Survival analysis for the inverse Gaussian distribution with the Gibbs sampler.

This paper describes a comprehensive survival analysis for the inverse Gaussian distribution employing Bayesian and Fiducial approaches. It focuses on making inferences on the inverse Gaussian (IG) parameters µ and λ and the average remaining time of censored units. A flexible Gibbs sampling approach applicable in the presence of censoring is discussed and illustrations with Type II, progressive Type II, and random rightly censored observations are included. The analyses are performed using both simulated IG data and empirical data examples. Further, the bootstrap comparisons are made between the Bayesian and Fiducial estimates. It is concluded that the shape parameter ( ϕ = λ / µ ) of the inverse Gaussian distribution has the most impact on the two analyses, Bayesian vs. Fiducial, and so does the size of censoring in data to a lesser extent. Overall, both these approaches are effective in estimating IG parameters and the average remaining lifetime. The suggested Gibbs sampler allowed a great deal of flexibility in implementation for all types of censoring considered.

Protective mechanisms in hypobaric decompression.

BACKGROUND: To reduce bubble formation and growth during hypobaric exposures, a denitrogenation or nitrogen "washout" procedure is performed. This procedure consists of prebreathing oxygen fractions as close to one as possible (oxygen prebreathe) prior to depressurization before ascending to the working altitude or low spacesuit pressures. During the NASA prebreathe reduction program (PRP), it was determined that the addition of a light arm exercise to short, individually designed, performance-based heavy exercise (dual cycle ergometry) during an abbreviated 2-h prebreathe (F1O2 - 1.0) reduced the occurrence of decompression sickness (DCS). Heavy-exercise-induced DCS reduction is likely to be related to the enhancement of the tissue nitrogen washout during the oxygen prebreathe. In addition to the heavy-exercise-induced microcirculatory adaptation, we hypothesized that the light exercise would not cause sufficient microcirculatory changes in the limbs to explain alone this further DCS protection. We evaluated microcirculatory changes as minimal by replicating the exercise characteristics of the PRP trials in 13 healthy subjects. METHODS: Noninvasive near infrared spectroscopy (NIRS) allowed observation of instantaneous variations of total, oxygenated, and deoxygenated hemoglobin/myoglobin concentrations in the microcirculatory networks (probes facing the vastus lateralis and deltoid muscles) of active limbs during dynamic exercise. RESULTS: The high-intensity leg exercise alone produced the changes in NIRS parameters; the light arm exercise induced minimal microcirculatory volume changes. However, this coupling appeared to be critical in previous altitude PRP chamber studies by reducing DCS. DISCUSSION: With only minimal microcirculatory blood volume changes, it is unlikely that light exercise alone causes significant nitrogen tissue washout. Therefore, our results suggest that in addition to nitrogen tissue washout, another unknown exercise-induced effect may have further enhanced the DCS protection, possibly mediated via the anti-inflammatory effect of exercise, gas micronuclei reduction, NO pathways, or other molecular mechanisms.

Moderate increases in ambient PM2.5 and ozone are associated with lung function decreases in beach lifeguards.

OBJECTIVE: Exposure to pollutants would adversely affect lung function of healthy athletes. METHODS: Pulmonary function was recorded on beach lifeguards at three different times during the day. Daily and average peak pollutant levels were calculated. Linear regression analyses were made comparing lung function changes in response to pollutant levels. A multivariate model was constructed to explain the combined effects of pollutants. RESULTS: Afternoon forced vital capacity (FVC) and forced expired volume in 1 second (FEV1) decreased significantly compared with morning values and decreased with increasing fine particulates (PM2.5). FEV1/FVC decreased with increasing ozone (O3) levels. CONCLUSION: The deleterious effect of PM2.5 and O3 were transient and occurred at pollutant levels far below national standards. At low levels of exposure, PM2.5 was associated with reduced lung volumes, while increasing O3 levels were associated with airway obstruction.