Non-invasive intracranial monitor

Abstract

A method of estimating at least one intracranial hemodynamic parameter in a subject, the method comprising: a) obtaining data of changes in electrical impedance across the subject's head as a function of time; b) analyzing the data; and c) estimating one or more of intracranial pressure, cerebral blood volume, and a factor related to at least one of cerebral perfusion pressure and a mean transit time through cerebral capillaries.

1 . A method of estimating at least one intracranial hemodynamic parameter in a subject, the method comprising:
 obtaining data relating to changes in electrical impedance in a head of the subject;   analyzing the data; and   estimating one or more of intracranial pressure, cerebral blood volume, and a factor related to at least one of cerebral perfusion pressure and a mean transit time through cerebral capillaries.   
     
     
         2 . A method according to  claim 1 , wherein analyzing the data comprises one or more of smoothing the data, removing variations in the data due to the subject's breathing cycle, and selecting data only from a portion of the subject's cardiac cycles. 
     
     
         3 . A method according to  claim 1 , wherein analyzing the data comprises finding a measure of the range of impedance, and estimating comprises estimating one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the range of impedance. 
     
     
         4 . A method according to  claim 1 , wherein analyzing the data comprises finding a measure of a maximum rate of fall of the impedance, and estimating comprises estimating one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the maximum rate of fall. 
     
     
         5 . A method according to  claim 1 , wherein analyzing the data comprises finding a measure of a maximum rate of rise of the impedance, and estimating comprises estimating the factor related to one or more of cerebral perfusion pressure and the mean transit time through cerebral capillaries, responsive to the measure of the maximum rate of rise. 
     
     
         6 . A method according to  claim 5 , wherein the factor is related to cerebral perfusion pressure. 
     
     
         7 . A method according to  claim 5 , wherein the factor is related to the mean transit time through cerebral capillaries. 
     
     
         8 . A method according to  claim 1 , wherein analyzing the data comprises finding a measure of a height of at least one of a first local maximum of impedance and a first local minimum in rate of rise of impedance, following a diastolic phase of a cardiac cycle, and estimating comprises estimating at least one of cerebral perfusion pressure, intracranial pressure, and the mean transit time through cerebral capillaries using at least one of the height of the first local maximum of impedance and the first local minimum of rate of rise of impedance. 
     
     
         9 . A method according to  claim 8 , wherein analyzing the data comprises normalizing the measure to an additional measure of a height of a second local maximum in impedance, following the diastolic phase of the cardiac cycle and at least one of the first local maximum of impedance and the minimum in rate of rise of impedance. 
     
     
         10 . A method according to  claim 8 , wherein the factor is related to cerebral perfusion pressure. 
     
     
         11 . A method according to  claim 8 , wherein the factor is related to the mean transit time through cerebral capillaries. 
     
     
         12 . A method according to  claim 8 , wherein analyzing the data also comprises finding a measure of a maximum rate of rise of the impedance, and estimating the factor related to one or more of cerebral perfusion pressure and the mean transit time through cerebral capillaries is responsive to a combination of the measure of a maximum rate of rise of the impedance, and the measure of a first local maximum in impedance or first local minimum in rate of rise of impedance. 
     
     
         13 . A method according to  claim 1 , wherein analyzing the data comprises normalizing to a measure of the total range of impedance. 
     
     
         14 . A method according to  claim 1 , wherein analyzing the data comprises finding a measure of a latency time, and estimating comprising estimating intracranial pressure responsive to the measure of the latency time. 
     
     
         15 . A method according to  claim 1 , wherein analyzing the data comprises normalizing time to a cardiac period. 
     
     
         16 . A method according to  claim 1 , wherein analyzing the data comprises smoothing of data over time. 
     
     
         17 . A method according to  claim 1 , wherein analyzing the data comprises finding a measure of the at least one intracranial parameter and averaging the measure over a plurality of cardiac cycles. 
     
     
         18 . A method according to  claim 1 , wherein analyzing the data comprises averaging data from a same phase of different cardiac cycles. 
     
     
         19 . A method according to  claim 1 , wherein analyzing the data comprises excluding values of impedance, or values of rate of change of impedance, or both, that do not fall within an expected range of magnitude or do not occur within an expected range of time relative to the cardiac cycle, or both. 
     
     
         20 . A method according to  claim 1 , wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject undergoing surgery. 
     
     
         21 . A method according to  claim 1 , wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject who is a stroke patient. 
     
     
         22 . A method according to  claim 1 , wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject suffering from a traumatic head injury. 
     
     
         23 . A method according to  claim 1 , wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject suffering from a chronic condition. 
     
     
         24 . A method according to  claim 1 , wherein the at least one hemodynamic parameter is monitored substantially continuously for a subject who is a neonate. 
     
     
         25 . Apparatus for estimating one or more intracranial hemodynamic parameters, the apparatus comprising:
 at least one controller configured to:   obtain electrical impedance data, associated with a head of a subject, relative to timing of a cardiac cycle; and   estimate from the data at least one of intracranial pressure, cerebral blood volume, and a factor related to one or more of cerebral perfusion pressure and a mean transit time through cerebral capillaries.   
     
     
         26 . Apparatus according to  claim 25 , wherein the controller is configured to analyze the data to find a measure of the range of impedance, and to estimate one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the range of impedance. 
     
     
         27 . Apparatus according to  claim 25 , wherein the controller is configured to analyze the data to find a measure of a maximum rate of fall of impedance, and to estimate one or more of intracranial pressure and cerebral blood volume, responsive to the measure of the maximum rate of fall of impedance. 
     
     
         28 . Apparatus according to  claim 25 , wherein the controller is configured to analyze the data to find a measure of a maximum rate of rise of impedance, and to estimate the factor related to one or more of cerebral perfusion pressure and the mean transit time, responsive to the measure of the maximum rate of rise of impedance. 
     
     
         29 . Apparatus according to  claim 25 , wherein the controller is configured to analyze the data to find a measure of a height of at least one of a first local maximum of impedance and a first local minimum in rate of rise of impedance, following a diastolic phase of a cardiac cycle, and to estimate at least one of cerebral perfusion pressure, intracranial pressure, and mean transit time, using at least one of the height of the first local maximum of impedance and the minimum in rate of rise of impedance. 
     
     
         30 . Apparatus according to  claim 25 , wherein the controller is configured to analyze the data to find a measure of a latency time, and to estimate intracranial pressure, responsive to the measure of the latency time. 
     
     
         31 . Apparatus according to  claim 29 , wherein the controller is configured to analyze the data to normalize the measure to an additional measure of a second local maximum in impedance, following the diastolic phase of the cardiac cycle and at least one of the first local maximum of impedance and the minimum in rate of rise of impedance. 
     
     
         32 . Apparatus according to  claim 25 , wherein the controller is configured to estimate the intracranial pressure directly from a current value of the impedance data.