Physiologic Relationships Between Intrathoracic, Intraspinal and Arterial Pressures

In 1934 one of us with Brewer and Brotman1described an optical manometer which offered certain advantages over those in use at that time. The customary2rubber membrane carrying a flat mirror was discarded for a thin metal disk and a 0.5 diopter planoconvex lens silvered on the plane side. The new mirror design made it possible to lengthen the optical lever and to get photographic tracings of unusual clarity, and this with the simplest of optical arrangements. The disk (coin silver 0.0015 inch thick) increased the volume elasticity coefficient of the system to such a degree that it was possible to increase its effective mass 500 fold or more. In accordance with the mathematical principles laid down by Otto Frank3we were free from the limitations imposed by a small effective mass and could construct a manometer that was much more convenient, flexible and adaptable than