees C and cooled to 25 degrees C. Vapor concentrations were compared with those in bags prepared without water. Differences between mean concentrations in wet and dry bags were significant only for methanol, which yielded a mean wet-bag concentration approximately 10% lower than for dry bags. In a second series of experiments the same initial concentration of solvent vapor was generated in 1 dry bag and 5 bags containing 1 to 20 times the amount of water expected to condense in a 500-mL breath sample. Significant differences between wet and dry bag concentrations were seen for methanol, acetone, and 2-butanone; however, the quantity of water required to produce this difference in the acetone and 2-butanone bags exceeded three times that expected to condense in a breath sample. Results were in good agreement with predictions based on Henry's law. In both experiments permeation of water vapor out of the bags led to a decrease in the quantity of condensed water, thereby reducing the extent of organic vapor partitioning. These results indicate that solvent vapor loss to condensed water is not likely to be significant under typical conditions.

Body Water↗
PubMed2004

A field method for near real-time analysis of perchloroethylene in end-exhaled breath.

The field method for near real-time analysis of perchloroethylene (Perc) in breath is simple, fast, and reproducible for Perc breath analysis in field settings and should prove useful in industrial hygiene practice. The method allows Perc monitoring with good specificity to the sub-part per million (ppm) level within minutes of exposure. A commercially available, portable gas chromatograph with a photoionization detector was used in these analyses. Gas chromatograph settings were optimized in the laboratory for measurement of Perc in Tedlar bags. Laboratory development of the method included evaluation of the sensitivity, specificity, precision, and speed of analysis for Perc. Replicate aliquots of Perc at concentrations ranging from 0.01 to 100 ppm were used to construct a calibration curve. The mean retention time for Perc was 238 sec. The impact of potential interference by acetone, toluene, isoprene, methanol, ethanol, acetaldehyde, carbon tetrachloride, benzene, or chloroform was evaluated by mixing Perc with each compound and performing analyses. Measurements of Perc in human breath samples collected in Tedlar bags in a workplace setting were made and compared to measurements of the same samples made by an established analytical method using charcoal tubes (National Institute of Occupational Safety and Health [NIOSH] Method 1003). The accuracy, precision, and speed of the gas chromatograph method were determined. Measurements made with the new method were within a margin of +/- 8.8% (95% CI, n = 6) of measurements made according to NIOSH Method 1003 for field samples in the range of 0.9 to 6 ppm. Method precision was determined by calculating the pooled coefficient of variation for all measurements (replicates = 3) made in the field and was found to be 5.8%.

Automation↗
PubMed1978

In vivo measurement of calcium by the 37Ar method: a study of the effect of recirculating breath collection systems on the exhalation rate.

A study has been made of the effect that different methods of breath collection have on the measurement of calcium in vivo by the 40Ca(n,alpha) 37Ar method. The effect of open and rebreathing breath collection methods has been examined by using intravenous injections of 133Xe. This study has indicated that comparison of calcium measurements between individuals and between centres is likely to be accurate only if breath is collected on 'open circuit'.

Argon↗