Ventilatory assistance for treatment of cardiac failure and cheyne-stokes breathing

Abstract

Method and apparatus for the treatment of cardiac failure, Cheyne Stokes breathing or central sleep apnea are disclosed. A subject is provided with ventilatory support. Respiratory airflow is determined. From the respiratory airflow are derived a measure of instantaneous ventilation (for example half the absolute value of the respiratory airflow) and a measure of longterm average ventilation. A target ventilation is taken as 95% of the longterm average ventilation. The instantaneous ventilation is fed as the input signal to a clipped integral controller, with the target ventilation as the reference signal. The output of the controller determines the degree of ventilatory support. A third measure of ventilation, for example instantaneous ventilation low pass filtered with a time constant of 5 seconds, is calculated. Ventilatory support is in phase with the subject's respiratory airflow to the fuzzy extent that this ventilation is above target, and at a preset rate conversely.

1 . A method for treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising the steps of:
 providing a subject with ventilatory support;   deriving a measure of the subject's instantaneous ventilation; and   adjusting the degree of ventilatory support to reduce changes in said measure of instantaneous ventilation over a timescale similar to that of the waxing-waning cycle of untreated Cheyne-Stokes breathing or central sleep apnea, while allowing changes in said measure of instantaneous ventilation over a timescale much longer than said waxing-waning cycle.   
     
     
         2 . A method for treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising the steps of:
 providing a subject with ventilatory support;   deriving a measure of the subject's instantaneous ventilation;   deriving a measure of the subject's longterm average ventilation;   setting the controlled variable of a servo-controller to a function of said measure of the subject's instantaneous ventilation;   setting the reference variable of said servo-controller to a measure of the subject's longterm average ventilation; and   adjusting the magnitude of said ventilatory support in accordance with the output of said servo-controller.   
     
     
         3 . A method for treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising the steps of:
 providing a subject with ventilatory support;   deriving a measure of the subject's instantaneous ventilation;   high pass filtering said measure of the subject's instantaneous ventilation; and   adjusting the degree of said ventilatory support inversely with said high pass filtered measure of the subject's instantaneous ventilation.   
     
     
         4 . A method as claimed in  claim 1 , whereby the step of adjusting the degree of ventilator support comprises the steps of:
 low pass filtering said measure of instantaneous ventilation to derive a measure of longterm average ventilation;   setting a target signal equal to a fraction of said measure of longterm-average ventilation; and   servo-controlling said measure of instantaneous ventilation to at least equal the target ventilation.   
     
     
         5 . A method as claimed in  claim 1 , whereby ventilatory support is positive pressure ventilatory support. 
     
     
         6 . A method as claimed in  claim 5 , whereby the degree of ventilatory support is the difference between a peak inspiratory pressure and an end expiratory pressure. 
     
     
         7 . A method as claimed in  claim 1 , whereby deriving a measure of instantaneous ventilation comprises at least the steps of:
 deriving a signal proportional to the subject's respiratory airflow; and   rectifying said signal.   
     
     
         8 . A method as claimed in  claim 1 , whereby the degree of ventilatory support provided is clipped to exceed a minimum degree of support, chosen to be less than the degree of support that would perform the subject's entire work of breathing. 
     
     
         9 . A method as claimed in  claim 1 , whereby the degree of ventilatory support provided is clipped to not exceed a maximum degree of support, chosen to be sufficient to perform most or all of the subject's work of breathing, but not sufficient to be dangerous. 
     
     
         10 . A method as claimed in  claim 1 , including the further steps of:
 the severity of reduction in ventilation is determined;   if the severity of reduction in ventilation is high, then said ventilatory support is provided at a preset rate;   if the severity of reduction in ventilation is zero, then said ventilatory support is provided in phase with the subject's respiratory airflow; and   for intermediate degrees of severity of reduction in ventilation, support is provided at an intermediate rate.   
     
     
         11 . A method as claimed in  claim 10 , whereby the severity of reduction in ventilation is calculated by comparing the subject's ventilation with a low pass filtered ventilation. 
     
     
         12 . Apparatus for the treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising:
 a device for providing ventilatory support of controllable magnitude;   means for deriving a signal indicative of instantaneous ventilation of a subject; and   a servo-controller operable to control the degree of ventilatory support provided by said ventilatory support device to oppose short-term changes in said measure of instantaneous ventilation, but permit longterm changes in said measure of instantaneous ventilation.   
     
     
         13 . Apparatus as claimed in  claim 12 , wherein the ventilatory support device provides positive pressure ventilatory support. 
     
     
         14 . Apparatus for treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising:
 a controllable source of breathable gas at positive pressure;   means for delivering said breathable gas at positive pressure to a subject's airway;   means for deriving a measure of the subject's instantaneous ventilation; and   a servo-controller for adjusting the degree of ventilatory support to reduce changes in said measure of instantaneous ventilation over a timescale similar to that of the waxing-waning cycle of untreated Cheyne-Stokes breathing or central sleep apnea, while allowing changes in said measure of instantaneous ventilation over a timescale much longer than said waxing-waning cycle.   
     
     
         15 . Apparatus for treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising:
 a controllable source of breathable gas at positive pressure;   means for delivering said breathable gas at positive pressure to a subject's airway;   means for deriving a measure of the subject's instantaneous ventilation;   means for deriving a measure of the subject's longterm average ventilation;   means for deriving a target ventilation as a function of said measure of the subject's longterm average ventilation;   a servo-controller, whose input variable is a function of said measure of the subject's instantaneous ventilation, and whose reference variable is said target ventilation; and   means for adjusting the magnitude of said ventilatory support according to the output of the servo controller.   
     
     
         16 . Apparatus as claimed in  claim 12  or  claim 15 , wherein said measure of instantaneous ventilation is proportional to the absolute value of the respiratory airflow. 
     
     
         17 . Apparatus as claimed in  claim 15 , wherein said measure of the subject's recent average ventilation is proportional to the low pass filtered absolute value of the respiratory airflow, said low pass filter having a time constant of the order of, or longer than the waxing-waning cycle of untreated Cheyne-Stokes breathing. 
     
     
         18 . Apparatus for treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising:
 a controllable source of breathable gas at positive pressure;   means for delivering said breathable gas at positive pressure to a subject's airway;   means for deriving a measure of the subject's instantaneous ventilation;   means for high pass filtering said measure of the subject's instantaneous ventilation; and   a servo-controller whose input variable is a function of said high pass filtered measure of the subject's instantaneous ventilation, and which adjusts the magnitude of said ventilatory support inversely with said high pass filtered measure of the subject's instantaneous ventilation.   
     
     
         19 . Apparatus as claimed in  claim 18 , wherein said high pass filter has a time constant of the order of or longer than the waxing-waning cycle of untreated Cheyne-Stokes breathing. 
     
     
         20 . Apparatus as claimed in either one of  claim 17  or  claim 19 , wherein said time constant is 100 seconds. 
     
     
         21 . Apparatus as claimed in  claim 15 , wherein said target ventilation is a chosen fraction of the subject's recent average ventilation. 
     
     
         22 . Apparatus as claimed in  claim 15 , wherein the servo-control means is operable to servo-control said measure of instantaneous ventilation to at least equal the target ventilation. 
     
     
         23 . Apparatus as claimed in either one of  claim 15  or  claim 22 , wherein the servo-control means is operable to increase the degree of support if said measure of instantaneous ventilation is less than said target ventilation, and reduce the degree of support if said measure of instantaneous ventilation is greater than said target ventilation. 
     
     
         24 . Apparatus as claimed in  claim 12 , wherein the servo-control means is further operable to clip the degree of ventilatory support to exceed a minimum degree of support, chosen to be less than the degree of support that would perform a subject's entire work of breathing. 
     
     
         25 . Apparatus as claimed in  claim 12 , wherein the servo-control means is operable to modulate said positive said pressure in phase with respiratory air flow where the subject is breathing adequately, and to modulate said positive pressure at a preset rate where the subject is not breathing adequately. 
     
     
         26 . Apparatus as claimed in  claim 25 , wherein the servo-control means is operable to assess the adequacy of breathing by comparing a measure of instantaneous ventilation with a target ventilation. 
     
     
         27 . A method for the treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising the steps of:
 providing a subject with positive pressure ventilatory support, with controllable amplitude and rate;   deriving a measure of the subject's instantaneous ventilation;   adjusting said amplitude of positive pressure by:
 (a) low pass filtering said measure of instantaneous ventilation to derive a measure of recent average ventilation; 
 (b) setting a target ventilation equal to a fraction of said measure of recent average ventilation; and 
 (c) servo-controlling said measure of instantaneous ventilation to at least equal the target ventilation, by adjusting the degree of ventilator support; 
   and   continuously adjusting said rate by:
 (a) to the extent that the instantaneous ventilation equals or exceeds said target ventilation, modulating said positive pressure in phase with respiratory airflow; and 
 (b) to the extent that the instantaneous ventilation is less than said target ventilation, modulating said positive pressure at a preset rate. 
   
     
     
         28 . Apparatus for the treatment of cardiac failure, Cheyne-Stokes breathing or central sleep apnea, comprising:
 ventilator means for providing ventilatory support with controllable amplitude and rate;   sensor and processing means for deriving a signal indicative of instantaneous ventilation of a subject; and   servo-control means operable to adjust the amplitude of the pressure support by low pass filtering said instantaneous ventilation signal to derive a measure of recent average ventilation, setting a target ventilation equal to a fraction of said measure of recent average ventilation and servo-controlling said measure of instantaneous ventilation to at least equal the target ventilation, and further operable to continuously adjust said rate by modulating said positive pressure in phase with respiratory airflow to the extent that the instantaneous ventilation equals or exceeds said target ventilation, and modulating said positive pressure at a pre-set rate to the extent that the instantaneous ventilation is less than said target ventilation.   
     
     
         29 . A method for treatment of cardiac failure, Cheyne Stokes breathing or central sleep apnea, comprising the steps of:
 providing a subject with ventilatory support;   deriving a measure of instantaneous ventilation; and   adjusting the degree of ventilatory support to oppose short term changes in said measure of instantaneous ventilation, but permitting longterm changes in said measure of instantaneous ventilation.