Humidification system and positive airway pressure apparatus incorporating same

Abstract

Systems, apparatus, and methods for providing humidity in a positive airway pressure (PAP) device. In one embodiment, a humidifier is configured to periodically provide vapor to a flow of pressurized gas to produce flows of pressurized gas with added humidity. Each of the flows of pressurized gas with added humidity may be timed to reach a user interface primarily during a first portion of a breath cycle (e.g., during inspiration). Portions of the flow of pressurized gas that reach the user interface during a second portion of the breath cycle (e.g., during expiration) may include little or no added humidity.

What is claimed is: 
     
         1 . A positive airway pressure apparatus comprising:
 a flow generator comprising a housing containing a blower, the blower adapted to produce a flow of pressurized gas;   a user interface adapted to communicate the flow of pressurized gas to an airway during a breath cycle;   an elongate delivery tube positioned between the flow generator and the user interface, the delivery tube adapted to communicate the flow of pressurized gas from the blower to the user interface;   a humidifier defining an outlet that is in communication with the flow of pressurized gas, the humidifier comprising a vaporizing device and a water source, the outlet located between the blower and the delivery tube;   an electrical power source adapted to provide electrical power to the humidifier; and   a controller in communication with both the vaporizing device and the power source, the controller adapted to automatically modulate the electrical power provided to the humidifier during the breath cycle, wherein the electrical power is modulated in proportion to a flow rate of the flow of pressurized gas such that the humidifier adds water vapor at a rate that maintains a near constant humidity level in the flow of pressurized gas during the breath cycle.   
     
     
         2 . The apparatus of  claim 1 , wherein the controller is adapted to modulate the electrical power provided to the humidifier based upon one or more of: a pressure of the flow of pressurized gas; an intentional leak; an unintentional leak; a breathing flow; a breath rate; an inspiratory tidal volume; an expiratory volume; an I:E ratio; inspiratory and expiratory flow dynamics; start and end of inspiration; start and end of expiration; time of peak flow during inspiration; time of peak flow during expiration; ambient temperature; ambient humidity; an output power of the power source; a power-to-vaporization transfer function of the vaporizing device; a volume of the delivery tube and the user interface between the outlet of the vaporizing device and the airway; and a distance between the outlet of the vaporizing device and the user interface. 
     
     
         3 . The apparatus of  claim 1 , wherein the humidifier is located within the housing of the flow generator. 
     
     
         4 . The apparatus of  claim 1 , wherein the controller is adapted to automatically modulate the electrical power provided to the humidifier between: a minimum power level; and a maximum power level. 
     
     
         5 . The apparatus of  claim 4 , wherein the minimum power level is greater than zero watts. 
     
     
         6 . A positive airway pressure apparatus comprising:
 a flow generator comprising a housing containing a blower, the blower adapted to produce a flow of pressurized gas at a variable flow rate;   a user interface adapted to communicate the flow of pressurized gas to an airway during a target breath cycle;   an elongate delivery tube positioned between the flow generator and the user interface, the delivery tube adapted to communicate the flow of pressurized gas from the blower to the user interface;   a humidifier comprising a vaporizing device having an outlet in communication with the flow of pressurized gas, the outlet located upstream from the user interface;   an electrical power source adapted to provide electrical power to the vaporizing device; and   a controller in communication with both the power source and the vaporizing device, the controller adapted to provide the electrical power to the vaporizing device during a power interval such that the vaporizing device introduces water vapor into an inspiration portion of the flow of pressurized gas, during the power interval, to produce a flow of pressurized gas with added humidity, and wherein a start time and duration of the power interval are selected or calculated such that the flow of pressurized gas with added humidity arrives at the user interface beginning at or near an onset of an inspiratory phase of the target breath cycle and lasts for most or all of the inspiratory phase of the target breath cycle.   
     
     
         7 . The apparatus of  claim 6 , wherein the duration of the power interval is selected or calculated by the controller to terminate the introduction of the water vapor by the vaporizing device such that the flow of pressurized gas with added humidity that reaches the user interface ends at or near an end of the inspiratory phase or at or near an onset of an expiratory phase of the target breath cycle. 
     
     
         8 . The apparatus of  claim 6 , wherein the controller modulates power to the vaporizing device during the power interval to maintain a constant level of humidity within the flow of pressurized gas with added humidity. 
     
     
         9 . The apparatus of  claim 6 , wherein the controller reduces the electrical power provided to the vaporizing device to a minimum level after the power interval expires. 
     
     
         10 . The apparatus of  claim 6 , wherein the outlet of the vaporizing device is located in the housing of the flow generator. 
     
     
         11 . The apparatus of  claim 6 , wherein the controller is adapted to automatically predict when the onset of the inspiratory phase of the target breath cycle will begin based upon an analysis of one or more prior breath cycles. 
     
     
         12 . The apparatus of  claim 8 , wherein the controller is adapted to modulate the electrical power provided to the vaporizing device based upon one or more of: a pressure of the flow of pressurized gas; an intentional leak; an unintentional leak; a breathing flow; a breath rate; an inspiratory tidal volume; an expiratory volume; an I:E ratio; inspiratory and expiratory flow dynamics; start and end of inspiration; start and end of expiration; time of peak flow during inspiration; time of peak flow during expiration; ambient temperature; ambient humidity; an output power of the power source; a power-to-vaporization transfer function of the vaporizing device; and a distance between the outlet of the vaporizing device and the user interface. 
     
     
         13 . The apparatus of  claim 11 , wherein the controller is adapted to predict when the inspiratory portion of the flow of pressurized gas will reach the user interface by analyzing one or more of: a pressure of the flow of pressurized gas; an intentional leak; an unintentional leak; a breathing flow; a breath rate; an inspiratory tidal volume; an expiratory volume; an I:E ratio; inspiratory and expiratory flow dynamics; start and end of inspiration; start and end of expiration; time of peak flow during inspiration; time of peak flow during expiration; and a distance between the outlet of the vaporizing device and the user interface. 
     
     
         14 . A method for adding humidity to gas delivered by a positive airway pressure apparatus, the method comprising:
 producing, with a blower, a flow of pressurized gas at a variable flow rate;   transporting the flow of pressurized gas from the blower to a user interface via a delivery tube positioned between the blower and the user interface;   detecting, with a controller, one or both of an inspiratory phase and an expiratory phase of one or more breath cycles;   introducing, during a power interval, humidity into a portion of the flow of pressurized gas to produce a discrete flow of pressurized gas with added humidity, the humidity introduced by a vaporizing device having an outlet proximate the blower and in communication with the flow of pressurized gas; and   determining, automatically with the controller, a start time and duration of the power interval so that the flow of pressurized gas with added humidity reaches the user interface at or near an onset of an inspiratory phase of a current or future breath cycle and ends at or near an end of the inspiratory phase, or at or near an onset of an expiratory phase, of the current or future breath cycle.   
     
     
         15 . The method of  claim 14 , further comprising introducing the humidity periodically into the flow of pressurized gas to produce periodic flows of pressurized gas with added humidity, wherein each of the periodic flows of pressurized gas with added humidity is timed to reach the user interface at or near the onset of an inspiratory phase of one of the breath cycles. 
     
     
         16 . The method of  claim 14 , introducing the humidity into the flow of pressurized gas for the power interval comprises providing electrical power to the vaporizing device during the power interval. 
     
     
         17 . The method of  claim 16 , wherein providing the electrical power to the vaporizing device during the power interval comprises modulating the electrical power to the vaporizing device during the power interval. 
     
     
         18 . The method of  claim 14 , wherein determining the start time and duration of the power interval comprises analyzing one or more characteristics of the one or more breath cycles preceding the current or future breath cycle. 
     
     
         19 . The method of  claim 14 , wherein introducing the humidity into the portion of the flow of pressurized gas comprises introducing water vapor into the flow of pressurized gas at a variable rate proportional to a flow rate of the flow of pressurized gas. 
     
     
         20 . The method of  claim 14 , wherein determining the start time and duration of the power interval comprises selecting the start time and duration from a lookup table accessible by the controller. 
     
     
         21 . The method of  claim 14 , wherein determining the start time and duration of the power interval comprises calculating the start time and duration with the controller. 
     
     
         22 . The method of  claim 21 , wherein calculating the start time and duration of the power interval comprises:
 measuring one or more characteristics of a previous breath cycle;   determining ideal values of the start time and duration of the power interval for the previous breath cycle;   comparing the ideal values of the start time and duration of the power interval for the previous breath cycle to actual values of the start time and duration used;   calculating an error between the ideal values and the actual values of the start time and duration of the power interval for the previous breath cycle; and   predicting the start time and duration of the power interval for the current or future breath cycle based at least in part upon the error calculated.   
     
     
         23 . A method for adding humidity to gas provided by a positive airway pressure (PAP) apparatus, the method comprising:
 producing a continuous and variable flow of pressurized gas with a blower;   transporting the flow of pressurized gas from the blower to a user interface via a delivery tube positioned between the blower and the user interface;   predicting, automatically with a PAP controller, a start time and duration of an inspiratory phase of a target breath cycle based upon an analysis of a current or a preceding breath cycle;   calculating or selecting, automatically with a humidification controller, a delay time and duration of a power interval;   providing power, under control of the humidification controller, to a vaporizing device after expiration of the power interval delay time, the power lasting for the power interval duration, wherein the vaporizing device is located proximate an outlet of the blower and is in communication with the flow of pressurized gas;   introducing humidity with the vaporizing device into the flow of pressurized gas during the power interval duration to produce a flow of pressurized gas with added humidity that reaches the user interface at or near an onset of the inspiratory phase of the target breath cycle and terminates at or near a beginning of an expiratory phase of the target breath cycle.   
     
     
         24 . The method of  claim 23 , further comprising modulating the power provided to the vaporizing device in proportion to a flow rate of the flow of pressurized gas during the power interval duration such that a near constant humidity level is maintained in the flow of pressurized gas with added humidity. 
     
     
         25 . The method of  claim 23 , wherein one or both of the delay time and duration of the power interval are selected based, at least in part, upon one or more of: a pressure of the flow of pressurized gas; an intentional leak; an unintentional leak; a breathing flow; a breath rate; an inspiratory tidal volume; an expiratory volume; an I:E ratio; inspiratory and expiratory flow dynamics; start and end of inspiration; start and end of expiration; time of peak flow during inspiration; time of peak flow during expiration; ambient temperature; ambient humidity; an output power available to the vaporizing device; a power-to-vaporization transfer function of the vaporizing device; and a distance between the outlet of the vaporizing device and the user interface.