Investigating the Swimming of Microbial Pathogens Using Digital Holography.

To understand much of the behaviour of microbial pathogens, it is necessary to image living cells, their interactions with each other and with host cells. Species such as Escherichia coli are difficult subjects to image: they are typically microscopic, colourless and transparent. Traditional cell visualisation techniques such as fluorescent tagging or phase-contrast microscopy give excellent information on cell behaviour in two dimensions, but no information about cells moving in three dimensions. We review the use of digital holographic microscopy for three-dimensional imaging at high speeds, and demonstrate its use for capturing the shape and swimming behaviour of three important model pathogens: E. coli, Plasmodium spp. and Leishmania spp.

Is NIDDM a risk factor for noise-induced hearing loss in an occupationally noise exposed cohort?

Little is known about what factors, other than chronic exposure to noise, predispose individuals to noise-induced hearing loss (NIHL). The current retrospective study was designed to identify risk factors for NIHL in a population of 229 men [age 55-68 (mean = 63 years)] employed at a metal assembly plant. All men had been chronically occupationally noise-exposed for approximately 30 years (> or = 89 dBA) with an average Ea noise emission level) of 104.5. The clinical examination included a pure-tone threshold audiometric evaluation, discrimination of speech in background noise [W-22 Max (> 60% indicating better hearing)], blood pressure measurement, evaluation of lifestyle (alcohol consumption, cigarette smoking, noisy hobbies) and occupational and military history. Severe NIHL was defined as > or = 65 db loss at 3, 4 or 6 kHz in at least one ear +/- 20 db threshold in the contralateral ear. History of non-insulin dependent diabetes mellitus (NIDDM) was reported by 16.4% of the 146 men with severe NIHL compared to 4.8% of the 83 men without severe NIHL (odds ratio = 3.9, C.I. 1.2-11.9, P = 0.05). Simultaneous evaluation of several potential risk factors using a multiple logistic regression indicates that the significant predictors of severe NIHL were diabetes (P < 0.05), Ea (P < 0.05) and age (P < 0.05). These results suggest that a person with NIDDM who is also occupationally noise-exposed is more likely to develop severe NIHL than those without NIDDM. Longitudinal studies are necessary to confirm the temporal relationship between NIDDM and NIHL and to determine the exact mechanisms that are involved with this increased risk of hearing loss.

Noise-induced hearing loss: a possible marker for high blood pressure in older noise-exposed populations.

The present study assessed the relationships among occupational noise exposure, noise-induced hearing loss, and high blood pressure. The study population consisted of 245 retired metal assembly workers from Pittsburgh aged 56 to 68 with chronic noise exposure of 30 or more years at greater than or equal to 89 dBA. Results of the audiometric testing indicated 52% of the younger workers (ages 56 to 63) have severe noise-induced hearing loss (greater than or equal to 65 dBA loss at 3, 4, or 6 kHz) and 67% of older workers (ages 64 to 68). Body mass index and alcohol intake were significantly related to systolic and diastolic blood pressure. Among older men, there was a marginally significant increased prevalence of high blood pressure (greater than or equal to 90 mm diastolic or taking blood pressure medicine) among those with severe noise-induced hearing loss (P = .05). Moreover, another measure of hearing loss at high frequencies, speech discrimination score in noise (measured in the better ear), referred to as the W-22 MAX score, was also found to be related to the prevalence of high blood pressure in the older (64 to 68) age group (P less than .05). Multiple regression analysis revealed W-22 MAX and severe noise-induced hearing loss were independent predictors of hypertension in the older, but not in the younger group of retired workers.

Effects of subtle mid-frequency auditory dysfunction upon speech discrimination in noise.

Earlier studies have indicated mid-frequency auditory dysfunction and depressed ability to discriminate speech in noise among noise-exposed listeners with high-frequency hearing loss. The present study was designed to determine whether mid-frequency dysfunction contributed to the depressed speech discrimination performance. Normal listeners, and noise-exposed and older listeners with high-frequency hearing loss listened to word lists presented in competing 'cocktail party' noise under unfiltered and low-pass filter conditions. In the low-pass filter condition the performance of the noise-exposed listeners was superior to that normal listeners, indicating that mid-frequency auditory dysfunction on the part of noise-exposed listeners does not contribute to their difficulties discriminating unfiltered speech in noise. The performance of the older listeners was below that of the two other groups in both filtered and unfiltered conditions, indicating greater difficulty discriminating speech than would be predicted only on the basis of high-frequency hearing loss.

Auditory dysfunction accompanying noise-induced hearing loss.

Two groups of 16 young male subjects with normal low- and midfrequency hearing were compared on a series of audiometric measures. One group was composed of subjects with 12- to 24-month histories of noise exposure and hearing loss at 4000 Hz greater than 40 dB; the other group was composed of normal-hearing subjects with no history of unusual noise exposure. On fixed-frequency Bekesy audiometry at 2000 Hz, 12 of the noise-exposed subjects demonstrated separation of 5 dB or more between pulsed- and continuous-tone tracings; similar separation occurred for only one of the non-noise-exposed subjects. Significant between-group differences also occurred on three tests of speech discrimination: PB-50 word lists and CID W-22 lists presented with two forms of competing noise.

Masking level difference for speech: effects of ear dominance and age.

A comparison was made of right and left ear discrimination of monosyllables presented with competing 'cocktail party' in conditions of signal monaural-noise monaural, and signal monaural-noise binaural and in-phase interaurally. The effects of these conditions were compared in 20 normal children aged 5-6 years, 40 normal young adults and 20 adults aged 66-76 years. The magnitudes of right and left ear masking level differences (MLDs) were compared at each age level. (1) MLDs occurred for all three age groups; (2) for the two adult age groups, mean right ear scores exceeded mean left ear scores in the case of monaural noise presentation, although the difference was significant only for the young adults; (3) no interaural difference appeared for the children, and (4) marked variability of the magnitude of the MLDs occurred among subjects of all three age groups.