Patent GB-1385037-A (GB)
Title: Spirometers
IPC: A61B5/087
Filed: 1972-02-19
Abstract: 1385037 Spirometers WILKINSON SWORD Ltd 30 Jan 1973 [19 Feb 1972] 7803/72 Heading ASK Flexible Bag Spirometer: A spirometer comprises a container, means defining a flexible chamber in the container for receiving air exhaled by a patient, means responsive to the receipt of exhaled air for indicating an instant when a predetermined period of time elapses after the initial receipt of the exhaled air, and indicating means for indicating the volume of air received up to that instant. The expansible chamber is a flexible bag 1, Fig. 1, within a rigid casing 2 whose capacity is about 6 litres. An inlet tube 3 is connected to the container 2 and to a flexible pipe and a disposable mouthpiece. A light and stiff plate 4 lies on top of the bag 1 and carries a light tube 6 at its centre and its edges are clear of the walls of the casing 2 and freely movable therein such that the bag 1 forms a rolling seal 5. A lowfriction bearing 7 allows the tube 6 to slide through the top of the casing 1. A low-friction ring 8 carrying a ferromagnetic ring 9 is carried with the tube 6 when it moves, unless restrained by an electromagnet 10. A projection 11 on top of the tube 6 actuates a microswitch 12 when the tube 6 moves upwardly from its lowermost position. The microswitch 12 actuates a timer 13 which controls the electromagnet 10. In use, the electromagnet 10 is initially energised and the tube 6 is in its lowermost position. When the patient exhales into the bag 1, the tube 6 rises and actuates the microswitch 12 and the timer 13, while the ring 8 remains adjacent the electromagnet 10. After a period of ¢, 1 or 2 seconds, the timer de-energises the electromagnet 10 whereupon the ring 8 is released to travel upwardly withthe tube 6. Using a scale inscribed on the tube 6, the position of the ring 9 gives the forced expiratory volume (F.E.V.) and the position of the top of the bearing 7 gives the forced vital capacity (F.V.C.) of the patient: Bellows Spirometer: In an alternative embodiment, a bellows 32, Fig. 3, slides horizontally in a casing 30. A vertical arm 38, fixed to a movable end plate 36 of the bellows 32, is attached to a trolley 40 which is supported by rollers (44), Fig. 4, (not shown) that engage rails inside a support tube 46. An FVC indicator (48), attached to the trolley 40, moves over a scale (50). A ferromagnetic FEV indicator (58) is secured to an endless cord 52 between pulleys 54 on the ends of the casing 30. A microswitch 62 is operated by the trolley 40 and actuates a timer 64 and a brake unit 56. Initially, the bellows 32 is fully deflated and a magnet (60) holds the indicators (48), (58) in alignment. On initial expansion of the bellows 32, the indicators (48), (58) move with it and the microswitch 62 actuates the timer 64. After the predetermined period elapses, the timer 64 actuates the brake unit 56 which locks the pulley 54 and holds the indicator (58) stationary. On completion of the exhalation, the indicators (48), (58) give the FVC and FEV respectively of the patient.  Extension Pieces: An extension piece (14), Fig. 2, (not shown), incorporating a flap valve (16) which controls an inlet (18), may be attached to the inlets of the casings 1, 30. The valve (16) prevents escape of air when the exhalation ceases and keeps the expansible chambers inflated. The flap valve (16) may be used to actuate a micro switch (20) to trigger the timers 13, 64. A second timer, operated by the microswitch (20) may be used to give the times of opening and closing of the flap valve (16), and hence the exhalation time. A second extension piece (70), Fig. 5, (not shown) may be used to determine the relaxed vital capacity (VC) of the patient. The extension (70) comprises a tube (72) for attaching to the inlet tube of the expansible chamber and has a side extension (80). A flap valve (74) controls the exit of the tube (72) and a flap valve (82) controls the extension (80). On inhalation through a mouthpiece (86), the valve (82) closes and the valve (74) opens to allow exhaled air to enter the expansible chamber. The patient breathes in a relaxed manner and after a measured number of breathing cycles the VC is determined from the volume of the expansible chamber. The number of breathing cycles may be counted on a counter (90) which is triggered by a switch (88) operated by the flap valve (74). A manually operated exhaust valve, between the valves (74, 82) may be used to establish relaxed breathing before the test is started. Means may be provided to open the valve (74) when the test is completed, to exhaust the expansible chamber. In another embodiment, a spirometer has a maximum volume less than the volume of patients' lungs and consists of a cylinder divided into two halves by a flexible diaphragm coupled to a rachet mechanism for indicating incremental movements. A slide valve alternately connects the two halves of the cylinder to the lungs and exhaust respectively, and the connection being reversed each time the diaphragm reaches its limit of movement, and thereby gives the total volume exhaled. A timer is operated, after the preset period, to release a hitherto fixed pointer which would then move with a rotary scale to indicate the FEV. Pistons slidable in cylinders can be used to provide the expandible chambers.