Capillary refill time diagnostic apparatus and methods

Abstract

An apparatus for measuring capillary refill time has a measurement module containing at least two radiation sources and at least one detector configured to detect radiation from each source that interacts with and is received from a measurement region of a patient or subject. One radiation source may be characterized by a wavelength that is absorbed substantially equally by oxyhemoglobin and deoxyhemoglobin. The other radiation source may be substantially unaffected by the presence or absence of blood in the measurement region. The measurement module may be applied against a measurement region of a patient for a first time period, and the released from the measurement region for a second time period, and detected signals processed to quantitatively evaluate capillary refill time.

What is claimed is: 
     
         1 . An apparatus for measuring capillary refill time comprising:
 at least one source configured to emit first radiation having a first wavelength and configured to emit second radiation having a second wavelength as a reference wavelength and configured to radiate a measurement region of a subject with the first radiation and the second radiation, wherein the first wavelength has approximately equal absorption by same amounts of oxyhemoglobin and deoxyhemoglobin for detecting a rate of change in an amount of blood in the measurement region;   at least one detector configured to detect the first radiation and the second radiation received from the measurement region; and   a controller configured to activate the at least one source and receive first signals from the at least one detector that are indicative of the first radiation and second signals from the at least one detector that are indicative of the second radiation.   
     
     
         2 . The apparatus of  claim 1 , further comprising a probe having a contact member that is configured to be applied to the measurement region and force blood from the measurement region. 
     
     
         3 . The apparatus of  claim 2 , wherein the contact member includes a surface configured to be applied against the measurement region to exclude blood from a capillary bed and to be controllably released from the measurement region to allow perfusion of blood into the capillary bed. 
     
     
         4 . The apparatus of  claim 2 , wherein the surface of the contact member is convex. 
     
     
         5 . The apparatus of  claim 2 , wherein at least a portion of the contact member comprising the surface is transparent to the first radiation and second radiation. 
     
     
         6 . The apparatus of  claim 5 , wherein the at least one source is configured to emit the first and second radiations through the at least a portion of the contact member and the at least one detector is configured to detect the first radiation and/or second radiation returned through the at least a portion of the contact member. 
     
     
         7 . The apparatus of  claim 2 , wherein at least a portion of the contact member is configured to at least partially collimate or at least partially focus the first radiation and/or the second radiation. 
     
     
         8 . The apparatus of  claim 1 , wherein the first wavelength is in a range between about 500 nm and about 550 nm. 
     
     
         9 . The apparatus of  claim 1 , wherein the second wavelength is in a range between about 600 nm and about 750 nm and is substantially unaffected by the presence or absence of blood in the measurement region. 
     
     
         10 . The apparatus of  claim 1 , wherein the controller is further configured to:
 cause the at least one source to emit first and second radiations during a first period;   calculate first ratios, for a first plurality of times during the first period, of the first signals and the second signals received from the at least one detector during the first period;   identify an end to the first period based on a first trend in the first ratios or a value of one of the first ratios;   cause the at least one source to emit first and second radiations during a second period; and   calculate second ratios, for a second plurality of times during the second period, of third signals and fourth signals received from the at least one detector, wherein the third signals are representative of an amount of the first radiation received from the measurement region and the fourth signals are representative of an amount of the second radiation received from the measurement region during the second period.   
     
     
         11 . The apparatus of  claim 1 , wherein the at least one detector comprises:
 at least one first detector including a first radiation filter, the at least one first detector and first radiation filter configured to detect substantially only the first radiation received from the measurement region; and   at least one second detector including a second radiation filter, the at least one second detector and second radiation filter configured to detect substantially only the second radiation received from the measurement region.   
     
     
         12 . A method for measuring capillary refill time comprising:
 activating, by a controller, at least one source;   emitting, by the at least one source, a first radiation having a first wavelength onto a measurement region of a subject, wherein the first wavelength has approximately equal absorption by same amounts of oxyhemoglobin and deoxyhemoglobin for detecting a rate of change in an amount of blood in the measurement region;   emitting, by the at least one source, a second radiation having a second wavelength onto the measurement region, wherein the second radiation comprises a reference wavelength;   detecting, by at least one detector, the first radiation and the second radiation received from the measurement region;   receiving, with a controller, first signals from the at least one detector that are indicative of the first radiation received from the measurement region and second signals received from the at least one detector that are indicative of the second radiation signals received from the measurement region.   
     
     
         13 . The method of  claim 12 , further comprising:
 controllably applying a contact member of a probe against the measurement region to exclude blood from a capillary bed; and   releasing the contact member from the measurement region to allow perfusion of blood into the capillary bed.   
     
     
         14 . The method of  claim 12 , further comprising modulating, by the controller, the at least one source to produce modulations in intensity of the first radiation. 
     
     
         15 . The method of  claim 13 , wherein controllably applying the contact member comprises providing an indication to a user to apply the contact member to the measurement region. 
     
     
         16 . The apparatus of  claim 1 , wherein the controller is further configured to determine a value indicative of capillary refill time in the measurement region based on an analysis of the first signals and the second signals. 
     
     
         17 . The apparatus of  claim 1 , wherein the at least one detector comprises:
 a first detector having an optical wavelength filter configured to detect the first wavelength; and   a second detector configured to detect the second wavelength.   
     
     
         18 . The apparatus of  claim 2 , wherein the probe, the at least one source, the at least one detector, and the controller are combined in one physical assembly. 
     
     
         19 . The apparatus of  claim 10 , wherein the controller is further configured to calculate a capillary refill time based on a second trend of the second ratios or a value of one of the second ratios. 
     
     
         20 . The apparatus of  claim 2 , wherein the probe further includes a temperature sensor arranged to sense a temperature of the measurement region.