In this report, the results of complementary studies of pressure-volume (p-
V)measurements on balloon catheters with balloons of low (LC) and high comp
liance (HC) used for percutaneous transluminal coronary angioplasty are dis
cussed. The measurements were performed with balloons unconfined in air (fr
ee dilatation) and also confined in different shells, in the case of rigid
shells, a surprisingly high self-expansion of the catheters was found. Alth
ough this self-expansion does not contribute to the radial dilatation, it c
annot be neglected, but must be taken into account when the success of ball
oon dilatation is determined on the basis of measured p-V curves. The inves
tigations performed using wrapped shells clearly show the different dilatat
ion properties of LC and HC balloons. The results provide important informa
tion on the feasibility of controlled balloon dilatation on the basis of p-
V measurements performed on-line during PTCA.