Breathing responsive device and method
United States Patent 3898987

A smooth, accurately spherical, lightweight ball is located in a smooth, accurately cylindrical glass tube. The ball forms a nearly gas-tight seal with the tube wall, but is free to move easily in the tube in response to small gas pressure changes on the ball. The tube is connected to receive the breath-induced pressure changes during breathing of a medical patient so as to indicate the instantaneous or "tidal" volume of breathing with a high degree of accuracy and sensitivity. The tube is isolated from direct contact with the breath of the patient by a thin bulbous rubber membrane or plastic bag in a chamber. One side of the membrane or the exterior of the bag is connected in the breathing circuit of the patient so that the bag or membrane tends to fill and cause the ball to rise in the tube when the patient inhales, and tends to empty and cause the ball to fall in the tube when the patient exhales. The device can be used to indicate the very small tidal volumes caused by the patient's diaphragm activity even when the patient is nearly completely paralyzed from the use of relaxant drugs used during surgery. The device can be connected so as not to indicate the volume of flow from a ventilator device if such a device is used in the breathing circuit. The volume of the bag or membrane is selected for each patient so that it will contain no more than the total "dead-space volume" of the patient's tracheal-bronchial tract so as to prevent the rebreathing of alveolar air by the patient.

Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
73/262, 116/70
International Classes:
A61B5/087; A61M16/00; (IPC1-7): A61M16/00
Field of Search:
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US Patent References:
3635215MEDICAL REMOVAL HOOK1972-01-18Rand
1684221Respiration gymnastic apparatus1928-09-11Gougnard

Primary Examiner:
Gaudet, Richard A.
Assistant Examiner:
Recla, Henry J.
Attorney, Agent or Firm:
Curtis, Morris & Safford
I claim

1. A breathing volume indicating device comprising gas conduit means for providing a substantially unimpeded guideway for a movable member, said conduit means having an elongated smooth internal surface, a movable gas-impervious lightweight member in said conduit means with a smooth outer surface and external dimensions slightly less than those of the interior of the conduit within relatively close tolerances so as to form a substantially gas-tight seal with said internal surface, means for communicating the pressure of breathing gases between a patient and said gas conduit means including means for isolating said internal surface and movable member from direct contact with said breathing gases, said isolating means further including a flexible membrane forming a chamber having a predetermined maximum volume, one side of said membrane communicating with said internal surface and said member, and the other side communicating with said gases, wherein said maximum volume is substantially equal to V, and V is given by the following equation: V T where T is the trachial-bronchial dead-space volume of the patient.

2. A device as in claim 1 in which said movable member is a hollow sphere and said internal surface is cylindrical.

3. A device as in claim 1 in which said isolating means includes a further gas-tight chamber communicating between said patient and said other side of said membrane.

4. A device as in claim 1 in which said conduit means includes a valve seat at one end, said seat being shaped to form an air-tight seal with said movable member.

5. A device as in claim 1 including at least one outlet port to said conduit adjacent one end thereof, said conduit extending past said port by a distance at least equal to the longitudinal extent of said movable member so as to allow said movable member to pass by said port and permit gas to flow through said port and said conduit.

6. A device as in claim 1 in which said flexible membrane is a thin plastic bag.

7. A device as in claim 1 in which said gas conduit means is a vertical glass tube and said movable member is a hollow sphere with thin walls.

8. A device as in claim 1 including a ventilator, driving means for driving said indicating device to zero in response to exhalation by the patient, and for driving said indicator away from zero in response to inhalation by the patient, and means for conducting the pressure of ventilation to hold said indicating device at zero so as to indicate only natural breathing volume.

9. A device as in claim 8 in which said driving means includes a chamber, said indicating device being connected to said chamber, a stop at zero for said movable member, an inspiratory conduit connected to said chamber, an expiratory conduit connected between said ventilator and said chamber, and a check valve between said ventilator and said chamber, said check valve being adapted to close to prevent flow from said chamber to said ventilator, but to open to permit flow from the ventilator to the chamber only after a predetermined volume of gas has been withdrawn from said chamber through said inspiratory conduit.

10. A device for indicating the breathing volume of a patient, said device comprising a precisely cylindrical elongated guide member, gas conduit means at the ends of said guide member for providing substantially umimpeded flow of gases to and from the interior of said cylindrical guide member, means for conducting gases to and from the patient and one of said gas conduit means, the other of said conduit means being open to the atmosphere, and a precisely spherical hollow indicator member movably positioned within said guide member and having external dimensions slightly less than those of the interior of the guide member within relatively close tolerances so as to form a substantially gas-tight seal therewith.

11. A device as in claim 10 in which said movable member is a very thin-walled metal sphere.

12. A breathing indicator device comprising an elongated tube with a smooth internal surface, a thin-walled, lightweight smooth ball in said tube forming a substantially air-tight seal with said internal surface, one end of said tube being open to the atmosphere, at least one port in said tube at a location spaced from said one end, a chamber an inspiratory breathing conduit, an expiratory breathing conduit, a flexible membrane in said chamber, further conduit means for conducting of said membrane and between said inspiratory breathing conduit and the other side of said membrane, inlet means for connecting said chamber to receive gas from said expiratory breathing conduit and from a fresh gas source, and a check valve means associated with said expiratory conduit for blocking flow from said chamber but permitting flow into said chamber after a predetermined volume of gas has been removed from chamber.

13. A device as in claim 8 in which said membrane is a polyethylene bag, and means for releasably securing said bag in place to accommodate replacement of the bag.

This invention relates to the monitoring of the breathing of medical patients. More particularly, this invention relates to devices and methods for measuring the instantaneous or tidal volume of breathing by a medical patient.

The need for an accurate and sensitive breathing indicator has existed for some time. It is an object of the invention to provide such a device, and a method of using such a device so that it is capable of measuring breathing volumes down to very low levels even when the patient is nearly completely paralyzed due to the use of relaxant drugs during surgery. It is a further object of the invention to provide such a device which is relatively easy to clean, safe and reliable to use, and sturdy in construction.

The foregoing objects have been met, in accordance with the present invention, by the provision of a breathing responsive device which includes a smooth-bore conduit with a lightweight indicator member movable in the conduit and forming a nearly gas-tight seal with the internal surface of the conduit. Preferably, the movable member is connected pneumatically to the patient's breathing circuit by means for isolating the internal surface and the movable member from direct contact with the gases being breathed by the patient. In using the device, it is preferred that the isolating means be a thin bulbous membrane or bag which tends to fill and empty with the inspiration and expiration by the patient. The volume of the bag or membrane is matched to the volume of the patient's tracheal-bronchial dead-space so as to prevent the rebreathing of alveolar air. The device preferably includes a check valve which prevents expiratory gases from moving through the breathing circuit in the wrong direction, and also has a delayed opening characteristic which facilitates the filling of the bag or membrane during inspiration.

The foregoing and other objects and advantages of the invention will be set forth or apparent in the following description and drawings. In the drawings:

FIG. 1 shows a breathing responsive device and system of the present invention, the responsive device being shown in cross-section and partially schematically; and

FIG. 2 shows a preferred form of membrane for the device of FIG. 1.

FIG. 1 shows schematically a breathing system 10 for medical patients. The system includes a tracheal tube 12 which communicates through a connector 14 to an inspiratory conduit 16 and an expiratory conduit 18. The expiratory conduit is connected to a CO2 absorber 21 and a source 20 of fresh gas. The fresh gas can be oxygen alone, or oxygen mixed with other gases such as those used for anaesthesia. The fresh gas is introduced througha coupling 22 into the conduit 18. A ventilating device 23 is provided for "ventilating," i.e., forcing fresh gases into the patient. The device 23 is a hand-operated artificial respiration bag. A pressure relief valve 24 also is provided.

The breathing indicator device 25 of the present invention is shown relatively larger than the other components of the system 10. Those other components are conventional and are shown by way of example of the various components which can be used in the breathing circuit. The device 25 includes a vertical glass tube 26 with a smooth interior surface and a spherical ball 28 inside the tube. The internal surface of the tube 26 not only is smooth but also is cylindrical with a high degree of precision. The ball 28 has a very smooth external surface and is spherical with a high degree of precision. The diameter of the ball 28 is slightly less than the inside diameter of the tube 26 so that the ball is free to move upwardly and downwardly in the tube, and yet maintain a nearly gas-tight seal with the tube.

At the lower end of the vertical portion of the tube 26 is an annularly-shaped valve seat 30. When the ball 28 rests against the seat 30, a gas-tight seal is formed so as to prevent gas from flowing downwardly through the tube 26. Near the upper end of the tube 26 is a plurality of ports 36 which permit gas to flow between the interior of the tube 26 and the interior of the envelope 38. The tube 26 is mounted in a glass envelope 38 which is mounted on top of a housing 40. The lower end of the tube 26 is bent and is open at point 34 to the atmosphere. The tube 26 is secured at its upper end 32 to the upper end of the glass envelope 38 by means of an adhesive material. The housing 40 forms an upper compartment 41 which forms a gas-tight seal around the lower portion of the tube 26.

The housing 40 forms a lower compartment 43 which is separated from the upper compartment 21 by a partition 42. The lower compartment 43 has an inlet tube 52 which is connected to the expiratory conduit 18, and a tube 50 which is connected to the inspiratory conduit 16. A passageway 44 is formed between the upper compartment 41 and the lower compartment 43 by a tube 46. Releasably secured to the tube 46 by means of a clamp 62 is a thin plastic bag 48, preferably made of polyethylene.

A cover 56 is attached to the bottom of the housing 40 by means of screw threads. The cover 56 is removable to facilitate cleaning of the interior of the chamber 43 and replacing the polyethylene bag 48.

A check valve 54 is provided at the inlet 52. The check valve closes to prevent flow in a direction opposite to the arrows marked on the expiratory conduit 18. However, it opens to permit flow in the direction of the arrows only after a certain decrease of gas pressure in the chamber 43 has been reached. The purpose of the valve will be explained in greater detail below.

In essence, the interior of the tube 26 receives the pressure changes caused by breathing of the patient so that the ball 28 moves up and down in the tube 26 to indicate the instantaneous or "tidal" volume of respiration of the patient. However, the tube 26 and the ball 28 never come in contact with the gases being breathed by the patient because of the isolation provided by the polyethylene bag 48.

During normal breathing by the patient, the device 25 operates as follows. First, the patient inhales gas through the inspiratory conduit 16. It should be pointed out that the connector 14 does not have the check valve which usually is present at the inspiratory conduit connection, for reasons which will be apparent from the following description. At the start of the inspiratory cycle, the bag 48 is collapsed and the ball 28 is at the bottom of the tube 26 resting against the valve seat 30. As the patient inhales, the pressure in the chamber 43 drops. At this time, the check valve 54 still is closed because of its delayed action. As the pressure in the chamber 43 drops, gas rushes into the interior of the envelope 38 through the ports 36 from the tube 26, and the bag 48 starts to fill with gas which flows through the opening 44. As this happens, the pressure on the upper surface of the ball 28 is reduced so that atmospheric pressure pushes the ball upwardly in the tube.

When the bag 48 is full, the pressure in the chamber causes check valve 54 to open the expiratory conduit 18. The patient breathes fresh and recirculated gas for the remainder of the inspiratory cycle. During normal breathing of an adult, an average of 700 cubic centimeters is inspired during each breath. Since the maximum volume indicated by the preferred embodiment of the device is only 120 c.c., around 580 c.c. of gas is inhaled without moving the ball. It should be noted that the coupling 14 does contain a check valve at 60 in the expiratory conduit as an extra precaution to prevent the inspiration of gas through the expiratory conduit.

If the volume of the gas which fills the bag 48 is greater than the maximum limit of travel of the ball 28, the ball moves to the position shown in dashed outline in the drawing at the top of tube 26, and gas continues to flow from the atmosphere into the tube and through the ports 36, but without driving the ball any further.

During the expiratory cycle, the patient exhales and, since there is no check valve in the inspiratory conduit 16, gas at first flows back through that conduit into the chamber 43. The check valve 54 is closed. As a result, the bag 48 collapses. This forces air upwardly into the tube 26 through the ports 36 and drives the ball 28 downwardly. When the bag has collapsed, the ball 28 will be seated against the valve seat 30, thus forming a check valve against the flow of any further air out of the outlet 34 into the atmosphere.

When the bag has collapsed, the gas exhaled by the patient goes through the expiratory conduit 18, the CO2 absorber 21, has fresh gas added to it at 22, etc.

Thus, the ball 28 rises and falls with normal breathing by the patient, but does not actually measure the full tidal volume.

The volume of the bag 48 is matched to the volume of the patient's tracheal-bronchial "dead-space." This dead-space volume is approximately 150 c.c. for most adults. For such adults, the volume of the bag is selected to be slightly lower, e.g. 120 c.c. The dimensions of the tube 26 and ball 28 are such that full-scale deflection of the ball gives a volume reading of 120 c.c., as it has been noted above. As a result, the filling and emptying of the bag 48 for adults causes substantially full-scale movement of the ball. However, for infant patients, the volume of the bag should be considerably less, with the result that the deflection of the ball 28 will not be full scale, even for infants who are breathing normally, because the maximum degree of movement of the ball depends on the volume of the bag. The reason for matching the volume of the bag 48 to the patient in this manner is to prevent the rebreathing of alveolar air by the patient. Since a volume of up to 120 c.c. of air is breathed into the chamber 43 at the start of each expiratory cycle, that same air is breathed by the patient during the subsequent inspiratory cycle. However, since the volume of this rebreathed gas is less than the tracheal-bronchial dead-space volume, the gases being rebreathed are not alveolar; that is they do not have increased CO2 and reduced oxygen content and are not harmful to the patient.

The ball 28 and the tube 26 must be made with care in order to prevent excessive leakage of air past the ball, which would reduce the accuracy and precision of the device. A tube 26 which has been built and tested successfully is a "Corning Precision Pyrex" tube with an internal diameter of 0.7501 inch and a wall thickness of 0.125 inch. The internal diameter of the tube is accurate to within one ten thousandth of an inch (0.0001 inch). A ball 26 which has been used successfully in the invention is a hollow nickel sphere with an outside diameter of 0.746 inch, which dimension also is maintained to within one ten thousandth of an inch (0.0001 inch). The weight of this sphere is 0.6 gram.

The Pyrex tube is manufactured by Corning glass, and the nickel sphere is manufactured by J. H. Emerson & Co. of Cambridge, Massachusetts.

It is believed that the sphere is manufactured according to the following procedure. First, the exterior of a hollow aluminum sphere is ground to a high degree of sphericity. Then it is plated with a nickel coating less than one thousandth (0.001 inch) of an inch thick. Holes then are drilled in the sphere, and then the aluminum is leached out of the inside with sodium hydroxide or other alkalis. Then the holes are filled. All that remains is a very thin, very lightweight, very precisely spherical hollow ball.

It has been found that a top quality table tennis or "ping-pong" ball also has the sphericity and light weight to be used as an indicator in the tube. However, table tennis balls are not made with a diameter which is suitable for the specific preferred embodiment of the invention shown in the drawings. Therefore, the spherical metal ball is preferred. However, it is believed that the process which is used to make table tennis balls also can be used to make a satisfactory ball of a smaller diameter for use in this invention.

FIG. 2 illustrates the preferred form of the membrane which is used to isolate the tube 26 from direct contact with the gases in the breathing circuit. Instead of the wall 42 and bag 48, a thin rubber diaphragm 70 is mounted so as to separate chamber 41 from chamber 43. The membrane 70 has concentric convolutions 72 and 74. The central convolution 74 is twice the diameter of the other. The membrane 70 provides a thin-walled flexible bulbous wall which fills and empties like the bag 48 of FIG. 1, but which is structurally more stable than the bag.

The membrane 70 is held place held in a pair of retainer rings which easily are forced into a friction fit with the walls of the housing 40.

The membrane 70 preferably is made of a thin (e.g. 0.002 to 0.005 thick) rubber material such as "Silastic" silicone rubber sold by Dow Corning, Inc.


The device of this invention appears to be particularly useful in measuring and indicating the very small tidal volumes which occur in the breathing of a patient who is under the influence of relaxant drugs such as curare, pancuronium, gallamine, etc. These drugs are used to relax the muscles of the patient so that they will not twitch and interfere with certain surgical operations. When such relaxant drugs are used, the patient must be made to breathe artificially, i.e. he is "ventilated," because his respiratory muscles are paralyzed. However, the diaphragm muscles of the patient are the last to become paralyzed under increasing doses of relaxant drugs. Thus, the highly sensitive indicator device 25 can be used to show the residual activity of the diaphragm in a patient to indicate the degree of relaxation and give the anaesthesiologist an indication of the need for further relaxant drugs, or an indication of an overdose. Thus, the device is useful as a relaxation detector.


Tidal volume can be read visually with the aid of either index marks 58 on the outer envelope 38, or similar marks on the outside of the inner tube 26. However, the position of the ball 28 can be detected by electrical or optical means and converted into electrical signals for driving recorders, drug dispensing equipment, etc. In fact, the indicator device shown in the drawings is particularly well-adapted to provide such an electrical readout. The reason for this is that the gas in the tube 26 is almost entirely atmospheric air and contains no nitrous oxide, water vapor, or other gaseous components found in relatively large quantities in the gases breathed by the patient. This is a result of the ioslation provided by the plastic bag 48. Thus, these gaseous components do not interfere with the optical or electrical sensing of the position of the ball 28. Additionally, it has been found, unexpectedly, that the water vapor from the patient's breath does not reach the ball or the tube 26, and thus does not produce condensation which might collect on the tube walls and impede the travel of the ball in the tube.

The device and method of this invention have advantages in addition to those mentioned above. One advantage is that of sterility and cleanability. The bag 48 can be made inexpensively and thus can be discarded after each use by a patient. The housing 40 preferably is made of a polycarbonate material and also is easy to clean. The membrane 70 is easy to remove, replace and clean.

As it has been pointed out above, the device 25 can be used with patients of varying size and age simply by changing the size of the bag 48 to match it to the size of the patient. The size of the membrane 70 similarly can be varied. Thus, the same device can be used for infants as well as adults.

When it is used with a ventilator producing inflation of the intermittent positive-pressure type, such as that provided by the manual respiration bag 23 shown in the drawings, the device 25 does not indicate the inflation pressure created by the ventilator. This is because the inflation pressure is applied after the expiration cycle of the patient, during the time which the bag 48 is collapsed and the ball 28 rests on the seat 30. Thus, the tidal volume indicator can be used to indicate solely the diaphragm activity of a ventilated patient.

The check valve 54 preferably is a conventional valve which has a relatively high degree of resistance to opening so that it requires negative pressures of the order of 1 or 2 centimeters of water before it will open. Additionally, a restricted orifice 57 is formed in the expiratory conduit just upstream from the check valve 54 by means of a short length of tubing 55. The orifice 57 helps to keep the check valve from opening too soon. For example, the inside diameter of the tube 52 at the inlet to the chamber 43 is 0.75 inch, whereas the inside diameter of the tubing 55 is 0.25 inch. Check valves with springs to keep them from opening sooner than desired also are known and usable.

The above description of the invention is intended to be illustrative and not limiting. Various changes or modifications in the embodiments described may occur to those skilled in the art and these can be made without departing from the spirit or scope of the invention.