FLOW-DRIVEN DIAMETER RESPONSE IN RAT FEMORAL ARTERIES PERFUSED IN-VITRO

The effects of flow and flow changes on arterial diameter were investi gated in vitro on isolated rat femoral arteries. Segments of femoral a rteries were excised, mounted on microcannulas, and perfused with Tyro de's solution (37 OC). Perfusion pressure was kept constant at 90 mm H g. The mean external diameter after equilibration at a transmural pres sure of 90 mm Hg was 720 +/- 50 mu m (n = 12). Vessels were then const ricted with norepinephrine (1 mu M in the superfusion solution) to 77% +/- 13% of the resting diameter; acetylcholine was used to check endo thelial function. The external diameter was measured continuously usin g video microscopy. The arteries were subjected to two different types of flow variations: (a) step changes in flow (increase and decrease, n=6) and (b) low-frequency sinusoidal flow variations (frequencies ran ging from 0.002 to 0.1 Hz, n = 11). Flow ranged from 0 to 800 mu l/min (shear stress ranging from 0 to 15 dyn/cm(2)). All measured vessels c onstricted as flow increased. Flow steps induced exponential-like cont ractions (flow increase) or relaxations (flow decrease) with mean char acteristic time constants 31+/-4 and 22+/-2 s, respectively. Sinusoida l flow oscillations induced sinusoidal diameter oscillations with a ti me delay. An increase in the frequency of the flow led to a decrease o f both the amplitude of the flow-induced diameter oscillations and the phase shift between how and diameter. The dynamic diameter response t o flow changes could be characterized by a first-order low-pass filter with a time constant of 22 s. (C) 1998 Biomedical Engineering Society .