Deep vein thrombosis (DVT) 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 DVT 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.
18 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.
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 were made immediately after exercise, then after 5 and 10 minutes.
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.
Figure 1. Median peak flow velocity measurements made in the stocking and control groups. Error bars represent the interquartile range.
Exercise using the Airogym 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 DVT.
There have now been a number of studies and reports suggesting travellers’ thrombosis is related to immobility. Immobility is associated with venostasis and that is an important part of Virchoff’s triad in terms of forming blood clots. Blood clots start in the calf and extend into the more proximal veins before embolising into the lung. Exercise, including walking, has been suggested as a mechanism whereby venostasis can be reduced, thus reducing the risk of deep vein thrombosis and subsequent pulmonary embolism.
The purpose of this study was to assess the effect of the Airogym on venous flow, comparing it with simple exercises and walking. Ten subjects – 7 female, 3 male – of ages ranging from 18-47 were assessed using duplex ultrasound imaging. Peak flow and quantitative flow measurements were assessed in each subject during rest, passive dorsiflexion and plantar flexion and during the use of the Airogym. Similar studies were carried out in the same subjects following exercise on a treadmill but it was not possible to record either peak flow velocity or quantitative flow measurements during ambulations.
The results were expressed as a percentage increase over resting flow value. There was minimal flow through the calf or popliteal veins when the subjects remained still. During passive exercise – moving the feet around without resistance (Pilates exercises were carried out) – there was a 5% increase in peak flow value and a 3% increase in total flow per minute. Total flow for the group was calculated as having increased by 3% above base line; peak flow for the group ranged from 0-6%.
Results following active movements using the Airogym showed an average peak flow increase of 24% with a range of 15-35%. The average total flow increased by 18% per minute. Results following exercise on a treadmill were difficult to interpret and not reported.
We were unable to demonstrate the true effect of walking on venous return. We were able to demonstrate quite clearly that exercise against resistance is very much more effective at increasing both peak flow velocity and absolute flow through the veins. The Airogym provides active resistance and closely simulates walking. This was a preliminary study designed to assess the efficacy of the Airogym and does demonstrate the benefit of active exercises against resistance. The results using the Airogym were more effective than results achieved in a previous study, in which a foot pump device designed to stimulate the plantar muscle pump was used. This study was not designed to show a reduction in deep vein thrombosis but simply to show that exercising with an Airogym is likely to be more effective than simply moving the feet around passively.