Heart failure

Heart failure’s used to describe a point at which the heart can’t supply enough blood to meet the body’s demands.

This can happen in two ways, either the heart’s ventricles can’t pump blood hard enough during systole, called systolic heart failure, or not enough blood fills into the ventricles during diastole, called diastolic heart failure.

In both cases, blood backs up into the lungs, causing congestion or fluid buildup, which is why it’s also often known as congestive heart failure, or just CHF.

Congestive heart failure affects millions of people around the world and since it means that the body’s needs are not being met, it can ultimately lead to death.

Part of the reason why so many people are affected by heart failure, is that there are a wide variety of heart diseases like ischemia and valvular disease that can impair the heart’s ability to pump out blood and—over time—can ultimately cause the heart to fail.

Alright, first up is systolic heart failure, kind of a mathematical way to think this one is that the heart needs to squeeze out a certain volume of blood each minute, called cardiac output, which can be rephrased as the heart rate (or the number of beats in a minute) multiplied by the stroke volume (the volume of blood squeezed out with each heart beat).

The heart rate is pretty intuitive, but the stroke volume’s a little tricky.

For example, in an adult the heart might beat 70 times per minute and the the left ventricle might squeeze out 70ml per beat, so 70 x 70 equals a cardiac output of 4900 ml per minute, which is almost 5 liters per minute.