Noise in the intensive care unit and its influence on sleep quality: a multicenter observational study in Dutch intensive care units.

BACKGROUND: High noise levels in the intensive care unit (ICU) are a well-known problem. Little is known about the effect of noise on sleep quality in ICU patients. The study aim is to determine the effect of noise on subjective sleep quality. METHODS: This was a multicenter observational study in six Dutch ICUs. Noise recording equipment was installed in 2-4 rooms per ICU. Adult patients were eligible for the study 48 h after ICU admission and were followed up to maximum of five nights in the ICU. Exclusion criteria were presence of delirium and/or inability to be assessed for sleep quality. Sleep was evaluated using the Richards Campbell Sleep Questionnaire (range 0-100 mm). Noise recordings were used for analysis of various auditory parameters, including the number and duration of restorative periods. Hierarchical mixed model regression analysis was used to determine associations between noise and sleep. RESULTS: In total, 64 patients (68% male), mean age 63.9 (± 11.7) years and mean Acute Physiology And Chronic Health Evaluation (APACHE) II score 21.1 (± 7.1) were included. Average sleep quality score was 56 ± 24 mm. The mean of the 24-h average sound pressure levels (LAeq, 24h) was 54.0 dBA (± 2.4). Mixed-effects regression analyses showed that background noise (ß = - 0.51, p < 0.05) had a negative impact on sleep quality, whereas number of restorative periods (ß = 0.53, p < 0.01) and female sex (ß = 1.25, p < 0.01) were weakly but significantly correlated with sleep. CONCLUSIONS: Noise levels are negatively associated and restorative periods and female gender are positively associated with subjective sleep quality in ICU patients. TRIAL REGISTRATION: www.ClinicalTrials.gov, NCT01826799 . Registered on 9 April 2013.

Cognitive disruption by noise-vocoded speech stimuli: Effects of spectral variation.

The effect of irrelevant sounds on short-term memory was investigated in two experiments using noise-vocoded speech stimuli (NVSS). Speech samples were systematically modified by a noise-vocoder and a set of stimuli varying from amplitude-modulated white noise to intelligible speech was created. Eight NVSS conditions, composed of 1-, 2-, 4-, 6-, 9-, 12-, 15-, and 18-bands, were used as the distracting stimuli in a digit-recall task next to the speech and silence conditions. The results showed that performance decreased with the number of frequency bands up to the 6-bands condition, but there was no influence of number of bands on performance beyond six bands. The results were analyzed using four acoustic metrics proposed in the literature: the frequency domain correlation coefficient (FDCC), the fluctuation strength, the speech transmission index (STI), and the normalized covariance measure (NCM). None of the metrics successfully predicted the results. However, the parameter values of the FDCC, the STI, and the NCM indicated that a prediction model for irrelevant sound effect should account for both temporal and spectral features of the irrelevant sounds.

The benefit of bilateral versus unilateral cochlear implantation to speech intelligibility in noise.

OBJECTIVES: To develop a predictive model of spatial release from masking (SRM) for cochlear implantees, and validate this model against data from the literature. To establish the spatial configurations for which the model predicts a large advantage of bilateral over unilateral implantation. To collect data to support these predictions and generate predictions of more typical advantages of bilateral implantation. DESIGN: The model initially assumed that bilateral cochlear implantees had equally effective implants on each side, with which they could perform optimal better-ear listening. Predictions were compared with measurements of SRM, using one and two implants with up to three interfering noises. The effect of relaxing the assumption of equally effective implants was explored. Novel measurements of SRM for eight unilateral implantees were collected, including measurements using speech and noise at azimuths of ± 60 degrees, and compared with prediction. A spatial map of bilateral implant benefit was generated for a situation with one interfering noise in anechoic conditions, and predictions of benefit were generated from binaural room impulse responses in a variety of real rooms. RESULTS: The model accurately predicted data from a previous study for multiple interfering noises in a variety of spatial configurations, even when implants were assumed to be equally effective (r = 0.97). It predicted that the maximum benefit of bilateral implantation was 18 dB. Predictions were little affected if the implants were not assumed to be equally effective. The new measurements supported the 18 dB advantage prediction. The spatial map of predicted benefit showed that, for a listener facing the target voice, bilateral implantees could enjoy an advantage of about 10 dB over unilateral implantees in a wide range of situations. Predictions based on real-room measurements with speech and noise at 1 m showed that large benefits can occur even in reverberant spaces. CONCLUSIONS: In optimal conditions, the benefit of bilateral implantation to speech intelligibility in noise can be much larger than has previously been reported. This benefit is thus considerably larger than reported benefits of summation or squelch and is robust in reverberation when the interfering source is close.

Binaural prediction of speech intelligibility in reverberant rooms with multiple noise sources.

When speech is in competition with interfering sources in rooms, monaural indicators of intelligibility fail to take account of the listener's abilities to separate target speech from interfering sounds using the binaural system. In order to incorporate these segregation abilities and their susceptibility to reverberation, Lavandier and Culling [J. Acoust. Soc. Am. 127, 387-399 (2010)] proposed a model which combines effects of better-ear listening and binaural unmasking. A computationally efficient version of this model is evaluated here under more realistic conditions that include head shadow, multiple stationary noise sources, and real-room acoustics. Three experiments are presented in which speech reception thresholds were measured in the presence of one to three interferers using real-room listening over headphones, simulated by convolving anechoic stimuli with binaural room impulse-responses measured with dummy-head transducers in five rooms. Without fitting any parameter of the model, there was close correspondence between measured and predicted differences in threshold across all tested conditions. The model's components of better-ear listening and binaural unmasking were validated both in isolation and in combination. The computational efficiency of this prediction method allows the generation of complex "intelligibility maps" from room designs.

Revision and validation of a binaural model for speech intelligibility in noise.

Lavandier and Culling [Lavandier, M. and Culling, J. F. 2010. Prediction of binaural speech intelligibility against noise in rooms. J. Acoust. Soc. Am. 127, 387-399] demonstrated a method of predicting human speech reception thresholds for speech in combined noise and reverberation. An updated version of the model is presented, which is substantially more computationally efficient. The updated model makes similar predictions for the SRT data considered by Lavandier and Culling, which tested the model's ability to predict effects of binaural unmasking and room colouration. In addition, we show here that the model accurately predicts the effects of headshadow and reproduces a range of data sets from the literature, including situations with multiple interfering sounds in anechoic conditions.