Apparatus and methods for ventilatory treatment

Abstract

Disclosed is an apparatus for treating a respiratory disorder, configured to compute a measure of typical recent ventilation such that a rate of adjustment of the measure of typical recent ventilation is reduced as a measure of recent uncompensated leak increases. Also disclosed is an apparatus for treating a respiratory disorder, configured to compute a target ventilation from a product of a measure of typical recent ventilation and a target fraction, wherein the target fraction is dependent on the recent pressure support.

1 . A servo-ventilator configured to:
 continuously compute a target ventilation such that the target ventilation rises more slowly as a measure of recent uncompensated leak increases, and   control the pressure of a supply of air so as to achieve the target ventilation.   
     
     
         2 . Apparatus for treating a respiratory disorder, configured to compute a measure of typical recent ventilation such that a rate of adjustment of the measure of typical recent ventilation is reduced as a measure of recent uncompensated leak increases. 
     
     
         3 . Apparatus according to  claim 2 , configured to compute the measure of typical recent ventilation by:
 computing an update proportion that generally decreases as the measure of recent uncompensated leak increases;   accumulating the update proportion on receipt of each input sample; and   computing an update to the measure of typical recent ventilation only when the accumulated update proportion exceeds one.   
     
     
         4 . Apparatus according to  claim 3 , wherein the update to the measure of typical recent ventilation is computed as a sum of input samples since the last update, weighted by the update proportion at each sample. 
     
     
         5 . Apparatus according to  claim 3  or  claim 4 , further comprising re-initializing the accumulated update proportion upon computing the update to the measure of typical recent ventilation. 
     
     
         6 . Apparatus according to any of  claims 3  to  5 , wherein the measure of typical recent ventilation is computed from a measure of instantaneous ventilation. 
     
     
         7 . Apparatus according to  claim 6 , further comprising applying a lowpass ventilation filter to the measure of typical recent ventilation. 
     
     
         8 . Apparatus according to any of  claims 3  to  7 , wherein the measure of typical recent ventilation is computed from the output of a lowpass ventilation filter that is applied to a measure of instantaneous ventilation. 
     
     
         9 . Apparatus for treating a respiratory disorder, configured to compute a target ventilation from a product of a measure of typical recent ventilation and a target fraction, wherein the target fraction is dependent on the recent pressure support. 
     
     
         10 . Apparatus according to  claim 9 , wherein the target fraction is decreased as the stability of recent pressure support increases. 
     
     
         11 . Apparatus according to  claim 10 , configured to compute the stability of recent pressure support as a fuzzy truth variable indicating the extent to which the pressure support has been stable for a first recent period and also for a second recent period substantially shorter than the first recent period. 
     
     
         12 . Apparatus according to  claim 11 , wherein the stability of pressure support over each period is computed based on order statistics of pressure support computed over that period. 
     
     
         13 . Apparatus according to  claim 11 , wherein the fuzzy truth variable includes the extent to which an amount of pressure support above a predetermined minimum pressure support has been nontrivial over the second recent period. 
     
     
         14 . Apparatus according to  claim 11 , wherein the fuzzy truth variable includes the extent to which the maximum value of pressure support above a predetermined minimum pressure support is large. 
     
     
         15 . Apparatus for treating a respiratory disorder, configured to compute a target ventilation from a product of a measure of typical recent ventilation and a target fraction, using a decreasing rate constant that is increased dependent on the stability of recent pressure support. 
     
     
         16 . Apparatus according to  claim 15 , configured to compute the stability of recent pressure support as a fuzzy truth variable indicating the extent to which the pressure support has been stable for a first recent period and also for a second recent period substantially shorter than the first recent period. 
     
     
         17 . Apparatus according to  claim 16 , wherein the stability of pressure support over each period is computed based on order statistics of pressure support computed over that period. 
     
     
         18 . Apparatus according to  claim 16  or  claim 17 , wherein the decreasing rate constant is increased by a factor that generally increases with the value of the fuzzy truth variable. 
     
     
         19 . Apparatus according to  claim 18 , wherein the factor is one plus twice the value of the fuzzy truth variable. 
     
     
         20 . Apparatus for treating a respiratory disorder, configured to compute a target ventilation from an instantaneous ventilation, wherein the rate of increase of the target ventilation is bounded by an upper limit on an upward slew rate of the target ventilation. 
     
     
         21 . Apparatus according to any one of  claim 9  and  claim 15  and  claim 20 , wherein the target ventilation is bounded below by a predetermined minimum target ventilation. 
     
     
         22 . Apparatus for treating a respiratory disorder, the apparatus being configured to:
 compute a duration of a detected episode of apnea or hypopnea, and   adjust a value of expiratory positive airway pressure (EPAP) according to the computed duration, such that with increasing duration, the adjusted value of EPAP exponentially approaches a value that is greater than a maximum EPAP value.   
     
     
         23 . Apparatus according to  claim 22 , wherein the rate constant of the exponential increase is decreased as the value that is greater than the maximum EPAP value increases. 
     
     
         24 . Apparatus according to  claim 22  or  claim 23 , further comprising limiting the adjusted value of EPAP to be no more than the maximum EPAP value. 
     
     
         25 . Apparatus according to any of  claims 22  to  24 , further comprising decaying the EPAP value toward a minimum EPAP value in the absence of any detected episode of apnea or hypopnea. 
     
     
         26 . Apparatus for treating a respiratory disorder, the apparatus being configured to:
 compute a measure of M-shaped inspiratory flow limitation, and   increase an expiratory positive airway pressure (EPAP) value according to the computed measure of M-shaped inspiratory flow limitation, such that the amount of increase is dependent on a ratio of breathwise ventilation to typical recent ventilation.   
     
     
         27 . Apparatus according to  claim 26 , further comprising decaying the EPAP value toward a minimum EPAP value if the computed measure of M-shaped inspiratory flow limitation is zero. 
     
     
         28 . Apparatus according to  claim 26  or  claim 27 , further comprising decaying the EPAP value to a minimum EPAP value if the inspiratory duration is greater than a threshold. 
     
     
         29 . Apparatus according to any of  claims 26  to  28 , wherein the amount of increase generally decreases as the ratio increases. 
     
     
         30 . Apparatus according to any of  claims 26  to  29 , wherein M-shaped inspiratory flow limitation is characterised by an inspiratory flow waveform having two local peaks, one at the leading edge, and one at the trailing edge, and a relatively flat portion or a dip between the two peaks. 
     
     
         31 . Apparatus for treating a respiratory disorder, the apparatus being configured to:
 compute a measure of reverse-chairness of inspiratory flow limitation, and   increase an expiratory positive airway pressure (EPAP) value according to the computed measure of reverse-chairness of inspiratory flow limitation, such that the amount of increase depends on the consistency of reverse-chairness between current and preceding breaths.   
     
     
         32 . Apparatus according to  claim 31 , wherein the consistency of reverse chairness is computed as a weighted geometric mean of the measures of reverse chairness computed for the current and preceding breaths. 
     
     
         33 . Apparatus according to  claim 31  or  claim 32 , wherein the amount of increase is proportional to a variable that transitions between the measure of reverse chairness of the current breath and the consistency of reverse-chairness between the current and preceding breaths as the current value of EPAP increases. 
     
     
         34 . Apparatus according to any of  claims 31  to  33 , wherein the amount of increase decreases with an increasing amount of leak. 
     
     
         35 . Apparatus according to any of  claims 31  to  34 , wherein the amount of increase decreases with an increasing value of current EPAP. 
     
     
         36 . Apparatus according to any of  claims 31  to  35 , further comprising decaying the EPAP value toward a minimum EPAP value if the computed measure of reverse-chairness of inspiratory flow limitation is less than a threshold. 
     
     
         37 . Apparatus according to any of  claims 31  to  36 , wherein reverse-chairness of inspiratory flow limitation is characterised by an inspiratory flow waveform having a relatively flat portion followed by single local peak, the peak being at the trailing edge. 
     
     
         38 . Apparatus for treating a respiratory disorder, the apparatus being configured to:
 compute a measure of inspiratory snore,   detect expiratory snore, and   increase an expiratory positive airway pressure (EPAP) value according to the measure of inspiratory snore, in the absence of expiratory snore.   
     
     
         39 . Apparatus according to  claim 38 , wherein the amount of increase is decreased as an amount of recent uncompensated leak increases. 
     
     
         40 . Apparatus according to  claim 39 , wherein the amount of recent uncompensated leak is computed as a maximum value during the current breath of a fuzzy truth variable indicating the extent of recent uncompensated leak. 
     
     
         41 . Apparatus according to any of  claims 38  to  40 , further comprising decaying the EPAP value toward a minimum EPAP value in the absence of inspiratory snore or in the presence of expiratory snore. 
     
     
         42 . Apparatus for treating a respiratory disorder, the apparatus being configured to estimate a phase of a current breathing cycle of a patient, wherein a weight given to a standard rate of change in the phase estimate is dependent on an extent to which the patient has recently been achieving ventilation at or above a target ventilation. 
     
     
         43 . Apparatus according to  claim 42 , wherein the extent to which the patient has recently been achieving ventilation at or above a target ventilation is computed as a fuzzy truth variable indicating the extent to which the current level of pressure support is large. 
     
     
         44 . Apparatus according to  claim 43 , wherein the fuzzy truth variable is computed relative to boundaries that increase as the minimum value of pressure support increases. 
     
     
         45 . Apparatus for treating a respiratory disorder, the apparatus being configured to deliver pressure support to a patient at a value that is a combination of:
 a value of pressure support that is sufficient to increase instantaneous ventilation to a target ventilation; and   a value of pressure support that is sufficient to increase gross alveolar ventilation to a target gross alveolar ventilation.   
     
     
         46 . Apparatus for detecting a hypopnea in a patient dependent on:
 an extent to which pressure support being delivered to the patient is large, and   an extent to which a measure of absolute value of airflow of the patient is small compared to a target absolute airflow.   
     
     
         47 . Apparatus according to  claim 46 , wherein the target absolute airflow is twice a current target ventilation. 
     
     
         48 . Apparatus according to  claim 46  or  claim 47 , wherein the measure of absolute airflow is computed as an output of a lowpass filter on the absolute value of airflow. 
     
     
         49 . Apparatus for computing a measure of M-shaped inspiratory, flow limitation of a patient based on a version of an inspiratory flow waveform that is symmetrised around a location of a notch in an inspiratory flow waveform. 
     
     
         50 . Apparatus according to  claim 49 , further comprising computing the location of the notch as the location of a peak of a combination of convolutions of the inspiratory airflow waveform with left and right halves of a V-shaped kernel. 
     
     
         51 . Apparatus according to  claim 50 , wherein the combination is a modified geometric mean. 
     
     
         52 . Apparatus according to any of  claims 49  to  51 , wherein the measure of M-shaped inspiratory flow limitation is an extent to which the symmetrised waveform resembles a third harmonic function. 
     
     
         53 . Apparatus according to  claim 52 , wherein the measure of M-shaped inspiratory flow limitation is computed as a ratio of a power in a third harmonic of the symmetrised waveform to a sum of powers in first and third harmonics of the symmetrised waveform. 
     
     
         54 . Apparatus according to any of  claims 49  to  53 , wherein M-shaped inspiratory flow limitation is characterised by the inspiratory flow waveform having two local peaks, one at the leading edge, and one at the trailing edge, and a relatively flat portion or a dip between the two peaks. 
     
     
         55 . Apparatus according to any of  claims 52  to  54 , wherein the measure of M-shaped inspiratory flow limitation is set to zero if a measure of symmetry of the inspiratory flow waveform about the notch location is below a threshold. 
     
     
         56 . Apparatus according to  claim 55 , wherein the measure of symmetry of the inspiratory flow waveform is computed as a ratio of a lesser of the third harmonic components of first and second halves of the symmetrised waveform to a sum of absolute values of the components. 
     
     
         57 . Apparatus for computing a measure of reverse chairness of inspiratory flow limitation of a patient dependent on the extent of recent uncompensated leak in the delivery of airflow to the patient. 
     
     
         58 . Apparatus according to  claim 57 , wherein the measure of reverse chairness is proportional to a generally decreasing function of a fuzzy truth variable indicating the extent of recent uncompensated leak. 
     
     
         59 . Apparatus according to  claim 57  or  claim 58 , wherein reverse-chairness of inspiratory flow limitation is characterised by an inspiratory flow waveform having a relatively flat portion followed by single local peak, the peak being at the trailing edge. 
     
     
         60 . Apparatus for computing a measure of inspiratory snore in a patient to whom airflow is being delivered via an interface, the apparatus being configured to compute the measure as a mean over an inspiratory portion of a current breath of a difference between the output of a snore filter on an instantaneous interface pressure and a threshold that is dependent on the instantaneous interface pressure. 
     
     
         61 . Apparatus according to  claim 60 , wherein the mean is weighted by a weighting function that is dependent on respiratory airflow of the patient. 
     
     
         62 . Apparatus according to  claim 61 , wherein the weighting function is low at low respiratory airflow and at high respiratory airflow. 
     
     
         63 . Apparatus according to any of  claims 60  to  62 , wherein the threshold is generally increasing with increasing interface pressure. 
     
     
         64 . Apparatus for detecting expiratory snore in a patient to whom airflow is being delivered via an interface, using joint thresholds on duration and intensity of the output of a snore filter on an instantaneous interface pressure during an expiratory portion of a current breath. 
     
     
         65 . Apparatus according to  claim 64 , wherein the joint thresholds are expressed in a predetermined critical function of snore intensity. 
     
     
         66 . Apparatus according to  claim 65 , wherein the predetermined critical snore function decreases generally with increasing snore intensity. 
     
     
         67 . Apparatus according to  claim 65  or  claim 66 , being configured to detect expiratory snore based on a comparison between a reverse cumulative distribution function of the intensity of the snore filter output and the predetermined critical snore function. 
     
     
         68 . Apparatus according to  claim 67 , wherein expiratory snore is detected if the reverse cumulative distribution function is above the critical reverse cumulative distribution function at any value of snore intensity above a minimum intensity. 
     
     
         69 . Apparatus for treating a respiratory disorder, the apparatus comprising:
 a pressure device configured to deliver a supply of air at a positive pressure to the airway of a patient over a conduit and an interface; and   a controller configured to:
 compute a measure of typical recent ventilation of the patient such that a rate of adjustment of the measure of typical recent ventilation is reduced as a measure of recent uncompensated leak in the conduit and/or the interface increases; and 
 control the pressure of the supply of air delivered by the pressure device dependent on the computed measure of typical recent ventilation so as to treat the respiratory disorder. 
   
     
     
         70 . Apparatus for detecting a respiratory condition in a patient, the apparatus comprising:
 one or more sensors configured to provide signals representing respiratory parameters of the patient, and   a processor configured to analyse the signals from the sensors so as to detect the respiratory condition, wherein:
 the respiratory condition is a hypopnea, 
 the respiratory parameter is an absolute airflow, and 
 the detection is dependent on an extent to which pressure support being delivered to the patient is large, and an extent to which the absolute airflow of the patient is small compared to a target absolute airflow. 
   
     
     
         71 . A method of treating a respiratory disorder, the method comprising:
 computing a measure of typical recent ventilation such that a rate of adjustment of the measure of typical recent ventilation is reduced as a measure of recent uncompensated leak increases.   
     
     
         72 . A method according to  claim 71 , wherein the computing comprises:
 computing an update proportion that generally decreases as the measure of recent uncompensated leak increases;   accumulating the update proportion on receipt of each input sample; and   computing an update to the measure of typical recent ventilation only when the accumulated update proportion exceeds one.   
     
     
         73 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 71  or  claim 72 . 
     
     
         74 . A method of treating a respiratory disorder, the method comprising:
 computing a target ventilation from a product of a measure of typical recent ventilation and a target fraction, wherein the target fraction is dependent on the recent pressure support.   
     
     
         75 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 74 . 
     
     
         76 . A method of treating a respiratory disorder, the method comprising:
 computing a target ventilation from a product of a measure of typical recent ventilation and a target fraction, using a decreasing rate constant that is increased dependent on the stability of recent pressure support.   
     
     
         77 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 76 . 
     
     
         78 . A method of treating a respiratory disorder, the method comprising:
 computing a target ventilation from an instantaneous ventilation, wherein the rate of increase of the target ventilation is bounded by an upper limit on an upward slew rate of the target ventilation.   
     
     
         79 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 78 . 
     
     
         80 . Apparatus for treating a respiratory disorder, the method comprising:
 computing a duration of a detected episode of apnea or hypopnea, and   adjusting a value of expiratory positive airway pressure (EPAP) according to the computed duration, such that with increasing duration, the adjusted value of EPAP exponentially approaches a value that is greater than a maximum EPAP value.   
     
     
         81 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 80 . 
     
     
         82 . A method of treating a respiratory disorder, the method comprising:
 computing a measure of M-shaped inspiratory flow limitation, and   increasing an expiratory positive airway pressure (EPAP) value according to the computed measure of M-shaped inspiratory flow limitation, such that the amount of increase is dependent on a ratio of breathwise ventilation to typical recent ventilation.   
     
     
         83 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 82 . 
     
     
         84 . A method of treating a respiratory disorder, the method comprising:
 computing a measure of reverse-chairness of inspiratory flow limitation, and   increasing an expiratory positive airway pressure (EPAP) value according to the computed measure of reverse-chairness of inspiratory flow limitation, such that the amount of increase depends on the consistency of reverse-chairness between current and preceding breaths.   
     
     
         85 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 84 . 
     
     
         86 . A method of treating a respiratory disorder, the method comprising:
 computing a measure of inspiratory snore,   detecting expiratory snore, and   increasing an expiratory positive airway pressure (EPAP) value according to the measure of inspiratory snore, in the absence of expiratory snore.   
     
     
         87 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 86 . 
     
     
         88 . A method of treating a respiratory disorder, the method comprising:
 estimating a phase of a current breathing cycle of a patient, wherein a weight given to a standard rate of change in the phase estimate is dependent on an extent to which the patient has recently been achieving ventilation at or above a target ventilation.   
     
     
         89 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 88 . 
     
     
         90 . A method of treating a respiratory disorder, the method comprising:
 delivering pressure support to a patient at a value that is a combination of:
 a value of pressure support that is sufficient to increase instantaneous ventilation to a target ventilation; and 
 a value of pressure support that is sufficient to increase gross alveolar ventilation to a target gross alveolar ventilation. 
   
     
     
         91 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method being in accordance with  claim 90 . 
     
     
         92 . A method of detecting a hypopnea in a patient, the method comprising:
 detecting the hypopnea dependent on:
 an extent to which pressure support being delivered to the patient is large, and 
 an extent to which a measure of absolute value of airflow of the patient is small compared to a target absolute airflow. 
   
     
     
         93 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of detecting a hypopnea in a patient, the method being in accordance with  claim 92 . 
     
     
         94 . A method of computing a measure of M-shaped inspiratory flow limitation of a patient based on a version of the inspiratory flow waveform that is symmetrised around a location of a notch in an inspiratory flow waveform. 
     
     
         95 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of computing a measure of M-shaped inspiratory flow limitation of a patient, the method being in accordance with  claim 94 . 
     
     
         96 . A method of computing a measure of reverse chairness of inspiratory flow limitation of a patient dependent on the extent of recent uncompensated leak in the delivery of airflow to the patient. 
     
     
         97 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of computing a measure of reverse chairness of inspiratory flow limitation of a patient, the method being in accordance with  claim 96 . 
     
     
         98 . A method of computing a measure of inspiratory snore in a patient to whom airflow is being delivered via an interface, the method comprising:
 computing a mean over an inspiratory portion of a current breath of a difference between the output of a snore filter on an instantaneous interface pressure and a threshold that is dependent on the instantaneous interface pressure.   
     
     
         99 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of computing a measure of inspiratory snore in a patient to whom airflow is being delivered via an interface, the method the method being in accordance with  claim 98 . 
     
     
         100 . A method of detecting expiratory snore in a patient to whom airflow is being delivered via an interface, the method comprising:
 using joint thresholds on duration and intensity of the output of a snore filter on an instantaneous interface pressure during an expiratory portion of a current breath.   
     
     
         101 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of detecting expiratory snore in a patient to whom airflow is being delivered via an interface, the method the method being in accordance with  claim 100 . 
     
     
         102 . A method of treating a respiratory disorder, the method comprising:
 delivering a supply of air at a positive pressure to the airway of a patient over a conduit and an interface;   computing a measure of typical recent ventilation of the patient such that the rate of adjustment of the measure of typical recent ventilation is reduced as a measure of recent uncompensated leak in the conduit and/or the interface increases; and   controlling the pressure of the supply of air dependent on the computed measure of typical recent ventilation so as to treat the respiratory disorder.   
     
     
         103 . A computer readable storage medium having recorded thereon computer program code that is configured to cause a processor to carry out a method of treating a respiratory disorder, the method the method being in accordance with  claim 102 .