Patent Application
20080029096
The drawings illustrate the best mode contemplated of carrying out the invention.
In the drawings:
As the patient 10 enters the expiratory phase of the respiratory cycle, the expired breathing gases are channeled to an expiratory conduit 30. Additional sensors may be disposed along the expiratory conduit 30, such as the flow sensor 32 depicted, but should not be read as limiting as other sensors, or none at all may be included in the expiratory conduit 30 as embodiments of the present invention. The flow sensor 32 will send a signal 34 to the microprocessor 28 representative of the flow of gas in the expiratory conduit 30. Alternatively, sensor 32 may be a pressure transducer, measuring the pressure within the expiratory conduit 30. At the end of the expiratory conduit 30 is an expiratory valve 36 which upon receiving a control signal from the microprocessor 28 releases the expired gases to the outside 38.
As the microprocessor 28 receives various signals (24, 26, 34) from the system, this information may be sent to a user interface 40 where it may be viewed by a clinician. The clinician may also use the user interface 40 to enter desired parameters and/or controls for the respiratory support that is being provided to the patient 10. The microprocessor 28 will use the clinician-defined controls as well as the received signals (24, 26, 34) as interpreted using stored reference calibration tables 42 to provide a control signal 44 to the motor controller 46. This control signal 44 will vary dependent with the stage the patient is in the respiratory cycle. If the patient is making a breath attempt, the control signal 44 will indicate that more pressure is needed. If the patient is exhaling, the control signal 44 will indicate that less pressure is needed to conserve energy.
The control signal 44 may control the motor controller 46 using pulse width modulation. Pulse width modulation (PWM) is used by the motor controller 46 to emulate an AC power signal 48 of variable fundamental frequency, variable voltage or current amplitude, and/or variable waveform. The power signal emulated could be a sine wave or any combination of sine waves of variable frequency and amplitude. A linear amplifier may also be used to generate this power signal 48. The power signal 48 drives the pump. For the present description, PWM generating a constant frequency, variable voltage amplitude, square waveform power signal 48 will be used, but is not intended to be limiting. The AC power signal 48 is provided to the pump 12. As the input voltage varies, it in effect varies the amplitude of the pump oscillation and correspondingly varies the flow output. This is an effective design for varying input voltage due to the large inductance of the pump that prevents significant pulsing in the motor current.
When an electrical current is applied to the motor windings 53 via leads 71, a magnetic field is produced within the motor cores in the exemplary direction of magnetic field lines 54. These fields push both magnets 52 in the rotor 51 in the same direction, thereby moving one end of the rotor 51 towards the outside of the linear oscillating pump 12 and the other magnet towards the center line 55 of the linear oscillating pump 12.
A pump assembly 56 is disposed on either side of the linear oscillating pump 12 in coaxial relationship to both the motor cores 50 and the magnets 52. Each pump assembly 56 comprises a rubber diaphragm 58, defining a pump chamber 57, an “in” one-way valve 60, and an “out” one-way valve 62.
As the magnetic field 54 through the motor cores 50 forces one of the magnets 52 towards the outside of the linear oscillating pump 12, this electrical force 64 pushes the rubber diaphragm 58 outwards thereby forcing the air in the pump chamber 57 out through the “out” one-way valve 62 into inspiratory conduit 18. On the other side of the linear oscillating pump 12, where the magnet 52 is proximal to the centerline 55 of the pump 12, this produces a mechanical force 66 pulling the rubber diaphragm 58 towards the center of the pump which pulls outside air 14 through the “in” one-way valve 60 to be stored in the pump chamber 57.
When the electrical charges on the motor cores 50 are reversed, the magnetic fields depicted by magnetic field lines 54 reverse forcing the magnets 52 in the opposite direction. As such, the air in the full pump assembly 56 is forced out through the “out” one-way valve 62 and into the inspiratory conduit 18 while the other pump assembly 56 that had been previously emptied now begins to fill with air from outside 14 through the “in” one-way valve 60. This cycle of charges on the motor cores 50 produces the desired output of pressurized gas into the inspiratory conduit 18.
In an embodiment of the present invention, the duty cycle of these two square waves is slightly less than 50% to create a dead time between switching voltage polarity of the pump. The creation of dead time prevents shoot through, the case when two mosfets on the same side of the H-Bridge are active and the positive voltage is therefore shorted to ground. First square wave 82 and second square wave 84 operate at a frequency that is equal to that of the motor AC operating frequency. The triangular wave 78 operates at a frequency much greater than the motor operating frequency to implement PWM voltage magnitude control. In a preferred embodiment, the motor drive signal is a 24 V 60 Hz pulse width modified square wave with the effective voltage magnitude of the wave being defined by the output signal 80 of the comparator 76. However, it is understood that any periodic signal capable of producing an oscillating motion in an oscillating pump may be used in accordance with the present invention.
The linear motor driven diaphragm 58 displaces air at a rate dependent on rotor position, thus causing the flow output to oscillate over each individual stroke of the rotor. This flow oscillation resembles a sine wave of a frequency that is twice the motor's electrical frequency. Such flow rate oscillation is depicted in
In embodiments of the present invention, the medical gas delivered to the patient is not limited to ambient air. The respiratory support system of the present invention may be implemented in conjunction with the delivery of an anesthetic agent. Patients receiving an anesthetic agent also often receive mechanical respiratory support as may be provided by the system of the present invention. Alternatively, in an embodiment of the present invention, the respiratory support system may be used in conjunction with the delivery of supplemental oxygen. The supplemental oxygen mixed with the delivery of the ambient air increases the oxygen content of the medical gas that is delivered to the patient and as such increases the efficiency of the gas exchange within the patient's lungs.
Two possible configurations for a ventilator system of the present invention using supplemental oxygen are configurations where the supplemental oxygen is added before the linear pump and configurations where the supplemental oxygen is added after the linear pump.
In an embodiment of the present invention, the linear oscillating pump of the present invention is not limited to the pump described above. Embodiments of the present invention may use an oscillating pump to produce non-linear motion by a rotor. This type of oscillating pump may produce rotational rotor movement or exert an alternative force on an alternative rotor such as a spring. Further embodiments of the linear oscillating pump as used in accordance with the present invention may comprise a single diaphragm.
The present invention presents the advantage of having very low average power consumption. The linear oscillating pump is efficient at producing low flow rates, but the power efficiency of the pump decreases as the flow rate increases. However, the majority of flow rates required to supplement an average breathing cycle are in the range of 0 to 40 liters per minute. These flow rates are well within the range where the pump efficiency is very high. As an example of the efficiency of the present invention, a laboratory test found that a respiratory support system driven by a flow diverting rotary pump consumed an average of 84 W while a similarly performing respiratory support system of the present invention utilizing a linear pump averaged only 2.9 W of power consumption over the same time period.
The electrical characteristics of the linear pump of the system of the present invention give this invention the advantage of a rapid response time to reach a designated target output pressure. During the acceleration of the linear pump, there are no large starting currents, low starting torque problems, nor are there any complex combinations of input voltage and electrical frequency necessary to start the motor as is often necessary in rotary devices. The linear pump takes approximately one full cycle of operation to accelerate to peak output and requires no special controls. As an example, at an electrical frequency of 60 Hz, the linear pump requires approximately 20 ms to accelerate to full flow output. This fast flow acceleration creates desirable response times for reaching target pressures. This facilitates delivering medical gas to the patient in conjunction with the patient entering the inspiratory phase of the respiration cycle.
The present invention also presents the additional benefit of added maintenance efficiency. Stock linear pumps have a long MTBF (mean time between failure) thereby running efficiently for a long time without need for replacement. This is directly related to the simple design of the linear pump and the absence of frictional moving parts. Therefore, the present invention has the additional benefit of requiring relatively low maintenance compared to current designs.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements of insubstantial difference from the literal language of the claims.
Various alternatives and embodiments are contemplated as being with in the scope of the following claims, particularly pointing out and distinctly claiming the subject matter regarded as the invention.
