Effect of Physical Activity after Recent Deep Venous Thrombosis: A Cohort Study

Ian Shrier; Susan R. Kahn

Disclosures

Med Sci Sports Exerc. 2005;37(4):630-634. 

In This Article

Discussion

Contrary to the potential concerns of some health care professionals and patients, our results suggest that increased habitual physical activity 1 month post-DVT does not increase the risk of worsening venous symptoms and signs during the subsequent 3 months. This is true even after controlling for disease severity at baseline or at 1 month. Before discussing these results in detail, the strengths and limitations of the study should be mentioned.

DVT was objectively diagnosed in all patients using current criterion standard methods.[11] We measured disease severity [12,13] and physical activity [6] using questionnaires that are reliable and valid. Although pre-DVT physical activity was obtained by recall, patients were interviewed within 1—2 d of being diagnosed with DVT, and the proportion of inactive and mildly to moderately active patients is approximately the same as in the general population.[3] Confounding by indication is important to consider in any observational study where the main independent variable (i.e., physical activity) can itself be affected by disease severity. Our results were consistent even after controlling for disease severity at baseline or at 1 month. Finally, although our sample size of 301 subjects is sufficient to address the effect of activity at 1 month post-DVT on venous symptoms and signs at 4 months post-DVT, the effect may be modified by a variety of factors (e.g., disease severity, sex, medications including hormone use in women, pre-DVT activity). Given that our main exposure had three categories and our outcome was dichotomous, the sample size is insufficient to perform stratified analyses. For example, stratifying on sex would leave 150 subjects for an analysis of three exposure categories, or only approximately 50 subjects per exposure category. The analysis would only have a power of 0.45 to detect even large differences such as 50% versus 30%. We look forward to addressing these questions as our cohort grows and numbers permit.

Our study is the first to describe the relationship between habitual physical activity soon after DVT and venous symptoms and signs a few months later. Considering our results, and that 1) an acute session of treadmill exercise 1 yr post-DVT did not worsen symptoms in DVT patients with or without PTS,[8] and 2) a 6-month, 2 × wk-1 stretching and strengthening and uphill walking exercise program in patients with chronic insufficiency improved the calf muscle pump and did not worsen reflux,[17] it is unlikely that our results will change with longer follow-up.

Although most patients did well with exercise, approximately 25% (55 of 220) of previously active subjects did not return to their pre-DVT physical activity level within 4 months, due to exercise-induced leg symptoms. There are two possible interpretations for this finding. First, exercise may indeed be detrimental for a small subgroup of patients. Second, the increase in symptoms with exercise may not necessarily be detrimental. For example, exercise to the point of discomfort is prescribed to patients with arterial claudication to stimulate angiogenesis, and a similar level of discomfort may be necessary in DVT patients. Whether the exercise-induced symptoms and signs are predictive of future PTS will be evaluated with our planned 2-yr follow-up of the study cohort. Regardless, the current results suggest that exercise does not provoke or worsen symptoms and signs in the vast majority of patients, and a more complete understanding of the mechanisms behind the increase in exercise-induced symptoms will help clinicians determine whether exercise should be promoted in all individuals or only in most patients.

The prevailing hypothesis for the cause of symptoms and signs in DVT patients is swelling due to venous hypertension, which itself is due to either obstructed flow or venous valve insufficiency.[9] Although the focus to date has been on venous flow abnormalities, swelling occurs when there is a mismatch between production of interstitial fluid (venous outflow) and its removal (via the lymphatics). On average, lymph flow is able to increase 20-fold when necessary. This provides a protection against edema equivalent to increasing the venous pressure by 17.3 mm Hg,[7] which suggests partial venous obstructions should not result in swelling. However, there are two reasons why this protective mechanism may not occur in some patients with DVT. If the lymphatics become injured close to the time of DVT (e.g., because of lower-limb fracture/surgery), there may be a higher likelihood for edema to form and persist. Second, although lymph flow can increase an average of 20-fold across the population,[7] there is undoubtedly a range of values across individuals. Those patients with poor lymph flow due to genetics or other pre-DVT factors may be more susceptible to developing PTS following a DVT.

In conclusion, increased habitual physical activity 1 month after DVT is not associated with an increased risk of worsening venous symptoms and signs over the subsequent 3 months (and may even be protective), even after adjusting for potential confounders. The potential role of exercise as a treatment modality for DVT patients should be explored. Finally, there is a need to identify risk factors for the development of PTS after DVT, and abnormal lymph flow should be considered one of the potential candidates.

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