Abstract:
In a method for detecting a physiological signal at least one ventilation parameter is measured. The device for detecting a physiological signal has at least one sensor for measuring a ventilation parameter and a control unit for the ventilation pressure. A device for monitoring at least one ventilation parameter while respiratory gas is being supplied to a patient is provided with a sensing device for detecting the behavior of the ventilation parameter as a function of time.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for detecting a physiological signal, in which method at least one ventilation parameter is measured and analyzed to control a ventilation pressure.  
         [0003]     The invention also concerns a device for detecting a physiological signal, which device has a sensor for measuring a ventilation parameter and a control unit for producing a ventilation pressure.  
         [0004]     The invention further concerns a device for monitoring at least one ventilation parameter while respiratory gas is being supplied to a patient, which monitoring device has a sensing device for detecting the behavior of the ventilation parameter as a function of time.  
         [0005]     2. Description of the Related Art  
         [0006]     Large numbers of persons suffer from sleep disorders, which affect the well-being of these persons during the day and in some cases have an adverse effect on their quality of life. One of these sleep disorders is sleep apnea, which is treated primarily by CPAP therapy (CPAP=continuous positive airway pressure), in which a flow of respiratory gas is continuously supplied to the patient through a nasal mask as the patient sleeps. A hose connects the mask with a ventilator, which includes a blower that produces a gas flow with, for example, a positive pressure of 5 to 20 mbars.  
         [0007]     The gas flow is supplied to the patient either at constant pressure or, to relieve the respiratory work of the patient, at a lower level during expiration.  
         [0008]     The lowering and raising of the ventilation pressure are effected on the basis of various events identified by the device and by measured respiratory parameters.  
         [0009]     The following are examples of such events: mouth expiration, mouth breathing, leakage, swallowing, speaking, sneezing, coughing, increase in respiratory flow, decrease in respiratory flow, flattening of the respiratory flow, cessation of respiratory flow, increase in resistance, leakage, apnea, hypopnea, snoring, inspiration, expiration, interruption of breathing, increase in respiratory volume, decrease in respiratory volume, inspiratory constriction of the respiratory flow, inspiratory peak flow, decrease in the inspiratory flow after peak flow, second maximum of the inspiratory peak flow, increase in the pressure of the respiratory gas, decrease in the pressure of the respiratory gas, increase in the flow of the respiratory gas, decrease in the flow of the respiratory gas, increase in the volume of respiratory gas delivered, decrease in the volume of respiratory gas delivered.  
       SUMMARY OF THE INVENTION  
       [0010]     The object of the present invention is to improve a method of the aforementioned type in such a way that pressure control is optimized.  
         [0011]     Another object of the present invention is to construct a device of the aforementioned type for optimization of pressure control.  
         [0012]     A further object of the present invention is to further optimize a device of the aforementioned type.  
         [0013]     The three objects listed above are met by the three combinations of features specified at the beginning.  
         [0014]     The method of the invention is aimed at detecting obstructive apneas, explicitly, at the end of an apnea, since these are usually difficult to distinguish from central apneas or difficult to detect at all. If apneas are detected exclusively by an approximately zero line in the flow, the distinction obstructive/central is not possible. Oscilloresistometry is available for this purpose (EP 0 705 615 B1), but it requires considerable design expense, results in higher production costs, and is not suitable for all types of masks.  
         [0015]     The method of the invention makes it possible to detect obstructive apnea more simply and reliably than methods that make use of pressure to detect the obstructive apnea. The device used in this method has a pressure sensor that senses the pressure signals in the patient system, which consists, for example, of a respiratory hose, pressure hose, patient interface, expiratory element, etc., and feeds them to an analyzer. The analyzer analyzes the pressure curve and makes use of the fact that, at the end of an episode of obstructive apnea, an abrupt pressure drop, obstructive pressure peak (OPP) can usually be measured when the respiratory passages suddenly open, and the pressure between the mask and the respiratory tract must be equalized.  
         [0016]     During the obstructive apnea, the lower respiratory tract of the patient is disconnected from the system respiratory hose/mask/upper respiratory tract, so that typically a pressure difference between the mask and the lower respiratory tract develops as a result of the respiratory excursions of the patient. When the respiratory tract reopens, this results in a pressure equalization, which can be detected as a pressure surge in the mask or in the patient system, as an abrupt increase in the rotational speed of the blower, or as an abrupt flow pulse. Typically, it is rapidly equalized by the control response of the therapeutic apparatus, but overshooting can occur, and this can lead to abrupt pressure increases.  
         [0017]     In central apneas, the lower respiratory tract always remains connected with the system respiratory hose/mask/upper respiratory tract, and there are no respiratory excursions of the patient. Therefore, a pressure difference that must be equalized at the end of the apnea cannot arise.  
         [0018]     These effects appear especially when the patient is already connected to the therapeutic apparatus and is receiving therapy, i.e., when a certain pressure is already being applied in the respiratory mask.  
         [0019]     Changes in the respiratory tract are usually accompanied by fluctuations near the maxima of the flow curve. These changes can be caused by obstruction or can have other causes, so that obstruction cannot be definitely identified.  
         [0020]     However, if the values of the pressure curve are also considered, the previously mentioned pressure peaks in the time interval of the maxima can also be recorded and recognized during obstructive respiratory tract changes, since the vibration of the tissue surrounding the upper respiratory passages represents a further cause of obstructive pressure peaks—especially at the instant of opening or closing. In this regard, it is important inspiratory and expiratory pressure peaks can arise due to artifacts, such as coughing, speaking, swallowing, leakage, and mouth expiration, and are an indication that the inspiratory pressure peaks in the corresponding segment are possibly not a reliable indication of obstructions. These pressure peaks make it possible to draw conclusions about the type of instruction.  
         [0021]     The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0022]     In the drawing:  
         [0023]      FIG. 1  shows a basic design of a ventilator.  
         [0024]      FIG. 2  is a schematic representation of a ventilator with the detection of flow fluctuations.  
         [0025]      FIG. 3  shows a flow curve in obstructive apnea and in central apnea.  
         [0026]      FIG. 4  shows a pressure curve in central apnea.  
         [0027]      FIG. 5  shows a pressure curve in obstructive apnea.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]      FIG. 1  shows the basic design of a ventilator. A respiratory gas pump is installed inside an apparatus housing  1 , which has an operating panel  2  and a display  3 . A connecting hose  5  is attached by a coupling  4 . The coupling  4  can be quickly and easily connected to the ventilator by an operating element  13 . An additional pressure-measuring hose  6 , which can be connected with the ventilator housing  1  by a pressure input connection  7 , can run along the connecting hose  5 . To allow data transmission, the ventilator housing  1  has an interface  8 . An expiratory element  14  is installed in an expanded area of the connecting hose  5  that faces away from the apparatus housing  1 . Not shown are a pressure gauge and a flowmeter, which are located near the patient in the vicinity of the patient interface, or in the vicinity of the ventilator, or in the vicinity of the connecting hose.  
         [0029]     A mask  9 , which is held on the patient&#39;s head by a headband  10 , can also be attached by the respiratory hose  5 .  
         [0030]     According to the embodiment in  FIG. 2 , a ventilator  15  for carrying out CPAP or APAP ventilation is connected with a mask  9  by a connecting hose  5 . The connecting hose  5  has a constant opening as the expiratory element  14 . The patient&#39;s lung  16  is also shown. A supply pressure P produced by the ventilator is present in the area of a section of line  17 . In the vicinity of the mask  9 , a pressure P 1  that corresponds to a CPAP pressure can be determined at a measuring point  18  on the patient side. A possible obstruction can occur in an airway  19 , and a pressure P 2  is present on the other side of the obstruction from the measuring point  18  at a measuring point  20  in the airway  19 .  
         [0031]     Excursions produced during an episode of apnea lead to pressure fluctuations at the measuring point  20 .  
         [0032]      FIG. 3  shows a flow curve that is typical in both obstructive and central apnea. Almost no flow is occurring during the apnea due to the obstruction of the airway, while typical flow fluctuation is observed before the occurrence of the apnea. A typical flow fluctuation is referred to as flattening and describes a flattening of the flow curve in the vicinity of the maximum flow. In accordance with the invention, the beginning of the apnea is identified at least by a flow fluctuation, and the end of the apnea is identified at least by a pressure fluctuation.  
         [0033]      FIG. 4  shows a pressure curve that corresponds to the flow curve in  FIG. 3  during the occurrence of an episode of central apnea. Typical small pressure fluctuations in the mask pressure occur during breathing due to the use of a pressure controller. At the time of the flow fluctuation, a corresponding pressure fluctuation also occurs in the case of central apnea.  
         [0034]      FIG. 5  shows a pressure curve associated with the occurrence of an episode of obstructive apnea. As in the case of the pressure curve in  FIG. 4 , we again find a pressure fluctuation corresponding to the flow fluctuation, but in this case there is also a brief additional pressure change shortly before the end of the apnea when the airways open due to a pressure equalization between the mask and the respiratory tract. The time axes of  FIGS. 3, 4 , and  5  are identical.  
         [0035]     If an episode of apnea is detected in the flow signal, the detection unit looks for short, significant deflections in the pressure channel. “Short” means much shorter than a typical respiratory period of a patient. Possible artifacts caused by movements of the patient, hose, etc., or by the patient&#39;s heartbeat are tuned out. This is accomplished by evaluating only deflections which occur in the last interval of the apnea or during the first breath after the apnea and which are greater than a detection threshold value. In an especially preferred embodiment of the invention, this threshold value can be automatically adaptively adjusted to allow optimum separation of artifacts and pressure deflections caused by obstructions.  
         [0036]     For example, in accordance with the invention, a pressure mean value is determined during an episode of apnea. If the pressure mean value changes or the amplitude of the pressure mean value rises, this indicates the end of an episode of apnea. A change in the pressure mean value is preferably used as a control parameter for controlling the ventilator.  
         [0037]     To achieve optimum therapy, this detection threshold value is additionally varied as a function of the therapeutic pressure, specifically, in such a way that, at low therapeutic pressures, the sensitivity of the detection of episodes of obstructive apnea is increased, and at higher therapeutic pressures, the specificity of the detection of episodes of obstructive apnea is increased.  
         [0038]     Especially in the case of partial obstructions, the pressure signal and the flow signal are considered together, and the ventilator is automatically controlled on the basis of the pressure and/or flow signals. Definable irregularities in the behavior of the pressure signal and the flow signal are detected and used as control parameters for controlling the ventilator.  
         [0039]     While specific embodiments of the invention have been described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.