What is the definition of pulsus paradoxus?

Pulsus paradoxus is defined as a drop in systolic blood pressure (SBP) of more than 10 mmHg during inspiration. This phenomenon occurs due to changes in intrathoracic pressure during the respiratory cycle. During inspiration, the negative pressure in the chest cavity can lead to increased venous return to the right side of the heart, which may temporarily decrease the output from the left side of the heart due to decreased filling and subsequent cardiac output. This results in a significant decrease in the SBP during inspiration, which is characteristic of pulsus paradoxus.

In contrast to this, the other options do not accurately describe the characteristics of pulsus paradoxus. Fall in diastolic blood pressure during expiration, increase in heart rate during inspiration, and increase in blood pressure during expiration do not relate to the classic definition of pulsus paradoxus and do not reflect the physiological mechanisms involved in this phenomenon. Understanding this condition is crucial in clinical practice, especially in cases of severe asthma, cardiac tamponade, and other situations where respiratory changes significantly influence hemodynamics.