by: Victor E. Battles, M.D.
With many regions of the United States having set or matched daily records for cold, prior to the winter solstice, itís not a bad idea to possess a home blood pressure monitor because of the effect of cold weather on blood pressure (BP). Seasonal variations in BP have been recognized and well documented in several research studies from the early 1980s through the late 1990s, but optimal use of the information derived from those studies cannot be achieved without the widespread use of home blood pressure monitor devices. By being aware of the seasonal changes in patients affected by this phenomenon doctors can make the appropriate adjustments to achieve and/or maintain good BP control and minimize the damaging effects of high BP on various parts of the body.
Research studies have shown an inverse relationship between environmental temperature and BP levels, with pressure readings being higher during cold weather and lower in warm and hot weather. A notable study conducted in France involved 8,801 adult patients greater than 65 years of age over a two-year period of time, during which time 33.4% of the individuals in the study had high BP readings during the winter compared to 23.8% during the summer. The elevated blood pressure readings during the winter were seen for both systolic and diastolic pressures but the study only reported the average systolic pressure elevation for the group, which was 5 points higher in the winter than in the summer.
Other studies performed using home blood pressure monitor technology or 24 hour ambulatory monitors have shown similar findings, with the most drastic variations in BP occurring in regions of the world with the most extreme seasonal changes in the temperature. The BP changes that occurred were similar between men and women studied.
The cause of this phenomenon, known in the health-care community as the seasonality of hypertension, is unknown, but a few theories have been proposed. One is that the sympathetic nervous system, which prepares the body to deal with stressful or emergency situations, is ramped up by cold weather which, in conjunction with decreased sodium excretion due to diminished sweating causes the BP to rise. The corollary hypothesis is that during warm and hot seasons larger amounts of sodium are excreted through sweating. The increased sodium excretion is accompanied by loss of fluid volume in the blood vessels, thereby reducing blood pressure.
Some have even postulated that high BP readings during the winter may be responsible for the increased occurrence of stroke and cardiovascular complications such as heart attack, congestive heart failure and angina during the winter months, which have been observed in some studies. Those who know or knew someone who suffered a heart attack or stroke while shoveling snow on a cold wintry day would most likely have no difficulty believing this theory, particularly if the victim had hypertension which was not being closely monitored between changes of seasons.
Not only is close BP tracking via the use of a home blood pressure monitor important during the cold seasons, but is also important as the weather warms and becomes hot, particularly if an individual with hypertension is taking a diuretic (a medication which increases urination and sodium excretion). Since diuretics not only cause a desired drop in BP, if the sodium excretion caused by them is excessive they can cause abnormally low readings, which in and of themselves can be problematic, particularly in the elderly where the risk of fainting and bodily injury are commonplace.
The season to acquire a home blood pressure monitor, if one is not already possessed, is therefore, not just when you can do so in exchange for a holiday gift you didnít like, but at any season of the year, with frequent and regular use of it to report the pressure readings to your physician. It is a responsible and could be a life-saving thing to do.
Victor E. Battles, M.D. is a board-certified internist with 30 + years of patient contact. Dr. Battles has been a principal investigator in several hypertension clinical research trials, and is the founder of Proactive Health Outlet.
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