Biological organisms maintain their functional integrity in varying environmental conditions through the activity of the innate immune system and controlled inflammation. During scuba diving, divers are exposed to greater than usual environmental changes, which challenges the entire body. The circulatory system is specifically stressed with an elevated partial pressure of oxygen and by decompression-induced gas bubbles on ascent to the surface. When the stress caused by the pressure changes exceeds a certain threshold, a variety of symptoms may occur after return to the surface — this is usually called decompression sickness (DCS).
DCS has been associated with the presence of a free gas phase in blood and tissues but we know little about the biological pathways and processes involved. While involvement of immune and inflammation cells and processes has been indicated previously, measurable changes are rarely present in asymptomatic divers, making it difficult to study the transition of physiological adaptive stress response into maladaptive or pathological reactions leading to loss of organ functions. We have reported in this blog about recent microparticle studies that may potentially shed more light on this gray area.
Another new approach is to map divers’ blood to identify genes, biological pathways and cell types perturbed by the physiological stress in asymptomatic scuba diving, as described in a recently published study by Eftedal et al.1 For the study, 10 experienced divers abstained from diving for two weeks and then performed a three-day series of daily dives to a depth of 18 m (60 fsw) for 47 minutes while breathing compressed air. Researchers collected blood from the subjects before and immediately after the first and last dives for analysis. Ten matched nondivers provided controls for a predive status comparison.
The study found that experienced divers, as compared with nondivers, showed persistent changes in pathways of apoptosis, inflammation and immune responses in the blood transcriptomes, indicating a cellular state of sustained alertness toward exogenous stress. Researchers suspected that this state might be an effect of extensive prior diving, but there were no measurable physiological differences between the divers and nondivers. It is unknown whether these changes affect the risk of DCS in later diving.
Changes found after scuba diving were typical of sublethal oxidative stress, with suppression of lymphocyte activity and activation of the myeloid innate immune system. It was not possible to distinguish possible effects of oxidative stress and of gas microbubbles. Changes were similar after the first and the third dive, and they returned to normal in between the dives. However, this study was done on experienced divers whose transcriptome was already changed in comparison with nondivers. It is not known what changes after dives would have been found in previously unexposed subjects and how much exposure is needed to induce changes found in experienced divers.
The study of transcriptome in divers is in its early stages, but those of us who would like to better understand what is going on with our bodies while diving look forward to reading more about this subject in the future. To learn more about transcriptomes, read the information provided by the National Human Genome Research Institute at http://www.genome.gov/13014330.
Eftedal I, Ljubkovic M, Flatberg A, Jørgensen A, Brubakk AO, Dujic Z. Acute and potentially persistent effects of scuba diving on the blood transcriptome of experienced divers. Physiol Genomics 2013 Oct 16; 45(20):965-972. doi:10.1152/physiolgenomics.00164.2012. Epub 2013 Aug 20.