Pulsus Paradoxus is an extreme change in blood pressure that occurs during inhalation. But before you can understand what pulsus paradoxus is, you need to understand how blood pressure works.
What is Pulsus Paradoxus?
When we check the blood pressure with an automatic machine we get two main readings, the big number on top is referred to as the Systolic Blood Pressure (SBP) which is measuring the strength that the heart exerts on the artery wall with each contraction. The second number underneath it is referred to as the Diastolic Blood Pressure, and this is measuring the strength that the heart exerts on the artery walls in between contractions.
When we inhale a slight negative pressure forms in our lungs, which means that the pressure inside our lungs is lower than the pressure outside of it. Since our heart is also in our chest close to the lungs, this change in pressure affects the blood leaving the left ventricle almost like a ‘little pull’ and there is a super small drop in Systolic Blood Pressure.
This drop usually goes around unnoticed because it is insignificantly small, but in Pulsus Paradoxus, the negative pressure inside the lungs is stronger and so the drop in Systolic Blood Pressure can be as big as 40mmHg.
Why does Pulsus Paradoxus happen?
Airway Obstruction: As we said above, in most people the pressure in the lungs will decrease slightly when inhaling, but that is assuming that their lung function is normal and nothing is obstructing the airways. If the airflow is obstructed by respiratory inflammations (ex. Asthma) or by a Pulmonary Embolism, then the decrease in pressure seen during inhalation is far more extreme. This extreme reduction in pressure reflects the same pressure drop in the Systolic Blood Pressure.
Cardiac Tamponade: If fluid builds up in the space around the heart it puts a lot of pressure onto the heart muscles and stops it from contracting effectively which changes the SBP.
Cardiomyopathy: Any damage caused to the cardiac chamber walls will affect its ability to contract and as a result affect the SBP.
Cardiac Arrest: A sudden blockage in blood supply to the heart, in particular, if it affects the right ventricle can cause Pulsus Paradoxus
Collapsed lung: An injury to the chest can allow air to escape the lungs and enter the space between the lung and the chest wall. This air puts pressure on the lungs stopping them from expanding fully, causing increased pressure in the chest wall and in turn affecting the SBP.