Heart failure, or HF, is a condition characterized by a decline in your heart's ability to pump blood. HF can result from a variety of causes, such as thyroid disease, hardening of the arteries, high blood pressure or infection. Some causes are correctable, but -- no matter the cause -- HF triggers a series of physiologic responses that are designed to compensate for a drop in the heart's output. Sodium retention is one of these reflex responses.
A Two-Sided Problem
Your heart is essentially a two-sided pump with two chambers on each side. The right side of your heart receives blood from your body and pumps it back out to your lungs. The left side receives blood from your lungs and pumps it back out to your body. While heart failure can primarily affect either side of the heart, both sides are usually affected to some degree because of the interconnectedness of the two systems.
Heart Failure Dynamics
When your heart's pumping ability diminishes, the flow of oxygen and nutrients to every organ in your body is impaired. When blood flow, or perfusion, drops to the point that the metabolic needs of certain organs cannot be met, they generate "messages" in the form of hormones and nerve impulses. These stimulate the heart to work harder and signal your body to retain fluids, to increase the effective volume in your blood vessels. However, if the heart is already having difficulty doing its job, these additional demands only tax it further.
The Kidneys' Role
Your kidneys are highly sensitive to any changes in blood pressure. In fact, one of the kidneys' primary roles is to regulate blood pressure. They do so by producing hormones, such as renin, and by fine-tuning the reabsorption of water and electrolytes, such as sodium, that help to maintain blood pressure. Through a series of metabolic conversions, hormones produced by your kidneys exert wide-ranging effects on your heart, adrenal glands, brain and nearly every tissue in your body. Sodium retained in your kidneys' soft tissues helps to pull water back into your body, thus sustaining blood volume and maintaining pressure.
Water Follows Sodium
When heart failure occurs, blood flow to the kidneys initially decreases. This reduces the kidneys' filtering pressure, which in turn reduces the loss of sodium in urine. In addition, the increase in kidney hormones eventually prompts an increase in sodium reabsorption. Because water tends to follow sodium in living tissue, this net gain in sodium within the kidneys contributes to significant fluid retention, which in turn increases the volume that must be handled by the heart.
A Vicious Cycle
The physiologic changes that take place in HF are compensatory mechanisms that are designed to maintain blood flow to the vital organs. However, the principal problem -- a weakened heart -- continues to worsen unless a root cause for the failure can be determined and corrected. The chronic outpouring of hormones that stimulate the heart and blood vessels, coupled with sodium retention and its commensurate increase in blood volume, eventually stretch the heart to a point of critical failure where medical intervention is required to preserve life.
Sodium Restriction
A 2008 article in "Nutrition in Clinical Practice" alludes to ongoing controversy over the ideal sodium intake for patients with HF. However, according to the Merck Manual of Diagnosis and Therapy, all individuals with HF, including those whose condition is well controlled, should restrict dietary salt intake, as this supposedly helps to limit fluid retention. Avoidance of salted foods and elimination of salt from the table and in cooking are initial measures. For the more seriously ill, a sodium intake of less than 1 g a day is recommended. Salt restriction is only one of many measures that must be addressed in HF, a condition that is extremely complex and difficult to manage.
References
- "Journal of Internal Medicine"; Renin-Angiotensin System Revisited; Fyhrquist F, Saijonmaa O; 2008
- "Nutrition in Clinical Practice"; The Heart Failure and Sodium Restriction Controversy: Challenging Conventional Practice; Beich K, Yancy C; 2008
- "The Merck Manual of Diagnosis and Therapy, 18th Edition: Heart Failure"; Mark H. Beers, M.D., Editor-In-Chief; 2006
