Surgery – Respiratory method or device – Means for supplying respiratory gas under positive pressure
Patent
1990-04-12
1993-03-23
Wiecking, David A.
Surgery
Respiratory method or device
Means for supplying respiratory gas under positive pressure
12820513, 12820517, 12820512, A61M 1600, A62B 704, A62B 710
Patent
active
051955164
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to breathing gas recirculation.
2. Background Information
One type of recirculation system is a gas reclaim system in which breathing gas is supplied at pressure to the user and the user's exhaust gases are recovered, reprocessed and pumped back to the user. Another type of recirculation system is a closed circuit rebreather system in which as the user breathes each breath is passed through a reprocessing circuit and returned to the user. A further type of recirculation system is a semi-closed circuit system in which part of the exhaust gases are recycled to the user, topped up with fresh breathing gas, and excess gas is expelled from the system.
In the case of a reclaim system the gas is mechanically driven around the breathing circuit; in a rebreather system the breathing action of the user has to drive the gas around the circuit. In all cases it is vital to supply adequate gas to the user without requiring him to exert great effort in breathing. A critical factor in the acceptability of any breathing apparatus to the user is the work of breathing (WOB) required: a high WOB will lead to discomfort and fatigue for the user, and may provide insufficient gas flow during heavy breathing, exertion and the like.
A large part of the WOB of any breathing gas recirculation system is associated with the energy absorbed by changes in gas flow through hoses, valves and other associated parts of the breathing apparatus. Both changes in flow rate and changes in flow direction increase the WOB.
As a user of a breathing gas recirculating apparatus breathes in and out the changes in gas flow cause pressure swings within the system. The present invention aims to minimise the pressure swings in a gas recirculation system and to provide an improved breathing gas flow to and from a user of a recirculation system. The advantages which result from this are a low system pressure drop over the breathing cycle and a low breathing resistance, hence a low WOB. The present invention aims to accommodate changes in gas flow due to the user's breathing action and thus to provide a breathing apparatus which allows a substantially constant gas flow for recirculation.
It is known to include in a breathing gas recirculation system a chamber of variable volume to accommodate breathing gas and which is capable of expanding and contracting in response to displacement of the user's own lungs which causes pressure swings in the breathing circuit. Such chambers are commonly made (at least partly) of a compliant material and are known in the art as counterlungs or breathing bags.
SUMMARY OF THE INVENTION
The present invention provides a breathing apparatus for use in recirculation of breathing gas and having a supply line for supply of gas to a user and a return line for return of exhaust gas from the user to be recirculated; the apparatus having two gas chambers of variable volume, a first in the supply line and a second in the return line; the chambers in the supply and return lines being capable of changing volume in unison with the user's breathing to accommodate a change in gas volume in the apparatus due to the user's breathing action; the first and second chambers being constrained to operate together in such a way that the variation of volume of either the first or second chamber is accompanied by a similar variation in the volume of the other chamber. Thus, both the supply- and return-line chambers would be full together (maximum operational volume), and both would be empty together (minimum operational volume).
Preferably the apparatus would be provided with a valve to shut off the supply line when the chambers contain their maximum operational volume of breathing gas and a valve to shut off the return line when the chambers contain their minimum operational volume (known as residual volume).
Preferably the variable volume is in the form of a counterlung. For example, a pair of linked counterlungs may be used, or preferably a double counterlung comprising a
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"A Clinical Guide to Cardiopulmonary Medicine", Cress et al., Printed by Puritan-Bennett Corporation, pp. 16, 17.
Asher Kimberly L.
Gas Services Offshore Limited
Wiecking David A.
LandOfFree
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