Inspiratory tube for a ventilator

An inspiratory tube intended to serve as at least part of an inspiratory line in a ventilator, has a tube wall, a distal end, a proximal end, a gas flow channel for carrying a flow of breathing gas and an opening in the wall at a specific distance from one end of the inspiratory tube, this opening being adapted for connection to an expiratory device (40). The inspiratory tube has a constriction in the gas flow channel between distal end of the inspiratory tube and the opening, a first channel that proceeds within the tube wall, generally parallel to the gas flow channel, and which opens into the gas flow channel between the distal end of the inspiratory tube and the constriction, and a second channel that proceeds within the wall, generally parallel to the gas flow channel, which opens into the gas flow channel between the constriction and the opening. The channels can be connected to a pressure gauge for determining the rate of flow and pressure of gas flowing in the gas flow channel.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is directed to an inspiratory tube intended for use 
as at least a part of an overall inspiratory line in a ventilator, the 
inspiratory tube being of the type having a tube wall, distal and proximal 
ends, a gas flow channel for carrying a flow of breathing gas, and an 
opening in the wall at a distance from the distal end of the tube, the 
opening being adapted for connection of an expiratory device thereto. 
2. Description of the Prior Art 
An inspiratory tube of the above type is described in PCT Application WO 
94/06499. This known ventilator has an inspiratory tube connected to a gas 
source at one end and to the patient at the other end. An expiratory valve 
is connected to the inspiratory tube at a specific distance from the 
patient. In one embodiment, the expiratory valve is connected to a second 
gas source for the purpose of maintaining a pre-adjustable Positive 
End-Expiratory Pressure (PEEP). In another embodiment, the expiratory 
valve is instead connected to the gas source via a valve system in order 
to maintain PEEP. A pressure gauge and flow meter are arranged in the 
inspiratory tube between the gas source and the expiratory valve. A 
control unit controls the entice ventilator. This known ventilator is 
primarily intended for use as a home care ventilator, i.e. a respirator a 
patient can use at home. 
Interest in home care ventilators is steadily increasing. This is because 
such a device is advantageous to the patient, who is able to be in her/his 
own home and can enjoy a greater degree of mobility. There are also public 
health benefits, since home care frees hospital resources by reducing 
in-patient treatment time, beds in intensive care being particularly 
costly. This type of ventilator can be battery-powered and is sometimes 
referred to as a `portable` ventilator. Despite this terminology, such a 
ventilator usually weighs quite a few kilograms and can only be carried 
around with some difficulty, even by healthy people. 
A genuinely portable ventilator, i.e. a ventilator (weighing up to 1 kg, 
preferably less than 500 g) the patient is easily able to carry, with a 
capacity sufficient to provide respiratory assistance for several hours, 
would be even more desirable for patients. Miniaturizing a ventilator to 
this extent, employing modern turbine, battery and microprocessor 
technology etc., is thoroughly feasible. One important factor in this 
process would be to retain every essential function available in a 
conventional ventilator, such as the ability to maintain a PEEP, to as 
large an extent as possible. Such a fully portable ventilator would be 
suitable for virtually every kind of patient. It even could be used as an 
emergency ventilator for a number of applications and could be included in 
the basic equipment of e.g. aircraft, buses, boats, ambulances, fire 
engines, etc. 
The known inspiratory tube described above has limitations, since a number 
of connectors are needed for the pressure gauge and flow meter. This known 
inspiratory tube also has a design that limits its usefulness and makes 
the use of separate gas sources or special valve systems necessary for 
controlling the expiratory valve etc. connected to the inspiratory line. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an inspiratory tube that 
can be used in a simple and safe fashion for a number of functions with no 
need for special, additional tubing. 
Another object of the invention is to provide an inspiratory tube that is 
primarily suitable for miniaturization for achieving a fully portable 
ventilator. 
The above objects are achieved in accordance with the principles of the 
present invention in an inspiratory tube of the initially-described type, 
having a constriction disposed in the gas flow channel between the distal 
end of the inspiratory tube and the opening adapted for connection to an 
expiratory device, a first channel proceeding within the wall generally 
parallel to the gas flow channel and opening into the gas flow channel at 
a location between the distal end of the inspiratory tube and the 
constriction, and a second channel proceeding within the wall generally 
parallel to the gas flow channel, and opening into the gas flow channel 
between the constriction and the opening adapted for connection to an 
expiratory device, with the first and second channels being adapted for 
connection to a pressure gauge for determining a rate of flow and pressure 
of gas flowing in the gas flow channel. 
A number of advantages are achieved when the inspiratory valve is devised 
with a constriction in the gas flow channel, between one end of the 
inspiratory tube and an opening for an expiratory device, and channels 
that proceed inside the wall of the inspiratory tube and open into the gas 
flow channel at either side of the constriction. The pressure gauge/flow 
meter can be connected to the channels and measure pressure/flow between 
the expiratory valve and the distal end of the inspiratory tube, i.e. 
close to the patient. These measurements are a prerequisite for a control 
unit to calculate and regulate a flow of gas in such a way that the flow 
of gas maintains a PEEP for the patient when the tube is used with a 
ventilator. 
Placing pressure/flow rate measurement functions near the patient also 
means that every attempt by the patient to inhale can be sensed in a 
simple and reliable manner. The patient can then be provided with rapid 
assistance for a new inspiration (inhalation). A flow of breathing gas is 
also already present at the expiratory valve. When this valve is closed, 
an inspiratory gas flow at a specific pressure and with a specific flow 
rate profile can be rapidly generated and supplied to the patient. This 
rapid response to attempted inspiration is not available with the 
aforementioned known inspiratory tube and ventilators. 
The inspiratory tube can be devised with a dispensing channel arranged in 
its wall, generally parallel to the gas flow channel, and the dispensing 
channel is arranged with an opening into the gas flow channel between the 
distally spaced opening and the distal end of the inspiratory tube. The 
dispensing channel can also be connected to a dispensing unit for 
dispensing an additive gas into the gas flow channel. 
In a corresponding manner, an additional channel, from which gas samples 
can be extracted, can be arranged in the wall of the inspiratory channel. 
This channel can appropriately open into the gas flow channel between the 
distally spaced opening and the distal end. 
The constriction can appropriately be integrally formed as part of the 
inspiratory tube. 
An expiratory control channel can also be arranged in the wall, generally 
parallel to the gas flow channel, and having an opening to ambient 
atmosphere between the distally spaced opening and the inspiratory tube's 
proximal end. The expiratory control channel can be connected to an 
expiratory valve and a source of compressed gas for controlling expiratory 
phases. 
The different channels proceed appropriately through one or more 
reinforcements of the wall of the inspiratory tube. These reinforcements 
can be devised so the cross-section of the inspiratory tube is unique and 
so the tube can only be connected to the ventilator in one way.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows how a patient 2 can become almost completely mobile with the 
aid of a fully portable ventilator 4. The patient 2 is connected to the 
ventilator 4 in some suitable fashion via an inspiratory tube 6. 
Connecting the fully portable ventilator 4 via a nasal route is 
preferable, since the patient 2 would then find it easier to speak and 
communicate with others. It should be noted that the fully portable 
ventilator 4 can also be connected in other ways, e.g. via a face mask, 
tracheal tube or tracheostomy/ tracheotomy tube. The latter implements are 
preferable when the ventilator 4 is used in emergencies or for patients 2 
requiring greater breathing assistance. 
FIGS. 2 and 3 show details of the inspiratory tube 6. It should be noted 
that the inspiratory tube 6 can be formed as a complete inspiratory line 
or can be a part of an inspiratory line in a ventilator system. The design 
of the inspiratory tube 6 makes it particularly suitable for portable 
ventilator systems. 
The inspiratory tube 6 according to the invention contains a gas flow 
channel 18 surrounded by a casing or wall 19. An opening 50 is arranged at 
a specific distance from the distal end 6A of the inspiratory tube 6. An 
expiratory device (described below) can be connected to this opening 50. A 
constriction 28 is arranged in the gas flow channel 18 between the opening 
50 and the distal end 6A. The constriction 28 causes a drop in the 
pressure of gas as which flows across the constriction 28, the drop being 
proportional to the rate of flow. This accordingly makes it possible to 
measure both flow and pressure near the distal end 6A (to which a patient 
is attached when the inspiratory tube 6 is used) in a simple, space-saving 
fashion. 
The wall 19 has reinforcements 21, 23 on the upper and lower sides of the 
inspiratory tube 6 to provide space for a number of channels. These 
reinforcements 21, 23 (and distribution of the channels around the gas 
flow channel 18) can naturally be devised in virtually any fashion but are 
advantageously asymmetrical or arranged in such a way that the 
cross-section of the inspiratory tube 6 is unique. This design then 
functions as a key-indexing to guarantee correct connection of the 
inspiratory tube 6 to a ventilator or some other device intended for the 
inspiratory tube 6. 
Thus, a first channel 24 proceeds through the upper reinforcement 21. The 
first channel 24 opens into the gas flow channel 18 between the 
constriction 28 and the opening 50. The first channel 24 can be connected 
at the other end to a pressure gauge (see below). A second channel 26 
proceeds parallel to the first channel 24 through the upper reinforcement 
21. The second channel 26 opens into the gas flow channel 18 between the 
constriction 28 and the distal end 6A. The second channel 26 can also be 
connected at the other end to a pressure gauge (see below). 
A gas sampling channel 32 and a dispensing channel 36, both of which open 
into the gas flow channel 18 between the constriction 28 and the distal 
end 6A, also proceed through the reinforcement 21 of the upper wall 19. An 
expiratory control channel 42 runs through the lower reinforcement of the 
wall 19. This channel opens into ambient atmosphere at a point proximal to 
the opening 50. The object of these channels 32, 36, 42 will be evident 
from the following. 
One embodiment of the ventilator 4, including the inspiratory tube 6, will 
now be described, referring simultaneously to FIGS. 4 and 6. Gas flow and 
pressure are generated by a turbine 8 connected to the atmosphere in some 
suitable fashion, e.g. via a number of openings 10 or the like. These 
openings 10 can also be equipped with filters to prevent any particles 
from being carried down into the lungs. The turbine 8 is connected to a 
pressure tank 12 holding breathing gas at a specific pressure generated by 
the turbine 8. The purpose of the pressure tank 12 is to make delivery to 
the patient 2 of breathing gas at a desired pressure and flow rate faster 
than if the turbine 8 were to generate pressure and flow from zero. The 
pressure tank 12 is relatively small, so it occupies less space and 
shortens the rise time for a pressure increase with a smaller volume. A 
control valve 14 is arranged after the pressure tank. In this instance, 
the control valve 14 is a `scissors` valve regulated by a stepper motor 
16. The control valve 14 regulates the flow of gas from the pressure tank 
12 into a gas flow channel 18 in the inspiratory tube 6. The control valve 
14 is also small, thereby enabling it to respond more rapidly to control 
signals (small inertia). This results, in turn, in the delivery of 
breathing gas, via the control valve 14, with steep gas pressure gradient. 
The gas flow channel 18 carries breathing gas to the patient 4 at the 
distal end 6A of the inspiratory tube 6. 
The turbine 8, pressure tank 12, control valve 14 and stepper motor 16 
jointly constitute a gas flow generator capable of generating an optional 
gas flow in the flow rate and pressure ranges relevant in the treatment of 
different kinds of patients. Although this construction of the gas flow 
generator is advantageous, especially in achieving fully portable 
ventilators 4, the gas flow generator can have other components. For 
example, a compressor or fan can replace the turbine 8. The turbine 8 can 
also be replaced with a pressurized source of gas, such as a gas cylinder 
or a piped compressed air system. The pressure tank 12 can be resilient or 
non-resilient or can be dispensed with completely. A resilient pressure 
tank can contribute to the generation of higher pressures by being 
compressible. In principle, the control valve 14 can be any kind of known 
valve. The stepper motor 16 can be dispensed with or replaced by some 
other known actuator, depending on the choice of the control valve 14. The 
components of the gas flow generator affect the size and portability of 
the ventilator 4. In principle, however, the same functionality can be 
achieved regardless of the components employed. The exact components used 
in the gas flow generator are not crucial to application of the invention. 
The turbine 8 and the stepper motor 16 are controlled by a control unit 20. 
The control unit 20 can be formed by hardware, or by software or a 
combination thereof. The control unit 20 controls all functions in the 
ventilator 4 so parameter settings (made via a user interface, not shown) 
are maintained. The control unit 20 receives information on pressure and 
flow for use in maintaining those functions. Flow information is received 
from a flow meter 22 which is connected to the distal end of the 
inspiratory tube 6 via a first channel 24 and a second channel 26. In 
principle, the channels 24, 26 proceed parallel to the gas flow channel 18 
in the wall of the inspiratory tube 6 and open onto either side of a 
constriction 28 in the gas flow channel 18. The pressure of the gas drops 
when it flows through the constriction 28, the magnitude of the drop being 
related to the magnitude of the flow. Flow through the flow meter 22 
therefore can be determined by measuring pressure on either side of the 
constriction 28. Since pressure is employed in this instance for 
determining the flow rate, the second channel 26 can be connected to a 
pressure gauge 30 in order to measure pressure at the distal end 6A of the 
inspiratory tube 6. 
It should be noted that other flow meters, suitable for placement near the 
distal end 6A, can replace the flow meter 22. A separate channel would 
then be necessary for the pressure gauge 30. Since the flow meter 22 
determines the flow rate from the pressure drop across the constriction 
28, the pressure signal can be obtained straight from the flow meter 22 
instead of from a separate pressure gauge 30. 
A gas sampling channel 32, which terminates at the distal end 6A, extends 
through the inspiratory tube 6. Gas samples can be taken from the gas 
sampling channel 32 and analyzed in a gas analysis unit 34. The gas 
analysis unit 34 appropriately contains a pump for extracting the gas 
samples to be analyzed. Gas analysis can be performed to monitor carbon 
dioxide levels or check to ensure that sufficient breathing assistance is 
being provided. Gas analysis can also be performed to check on the 
composition of the breathing gas being supplied to the patient 2. If the 
gas and flow meters used are fast enough, carbon dioxide output and oxygen 
consumption can also be determined. 
The latter is of interest when the inspiratory tube 6 contains a dispensing 
channel 36 for dispensing an additive gas to the patient 2. The dispensing 
channel 36 is connected to a dispensing unit 38 and opens into the gas 
flow channel 18 at the distal end 6A. The dispensing unit 38 includes a 
small gas cylinder containing additive gas and has a dispensing valve for 
regulating the amount dispensed. The additive gas can be oxygen or some 
other gas, such as NO. The dispensing unit 38 can also hold medication or 
some liquid additive which is dispensed through the dispensing channel 36 
into the gas flow channel 18. The additive can be vaporized in this 
channel or dispersed in small droplets (atomized) before being delivered 
to the patient 2. 
An expiratory valve 40 is also connected to the inspiratory tube 6. In the 
illustrated example, the expiratory valve 40 is built into the wall of the 
inspiratory tube 6 so it occupies as little space as possible. A tube or 
the like can also be connected between the inspiratory tube 6 and the 
expiratory valve 40 without affecting its function (as described below). 
The expiratory valve 40 is connected to the gas flow channel 18 so that the 
constriction 28 and the openings of the channels 24, 26, 32, 36 lie 
between the expiratory valve 40 and the distal end 6A. 
In this embodiment, the expiratory valve 40 is a pneumatically controlled 
ON/OFF valve (e.g. a mushroom valve). It is connected to the pressure tank 
12 via a control channel 42 and a switching valve 44. The control channel 
42 proceeds in the wall of the inspiratory tube 6, parallel to the gas 
flow channel 18 and other channels 24, 26, 32, 36. The switching valve 44 
is controlled by the control unit 20. 
During inspiratory phases (inhalation phases), the switching valve 44 is in 
a first position in which the control channel 42 is connected to the 
pressure tank 12 via a first gas connection 46. The expiratory valve 44 is 
then closed with the same actuating pressure (usually higher than the 
pressure of the breathing gas delivered to the patient 4) as the pressure 
in the pressure tank 12. 
During expiratory phases, the switching valve 44 is switched to a second 
position in which the expiratory valve 40 is connected to the atmosphere 
via the control channel 42, the switching valve 44 and a second gas 
connection 48. 
If a positive end-expiratory pressure (PEEP) is to be maintained for the 
patient 2, the control valve 14 is regulated so that a flow of gas is 
released through the gas flow channel 18 toward the patient 2, even during 
expiration. This flow of gas is controlled by the control unit 20 
according to the pressure and flow measured between the expiratory valve 
40 and the distal end 6A. This regulated flow of gas also flows out 
through the expiratory valve 40 but simultaneously serves as resistance in 
relation to the patient 4, who accordingly exhales against a pressure 
corresponding to the selected PEEP. 
This kind of PEEP regulation was not previously possible, especially not in 
portable ventilators. Here, the placement of pressure/flow measurement 
between the expiratory valve 40 and the distal end 6A (the patient 4) 
plays a decisive role. PEEP cannot be regulated and maintained in this way 
unless information is available on pressure/flow at the patient 2. 
This location for pressure/flow measurement also produces other advantages. 
For example, the ventilator 4 can be made to respond more rapidly to any 
efforts by the patient 2 to inhale (i.e. triggering). The ventilator 4 can 
in particular respond immediately to any inspiration commenced during 
expiration. Flow will then be registered as moving towards the patient 2, 
and the control unit 20 can respond immediately, closing the expiratory 
valve 40 and introducing an inspiratory flow of gas. This flow commences 
relatively quickly, since a flow of gas is already being maintained 
through the gas flow channel 18. 
The placement of just about all the components in a common enclosure, with 
all the necessary gas channels arranged in the inspiratory tube 6, makes 
the ventilator 4 very compact and easy to use. The few parts (the 
enclosure and inspiratory tube 6) are interconnected in a suitable 
fashion. For example, known types of bayonet or pin (keyed) index 
connectors can be used. No additional cords or tubing, which could become 
entangled with each other or other objects, are needed. As noted above, 
the described embodiment is one advantageous version of a fully portable 
ventilator, but the embodiment can be utilized for a number of different 
applications. For example, it can be used as a home care ventilator for 
patients who do not require constant monitoring. It can also be used in 
ambulances or as an emergency ventilator. A third option is to use it for 
non-acute (non-critical care) treatment in hospitals. In other words, it 
can be employed for virtually every application for which a ventilator is 
needed. In all of these options, ventilator use is facilitated by the 
design of the inspiratory tube 6. 
The portable ventilator is battery-powered. The batteries can naturally be 
rechargeable, and the provision of a parallel AC power source is a an 
option. 
The ventilator does not need to incorporate every option. The ventilator 4 
can be devised in both simpler and more complex versions. In principle, a 
simple version includes the turbine 8, pressure tank 12, control valve 14, 
stepper motor 16, control unit 20, flow meter 22 (doubling as a pressure 
gauge), inspiratory tube 6 (with the channels 18, 24, 26 and 42), 
expiratory valve 40, switching valve 44 and batteries (not shown). This 
kind of simple version of the ventilator 4, utilizing existing components, 
can be manufactured in about the same size as a portable cassette or CD 
player, i.e. about 10.times.10.times.2 cm and weigh a few hundred grams. 
Although modifications and changes may be suggested by those skilled in the 
art, it is the intention of the inventor to embody within the patent 
warranted hereon all changes and modifications as reasonably and properly 
come within the scope of his contribution to the art.