Self-compensating blood pressure bleed valve

Abstract

A bleed flow valve for venting air from a blood pressure cuff includes a valve body having an axially extending central bore. 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. A piston is disposed within the central bore of the valve body and is axially translatable within the central bore of the valve body. An annular orifice is defined between an outer circumferential surface on the piston and the transition section of the central bore. The bleed valve is self-compensating as the pressure within the cuff 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 deflation process.

1 . A bleed valve for controlling the pressure change rate in a reservoir of fluid under pressure when venting fluid therefrom through said valve, said valve comprising: 
 a valve body having a central bore extending axially therethrough, the central bore having a transition section transitioning from a relatively larger diameter upstream of the transition section to a relatively smaller diameter downstream of the transition section, a fluid inlet port opening through said valve body into the central bore upstream of the transition section, and a fluid outlet port opening through said value body into the central bore downstream of the transition section;    a piston disposed within the central bore of said valve body, said piston having an outer circumferential surface facing the transition section of the central bore thereby establishing an annular orifice defining a flow area between the outer circumferential surface on said piston and the transition section of the central bore, said piston being axially translatable within the central bore of said valve body;    a biasing device operatively associated with said piston for exerting a force on said piston, said biasing device acting to translate said piston in an upstream direction in opposition to a fluid pressure force on said piston acting to translate said piston in a downstream direction, whereby said 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 pressure change rate in said reservoir.    
   
   
       2 . A bleed valve as recited in  claim 1  wherein said biasing device comprises a spring member and a preload device, said preload device for compressing said spring member to establish an initial preload force of said spring on said piston, said spring acting to translate said piston in an upstream direction.  
   
   
       3 . A bleed valve as recited in  claim 2  wherein: 
 said spring member comprises a compressible coil spring disposed about a downstream portion of said piston; and    said preload device comprises a closure member disposed within the central bore downstream of and abutting said spring member, said closure member being selectively axially positioned so as to adjust the preload force on said piston.    
   
   
       4 . A bleed valve as recited in  claim 1  wherein the transition section comprises a step transition from the relatively larger diameter to the relatively smaller diameter.  
   
   
       5 . A bleed valve as recited in  claim 4  wherein a portion of the outer circumferential surface of the piston faces the step transition section and has a tapered surface.  
   
   
       6 . A bleed valve as recited in  claim 1  wherein the transition section comprises a tapered surface facing the outer circumferential surface of said piston.  
   
   
       7 . A bleed valve as recited in  claim 6  wherein said piston has a circumferential ridge extending thereabout.  
   
   
       8 . A bleed valve as recited in  claim 7  wherein the circumferential ridge has a tapered outer circumferential surface.  
   
   
       9 . A bleed valve as recited in  claim 1  further comprising a first closure member closing a first end of said valve body and a second closure member closing a second end of said valve body.  
   
   
       10 . A bleed valve as recited in  claim 9  further comprising a low pressure stop supported by said first closure member, said low pressure stop being selectively axially translatable.  
   
   
       11 . A bleed valve as recited in  claim 10  wherein said first closure member comprises an end cap.  
   
   
       12 . A bleed valve as recited in  claim 9  further comprising a high pressure stop supported by said second closure member, said high pressure stop being selectively axially translatable.  
   
   
       13 . A bleed valve as recited in  claim 12  wherein said second closure member comprises an end plug.  
   
   
       14 . A bleed valve as recited in  claim 12  wherein said high pressure stop limits translation of said piston so as to prevent the outer circumferential surface of said piston from contacting the transition section of the central bore.  
   
   
       15 . A bleed valve for controlling the rate of change of pressure in an inflated blood pressure cuff when venting air from the blood pressure cuff to deflate the blood pressure cuff, said valve comprising: 
 an axially elongated valve body having a first end and a second end and having a central bore extending axially therethrough, the central bore having a first generally cylindrical cavity, a second generally cylindrical cavity, and third cavity disposed between the first and second cavities, said third cavity having a transition section;    a first closure member closing the first end of said valve body;    a second closure member closing the second end of said valve body;    a piston disposed within the central bore of said valve body, said piston having a generally cylindrical body including an outer circumferential surface on said valve body facing the transition section of the central bore thereby establishing an annular orifice defining a flow area between the outer circumferential surface on said piston and the transition section of the central bore, said piston being axially translatable within the central bore of said valve body;    a first port opening through said valve body into said first cavity upstream of said transition section, said first port pneumatically coupled to the blood pressure cuff;    a second port opening through said valve body into said third cavity downstream of said transition section, said second port being a vent; and    a biasing device operatively associated with said piston for exerting a force on said piston acting to translate said piston in an upstream direction in opposition to a fluid pressure force on said piston acting to translate said piston in a downstream direction, whereby said 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.    
   
   
       16 . A bleed valve as recited in  claim 15  wherein said third cavity of the central bore of said valve body has a tapered transition section.  
   
   
       17 . A bleed valve as recited in  claim 15  wherein said piston has a tapered outer circumferential surface facing the transition section of the central bore.  
   
   
       18 . A bleed valve as recited in  claim 15  wherein said biasing device comprises a spring member and a preload device, said preload device for compressing said spring member to establish an initial force of said spring on said piston, said spring acting to translate said piston in an upstream direction.  
   
   
       19 . A bleed valve as recited in  claim 15  further comprising a low pressure stop supported by said first closure member, said low pressure stop being selectively axially translatable.  
   
   
       20 . A bleed valve as recited in  claim 15  further comprising a high pressure stop supported by said second closure member, said high pressure stop being selectively axially translatable.  
   
   
       21 . A bleed valve as recited in  claim 15  further comprising a vent control valve operatively associated with said second port of said bleed valve, said vent control valve being selectively positioned in a first position wherein bleed flow can not vent through said second port of said bleed valve to atmospheric pressure and a second position wherein bleed flow can vent through said second port of said bleed valve.  
   
   
       22 . A bleed valve as recited in  claim 15  wherein said 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.  
   
   
       23 . A bleed valve as recited in  claim 15  further comprising a vent control valve having: 
 a vent control valve body having a cavity therein, said vent control valve body having a first port opening to the cavity and in flow communication with said blood pressure cuff, a second port opening to the cavity and in flow communication with said second port of said bleed valve, and a third port opening to the cavity and venting to atmospheric pressure; and    a member operatively associated with said vent control valve body, said member selectively positioned in a first position wherein neither of the first port nor the second port of said vent control valve is in flow communication with the third port of said vent control valve, in a second position wherein only the second port of said vent control valve is in flow communication with the third port of said vent control valve, and a third position wherein only the first port of said vent control valve is in flow communication with the third port of said vent control valve.    
   
   
       24 . A method for venting air from an inflated blood pressure cuff through a bleed valve at a relatively constant cuff pressure change rate comprising the steps of: 
 providing an annular orifice between an upstream cavity and a downstream cavity in said bleed valve, the annular orifice providing a flow path having a variable flow area between the upstream cavity and the downstream cavity;    passing air under pressure from the blood pressure cuff to the upstream cavity;    venting air from the downstream cavity; and    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.    
   
   
       25 . A method as recited in  claim 24  further comprising 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.  
   
   
       26 . A method as recited in  claim 24  further comprising 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 an increase in the pressure of the air within the upstream cavity to a predetermined minimum flow area at a predetermined relatively high pressure.  
   
   
       27 . A method as recited in  claim 24  wherein the step of 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 comprises increasing the flow area in response to a decrease in the pressure of the air within the upstream cavity and decreasing the flow area in response to an increase in the pressure of the air within the upstream cavity.  
   
   
       28 . A method as recited in  claim 27  further comprising the step of: 
 exerting a biasing force on a piston, said biasing force acting to translate the piston in an upstream direction in opposition to a fluid pressure force on the piston, the fluid pressure force 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 said relatively constant cuff pressure change rate.    
   
   
       29 . A method as recited in  claim 28  further comprising the step of: 
 establishing an initial biasing force on the piston acting to translate the piston in an upstream direction, whereby a desired pressure change rate is preset.    
   
   
       30 . A method as recited in  claim 28  further comprising the step of: 
 adjusting the biasing force on the piston acting to translate the piston in an upstream direction, whereby a desired pressure change rate may be selectively set.    
   
   
       31 . A method as recited in  claim 28  further comprising the step of: 
 adjusting the biasing force on the piston acting to translate the piston in an upstream direction in response to substantially large changes in cuff size, whereby a desired pressure change rate may be selectively set.    
   
   
       32 . A method as recited in  claim 28  further comprising the step of: 
 adjusting the biasing force on the piston acting to translate the piston in an upstream direction in response to a heart rate of a patient, whereby a desired pressure change rate may be selectively set.    
   
   
       33 . A method as recited in  claim 24  wherein the step of providing an annular orifice between an upstream cavity and a downstream cavity in said bleed valve comprises providing a valve body having a central bore extending axially therethrough and having a transition section and an axially translatable piston disposed within the central bore of the valve body, the piston having an outer circumferential surface facing the transition section of the central bore thereby defining the annular orifice.  
   
   
       34 . A method as recited in  claim 33  wherein the step of providing an annular orifice between an upstream cavity and a downstream cavity in said bleed valve further comprises providing a valve body having a central bore having a tapered transition section.  
   
   
       35 . A method as recited in  claim 33  wherein the step of providing an annular orifice between an upstream cavity and a downstream cavity in said bleed valve further comprises providing a piston having a tapered outer circumferential surface facing the transition section of the central bore.  
   
   
       36 . A method as recited in  claim 33  further comprising 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 said piston acting to translate said piston in a downstream direction, whereby said piston self adjusts axially within the central bore to adjust the annular orifice so as to maintain a relatively constant cuff pressure change rate.    
   
   
       37 . A method as recited in  claim 24  wherein 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 comprises 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.