Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Reexamination Certificate
2000-01-07
2002-08-13
Weiss, John G. (Department: 3761)
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
C128S205240, C128S207120, C128S207160, C137S003000
Reexamination Certificate
active
06431170
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to an apparatus in a fluid supply system that mixes a primary fluid flow with a secondary fluid flow, and, in particular, to a fluid mixing apparatus, delivery system, and method in which the secondary fluid flow is introduced into the primary fluid flow in such a manner so as to minimize disruption of the fluid flow profile of the primary fluid flow.
2. Description of the Related Art
It is known to provide a flow of breathing gas to a patient to treat a medical disorder. For example, ventilators, either invasive or non-invasive, are used to augment a patient's respiratory effort or to take over that function entirely by providing a flow of breathing gas, such as air, oxygen, or an oxygen mixture, to the patient. It is also known to provide breathing gas to a patient via a pressure support device to treat other breathing disorders, such as sleep apnea syndrome. For example, it is known to use a continuous positive airway pressure (CPAP) device to supply a constant positive pressure to the patient to treat obstructive sleep apnea (OSA). It is also known to provide a positive pressure that varies with the patient's breathing cycle or that varies with the patient's effort to treat OSA and/or ventilate a patient.
Ventilators and pressure support devices typically include a pressure generator, e.g., a blower, piston or bellows, that generates a primary fluid flow at a pressure that is elevated above ambient pressure. A patient circuit delivers this flow of breathing gas from the pressure generator to an airway of the patient. In treating OSA, the pressure delivered to the patient's airway “splints” the airway, thereby preventing its collapse, which is a cause of OSA. A patient interface device, such as a nasal and/or oral mask, trachea tube, or nasal cannula, couples the patient circuit to the patient's airway for delivering the positive pressure breathing gas to the patient.
When using a pressure generating system, such as a ventilator or pressure support device, to deliver a primary flow of breathing gas to a patient, it is often also desirable to provide the patient with a secondary fluid flow, such as oxygen, an oxygen mixture, therapeutic gases or a medicated gas, in addition to the primary fluid flow, which is typically air. It is conventional to introduce the secondary fluid flow into the patient conduit in which the primary fluid flow is traveling. This is often done in the ventilator or pressure support housing itself so that the introduction of the secondary fluid flow can be measured and/or controlled in the pressure generating system.
FIG. 1
illustrates a portion of such a conventional fluid delivery system in which a secondary fluid flow is introduced into a primary fluid flow in a pressure generating system
As shown in
FIG. 1
, a conventional fluid delivery system
30
includes a first conduit
32
that carries a primary fluid flow from a source thereof (not shown), such as a pressure generator or a tank of pressurized fluid, to a patient (also not shown). Arrow
34
indicates a main direction of travel for the primary fluid flow in first conduit
32
. A second conduit
36
carries a secondary fluid flow from a source thereof (not shown), such as an oxygen concentrator or tank containing the secondary fluid, to first conduit
32
. Arrow
38
indicates a main direction of travel for the secondary fluid flow in second conduit
36
. In this conventional system, a T-joint
40
couples second conduit
36
to first conduit
32
. Due to space limitations in the ventilator/pressure support device, the T-joint is positioned very close to the other components in the fluid delivery system. Dashed lines
42
,
44
, and
46
illustrate where T-joint
40
couples to the fluid delivery system.
Conventional fluid delivery system
30
also includes a pressure regulation valve
48
upstream of T-joint
40
. In pressure regulation valve
48
, a valve member
50
moves between an open and closed position to vent fluid from first conduit
32
, thereby controlling the pressure of the primary fluid flow in first conduit
32
. Valve member
50
is shown in an
40
open position in
FIG. 1. A
flow meter
52
is coupled to first conduit
32
immediately downstream of T-joint
40
. A typical flow meter measures the flow of fluid passing therethrough by measuring a pressure differential on either side of a flow element
54
, which induces a pressure drop in the primary fluid flow to create this pressure differential. Typically, relatively small conduits
56
and
58
are provided on each side of flow element
54
for communicating pressures P
1
and P
2
, respectively, on either side of the flow element to pressure sensors (not shown) so that the pressure differential can be determined. Once this pressure differential is known, the flow rate of the primary fluid flow through the flow meter can be determined. The fluid flow exiting flow meter
52
is delivered by first conduit
32
to the patient, and a patient interface device (not shown), as discussed above, couples the first conduit to the patient's airway. It should be noted that other flow meters, pressure sensors, bacteria filters, temperature sensors, humidifiers, valves and other elements can be provided at other locations in the first and second conduit. However, due to space constraints in conventional fluid delivery systems, pressure regulation valve
48
is preferably immediately upstream of T-joint
40
and flow meter
52
is immediately downstream, i.e., adjacent, T-joint
40
.
There is a significant drawback to the above-described fluid delivery system. As the secondary fluid flow enters the primary fluid flow at T-joint
40
, the secondary fluid flow disrupts the fluid profile of the primary fluid flow. The fluid profile of the primary fluid flow entering flow meter
52
affects the differential pressure across flow element
54
. That is, different fluid profiles for the primary fluid flow entering the flow meter can cause the flow meter to register different flow rates and, hence, flow volumes, even though the actual flow and volume of fluid through the system remains unchanged. This is due to the specific calibration of the flow meter for a particular fluid profile and/or the turbulence resulting from directing the secondary fluid flow at a 90° angle into the primary fluid flow.
One solution for the problem caused by the disruption of the fluid profile in the primary fluid flow due to introducing the secondary fluid flow into the primary fluid flow using a conventional T-joint is to locate the flow meter several pipe diameters downstream of the T-joint. This extra distance between the T-joint and the flow meter gives the primary fluid flow time to settle so that a constant flow profile is again achieved before the fluid enters the flow meter. This solution, however, is not practical because of the limited space in conventional fluid delivery systems and the continuing demand that such systems be kept as small as possible. The extra length for the conduit undesirably increases the size of the housing.
A possible second solution for introducing the secondary fluid flow into the primary fluid flow is to change the pathway of the primary fluid flow and the secondary fluid flow so that the two mix in a homogenous fashion. However, this solution requires a relatively large amount of space for the new pathways, and, perhaps, more importantly, introduces a pressure drop in the primary fluid flow. This pressure drop is undesirable because it adversely affects the operating ability of the ventilation and/or pressure support system. For example, such systems measure flow at the patient based on the measured flow rate at a location distal from the patient and based on the known pressure drop through the patient circuit. Introducing an additional pressure drop in the fluid mixing arrangement alters the operating parameters of the ventilation and/or pressure support system. This alteration requires costly and time consuming
Bobeck Michael
Truitt Patrick W.
Haas Michael W.
Mendoza Michael
Respironics Inc.
Weiss John G.
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