Precautions for measuring blood flow during anemia with the microsphere technique

Area of Science:

• Physiology
• Cardiovascular Research
• Hemodynamics

Background:

• Cardiac output measurement discrepancies were observed between the microsphere technique and Fick principle.
• Anemia was suspected to cause underestimation of arterial microsphere concentration, leading to falsely elevated blood flow values.

Purpose of the Study:

• To investigate the cause of discrepancies in cardiac output measurements during anemia.
• To compare microsphere concentrations in arterial blood using different reference sample withdrawal methods.

Main Methods:

• Compared microsphere concentrations using two catheters with different withdrawal rates (1.3 ml/min vs. 7.89 ml/min).
• Investigated effects of hematocrit levels (below and above 32%) on microsphere distribution.
• Evaluated the impact of changing injection sites (left ventricle vs. left atrium).
• Tested a faster withdrawal rate (2.46 ml/min) from the smaller catheter.

Main Results:

• Below 32% hematocrit, the larger catheter (7.89 ml/min) showed 30-50% higher microsphere concentrations than the smaller catheter (1.3 ml/min).
• Discrepancies were independent of injection site, suggesting issues beyond cardiac mixing.
• Faster withdrawal from the smaller catheter (2.46 ml/min) eliminated the concentration difference.

Conclusions:

• Anemia-induced laminar flow and axial streaming may cause nonhomogeneous microsphere distribution in larger vessels.
• Reference sample withdrawal rate significantly impacts accuracy of microsphere-based blood flow measurements, especially in anemic states.
• Optimizing reference sample collection is crucial for accurate hemodynamic assessments.