Brachial artery differential characteristic impedance: Contributions from changes in young's modulus and diameter.

This examination of brachial artery (BA) differential characteristic impedance, DeltaZ (c), illustrates that changes in Z (c) can occur from changes in either BA wall stiffness (Young's modulus, E) and/or its diameter, D. Furthermore, we assessed how changes in both E and D combine in either an isolated, synergistic, or antagonistic manner to yield the net change in BA Z (c). The basis of this analysis is a partial differential equation which approximates DeltaZ (c) as a total differential. The effects on BA DeltaZ (c) of acetylcholine, atenolol, fenoldapine, nitroglycerin, hydrochlorothiazide and other medications are examined using data from previously published studies. Clinical situations which alter BA Z (c), such as congestive heart failure, hypertension, and hyperemia, are also analyzed. Results illustrate the usefulness of the present approach in differentiating how medications, hyperemia, and pathological conditions affect BA DeltaZ (c) by causing independent changes to E and/or D.