Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Reexamination Certificate
2001-12-19
2003-11-11
Lo, Weilun (Department: 3761)
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
C128S204180, C128S204210
Reexamination Certificate
active
06644311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a technique for measuring gas flow and/or volume in a pressure support system, and, more particularly, to a gas flow and/or volume measurement technique in which a pressure differential occurring between two points in a tortuous gas flow path in the pressure support system is used to measure the gas flow and/or gas volume passing through the tortuous gas flow path, thereby eliminating the need for a dedicated flow element in the gas flow path to create the pressure differential for flow/volume measurement purposes.
2. Description of the Related Art
Pressure support systems that provide a flow of gas to an airway of a patient at an elevated pressure via a patient circuit to treat a medical disorder are well known. For example, it is known to use a continuous positive airway pressure (CPAP) device to supply a constant positive pressure to the airway of a patient to treat obstructive sleep apnea (OSA) as well as other disorders. It is also known to provide a positive pressure therapy in which the pressure of gas delivered to the patient varies with the patient's breathing cycle, or varies with the patient's effort to increase the comfort to the patient, which is typically referred to as bi-level pressure support. It is further known to provide a positive pressure therapy in which the pressure provided to the patient changes based on the detected conditions of the patient, such as whether the patient is snoring or experiencing an apnea, hypopnea or upper airway resistance. This typically is referred to as an auto-titration mode of pressure support because the pressure support system automatically attempts to titrate the pressure support to suit the needs of the patient.
As shown in
FIG. 1
, a conventional pressure support system
10
typically includes a pressure generator
12
, for example, a blower, piston, or bellows, that receives a supply of gas from a gas source, such as ambient atmosphere, as indicated by arrow A, and creates a flow of breathing gas, as indicated by arrows B, having a pressure greater than the ambient atmospheric pressure. A patient circuit
14
, which is typically a flexible conduit, delivers the elevated pressure breathing gas to the airway of the patient. Typically, the patient circuit is a single limb conduit or lumen having one end coupled to the pressure generator and a patient interface device
16
coupled to the other end.
Patient interface device
16
connects patient circuit
14
with the airway of the patient so that the elevated pressure gas flow is delivered to the patient's airway. Examples of patient interface devices include a nasal mask, nasal and oral mask, full face mask, nasal cannula, oral mouthpiece, tracheal tube, endotracheal tube, or hood. A single limb patient circuit shown in
FIG. 1
includes an exhalation port
18
, also referred to as an exhalation vent, exhaust port, or exhaust vent, to allow gas, such as expired gas from the patient, to exhaust to atmosphere, as indicated by arrow C. Generally, exhaust vent
18
is located in patient circuit
14
near patient interface device
16
or in the patient interface device itself.
More sophisticated pressure support devices include a flow sensor
20
, pressure sensor
22
or both that monitor the flow and/or pressure of gas passing in patient circuit
14
. The flow information can also be used to determine the volume of gas passing through patient circuit
14
. The information from flow sensor
20
and/or pressure sensor
22
is used, for example, to control the pressure or flow of gas provided to the patient, monitor the condition of the patient, monitor the usage of the pressure support device (patient compliance), or any combination thereof.
FIG. 1
illustrates a flow sensor
20
and pressure sensor
22
downstream of pressure generator
12
.
As shown in
FIG. 2
, which illustrates an example of a typical flow sensor, flow sensor
20
includes a conduit
24
having ends
26
and
28
so that gas can flow through the conduit, as indicated by arrow D. A flow element
30
is provided in conduit
24
between ends
26
and
28
to create a pressure drop (&Dgr;P) in the conduit. That is, flow element
30
causes a pressure difference &Dgr;P between pressure P
1
and pressure P
2
so that &Dgr;P=P
2
−P
1
.
In one type of conventional sensor, pressure differential &Dgr;P is measured directly by a pressure sensor
32
, which is connected to conduit
24
on each side of flow element
30
via ports
34
and
36
. This pressure differential is used to calculate the flow of gas passing through conduit
24
, which, in turn, is used to calculate the volume of gas flowing through conduit
24
over any given period of time.
In another type of conventional flow sensor, pressure differential &Dgr;P is not measured directly. Instead, a conduit is coupled between ports
34
and
36
. The pressure differential between these ports causes a sidestream flow of gas to flow through this conduit connecting ports
34
and
36
. A mass flow sensor
32
′ is provided in place of pressure sensor
32
to measure the sidestream flow passing between ports
34
and
36
. This sidestream flow is then used to calculate the flow of gas in conduit
24
and also the volume of gas flowing through conduit
24
over any given period of time.
The signal from flow sensor
20
, whether from pressure sensor
32
or mass flow sensor
32
′, is provided to a controller
38
where it is used for the purposes noted above, such as to control the pressure or flow of gas provided to the patient or monitor the patient's usage of the medical device. One conventional pressure/flow control method involves providing a valve
40
in the patient circuit downstream of pressure generator
12
to exhaust a portion of the breathing gas output by the pressure generator through an exhaust conduit, as indicated by arrow E, thereby decreasing the pressure and flow delivered to the patient.
Another conventional pressure/flow control method involves controlling the operating speed of pressure generator
12
, e.g., controlling the motor speed of a blower that is used to create a flow of gas so that the pressure generator outputs the gas at the desired rate or pressure without an additional pressure control valve. It is also known to use a combination of valve
40
and motor speed control to control the pressure or flow of breathing gas output to the patient.
Controller
38
receives the signals output from sensors
20
and
22
and controls the operation of valve
40
, pressure generator
12
, or a combination thereof in a feedback fashion based on these received signals. For example, in a simple CPAP device, controller
38
monitors the pressure or flow of breathing gas delivered to the patient and adjusts the pressure or flow in a feedback fashion to meet the desired prescription pressure level. In a more sophisticated bi-level pressure support system, where the pressure is greater during inspiration than during expiration, controller
38
receives the flow signal and the pressure signal from flow sensor
20
and pressure sensor
22
, respectively, and uses this information to determine when the patient has transitioned from the inspiratory phase to the expiratory phase of the breathing cycle, or vice versa, to control the pressure accordingly. In the auto-titration mode of pressure support, where the flow of breathing gas and the pressure level thereof is controlled based on the conditions of the patient, these pressure and flow sensors, or other sensors, such as a microphone, are used to detect snoring, apneas, hypopneas, etc. The pressure and/or flow is then controlled to counteract or prevent these conditions.
An input/output device
42
, such as a keypad, buttons, lights, LED or LCD display, and/or an audio device, is used to enter information and commands to the pressure support system and to display information. For example, an input device can be used to enter the operating pressure in a CPAP system, the inspir
Duff Winslow K.
Truitt Patrick W.
Haas Michael W.
Lo Weilun
Patel Mital
Respironics Inc.
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