Comparison of aortic and brachial cuff pressures in flat supine and lateral recumbent positions.

Systolic, diastolic, and mean aortic pressures and bilateral systolic and diastolic brachial pressures were measured in supine and right and left lateral recumbent positions. There were no significant differences between aortic pressures recorded in supine and lateral positions. Brachial pressures measured in lateral positions (up arm, down arm) were corrected for hydrostatic effects. Uncorrected up-arm pressures demonstrated a mean drop of 13 to 14 mm Hg in systolic pressure and 14 to 17 mm Hg in diastolic pressure below corresponding supine pressures. Corrected up-arm pressures were within 3 mm Hg of their respective supine pressures. Hydrostatic effects are the most likely cause of the drop in up-arm pressures. Down-arm pressure findings were inconsistent. Influences including hydrostatic effects and flow changes resulting from compression of the brachial artery by the weight of the person's body on the arm may account for this inconsistency. Brachial pressures, when possible, should be taken in supine or sitting positions. When pressures are taken with the patient in the lateral recumbent position, the up arm should be used. Up-arm pressures will be predictably lower than respective supine pressures, whereas down-arm pressures are inconsistent.