Figure 32-12 Effect of pressure transducer level on measurement of blood pressure. A, In a supine patient, the same arterial blood pressure (ART) is measured at the level of the heart or the brain. B, With the patient in the sitting position, blood pressure recorded from a transducer that remains at heart level (#1) will be unchanged, but blood pressure recorded from a transducer adjusted to the level of the brain (#2) will be lower by an amount equal to the hydrostatic pressure difference between these two transducer positions (20 cm H₂ O or approximately 15 mm Hg). (Redrawn from Mark JB: Atlas of Cardiovascular Monitoring. New York, Churchill Livingstone, 1998, Fig. 9-19.)