Apparatus and method for measuring pulse transit time

Abstract

In a method of measuring pulse transit time of a living subject, first and second pulse wave signals are produced by sensing the pulse at first and second pulse points, respectively, the first and second pulse points being spaced from one another. The first and second pulse wave signals are differentiated, and based on the results, corresponding points of the first and second pulse wave signals are selected (e.g., points of maximum slope). The time delay between the selected points is determined, thus yielding the pulse transit time. A preferred apparatus measures pulse transit time using at least one fiberoptic pulse sensor including a fused-fiber coupling region having at least a portion that can be deflected without putting the coupling region under tension.

What is claimed is:  
     
         1 . A method of monitoring heartbeat of a living subject, comprising: 
 coupling a pulse sensor to a pulse point of the subject through a fluid contained in a fluid-filled structure, the fluid-filled structure having a portion secured to the subject with a surface positioned over the pulse point, such that pulsations are transmitted from the pulse point to the pulse sensor via the fluid-filled structure, the pulse sensor providing an output signal that changes in accordance with the pulsations; and    monitoring the output signal from the pulse sensor over a period of time while maintaining the coupling of the pulse sensor to the pulse point through a set amount of the fluid, said period of time being of sufficient duration that said output signal is subject to modulation due to a plurality of breathing cycles.    
     
     
         2 . A method according to  claim 1 , wherein said fluid-filled structure includes a pair of surfaces coupled through a fluid column, one of said pair of surfaces being the surface positioned over the pulse point.  
     
     
         3 . A method according to  claim 2 , wherein the pulse point is associated with the radial artery.  
     
     
         4 . A method according to  claim 2 , wherein the pulse point is associated with the brachial artery.  
     
     
         5 . A method according to  claim 2 , wherein the pulse sensor is disposed at the other of said pair of surfaces.  
     
     
         6 . A method according to  claim 5 , wherein said other surface is an elastic surface, the pulse sensor has a portion engaged with said elastic surface and which deflects in response to pulsations transmitted by said elastic surface, said output signal changing in accordance with the deflection of the pulse sensor.  
     
     
         7 . A method according to  claim 6 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a fused-fiber coupling region configured such that at least a portion of said coupling region can be deflected to change a distribution of light from said input optical fiber to said output optical fibers with said coupling region being subjected to substantially no tension.  
     
     
         8 . A method according to  claim 6 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a substantially U-shaped fused-fiber coupling region which can be deflected to change a distribution of light from said input optical fiber to said output optical fibers.  
     
     
         9 . A method according to  claim 1 , wherein said fluid-filled structure includes a fluid-filled pillow.  
     
     
         10 . A method according to  claim 9 , wherein said fluid-filled pillow is secured to an arm of the subject.  
     
     
         11 . A method according to  claim 10 , wherein the pulse point is associated with the radial artery.  
     
     
         12 . A method according to  claim 10 , wherein the pulse point is associated with the brachial artery.  
     
     
         13 . A method according to  claim 9 , wherein said fluid-filled pillow has an elastic surface, the pulse sensor has a portion engaged with said elastic surface and which deflects in response to pulsations transmitted by said elastic surface, said output signal changing in accordance with the deflection of the pulse sensor.  
     
     
         14 . A method according to  claim 13 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a fused-fiber coupling region configured such that at least a portion of said coupling region can be deflected to change a distribution of light from said input optical fiber to said output optical fibers with said coupling region being subjected to substantially no tension.  
     
     
         15 . A method according to  claim 13 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a substantially U-shaped fused-fiber coupling region which can be deflected to change a distribution of light from said input optical fiber to said output optical fibers.  
     
     
         16 . Apparatus for monitoring heartbeat of a living subject, comprising: 
 a pulse sensor coupled to a pulse point of the subject through a fluid contained in a fluid-filled structure, the fluid-filled structure having a portion secured to the subject with a surface positioned over the pulse point, such that pulsations are transmitted from the pulse point to the pulse sensor via the fluid-filled structure, the pulse sensor providing an output signal that changes in accordance with the pulsations; and    a system operative to monitor the output signal from the pulse sensor over a period of time in which the coupling of the pulse sensor to the pulse point is maintained through a set amount of the fluid for a sufficient duration that said output signal is subject to modulation due to a plurality of breathing cycles.    
     
     
         17 . An apparatus according to  claim 16 , wherein said fluid-filled structure includes a pair of surfaces coupled through a fluid column, one of said pair of surfaces being the surface positioned over the pulse point.  
     
     
         18 . An apparatus according to  claim 17 , wherein the pulse point is associated with the radial artery.  
     
     
         19 . An apparatus according to  claim 17 , wherein the pulse point is associated with the brachial artery.  
     
     
         20 . An apparatus according to  claim 17 , wherein the pulse sensor is disposed at the other of said pair of surfaces.  
     
     
         21 . An apparatus according to  claim 20 , wherein said other surface is an elastic surface, the pulse sensor has a portion engaged with said elastic surface and which deflects in response to pulsations transmitted by said elastic surface, said output signal changing in accordance with the deflection of the pulse sensor.  
     
     
         22 . An apparatus according to  claim 21 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a fused-fiber coupling region configured such that at least a portion of said coupling region can be deflected to change a distribution of light from said input optical fiber to said output optical fibers with said coupling region being subjected to substantially no tension.  
     
     
         23 . An apparatus according to  claim 21 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a substantially U-shaped fused-fiber coupling region which can be deflected to change a distribution of light from said input optical fiber to said output optical fibers.  
     
     
         24 . An apparatus according to  claim 16 , wherein said fluid-filled structure includes a fluid-filled pillow.  
     
     
         25 . An apparatus according to  claim 24 , wherein said fluid-filled pillow is secured to an arm of the subject.  
     
     
         26 . An apparatus according to  claim 25 , wherein the pulse point is associated with the radial artery.  
     
     
         27 . An apparatus according to  claim 25 , wherein the pulse point is associated with the brachial artery.  
     
     
         28 . An apparatus according to  claim 24 , wherein said fluid-filled pillow has an elastic surface, the pulse sensor has a portion engaged with said elastic surface and which deflects in response to pulsations transmitted by said elastic surface, said output signal changing in accordance with the deflection of the pulse sensor.  
     
     
         29 . An apparatus according to  claim 28 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a fused-fiber coupling region configured such that at least a portion of said coupling region can be deflected to change a distribution of light from said input optical fiber to said output optical fibers with said coupling region being subjected to substantially no tension.  
     
     
         30 . An apparatus according to  claim 28 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a substantially U-shaped fused-fiber coupling region which can be deflected to change a distribution of light from said input optical fiber to said output optical fibers.  
     
     
         31 . Apparatus for monitoring heartbeat of a living subject, comprising: 
 a structure constructed to contain a fluid and having a portion constructed to be secured to the subject with a surface positioned over a pulse point of the subject to provide coupling of the pulse point to the fluid;    a pulse sensor arranged to be coupled to the pulse point through the fluid and providing an output signal that changes in accordance with pulsations received from the pulse point via the fluid; and    a system operative to monitor the output signal from the pulse sensor over a period of time in which the coupling of the pulse sensor to the pulse point is maintained through a set amount of the fluid for a sufficient duration that said output signal is subject to modulation due to a plurality of breathing cycles.    
     
     
         32 . An apparatus according to  claim 31 , wherein said structure includes a pair of surfaces, one of which is the surface to be positioned over the pulse point, and a portion to define a fluid column to couple said pair of surfaces via the fluid.  
     
     
         33 . An apparatus according to  claim 32 , wherein the pulse point is associated with the radial artery.  
     
     
         34 . An apparatus according to  claim 32 , wherein the pulse point is associated with the brachial artery.  
     
     
         35 . An apparatus according to  claim 32 , wherein the pulse sensor is disposed at the other of said pair of surfaces.  
     
     
         36 . An apparatus according to  claim 35 , wherein said other surface is an elastic surface, the pulse sensor has a portion disposed to engage said elastic surface and which deflects in response to pulsations transmitted by said elastic surface, said output signal changing in accordance with the deflection of the pulse sensor.  
     
     
         37 . An apparatus according to  claim 36 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a fused-fiber coupling region configured such that at least a portion of said coupling region can be deflected to change a distribution of light from said input optical fiber to said output optical fibers with said coupling region being subjected to substantially no tension.  
     
     
         38 . An apparatus according to  claim 36 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a substantially U-shaped fused-fiber coupling region which can be deflected to change a distribution of light from said input optical fiber to said output optical fibers.  
     
     
         39 . An apparatus according to  claim 31 , wherein said structure includes a pillow to contain a portion of the fluid.  
     
     
         40 . An apparatus according to  claim 39 , wherein said structure includes a portion constructed to secure said pillow to an arm of the subject.  
     
     
         41 . An apparatus according to  claim 40 , wherein the pulse point is associated with the radial artery.  
     
     
         42 . An apparatus according to  claim 40 , wherein the pulse point is associated with the brachial artery.  
     
     
         43 . An apparatus according to  claim 39 , wherein said pillow has an elastic surface, the pulse sensor has a portion disposed to engage said elastic surface and which deflects in response to pulsations transmitted by said elastic surface, said output signal changing in accordance with the deflection of the pulse sensor  
     
     
         44 . An apparatus according to  claim 43 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a fused-fiber coupling region configured such that at least a portion of said coupling region can be deflected to change a distribution of light from said input optical fiber to said output optical fibers with said coupling region being subjected to substantially no tension.  
     
     
         45 . An apparatus according to  claim 43 , wherein the pulse sensor is a fiberoptic coupler sensor in which at least one input optical fiber is joined to a plurality of output optical fibers through a substantially U-shaped fused-fiber coupling region which can be deflected to change a distribution of light from said input optical fiber to said output optical fibers.  
     
     
         46 . An apparatus according to  claim 1 , wherein said portion of said structure is constructed to be secured about the arm.  
     
     
         47 . An apparatus according to  claim 16 , wherein said portion of said structure is constructed to be secured about the wrist.  
     
     
         48 . An apparatus according to  claim 8 , wherein said coupling region is disposed substantially in a plane, and is deflected by said elastic surface along a direction perpendicular to said plane.  
     
     
         49 . An apparatus according to  claim 15 , wherein said coupling region is disposed substantially in a plane, and is deflected by said elastic surface along a direction perpendicular to said plane.  
     
     
         50 . An apparatus according to  claim 23 , wherein said coupling region is disposed substantially in a plane, and is deflected by said elastic surface along a direction perpendicular to said plane.  
     
     
         51 . An apparatus according to  claim 30 , wherein said coupling region is disposed substantially in a plane, and is deflected by said elastic surface along a direction perpendicular to said plane.  
     
     
         52 . An apparatus according to  claim 38 , wherein said coupling region is disposed substantially in a plane, and is deflected by said elastic surface along a direction perpendicular to said plane.  
     
     
         53 . An apparatus according to  claim 45 , wherein said coupling region is disposed substantially in a plane, and is deflected by said elastic surface along a direction perpendicular to said plane.