PT on the Net Research

Blood Pressure and Sodium


Question:

How exactly does salt elevate blood pressure? What is the science behind the effect? Would you recommend a client with low blood pressure increase sodium intake?

Answer:

The blood has many different types of "salts," like potassium, chloride, magnesium, calcium and sodium. These are the main players and are referred to as electrolytes and are responsible for cell membrane function and nerve conduction. There can be problems if they get out of wack.

The understanding of how sodium salt effects blood pressure is somewhat involved. The renal system (the kidneys) are responsible for regulating the body's circulating fluids. The renin-angiotensin system operates off a negative feedback loop, that functions off the levels of a few hormones (aldosterone, angiotensenogen and anti diuretic hormone or ADH) and the electrolytes in the blood. The blood passes through the kidneys and is constantly monitored, like a thermostat in your house. When an element in the blood gets to low or high the kidneys send signals through out the body to start to adjust and compensate.

Sodium is the most abundant electrolyte in the blood. It attracts water, bicarbonate and chloride ions. As sodium levels rise, water levels rise, which translate into increased blood levels, also referred to as plasma volume and usually translates into increased filling pressures in the venous system, presenting a greater venous return to the heart. This in turn provides greater cardiac output and increased arterial pressure. Some people are not immediately sensitive to dietary salt intake. It may take several days to get changes to occur when adding or subtracting salt in the diet.

If your client is healthy and demonstrates low blood pressure for "normal" reasons, not from medication, heart problems or vessel occlusion, sodium may help. However, before you suggest anything, have your client check with his or her health care person. This is the abbreviated version of sodium salt and water balance. Some health care professionals specialize in the renal system because of its complexity. Good luck with your training.

References:

  1. Berkow,R. et al. The Merck Manual of Diagnosis and Therapy. 16th edition.1992 Merck Research Labs. NJ
  2. Spence,A. and E.Mason. Human Anatomy and Physiology 1979 Cummings Publishing, Sydney
  3. Guyton,A. and J.Hall. Textbook of Medical Physiology. 10th edition. W.B.Saunders. Philadelphia