Deflation control valve

A deflation control valve that automatically varies the rate of gas flow through said control valve to maintain a constant deflation rate during the deflation or exhaust of gas held in a closed pressurisable vessel to which said valve is connectable, wherein said control valve is manually adjustable to set the deflation rate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to UK 0610300.6 filed May 24, 2006 and UK 0704186.6 filed Mar. 5, 2007, which applications are hereby incorporated by reference in their entirety.

The present invention relates to a deflation control valve for a sphygmomanometer. The valve of the present application is a deflation control valve particularly but not exclusively for use with our latest sphygmomanometer monitor (which is sold under the name “Greenlight”) which is to replace mercury and Bourden manometers and which is an accurate: self calibrating electronic manometer. Mercury is no longer acceptable for blood pressure measurement and Bourden gauges, though cheap and small: lose calibration fairly quickly. Automatic sphygmomanometers do not use the auscultatory technique and clinicians have concerns about their accuracy and appropriateness. Our new electronic manometer provides an effective solution. However, our new monitor demands more from the deflation control valve. The monitor incorporates a deflation rate indicator. Standards set an acceptable deflation rate (2 mmHglsec) for the measurement of blood pressure in the systolic and diastolic pressure zones and this deflation rate is indicated on our monitor. The valve has to be accurate and controllable enough to allow clinicians to adjust the deflation rate easily to the correct value. This is made more difficult as the volume of air held in the electronic monitor is small compared to that held in a mercury sphygmomanometer and the valve has to be able to control smaller air flow rates for a given deflation rate than when used with a mercury sphygmomanometer.

There are two types of deflation valve commonly in use, needle valves and sleeve/piston valves. Needle valves are the most widespread; they do not give sufficiently precise control of the deflation rate at such low air flow to be able to set it easily to 2 mm Hg/sec. Sleeve valves are better, but neither type compensate for reducing flow rate as the cuff pressure drops or give a tactile indication of the setting zone.

After development of the valve of the present invention, there was discovered U.S. Pat. No. 4,198,031 of Gulf & Western Industries which discloses an automatic air deflation valve for use with a sphygmomanometer and comprising a housing having an air flow channel extending through the longitudinal extent thereof and at least one air deflation port extending outwardly from said channel. The port includes a deformable diaphragm, which may be two part, sealingly supported only on its outer edges and otherwise without restraint and having a central aperture extending through the thickness thereof. The diaphragm and aperture are adapted to deform in accordance with the air pressure applied against it from said channel to automatically adjust the size and shape of said aperture, thus producing a constant air deflation rate therethrough. The valve has an override (dump) valve for fast deflation; it is not adjustable for different deflation rates, cuff or arm sizes. The valve cannot be closed, has no manual control or adjustment and appears to be designed for use on automated devices.

Features sought in an improved deflation control valve includes any of the following considerations:

1. The valve has to be sensitive and accurate enough to set the deflation rate correctly.2. The valve needs to be able to maintain the deflation rate consistently as the pressure in the cuff and monitor is dropping. The valve should compensate for the reducing pressure in the measurement zones, keeping the deflation rate as constant as possible and allowing the clinician to concentrate on the diagnosis rather than the manipulation of the valve.3. Clinicians need to be able to find the correct valve position quickly at the systolic and diastolic pressures and to increase airflow easily outside these pressure zones so that the cuff remains inflated on a patient's arm for as short a period as possible. Some tactile features that help the clinician find the operating zone of the valve will be helpful.4. The relationship between the angular position of the knob and the deflation rate should be perceived by the clinician as proportional and easily controlled. The rotation of the knob to vary the deflation rate from 2 mm Hg per second to say 8 mm Hg per second for the smallest cuff size should ideally be similar to that needed to vary the deflation rate of the largest cuff size over the same range (though it is likely that the absolute position of the knob to achieve a given flow rate will vary according to cuff size). The valve should also be able to be opened and closed fully quickly—the knob rotation from the start or end of the adjustment zone to the fully open or fully closed position should be appropriate. These requirements indicate that the relationship between the angular rotation of the knob and the position of the platen is unlikely to be either linear or directly proportional.5. The valve should connect to other components in the system with a push taper connection.6. The valve, though precise and accurate must be robust in use.7. The valve should be as small as possible.

A number of different methods of controlling air flow were considered in the evolution of the present invention including accurate needle valves controlled by a more precise mechanism, improved sleeve valves and face valves. Of the types considered, it was discovered face valves offered a way of compensating flow rate for diminishing pressure in the cuff and keeping a steady deflation rate without continual adjustment of the valve. They also seemed effective at controlling low air flow rates. A number of test rigs were made to learn more about the behavior of face valves.

According to the present invention there is provided a deflation control valve according to claim1. Also according to another aspect of the invention there is provided a deflation control valve in the form of a face valve for a sphygmomanometer comprising a valve body having a first outlet passage connectable to be communicatable with a pressurisable tube connected to a cuff of a sphygmomanometer and an inlet passage connectable to a rubber bulb pump or like inflation means, said valve body defining a valve chamber in which a flexible diaphragm is provided partially or substantially closing the chamber and said diaphragm having a deflation, air-flow passage which on one side of the diaphragm is in communication with said inlet and outlet passage and, on the opposite side of the diaphragm, is in communication with an exhaust outlet or atmosphere and is closeable or partially closeable during inflation by a displaceable closure disc, plate or platen which is releasably held in the closing position against said passage by a manually operable, controllable or adjustable release means.

The flexible diaphragm is preferably resilient.

Preferably the manually operable release means is a reversibly rotatable and axially displaceable control knob bearable on the platen, or such is a non-axially displaceable rotary knob with cam and lever means for reversibly urging the platen into a closing position. Preferably the displacement means associated with the knob (such as a screw thread or tapered cam surface) is geared such that the movement is amplified and thus greater movement of the knob enables a smaller movement of the disc or platen.

Preferably the platen and/or diaphragm has an air escape passage or means which varies in cross-section as the pressure under the diaphragm is reduced and which can be controlled by lifting and lowering the platen. It is alternately or additionally possible for air escape means to be provided on/in the diaphragm as indicated. Preferably this escape passage is provided by a recess and preferably a small groove or channel or other airflow control enhancing feature on or in its surface facing said diaphragm to compensate, in use, for falling pressure in the cuff and enable the deflation rate to be controlled. The groove is preferably elongate and diametrical and central and of differing cross-sectional area, largest in the center of the platen and reducing to zero nearer to the edge of the platen. Preferably the disc or platen has a flat normally lower surface in which the groove is also located and the root of the groove is curved. Instead of an elongate groove, a recess of other shape may be provided. Other airflow control enhancing features preferably additionally or alternatively include the surface finish of the platen and/or the diaphragm and/or the shape of both parts and/or the softness and/or thickness of the diaphragm.

Thus in its broadest aspect here compensating means are provided to enable the restriction or opening of the path between the diaphragm and platen to achieve a compensating affect using the changing curvature of the diaphragm and thus may be by way of the means indicated above e.g. by forming on the platen and/or diaphragm.

When the valve is closed, this exhaust hole or port is sealed or substantially closed by the disc or platen, which is held down by means extending from the release means which is preferably an axially displaceable rotary knob secured with a fine screw thread to the valve body or a non-axially displaceable rotary knob having a cam which acts on lever means to achieve the same effect. When the release means is in such position, the pressure in the cuff and monitor can be raised by pumping the inflation means typically to above systolic pressure. The relationship between the platen and diaphragm is preferred such that releasing the release means slightly, allows the platen to rise and air can seep from (the high pressure area) of the valve/chamber thereon through the port in the diaphragm and between the face of the platen and diaphragm to atmosphere to allow the pressure of the cuff and monitor to drop. Adjusting the release means, normally by rotation, to open and closed positions or intermediate positions controls the rate at which air flows through the valve.

It is to be appreciated that an air passage is created between the diaphragm and platen which varies in size depending on the pressure on the diaphragm (and unlike the mentioned U.S. prior art, not solely dependent on the deformation of the hole in the diaphragm). The groove is formed in the platen as an open channel of varying/differing cross-section and which is partially closed by contact with the diaphragm. The amount of groove sealed by the diaphragm is desirably controlled by the curvature of the diaphragm (created by the cuff pressure) and the position of the platen. Altering the position of the platen allows the flow rate through the valve to be adjusted for different cuff and arm sizes. The preferably elastomeric diaphragm and the platen are such that the diaphragm will, if not constrained by the platen, lift (be deformed) by the cuff air pressure. If the cuff is pressurized and the platen is raised, the diaphragm will tend to follow the platen, closing the air passage formed in the groove between the diaphragm and the platen by an amount proportional to the difference between the cuff pressure and atmospheric pressure. As the pressure in the cuff drops, the diaphragm will deform less, exposing more of the groove formed in the platen to atmosphere and opening the air passage formed in the groove between the platen and diaphragm, slightly and compensating for the falling pressure in the cuff. The screw action and the cam arrangement embodiments give the clinician a familiar action, a proportional response—more rotation, more flow—allowing the flow rate to be adjusted as required. Pressure compensation matches the chosen flow rate. The clinician can stop the flow or open it partially or fully. The components are also easy to mould—an open slot rather than a fine hole. The advantages of the valve of the present invention resides in its great simplicity, and enables the valve to be shut off or fully opened and to have one knob that controls everything.

Click or pawl and ratchet means associated with the release means regulate the movement of the control knob and provide audible and/or physical feedback to the clinician.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A rubber squeeze-bulb1(only shown in part but similar to bulb12inFIGS. 5 and 6) is provided for inflating a cuff100of a sphygmomanometer and is provided in known manner with an inlet aperture at one end for receiving a one-way inlet valve (not shown). At the opposite end outlet side of bulb1there is an outlet sleeve portion1A sealed around a one way rubber valve or check valve2contained in an inlet of a valve body3. The inlet of body3leads into the valve chamber formed by the valve body3having a tubular upper portion forming a scat for a flexible valve member or diaphragm4. An outlet3A leads to the cuff. Elastomeric disc-like diaphragm4(about 45 shore A material), is seated in the body3and sealed at its periphery against the seat by means of a sealing cap6including an externally threaded tubular portion which is threadingly engaged and secured in an upper portion of valve body3and urges the diaphragm4into sealing engagement with its seat. The cap6has a central aperture6A for exhaust of air from the valve when opened and to enable a pin or boss to extend therethrough to act on the diaphragm4via a disc or platen. Diaphragm4has a central passage or hole or port4A for flow of air which is controlled/stopped via a disc like platen5. A rotary control knob8is provided threadingly mounted on valve body3which has a fine thread and axially displaceable by rotation to move towards and away from the platen5. Knob8has a platen engagement pin or boss8A on its lower inner side forming a control portion of the knob as it extends through aperture6A in cap6and may bear against the upper surface of platen5. A metal click spring7is mounted on the top of cap6on two retaining pins6B,6C extending through spring holes7B and the knob8has a circle of serrations on its inner side engageable by a pawl portion7C of spring7. Click spring7and in particular pawl or dimple portion7C operates against the ridges or serrations8B on the underside of the knob8. Spring7comprises two spaced apart flap-like portions7D lying in the same plane and from which, in its position of use, two yoke-like springs arm portions7E extend inclined downwardly to two spaced apart flat web-like mounting portions7F both lying in the same plane and in which holes7B are found. The small dimple7D on one portion runs against the cap serrations8B to create the click action. The other portion7D also runs against the cap surface but on a smooth section inboard of the serrations. The spring7pivots against the clamp on the portion7F of its surface with the two holes7B and the cap6presses against both the bottom and top legs of the spring, ensuring the spring dimple clicks against the cap serrations. The platen/lever/cam assembly have the capability of closing the valve completely.

Air from the atmosphere is pumped into and through the valve body3by the rubber bulb1, entering through the one way valve2. The outlet of the body3has a rubber tube3A running to the manometer and cuff. Diaphragm4is sealed to valve body3around its periphery by cap6. There is a second outlet from valve body3via the port4A in the center of diaphragm4for exhausting/deflating the cuff. When the valve is closed, this exhaust hole or port4A is sealed or substantially closed by platen5, which is held down by the boss8A on knob8which secured with a fine screw thread to valve body3. When knob8is screwed closed (down), the pressure in the cuff and monitor can be raised by pumping bulb1, typically to above systolic pressure. Unscrewing knob8slightly allows platen5to rise. Air can seep from valve body3(the high pressure area) through port4A, along the passage formed by the groove5A in the platen, between the face of platen5and diaphragm4and through a hole in the knob8, or otherwise to atmosphere, allowing the pressure in the cuff and monitor to drop. Opening and closing knob8controls the rate at which air flows through the valve.

A second effect provides pressure compensation. The underside of diaphragm4is subject to cuff pressure. The elastomeric diaphragm4will, if not constrained by the platen, lift (be deformed) by this pressure. If the cuff is pressurized and the platen5is raised, the diaphragm will tend to follow the platen, exposing the groove formed in the platen that connects port4A to atmosphere by an amount proportional to the difference between the cuff pressure and atmosphere. As the pressure in the cuff drops, the diaphragm will deform less, increasing the size of the air passage leading from port4A via the platen groove to atmosphere by exposing a section of the groove in the platen with a wider cross-sectional area. This effect, if correctly exploited, will compensate for the falling pressure in the cuff and mean that a clinician, once the correct flow rate has been achieved, will not have to continue to adjust the valve as the pressure drops.

It has been discovered that this effect is influenced by the surface finish of the platen and diaphragm, the shape of both parts and the softness of the diaphragm. Difficulties can be experienced achieving a precise control of the deflation rate and compensate for pressure effectively using a flat diaphragm and platen. The valve may tend either not to compensate enough for pressure (operate like a needle valve) or to overcompensate and increase flow rate dramatically as the pressure dropped. It has been discovered that adding a small groove5A to the face of the platen overcomes these difficulties and makes the compensation work well and the airflow control accurate and provides a preferred embodiment. The groove5A is at its deepest and widest over port4A and tapers to nothing about 5 mm either side of port4A.

The amount of the groove5A revealed by the diaphragm defines the size of the gap through which air can flow, the more the diaphragm bulges, the more of the platen face it covers and the smaller the passage for air to flow through. This additional feature is easily mouldable and makes the pressure compensation and flow control much more reliable and precise. Good compensation can be achieved by choosing the correct groove profile, diaphragm material, thickness and texture and overall geometry.

One of the characteristics of a face valve is that very small movements of the platen can have a large effect on airflow. The elasticity of the diaphragm and the application of pressure to most of its under surface (causing it to bulge under pressure) increase the amount of movement needed to change the air flow rate. The provision of a groove or slot helps further. It is desirable that the screw thread should have some tolerance, and gripping the knob in different ways can also significantly affect the flow rate through the valve. A screw thread gives a linear relationship between the rotation of the knob and its axial movement. This is not helpful when designing one valve to cope with different cuff and patient sizes—much more air needs to flow from a large cuff on a large patient than a small cuff on a child to deliver the same deflation rate. Nor does the clinician want to turn the knob8far to shut off or fully open the valve (both actions are needed during a blood pressure test).

A second and preferred embodiment of deflection control valve10is illustrated inFIGS. 5 to 15wherein a known rubber squeeze inflation bulb12is provided with inlet check valve12A at its inlet end and connected at its outlet end via check valve11to the inlet portion of the valve body13which has knob-mounting spindle13A extending from the top thereof and, like inFIG. 4, defines a scat in a chamber on one side of its air through-flow passage and on which seat a diaphragm14is clamped by means of a clamp16which snap-fits onto the body13sealing the diaphragm14against the seat.

Diaphragm14has a central aperture or port14A similar to that described previously and communicates the through-flow passage with the upper side of the diaphragm from whence air under pressure may escape to atmosphere. A disc or platen15is provided identical or similar to platen5described previously with a double tapered groove15A part way along its diameter as described previously. Platen15is releasably urgeable against diaphragm14to close or partially close aperture14A by means of a lever19which has an annular or ring-like portion19A on which a cam18A of raising knob18may slidingly act, and has a plate-like portion19B which is displaceable in aperture16A of clamp16to act on platen15. Lever19is a pivotally mounted at19B on clamp16. Clamp16has diametrically opposite recesses16B,16C in which flanges13B,13C of the valve body13locate to prevent relative rotation. Two clam shells on upper and lower cases20A,20B, clamp together and hold knob18rotatable on spindle13A.

The disk or platen15(identical or similar to platen5described previously) is controlled by the action of the cam18A on the face of the knob18which is rotatable on spindle13A. This cam18A is preferably shaped so that the valve behaves to the user in an apparently linear way in the adjustment zone, does not have to be turned much more for large cuffs than for small, or to reach closed and fully open states. Placing the knob on the opposite side of the valve the platen15and the diaphragm14brings a number of advantages. Mechanical advantage can be built into the lever19that transmits the cam18A movement to the face of the platen15, so that there is more travel at the knob cam18A than at the platen15—this helps reduce the effect of knob bearing tolerance and any sideways movements of the knob caused by the clinicians holding the valve in unexpected ways.

Any axial movement of the knob which is more difficult to control does not affect the position of the lever or platen. The knob bearing shaft or spindle13A is mounted directly to the back of top face of the valve body and is provided with rotation stops13E, and knob8is located axially between abutment surfaces on the valve body and on the inside of case20B so that the knob can be handled reasonably roughly without applying forces to the valve mechanism. A click action (click17A and metal click spring17B operating on knob ridges8B) can also be assembled easily in such a way that the forces generated by the spring17B and click17A do not affect the position of the lever19or platen15. The diaphragm14is sealed to the body with snap-fit clamp16. Clamp16also provides a pivot19B & C for lever19and pivot17AA for click17A. The two body halves20A and20B, protect the mechanics of the valve.

The rotary knob18turns freely on the spindle13A (through approximately 310° as controlled by stop13E (FIG. 8). The cam is radially tapered and moves lever19which acts on the platen15and therefore on diaphragm14. Lever19pivots in bearing holes19B & C in clamp16. The platen15is not scalingly mounted to the valve body. The diaphragm14is sealed to the body by a periphery at edge of clamp16, which snaps onto the body13. Air cannot escape from the valve body through hole14A in the diaphragm to atmosphere when the diaphragm is pressed flat against the valve body by the platen (the platen is forced against the diaphragm by the lever19and knob cam18A). The diaphragm14seals against the platen15around the periphery of the platen (not a particularly good seal) and also against the spigot13F formed in the center of the valve body (which contacts the raised annular wall14B on the diaphragm14—this thin wall14B reduces the force needed to seal the diaphragm and reduces the likelihood of parts creeping over time if the valve is left tight shut for long periods).

When the knob18is turned and the platen15allowed to lift away from the valve body, the pressure in the valve flexes the diaphragm14and lifts the platen15. The diaphragm14flexes at its center (it is held around its periphery), and an escape path is created for the pressurized air in the valve body past the thin sealing rib on the diaphragm and the valve spigot, through the hole in the center of the diaphragm, down the two passages formed between the platen groove and the diaphragm and, if the curvature of the diaphragm is sufficient, to atmosphere. The more the diaphragm is curved (flexed), the more of the ends of the platen groove are revealed and the larger the air escape path cross section becomes. The diaphragm curvature depends on the position of the platen (controlled by the cam and lever) and on the pressure drop across the diaphragm (as mentioned previously, the higher the pressure in the valve, the greater the diaphragm deflection, the more the platen groove is covered, the smaller the air escape orifice—hence pressure compensation).

Whilst there is axial movement of the knob in the first embodiment there is no movement along the axis of rotation in this second embodiment merely about said axis. Thus it is possible to have whatever desired relationship between the knob rotation and platen movement thereof, (if need not be linear, and can be adjusted so that the relationship between the knob rotation and deflation rate (rather than platen movement) appears linear to the user). The knob bearing is easy to form, the knob can be robust, the delicate mechanics of the valve protected and a tactile ‘click’ is provided.

The click action of the tactile means is created here by a flat spring, trapped at its center on the valve body (the post-like moulding13D locates the click spring) driving the plastic pawl17C (called the click) against serrations or ridges18B. The pawl17C is pivoted on the clamp16to prevent any sideways movement. The reason for using a plastic pawl17C (rather than simply having a detail on the spring that engages on the ridges18B on the underside of the knob18) is to control the feel of the click with greater accuracy—these clicks happen every 6° of knob rotation, which is a small movement to identify with the click. The shape of the ridges on the underside of the knob and the co-operating boss on the face of the plastic pawl or ‘click’ component create the feel. The ridges do not cover all the rotation of the knob—they define the ‘working zone’.

Taking the knob zero point (cam point18C against19A) as being when the valve is fully shut off, the first click is felt after 48° of rotation. With the smallest cuff size used on a child, the correct deflation rate for reading systolic or diastolic blood pressure will be reached after about 6 clicks, or a further 36° rotation (at normal room temperature). The knob is turned a further 15 or so clicks (approximately 90°) to deflate the cuff reasonably fast between measuring points. The correct deflation rate for measuring the blood pressure of an obese adult is reached about 15-20 clicks in (rather than 6 for a child). A total of 38 clicks (or 228° of rotation) has been provided, so that a clinician should in most cases be working within the ‘click’ zone while taking pressure readings and moving between measuring points. Once the blood pressure has been measured, the valve is opened fully to give the quickest deflation. The valve is fully open (18D adjacent19A) when the knob is rotated 310° from the zero (or closed) position and the last 34° of valve movement have no clicks. One stop for knob rotation is provided—it can be seen on the valve body on the bulb side of the knob spindle13A and there is a corresponding rib18E on the underside of the knob.

Thus in summary, the present invention provides an adjustable face valve connectable to a pressurisable cuff or other vessel to control air flow from the cuff, preferably with pressure compensation such that valve automatically maintains a constant rate of pressure change in the cuff for a given setting of the valve regardless of the pressure in the cuff, the main reason for pressure compensation being to provide the clinician with a valve that does not need to be adjusted as the pressure in the cuff falls. The advantages of driving the platen with a cam, other than the mechanical and structural advantages of the cam arrangement we have arrived at (mechanical advantage, minimal disturbance of the platen position if the user applies pressure to the knob while holding it, disconnection of the more delicate parts of the valve from the user so that they cannot be abused easily), include making the relationship between knob rotation and deflation rate more intuitive to the user—more proportional, which means that the cam profile has to be slightly unusual such that it has a shut off ramp operating to close the valve, which reduces to a very gradual spiral angle at the beginning of the deflation zone (for controlling small cuffs). The spiral angle then increases as the valve is opened further for controlling larger cuffs or quick exhaust.

It is intended the technique of and valve for controlling small air flow with pressure compensation, has applications other than for sphygmomanometers.