Last Updated:  06/28/2009

The information in this column is intended for informational purposes only, and does not constitute medical advice or recommendations by the author.  Please consult with your physician before making any lifestyle or medication changes, or if you have any other concerns regarding your health.

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AIR POLLUTION & THE RISK OF DEEP VENOUS THROMBOSIS (DVT)

As I’ve mentioned in previous columns, venous thromboembolic (VTE) disorders are a major cause of disability and death throughout the world.  Deep venous thrombosis (DVT) results when blood clots form within the deep veins of the body (most commonly within the large veins of the legs and pelvis).  A variety of conditions and circumstances can lead to DVT formation.  These include decreased blood flow, or “stasis,” involving the body’s deep veins, injury or inflammation of the internal surfaces (endothelium) of these veins, and any underlying health condition that increases the blood’s tendency to form blood clots (hypercoagulable state).  Pulmonary embolism (PE) is a potentially life-threatening condition, and most commonly arises in patients who have already developed DVT (PE occurs when chunks of DVT-associated clots break away and travel to the lungs).  When the lungs’ circulation becomes clogged-up with these itinerant clots (emboli), patients may experience shortness of breath, chest pain, or in severe cases of PE, complete cardiovascular collapse and death. 

VTE remains an underappreciated cause of serious illness, disability, and death.  Patients with severe or repeated cases of DVT often develop chronic swelling, pain, and skin damage of the affected extremities, due to the progressive destruction of the one-way valves in the large veins of the lower body that help to prevent pooling of blood in these dependent areas (post-thrombotic syndrome).  Patients who survive significant PEs may also go on to develop permanent damage to the venous circulation of the lungs, leaving them with decreased blood flow to the lungs (pulmonary hypertension) and, in severe cases, chronic shortness of breath, lung injury, and heart damage (PE also remains the most common cause of unexpected death in hospitalized patients).  An estimated 900,000 new cases of VTE occur in the United States each year, and as many as one-third of these cases of VTE are fatal, which makes VTE a more common cause of death than either heart attacks or strokes!  As these statistics suggest, VTE remains a very serious public health problem in the United States, and throughout much of the world, as well.

While exposure to particulate air pollution from diesel and gasoline engines has previously been linked to an increased risk of coronary artery disease, the effects of these environmental pollutants on the body’s venous system, if any, are less clear.  Now, an innovative new study from Italy suggests that chronic exposure to automobile and truck exhaust may actually increase the risk of VTE.  In this study, which has just been published in the journal Circulation, 663 patients who were diagnosed with DVT were compared with 859 age-matched “control” patients without any history of DVT.  All patients who were included in this study lived in cities with a population of more than 15,000 inhabitants in the Lombardia region of Italy.  In this study, the researchers calculated the distance that each study volunteer lived from major highways and high-traffic streets.  The researchers also factored other DVT risk factors, for each of the patient volunteers, into their analysis of the data collected in this study.  Among those patient volunteers who lived between 0 feet and 2,400 feet from major highways and high-traffic streets, the risk of developing DVT was more or less linearly proportional to the distance between these patients’ homes and the site of increased automobile and truck traffic.  When comparing the patients who lived approximately 10 feet from major streets and highways with patients who lived 800 feet away from major thoroughfares, and after adjusting for other risk factors for DVT among these 1,522 patient volunteers, the researchers noted a 47 percent greater risk of DVT among the patient volunteers who lived closer to high-traffic highways and streets. 

Therefore, the findings of this study strongly suggest that chronic exposure to particulate air pollution from vehicle exhaust significantly increases the risk of developing DVT.  Other well established risk factors for DVT include prolonged immobility (e.g., sitting for long periods on a plane or in a car; or prolonged bed rest), cancer, recent major injury or surgery, pregnancy, birth control pills or other forms of hormonal therapy, heart failure, obesity, smoking, severe infections, older age, high blood pressure, chronic lung disease, inherited clotting abnormalities, and a family history of DVT or other forms of VTE.

As many of the known risk factors for DVT, and other forms of VTE, are preventable, it is possible to reduce the risk of developing potentially life-threatening blood clots by taking steps to avoid as many of these risks as possible.  For example, if you must take a long plane or automobile ride, you should take frequent walking breaks, and remember to also frequently exercise your legs while you are seated.  Drinking plenty of caffeine-free and alcohol-free drinks will also reduce the risk of DVT during long trips.  If you also have one or more non-modifiable risk factors for VTE and you must take a long trip, you might also want to talk with your doctor about taking aspirin or/and anticoagulant medications before and during your trip, as well as wearing compression stockings on your legs during your long trip.  As for the risk of DVT associated with increased exposure to gasoline and diesel engine exhaust (in addition to an increased risk of lung disease and heart disease), this new clinical research study suggests that it is best to avoid living close to busy highways and high-traffic streets, if at all possible.

Disclaimer:  As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity

 

Dr. Wascher is an oncologic surgeon, a professor of surgery, a widely published author, and the Physician-in-Chief for Surgical Oncology at the Kaiser Permanente healthcare system in Orange County, California

  

 

(Anticipated Publication Date:  March 2010)

(Click above image for TV36 interview of Dr. Wascher)

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