GB1489864A - Spirometer for recording a plot of the volume of expiration flow of a patient - Google Patents

Abstract

1489864 Spirometers THERMO ELECTRON CORP 16 Aug 1976 34005/76 Heading ASK [Also in Division G1] A spirometer for recording a plot of the volume of expiration flow of a patient comprises a casing 10, 12 defining a chamber, a piston 14 mounted in said chamber and dividing the latter into a lower compartment 22 for receiving exhaled air through opening 28 and an upper compartment 24 open to the atmosphere, a plate 34 having clips 36 for holding a paper recording cord 38, said plate 34 being mounted on piston 14 by means of posts 32 which bear on guides 30 attached to upper casing 12, and a pen 42 mounted on a holder 44 which is driven at a constant rate by screw 46 driven by a synchronous motor in housing 54, whereby a plot of expiration volume versus time may be produced. A rolling membrane 20 is secured between piston 14 and the upper and lower casings 12, 10 to provide a seal between compartments 22 and 24. The motor is controlled by a control circuit, Fig. 2 (not shown) movement of the pen from left to right in Fig. 1 being controlled by a piston movement switch 74 and a flow switch, Figs. 3a+b (not shown), which comprises a hinged cone attached to a tab whereby air flow moves the tab out of a light beam to activate the switch. The piston movement switch 74 and the flow switch are in parallel. Movement of the pen from right to left is controlled by a further switch, during this return movement the pen 42 is pulled off the cord 38 by the rotation of screw 46. The synchronous motor may be replaced by a motor with a variable speed and means to vary that speed in a predictable manner during a traverse.