Patients with lung conditions such as asthma or COPD may need to be cleared for situations such as high-altitude climbing, deep-sea diving, snorkeling, or scuba diving. During the session, HIGH and LOW: A Deep Dive Into Barometric Pulmonary Physiology, at the CHEST Annual Meeting in Honolulu, a panel of experts discussed the impact of barometric pressure on pulmonary physiology and the clinical considerations for patients in these special situations.
Meredith Turetz, MD, Assistant Professor of Pulmonary and Critical Care Medicine at Weill Cornell Medical College, opened the session with a review of physiologic responses to high altitude, including hypobaric hypoxia, and the risk of acute high-altitude illnesses in patients with lung disease.
The generally accepted definition of high altitude begins at 2,500 meters, she said, and that is the height at which altitude-related illness typically starts.
“With increasing altitude, there is a nonlinear decrease in the barometric pressure,” Dr. Turetz said, “and that ends up leading to a decrease in the ambient partial pressure of the oxygen and, subsequently, a decrease in the partial pressure of oxygen every step along the oxygen transport cascade.”
When a person is at high altitude and the partial pressure of oxygen is reduced, particularly if they are exercising and require more oxygen delivery, that is when tissues end up becoming hypoxic, and people can develop hypobaric hypoxia.
“If you keep all this physiology in mind, you want to make sure you’re identifying patients with comorbidities that put them at risk for flying or high-altitude travel,” Dr. Turetz said, referring to patients at risk for severe hypoxemia or impaired oxygen delivery (patients with COPD or heart failure), patients at risk for impaired ventilatory response (patients with neuromuscular disease or interstitial lung disease), as well as patients who already have pulmonary hypertension.
Scuba or deep-sea diving
Peter Lindholm, MD, PhD, Professor and Gurnee Endowed Chair of Hyperbaric and Diving Medicine Research at the University of California, San Diego, followed with a discussion of the pulmonary physiology of scuba or deep-sea diving and the implications for patients with respiratory illness.
For patients with asthma, for example, he said a major concern is regional air trapping and the risk of barotrauma during ascent.
“What we try to do is to look at exercise capacity and also look at the risk of having an acute asthma attack underwater. It is generally considered that [people with asthma] can do recreational diving if it’s well-controlled or very mild asthma,” Dr. Lindholm said.
For patients with COPD or pulmonary fibrosis, current recommendations suggest that diving should be avoided completely, he said. However, he noted that there have been no clinical trials in this area and that recommendations are based on expert opinion.
“There are a lot of people with COPD, and there are probably a lot of people with COPD who dive,” Dr. Lindholm said. “There is an ongoing question on how risky is this and what do we do.”
Evaluating patient fitness
O’Neil Green, MBBS, FCCP, Assistant Professor of Medicine at UMass Medical School and Director of the Baystate Health NTM & Bronchiectasis Clinic, concluded the session with an overview of current guidelines and recommendations for the clinical evaluation of patients for fitness for high-altitude travel and diving.
With regards to air travel and the preflight evaluation of patients with severe COPD or asthma, particularly patients with previous air travel intolerance, current British Thoracic Society guidelines suggest that patients with an FEV1 less than 50% need to be evaluated carefully, he said.
“This serves as a guideline, I think, more than being prescriptive about what we should do,” Dr. Green said. “It simply says to think about the patient, think about how short of breath they are, think about how hypoxic they are at rest, and do something else. And that something else should be guided by clinical judgment and the resources you’ve got available.” Similarly, he said that the clinical evaluation of a patient with significant respiratory disease and their fitness for diving should be done carefully and tailored to the individual patient and the clinical situation.