Effects of Occupational Noise Exposure on 24-Hour Ambulatory Vascular Properties in Male Workers

BACKGROUND: Epidemiologic studies have demonstrated that occupational noise exposure is associated with hypertension, but the related mechanism in vascular structural changes is unclear. OBJECTIVE: This panel study aimed to investigate effects of occupational noise exposure on ambulatory vascular structural properties in male workers. METHODS: We recruited 20 volunteers and divided them into a high-noise- exposure group of 15 and a low-noise-exposure group of 5 based on environmental noise measurement in an automobile manufacturing company. We determined individual noise exposure and measured personal ambulatory vascular property parameters simultaneously during 24 hr. Linear mixed-effects regression models were used to estimate transient and sustained effects of noise exposure on vascular parameters by adjusting some confounders collected from self- administrated questionnaires and health checkups. RESULTS: The high-noise- exposed (85 ± 8 dBA) workers had significantly higher systemic vascular resistance (SVR) than the low-noise-exposed workers (59 ± 4 dBA) during work and sleep periods. Contrarily, low-noise-exposed workers had significantly higher brachial artery compliance (BAC), brachial artery distensibility (BAD), and systemic vascular compliance (SVC; marginal, p = 0.07) than high-noise-exposed workers during off-duty periods. We also found that high- noise-exposed workers had significantly lower BAC (1.38 ± 0 .55 %mL/mmHg) and BAD (1.29 ± 0.51 %/mmHg), as well as lower SVC (0. 24 ± 0.10 mL/L/mmHg), but higher SVR (1.93 ±0.67 mL/L/min) compared with low-noise-exposed workers over a 24-hr period. CONCLUSIONS: Our findings suggest that in automobile workers, occupational noise exposure may have sustained, not transient, effects on vascular properties and also enhances the development of hypertension. [ABSTRACT FROM AUTHOR] Copyright of Environmental Health Perspectives is the property of Superintendent of Documents and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data