What happens: Sitting for 6 to 12 hours reduces venous return in the legs, thickens blood due to dehydration, and promotes the formation of clots that can travel to the lungs (embolism).
Warning signs: pain or heaviness in the calves, unilateral swelling, localized heat.
How to reduce the risk: Stay hydrated, walk every 60 to 90 minutes, wear graduated compression stockings, choose an aisle seat, and ask if you need prophylaxis if you are taking blood thinners or have a history of heart disease.
2) Cardiopulmonary stress due to altitude, cabin pressure and extreme weather.
What happens: Pressurized cabins are equivalent to an altitude of 1800 to 2400 meters; there is less oxygen per breath. Extreme heat, humidity, or cold require quick adjustments of the heart and lungs.
Warning signs: unusual shortness of breath, chest tightness, dizziness, palpitations, swollen ankles.
How to reduce the risk: Choose destinations with temperate climates, take shorter trips, use a portable pulse oximeter if you have COPD/heart failure, and plan with your cardiologist or pulmonologist before long flights.
