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Claims  |
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What is claimed is:
1. In an arrangement for taking blood pressure in which a cuff wrapped
around a body part of a patient is first pressurized to a given level and
then depressurized sufficient to detect the patient's systolic and
diastolic pressures, the improvement comprising means acting on said cuff
after the latter has been pressurized to said given level for causing it
to depressurize in a substantially linear way independent of the
pressurized volume of the cuff, said depressurizing means including; a
housing defining adjacent internal active and control pressure chambers
separated from one another in an air sealed manner by a diaphragm; first
means for placing said active and control chambers and said cuff in
air-flow communication with one another whereby all three thereof are
initially pressurized to said given level; and second means cooperating
with said diaphragm for placing said active chamber in air-flow
communication with the ambient surroundings only as long as the pressure
within said control chamber is at most greater than the pressure in said
active chamber by a particular relatively small amount, said second means
closing the air flow communication between said active chamber and ambient
surroundings if the pressure within said control chamber is greater than
the pressure with said active chamber by more than said particular amount.
2. The improvement according to claim 1 wherein said particular relatively
small amount of pressure is on the order of 3 torr.
3. The improvement according to claim 1 wherein said depressurizing means
includes means for changing the way in which said cuff is linearly
depressurized.
4. The improvement according to claim 3 wherein said changing means
includes means for changing the effective volume of said control chamber
whereby the manner in which said cuff is linearly depressurized changes as
a function thereof.
5. The improvement according to claim 4 wherein said volume changing means
includes means for placing one of a plurality of different auxiliary
chambers of varying sized in air-flow communication with said control
chamber whereby the effective volume of said control chamber can be
changed by changing the size of said auxiliary chamber.
6. In an arrangement for taking blood pressure in which a cuff wrapped
around a body part of a patient is first pressurized to a given level and
then depressurized sufficient to detect the patient's systolic and
diastolic pressures, a device configured to cooperate with said cuff for
causing the latter to depressurize after it has been pressurized to a
given level in a substantially linear, fixed manner independent of the
pressurized volume of the cuff, said device comprising:
(a) a housing defining adjacent internal active and control pressure
chambers separated from one another in an air sealed manner by a diaphragm
which is movable within said housing in predetermined ways responsive to
the differences in pressure within said active and control chambers;
(b) an auxiliary container of fixed volume;
(c) an assembly of tubular means including a first tubular means for
placing said control chamber and said auxiliary container in fluid
communication with another, a second tubular means for placing said active
chamber and said cuff in fluid communication with one another, and third
tubular means for placing said active and control chambers in fluid
communication with one another, said third tubular means including a flow
constriction device having a constricted flow passage in the flow path
between said chambers; and
(d) a separate tubular means extending through said housing between said
active chamber and the ambient surroundings and cooperating with said
diaphragm for placing said active chamber in air-flow communication with
the ambient surroundings only so long as the pressure within said control
chamber is at most greater than the pressure in said active chamber by a
particular relatively small amount, said separate tubular means closing
the air flow communication between said active chamber and ambient
surroundings if the pressure within said control chamber is greater than
the pressure within said active chamber by more than said particular
amount, whereby the overall arrangement acts on said cuff, causing the
latter to depressurize after it has been pressurized to a given level in a
substantially linear, fixed manner independent of the pressurized volume
of the cuff.
7. An arrangement comprising means acting on a container after the latter
has been pressurized to a given level for causing it to depressurize in a
substantially linear fixed manner, said depressurizing means including: a
housing defining adjacent internal active and control pressure chambers
separated from one another in an air sealed manner by a diaphragm; first
means for placing said active and control chambers and said container in
air-flow communication with one another whereby all three thereof are
initially pressurized to said given level; and second means cooperating
with said diaphragm for placing said active chamber in air-flow
communication with the ambient surroundings only as long as the pressure
within said control chamber is at most greater than the pressure in said
active chamber by a particular relatively small amount, said second means
closing the air flow communication between said active chamber and ambient
surroundings if the pressure within said control chamber is greater than
the pressure within said active chamber by more than said particular
amount.
8. In an arrangement for taking blood pressure in which a cuff wrapped
around a body part of a patient is first pressurized to a given level and
then depressurized sufficient to detect the patient's systolic and
diastolic pressures, the improvement comprising means for pressurizing
said cuff to said given level in a substantially linear, fixed manner,
said pressurizing means including: a housing defining adjacent internal
active and control pressure chambers separated from one another in an air
sealed manner by a diaphragm; first means for placing said active and
control chambers and said cuff in air-flow communication with one another
whereby all three thereof are initially maintained at ambient pressure;
and second means cooperating with said diaphragm for placing said active
chamber in air-flow communication with a pump only as long as the pressure
within said active chamber is at most greater than the pressure in said
control chamber by a particular relatively small amount, said second
closing the air flow communication between said active chamber and said
pump means if the pressure within said active chamber is greater than the
pressure within said control chamber by more than said particular amount.
9. An arrangement comprising means for pressurizing a container in a
substantially linear fixed manner, said pressurizing means including: a
housing defining adjacent internal active and control pressure chambers
separated from one another in an air sealed manner by a diaphragm; first
means for placing said active and control chambers and said container in
air-flow communication with one another whereby all three thereof are
initially maintained at ambient pressure; and second means cooperating
with said diaphragm for placing said active chamber in air-flow
communication with a pump only as long as the pressure within said active
chamber is at most greater than the pressure in said control chamber by a
particular relatively small amount, said second means closing the air-flow
communication between said active chamber and said pump if the pressure
within said active chamber is greater than the pressure within said
control chamber by more than said particular amount.
10. In an arrangement for taking blood pressure in which a cuff wrapped
around a body part of a patient is first pressurized to a given level and
then depressurized sufficient to detect the patient's systolic and
diastolic pressures, a device configured to cooperate with said cuff for
causing the latter to depressurize after it has been pressurized to a
given level in a substantially linear, fixed manner independent of the
pressurized volume of the cuff, said device comprising:
(a) a housing defining adjacent internal active and control pressure
chambers separated from one another in an air sealed manner by a diaphragm
which is movable within said housing in predetermined ways responsive to
the differences in pressure within said active and control chambers;
(b) means for placing said active chamber and said cuff in fluid
communication with one another;
(c) means for placing said active and control chambers in fluid
communication with one another, said last-mentioned means including a
constricted flow passage in the flow path between said chambers; and
(d) means cooperating with said diaphragm for placing said active chamber
in air-flow communication with the ambient surroundings only so long as
the pressure within said control chamber is at most greater than the
pressure in said active chamber by a particular relatively small amount,
said last-mentioned means closing air flow communication between said
active chamber and ambient surroundings if the pressure within said
control chamber is greater than the pressure within said active chamber by
more than said particular amount, whereby the overall arrangement acts on
said cuff for causing the latter to depressurize after it has ben
pressurized to a given level in a substantially linear, fixed manner
independent of the pressurized volume of the cuff.
11. In an arrangement for taking blood pressure in which a cuff wrapped
around a body part of a patient is first pressurized to a given level and
then depressurized sufficient to detect the patient's systolic and
diastolic pressures, a device configured to cooperate with said cuff for
causing the latter to pressurize to a given level in a substantially
linear, fixed manner independent of the pressurized volume of the cuff,
said device comprising:
(a) a housing defining adjacent internal active and control pressure
chambers separated from one another in an air sealed manner by a diaphragm
which is movable within said housing in predetermined ways responsive to
the differences in pressure within said active and control chambers;
(b) an auxiliary container of fixed volume;
(c) an assembly of tubular means including a first tubular means for
placing said control chamber and said auxiliary container in fluid
communication with another, a second tubular means for placing said active
chamber and said cuff in fluid communication with one another and third
tubular means for placing said active and control chambers in fluid
communication with one another, said third tubular means including a flow
constriction device having a constricted flow passage in the flow path
between said chambers; and
(d) means cooperating with said diaphragm for placing said active chamber
in air-flow communication with a pump only so long as the pressure within
said active chamber is at most greater than the pressure in said control
chamber by a particular relatively small amount, said last-mentioned means
closing air flow communication between said active chamber and said pump
if the pressure within said active chamber is greater than the pressure
within said control chamber by more than said particular amount, whereby
the overall arrangement acts on said cuff for causing the latter to
pressurize in a substantially linear, fixed manner independent of the
pressurized volume of the cuff.
12. In an arrangement for taking blood pressure in which a cuff wrapped
around a body part of a patient is first pressurized to a given level and
then depressurized sufficient to detect the patient's systolic and
diastolic pressures, a device configured to cooperate with said cuff for
causing the latter to pressurize to a given level in a substantially
linear, fixed manner independent of the pressurized volume of the cuff,
said device comprising:
(a) a housing defining adjacent internal active and control pressure
chambers separated from one another in an air sealed manner by a diaphragm
which is movable within sealed housing in predetermined ways responsive to
the differences in pressure within said active and control chambers;
(b) first means for placing said active chamber and said cuff in fluid
communication with one another;
(c) means for placing said active and control chambers in fluid
communication with one another, said last-mentioned means including a
constricted flow passage in the flow path between said chambers; and
(d) means cooperating with said diaphragm for placing said active chamber
in air-flow communication with a pump only so long as the pressure within
said active chamber is at most greater than the pressure in said control
chamber by a particular relatively small amount, said last-mentioned
closing air flow communication between said active chamber and said pump
if the pressure within said active chamber is greater than the pressure
within said control chamber by more than said particular amount, whereby
the overall arrangement acts on said cuff for causing the latter to
pressurize in a substantially linear, fixed manner independent of the
pressurized volume of the cuff. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates generally to a technique for pressurizing and
depressurizing a pressurizable container or housing and more particularly
to a device which is capable of pressurizing or depressurizing the
container or housing in a linear, fixed manner. As will be seen
hereinafter, this device is especially suitable for use in an arrangement
for taking blood pressure in which a cuff wrapped around the arm or other
suitable body part of a patient is first pressurized to a given level and
then depressurized sufficient to detect the patient's systolic and
diastolic pressures.
Turning briefly to the drawings and specifically FIG. 1, a conventional
arrangement for taking blood pressure of a given patient is
diagrammatically illustrated and designed by the reference numeral 10.
This arrangement includes a standard pressurizable cuff 12 wrapped around
the arm 13 (or other suitable body part) of a patient and means generally
indicated at 14 for first pressurizing the cuff to a given level above the
patient's anticipated systolic pressure and then depressurizing it to a
level below the patient's anticipated diastolic pressure. While not shown,
the overall arrangement includes suitable means for actually detecting the
patient's systolic and diastolic pressures as the cuff is depressurized.
For example, in the case of those arrangements which utilized Korotkoff
sounds, a stethoscope or a functionally equivalent electronic means may be
provided.
In the conventional arrangement described immediately above, once the cuff
is pressurized to the desired level and then caused to depressurize, it
typically does so in a non-linear, somewhat exponential fashion, as
illustrated best in FIG. 2. This Figure graphically illustrates the
depressurization of cuff 12 with time for three different sizes of cuffs,
a medium size cuff A, a large cuff B and a small cuff C. In each case, the
rate of depressurization is greatest in the early stages and then slows
down as the pressure within the cuff decreases. As a result, it takes
substantially longer to measure the patient's systolic and diastolic
pressures then would be case if the cuff could be made to depressurize
linearly. Take for example the depressurization ramp (curve) A for a
medium cuff. The cuff is initially pressurized to a level above the
patients systolic pressure and as it depressurizes, it reaches the
systolic pressure S at the time t1 and then the patient's diastolic
pressure at the time t3. If the cuff could be made to depressurize
linearly, as indicated by the linear ramp (curve) A' the patient's
diastolic pressure D would be measured at time t2, substantially earlier
than time t3. This time differential between t3 and t2 for standard size
arm cuffs is on the order of approximately 10 seconds.
Because arrangement 10 does not depressurize its cuff in a linear fashion
but rather exponentially (as described above), it has the disadvantage of
being slower than it would be if the cuff could be linearly depressurized.
Another disadvantage of the arrangement illustrated relates to the size of
cuff 12. Specifically, cuffs of different sizes result in depressurization
ramps of different configurations. As illustrated in FIG. 2, the ramp A
corresponds to a medium size cuff, the ramp B corresponds to a larger
cuff, and the ramp C corresponds to a smaller cuff. Thus, if arrangement
10 includes an electronic means for detecting the patient's systolic and
diastolic pressures and if the arrangement uses cuffs of different sizes,
suitable circuitry and an adjustment switch would be required to
compensate for the different sized cuffs to make the ramps for all cuff
sizes approximately equal.
SUMMARY OF THE INVENTION AND OBJECTS
In view of the foregoing, it is a specific object of the present invention
to provide an arrangement for taking blood pressure of the general type
described in FIG. 1, that is, one in which a cuff wrapped around the arm
or other suitable body part of a patient is first pressurized to a given
level and the depressurized sufficient to detect the patient's systolic
and diastolic pressures, but particularly to an arrangement in which the
cuff is depressurized linearly rather than the exponential fashion
illustrated in FIG. 2.
Another specific object of the present invention is to provide an
arrangement of the last mentioned type in which the cuff is depressurized
at the same linear rate regardless of the size of the cuff used.
Still another specific object of the present invention is to provide an
arrangement of the last mentioned type in which its cuff is capable of
being pressurized at a substantially linear, fixed rate regardless of cuff
size.
A further object of the present invention is to provide an arrangement for
pressurizing or depressurizing a pressurizable container or housing
generally (including but not limited to a blood pressure cuff) at a
substantially linear, fixed rate, preferably independent of the volume of
the container or housing.
As will be described in more detail hereinafter, a particular "down ramp"
device is disclosed herein for depressurizing a blood pressure cuff after
the latter has been pressurized to a given level and includes a housing
defining adjacent internal active and control pressure chambers separated
from one another in an air sealed manner by a diaphragm which moves in a
predetermined way within the housing depending upon the differences in
pressures within the active and control chambers. The device also includes
first means for placing the active and controlled chambers and the cuff in
air-flow communication with one another whereby all three thereof are
initially pressurized to the given level. Second means cooperating with
the diaphragm places the active chamber in air-flow communication with the
ambient surroundings only so long as the pressure within the control
chamber is greater than the pressure in the active chamber by at most a
particular, relatively small amount. In this way, the device forces the
cuff to depressurize at a substantially linear, fixed rate, independent of
the pressurized volume (e.g. the size) of the cuff.
BRIEF DESCRIPTION OF THE DRAWINGS
The linear down ramp or depressurizing device just described briefly will
be described in more detail hereinafter in conjunction with the drawings
wherein:
FIG. 1 diagrammatically illustrates a conventional (prior art) arrangement
for taking blood pressure, as stated previously;
FIG. 2 graphically illustrates how blood pressure cuffs of different sizes
forming part of the arrangement of FIG. 1 depressurize non-linearly, as
also stated above;
FIG. 3 diagrammatically illustrates a device especially suitable for use in
an arrangement for taking blood pressure and specifically a device
designed in accordance with the present invention to cause the cuff
forming part of the overall arrangement to be pressurized and then
depressurized in a substantially linear, fixed manner independent of the
pressurized volume of the cuff; and
FIG. 4 graphically illustrates a particular operating feature of the device
illustrated in FIG. 3.
Also, as will be described in more detail hereinafter, a particular "up
ramp" device is disclosed herein for pressurizing a blood pressure cuff
using an appropriate pump and includes a housing defining adjacent
internal active and control pressure chambers separated from one another
in an air sealed manner by a diaphragm which moves in a predetermined way
within the housing depending upon the differences in pressures within the
active and control chambers. The device also includes first means for
placing the active and controlled chambers and the cuff in air-flow
communication with one another whereby all three thereof are initially
pressurized to the given level. Second means cooperating with the
diaphragm places the active chamber in air-flow communication with the
ambient surroundings only so long as the pressure within the control
chamber is less than the pressure in the active chamber by a particular,
relatively small amount. In this way, the device forces the cuff to
pressurize at a substantially linear, fixed rate, dependent of the
pressurized volume (e.g. the size) of the cuff or of the pressure applied
by the pump.
The up ramp or pressurizing device just described briefly will be described
in more detail hereinafter in conjunction with the drawings wherein:
FIG. 1a diagrammatically illustrates a conventional (prior art) arrangement
for taking blood pressure;
FIG. 2a graphically illustrates how blood pressure cuffs of different sizes
forming part of the arrangement of FIG. 1a pressurize non-linearly;
FIG. 3a diagrammatically illustrates a device especially suitable for use
in an arrangement for taking blood pressure and specifically a device
designed in accordance with the pressure invention to cause the cuff
forming part of the overall arrangement to be pressurized in a
substantially linear, fixed manner independent of the pressurized volume
of the cuff; and
FIG. 4a graphically illustrates a particular operating feature of the
device illustrated in FIG. 3.
In addition to the foregoing:
FIG. 5 diagrammatically illustrates a modified arrangement corresponding to
the one illustrated in FIG. 3.
DETAILED DESCRIPTION
Turning now to the drawing, attention is immediately directed to FIG. 3
inasmuch as FIGS. 1 and 2 were discussed previously. In FIG. 3, an overall
arrangement for taking blood pressure is illustrated and generally
designated by the reference numeral 18. This arrangement includes (1) a
suitable blood pressure cuff 20 which while not shown is wrapped around
the arm of a patient, (2) means 23 including a source of air pressure and
a device generally indicated at 24 for pressurizing and depressurizing the
cuff, and (3) suitable means (not shown) for detecting the patient's
systolic and diastolic blood pressures as cuff 20 is depressurized. This
last mentioned means and the cuff itself are readily providable and hence
will not be described herein. On the other hand, device 24 is designed in
accordance with the present invention to insure that cuff 20 after
pressurization thereof is depressurized in a substantially linear, fixed
manner, independent of the size of the cuff, that is, its pressurized
volume, as will be described in detail below.
Still referring to FIG. 3, device 24 is shown including a diaphragm
operated pressure regulator 26 which may be of the general type made
available for example by the Air Logic company under product number
F4103-25. Regulator 26 is shown including a housing 28 defining adjacent
internal pressure chambers, an active chamber 30 and a control chamber 32,
separated from one another in an air sealed manner by a flexible diaphragm
34 which moves in a manner to be discussed below in response to
differences in pressure within chambers 30 and 32. Housing 28 includes
inlet ports 35, 36 and outlet port 38 into and out of chamber 30,
respectively, and a control port 40 into chamber 32. A valve stem 42,
attached at one end to the diaphragm 34, actuates a valve 45 attached to
its other end in response to movements of the diaphragm 34. While a
suitable closure valve 46 is shown for opening and closing the flow path
through port 38 to the ambient surroundings, this valve functions as a
part of the overall device, as will be discussed hereinafter, and does not
normally form part of the commercially available pressure regulator.
In order to more fully understand how overall device 24 operates, it is
important to understand the way in which regulator 26 functions as a
pressure comparator apart from the rest of the device. To this end, let it
be assumed that the port 38 is always opened through valve 46. Let it also
be assumed that the control chamber 32 is initially at atmospheric
(ambient) pressure. Under these circumstances, air (or other fluid)
flowing into active chamber 30 through inlet 36 will flow back out of the
chamber through outlet port 38. This is because the inflow of air into
chamber 30 increases the pressure therein over that of the ambient
pressure within chamber 32, so as to cause the diaphragm to stretch away
from end 44 of chamber 30, as diagrammatically illustrated by the dotted
line 48 and thereby prevent valve 45 from closing port 38. In order to
prevent air from escaping chamber 30 through port 38, it is necessary to
pressurize chamber 32 to a level sufficiently greater than the pressure
within chamber 30 so as to cause diaphragm 34 to stretch in the opposite
direction, that is, into chamber 30 sufficient to cause valve 45 to seal
port 38, as diagrammatically illustrated by dotted lines 50. Thus, if at
any given time the pressure within chamber 30 is at a given level, for
example 30 torr, it is necessary to pressurize chamber 32 to a
sufficiently greater pressure, for example 33 torr in order to cause the
diaphragm to move to its valve closing position. This three torr
difference is determined by the stretchability of the diaphragm and may be
readily designed into the regulator.
Having briefly described regulator 26 and the way it functions apart from
device 24 attention is now directed to the remaining components making up
this device. This components include an auxiliary container 52 defining an
internal auxiliary chamber 53 having a fixed volume V1 and an array of
tubes including (1) a tubular assembly 54 for placing control chamber 32
in fluid communication with auxiliary chamber 53, (2) tubular assembly 56
for placing chamber 30 in fluid communication with the interior of cuff
20, and (3) a tubular assembly 58 for placing the chambers 30 and 32 in
fluid communication with one another (with the aid of assembly 54). A flow
construction arrangement or pneumatic resistor 60 forms part of tubular
assembly 58 and includes a constructed passageway 62 in the flow path
between chambers 30 and 32. For reasons to be discussed hereinafter, both
the auxiliary container 52 and the flow constriction member 60 are
removably connected into their respective operating positions illustrated
in FIG. 3. To this end, suitable coupling means generally indicated at 64
and 66 are provided.
Device 24 operates in the following manner to cause cuff 20 to depressurize
in a substantially linear, fixed manner independent of the size of cuff
20, after the cuff has been pressurized to a given level. First, the cuff
needs to be pressurized. To this end, previously recited pressurized air
supply means 23, is interconnected with the cuff by suitable tubular means
70 through an open/shut valve 71. Since the cuff is in direct fluid
communication with both chambers 30 and 32 and auxiliary chamber 53 by
means of tubular assemblies 54, 56 and 58, it is necessary to initially
pressurize all three of these latter chambers to the desired level along
with the cuff. In order to do this it is of course necessary to maintain
port 38 closed by suitable means such as the closure valve 46.
Once cuff 20 is pressurized to the desired level (along the chambers 30, 32
and 53), the cuff can be depressurized by merely opening up port 38 by
means of valve 46. This causes air initially to escape to the ambient
surroundings from chamber 30, thereby dropping the pressure therein.
However, because of diaphragm 34, as soon as the pressure within chamber
30 drops to a predetermined level below the pressure in chamber 32, the
diaphragm closes port 38. At the same time, air from chambers 32 and 53
and from cuff 20 enter chamber 30 through inlet ports 35 and 36
respectively, thereby increasing the pressure within chamber 30 sufficient
to force the diaphragm away from port 38 for opening the latter. Thus,
diaphragm 34 may continue to open and close tube 42 to depressurize
chambers 30, 32 and 53 and cuff 20. More frequently diaphragm 34 hovers in
such a position as to maintain exactly equal the rates of pressure drop in
chambers 32 and 53 on the one hand and chamber 30 and cuff 20 on the other
hand. As it does so, the pressure differential between chambers 30 and 32
will remain at a fixed level depending upon the stretch characteristics of
the diaphragm, for example the three torr pressure value discussed
previously. This fixed pressure differential appears across constricted
passageway 62 at all times. This means that the flow rate through the
constricted passageway in the direction of port 35 is constant at all
times. Since the flow rate through the constricted passageway is constant,
the pressure within compartments 32 and 53 must drop at a constant or
fixed rate, that is, a linear rate.
Since the chamber 32 drops in pressure at a linear rate as described above,
the pressure in chamber 30 must also drop at the same linear rate (e.g.
following the drop in pressure in chamber 32 by a fixed amount, for
example the 3 torr value mentioned above). This is best exemplified in
FIG. 4 which graphically illustrates a curve D corresponding to the linear
drop in pressure in chamber 32 and a curve E which corresponds to the
linear drop in pressure in chamber 30. Note that curve E has the same
slope as curve D but always follows curve D by a constant amount which is
determined by the stretchability characteristics of diaphragm 34, for
example the three torr level mentioned above. Since chamber 30 drops in
pressure linearly, so will cuff 20 since it is in fluid communication with
this latter chamber. This, device 24 causes cuff 20 to depressurize in the
linear manner illustrated by curve E in FIG. 4. The actual change in
pressure with time or ramp rate (dP/dt) is governed by the following
equation:
##EQU1##
Where P.sub.o is equal to an average pressure (about 760 torr); V.sub.1
and V.sub.2 respectively equal the volumes in chambers 53 and 32; .DELTA.P
equals a fixed constant depending upon the stretchability characteristics
of the diaphragm, for example 3 torr; and R is a constant air resistant
factor (functionally equivalent to electrical resistance) depending upon
the cross section of constricted passageway 62. Thus, in an actual
embodiment, if V.sub.1 plus V.sub.2 is approximately equal to 30 cubic
centimeters, if .DELTA.P equals 3 torr and if R equals 12 Torr sec
cm.sup.-3 (corresponding to about a 10 mil diameter hole), then dP/dt is
approximately equal to 6 Torr per second.
It should be noted that the equation for dP/dt above is independent of the
volume of cuff 20. Therefore, the rate of depressurization of cuff 20 by
means of device 24 is independent of the volume of cuff 20 which means
that the device will cause different sized cuffs to depressurize in the
same way. This, in turn, means that the overall arrangement does not have
to concern itself with the size of the cuff being depressurized. At the
same time, the ramp rate dP/dt of device 24 can be varied by changing
V.sub.1, V.sub.2 and/or R. It is impractical to change the volume V.sub.2.
Therefore, the most practical means of varying the ramp rate is to vary
the volume V.sub.1 by using different containers 52 of different volumes
or by varying the pneumatic resistance R indicated at 60 in FIG. 3. By
increasing the volume V.sub.1, the slope of curve E is decreased and vice
versa. Couplings 64, 66 are used to provide different containers and/or
pneumatic resistors.
From the foregoing discussion, it should be apparent that device 24 can be
used to depressurize cuff 20 at a substantially linear, constant rate,
independent of the size of the cuff. It should be equally apparent that
device 24 can be utilized with pressurizable containers or housings other
than a blood pressure cuff for depressurizing these other containers and
housings at substantially linear, fixed rates, independent of the size of
these latter containers or housings. For example, device 24 could be used
to pressurize and then depressurize a pneumatic accumulator.
Referring now to FIGS. 1a and 2a there is illustrated the same type of
blood pressure measurement arrangement as above illustrated in FIGS. 1 and
2 with the exception that the pressure in the blood pressure cuff is
designed to ramp upward instead of downward. Thus an arrangement 10' using
a cuff 12' positioned around the arm 13' of a patient is shown in FIG. 1a
along the means 14' for first pressurizing and then depressurizing the
cuff. FIG. 2a shows exponential pressurizing curves A', B', C'
corresponding to medium, large and small cuffs and cuff A" corresponding
to a linear pressurization curve which illustrates that it would be faster
to pressurize linearly than exponentially..
In FIG. 3a, an overall arrangement for taking blood pressure is illustrated
and generally designated by the reference numeral 18'. This arrangement
includes (1) a suitable blood pressure cuff 20' shown wrapped around the
arm of a patient, (2) means 23' including a source of air pressure and a
device generally indicated at 24' for pressurizing the cuff, and (3)
suitable means (not shown) for detecting the patient's systolic and
diastolic blood pressures as cuff 20' is pressurized. This last mentioned
means and the cuff itself are readily providable and hence will not be
described herein. On the other hand, device 24' is designed in accordance
with the present invention to insure that cuff 20' is pressurized in a
substantially linear, fixed manner, independent of the size of the cuff,
that is, its pressurized volume as will be described in detail below.
Still referring to FIG. 3a, device 24' is shown including a diaphragm
operated pressure regulator 26'. Regulator 26' is shown including a
housing 28' defining adjacent internal pressure chambers, an active
chamber 30' and a control chamber 32', separated from one another in an
air sealed manner by a flexible diaphragm 34' which moves in a manner to
be discussed below in response to differences in pressure within chambers
30' and 32'. Housing 28' includes inlet ports 35', 36' and outlet port 38'
into and out of chamber 30', respectively, and a control port 40' into
chamber 32'. A valve stem 42', attached at one end to the diaphragm 34',
actuates a valve 45' attached to its other end in response to movements of
the diaphragm 34'. While a suitable closure valve 46' is shown for opening
and closing the flow path into chamber 32' through port 38', this valve
functions as a part of the overall device, as will be discussed
hereinafter, and does not normally form part of the commercially available
pressure regulator.
In order to more fully understand how overall device 24' operates, it is
important to understand the way in which regulator 26' functions as a
pressure comparator apart from the rest of the device. To this end, let it
be assumed that valve 46' is always opened. Let is also be assumed that
the control chamber 32' is initially at atmospheric (ambient) pressure. It
should also be pointed out that the relaxed position or set of diaphragm
34' is shown as a solid line at 34'. Under these circumstances, air (or
other fluid) flowing cannot freely flow into active chamber 30' through
port 38' (ignoring for the moment that the pump is connected thereto).
This is because any inflow of air into chamber 30' increases the pressure
therein over that of the ambient pressure within chamber 32', so as to
cause the diaphragm to stretch away from chamber 30', as diagrammatically
illustrated by the dotted line 48' and thereby close port 38'. To allow
air to pass into chamber 30' through port 38', it is necessary to
pressurize chamber 32' to a sufficient level as compared to the pressure
within chamber 30' so as to cause diaphragm 34' to relax or stretch in the
opposite direction, that is, in the direction of chamber 30' sufficient to
open port 38' as diagrammatically illustrated by dotted lines 50'. Thus,
if at any given time the pressure within chamber 30' is at a given level,
for example 30 torr, it is necessary to pressurize chamber 32' to a
sufficient pressure, for example 27 torr in order to cause the diaphragm
to move to its valve opening position. This three torr difference is
determined by the stretchability and the designed set of the diaphragm and
may be readily designed into the regulator.
Having briefly described regulator 28' and the way it functions apart from
device 24' attention is now directed to the remaining components making up
this device. These components include an auxiliary container 52' defining
an internal auxiliary chamber 53' having a fixed volume V1 and an array of
tubes including (1) a tubular assembly 54' for placing control chamber 32'
in fluid communication with auxiliary chamber 53', (2) tubular assembly
56' for placing chamber 30' in fluid communication with the interior of
cuff 20', and (3) a tubular assembly 58' for placing the chambers 30' and
32' in fluid communication with one another (with the aid of assembly
54'). An additional tubular assembly 70' places pump 23' in fluid
communication with port 38' through valve 46'. A flow constriction
arrangement or pneumatic resistor 60' forms part of tubular assembly 58'
and includes a constricted passageway 62' in the flow path between
chambers 30' and 32'. For the reasons discussed previously with respect to
FIG. 3 both the auxiliary container 52' and the flow constriction member
60' are removably connected into their respective operating positions
illustrated in FIG. 3a. To this end, suitable coupling means generally
indicated at 64' and 66' are provided.
Device 24' operates in the following manner to cause cuff 20' to pressurize
in a substantially linear, fixed manner independent of the size of cuff
20'. First, the pressurizing means 23' is turned on. The cuff can then be
pressurized by merely opening up tubular assembly 70' by means of valve
46'. This causes limited air initially to pass into chamber 30', thereby
increasing the pressure therein. However, because of diaphragm 34', as
soon as the pressure within chamber 30' increases to a predetermined level
above the pressure in chamber 32', the diaphragm closes port 38'. At the
same time, air enters chambers 32' and 53' from cuff 20' and chamber 30'
through tubular assemblies 58' and 54', thereby increasing the pressure
within chamber 32' sufficient to force the diaphragm toward chamber 30'
thus opening port 38' again. Thus, diaphragm 34' continues to open and
close port 38' to pressurize chambers 30', 32' and 53' and cuff 20'. More
frequently diaphragm 34' hovers in such a position as to maintain exactly
equal the rates of pressure rise in chambers 32' and 53' on the one hand
and chamber 30' and cuff 20' on the other. As it does so, the pressure
differential between chambers 30' and 32' will remain at a fixed level
depending upon the stretch characteristics and the set of the diaphragm,
for example the three torr pressure value discussed previously. This fixed
pressure differential appears across constricted passageway 60 at all
times. This means that the flow rate through the constricted passageway in
the direction of port 40' is constant at all times. Since the flow rate
through the constricted passageway is constant, the pressure within
compartments 32' and 53' must rise at a constant or fixed rate, that is, a
linear rate. Since the chamber 32' rises in pressure at a linear rate, the
pressure in chamber 30' must also rise at the same linear rate (e.g.
preceding the rise in pressure in chamber 32' by a fixed amount, for
example the 3 torr value mentioned above). This is best exemplified in
FIG. 4a which graphically illustrates a curve D' corresponding to the
linear rise in pressure in chamber 32' and a curve E' which corresponds to
the linear rise in pressure in chamber 30'. Note that curve D' has the
same slope as curve E' but always follows curve E' by a constant amount
which is determined by the stretchability and set characteristics of
diaphragm 34', for example the three torr level mentioned above. Since
chamber 30' rises in pressure linearly, so will cuff 20' since it is in
fluid communication with this latter chamber. Thus, device 24' causes cuff
20' to pressurize in the linear manner illustrated by curve E' in FIG. 4a.
The actual change in pressure with time or ramp rate (dP/dt) is governed
by the following equation:
##EQU2##
Where P.sub.o is equal to an average pressure (about 760 torr); V.sub.1
and V.sub.2 respectively equal the volumes in chambers 53' and 32';
.DELTA.P equals a fixed constant depending upon the stretchability
characteristics of the diaphragm, for example 3 torr; and R is a constant
air resistant factor (functionally equivalent to electrical resistance)
depending upon the cross section of constricted passageway 62'. Thus, in
an actual embodiment, if V.sub.1 plus V.sub.2 is approximately equal to 30
cubic centimeters, if .DELTA.P equals 3 torr and if R equals 12 Torr sec
cm.sup.-3 (corresponding to about a 10 mil diameter hole), then dP/dt is
approximately equal to 6 Torr per second.
It should be noted that the equation (2) for dP/dt above is independent of
the volume of cuff 20'. Therefore, the rate of pressurization of cuff 20'
by means of device 24' is independent of the volume of cuff 20' which
means that the device will cause different sized cuffs to pressurize in
the same way. This, in turn, means that the overall arrangement does not
have to concern itself with the size of the cuff being pressurized. At the
same time, the ramp rate dP/dt of device 24' can be varied by changing
V.sub.1, V.sub.2 and/or R. It is impractical to change the volume V.sub.2.
Therefore, the most practical means of varying the ramp rate is to vary
the volume V.sub.1 by using different containers 52' of different volumes
or by varying the pneumatic resistance R indicated at 60' in FIG. 3a. By
increasing the volume V.sub.1, the slope of curve E is decreased and vice
versa.
From the foregoing discussion, it should be apparent that device 24' can be
used to pressurize cuff 20' at a substantially linear, constant rate,
independent of the size of the cuff. It should be equally apparent that
device 24 can be utilized with pressurizable containers or housings other
than a blood pressure cuff for pressurizing these other containers and
housings at substantially linear, fixed rates, independent of the size of
these latter containers or housings. For example, device 24' could be used
to pressurize or depressurize a pneumatic accumulator.
Turning now to FIG. 5, an | | |
