A review of the relationship between patent foramen ovale and type II decomposition sickness

The significance of patent foramen ovale (PFO) in the pathophysiology of Ty pe II decompression sickness (DCS) remains controversial. PFOs are common, occurring in approximately one quarter of the normal population, thus makin g right-to-left shunting of venous gas emboli (VGE) a theoretical concern i n both hyper- and hypobaric situations. Despite this high prevalence of PFO in the general population, and the relatively common occurrence of venous gas bubbles in diving and altitude exposures, the incidence of Type II DCS in diving or with altitude is remarkably low. Although the literature suppo rts a relationship between the presence and size of PFO and cryptogenic str oke, and an increased relative risk of Type II DCS with a PFO in divers, th e absolute increase in risk accrued is small. Hence, the value of screening is also controversial. This paper presents a summary of the literature on PFOs and DCS in animals, and in human altitude and diving, focusing on the latter; as well the analogous literature on cryptogenic stroke. The results of an examination of the literature on detection of, screening for, and tr eatment of PFOs is also presented.