578 
HEMODYNAMICS 
Figure 2. — Typical experimental setup to study middle descending thoracic aorta. A and B = lead wires from 
electrical calipers and the force gauge, respectively; C =: supporting bracket; D = reservoir; E = descending 
thoracic aorta with bypass; F = variable length-force gauge device; P = pressure transducer; R — radial 
displacement sensing device. From Patel, D. J., Janicki, J. S., and Carew, T. E. Static anisotropic elastic 
properties of the aorta in living dogs. Circ. Res. 25:765, 1969. 
following: The variable length-force gauge de- 
vice (F) was modified so that the proximal leg 
could be moved sinusoidally ; and (2) a sine 
wave fluid displacement pump was connected 
to the distal end of the segment via a rigid tube 
so that the segment volume could be sinusoi- 
dally varied. As seen, the segment was isolated 
and bypassed from the main systemic circula- 
tion (E position in Fig. 2). The proximal end of 
the segment was connected to a reservoir of 
oxygenated blood (D), the height of which 
maintained constant pressures in the vessel 
segment. Lateral pressure was measured at the 
mid-portion of the segment either through a 
cannulated intercostal artery (static studies) 
or through a thin needle placed coincident with 
the longitudinal axis (dynamic studies). The 
remaining intercostal arteries were ligated. A 
displacement sensing device (R) for continuous 
measurement of radius was sutured to the mid- 
portion of the pressurized segment. Finally, the 
variable length-force gauge device was attached 
to the plugs. 
Prior to recording data, hysteresis effects 
were minimized by inflating and deflating the 
vessel segment for two cycles over the pressure 
range of 20 to 200 cm HoO. Following this, the 
vessel was stressed to physiologic values by (1) 
adjusting the pressure to that value at which 
the vessel was measured and marked, and (2) 
adding an additional longitudinal force to re- 
store the vessel length to L. In accordance with 
