Determinants of intravascular volume
Amount of water being taken in
The intravascular volume (IV) refers to the total amount of fluid that is in your blood vessels. If you are dehydrated, resulting from either severe physical exercises or severe loose bowel movement, otherwise known as diarrhea, your IV shrinks, and your blood pressure decreases. Thus, when you are sweating a lot as a consequence of doing physical exercises, you need to take in waterregularly so that the water that you lost will be replenished.If you have been suffering from severe diarrhea, you need to take in water as needed, or to be inserted with intravenous fluid so that your lost water will be replaced. This process of replacing your lost water is called hydration.
Amount of salt being taken in
When you sweat as a result of doing physical exercises and of hot weather, salt in your body, otherwise known as sodium chloride (NaCl), is lost. Sodium chloride is also lost when you have diarrhea for some time. For this reason, when you do intense physical exercises, or when you are exposed to hot temperature in your work, or when you are having diarrhea, you need to take some amount of salt. For strenuous sport like tennis, there are special drinks which are recommended, and these contain some amount of sodium chloride. For hot temperature, in your work or in your place of residence, it is enough that you take diet with adequate salt—not low or high. For diarrhea, there are tablets containing electrolytes, such as sodium chloride and potassium, that you can take.
The importance of sodium chloride in the maintenance of intravascular volume can be explained through the biological mechanism known as osmosis. The principle of osmosis states that in a compartment where the concentration of sodium is high, much water will go to that compartment until such time that the concentration of the said salt is equal to the other compartments. The net effect is that with high concentration of sodium in a compartment, such as your blood vessels, much water will be retained, increasing your intravascular volume.
Need for hydration
From the preceding discussion, it is clear that hydration is very important while you do physical exercises. To avoid dehydration and other complications of intense physical exercises, you need to observe and remember the following:
- You must drink, drink, drink—before, during, and after doing any physical exercise and throughout the day;
- When the temperature of the day is higher than usual, you need to take more water and other forms of fluid;
- If you lack carbohydrates and other sources of sugar, you may slow down in your movements; but if you lack water, you may die from it;
- If the pacing of your physical exercise is more intense than usual, you will lose more water than you used to be;
- If you physically exercise in a windy place, lowering the environmental temperature, you will sweat less;
- If your fitness level is high, you will have more and enlarged sweat glands producing more sweat to cool your body. You also perspire sooner compared to others with low fitness level;
- Genetics has role in your degree of sweating. If your family members have been sweating a lot, it is greatly possible that you will also have the same predisposition;
- If you have a bigger body, you will sweat more than those with smaller ones ;
- If you are a man, expectedly, you will sweat more than a woman.
(To be continued)
Glover B, Shepherd J, Glover SF. Hydration for Running. In: The Runner’s Handbook. 2nd revised ed. New York: Penguin Books USA Inc.; 1996:300-315.