Unified structural equation modeling approach for the analysis of multisubject, multivariate functional MRI data

The ultimate goal of brain connectivity studies is to propose, test, modify, and compare certain directional brain pathways. Path analysis or structural equation modeling (SEM) is an ideal statistical method for such studies. In this work, we propose a two-stage unified SEM plus GLM (General Linear Model) approach for the analysis of multisubject, multivariate functional magnetic resonance imaging (fMRI) time series data with subject-level covariates. In Stage 1, we analyze the fMRI multivariate time series for each subject individually via a unified SEM model by combining longitudinal pathways represented by a multivariate autoregressive (MAR) model, and contemporaneous pathways represented by a conventional SEM. In Stage 2, the resulting subject-level path coefficients are merged with subject-level covariates such as gender, age, IQ, etc., to examine the impact of these covariates on effective connectivity via a GLM. Our approach is exemplified via the analysis of an fMRI visual attention experiment. Furthermore, the significant path network from the unified SEM analysis is compared to that from a conventional SEM analysis without incorporating the longitudinal information as well as that from a Dynamic Causal Modeling (DCM) approach.     

Cardiac conduction improvement in two heterozygotes for primary carnitine deficiency on l‐carnitine supplementation

Sarafoglou K, Tridgell AHC, Bentler K, Redlinger‐Grosse K, Berry SA, Schimmenti LA. Cardiac conduction improvement in two heterozygotes for primary carnitine deficiency on l ‐carnitine supplementation. Expanded newborn screening (NBS) for free carnitine levels has led to the identification of a larger number of heterozygous infants of undiagnosed mothers affected with systemic primary carnitine deficiency (PCD), which in turn leads to the identification of other undiagnosed heterozygous family members. There is an increasing recognition that individuals heterozygous for mutations of genes involved in fatty acid oxidation (FAO) may become symptomatic under environmental stress (fasting, prolonged exercise and illness). Considering the importance of carnitine in FAO, its role in heart and bowel function and in lipid metabolism, what is still little known is the phenotypic variability, biochemical parameters and clinical course of PCD heterozygotes with consistently low‐to‐normal levels to low levels of carnitine over a lifetime. We report on three generations of a family—an asymptomatic PCD heterozygous infant identified through NBS that led to the diagnosis of her asymptomatic PCD‐affected mother and the heterozygous status of the maternal grandparents who report some cardiac symptoms that overlap with PCD that improved with l ‐carnitine supplementation.     

Mechanical ventilation in rural ICUs

Background  

In recent years, rural hospitals have expanded their scope ofspecialized services, which has led to the development and staffing of ruralintensive care units (ICUs). There is little information about the breadth,quality or outcomes of these services. This is particularly true forspecialized ICU services such as mechanical ventilation, where little, if any,information exists specifically for rural hospitals. The long-term objectivesof this project were to evaluate the quality of medical care provided tomechanically ventilated patients in rural ICUs and to improve patient carethrough an educational intervention. This paper reports baseline data onpatient and hospital characteristics for both rural and rural referralhospitals.     

Prognostic factors for persons with idiopathic chronic fatigue

BACKGROUND: The simultaneous examination of a large number of patient characteristics in a prospective study of patients with chronic fatigue. OBJECTIVE: To compare the relative importance of these characteristics as prognostic factors. METHODS: The data analyzed were from 199 subjects in a registry of persons who were aged 18 years or older and had idiopathic fatigue for at least 6 months. All subjects completed an extensive baseline questionnaire that provided information about fatigue, demographic characteristics, medical conditions, lifestyle, sleeping habits, psychological characteristics, and the presence of criteria for chronic fatigue syndrome. Changes in fatigue severity from baseline to 2-year follow-up were tested for an association with risk factors at baseline and with changes in symptoms other than fatigue during the follow-up period. RESULTS: The following characteristics at baseline significantly and independently predicted greater fatigue improvement: less unclear thinking, fewer somatoform symptoms not used to define chronic fatigue syndrome, infrequent awakening, fewer hours sleeping, and being married. Of 29 subjects who at baseline reported no somatoform symptoms unrelated to chronic fatigue syndrome and who thought clearly most of the time, 8 substantially improved, compared with 1 of 29 subjects who had more than 2 somatoform symptoms and never thought clearly (P = .01). Improvements in the following symptoms were significantly and independently associated with improvements in fatigue: unclear thinking, depression, muscle aches, and trouble falling asleep. CONCLUSIONS: This study identified characteristics of subjects that seem to be of prognostic importance for idiopathic chronic fatigue. Symptoms that change concomitantly with changes in fatigue may be intrinsically linked to fatigue.     

External ear resonance characteristics in children

External ear resonance characteristics were determined for 78 children ages 3-13 using an ear canal probe tube microphone system. The average peak resonant frequency was 2848 Hz (range: 1774-4039), and the average measured gain at the eardrum was 18.9 dB (range: 11.5-26.7). Correlations of average peak resonant frequency and peak resonant amplitudes with age, height, weight, head circumference, and/or canal opening area were poor. These values are very similar to the adult data reported by Shaw (1974). Slight deviations can be attributed, in part, to the different sound field calibration methods used.     

Effects of mild and moderate hearing impairments on language, educational, and psychosocial behavior of children

An extensive psychoeducational evaluation was administered to 40 hearing-impaired children to investigate the effects of degree of hearing impairment, age, and other factors on intellectual, social, academic, and language behavior. Although children varied greatly in performance, hearing loss of any degree appeared to affect psychoeducational development adversely, leading to the conclusion that even minimal hearing loss places children at risk for language and learning problems.     

Compression-dependent differences in hearing aid gain between speech and nonspeech input signals

OBJECTIVE: A primary purpose of fitting hearing aids is to improve the audibility of speech; however, hearing aid gain is typically measured by using standardized nonspeech signals, e.g., swept pure tones, speech-weighted broadband noise, or modulated noise. When compression hearing aids are tested with these nonspeech input signals, the measured gain can be substantially different than if a real speech input signal were used. The purpose of this study was to systematically evaluate the effects of release time, compression ratio, and number of compression channels, as well as interactions of these parameters, on the gain difference between several common nonspeech hearing aid test signals and speech. It was hypothesized that the difference in hearing aid gain between static nonspeech signals and speech would increase as release time, compression ratio, and number of channels increased. DESIGN: Speech and several common nonspeech hearing aid test signals, matched at overall root-mean-square levels corresponding to average (65 dB SPL) and loud (80 dB SPL) conversational speech, were input into a master hearing aid circuit, and the gain of the circuit was measured in one-third octave bands. The hearing aid was programmed as a moderate-gain (23 dB) wide dynamic range compression instrument with a compression threshold of 50 dB SPL. The release time, compression ratio, and number of compression channels of the circuit were systematically adjusted by programming software. The one-third octave band gain differences between the nonspeech signals and speech were measured for all combinations of the compression settings. Multiple regression analysis was used to evaluate the effects of each compression parameter, and interactions of the parameters, on the gain difference between each nonspeech signal and speech. RESULTS: One-third octave band gain differences between nonspeech and speech signals (calculated as nonspeech signal minus speech signal) ranged from -3.1 to 10.4 dB, depending on frequency, nonspeech test signal, and input signal level. In most cases, the compression parameters accounted for more than 70% of the variance in gain differences between the speech and nonspeech signals. At an input level of 65 dB, increases in the release time and compression ratio led to an increase in the gain difference between most nonspeech signals and speech at most frequencies. Increases in the number of channels caused an increase in the gain difference when the spectra of the nonspeech signals differed from the speech spectrum. The effects of release time and number of channels increased as the compression ratio increased. At an 80 dB input level, increasing the compression ratio led to a decrease in the gain difference between the nonspeech signals and speech. Release time and number of channels had little to no effect at the higher input level. CONCLUSIONS: The compression parameters of release time, compression ratio, and number of compression channels explain most of the variance in differences in hearing aid gain between nonspeech and speech signals. It may be cumbersome, however, to quantitatively define this relationship for all hearing aid circuits. It is therefore recommended that hearing aid "use" gain or output be measured with a real speech signal. If a nonspeech signal must be used, then it should have spectral and temporal properties that are similar to speech.