Biomedical subjects

Wensheng Guo

Publications and source records attributed to Wensheng Guo.

4 recordsLinked to original sources

PubMed2003

The validity and feasibility of saliva melatonin assessment in the elderly.

Recent work in young and middle-aged subjects suggests that melatonin levels in saliva may represent a viable alternative to serum melatonin measurement. We hypothesized that it may be a valid measure of melatonin levels in older adults as well, but features unique to the elderly may limit its utility. To study this, subjects were admitted to an academic medical center where saliva and serum specimens were collected concurrently in dim light conditions during a 14-hr overnight study period and analyzed for melatonin levels with radioimmunoassays (RIAs). Eighty-five subjects over the age of 65 with a broad range of medical conditions participated in the study. Subjects with dementia, depression and anemia were excluded. We found that saliva volume was inadequate for analysis (<200 microL) in 23.6% of specimens, with the majority of inadequate volume specimens occurring after midnight and inadequate specimens occurring more frequently in females than in males. The correlation coefficient for saliva melatonin and serum melatonin was r = 0.659 (Spearman, P < 0.001), and r = 0.466 for saliva dim light melatonin onset (DLMO) and serum DLMO. Saliva melatonin levels were 30.9% of serum melatonin levels, with a wide range of ratios noted between subjects. Overall melatonin levels influenced both the correlation and ratio of saliva melatonin to serum melatonin; higher correlations and lower ratios were noted when melatonin levels were high. Saliva specimens provide an economical and practical method for melatonin assessment, however, in older adults, issues such as hyposalivation and low melatonin levels limit the feasibility and validity, respectively, of saliva melatonin.

Aged↗

PubMed2002

Time-frequency spectral estimation of multichannel EEG using the Auto-SLEX method.

In this paper, we apply a new time-frequency spectral estimation method for multichannel data to epileptiform electroencephalography (EEG). The method is based on the smooth localized complex exponentials (SLEX) functions which are time-frequency localized versions of the Fourier functions and, hence, are ideal for analyzing nonstationary signals whose spectral properties evolve over time. The SLEX functions are simultaneously orthogonal and localized in time and frequency because they are obtained by applying a projection operator rather than a window or taper. In this paper, we present the Auto-SLEX method which is a statistical method that 1) computes the periodogram using the SLEX transform, 2) automatically segments the signal into approximately stationary segments using an objective criterion that is based on log energy, and 3) automatically selects the optimal bandwidth of the spectral smoothing window. The method is applied to the intracranial EEG from a patient with temporal lobe epilepsy. This analysis reveals a reduction in average duration of stationarity in preseizure epochs of data compared to baseline. These changes begin up to hours prior to electrical seizure onset in this patient.

Algorithms↗

PubMed2002

Functional mixed effects models.

In this article, a new class of functional models in which smoothing splines are used to model fixed effects as well as random effects is introduced. The linear mixed effects models are extended to nonparametric mixed effects models by introducing functional random effects, which are modeled as realizations of zero-mean stochastic processes. The fixed functional effects and the random functional effects are modeled in the same functional space, which guarantee the population-average and subject-specific curves have the same smoothness property. These models inherit the flexibility of the linear mixed effects models in handling complex designs and correlation structures, can include continuous covariates as well as dummy factors in both the fixed or random design matrices, and include the nested curves models as special cases. Two estimation procedures are proposed. The first estimation procedure exploits the connection between linear mixed effects models and smoothing splines and can be fitted using existing software. The second procedure is a sequential estimation procedure using Kalman filtering. This algorithm avoids inversion of large dimensional matrices and therefore can be applied to large data sets. A generalized maximum likelihood (GML) ratio test is proposed for inference and model selection. An application to comparison of cortisol profiles is used as an illustration.

Bayes Theorem↗

PubMed2002

Iron administration and clinical outcomes in hemodialysis patients.

To evaluate the impact of parenteral iron administration on the survival and rate of hospitalization of US hemodialysis patients, a nonconcurrent cohort study of 10,169 hemodialysis patients in the United States in 1994 was conducted. The main outcome measures were patient survival and rate of hospitalization. After adjusting for 23 demographic and comorbidity characteristics among 5833 patients included in multivariable analysis, bills for 10 vials showed a statistically significant elevated rate of death (adjusted RR = 1.11; 95% CI, 1.00 to 1.24; P = 0.05). Bills for 10 vials showed statistically significant elevated risk (adjusted RR = 1.12; 95% CI, 1.01 to 1.25; P = 0.03). Prescribing iron in quantities of 10 vials (1000 mg) of iron dextran over a period of 6 mo.

Cohort Studies↗