This prospective cohort study will compare popliteal vein diameter changes in international travelers who independently fly to Bogota in premium business/first class or economy class. Standardized bilateral ultrasound will be performed before flight, within 2 hours after arrival, and at 24 and 48 hours. The primary outcome is the adjusted between-group difference in change from preflight diameter to arrival. Travel behavior and venous-risk confounders will be measured prospectively.
Age 18 to 65 years.
Commercial flight to Bogota with at least 4 hours of total airborne time.
Prebooked premium business/first-class or economy-class seat documented before enrollment.
Standardized preflight ultrasound within 24 hours before departure.
Current or prior unprovoked deep venous thrombosis requiring therapeutic anticoagulation.
Therapeutic anticoagulation during the study window.
Current pregnancy.
Lower-extremity condition preventing standardized bilateral popliteal ultrasound.
Adult international medical travelers with prebooked premium business/first-class or economy-class itineraries of at least 4 hours.
Cohort
Prospective
Premium Cabin Air Travel Exposure
Other interventionPreexisting travel exposure defined by the cabin actually flown. Seat pitch, recline, lie-flat capability, aisle/window position, and ambulation opportunities will be recorded. Linked arm/group(s): Premium Cabin Travelers.
Economy Cabin Air Travel Exposure
Other interventionPreexisting economy-cabin exposure with documentation of seat characteristics, position, movement, hydration, and other travel behaviors. Linked arm/group(s): Economy Cabin Travelers.
Standardized Bilateral Popliteal Vein Ultrasound
Diagnostic testTriplicate anteroposterior and transverse diameter and cross-sectional-area measurements in both legs after a standardized resting period, with compressibility and flow assessment. Linked arm/group(s): Premium Cabin Travelers, Economy Cabin Travelers.
Between-Cabin Difference in Change in Mean Bilateral Popliteal Vein Diameter
Difference between premium and economy groups in the participant-level change from preflight baseline to arrival. Diameter will be the mean of triplicate anteroposterior measurements in both legs and will be reported in millimeters.
Incidental Venous Thrombosis or Abnormal Compressibility
Number and proportion with a new abnormality requiring immediate clinical assessment.
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