What are Starling curves?

Starling curves are a graphical representation of the relationship between cardiac output and venous return in the cardiovascular system. The curves are named after Ernest Starling, a physiologist who first described them in the early 20th century. The curve shows how the heart’s output (measured in cardiac output) increases as the amount of blood returning to the heart (measured in venous return) increases. The slope of the curve is determined by the Frank-Starling mechanism, which states that the more the ventricles are stretched (by an increase in venous return), the more forcefully they contract, leading to an increase in cardiac output.

 

How does Starling law relate to heart failure?

The Starling law of the heart describes the relationship between cardiac output and venous return, and how changes in one affect the other. In heart failure, the heart is not able to pump blood as efficiently as it should, which results in a decrease in cardiac output. This decrease in cardiac output can cause an increase in venous return, which according to the Starling law, should lead to an increase in cardiac output. However, in heart failure, the heart is not able to respond to this increase in venous return and the cardiac output remains low. This is called “Starling’s Law of the Heart failure”

In addition, patients with heart failure may have a decrease in the ability of the ventricular wall to stretch (preload) which is one of the factors that contributes to the Frank-Starling mechanism. This decrease in preload leads to a leftward shift of the Starling curve, meaning that the heart needs a greater amount of venous return to generate the same cardiac output. This is one of the reasons why patients with heart failure may experience symptoms such as shortness of breath and fatigue, as the heart is not able to pump enough blood to meet the body’s demands.

 

How does Starling law affect blood pressure?

The Starling law of the heart states that the force of contraction of the heart’s ventricles is directly proportional to the amount of blood filling them. In other words, the greater the volume of blood in the ventricles, the stronger the contraction and the higher the blood pressure. When the volume of blood in the ventricles decreases, the contraction of the heart weakens and the blood pressure drops. So, the Starling law of the heart explains how the blood pressure is affected by the volume of blood in the ventricles.

 

What shifts the Frank Starling curve?

The Frank-Starling curve illustrates the relationship between the volume of blood in the ventricles and the force of contraction of the heart. The curve shifts in response to changes in several physiological factors, including:

  1. Preload: The volume of blood in the ventricles before contraction. An increase in preload shifts the curve upward and to the right, while a decrease shifts the curve downward and to the left.
  2. Afterload: The resistance that the ventricles must overcome to pump blood. An increase in afterload shifts the curve downward and to the left, while a decrease shifts the curve upward and to the right.
  3. Contractility: The inherent ability of the heart muscle to contract. An increase in contractility shifts the curve upward and to the right, while a decrease shifts the curve downward and to the left.
  4. Heart rate: The number of times the heart beats per minute. An increase in heart rate shifts the curve upward and to the right, while a decrease shifts the curve downward and to the left.
  5. Cardiac output : The amount of blood pumped by the heart per minute. An increase in cardiac output shifts the curve upward and to the right, while a decrease shifts the curve downward and to the left.

Changes in these factors can affect the position and shape of the Frank-Starling curve and ultimately affect the cardiac output and blood pressure.