Essential nonlinearities in hearing

Our hearing organ, the cochlea, evidently poises itself at a Hopf bifurcation to maximize tuning and amplification. We show that in this condition several effects are expected to be generic: compression of the dynamic range, infinitely shrap tuning at zero input, and generation of combination tones. These effects are "essentially" nonlinear in that they become more marked the smaller the forcing: there is no audible sound soft enough not to evoke them. All the well-documented nonlinear aspects of hearing therefore appear to be consequences of the same underlying mechanism.Comment: 4 pages, 3 figure

Clustering patterns of physical activity, sedentary and dietary behavior among European adolescents: The HELENA study.

Evidence suggests possible synergetic effects of multiple lifestyle behaviors on health risks like obesity and other health outcomes. A better insight in the clustering of those behaviors, could help to identify groups who are at risk in developing chronic diseases. This study examines the prevalence and clustering of physical activity, sedentary and dietary patterns among European adolescents and investigates if the identified clusters could be characterized by socio-demographic factors. METHODS: The study comprised a total of 2084 adolescents (45.6% male), from eight European cities participating in the HELENA (Healthy Lifestyle in Europe by Nutrition in Adolescence) study. Physical activity and sedentary behavior were measured using self-reported questionnaires and diet quality was assessed based on dietary recall. Based on the results of those three indices, cluster analyses were performed. To identify gender differences and associations with socio-demographic variables, chi-square tests were executed. RESULTS: Five stable and meaningful clusters were found. Only 18% of the adolescents showed healthy and 21% unhealthy scores on all three included indices. Males were highly presented in the cluster with high levels of moderate to vigorous physical activity (MVPA) and low quality diets. The clusters with low levels of MVPA and high quality diets comprised more female adolescents. Adolescents with low educated parents had diets of lower quality and spent more time in sedentary activities. In addition, the clusters with high levels of MVPA comprised more adolescents of the younger age category. CONCLUSION: In order to develop effective primary prevention strategies, it would be important to consider multiple health indices when identifying high risk groups.Peer Reviewe

Hair Cell Bundles: Flexoelectric Motors of the Inner Ear

Microvilli (stereocilia) projecting from the apex of hair cells in the inner ear are actively motile structures that feed energy into the vibration of the inner ear and enhance sensitivity to sound. The biophysical mechanism underlying the hair bundle motor is unknown. In this study, we examined a membrane flexoelectric origin for active movements in stereocilia and conclude that it is likely to be an important contributor to mechanical power output by hair bundles. We formulated a realistic biophysical model of stereocilia incorporating stereocilia dimensions, the known flexoelectric coefficient of lipid membranes, mechanical compliance, and fluid drag. Electrical power enters the stereocilia through displacement sensitive ion channels and, due to the small diameter of stereocilia, is converted to useful mechanical power output by flexoelectricity. This motor augments molecular motors associated with the mechanosensitive apparatus itself that have been described previously. The model reveals stereocilia to be highly efficient and fast flexoelectric motors that capture the energy in the extracellular electro-chemical potential of the inner ear to generate mechanical power output. The power analysis provides an explanation for the correlation between stereocilia height and the tonotopic organization of hearing organs. Further, results suggest that flexoelectricity may be essential to the exquisite sensitivity and frequency selectivity of non-mammalian hearing organs at high auditory frequencies, and may contribute to the “cochlear amplifier” in mammals

Clustering patterns of physical activity, sedentary and dietary behavior among European adolescents: The HELENA study

<p>Abstract</p> <p>Background</p> <p>Evidence suggests possible synergetic effects of multiple lifestyle behaviors on health risks like obesity and other health outcomes. A better insight in the clustering of those behaviors, could help to identify groups who are at risk in developing chronic diseases. This study examines the prevalence and clustering of physical activity, sedentary and dietary patterns among European adolescents and investigates if the identified clusters could be characterized by socio-demographic factors.</p> <p>Methods</p> <p>The study comprised a total of 2084 adolescents (45.6% male), from eight European cities participating in the HELENA (Healthy Lifestyle in Europe by Nutrition in Adolescence) study. Physical activity and sedentary behavior were measured using self-reported questionnaires and diet quality was assessed based on dietary recall. Based on the results of those three indices, cluster analyses were performed. To identify gender differences and associations with socio-demographic variables, chi-square tests were executed.</p> <p>Results</p> <p>Five stable and meaningful clusters were found. Only 18% of the adolescents showed healthy and 21% unhealthy scores on all three included indices. Males were highly presented in the cluster with high levels of moderate to vigorous physical activity (MVPA) and low quality diets. The clusters with low levels of MVPA and high quality diets comprised more female adolescents. Adolescents with low educated parents had diets of lower quality and spent more time in sedentary activities. In addition, the clusters with high levels of MVPA comprised more adolescents of the younger age category.</p> <p>Conclusion</p> <p>In order to develop effective primary prevention strategies, it would be important to consider multiple health indices when identifying high risk groups.</p

A Opçao de Programaçao Rate Drop Response (Resposta à Queda de Freqüência) Previne a Hipotensao Ortostática em Pacientes Idosos, Portadores de Marcapasso e com Incompetência Cronotrópica?

Introduçao: Pacientes idosos, portadores de marcapasso e com incompetência cronotrópica (IC) podem apresentar hipotensao em posiçao ortostática (HO). Objetivo: Determinar se o aumento transitório da freqüência cardíaca, por meio da opçao de programaçao rate drop response (resposta à queda da freqüência cardíaca), previne a HO em pacientes idosos, portadores de marcapasso, em posiçao vertical. Casuística e Método: Foram estudados os efeitos da rate drop response para alívio da queda da pressao arterial em 62 pacientes portadores de marcapasso (77 ± 6 anos, 32 F) em posiçao vertical. O modo de comando foi o de dupla-câmara (DDD) e as indicaçoes para o implante foram doença do nodo sinusal (n=40) ou bloqueio atrioventricular (n=22). Todos os pacientes foram submetidos a dois procedimentos na posiçao ereta, em ordem aleatória: controle com freqüência básica de 60 bpm e com rate drop response no modo DDD (com possibilidade de aumento de 35 bpm acima da freqüência de base), durante 2 minutos, após ficarem na posiçao vertical. A pressao arterial sistólica (PAS), a pressao arterial diastólica (PSD) e a freqüência cardíaca foram aferidas na posiçao vertical (linha de base) e um, dois e três minutos após o abandono dessa posiçao. A HO foi definida como uma queda da pressao arterial sistólica (PAS) ≥ 20 mmHg ou da pressao arterial diastólica (PSD) ≥ 10 mmHg, em posiçao vertical. A incompetência cronotrópica (IC) foi definida como ausência de aumento da freqüência cardíaca superior a 10 bpm, enquanto na posiçao de pé. Resultados: Um total de 17 pacientes (27%) desenvolveu HO na posiçao em pé. As características clínicas básicas (idade, sexo, prevalência de diabetes, uso de medicamentos vasoativos e doença do nodo sinusal) foram similares nos dois grupos, com ou sem HO. Na posiçao vertical, o rate drop response aumentou a PAS e PSD, em comparaçao com a linha de base (PConclusao: A HO é comum e está presente em 27% da populaçao idosa portadora de marcapasso. Em apenas um subgrupo desses pacientes, a IC pode ser a responsável pela ocorrência de HO e pode ser prevenida pela rate drop response na posiçao vertical

A Opçao de Programaçao Rate Drop Response (Resposta à Queda de Freqüência) Previne a Hipotensao Ortostática em Pacientes Idosos, Portadores de Marcapasso e com Incompetência Cronotrópica?

Introduçao: Pacientes idosos, portadores de marcapasso e com incompetência cronotrópica (IC) podem apresentar hipotensao em posiçao ortostática (HO). Objetivo: Determinar se o aumento transitório da freqüência cardíaca, por meio da opçao de programaçao rate drop response (resposta à queda da freqüência cardíaca), previne a HO em pacientes idosos, portadores de marcapasso, em posiçao vertical. Casuística e Método: Foram estudados os efeitos da rate drop response para alívio da queda da pressao arterial em 62 pacientes portadores de marcapasso (77 ± 6 anos, 32 F) em posiçao vertical. O modo de comando foi o de dupla-câmara (DDD) e as indicaçoes para o implante foram doença do nodo sinusal (n=40) ou bloqueio atrioventricular (n=22). Todos os pacientes foram submetidos a dois procedimentos na posiçao ereta, em ordem aleatória: controle com freqüência básica de 60 bpm e com rate drop response no modo DDD (com possibilidade de aumento de 35 bpm acima da freqüência de base), durante 2 minutos, após ficarem na posiçao vertical. A pressao arterial sistólica (PAS), a pressao arterial diastólica (PSD) e a freqüência cardíaca foram aferidas na posiçao vertical (linha de base) e um, dois e três minutos após o abandono dessa posiçao. A HO foi definida como uma queda da pressao arterial sistólica (PAS) ≥ 20 mmHg ou da pressao arterial diastólica (PSD) ≥ 10 mmHg, em posiçao vertical. A incompetência cronotrópica (IC) foi definida como ausência de aumento da freqüência cardíaca superior a 10 bpm, enquanto na posiçao de pé. Resultados: Um total de 17 pacientes (27%) desenvolveu HO na posiçao em pé. As características clínicas básicas (idade, sexo, prevalência de diabetes, uso de medicamentos vasoativos e doença do nodo sinusal) foram similares nos dois grupos, com ou sem HO. Na posiçao vertical, o rate drop response aumentou a PAS e PSD, em comparaçao com a linha de base (PConclusao: A HO é comum e está presente em 27% da populaçao idosa portadora de marcapasso. Em apenas um subgrupo desses pacientes, a IC pode ser a responsável pela ocorrência de HO e pode ser prevenida pela rate drop response na posiçao vertical

The diverse effects of mechanical loading on active hair bundles

Hair cells in the auditory, vestibular, and lateral-line systems of vertebrates receive inputs through a remarkable variety of accessory structures that impose complex mechanical loads on the mechanoreceptive hair bundles. Although the physiological and morphological properties of the hair bundles in each organ are specialized for detecting the relevant inputs, we propose that the mechanical load on the bundles also adjusts their responsiveness to external signals. We use a parsimonious description of active hair-bundle motility to show how the mechanical environment can regulate a bundle’s innate behavior and response to input. We find that an unloaded hair bundle can behave very differently from one subjected to a mechanical load. Depending on how it is loaded, a hair bundle can function as a switch, active oscillator, quiescent resonator, or low-pass filter. Moreover, a bundle displays a sharply tuned, nonlinear, and sensitive response for some loading conditions and an untuned or weakly tuned, linear, and insensitive response under other circumstances. Our simple characterization of active hair-bundle motility explains qualitatively most of the observed features of bundle motion from different organs and organisms. The predictions stemming from this description provide insight into the operation of hair bundles in a variety of contexts