Reducing risk of in-flight DVT

About

During quiet sitting, gravity pulls the blood and interstitial fluid in the body down into the feet and legs. This commonly results in swollen feet, ankles, and lower legs, but as well, because this fluid is not being returned to the heart, cardiac output also falls. When cardiac output falls, circulation decreases along with blood pressure. In the upper body, reduced cardiac output leads to reduced cerebral blood flow and cognitive dysfunction. In the lower body, reduced cardiac output combined with the increased interstitial pressure leads to greatly reduced circulation in the lower limbs.   Reduced lower limb circulation is of general medical concern as it results in neuropathy, slow wound healing, varicose veins, etc. However, in the context of air travel, the reduced cardiac output can lead to a condition referred to as deep vein thrombosis (DVT), that is, the venous flow rates in the lower limbs becomes so slow that the blood in the veins will clot. (Note, that risk of DVT during flight is also increased by the fact that cabin air pressure is usually less than one atmosphere – typically about ¾ atmosphere). DVT is a very painful condition, but can usually be treated with “blood thinners.” However, a deep vein thrombosis can also break up, with part of the clot returning to the right side of the heart and on into the lungs, a condition referred to as pulmonary embolism. This is a very dangerous, and often fatal, situation; an estimated 100,000 to 200,000 U.S. residents die from PE each year. Correspondingly, many individuals who fly regularly (such as business people) or fly on long distance flights, often have a great fear of developing a DVT.   In a healthy young individual, the influence of gravity on fluids in the body when seated is slowed (though not prevented) by the action of the soleus muscles in the lower legs. The soleus muscles serve as the “secondary hearts” in the body, returning blood and interstitial fluid back to the heart when an individual is sitting or standing quietly. Unfortunately, our modern life style results in many adults having inadequate soleus muscle activity (perhaps 50% of more of adults). While our ancestors invariably squatted when resting, resulting in substantial activation of the soleus muscles, in the modern world people tend to sit when resting, in fact, the typical American adult sits for over 12 hours per day. Extended sitting results in degradation of soleus performance over time.   Fortunately, like all muscles, the soleus muscles can be trained back up with appropriate exercise. However, the soleus muscles are deep postural muscles, and so require long duration (i.e. hours), of low level activity each day. Squatting, of course, is an excellent exercise for training up the soleus muscles, though not popular in the U.S. and Europe. Knee raises and toe standing also work, though most people cannot perform these exercises for more than a few minutes.   Over the last decade, soleus muscle physiology has been a major focus of research in the Clinical Science and Engineering Research Lab at Binghamton University. The end result of this work is that a non-invasive, and passive, means for stimulating the soleus muscles has been developed. Specifically, the soleus muscles can be stimulated to contract by activating a specific class of mechano-receptors on the frontal plantar surface (sole) of the foot. Because these mechanoreceptors are a type of nerve ending, they can be activated either mechanically, or electrically. The technology works effectively with the individual wearing shoes and socks if desired, and there is no sensation of the soleus muscle contracting.   This research has led to a University spin-off venture, Sonostics, Inc. Sonostics elected to initially develop this technology using a micro-mechanical stimulation approach. Their HeartPartner device has been shown to be capable of increasing lower limb blood flow by 50% during quiet upright sitting. The HeartPartner is currently being sold to individuals suffering from secondary heart failure, a condition which is evidenced by lower limb swelling, varicose veins, night-time leg cramps, chronic fatigue, and cognitive dysfunction.   While the HeartPartner is a simple and effective intervention for training up the soleus muscles in the home or workplace, it is probably not practical for use during air travel. However, we have shown that the same level of improvement in lower limb circulation can be achieved through electromagnetic stimulation of the mechano-receptors on the sole of the foot. This can be accomplished with an insole product in a sock/slipper/shoe, or in a slim pad which can be placed under an individual’s feet when they are sitting. Electrical power requirements for such a device are minimal, and in fact, over 12 hours of operation can be provided using a battery as small as a cell phone battery.   We propose to work with Virgin Atlantic to develop this second generation of the HeartPartner which would be appropriate for use in air travel. Not only will the continuous activation of the solues muscles dramatically reduce the risk of deep vein thrombosis among air travelers, but the enhanced venous return and corresponding increase in cardiac output will result in decreased fatigue and improved cognitive performance, such that the business traveller will be in a much better position to tackle the challenges facing him/her when they arrive at their destination.