Method and apparatus for determining alveolar opening and closing

Abstract

The invention refers to a method for the regional determination of the alveolar opening and alveolar closing of the lung depending on the respiration pressure, wherein according to the method of electrical impedance tomography, an impedance signal is measured in at least one lung zone depending on the respiration pressure. The alveolar opening or closing of a lung zone is determined, in particular to enable an improved artificial respiration.

We claim:  
     
         1 . Method for determination of the alveolar opening and alveolar closing of the lung, comprising the steps of: 
 measuring according to the method of electrical impedance tomography an impedance signal (AU) in at least one lung zone depending on the respiration pressure,    determining from the impedance signal a first respiration pressure value which corresponds to the alveolar closing of the corresponding lung zone, and    determining from the impedance signal a second respiration pressure value which corresponds to the alveolar opening of the corresponding lung zone.    
     
     
         2 . Method according to  claim 1 , wherein for the corresponding lung zone the first respiration pressure value is found as soon as the mean change in the impedance signal based on breathing movements (A 1 , A 2 , A 1 ′, A 2 ′) falls below a first breathing movement comparative value and wherein the second respiration pressure value is found as soon as the mean change in the impedance signal due to breathing movements (A 1 , A 2 , A 1 ′, A 2 ′) moves above a fixed second breathing movement comparative value.  
     
     
         3 . Method according to  claim 2 , wherein based on a respiration pressure, with which the lung alveoli are opened in almost all the lung zones, the respiration pressure is reduced step by step, until in one lung zone alveolar closing of a lung zone is determined.  
     
     
         4 . Method according to  claim 2 , wherein the mean change of the impedance signal due to breathing movements (A 1 , A 2 , A 1 ′, A 2 ′) is determined based on the unaveraged mean square root of the impedance signal over a plurality of inspirations.  
     
     
         5 . Method according to  claim 2 , wherein the mean change in the impedance signal due to breathing movements is determined on the basis of an average peak to peak value of the impedance signal over a plurality of inspirations.  
     
     
         6 . Method according to  claim 2 , wherein the first breathing movement comparative value and/or the second breathing movement comparative value are predetermined.  
     
     
         7 . Method according to  claim 2 , wherein the first breathing movement comparative value and/or the second breathing movement comparative value are determined dynamically from the mean change in the impedance signal due to breathing movements in a different lung zone.  
     
     
         8 . Method according to  claim 7 , wherein the other lung zone is a zone which is above the lung zone concerned in the direction of the gravity vector.  
     
     
         9 . Method according to  claim 1 , wherein for the corresponding lung zone the first respiration pressure value is found as soon as the average change in the impedance signal due to the opening/collapse of the alveoli (B, B′) falls below a collapse comparative value and wherein the second respiration pressure value is found as soon as the average change in the impedance signal due to the opening/collapse of the alveoli (B, B′) moves above an opening comparative value.  
     
     
         10 . Method according to  claim 9 , wherein setting out from a respiration pressure wherein the lung alveoli are almost all open in one lung zone, the respiration pressure is reduced step by step, until in the lung zone an alveolar closing is found and in that setting out from a respiration pressure, wherein the lung alveoli in one lung zone are almost all closed, the respiration pressure is increased step by step until an alveolar opening is found in the lung zone.  
     
     
         11 . Method according to  claim 9 , wherein the average change in the impedance signal due to the collapse/opening of the alveoli (B, B′) is determined on the basis of the average gradient of the impedance signal depending on the respiration pressure.  
     
     
         12 . Method according to  claim 9 , wherein the average change in the impedance signal due to the collapse/opening of the alveoli (B, B′) is determined on the basis of a straight line adaptation according to the Gauβ compensation calculation.  
     
     
         13 . Method according to  claim 9 , wherein the collapse comparative value and/or the opening comparative value are predetermined.  
     
     
         14 . Method according to  claim 9 , wherein the collapse comparative value and/or the opening comparative value are determined dynamically from the average change in the impedance signal due to the collapse of the alveoli in another lung zone.  
     
     
         15 . Method according to  claim 14 , wherein the other lung zone is a zone which is above the lung zone concerned in the direction of the gravity vector.  
     
     
         16 . Method according to  claim 1 , wherein for a corresponding lung zone the first respiration pressure value is found as soon as the average change in the impedance signal due to respiration pressure changes (C, C′) falls below a first respiration comparative value and wherein the second respiration pressure value is found, as soon as the average change in the impedance signal due to respiration pressure changes (C, C′) moves above a fixed second respiration pressure comparative value.  
     
     
         17 . Method according to  claim 16 , wherein on the basis of a respiration pressure at which the lung alveoli are open in almost all lung zones, the respiration pressure is reduced step by step, until in one lung zone an alveolar closing of a lung zone is found.  
     
     
         18 . Method according to  claim 16 , wherein the change in the impedance signal due to respiration pressure changes (C, C′) is determined on the basis of the average initial gradient of the impedance signal after a sudden increase in respiration pressure.  
     
     
         19 . Method according to  claim 16 , wherein the change in the impedance signal due to respiration pressure changes (C, C′) is determined on the basis of the time constant with which the impedance signal follows a change in respiration pressure.  
     
     
         20 . Method according to  claim 16 , wherein the first respiration pressure comparative value and/or the second respiration pressure comparative value are prescribed.  
     
     
         21 . Method according to  claim 16 , wherein the first respiration pressure comparative value and/or the second respiration pressure comparative value is/are determined dynamically from the average change in the impedance signal due to respiration pressure changes in another lung zone.  
     
     
         22 . Method according to  claim 21 , wherein the other lung zone is a zone which is above the lung zone concerned in the direction of the gravity vector.  
     
     
         23 . Method according to  claim 1 , wherein the lung is subdivided into a plurality of zone planes in the direction of the gravity vector.  
     
     
         24 . Method according to  claim 1 , wherein the lung is divided into a plurality of radial sectors, wherein the centre point axis of the sectors is located in the direction of the gravity vector.  
     
     
         25 . Apparatus for determination of the alveolar opening and the alveolar closing of the lung, comprising: 
 means for measuring according to the method of electrical impedance tomography an impedance signal (AU) in at least one lung zone depending on the respiration pressure,    means for determining from the impedance signal a first respiration pressure value which corresponds to the alveolar closing of the corresponding lung zone, and    means for determining from the impedance signal a second respiration pressure value which corresponds to the alveolar opening of the corresponding lung zone.    
     
     
         26 . Apparatus according to  claim 25 , comprising: 
 a plurality of electrodes which are applied around the thorax,    an electrical impedance tomograph for the control of individual electrodes and for the evaluation of impedance signals on electrodes which are not controlled, in order to obtain a regional impedance signal in the thorax, and    a processing unit to evaluate the regional impedance signals for determining the first respiration pressure value and the second respiration pressure value.    
     
     
         27 . Apparatus according to  claim 25 , wherein a sensor is provided for the measurement of the changing periphery of the thorax on the basis of breathing movements and in that the electrical impedance tomograph has a correction unit, wherein the change in the impedance signals of the electrodes are corrected on the basis of breathing movements by including the sensor signal.  
     
     
         28 . Apparatus according to  claim 25 , further comprising: 
 an artificial respiration unit, and    a control unit which is connected to the artificial respiration unit and the processing unit, whereby the first respiration pressure value and the second respiration pressure value is fed from the processing unit to the control unit to control the artificial respiration.    
     
     
         29 . Apparatus according to  claim 28 , wherein the lower respiration pressure of artificial respiration is controlled such that a predetermined pressure is artificially maintained in the lung, which just makes possible keeping open all the alveoli.  
     
     
         30 . Apparatus according to  claim 25 , further comprising: 
 a monitoring unit for monitoring the first respiration pressure value and the second respiration pressure value.