During a run, your heart rate increases, boosting your cardiac output. At the same time, your peripheral blood-vessel resistance increases. The result is an increase in blood pressure, or BP, during exercise. However, a rapid decline in BP upon the cessation of running is common and is termed post-exercise hypotension, or PEH. Depending on the underlying cause, PEH may be benign or it may signal a serious problem.
Definitions and Details
According to a 2002 study in "Nature," PEH is characterized by a decrease in blood pressure lasting minutes or hours after the completion of a bout of exercise. There is no standard definition for the size of the BP decrease required to establish the presence of PEH. Individuals who have hypertension or are close to having hypertension are more susceptible. The effect is mediated by a decrease in circulating adrenalin after exercise stops. The phenomenon appears to be age- and gender-independent.
Causes
As reported in Science Daily, an exaggerated response to the compound histamine may be responsible for PEH. This idea is supported by the observation that the administration of antihistamines before endurance exercise prevents the PEH observed in athletes previously experiencing the phenomenon. The magnitude of PEH -- which may last as long as 12 hours -- appears to be related to the duration of the exercise bout, with longer runs translating into a greater lowering of BP. This effect is much more common in people with hypertension than in people with normal BP.
Effects
A significant lowering of BP under any circumstances has a number of predictable effects. Among these is fainting, which can be dangerous, especially if the onset of PEH occurs soon after you stop running and you are still standing or rise to a standing position after sitting down. Also, running typically leads to a reduction in plasma volume as a result of fluid losses in sweat, and this can increase the magnitude of PEH and exaggerate its physiological effects.
Prevention and Treatment
In many cases, PEH is a desirable result, given that most runners who experience the phenomenon have high BP. Daily or at least regular running in such people may reduce or eliminate the need for anti-hypertensive medications, as long as the drop in BP after a run is not marked enough to produce fainting and other untoward effects. To prevent PEH, antihistamines taken beforehand have proven effective, and according to the journal "Hypertension," high doses of the opioid antagonist naloxone have also been shown to have a similar effect.
References
- "Nature"; Potential Causes, Mechanisms, and Implications of Post-exercise Hypotension; J.R. MacDonald; April 2002
- Science Daily; Finding May Explain Biggest Cause Of Post-Exercise Fainting; Oct. 13, 2006
- "Hypertension"; Postexercise Hypotension. Key Features, Mechanisms, and Clinical Significance; M.J. Kenney and D.R. Seals; November 1993
