The government still denies that there is any correlation between burn pits and health problems but the government has started an "Airborne Hazards and Open Burn Pit Registry" to begin tracking the health of veterans who were exposed to burn pits to see if there is a connection. E-cigarettes
The American Lung Association lists flavored e-cigarettes as a risk in 2016. Health Canada has, however seen no cases as of 2019. Public Health England writes that the association has come about as "some flavourings used in e-liquids to provide a buttery flavour contain the chemical diacetyl... however, diacetyl is banned as an ingredient from e-cigarettes and e-liquids in the UK." Mechanism
The underlying mechanism involves injury and inflammation of epithelial and sub-epithelial cells. These cells then lose the ability to repair the tissue, in particular they lose the ability to regenerate the epithelial or outermost layer, leading to the excess growth of cells that cause scarring. There are multiple pathways of the disease including fibrotic, lymphocytic, and antibody-mediated that have been described. However, while each pathway has a more unique starting point and cause, the result is still injury and inflammation leading to scarring of the lung tissue. The scarred tissue then makes the expiration phase of respiration more difficult, leading to air not being expelled from the lungs. This is termed "air-trapping", which can be seen on medical imaging. Since the scarring is non-reversible, the disease generally does not improve over time, and depending on the inciting can progress to death.
As the disease progresses they begin to have symptoms of shortness of breath, cough, and wheezing as their lung function declines. The Journal of Heart and Lung Transplantation published updated guidelines in 2001 for grading the severity of BOS. The original guidelines and classification system were published in 1993 by the International Society for Heart and Lung Transplantation. Their scoring system is based on the changes in FEV1 in patients from their baseline. When patients are first diagnosed with BOS they have their baseline lung function established by doing pulmonary function testing at the time of diagnosis. The BOS scoring system is as follows:
BOS 0: FEV1 > 90% of baseline and FEF25-75 > 75% of baseline
BOS 0-p: FEV1 81-89% of baseline and/or FEF25-75 <= 75% of baseline
BOS 1: FEV1 66-80% of baseline
BOS 2: FEV1 51-65% of baseline
BOS 3: FEV1 50% or less of baseline
The scoring system shows an increased severity of the disease as the BOS number increases. Hematopoietic stem cell transplant
Bronchiolitis obliterans affects up to 5.5% of people who have received HSCT. One of the biggest risk factors after HSCT is the development of GVHD with a 14% risk. Other risk factors post transplant including tobacco use, age of donor, age of recipient, lower baseline FEV1/FVC ratio, non-caucasian race, peripheral and lower circulating IgG levels. Studies have, however, shown mixed results regarding these other risk factors. There has been an association shown between the increased use of peripheral stem cells and the risk of developing bronchiolitis obliterans.