Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
2000-08-31
2004-03-23
Lewis, Aaron J. (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204210, C128S205240
Reexamination Certificate
active
06708690
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to an apparatus and method for providing high frequency variable pressure to a patient to treat a respiratory disorder, and, in particular, to an apparatus and method in which a rotating valve located in the patient circuit creates an oscillating pressure in the flow of gas to or from the patient.
2. Description of the Related Art
It is well known to provide ventilatory assistance to a patient suffering from a respiratory disorder using a pressure support system, such as a ventilator, to deliver a flow of breathing gas at a positive pressure to the patient's respiratory system. For patients with complete respiratory failure, a ventilator or other suitable pressure support device delivers a life supporting flow of breathing gas to the lungs. In less severe situations, the ventilator augments the patient's respiratory function to assist with the patient's work of breathing. In either of these situations, it is not uncommon for the patient using the ventilator to face gas diffusion problems, secretion clearance problems, or both.
Gas diffusion problems occur when the breathing gas supplied to the patient is not uniformly distributed through the lungs. When positive pressure ventilation is applied to some patients, the applied pressure and gas flow, instead of being uniformly distributed throughout the lungs, tends to extend the healthy part of the lungs farther than the not-as-healthy part of the lung, so that gas is distributed mainly to the health tissues in the lung. This difference between the extension in the healthy part and the not-as-healthy part of the lung can exacerbate the patient's lung condition, create a disproportionate gas exchange in the lungs, and may eventually damage the entire lung. Thus, it is desirable to minimize the pressure level applied to the patient's respiratory system while maximizing the diffusion of gas throughout the lungs in order to reduce the degree of difference between the extension in the healthy parts and the not-as-healthy parts of the lung.
Secretion clearance problems occur when there is a build up of secretions in the patient's respiratory system. In healthy patients, accumulated secretions are removed from the respiratory system by clearing the throat or coughing. In a ventilated patient, however, these secretion clearing movements cannot be performed easily, and, in some cases, cannot be performed at all. If the secretions are not removed in some other manner, they can accumulate in the patient, which increases the difficulty of properly ventilating the patient. A likely consequence is that even higher pressure levels must be provided to the patient in order to deliver the desired flow of breathing gas to the lungs. As noted above, it is preferable in many patients to keep the pressure levels of breathing gas delivered to a patient at a minimum.
A ventilation technique commonly known as “high frequency ventilation”is one method that addresses the gas diffusion and secretion clearance problems. According to this technique, the pressure of the gas flow delivered to the patient oscillates between two levels at a relatively rapid rate. Several mechanisms are known for introducing the pressure fluctuations in the gas flow. One common mechanism is to provide a flexible diaphragm in fluid communication with the gas flow in the patient circuit. For purposes of this disclosure, the patient circuit includes all components of a ventilation system that delivers the flow of breathing gas from the gas source, such as a pressure generator, to the patient. Vibrating the diaphragm generates pressure oscillations in the flow of gas in the patient circuit. Another mechanism for generating the pressure fluctuations in the gas flow is to introduce a series of small bursts of breathing gas into the primary gas flow.
While these ventilation techniques are believed to be effective in creating pressure oscillations in the primary flow of gas, they are disadvantageous in that they do not allow the pressure delivered to the patient to be a negative pressure during the oscillation cycle. In addition, it is difficult to control the oscillation magnitude and frequency with a high degree of precision and controllability while at the same time minimizing the complexity of the pressure oscillation generating mechanisms. Also, the above-described pressure oscillation techniques can only provide a somewhat limited range of magnitudes for the pressure variations in each oscillation cycle. For ventilation devices that use a flexible diaphragm to create the pressure oscillations, this limited range of magnitude in the pressure variation is due to the fact that a diaphragm displaces a finite amount of gas. For devices that use bursts of gas to create the pressure oscillations, this limited range of magnitude in the pressure variation is due to the fact that the magnitude of the gas pulses introduced into the primary flow must be limited so as to avoid introducing too much gas into the patient circuit. In addition, the gas pulses have a limited affect on the primary gas flow.
Secretion clearance can also be a problem in patients that are not using a ventilator. For example, a patient with a weakened respiratory system may not be physically able to perform a secretion clearing movement with sufficient strength or force to remove or loosen the secretions. For these patients, devices exist that create an abrupt pressure increase in the patient's airway to assist in dislodging or removing secretions. An example of such a device is a hand-held flutter valve, which uses a ball valve to create the pressure oscillations in the patient's airway. When the patient breathes into the flutter valve, the force of the patient's exhalation moves a ball off of a valve seat to open the valve. Gravity immediately urges the ball valve back onto the seat to obstruct the patient's expiratory flow until that the pressure is built up enough again to urge the ball off of the seat. This process repeats as the patient exhales until the patient's expiratory pressure is not great enough to move the ball off of the seat. A series of the pressure spikes occur in the patient's airway as a result of the temporary flow interruption caused by the closing and opening of the ball valve to facilitate loosening and removal of the patient's airway secretions.
There are disadvantages associated with the flutter valve secretion clearance device. For example, proper seating of the ball on the valve seat is only possible if the device is held in its upright position. Therefore, the device is very position sensitive. In addition, because the patient's own expiratory force is used to move the ball to the open position, the flutter valve cannot be used by patients with very weak respiratory systems who have very low expiratory flow.
Another device that is typically used by a patient who is not using a ventilator, and that provides pressure oscillations in which the pressure supplied to the patient can be made negative during a portion of the oscillation cycle, is the Emerson Cough-a-Lator produced by Emerson, Inc. This devices includes a mechanism that physically moves a portion of the patient circuit in a windshield wiper fashion between a position where the positive pressure output from a blower is coupled to the patient and position where the negative pressure at the input of the blower is coupled to the patient.
There is a significant disadvantage in the above-described pressure oscillation technique. Namely, the frequency of oscillation is limited to a relatively low level due to the fact that the device physically moves a portion of the patient circuit in a windshield wiper fashion. It is simply not possible to provide an oscillation frequency greater than approximately 2 Hz using this system. In addition, this system does not allow a pressure oscillation waveform to be superimposed on a second pressure waveform.
SUMMARY OF THE INVENTION
Accordingly, it is an
Bobeck Michael
Hete Bernie F.
Haas Michael W.
Lewis Aaron J.
Patel Mital
Respironics Inc.
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