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The process of blood flow in the leg, against gravity and towards the heart is instigated by compression of the veins in the foot. Contraction of the calf muscles results in an ejection volume (EV) of blood towards the heart, completing the process. Research studies have shown an association between flight travel and deep vein thrombosis (DVT). Stasis of blood flow can lead to the development of thrombus formation. Deep Vein Thrombosis occurs in situations where people are immobile for long periods of time, whether this is a result of ill health or travel on land or in the air. This alteration in venous haemodynamics may contribute to the development of DVT. A novel prototype design of an in-flight exercise device to stimulate blood flow in the seated position was designed and developed. It consisted of a foot pedal attached to a base by a hinge mechanism and a spring. Four test set-ups, 1 to 4, of differing resistance were evaluated. Calf muscle pump function was assessed by the technique of Air Plethysmogrpahy (APG) in ten healthy volunteers. Ejection Volume Fractions (EVF) and Residual Volume Fractions (RVF) were determined in the standing position (control) and compared to those achieved in the seated position, by compression of the four pedals. The normal EVF is greater than or equal to 60%. It is the volume of blood ejected towards the heart when a participant stood on their tip-toes for five seconds. The normal residual volume (RV), the amount of blood remaining in the veins after exercise, is less than or equal to 35% and is an ideal indicator toward the prevention of venous stasis. Two devices (test set-up 2 and 3) achieved comparable EVF and RVF values to those achieved by the tiptoe control manoeuvre. As Test set-up 3 was more user friendly, its spring parameters were used in the subsequent device designs, namely demonstrator A (DA) and demonstrator B (DB). These prototypes were more streamlined versions designed with the shape of a foot in mind. They had differing dimensions meaning the springs would be positioned differently in relation to the foot. An assessment was conducted to determine if a significant difference existed between the two. DA produced more efficient results and so was used in the follow up study, conducted in Beaumont Hospital, Dublin. The aim of which was to determine if any of the in-flight exercises (advocated by airlines) conducted in the seated position were efficient at creating venous return. This study consisted of two parts. Volunteers first conducted the standard APG assessment, followed by walking, DA and three foot exercises in the seated position. The second part of the study was conducted in the same sequence however participants wore Mediven® Travel Compression Stockings. DA in the seated position was effective at creating venous return however the in-flight exercises did not achieve the required EVF of greater than 60 percent. The concept of the Tromped was integrated into an aircraft footrest. An assessment was conducted with 18 volunteers, six obese, six healthy individuals and with six women taking the contraceptive pill. The four footrest prototypes were compared to tiptoe (control) in the standing position and DA used in an aircraft seat. This seat had an incline of approximately 40mm from the front to the rear of the cushion and differed from previous assessments which were conducted in situ on a level examination couch. Neither of these footrests achieved the required EVF or RVF values. DA was only efficient in the obese group. Further research is recommended, particularly in redesigning the ergonomics of an aircraft seat to specifically enhance venous return in the seated position.
Collins, Carolyn : The tromped, a means of prophylaxis for flight related deep vein thrombosis. Dublin : Dublin Institute of Technology, 2009