Patent Application
20070060825
The present invention relates generally to the field of blood pressure measurement devices and, more particularly, to a nearly constant flow rate bleed valve for use in either manual or automatic blood pressure measurement devices.
Blood pressure measurement devices, also referred to as sphygmomanometers, of the type commonly used to measure arterial blood pressure include an inflatable sleeve, commonly referred to as a cuff, adapted to fit around a limb, e.g. an arm or leg, of a patient. The cuff includes an interior chamber that is in fluid communication with a device for selectively inflating the interior chamber of the cuff with pressurized air. A gage is operatively connected in fluid communication with the interior chamber of the cuff for monitoring the air pressure within the cuff. A bleed valve is also operatively connected in fluid communication with the interior chamber to permit selective depressuring of the interior chamber when it is desired to deflate the cuff.
In conventional manual sphygmomanometers, the interior chamber of the cuff is connected through a length of flexible tubing to a pneumatic bulb. In operation, the cuff is fitted, e.g. wrapped, about the arm of the patient and, once so positioned; the cuff is inflated by squeezing the pneumatic bulb to force air through the tubing into the interior chamber of the cuff. Once the interior chamber of the cuff has been inflated to a desired level, as indicated on the pressure gage, the cuff is deflated by opening the bleed valve to allow the pressurized air within the interior chamber of the cuff to vent to atmosphere. A stethoscope is positioned under the cuff and over the patient's artery to monitor the patient's arterial pulses as the cuff deflates, thereby allowing the systolic and diastolic blood pressures to be determined by listening for the Korotkoff sounds. It can also be done oscillometrically by detecting the minute changes in the cuff pressure due to flow through the brachial artery.
Electronic oscillometric blood pressure measurement devices that utilize an inflatable cuff are also known in the art. Such devices generally employ one or more pressure sensing devices, such as a transducer, to monitor the pressure within the interior chamber of the cuff, as well as the minute changes in the cuff pressure due to flow in the patient's artery, as the cuff deflates. Electronic circuitry is provided that processes the signals from the pressure sensing devices and determines the systolic and diastolic blood pressures. A motor driven pump is usually provided to inflate the cuff. However, the inflation can be done by a pneumatic bulb. Typically, a digital display is provided for displaying the systolic and diastolic blood pressures.
To obtain accurate measurements, it is necessary to deflate the inflated cuff at a relatively constant rate in the range of about 2 to about 3 millimeters mercury (2-3 mmHg) per second or about 2 to about 3 millimeters mercury (2-3 mmHg) per heartbeat. Maintaining a relatively constant bleed flow rate has been a problem when using many prior art sphygmomanometers, particularly when used by untrained personnel. In prior art sphygmomanometers, the bleed commonly comprises a fixed orifice vent valve, that is a valve which vents the interior chamber of the inflated cuff through a fixed area port. With a fixed area port, the vent flow rate varies as a function of the pressure differential across the port at any given time in the venting process. As the pressure within the interior chamber will continuously decrease during the deflation process, the pressure differential, that is the difference between the air pressure within the interior chamber of the cuff and ambient pressure, will also continuously decrease. Therefore, as the pressure differential across the vent port is continuously decreasing, the vent flow rate will not remain relatively constant during the deflation process, but rather will continuously decrease. U.S. Pat. No. 4,690,171, for example, discloses a bleed valve having a fixed air bleed orifice assembly for metering the vent flow to slowly deflate the cuff and a separate opening for rapid deflation of the cuff.
Constant-rate deflation valves using a flexible valve member to vary the effective vent port area are known in the art for use in connection with sphygmomanometers. For example, U.S. Pat. No. 5,833,620 discloses a constant rate deflator including a ventilation adjusting shaft that has a recess formed on one end thereof, and a ventilation valve having a hole formed at the center thereof and a projection having almost the same shape as that of the recess in the ventilation adjusting shaft. The ventilation valve is made of a flexible material, such as rubber, whereby the width of the clearance between the projection from the ventilation valve and the valve recess increases as the pressure of the air venting through the valve decreases such that the flow rate through the clearance remains relatively constant. U.S. Pat. No. 5,143,077 also discloses a constant rate discharge valve for a sphygmomanometer utilizing a flexible valve body to move a valve stem to control vent port size in response to the pressure of the fluid venting therethrough.
For proper functioning in controlling the rate of vent flow, such constant-rate valves rely upon a predictable response of the flexible valve member to changes in pressure differential across the flexible member. Over repeated flexing, the potential exists for such flexible members to lose some degree of flexibility and even to crack or otherwise fail from fatigue after repetitive flexure under pressure.
It is an object of one aspect of the invention to provide a self-compensating bleed valve exhibiting a relatively constant bleed flow rate.
It is an object of one aspect of the invention to provide a relatively constant flow rate bleed valve that does not employ any flexible diaphragm to adjust the flow area of vent port in response to varying pressure differential across the vent port.
It is an object of one aspect of the invention to provide a bleed flow valve for use in connection with deflating a blood pressure cuff.
It is an object of one aspect of the invention to provide a method of deflating a blood pressure cuff.
In one aspect of the invention, a bleed flow valve is provided for controlling the pressure change rate in a reservoir of fluid under pressure when venting fluid therefrom through the valve. The bleed valve includes a valve body having a central bore extending axially therethrough. The central bore has a transition section, a fluid inlet port opening into the central bore upstream of the transition section and a fluid outlet port opening into the central bore downstream of the transition section. The transition section may be provided by a step change from a larger diameter upstream cavity to a smaller diameter downstream cavity or by an inwardly tapered surface extending between a larger diameter upstream cavity and a smaller diameter downstream cavity. A piston is disposed within the central bore of the valve body and is axially translatable within the central bore of the valve body. The piston includes an outer circumferential surface facing the transition section of the central bore. An annular orifice is defined between the outer circumferential surface on the piston and the transition section of the central bore. A biasing device operatively associated with the piston exerts a force on the piston acting to translate the piston in an upstream direction in opposition to a fluid pressure force on the piston acting to translate the piston in a downstream direction. In this manner, the bleed valve of the invention is self-compensating as the pressure within the reservoir decreases in that the piston self adjusts axially within the central bore to adjust the area of the annular orifice so as to maintain a relatively constant pressure change rate in reservoir pressure throughout the venting process.
In one embodiment, the biasing device comprises a spring member and a preload device for compressing the spring member to establish an initial preload force on the piston acting to translate the piston in an upstream direction. The spring member may be a compressible coil spring disposed about a downstream portion of the piston. The preload device may be a closure member disposed within the central bore downstream of and abutting the spring member, the closure member being selectively axially positioned so as to adjust the preload force on the piston.
In an embodiment, the outer circumferential surface on the piston may be a tapered outer circumferential surface. In another embodiment, the outer circumferential surface may be provided on a circumferential ridge extending about the piston. In another embodiment, a circumferential ridge having an tapered outer circumferential surface may be provided on the piston.
In an embodiment, a first proximal closure member closes the first end of the valve body and a second distal closure member closes the second end of the valve body. Further, a low pressure stop that is selectively axially translatable may be supported by the first closure member and a high pressure stop that is selectively axially translatable may be supported by the second closure member.
In a further aspect of the invention, a bleed flow valve is provided for controlling the pressure change rate experienced by a flow of air under pressure venting from a blood pressure cuff. The valve includes an axially elongated valve body having a first end, a second end, and a central bore extending axially therethrough. The central bore has a first generally cylindrical cavity, a second generally cylindrical cavity, and third cavity disposed between the first and second cavities with the third cavity having a tapered transition section. A first closure member closes the first end of the valve body and a second closure member closes the second end of the valve body. A piston is disposed within the central bore of the valve body. The piston has a generally cylindrical configuration and includes a tapered outer circumferential surface facing the tapered transition section of the central bore, thereby defining an annular orifice between the tapered outer circumferential surface on the piston and the tapered transition section of the central bore. The piston is axially translatable within the central bore of the valve body. A first port, which opens through the valve body into the first cavity upstream of the tapered outer circumferential surface on the piston, is pneumatically coupled to the blood pressure cuff. A second port, which opens through the valve body into the second cavity downstream of the tapered outer circumferential surface on the piston, provides a vent hole. A biasing device operatively associated with the piston exerts a force on the piston acting to translate the piston in an upstream direction in opposition to a fluid pressure force on the piston acting to translate the piston in a downstream direction. In this manner, the bleed valve of the invention is self-compensating as the pressure within the reservoir decreases in that the piston self adjusts axially within the central bore to adjust the area of the annular orifice so as to maintain a relatively constant cuff pressure change rate throughout the venting process. The piston self adjusts axially within the central bore to vary the flow area defined by the annular orifice so as to maintain a relatively constant cuff pressure change rate substantially independently of the size of the blood pressure cuff.
In one embodiment, the biasing device comprises a spring member and a preload device for compressing the spring member to establish an initial preload force on the piston acting to translate the piston in an upstream direction. The spring member may be a compressible coil spring disposed about a downstream portion of the piston. The preload device may be a closure member disposed within the central bore downstream of and abutting the spring member, the closure member being selectively axially positioned so as to adjust the preload force on the piston. Advantageously, the first closure member may be an end cap and the second end closure may be an end plug. Further, a low pressure stop that is selectively axially translatable may be supported by the first closure member and a high pressure stop that is selectively axially translatable may be supported by the second closure member.
In one embodiment, a selectively positioned vent control valve is operatively associated with the bleed valve to provide for selectively closing the second port of the bleed valve or opening the second port of the bleed valve to vent to atmosphere pressure. Advantageously, the vent control valve may include a valve body having a cavity therein having a first port opening to the cavity and in flow communication with the blood pressure cuff, a second port opening to the cavity and in flow communication with the second port of the bleed valve, and a third port opening to the cavity and venting to atmospheric pressure. A selectively positionable member is operatively associated with the valve body. The member is selectively positioned in a first position wherein neither of the first port or the second port of the vent control valve is in flow communication with the third port of the vent control valve, in a second position wherein only the second port of the vent control valve is in vent communication with the third port of the flow control valve, and a third position wherein only the first port of the vent control valve is in flow communication with the third port of the vent control valve.
In a further aspect of the invention, a method is provided for venting an inflated blood pressure cuff through a bleed valve at a relatively constant cuff pressure change rate. The method includes the steps of: providing an annular orifice having a variable flow area between an upstream cavity and a downstream cavity; passing air under pressure from the blood pressure cuff to the upstream cavity; venting air from the downstream cavity; and varying the flow area of the flow path between the upstream cavity and the downstream cavity in response to a change in the pressure of the air within the upstream cavity so as to maintain a relatively constant cuff pressure change rate. Further, the method may include the step of preventing an increase in the flow area of the flow path between the upstream cavity and the downstream cavity in response to a decrease in the pressure of the air within the upstream cavity to a predetermined maximum flow area at a predetermined relatively low pressure. The method may also include the step of preventing a decrease in the flow area of the flow path between the upstream cavity and the downstream cavity in response to a change in the pressure of the air within the upstream cavity to a predetermined minimum flow area at a predetermined relatively high pressure.
The method may include the step of exerting a biasing force on the piston acting to translate the piston in an upstream direction in opposition to a fluid pressure force on the piston acting to translate the piston in a downstream direction, whereby the piston self adjusts axially within the central bore to adjust the annular orifice so as to maintain a relatively constant cuff pressure change rate. The method may include the step of establishing an initial biasing force on the piston acting to translate the piston in an upstream direction, whereby a desired cuff pressure change rate is preset. The method may include the step of adjusting the biasing force on the piston acting to translate the piston in an upstream direction, whereby a desired cuff pressure change rate may be selectively set. The biasing force may be adjusted in response to a change cuff size from that for which the biasing force was preset; or in response to heart rate of the patient being significantly different from the normal heart rate for which the biasing force was preset.
In another aspect, a method is provided for automatically varying the flow area of the flow path between the upstream cavity and the downstream cavity in response to a change in the pressure of the air within the upstream cavity so as to maintain said relatively constant cuff pressure change rate substantially independently of blood pressure cuff size.
Referring now to
In the embodiment shown, the first end fitting comprises an end cap 40 provided with a set of threads 41 on an internal end bore 43 that are compatible with the first set of threads 31 on body 30 whereby the end cap 40 may be releaseably mounted to the body 30 by screwing the set of threads 41 onto the set of threads 31. A circumferential seal 91, for example an O-ring seal, is disposed in the bore 43 of the end cap 40 intermediate the body 30 and the end cap 40 and is supported in a circumferential groove 92. The circumferential groove 92 may be formed in the exterior surface of the body 30, as shown in the depicted embodiment, or formed in the surface of the bore 43 in the end cap 40.
Additionally, the end cap 40 has a central bore 45 in its end surface which extends to and opens into the bore 43 of the cap 40. The low pressure stop 42 has a head 44, a shaft 46 extending from the head 44, and a tip 48 that extends axially from the shaft 46 into the bore 32 of the body 30. A circumferential seal 93, for example an O-ring seal supported in a circumferential groove 94, is disposed in the central bore 45 of the end cap 40 to seal the clearance between the surface of the bore 45 in the end cap 40 and the shaft 46 of the low pressure stop 42. The circumferential groove 94 may be formed in the surface of the low pressure stop 42, as shown in the depicted embodiment, or formed in the surface of the central bore 45. The tip 48 has threads 47 by means of which the low pressure stop 42 may be threaded into threads 49 provided in the surface of the passage between the central bore 45 and the end bore 43 of the end cap 40. Advantageously, the low pressure stop 42 may be selectively axially adjustable within the central bore 45 by screwing or turning the head 44 of the low pressure stop 42 either clockwise or counter clockwise thereby selectively positioning the tip 48 of the low pressure stop 42 within end chamber 37 of the bore 32 of the body 30.
In the embodiment shown, the second end fitting comprises an end plug 50 provided with a set of threads 51 on its outer surface that are compatible with the second set of threads 33 on body 30 whereby the end plug 50 may be releaseably mounted to the body 30 by screwing the set of threads 51 into the second set of threads 33 on the body 30. Referring now in particular to
As noted hereinbefore, the axially elongated bore 32 of the body 30 of the valve 10 includes a central chamber 35 disposed between a pair of axially spaced, relatively larger diameter, generally cylindrical, end cavities 37 and 39, as best seen in
Referring now to
A spring member 80 is disposed about the shaft 76 between the distal end of the body 72 and the end face 78 of the tip 58 of the end cap 50 which serves as a stop for the spring member 80. The spring member 80 may be a resilient compression coil spring, such as shown in the depicted embodiment, or other type of resilient member capable of compression and expansion.
Referring again now to
In operation, the first port 60 lies upstream of the conical transition section 65 of the central cavity 35 with respect to fluid flow through the central bore 32 of the valve 10 and the second port 62 lies downstream of the conical transition section 65 of the central cavity 35 with respect to fluid flow through the central bore 32 of the valve body 30. In accord with one aspect of the invention, a circumferential ridge 75 is provided on the piston 72 as a means of throttling fluid flow through the central bore 32 of the valve body 30. In the embodiment depicted in
The circumferential ridge 75 is disposed within the conical transition section 65 of the central cavity 35 and translates axially within the conical transition section 65 as the piston translates. In cooperation, the tapered wall 67, best seen in
When the valve 10 is connected to a blood pressure measurement device, or other reservoir of pressurized fluid, typically air, fluid flow will enter the cavity 37 through the first port 60 and establish a pressure within the cavity 37 that will be approximately equal to the cuff pressure. The fluid flow entering through the first port 60 will fill the cavity 37 and exert a force on the end face 71 of the piston 72 that will act against the force exerted by the coil spring 80 on the piston 72. The force exerted by the fluid pressure within the cavity 37 upon the piston 72 will cause the piston to translate axially towards the high pressure stop 52. As the piston translates toward the high pressure stop 52, as illustrated by position A in
Conversely, as the pressure within the cavity 37 decreases, for example during deflation of the cuff, the piston translates toward the low pressure stop 42, as illustrated by position B in
The flow rate of fluid flow passing through the annular orifice 85 will change as a function of the flow area provided by the annular orifice 85. When the pressure within the cavity 37 is high, the flow area provided by the annular orifice 85 is relatively small. Conversely, when the pressure within the cavity 37 is low, the flow area provided by the annular orifice 85 is relatively large. As the pressure within the cavity 37 decreases during fluid passage through the annular orifice from the cavity 37 into section 63 of the central cavity 35 and out the vent port 62, the flow area at the annular orifice 85 increases, thereby resulting in an increase in the bleed flow rate and thereby also tending to maintain a constant cuff pressure decrease rate. Therefore, the bleed flow valve 10 is self-compensating in that the flow area changes inversely with the pressure within the cavity 37 and therefore inversely to the cuff pressure or pressure within whatever reservoir to which the first port 60 is connected. The self-compensating characteristic of the bleed flow valve 10 of the invention enables the cuff or reservoir bleed pressure change rate to effectively be maintained at a relatively constant value over a major portion of the pressure bleeding process.
In normal operation, the pressure change rate is controlled by the equilibrium balancing between the opposing air pressure and spring forces on the piston. The low pressure stop 42 and the high pressure stop 52 do not control the cuff pressure change rate during normal operation, but rather serve to provide limits on the minimum cuff pressure change rate and maximum cuff pressure change rate. The spring member 80 and its preload are selected to provide a desired spring characteristic that will ensure a cuff pressure change rate within a specified range of desired cuff pressure change rates. End plug 50 serves to preload the spring 80. The preload on the spring 80 may be adjusted as desired simply by turning the end plug 50 clockwise or counterclockwise. The preload on the spring 80, in conjunction with the spring geometry and the taper angles, determine the operational characteristic of the valve 10, that is the bleed pressure change rate of the cuff. The desired cuff pressure change rate can be set at the factory to the recommend rate or can be set or adjust by a skilled medical practitioner by adjusting the preload on the spring 80 as previously discussed.
The self-compensating characteristic of the bleed flow valve 10 of the invention offers a distinct advantage when used in connection with blood pressure measurement devices, such as manually operated sphygmomanometers and automated electronic blood pressure monitors. By proper positioning of the low pressure stop 42 and the high pressure stop 52, and by proper adjustment of the preload on the spring 80, the bleed pressure change rate during deflation of the blood pressure cuff may be constrained within desired minimum and maximum limits, or near the desired 2-3 mm Hg per second rate. In traditional manually operated sphygmomanometers, the user must continually adjust the valve as the pressure decreases to attempt to maintain a relatively constant cuff pressure change rate. Conventionally, automated electronic blood pressure monitors are provided with pressure transducers and an electronic circuitry that automatically controls and adjusts a bleed valve as pressure decreases so as to maintain a relatively constant pressure drop rate. The required pressure transducers, electronic circuitry and electronically-controlled bleed valve are expensive.
The bleed valve 10 of the present invention may advantageously be employed in operative association with an on/off vent valve, particularly in blood pressure measurement applications. For example, a conventional thumb screw valve, such as commonly included in association with the inflation bulb on manual blood pressure sphygmomanometers, may be operatively associated with the vent port 62 of the bleed valve 10 for enabling the user to selectively open or close the vent port 62. When inflating the blood pressure cuff, the user would position the thumb screw vent valve in a fully closed position. When the cuff has been inflated to the desired pressure level, the user would simply reposition the thumb screw valve to its fully open position and the bleed valve 10 would control the rate of deflation of the cuff as hereinbefore described to maintain a relatively constant cuff pressure change rate throughout the deflation process.
However, in blood pressure measurement applications, it may be desirable, for example for patient comfort, to rapidly deflate the cuff once the diastolic blood pressure measurement has been completed. Referring now to
In the exemplary embodiment depicted in
The central bore 124 is sealed at the proximal and distal ends of the valve body 120 by means of seals 128 and 129, respectively. The seals 128 and 129 seal the gap between the axially translatable plunger rod 126 and wall of the valve body 120 defining the central bore 124. Each of the seals 128 and 129 may constitute an O-ring of conventional sealing material carried in circumferential glands provided in the wall bounding the central bore 124. Additionally, a pair of axially spaced ring seals 130 and 132 is carried in corresponding circumferential grooves on the plunger rod 126. As with the seals 128 and 129, the ring seals 130 and 132 also seal the gap between the axially translatable plunger rod 126 and wall of the valve body 120 defining the central bore 124. Therefore, three sealed cavities are established within the central bore 124 of the valve body 122 irrespective of the position of the plunger rod 126 within the central bore 124. A first cavity 133 is formed between the proximal seal ring 128 and the ring seal 130, a second cavity 135 is formed between the axially spaced seal rings 130 and 132, and a third cavity is formed between the ring seal 132 and the distal seal ring 129.
Referring now to
Referring now to
Referring now to
Referring to
In the embodiment of the bleed valve 10 of the invention depicted in
For example, referring now to
As noted before, the bleed valve 10 is particularly useful in blood pressure measurement applications. For example, in a typical blood pressure measurement procedure, the user, whether a physician, nurse, EMT, other trained professional, or the patient, first connects the measurement cuff to the pump of an automated electronic measurement apparatus or the inflation bulb of a manual sphygmomanometer, if not already connected, and then wraps the cuff about the patient's arm as in conventional practice. The user then closes the vent port 62, for example by closing a thumb screw or, if the bleed valve 10 is connected to a vent control valve, such as the plunger type vent control valve 120, position the vent control valve in its closed (first) position. With the vent port 62 closed, the cuff is inflated with the pump or the sphygmomanometer bulb to a pressure somewhat above, for example approximately 30 millimeters Hg, the expected systolic pressure. Once the cuff is inflated to the desired pressure, the user opens the vent port 62, either by opening a thumb screw or, if the bleed valve 10 is connected to a vent control valve, such as the plunger type vent control valve 120, positions the vent control valve in its open (second) position. With the vent port 62 now open to atmospheric pressure, the cuff will deflate through the bleed valve 10 in a controlled manner at the desired pressure decrease rate, for example at the American Heart Association recommended rate of approximately 2-3 mm Hg per heartbeat. As the bleed valve 10 is self-compensating for cuff pressure, the piston 70 will self-adjust the area of the orifice 85 within the bleed valve 10 to maintain the rate of decrease in cuff pressure relatively constant as the cuff deflates through the bleed valve 10. Once the diastolic blood pressure reading has been obtained the cuff will continue to deflate at the controlled rate. However, if the bleed valve 10 is coupled to a vent control valve having a third position, such as the vent control valve 120, wherein the bleed valve 10 can be bypassed to permit a direct venting of the cuff to atmosphere, the user may selectively reposition the vent control valve to its rapid deflate position and proceed to rapidly deflate the cuff.
It is contemplated that the bleed valve 10 will be factory-calibrated during manufacturing to provide a relatively constant pressure decrease rate at the aforementioned AHA recommend rate for adult blood pressure measurement when a typical adult cuff is used. The pressure decrease rate, as well as other operational characteristics of the bleed valve 10, are determined by the spring constant of the spring 80, by the preload on the spring, by the specific valve geometry (for example the taper angle for the conical transition section 65), and by the effective cross-sectional piston and valve orifice areas at the annular orifice 85. Those skilled in the art will recognize that the particular dimensions, spring selection, spring preload and other design factors may be selected to provide the desired operational characteristics. For the range of cuff sizes needed, that is from neonate cuffs to large adult cuffs, a proper selection of the spring, orifice area and piston area provide relative independence of the cuff pressure decrease rate relative to the cuff size range.
Since the bleed valve 10 operates in response to the pressure differential across the orifice, and not in response to the volume of air in the cuff, the operation of the bleed valve 10 provides a cuff pressure decrease rate that is theoretically dependent on cuff size. However, with proper selection of bleed valve components, this dependence has been found to be sufficiently small, so that the bleed valve 10 may be used with various size cuffs. Nevertheless, depending upon cuff size or the preference of the user, the bleed valve 10 may require field adjustment to provide a pressure change rate somewhat different than the factory-calibrated pressure change rate. For example, if the bleed valve is employed with a non-adult cuff or the adult patient has a heart beat elevated well above about sixty beats per minute, it may be desirable to adjust the rate of pressure decrease during deflation of the cuff through the bleed valve 10. The rate of pressure decrease may be adjusted by changing the preload on the spring 80. To do so, the user merely turns the end fitting clockwise or counter-clockwise as appropriate to further compress the spring 80 to increase the preload on the spring 80 or to lessen the compression of the spring 80 to decrease the preload on the spring 80.
While the present invention has been particularly shown and described with reference to the exemplary embodiments as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail and design may be effected therein without departing from the spirit and scope of the invention as defined by the claims.
