Background: Acute Mountain Sickness (AMS) occurs in 30-55% of people at altitudes above 8,200 feet consisting of headache, gastrointestinal upset, fatigue, lightheadedness, and difficulty sleeping. AMS can develop into life threatening conditions such as High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema. It is not known why some patients develop AMS while others do not. Some contributing factors include the number of days spent at high altitude during the preceding two months and rate of ascent to higher altitudes. Another hypothesized contributor to the susceptibility of developing hypoxemia and AMS is the presence of a Patent Foramen Ovale (PFO). A PFO is a right-to-left cardiac shunt that allows deoxygenated venous blood from the right side of the heart to cross the atrial septum and enter the arterial circulation – leading to a decrease in the overall oxygen saturation of the circulating blood. Previous evidence has implicated PFO in HAPE. The goal of this research is to determine if there is a statistically significant difference in the incidence of PFO in people with AMS versus those without AMS. In addition, this work aims to determine if there is a correlation between blood oxygen levels and the presence of PFO at higher elevations.
Methods: Subjects who have hiked Mount Whitney to altitudes above 11,000 feet will be recruited for this study. To determine whether patients are suffering from AMS, we will use a consensus called the Lake Louise Score for Altitude Sickness, which is the standard for diagnosing AMS. At recruitment sites, blood oxygen saturation will be measured by a finger pulse oximeter. After this is done, participants will then be directed to South Inyo Hospital which is located in Lone Pine, California. There, a transcranial Doppler (TCD) study will be performed. TCD has been shown to be a safe, noninvasive, and cost-effective screening tool for the diagnosis of cardiac right-to-left shunt. Our laboratory plans on using the Spencer Logarithmic Scale, which has a grade of 0-5 for determining the level of shunting: 0 denoting absence of shunt and 5 denoting the presence of a large shunt. The cutoff for a positive test is Grade 3, which corresponds with the presence of a PFO at heart catheterization. Participants will be tested both at rest and during the Valsalva maneuver.
Results: In Summer 2017, 70 subjects were examined for presence of AMS and PFO. Of these hikers, 15 (21%) had symptoms consistent with AMS and 55 (79%) did not. Although there was a trend for a relatively higher frequency of PFO in hikers with AMS 8/16 (50%) it was not statistically different from the frequency of PFO in hikers without AMS 20/56 (36%); 𝝌2, p = 0.30.
Conclusions: Initial data suggests there is no statistically significant correlation between the presence of a PFO and the development of AMS at high altitudes. However, it is possible that with more data to be collected this August, the statistical significance of this correlation will be shown. This is because for the group that did not develop AMS, there was a higher prevalence of PFO than in the general population. Ultimately, we believe that this work will help clinicians better advise patients with PFO when they go to altitude. In addition, those patients with a history of AMS should be tested for the presence of a PFO.