Assessing cardiac function, blood pressure and hemodynamic status play an important role during our overall patient assessment and treatment. Although 12 lead ECG evaluation is an essential part of patient assessment, especially cardiac etiology, understanding basic cardiac function plays a major role during treatment and overall patient status.
During normal hemodynamic conditions, inspiration leads to decreased intrathoracic pressures. Changes that occur during these events, lead to changes in blood pressures. Keep in mind, when we measure non-invasive blood pressures, we are assessing arterial pressures, not venous.
• Normally during exhalation and early inspiration, thoracic pressures increase (equializing with external pressures) and Cardiac Output (CO) decreases slightly, since the Left Ventricle (LV) does not have the adequate amount of space to expand for full capacity preload
•This drop in blood pressure is normally < 10mmHg
•The heart rate also increases as a compensatory mechanism, in an attempt to maintain normal Oxygen Delivery (DO2)
In a short summary, this occurs due to:
• Decreased intrathoracic pressures increase venous return to the Right Ventricle (RV), while increased pressures during exhalation, reduce venous return
•This increase in Central Venous Pressure (1-6mmHg) which reflects the pressure of the RV, increases the RV volume and capacity, forcing the Interventricular Septum (the wall dividing the ventricles) towards the left
•This Septum shift towards the left slightly reduces the LV capacity. This is even more marked during a Pericardial Effusion (fluid in the pericardial sac), where the LV can’t expand properly due to the pressure from the Septum and the pericardial sac, decreasing it’s internal diameter, leading to decreased Stroke Volume (SV) since it can’t produce a strong contraction
•A decrease in pulmonary vein blood volume to the LV due to blood pooling from increased lung expansion also reduces the amount of blood brought to the LV
A decrease >10mmHg during the systolic pressures during inspiration, is considered a significant decrease in Left Ventricular (LV) volume, known as Pulsus Paradoxus. The term paradox refers to an audible cardiac cycle without a palpable pulse during this event.
An easy way to assess for Pulsus Paradoxus is by manual BP assessment.
- Inflate the blood pressure cuff until no sounds are heard
- Begin deflating the cuff at approximately 2-3mmHg/sec, until the first Korotkoff sound (normal auscultated blood pressure sound) during exhalation
- Then listen for the next Korotkoff sound during inspiration
- If the drop between the first sound and the next is > 10mmHg, then there is positive Pulsus Paradoxus
What does this mean?
The presence of Pulsus Paradoxus means that there is reduced Venous return to the heart which leads to reduced arterial blood pressure, decreasing CO.
The most common causes of of Pulsus Paradoxus include:
. Increased Pulmonary pressures during COPD (Chronic Obstructive Pulmonary Diesease) exacerbation or Asthma
For further information about Pulmonary Pressures, click on the link below:
. Cardiac Tamponade
. Pericardial effusions (can lead to tamponade)
. Post large Myocardial Infarction