Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a new and improved volume sensing cuff
inflation means for determining blood pressure without the use of a
stethoscope or transducer. More particularly, the invention relates to a
cuff which may be placed around a finger, thumb, wrist, or other extremity
of the body and inflated to perform a function analogous to that of the
standard cuf~ used with a sphygmomanometer. The cuff is inflated by means
of a transparent cylinder having a plunger resembling a large syringe.
Since the pressure in the cuff is related to the volume of the air expelled
from the syringe, a pressure reading is obtainable.
It has been found by the inventor that with very little practice
or training the average person can sense in the finger, wrist, or arm the
onset and cessation of conditions which are ordinarily detected by auscult-
ation, conventionally by the use of a stethoscope, to determine systolic
and diastolic readings of pressure.
By using a cuff of the structure herein described and by eliminat-
ing the use of a transducer or even a stethoscope, a simplified device for
determining a patient's own blood pressure for home use is thus provided.
Accordingly, a principal purpose of the present invention is to
simplify the equipment required to determine blood pressure in two principal
respects. In the first place, the manometer, be it the mercury column type
or the aneroid type, is eliminated, and there is substituted a manually
operated plunger and cylinder which is much less delicate, less expensive,
and more easily used by the patient. In the second place, the use of a
transducer or a stethoscope is eliminated in that the patient's own sensations
in the finger or other extremity are used to determine the times at which
the systolic or diastolic pressure reading would otherwise be taken.
The development of modern blood pressure measurements is attributed
primarily to two individuals. The first important advance was in 1896 by
Riva Rocci who invented an inflated pneumatic cuff for the upper arm used
to obliterate the pulse at the wrist. The second advance was in 1905 by
Korotkoff who suggested that the sounds heard over the artery just distal
to the cuff should be used as indices of systolic and diastolic pressure.
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Since 1905, there has been considerable reinement and automation of equip-
ment, but, nevertheless at the present time, blood pressure is ordinarily
determined by a physician or trained technician employing an inflatable
cuff, usually attached to the upper arm, and a stethoscope placed over an
artery below the cuff. Alternatively, the physician's function is sometimes
performed by automated equipment and the stethoscope is replaced by a micro-
phone or other transducer. In any case, the cuff is inflated until circul-
ation through the artery is stopped; then the pressure is gradually reduced
and the pressure on the manometer noted ~or recorded) when the first sound
is detected corresponding to the s~ystolic pressure, and then the pressure
reading on the manometer is noted when the last sound disappears (or fades)
corresponding to diastolic pressure.
As has previously been mentioned, the present invention is based
on a new concept, namely, that the subject can sense said sensation of the
phenomenon of his blood flow which is responsible for producing the Korotkoff
sounds. Hence the need for a stethoscope or transducer is eliminated and
the subject merely measures the pressures at which the sensations begin
and subside as applied pressure is increased or reduced.
Another simplification accomplished by the present invention
replaces manometric pressure measurement with measurement of the volume
; required to produce that pressure. This is accomplished by making use of
the pçrfect gas law and observ mg that the process of the present case is
an isothermal one so that the temperature remains constant. The gas law
then shows that the pressure varies inversely with the volume. Therefore,
by measuring change in air volume caused by compression, the volume change
can be calibrated in terms of pressure change and thus determine the applied
pressure.
Another feature of the invention is the zeroing of the system,
using a flexible diaphragm which distends when inflated, by adjusting a
slideable pressure scale so that the zero is properly adjusted to the
particular digit being tested. It will be understood that the thickness of
the finger, thumb or wrist varies from one patient to another, and since the
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measurement of pressure is being gauged by change in volume, it is important
that there be a zero adjustment for the particular limb being tested. In
accordance with the present invention, a simplified means for zero adjust-
ment is provided comprising a sliding transparent cylinder fitting around
the barrel of the syringe and containing indicia for volume.
Other objects of the present invention will become apparent upon
reading the following specification and referring to the accompanying draw-
ings in which similar characters of reference represent corresponding parts
in each of the several views.
In the drawings:
Fig. 1 is an elevational view, partly broken away in section and
to reduce size, showing a device in accordance with the present invention
as applied to the finger of the user.
Fig. 2 is a sectional view through a portion of the structure of
Fig. 1.
Fig. 3 is an end elevation of the structure of Fig. 2.
Fig. 4 is a fragmentary elevational view showing the pressure
scale sleeve in one position and the plunger retracted.
Fig. 5 is a view similar to Fig. 4 showing the plunger partly
retracted.
Fig. 6 is a view similar to Fig. 5 showing the scale adjusted
for zero.
Fig. 7 is a fragmentary, schematic view of a modification.
The perfect gas law may be expressed as follows:
pV = RT
Log p + Log V = Log R + Log T
dp + dV = dT
p V T
If dT = O, then
dp = -dV
Hence a 10% reduction in the overall air volume of the system by compressing
the plunger would produce a cuff pressure of 10% of 1 atmosphere or 76 mm.
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Hg at sea level.
The foregoing principle is applied to the present invention for
monitoring blood pressure. The resulting relationship between pressure and
volume is not quite linear but is determined for the particular device by
a one-time calibration against a manometer.
A cuff ll is provided dimensioned to fit over the finger 28 or
wrist or arm of the user, preferably between the first and second joints of
the former. Cuff 11 has a rigid casing 12, and in the interior thereof is
a cylindrical diaphragm 13, the ends 14 of which are brought around the out-
side of casing 12 and secured thereto by cement, bands (not shown) or othermeans. The relaxed diaphragm 13 is sufficiently large to conveniently fit
over the finger 28. For use on the wrist, a hinge (not shown) may be
provided in the casing, suitably latched shut when the cuff has been install-
ed,
Opening 16 is formed in casing 12 on the outside of diaphragm 13
and connects to a tube 17 which, in the form of the invention shown in
Fig. 4-6, is fixed to the lower end of cylinder 18 of a type conventionally
used in injections but preferably of such volume and diameter to afford
accurate volume determinations in accordance with the above equations.
Fitting tightly in the inside of cylinder 18 is a plunger 19 of any conven-
tional type.
In order to make it possible to insert the plunger I9 into the
cylinder 18 without inflating the diaphragm, a small bleed hole 21 is formed
in the wall of cylinder 18. At the end of cylinder 18 adjacent to tube 17
is a small opening closed by a "bubble" 22 formed of a flexible piece of
material so that when pressure is applied inside cylinder 18 the bubble 22
, bulges outwardly (compare Fig. 5 with Fig. 4) indicating that there is a
slight pressure on the inside of diaphragm 13.
Slideable on the outside of cylinder 18 is a transparent sleeve
23 ormed with indicia 24.indicating pressure.
In the form of the invention shown in Fig. 1, a flexible but in-
elastic tube 26 of extended length is used, whereas in the forms of the
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invention shown in Figs. 2-6 the tube 17 is quite small and close coupled.
The volume requirements of the above equations dictate the cylinder size
for each case.
In use of the device with the diaphragm 13 relaxed, the cuff 11
is slipped over the finger to the position shown in Fig. 1. If the plunger
19 has not previously been inserted in the cylinder 18, this is then done,
air escaping through hole 21 until the end of the plunger closes off the
top opening 21.
As has previously been expressed, the siæe of finger 28 or other
extremity varies with the user. It is important to the determination of
zero pressure to be able to observe when inflated diaphragm 13 is in firm
engagement with the skin of the finger but pressure has not been applied
which affects the flow of the blood through the arteries. For this purpose,
the bubble 22 is observed. '~hen the bubble begins to distend from the
relaxed position of Fig. 4 to the distended position of Fig. 5, then the
cuff is in firm engagement with finger 28. This point is noted and the
sliding scale 23 is adjusted in position so that the zero marking is oppo-
site the then position of the inner end of the plunger 19. The plunger 19
is then moved slowly farther into the cylinder 18 causing the diaphragm 13
to expand and gradually cut off circulation through the artery leading to
the tip of finger 28. At some point during this process, the subject can
feel a slight tingling or throbbing sensation in the finger inside the cuff
11 which corresponds to the diastolic blood pressure. The location of the
end of the plunger 19 relative to the scale marking 24 is then noted. The
plunger 19 is further depressed until the subject notes the point at which
the throbbingstops, which indicates the systolic pressure has been reached
and again the marking 24 on the sleeve 23 with relation to the end of the
plunger 19 is noted and this indicates the systolic blood pressure.
Preliminary to use of the device the markings 24 on sleeve 23 have been
calibra~ed with a standard manometer so that direct readings of blood
pressure on the indicia 24 are obtainable.
It will be ~nderstood that a reverse procedure may be followed,
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namely, the diaphragm is fully inflated by depressing plunger 19, the
plunger is then slowly withdrawn until throbbing first commences and a
reading made of systolic pressure, then the plunger is further withdrawn
until the tingling sensation ends and a reading made of diastolic pressure.
The claims hereinafter set forth are to be thus interpreted.
As shown in Fig. 7 a rigid plenum chamber 29 is interposed
between tube 17_ and tube 26a which communicates with the cuff. By
including the volume of the plenum cham~er in the total volume of the
system, greater sensitivity is achieved. In other respects the structure
of the modification of Fig. 7 may resemble the preceding modifications.
