Arterial microsphere concentrations in cats are not affected by changes in hematocrit

Area of Science:

• Physiology
• Medical Imaging
• Biomedical Engineering

Background:

• Radioactive microspheres are used to measure blood flow.
• Acute anemia and hemodilution can affect microsphere concentrations in arterial samples.
• This can lead to inaccurate cerebral blood flow (CBF) measurements.

Purpose of the Study:

• To investigate the impact of hematocrit, withdrawal rate, and vessel location on arterial microsphere concentrations.
• To determine if hemodilution affects the accuracy of microsphere-based blood flow measurements.
• To identify potential sources of error in CBF studies.

Main Methods:

• Anesthetized cats underwent microsphere injections into the left atrium.
• Arterial reference samples were withdrawn from the aorta and brachial arteries at two rates (1.03 mL/min and 2.06 mL/min).
• The study assessed the ratio of microspheres in paired samples under varying hematocrit levels (achieved through hemodilution) and withdrawal parameters.

Main Results:

• Hematocrit levels did not significantly affect microsphere concentrations.
• Slow withdrawal (1.03 mL/min) from the aorta resulted in significantly lower microsphere ratios (<1).
• Rapid withdrawal (2.06 mL/min) or slow withdrawal from brachial arteries also yielded ratios significantly less than 1.

Conclusions:

• Hemodilution does not compromise the accuracy of microsphere blood flow determinations.
• Slow withdrawal rates from large arteries (like the aorta) can lead to an underestimation of arterial microsphere concentrations.
• Careful consideration of sampling technique is crucial for accurate CBF measurements.