U.S. patent number 3,742,939 [Application Number 05/118,280] was granted by the patent office on 1973-07-03 for method and apparatus for determining respiratory airway resistance.
Invention is credited to William J. Sayer.
United States Patent |
3,742,939 |
Sayer |
July 3, 1973 |
METHOD AND APPARATUS FOR DETERMINING RESPIRATORY AIRWAY
RESISTANCE
Abstract
A method and apparatus for determining nasal or tracheobronchial
respiratory airway resistance in a person. The volume of freely
breathed air, pharyngeal pressure, and time duration of a breath
are measured or recorded. Preferably, a narrow pharyngeal pressure
range is chosen to optimize the validity of the data. Further, the
choice of data in which the volume of air breathed per unit time is
substantially constant enhances the validity of the data.
Inventors: |
Sayer; William J. (Palo Alto,
CA) |
Family
ID: |
22377612 |
Appl.
No.: |
05/118,280 |
Filed: |
February 24, 1971 |
Current U.S.
Class: |
600/533;
411/937.2 |
Current CPC
Class: |
A61B
5/0935 (20130101); A61B 5/085 (20130101) |
Current International
Class: |
A61B
5/093 (20060101); A61B 5/085 (20060101); A61B
5/08 (20060101); A61b 005/08 () |
Field of
Search: |
;128/2.08,2.07,2C,2R,2.08 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
1,508,303 |
|
Nov 1967 |
|
FR |
|
1,915,959 |
|
Oct 1970 |
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DT |
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Other References
Gulesian, P.J., IEEE Trans on Bio-Med Engineering, Sept.,
1971,pp.378-382, (copy in GR.335, 128/2.08) .
Jaeger, J.J., et al, Journ. of Applied Physiology, Vol. 19, No. 4,
July,1964, pp.813-820, (Copy in GR.335,128/2.08).
|
Primary Examiner: Howell; Kyle L.
Claims
I claim:
1. A method of deriving data for use in calculating nasal or
tracheobronchial airway resistance of a person comprising the
simultaneous steps of
measuring and recording the volume of air freely inspired or
expired during a breath through either the mouth or nasal passages
of a person,
measuring and recording time during the breath,
measuring the pharyngeal pressure of the person during the breath,
and selecting the data for calculation only when the volume of air
per unit time is substantially constant during the breath.
2. The method of claim 1 wherein said volume of air and time
duration are measured only when the pharyngeal pressure of the
person is within a limited pressure range where the volume of air
per unit time is substantially constant during the breath.
3. Apparatus for deriving data for use in calculating nasal or
tracheobronchial airway resistance of a person comprising
means for measuring and recording the volume of air freely inspired
or expired during a breath through either the mouth or nasal
passages of a person,
means for measuring and recording the time during said breath,
means responsive to said means for measuring the pharyngeal
pressure to actuate said means for measuring and recording the
volume of air and said means for measuring and recording time only
when the volume of air per unit time is substantially constant.
means for measuring the pharyngeal pressure of the person during
said breath.
4. Apparatus according to claim 3 wherein the means for measuring
and recording the volume of air includes:
substantially air-tight mask means adapted to fit over the nostrils
or mouth of the person,
spirometer means, and
tube means connecting said spirometer means to said mask means.
5. Apparatus according to claim 4 wherein the means for measuring
pharyngeal pressure comprises:
a hollow mouthpiece insertable into the mouth of the person,
pressure measuring means, and
tube means for connecting said mouthpiece to said pressure
measuring means.
6. Apparatus according to claim 5 wherein the means for measuring
and recording time during the breath comprises a kymograph pen and
ink chart recorder.
7. A method of determining the nasal or tracheobronchial airway
resistance of a person comprising the simultaneous steps of
measuring and recording the volume of air freely inspired or
expired during a breath through either the mouth or nasal passages
of a person,
measuring and recording time during the breath,
measuring the pharyngeal pressure of the person during the breath,
selecting the measured volume and time where the volume of air per
unit time is substantially constant, followed by the step of
calculating the nasal airway resistance of the patient using only
the data where the volume of air per unit time is substantially
constant according to the relationship
R = Po - Pp/V/t ,
where R is the nasal airway resistance, Po is the atmospheric
pressure, Pp is the average pharyngeal pressure during the breath
and V/t is the volume of air per unit time inspired during the
breath.
8. The method of claim 7 wherein said volume of air and time
duration are measured and recorded only when the pharyngeal
pressure of the person is within a limited pressure range during
the breath.
Description
BACKGROUND OF THE INVENTION
Medical attempts to evaluate nasal airway capacity or "nasal
congestion" date back at least to 1889 when Zwaardemeker wrote
about his cold mirror test. It is accepted that a patient's own
observations about his nose are not determinative and looking in
the nose also fails to yield the complete picture. Therefore, an
accurate measurement of nasal and/or tracheobronchial airway
capacity is important to both the clinical practitioner and medical
researchers.
The condition of the nasal passages affects the resistance to air
flow through the nostrils in the same way that air flow in any tube
depends on its structure (length, diameter, shape) according to
Poiseuille's Law. In his text Physiology of Respiration by Julius
H. Comroe, Jr., M.D. Year Book Medical Publishers, Inc., 1965, air
flow in patients' is compared to air flow in tubes. Dr. Comroe
points out that air flow resistance is a calculated dimension and
that resistance across the nasal or tracheobronchial airways is
equal to:
Atmospheric pressure -- pressure in the oropharynx/flow. The
determination of nasal or tracheobronchial airway resistance has
been a difficult task, particularly because the pharyngeal pressure
(pressure in the nasopharynx) varies substantially during the
inspiration - respiration cycle. Also, the simple linear
relationship between pressure and flow to yield the airway
resistance has been proven invalid as hysteresis occurs at very low
and very high pressures.
One prior art method was originally presented in 1939. In that
approach a transducer is used to measure the difference in pressure
between the nasopharynx and a nasal mask. The air flow is measured
and plotted opposite the pressure at each instant of time to obtain
a plot of resistance. This method provides results of questionable
validity because it attempts to apply the simple first order
relationship of pressure divided by flow values for all pressure
encountered, whereas this relationship holds true only for a common
pipe having laminar flow therein.
Another prior art approach, recognizing the diminished significance
of testing over a wide pressure range, eliminates completing the
pressure measurement and relies solely on a measurement of air flow
through the nasal airway. This method is described in an article
"Nasal Spirometry" by Murray D. Morrison, M.D., in Arch Otolaryng,
Vol. 90, Nov. 1969.
In a further prior art approach, a mask with selected inlet members
measures pharyngeal pressure and pressure at the inlet to the
nostrils during breathing, but without measuring volume.
One prior art U.S. Patent provides a rather complex instrument for
measuring nasal airway resistance. Air flow is indirectly measured
by looking at a pressure differential. The device appears to be an
elaborate successor to the 1939 method, and because it tests over a
wide pressure range it suffers from the same inaccuracies.
SUMMARY OF THE INVENTION
The apparatus and method of the present invention overcome the
shortcomings of the prior art by measuring parameters from which
nasal or tracheobronchial airway resistance may be calculated in a
narrow pharyngeal pressure range, allowing selection of that range
in which the linear relationship between pressure and air flow
volume is most nearly valid. In one embodiment of the invention,
the pharyngeal pressure is monitored during a patient's expiratory
or inspiratory phase and when the pressure fits within prescribed
limits the nasal or tracheobronchial air flow is measured and
recorded. The nasal or tracheobronchial airway resistance may then
be calculated by dividing the difference between atmospheric
pressure and the selected pharyngeal pressure by the air flow. The
details of the apparatus and method of the present invention along
with further advantages thereof will become evident as the detailed
description of the preferred embodiment is read and understood.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic side view of the apparatus of the present
invention as used with a patient.
FIG. 2 is a perspective view of a two-way valve forming a portion
of the apparatus of the present invention.
FIG. 3 is a schematic end view of a portion of the apparatus of the
present invention.
FIG. 4 is a perspective view of a three-way stop-cock valve forming
a portion of the apparatus of the invention.
FIG. 5 is a graph of air volume per unit of time (air flow)
generated by the kymograph and pen that forms a portion of the
apparatus of the invention.
FIG. 6 is a schematic view of a portion of the apparatus having a
modified face mask as used with a patient.
FIG. 7 is a side elevation view of a mouthpiece adapted for use in
measuring tracheobronchial airway resistance.
FIG. 8 is a schematic end view of a portion of the apparatus of
FIG. 3 modified for measurement of tracheobronchial airway
resistance.
FIG. 9 is a schematic view of the mouthpiece of FIG. 7 as used with
a patient to measure tracheobronchial airway resistance.
FIG. 10 is a schematic end view of the apparatus of FIG. 8 modified
to include a pair of gauge switches.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now particularly to FIGS. 1 and 3 of the drawings, a
conventional spirometer 2 and kymograph 4 is shown supported on a
suitable base means 6. A suitable spirometer and kymograph is the
Warren E. Collins, Inc., "Respirometer" No. P-900 described in that
company's 1966 catalog. For use in this invention the Collins
"Respirometer" may be used virtually as provided or if less
resistance to air flow is desired it is modified by removing the
inner soda lime cannister and rubber flutter valve. Either device,
for which any suitable equivalent means may be substituted, is
essentially a source of air, the volume of which can be accurately
measured with respect to time. Thus, the bell 8 is filled with air
when it is raised by the chain and counterbalance 10. The three-way
stop-cock valve 12 is rotated to permit room air to be drawn
through tube 14 to fill the bell 8. Tube 16 is in parallel to tube
14 and could be eliminated if desired. Tubes 14 and 16 are
supported by a pair of flexible goose-neck supports 18 and 20.
The kymograph 4 has a removable paper chart 22 mounted on a
motor-driven cylinder 26 and a moving pen 24 for marking thereon.
As described hereinafter, the cylinder 26 is driven only when the
patient's pharyngeal pressure is within the prescribed limits, thus
creating a chart record only during those time periods.
Tubes 14 and 16 are joined in a two-way valve 28, shown in greater
detail in FIG. 2. When the lever 30 is in the position shown,
openings 32, 34 and 36 are connected in a closed system, thus
connecting tubes 14 and 16 together to tube 40. When the lever is
rotated 90.degree., tubes 14 and 16 are connected together in a
closed system and tube 40 at opening 36 is open to the room air via
slot 42. Tube 40 is attached via a coupling 42 to a scuba-type face
mask 44 that fits over the patient's nose in an air-tight manner. A
disposable mouthpiece 46 is placed into the patient's mouth, over
his tongue, and is connected to a tube 48 that may be of relatively
small diameter because its purpose is to conduct the pharyngeal
pressure, as present in the mouth, to a combination meter and
switching device 50. Device 50 has a pressure reading needle 52 and
a pair of adjustable needles 54 for setting the desired pressure
range. When the patient's pharyngeal pressure read by needle 52 is
within the limits as set by needles 54, then device 50 closes a
switch to activate the kymograph motor. As the motor turns cylinder
26, the volume of air present in spirometer 2 is recorded by pen
24. As will be explained below, the record on chart 22 will provide
the data necessary to calculate the nasal airway resistance of the
patient. Device 50 is a commercially available product marketed as
a photohelic gauge switch by Dwyer Instruments, Inc., of Michigan
City, Ind., as described in U.S. Pat. No. 3,397,319 to J.P. Locke.
The device 50 has both positive and negative pressure inputs.
In inspiratory nasal airway measurement operation, valve 28 is
rotated to connect tubes 14 and 16 together and to open tube 40 to
the room air. Mask 44 may be placed on the patient at this time
since room air is available at the mask. Valve 12 is rotated to
open tube 12 to the room air. Bell 8 is raised to fill the
spirometer 2 with room air and then valve 12 is rotated to provide
a closed path between the spirometer 2 and valve 28. The patient is
instructed to breath in through his nostrils while at the same time
holding mouthpiece 46 in his mouth with his mouth closed around it.
He is instructed to exhale through his mouth around the mouthpiece,
holding the mouthpiece in place with his teeth. The patient is
allowed to practice this before the actual recording procedure is
begun. The patient is also instructed to practice inhaling so as to
provide a pharyngeal pressure falling within the limits set on
device 50. Since the meter face of device 50 is visible to the
patient he may watch it until he achieves the desired pressure. In
actual practice it has been found that patients can achieve the
desired pressure after a relatively brief period of practice. The
linear relation-ship between pressure and flow expressed in the
equation R = Po - Pp/V/t, where R is the nasal airway resistance,
Po is the atmospheric pressure, Pp is the pharyngeal pressure, and
V/t is the volume of air per unit of time, is most valid in the
range of about 15 to 35 mm H.sub.2 O. It has been found that
substantially all of the patients tested can achieve a pressure in
this range for a duration of 11/2 seconds or more. A typical
pressure achievable by patients is on the order of 25 mm H.sub.2 O.
After the patient has succeeded in achieving the desired pressure
after practice, the valve 28 may be rotated to connect the
spirometer air supply to the patient's face mask via tubes 14, 16
and 40. As the patient inhales a chart of the spirometer volume
level will be recorded whenever the pharyngeal pressure measured by
device 50 through tube 48 and mouthpiece 46 is within the
prescribed range.
Alternatively, expiratory nasal airway measurements may be made,
although most patients find the inspiratory measurements to be more
comfortable. Also, there is less air leakage around the face mask
during inspiratory measurements. Expiratory nasal airway
measurements are made in a manner identical to the taking of
inspiratory measurements except that the patient breathes out
through his nostrils while holding mouthpiece 46 in his mouth with
his mouth closed around it. The patient breathes in by holding the
mouthpiece between his teeth and inhaling through his mouth around
the mouthpiece. Tube 48 must be connected to the positive pressure
input of pressure gauge 50 during expiratory measurements.
An actual reproduction of a patient's chart of spirometer air
volume versus time is shown in FIG. 5. The longest straight lines
indicate periods in which the patient achieved continuous
inhalation within the prescribed pharyngeal pressure limits for the
longest times. To convert the chart data to nasal airway
resistance, the longest straight line is chosen, preferably lasting
11/2 seconds or more, and the angle to the horizontal is measured
to derive the slope of the line from which the volume per unit time
can be calculated. The nasal resistance is then the average
pressure between the two limits set on device 50 divided by the
volume per unit time taken from the chart. Thus, for constant
settings of pressure limits on device 50, the practitioner need
only deal with the volume per unit time since it will be related to
nasal resistance by a constant.
Further techniques employed with the invention include plugging
each nostril in turn to provide resistance data for the nasal
airway with both nostrils uncovered, the left covered, and the
right covered. The nostrils may be covered by using cellophane tape
or the like, being careful not to deform the nostril. In addition,
it is convenient to employ a clock in conjunction with the
apparatus so that the operator may record the times at which the
data was taken. It will be apparent that in a computerized version
of the invention that time could be included along with the data
taken.
FIG. 6 shows a modified face mask 60 that may be used with the
apparatus of FIGS. 1 and 3. Mask 60 is hand-held by the patient and
is advantageously used with patients who wear glasses or who feel
uneasy with the mask strapped to their head. Tube 40 as in FIG. 1
is connected via a coupling 62 to the mask 60. Tube 48 as in FIG. 1
is connected to a mouthpiece 66 that passes through an air-tight
fitting 64 in the mask 66. In operation, the mask 60 is held firmly
by the patient over his nose and mouth with mouthpiece 66 in his
mouth. The assembly functions in like manner to mask 44 and
mouthpiece 46 of FIG. 1. Tube 40 carries air to or from the nose
just as it does with mask 44. In order to breath out through the
mouth during inspiratory nasal airway measurements or to breath in
through the mouth during expiratory nasal airway measurements the
patient simply moves the mask away from his face. Alternatively, a
relief valve (not shown) could be incorporated in the mask so that
the patient could continually hold the mask against his face.
FIGS. 7-10 relate to an embodiment of the invention adapted for
measuring tracheobronchial airway resistance.
FIG. 7 shows a side elevation view of a mouthpiece 68 adapted for
measuring tracheobronchial airway resistance. An air hose such as
tube 40 (in FIG. 8) is connected to the right end of the
mouthpiece. A tube 72 (see also FIG. 8) for measuring pressure is
connected to a tap 70 in the periphery of the mouthpiece.
FIG. 8 shows a modification of FIGS. 1 and 3 adapted for
tracheobronchial measurements. The mouthpiece 68 of FIG. 7 is
employed with the apparatus of FIG. 8. Pressure gauge 50 has two
inputs: for measuring negative and positive pressures. Tube 78
connects to one input and tube 76 connects to the other input. A
solenoid operated electric switch 73 connects the pressure
measuring line 72 to one of the tubes 76 or 78 depending on whether
or not electric leads 74 are energized. Thus the apparatus can
measure pressure during expiration (positive pressure) or
inspiration (negative pressure).
FIG. 9 shows a patient using the mouthpiece of FIG. 7 as it is used
for tracheobronchial airway measurements. A nose clamp 80 is placed
over the patient's nose to prevent any nasal airflow. For
inspiratory measurements, the switch 73 is selected to connect tube
72 to the negative input of gauge 50. The patient breathes in
through his mouth and attempts to maintain a pressure within the
preselected range on gauge 50 in a manner analogous to the taking
of nasal measurements. The pressure measured by tube 72 is the
pharyngeal pressure as in the nasal measurements and the
measurement is still a differential pressure; the other pressure
being the atmospheric pressure that surrounds the lungs, against
which the lungs must work. Thus the same equations and computations
are used to calculate the tracheobronchial airway resistance.
If it is desired to measure the expiratory airway resistance, the
switch 73 is changed to connect pressure tube 72 to the positive
pressure input of gauge 50 and the patient attempts to maintain the
preset pressure on gauge 50 when he breathes out.
As in the nasal measurements, the patient breathes around the
mouthpiece while holding it in place with his teeth when a
measurement is not being taken.
FIG. 10 shows a further modification of the embodiment of FIG. 8. A
pair of "photohelic" pressure gauge switches 50 and 51 are used in
conjunction with a Y connection 75 and tubes 76 and 78. Gauge 50
has tube 76 connected to its negative input and gauge 51 has tube
78 connected to its positive input. This arrangement is desirable
in taking tracheobronchial measurements when the pressures
achievable by the typical patient are different for expiration and
inspiration. By using two gauges, the pressure range need not be
reset when changing from expiration to inspiration measurements. It
has been found that when using two photohelic gauge switches, a
simple Y connection may be used in lieu of a manual or solenoid
switch in the pressure measuring line. When a single photohelic
gauge switch is used, the pressure lines must be switched from the
negative to positive input.
It will be recognized by those of ordinary skill in the art that
the apparatus of the present invention may be substantially
modified and yet provide the same function and results provided the
teachings of the invention are followed. For example, any means
providing a measurable source of air supply such as a
pneumotachograph may be substituted for the spirometer 2. Also, the
recordation of the air supply volume with respect to time can be
achieved by devices other than the kymograph 4. For example, such
recordation could be done on an X-Y plotter, a storage-type
oscilloscope, or the data could be stored in an analog or digital
memory device. Likewise, the photohelic switch could be replaced by
another pressure measuring arrangement and apparatus wherein a
selected pressure range provides a control signal. In addition, it
will be apparent that the computation of the nasal resistance may
be carried out by a programmed machine such as an analog or digital
computer. Therefore, the invention is to be limited only by the
scope of the appended claims.
* * * * *