On Suitability of Mixture of Generalized Exponential Models in Modeling Right-Censored Medical Datasets Using Conditional Expectations.

The exploration of suitable models for modeling censored medical datasets is of great importance. There are numerous studies dealing with modeling the censored medical datasets. However, majority of the earlier contributions have utilized the conventional models for modeling the said datasets. Unfortunately, the conventional models are not capable of capturing the behavior of the heterogeneous datasets involving the mixture of two or more subpopulations. In addition, the earlier contributions have considered conventional censoring schemes by replacing all the censored items with the largest failed item. This paper is aimed at proposing the analysis of right-censored mixture medical datasets. The mixture of the generalized exponential distribution has been proposed to model the right-censored heterogeneous medical datasets. In converse to conventional censoring schemes, we have proposed censoring schemes which replace the censored items with conditional expectation (CE) of the random variable. In addition, the Bayesian methods have been proposed to estimate the model parameters. The performance and sensitivity of the proposed estimators have been evaluated using a detailed simulation study. The detailed simulation study suggests that censoring schemes based on CE provide improved estimation as compared to conventional censoring schemes. The suitability of the model in modeling heterogeneous datasets has been verified by modeling two real right-censored medical datasets. The comparison of the proposed model with existing mixture model under Bayesian methods advocated the improved performance of the proposed model.

Progressive censoring schemes for marshall-olkin pareto distribution with applications: Estimation and prediction.

In this paper two prediction methods are used to predict the non-observed (censored) units under progressive Type-II censored samples. The lifetimes of the units follow Marshall-Olkin Pareto distribution. We observe the posterior predictive density of the non-observed units and construct predictive intervals as well. Furthermore, we provide inference on the unknown parameters of the Marshall-Olkin model, so we observe point and interval estimation by using maximum likelihood and Bayesian estimation methods. Bayes estimation methods are obtained under quadratic loss function. EM algorithm is used to obtain numerical values of the Maximum likelihood method and Gibbs and the Monte Carlo Markov chain techniques are utilized for Bayesian calculations. A simulation study is performed to evaluate the performance of the estimators with respect to the mean square errors and the biases. Finally, we find the best prediction method by implementing a real data example under progressive Type-II censoring schemes.

The nonallergic asthma of obesity. A matter of distal lung compliance.

RATIONALE: The pathogenesis of asthma in obesity is poorly understood, but may be related to breathing at low lung volumes. OBJECTIVES: To determine if lung function in obese patients with asthma and control subjects would respond differently to weight loss. METHODS: Lung function was evaluated by conventional clinical tests and by impulse oscillometry in female late-onset, nonallergic patients with asthma and control subjects before, and 12 months after, bariatric surgery. MEASUREMENTS AND MAIN RESULTS: Patients with asthma (n = 10) had significantly lower FEV1 (79.8 ± 10.6 vs. 95.5 ± 7.0%) and FVC (82.4 ± 13.2 vs. 93.7 ± 8.9%) compared with control subjects (n = 13). There were no significant differences in FRC or TLC at baseline. Twelve months after surgery, control subjects had significant increases in FEV1 (95.5 ± 7.0 to 100.7 ± 5.9), FVC (93.6 ± 8.9 to 98.6 ± 8.3%), FRC (45.4 ± 18.5 to 62.1 ± 15.3%), and TLC (84.8 ± 15.0 to 103.1 ± 15.3%), whereas patients with asthma had improvement only in FEV1 (79.8 ± 10.6 to 87.2 ± 11.5). Control subjects and patients with asthma had a significantly different change in respiratory system resistance with weight loss: control subjects exhibited a uniform decrease in respiratory system resistance at all frequencies, whereas patients with asthma exhibited a decrease in frequency dependence of resistance. Fits of a mathematical model of lung mechanics to these impedance spectra suggest that the lung periphery was more collapsed by obesity in patients with asthma compared with control subjects. CONCLUSIONS: Weight loss decompresses the lung in both obese control subjects and patients with asthma, but the more pronounced effects of weight loss on lung elastance suggest that the distal lung is inherently more collapsible in people with asthma.

Cardiopulmonary resuscitation among mechanically ventilated patients.

PURPOSE: To evaluate the outcomes, including long-term survival, after cardiopulmonary resuscitation (CPR) in mechanically ventilated patients. METHODS: We analyzed Medicare data from 1994 to 2005 to identify beneficiaries who underwent in-hospital CPR. We then identified a subgroup receiving CPR one or more days after mechanical ventilation was initiated [defined by ICD-9 procedure code for intubation (96.04) or mechanical ventilation (96.7x) one or more days prior to procedure code for CPR (99.60 or 99.63)]. RESULTS: We identified 471,962 patients who received in-hospital CPR with an overall survival to hospital discharge of 18.4 % [95 % confidence interval (CI) 18.3-18.5 %]. Of those, 42,163 received CPR one or more days after mechanical ventilation initiation. Survival to hospital discharge after CPR in ventilated patients was 10.1 % (95 % CI 9.8-10.4 %), compared to 19.2 % (95 % CI 19.1-19.3 %) in non-ventilated patients (p < 0.001). Among this group, older age, race other than white, higher burden of chronic illness, and admission from a nursing facility were associated with decreased survival in multivariable analyses. Among all CPR recipients, those who were ventilated had 52 % lower odds of survival (OR 0.48, 95 % CI 0.46-0.49, p < 0.001). Median long-term survival in ventilated patients receiving CPR who survived to hospital discharge was 6.0 months (95 % CI 5.3-6.8 months), compared to 19.0 months (95 % CI 18.6-19.5 months) among the non-ventilated survivors (p < 0.001 by logrank test). Of all patients receiving CPR while ventilated, only 4.1 % were alive at 1 year. CONCLUSIONS: Survival after in-hospital CPR is decreased among ventilated patients compared to those who are not ventilated. This information is important for clinicians, patients, and family members when discussing CPR in critically ill patients.

Vocal cord dysfunction in athletes: clinical presentation and review of the literature.

Vocal cord dysfunction (VCD) is a syndrome characterized by the intermittent, abnormal paradoxical adduction of the true vocal cords during respiration resulting in variable upper airway obstruction. It is also commonly referred to as paradoxical vocal fold motion disorder. Patients with VCD usually present with intermittent shortness of breath of varying intensity, wheezing, stridor, choking, throat tightness, voice changes, or cough, and these symptoms often resolve quickly after relaxation or cessation of activity. Since first described as a distinct clinical entity in 1983, VCD remains underrecognized and the underlying cause(s) is not fully understood. Several studies suggest psychogenic or laryngeal hyperresponsiveness as possible underlying causes. Although VCD may have many causes, it can be a unique problem, especially in athletes because it often mimics and can be easily mistaken for exercise-induced bronchospasm, which may result in unnecessary medical treatment and delay in diagnosis. A detailed history, physical examination, and pulmonary function tests with flow-volume loops are important for excluding other diagnoses; however, the gold standard method for diagnosing VCD is by observation of the vocal cords with flexible laryngoscopy. The mainstay of treatment includes behavioral management guided by a speech-language pathologist, but optimal therapy often requires a multidisciplinary team involving a variety of specialties, including certified athletic training, pulmonology, otolaryngology, speech-language pathology, gastroenterology, allergy and immunology, and psychology, as appropriate. We reviewed the medical literature for VCD specifically in athletes, and this article discusses in detail the definition, epidemiology, possible pathophysiology, diagnosis, and treatment options.