What effects does flying in an airplane have on the body's cardiovascular system?

Effects of Air Travel on the Cardiovascular System

Air travel primarily increases the risk of venous thromboembolism (VTE) through prolonged immobility, with the absolute risk of symptomatic VTE being approximately 1 in 4,600 flights lasting over 4 hours, increasing by 18% for each additional 2 hours of flight duration. 1

Primary Cardiovascular Effects

Venous Thromboembolism Risk

• Prolonged air travel creates a 2.8-fold increased risk of VTE compared to non-travelers, with the association strongest for flights exceeding 8-10 hours 1
• The risk increases through the Virchow triad mechanism: immobility-induced venous stasis, hypercoagulability, and endothelial injury 1
• Window seating doubles the VTE risk compared to aisle seating, and increases risk sixfold in individuals with BMI >30 kg/m² 1
• Patients with chronic heart failure face a 1.57-fold higher risk of VTE compared to the general population 1

Cardiac Emergencies During Flight

• Cardiac emergencies account for 43% of all on-board medical incidents, based on analysis of approximately 20,000 in-flight medical events 1
• Common cardiac issues include circulatory collapse, hypertension, chest symptoms, and dehydration 1
• Blood pressure management is required in 76% of cardiac incidents, oxygen delivery in 48%, and automated external defibrillator use in 6% 1

Physiological Changes from Cabin Environment

• Hypobaric hypoxia from reduced cabin pressure decreases oxygen partial pressure, causing blood redistribution to the brain and heart while reducing perfusion to kidneys and skin 2
• Tachycardia develops during hypoxia, though stroke volume remains unchanged initially 2
• Coronary blood flow increases with cardiac output, but severe hypoxia can lead to myocardial depression 2

Risk Factors Requiring Special Attention

High-Risk Cardiovascular Conditions

• Patients with recent myocardial infarction, uncontrolled hypertension, recent cardiac surgery (CABG or PCI), or uncontrolled arrhythmias require medical clearance before flying 1
• Those with heart failure with reduced ejection fraction (HFrEF) or recurrent syncope need medication optimization and symptom assessment pre-departure 1
• Uncontrolled hypertension increases risk of hypertensive crisis during flight 1

Additional VTE Risk Factors

• Individual risk factors include previous VTE, recent surgery or trauma, active malignancy, pregnancy, estrogen use, advanced age, limited mobility, severe obesity, and thrombophilic disorders 1
• Coagulation activation after 8-hour flights is greater in factor V Leiden carriers and women taking oral contraceptives 1

Prevention Strategies

For All Travelers on Flights >4 Hours

• Frequent ambulation (walking cabin aisles every 2 hours minimum) and calf muscle exercises are the cornerstone of DVT prevention 1, 3
• Leg exercises improve popliteal venous flow during prolonged seated immobility 1
• Adequate hydration with 0.5-1 L additional non-alcoholic fluid intake is recommended 1, 4
• Wearing loose, appropriate clothing helps prevent venous compression 1

For High-Risk Travelers

• Below-knee graduated compression stockings (15-30 mmHg at ankle) should be worn during the entire flight by those with VTE risk factors 1, 3
• A systematic review of 11 randomized trials (2,906 individuals) demonstrated compression stockings reduce asymptomatic DVT incidence 1
• Requesting an aisle seat facilitates movement and reduces VTE risk compared to window seating 1, 3

Pharmacologic Prophylaxis

• Aspirin is NOT recommended for VTE prevention during air travel due to insufficient evidence of benefit and meaningful bleeding risk 1, 3
• For substantially high-risk individuals, one dose of low-molecular-weight heparin (enoxaparin) may be considered, though evidence is limited 1
• The LONFLIT-3 study showed 0% asymptomatic DVT with enoxaparin versus 4.8% in controls, but this was a small study of only 300 high-risk individuals 1

Critical Pitfalls to Avoid

• Do not prescribe aspirin reflexively for flight DVT prevention - it works on arterial (not venous) thrombosis and carries gastrointestinal bleeding risk of 5 per 1,000 patients annually 3
• Do not allow patients with uncontrolled cardiovascular conditions to fly without medical optimization - cardiac emergencies represent nearly half of in-flight medical incidents 1
• Do not overlook bilateral DVT risk - travel-related bilateral DVT occurs in up to 18% of patients with unilateral symptoms and 17% with bilateral symptoms 4
• Dehydration risk is real but often overstated - there is no definitive evidence that dehydration alone causes VTE, though adequate hydration remains prudent 1

Special Considerations for Heart Failure Patients

• Patients with stable heart failure can travel by air, but require careful fluid and medication management 1
• Fluid restriction of 1.5-2.0 L per day may be needed for severe heart failure, with additional 0.5-1.0 L for hot/dry destinations 1
• Patients should carry sufficient medication in carry-on luggage, medication lists, device interrogation printouts, and emergency contact information 1
• Signs of volume depletion (fatigue, postural dizziness, low urine output) require temporary reduction or discontinuation of diuretics and RAAS inhibitors 1