No one is quite sure why certain conditions lead to a bigger drop in blood pressure during inhalation than the drop seen in healthy individuals. There is probably a clue in the types of conditions that cause pulsus paradoxus. They all have to do with extra pressure being exerted on the heart.
The following is a list of medical conditions that can cause pulsus paradoxus.
Bleeding from the heart can sometimes lead to blood getting trapped between the heart and the membrane that surrounds the heart (pericardium). The pericardium is very tough and unforgiving. When blood seeps into it, the pericardium doesn’t stretch much. The heart gets squeezed by the lack of space left over as blood collects. This condition is known as cardiac tamponade, or sometimes as pericardial tamponade.
Like blood collecting between the heart and the pericardium, air can leak from damaged lungs and become trapped between the lungs and the chest wall. In many cases, the leak is self-limiting. However, when enough air continues to leak and begins to put pressure on the lungs, heart, and major blood vessels, it’s known as a tension pneumothorax.
One hallmark of the tension pneumothorax is a significant and consistent drop in blood pressure. Pulsus paradoxus is an earlier sign that occurs as the tension pneumothorax is developing.
Besides cardiac tamponade, the pericardium can also cause problems if it becomes infected or inflamed. The stiffening and swelling of the pericardium during an episode of severe inflammation called pericarditis can lead to strain on the heart, interfering with an expansion of the ventricles during diastole.
Congestive Heart Failure
Decreased function in the ventricles usually following heart muscle damage from a heart attack can lead to a build-up of pressure in the circulatory system. This blood vessel traffic jam is known as congestive heart failure (CHF).
Left ventricular CHF, often simply referred to as left-sided heart failure, leads to pressure building up in the circulation of the lungs.
Right ventricular CHF, on the other hand, can sometimes precipitate the opposite effect of pulsus paradoxus, which is known as reverse pulsus paradoxus, during positive pressure ventilation. Instead of the increased thoracic pressure leading to a decrease in blood return to the left ventricle, it can instead improve blood flow from the right side into the left ventricle, which leads to better cardiac output and higher blood pressures.
Difficulty breathing from bronchospasm during acute asthma causes the patient to increase negative pressure in the thorax to compensate. The increased effort has an effect similar to that of backward pressure on circulation from the circulatory conditions listed above. Or, it could be seen as similar to the effect of positive pressure ventilation as described.
Chronic Obstructive Pulmonary Disease
Respiratory conditions that lead to increased work of breathing have similar effects on blood pressure. COPD causes the alveoli in the lungs to become delicate and lose their elasticity. Instead of a million rubber balloons, the alveoli become a million sandwich bags that won’t push air out during expiration.
Air trapped in the lungs from COPD can lead to a similar type of increased pressure on the circulatory system as CHF creates. And, like acute asthma, chronic obstructive pulmonary disease (COPD) can lead to more work of breathing.
A Word From Verywell
Even with modern medicine, there isn’t much consensus on what causes pulsus paradoxus. All we know so far is that it has to do with pressure in the thoracic cavity. All of the conditions that cause pulsus paradoxus affect the pressure inside the chest and breathing always affects that pressure gradient. Indeed, pressure is what keeps blood going round and round, and air going in and out.
Officially, pulsus paradoxus starts with a blood pressure drop of 10 mmHg, but the body doesn’t really follow hard and fast rules. We are organic beings that live on a continuum, a sliding scale of presentations, conditions, symptoms, signs, and oddities. Pulsus paradoxus happens because a constantly changing combination of factors leads to more pressure than expected pressing on the heart when we inhale. If we—the caregivers—pay close attention to what our monitors are telling us, pulsus paradoxus can be a great tool for identifying a very sick patient before her condition becomes dire.