Small airway segmentation in thoracic computed tomography scans: a machine learning approach.

Small airway obstruction is a main cause for chronic obstructive pulmonary disease (COPD). We propose a novel method based on machine learning to extract the airway system from a thoracic computed tomography (CT) scan. The emphasis of the proposed method is on including the smallest airways that are still visible on CT. We used an optimized sampling procedure to extract airway and non-airway voxel samples from a large set of scans for which a semi-automatically constructed reference standard was available. We created a set of features which represent tubular and texture properties that are characteristic for small airway voxels. A random forest classifier was used to determine for each voxel if it belongs to the airway class. Our method was validated on a set of 20 clinical thoracic CT scans from the COPDGene study. Experiments show that our method is effective in extracting the full airway system and in detecting a large number of small airways that were missed by the semi-automatically constructed reference standard.

Increase in sweating sensitivity by endurance conditioning in man.

Sweating sensitivity has been evaluated at rest in 10 competitive athletes (cross-country skiers and swimmers). Three sedentary men underwent a 3-mo period of endurance training in a temperate climate, (dry bulb temperature (Tdb): 18 degrees C) and had their sweating sensitivity measured before and after the training period. Mean maximum oxygen uptake (Vo2max, ml.min(-1).kg(-1)) was: skiers: 66.5; swimmers 65.8; sedentary men, pretraining 40.9; posttraining: 48.3 (+18%). Sweat output of athletes under a given stress (passive heating) was markedly higher than that of sedentary men. Skiers exhibited a high level of heat tolerance and were better acclimatized than swimmers, although they had never experienced exposure to heat. The increase in Vo2max of sedentary men was accompanied by 1) an increase in sweating sensitivity with a decrease of body heat storage at steady state (pretraining: 5.4 kJ.kg(-1); posttraining: 3.5 kJ.kg(-1); P less than 0.05); 2) significant shift down the temperature scale with reduced rectal temperature (Tre) for sweat onset; 3) an increase of gain constants of sweating (W.m-2 degrees C(-1) (pretraining: 168; posttraining: 269; gain constant of swimmers: 222). It was suggested that endurance training in cold or temperate conditions with significant increase of Vo2max could act on the thermoregulatory function in a way similar to body heating procedures, such as work in heat, and could contribute to heat acclimatization.