US 3363260 A
Description (OCR text may contain errors)
Jan. 9, 1968 D. R. GARBE 3,36
VOLUMETRIC RECORDER WITH RESILIENT LOADING ON EXPANDABLE BAG Filed Dec. '7, 1965 v 5 Sheets-Sheet 1 Inventor DIET/"MR RuooLr Gnnaa B fazae W A ttorne yb D. R. GARBE 3,363,260.
VOLUMETRIC RECORDER WITH RESILIENT LOADING ON EXPANDABLE BAG Jan. 9, 1968 5 Shees-Shet 2 Filed Dec. 7, 1965 Inventor DIET/MA Av 001.; 04MB: B /MJ Y A Home y:
D. R. GARBE Jan. 9, 1968 v VOLUMETRIC RECORDER WITH RESILIENT LOADING on EXPANDABLE BAG Filed Dec. 7, 1965 5 Sheets-Sheet 5 Invenlor DIET/mm llbhcLF MRPE 1 A Home I United States Patent 3,363,260 VOLUMETRIC RECORDER WITH RESILIENT LOADING 0N EXPANDABLE BAG Dietmar R'Garbe, Maids Moreton House, Maids Moreton, Buckinghamshire, England Filed Dec. 7, 1965, Ser. No. 512,114
Claims priority, application Great Britain, Dec. 11, 1964,
50,657/64 Claims. (Cl. 346-72) ABSTRACT OF THE DISCLOSURE The invention is concerned with recording spirometers of the inflatable bag type of which the apparatus shown in Shipley, US. Patent No. 2,999,495 is a typical prior example. With such spirometers the patient exhales forcibly into an inflatable bag and the movement of the bag during inflation is recorded against time upon a graph. The shape of the graph shows the pattern of forced exhalation and physicians can by suitable inspection and measurement detect and evaluate certain pulmonary conditions.
Heretofore, the graph has been distorted owing to the inertia of the part of the apparatus moved by the bag. It has been found by the applicant that the principal, and only significant distorting occurs at the beginning of an inflation when the inertia causes the part to lag in its movement and at the end of the inflation when the inertia causes the part to overshoot the true maximum and also to tend to give too high a reading as inflation slows before stopping. Applicant overcomes the difliculty by providing a resilient loading which pulls on the part at the beginning of inflation and opposes its motion at the end of inflation. In a typical arrangement shown in the drawings, the bag 6 drives a normally horizontal hinged part 3 and the resilient loading is provided in the form of over-centre spring 26 which in the rest position preferably just fails to lift the part 3. Inflation of the bag causes the spring arrangement to pass through its dead centre. Thereafter it tends to pull the member downwardly and thereby helps to slow the motion of the hinged part 3 as exhalation is be ing completed.
In the result a graph of much less distorted shape is obtained.
The present invention relates to recording spirometers and has as an object the provision of a recording spir0meter in a new and improved form.
In recent years it has come to be recognised that a record showing the volume of breath exhaled against time on a forced exhalation can be a useful aid in the diagnosis of various conditions. For producing such a record it is convenient to provide a recording spirometer which comprises a pivotally mounted member, a breath-receiving bag expandable on being inflated by the breath to move the member progressively about its pivot and a recording device operable to record the movement of the member as a function of time. Such a spirometer, however, gives a record which tends to be distorted.
The present invention is based on the discovery that the distortion is a result of the tendency of the inertia of the pivotally mounted member to cause it to move non-linearly with the flow of breath into the bag, and that this tendency can substantially be eliminated by providing the member with a resilient loading. Indeed the tendency may be eliminated to such an extent that it becomes feasible to adjust the spirometer under static conditions, in which the bag is supplied with various measured volumes of air, and thereby achieve an accuracy of plus or minus 1%.
In a preferred arrangement the resilient loading is a spring arranged to bias the member towards an intermediate position of its movement. Conveniently, the spring is a tension spring secured in over-centre relationship with the member.
The spirometer is most conveniently provided in such a form that the member is pivoted about a horizontal axis and lies horizontally when the bag is deflated, being raised as the bag is inflated. On the first entry of breath into the bag, movement of the member is assisted by the resilient loading so that, in spite of its inertia, it moves readily to permit the bag to expand. As exhalation by the patient is being completed, the rate of flow of breath into the bag diminishes and the resilient loading now acts to help the member to decelerate in response. Additionally, by loading the member, it compensates for the in crease of mechanical advantage of the bag thereon as the member approaches the vertical and the track of the center of gravity of the member approaches the horizontal.
In a preferred form of the spirometer, the member is connected with a stylus carried in operable relationship with a chart carrier movable by an electric drive motor, having equal starting and running torques, across the direction of the movement of the stylus caused by the member and the motor has an energising circuit which is energised by means responsive to movement of the member.
The following description of a preferred embodiment of the invention, in which description reference is made to the accompanying drawings, is given by way of illustration.
In the drawings:
FIGURE 1 is an end elevation of the embodiment,
FIGURE 2 is a plan of the embodiment, and
FIGURE 3 is a perspective view of the embodiment complete with a protective casing.
In the embodiment shown in the drawings, a base plate 1 has mounted thereon brackets 2, to which a member .3, constituted by a plate upwardly flanged at its perimeter, is pivotally carried on stub-spindles 5 by arms 4 which project from said member.
Between the member 3 and the base plate 1 is a bag 6 accordion pleated at three sides and connected by its fourth side, which is in its side nearest to the pivotal axis of the member 3, with a wide breath inlet conduit 7 leading from a coupling 8 which is accessible from the front of the protective casing 9 (FIGURE 3).
An arcuate arm 10, having its centre of curvature on the pivotal axis of the member 3 is secured to the side of the member 3 remote from the pivotal axis thereof. The outer end of the arm 10 which projects through an aperture 11 of the casing, carries a stylus 12 for marking a standard chart 13, printed on pressure sensitive card, held by a chart carrier 14.
The chart carrier, which is cylindrically curved about the pivotal axis of the member 3, is slidably carried at its upper edge upon a bearing rod 15 by self-oiling bearings 16.
To the underside of the lower edge of the chart carrier 14 is secured a nylon rack 17 engaged by a nylon pinion 18 having an electric drive motor 19. The bearing rod 15 and the rack 17 run parallel with the pivotal axis of the member 3. The motor 19, which is of a type having equal starting and running torques, is provided with an energising circuit which includes a micro-switch 20 responsive to a pin 21 carried by the member 3. The circuit also includes a control button 22 and pilot lights 23 and 24, the arrangement being such that the motor can only run whilst button 22 is held pressed, pilot light 24 glows when the apparatus is connected to the supply mains for use, and pilot light 23 glows only when the motor is energised by the micro-switch 20.
Between the bag 6 and the base plate 1 is positioned a platform 25. This platform is of such height and dimensions that it lies just within the accordion pleating to hold the opposite, i.e., the upper and lower, faces of the bag in contact when the bag is deflated and the member 3 is horizontal; in this way the dead-space within the bag, and therefore within the apparatus, is reduced to aminimum.
At each side of the member 3 a tension spring 26 is tensioned between an anchorage 27 near the edge of the member remote from the pivotal axis thereof, and an anchorage 28 carried by the brackets 2 at a greater height than the stub-spindles 5. Accordingly, when the bag is deflated and the member 3 is in its lowermost position, the tension in the springs acts against the weight of the member 3, the tension in fact being just insufficient in itself to cause the member 3 to rise. On inflation of the bag the member 3 passes through a dead-centre position, which corresponds with a 145 elevation of the member, the spring acts to oppose the pivotal movement of the member.
If a patient blows into the machine via a flexible tube connected with the coupling 8 whilst b'utton 22 is held pressed and pilot light 23 is glowing, the bag begins to inflate. The dead-space being very small, the member 3 begins to move almost immediately and the resulting movement of pin 21 actuates the microswitch to start the motor so that the chart 13 on the carrier 14, moves, parallel with the pivotal axis of the member 3, under the stylus 12 to provide the time component of a time/ volume curve which is traced upon the chart by the stylus. Because of the initial pull of the springs 26, the first movement of the member 3, and therefore the stylus 12 tends to be uninhibited by the inertia of the member 3 and the parts attached thereto. After passage through the dead centre position, deceleration of the member 3 as the flow rate of the breath decreases, is assisted by the tension of the springs and the curve traced by the stylus corresponds closely, e.g., as closely as 1% with the ideal.
The apparatus may be calibrated under static conditions by supplying the bag with a series of measured volumes of air and after each one loading the bag to produce the required stylus position by attaching lengths of wire 29 between the accordion pleats which are provided with pockets (not shown) to receive them.
By the present invention, a recording spirometer of considerable dynamic accuracy is provided in a very simple form.
1. A recording spirometer, which comprises a pivotally mounted member, a normally empty breath-receiving bag expandable on being inflated by the breath to move the member progressively about its pivot, a recording device connected to the pivotally mounted member to record the movement of the member as' a function of time and a resilient loading connected to the pivotally mounted member in over-centre relationship for the member by which resilient loading the tendency of the inertia of the member to cause it to start too slowly and subsequently overshoot and thereby move non-linearly with the flow of breath into the bag is substantially eliminated.
2. A recording spirometer according to claim 1 in which the member is pivoted about a horizontal axis and lies horizontally when the bag is deflated, being raised as the bag is inflated.
3. A recording spirometer, which comprises a pivotally mounted member, a normally empty breath-receiving bag expandable on being inflated by the breath to move the member about its pivot, a recording device connected to the pivotally mounted member to record the movement of the member as a function of time, the member being pivotally mounted about a horizontal axis, lying horizontally when the bag is deflated and being raised when the bag is inflated, a resilient loading connected to the pivotally mounted member in over-centre relationship which acts upon the member in such a direction as to raise it from the horizontal but just insufliciently to cause the member to rise in the absence of inflation of the bag and also acts upon the member'to oppose its motion and thereby prevent the. member overshooting as inflation ceases, said resilientmeans thereby substantially eliminating the tendency of the inertia of the member to cause it to move non-linearly with the flow of breath into the bag.
4. A recording spirometer according to claim 3 in which the bag is accordion pleated and has opposite faces which are held in contact by the member when the bag is deflated.
5. A recording spirometer according to claim 3 in which the member is connected with a stylus carried in operable relationship with a chart carrier movable by an electric drive motor, having equal starting and run ning torques, and the motor has an energising circuit which is energised by means responsive to movement of the member.
References Cited UNITED STATES PATENTS 408,938 8/1889 Tata 34672 1,863,929 16/ 1932 McKesson 1282.07 2,228,983 1/1941 Bloomheart 1282.07 2,569,849 10/1951 Emerson 128-2.08 2,999,495 9/1961 Shipley 1282.08 3,086,515 4/1963 Jones 1282.08
RICHARD B. WILKINSON, Primary Examiner.
J. W. HARTARY, Assistant Examiner.