Report:
Effect of exercise using the AiroGym on femoral vein flow velocity.

Philip D Coleridge Smith DM FRCS
Reader in Surgery, Royal Free and University College Medical School, London UK.

Introduction.
Deep vein thrombosis may occur following long haul airline travel. This has been attributed to passengers sitting in confined positions for extended periods without moving or exercising. Regular movements of the legs are needed to operate the calf muscle pump which returns blood from the legs to the heart. Prolonged periods of sitting allow blood to remain in the calf veins for long periods. This may be sufficient to initiate a deep vein thrombosis in some passengers.
Airlines recommend exercises for passengers to minimise this problem. However, these may be difficult to perform or ineffective when performed in the static seated position. An exercising device may assist the flow of blood in the veins in the leg.

Hypothesis.
Exercises performed using the AiroGym leg exerciser increase femoral vein flow velocity in seated volunteers.

Method.
Volunteers included in this study gave their informed written consent for inclusion. The study was approved by the Lister Hospital Committee for Medical Ethics. Volunteers were recruited from the staff of the Lister Hospital, Chelsea. Volunteers had no history or clinical evidence of venous or arterial disease of the lower limb. Initially volunteers sat at rest with legs dependant and applied a German Hohenstein class 1 below knee stocking (22 mm Hg compression at the ankle) to one limb, selected at random. This stocking has previously been shown to prevent DVT following long haul air travel.

The femoral vein flow velocity waveform was recorded at rest in the upper third of the thigh using duplex ultrasonography (Acuson XP/10, Acuson, Mountain View, CA, USA). A 7MHz linear array transducer was used to insonate the femoral vein in the upper third of the thigh. The transverse diameter of the vein was measured and the peak flow velocity (with respiration) recorded with angle correction. This was repeated in both lower limbs.

Volunteers then exercised whilst remaining in the sitting position using the AiroGym for a period of 5 minutes. Further recordings of peak femoral vein flow velocity were made in both lower limbs during the exercise period.

Volunteers then sat still and recordings of peak flow velocity made immediately after exercise, the after 5 and 10 minutes.

Data was entered into an Excel spreadsheet and represented as the median and inter-quartile range (IQR).

Results.
Forty limbs of 20 volunteers were studied, median age 33 years (IQR: 28 – 45).
Median femoral vein diameter: 10 mm (IQR 9 – 11).
Flow velocity observations: median (IQR) m/sec

The complete set of data is represented graphically in figure 1. This compares the peak femoral vein flow velocity at the five observation times in both the control and stocking limbs of the volunteers. In both groups peak flow velocity trebles during exercise but immediately falls to resting levels after the end of the exercise period.

Conclusion.

• Exercise using the AiroGym exercising device trebles the peak flow velocity measured in the femoral vein. This confirms that this device effectively activates the calf muscle pump mechanism returning blood to the heart.
• The duration of efficacy is limited to the duration of exercise.
• The observed effect is neither impaired nor enhanced by the wearing of compression stockings intended to prevent deep vein thrombosis.

Figure 1. Median peak flow velocity measurements made in the stocking and control groups. Error bars represent the interquartile range.