Your blood pressure is a reflection of the force needed to push blood through your arteries. The heart is primarily responsible for maintaining blood pressure. The heart works autonomously, or by itself, but its actions can be modulated by the autonomic nervous system, a branch of the nervous system responsible for controlling involuntary functions. Electrolyte changes can affect blood pressure by stimulating release of hormones that affect blood pressure.
Cardiac Regulation
The heart functions autonomously and is controlled by the SA node, or sinoatrial node. The SA node is the fastest pacemaker in the heart and therefore determines the resting heart rate. The heart rate is also modulated to meet the oxygen demands of heightened physical activity. The spark generated by the SA node travels through conduction pathways to disperse an electrical charge throughout the heart muscle.
Cardiac Contraction
The normal heart muscle has two functional states: muscle contraction and relaxation. When the heart is contracting, it's called systole, and when relaxing, it's called diastole. Normal blood pressure in an adult should be close to 120/80 mm Hg; the first number represents the systolic blood pressure, and the second number is the diastolic blood pressure. The heart works efficiently under optimal concentration of ions such as calcium, sodium and potassium. The pacemakers of the heart rely mainly on calcium, and the heart muscle on sodium and potassium.
Sodium Intake
Most of the body's sodium resides in the extracellular fluid, or the fluid contained in the space outside the cells. The majority of extracellular fluid is contained in blood vessels; in some cases, excess fluid leaves blood vessels and goes into the tissue, causing edema, or tissue swelling. Sodium acts like a water magnet; if a body compartment is high in sodium, it draws water to itself. Increasing sodium intake results in higher sodium in the blood, which causes volume expansion in blood vessels. The kidney compensates by increasing sodium excretion; failure to increase sodium excretion causes increased blood pressure.
Water Intake
Increased water intake results in volume expansion of blood, thereby causing transient elevation in blood pressure. The body corrects for volume expansion by excreting more sodium into the urine. A person with reduced water intake or increased water loss, such as in prolonged diarrhea and vomiting, has volume constriction of blood; the body tries to restrict water loss by increasing reabsorption of sodium.
