Effect of pharmacologically active agents upon the human myometrium in vivo. Theoretical and technical aspects.

Smooth muscle is capable of contracting in response to mechanical distension. Even though the structural basis for this phenomenon is not completely clear, a method has been designed by which the contractile response to mechanical distension of the human uterine muscle can be determined in vivo. The distension is enforced sinusoidally within the frequency range 0.006-1 Hz, by filling and emptying a rubber balloon introduced into the uterine cavity. A tonometric index of the myometrium is defined using Hook's law after the approximate evaluation of a contratile modulus and the tangential stress and strain in the innermost layer of the uterine wall. The regression lines of tonometric indices upon frequency are determined and intercepts of the equations for basic conditions are compared with those obtained during the administration of pharmacologically active agents. In a pilot study, this system, now modified for the evaluation of drug effects during early pregnancy, has been tested and found reliable.