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Патент USA US2409750

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Oct. 22, 1946.
2,409,749
J. H. ,FOULGER ET AL‘
INDICATING SYSTEM
Filed Nov. 20, 1943
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2,409,749
Patented Oct. 22, 1946
UNITED STATES PATENT OFFICE
2,409,749
INDICATING SYSTEM
John H. Foulger and Paul E. Smith, 'Jr.,'Wilming
ton, Del., assignors to E. I. du Pont tle Nemours
& Company, Wilmington, 'De1., ‘a corporation
of Delaware
‘Application November 20, 1943, Serial No. 5113030
9 Claims. (Cl. 128i—32.06)
:2
1
Itisanother object oftheinvention to provide
This invention relates generallyto systems for
indicating the relative contentof a predetermined
an ‘indicating system for indicating the relative
content of a ‘predetermined characteristic, for
example for “indicating the relative energy .con
tent, or the relative amplitude content, 'in two
predetermined frequency spectrums, one of which
is substantially wholly containedin theother.
It is a speci?cobject of the invention‘toprovide
an improved system for measuring the perform
anceof aheart, for example, of .alhumanheart.
.It is still‘ another object of .the invention to pro
vide .a .system of the type under consideration
which .is substantially insensitive to undesired
characteristic in two frequency spectrums, one
of which .-is substantially contained within the
other, and, while theinventioniis of general ap
plication, it isparticularly suitablefor indicating
changes in the energy content of human heart
sounds.
It is vfrequently‘desirable ,to-measure or ‘to in
dicate changes . in 1a ‘predetermined characteristic
within a predetermined frequency spectrum; for
example, .it is ‘frequently desirable to measure
changes .in the energy-frequency characteristic
of heart sounds. Where the phenomenon to be
measured consists of a single frequency compo
nent, the frequency of which may shift,..it is rela
tively ‘easy to provide ,a suitable indication -of
components .of relatively low amplitude such
as those produced by breathing, lbody .motion,
etc., where the performance of a heart is being
. examined.
.In accordance with. the invention, accardiometer
for indicating the relative content of .a predeter
ber of frequency components, it is not'su?icient 20 mined characteristic in two predetermined fre
frequency changes. However, where the phenom
enon to be investigated comprisesa ‘large num
to measure single frequency changes.
In some
prior art systems it has been customary, when
measuring heart sounds, ‘to consider only the
major frequency components or, at most, a few
frequency components. For example, one ‘prior 25
art. systemfor such purposes provides an ‘indica
tion of theamplitude as Well as an indication of
the frequency of the major sound component of
a heart sound spectrum. However, this is not
entirely'satisfactory for the reason that a con->
siderable portion of the energy of the spectrum
of heart sounds may be in other frequency com
ponents of the complex sound‘ wave.
Also, in many cases, where measurements of
the ‘type under ‘consideration are to be made,
there are present undesired components which
shouldnot'be ‘included in the measured result.
For example, in‘measuringheart sounds it fre
quently happens that continuous ‘low-amplitude
quency-spectrums ofheart soundscne of which
is. substantially. contained within the ‘ other, com
prises :means forderiving and translating a ?rst
electrical signal-corresponding to thecontent of
one of the spectrumsof heartsounds and means
including a series condenser and a shunt resistor
for .deriving and translating a second electrical
signalcorresponding to the content of the other
of the spectrums of heart sounds. The (system
also comprises meanacoupled to the means for
deriving and translating .the ‘above-mentioned
?rst signal, for-deriving a third signal varyinglin
accordance'with the content of said predetermined
characteristic in the'?rst electrical signal, as well
as ‘means, coupled to the means-for-deriving and
translating the above-mentioned ‘second signal,
for‘ deriving a fourth signal varying in accordance
with the content of ‘the above-mentioned pre
determined characteristic in the second electrical
signals caused byibreathing, muscle tremors, etc., 40 signal. vMeans differentially responsive to ‘the
are present. Such undesired components ‘may
cause errors in-both thefrequency and amplitude
. above-‘mentioned third and fourth signals are-pro
vided for indicating the above-mentioned rela
tive content ofithe two spectrums.
For a better understanding of the present in
under consideration which is substantially un 45
vention, together with other and further objects
responsive .toisuch undesired signal components.
thereof, referenceis had to the following descrip
It is an object of the invention, therefore, to
tion taken in connection with the accompanying
provide an vimproved indicating system .which is
drawing, and .its scope will be pointed out in
notsubject to one or more of theabove-mentioned
‘indications. Therefore, it isparticularly desirable
to provide an arrangement of the general type
disadvantages.‘
'
the appended claims.
3
2,409,749
Fig. -1 of the drawing is a, circuit diagram,
partly schematic, of a complete indicating sys
tem in accordance with the invention which is
useful for measuring the performance of a human
heart, while Fig. 2 illustrates a modi?cation of
_ a portion of the circuit of Fig. 1.
Referring now more speci?cally to Fig. 1 of
the drawing, the system illustrated is useful for
indicating changes in the relative content of a
predetermined characteristic in two predeter
mined frequency spectrums, one of which is sub
stantially contained within the other. This sys
tem is particularly useful in measuring the per
4
3|, a resistor 32, having an adjustable value,
being connected across the meter terminals.
Meter 3| is preferably a microammeter or a gal
vanometer. Provision is also made by means of
a switch 33 so that a condenser 34 can be con
nected across the meter terminals. Suitable an
ode operating potentials are provided for the
tubes by a source of potential 35 while suitable
?lament voltages are provided for the tubes by
10 means of a source of supply 36, the various tubes
being adapted to be energized through a double
pole single-throw switch 31. Control-electrode
biasing potentials for tube 25 are provided by
formance of a human heart where it is found
a source of potential 36'.
that a considerable portion of the heart sounds 15
In considering the operation of the system just
is contained in a, low-frequency spectrum. There
described, it will :be assumed that an adequate
fore, in accordance with the speci?c embodiment
sample of all of the sounds corresponding to a
of the invention illustrated, the heart perform
heart to be examined are picked up by the micro
ance is measured by a comparison of the energy
phone ID and converted into electrical frequency
content of the total spectrum of an adequate sam
components which are ampli?ed in the tube II,
ple of heart sounds with the energy content of
the ampli?ed signals being applied to tube I3 for
only a portion of the total frequency spectrum
further ampli?cation. The function of the diode
of this sample. Speci?cally, the energy content
portion of tube I3 will be considered more speci?
of a predetermined frequency spectrum which is
cally hereinafter. Signals which are ampli?ed
wholly contained Within the frequency spectrum 25 in tube I3 are applied with like polarity to the
comprising the total sample of heart sounds is
two input circuits of tube I8 so that a balanced
compared with the energy within the frequency
output signal is obtained across the two load cir
spectrum comprising the total sample of heart
cuits of tube I8. The values of condenser 22 and
sounds. Additionally, low-amplitude signals
resistor 23 are such that the entire frequency
caused by breathing, etc., are preferably elimi
nated from the signals which are compared.
The arrangement illustrated, therefore, com
prises a crystal microphone IIl adapted to convert
an adequate sample of all of the heart sounds
of a patient into corresponding electrical com
ponents. This crystal microphone may be asso
30 spectrum corresponding to the signals translated
by the triode section of tube I3 is translated to
the input circuit of the upper triode section of
tube 25. However, the values of condenser 26 and
resistor 21 are such that the lower frequency com
35 ponents of this spectrum are not translated to the
input circuit of the lower triode section of tube
ciated with any suitable device (not shown) for
25, only the higher frequency components of the
conveying heart sounds thereto and is coupled
spectrum being translated thereto. It is possible,
tothe input circuit of a vacuum-tube ampli?er
therefore, to adjust the tap on resistor 24 to
II, having a load resistor I2, from which signals 40 such a position that the energy content of the sig
are coupled, through a coupling condenser I 4
nals translated by the upper section of tube 25
and grid-leak resistor I5, to a succeeding ampli
is equal to that of the energy content of the sig
?er stage including an ampli?er tube I3. The
nal translated by the lower section of tube 25.
tube I3 is preferably of the diode-triode type
and the diode anode I3a thereof is connected
externally of the tube to the control electrode of
the tube. Tube I3, the triode section of which
is preferably of the sharp cut-off type, is provided
Under these conditions, the meter 3|, which is
preferably of the zero-center type, will have no
voltage applied thereto and will thus provide no
indication. However, under certain conditions
important in medicine, a shift in certain frequen
cies of the normal frequency spectrum may be
with a load resistor I6 from which potentials of
like polarity are coupled, through coupling con 50 encountered so that a major portion of the en
denser I1, to the control electrodes of a succeed
ergy is contained in the higher frequencies of the
ing balanced-ampli?er stage including a double
triode tube I8. Load resistors I9 and 20 are pro
vided for tube I8 and their common junction
is coupled to the cathode of tube I8 through con
denser 2I for alternating currents. Signals cor
responding to the entire frequency spectrum of
the signals translated by the triode section of
tube I3 are coupled from load resistor I9, through
a circuit including condenser 22 and resistors
23 and 24 connected as shown, to the input cir
cuit of one section of a succeeding double-triode
tube 25. Signals corresponding to only a por
tion Of the entire frequency spectrum of signals
heart spectrum.
Under these conditions, the
voltage developed in the load circuit of the upper
triode section of the tube 25 will no longer be
equal to the voltage developed in the lower triode
section thereof and this shift in frequency can
easily be observed on the meter 3|.
'
In some cases with a, properly designed micro
phone properly placed on the chest to pick up
heart sounds, sounds caused by breathing, muscle
tremors and normal room noise, while of low in
tensity, may seriously interfere with measure
ments of the type described above. It is for the
translated by the triode section of tube I3 are 65 purpose of excluding these undesirable compo
coupled from load resistor 20 to the input cir
nents that the diode section of tube I3 is pro
cuit of the other triode section of tube 25 through
vided. The time constant of the circuit includ
a circuit including condenser 26 and resistor 21
ing condenser I4 and grid-leak resistor I5 is so
connected as shown. The tube 25 is provided
chosen that a large grid current flows when the
with a balanced output circuit including resistors
normally unbiased grid of tube I3 is driven posi
70
28, 29 and 30 connected in series between the
tive and the condenser I4 is thereby charged nega
anodes of tube 25, a tap on resistor 29 being con
tively, biasing the tube I3 towards its cut-off
nected to the cathode of tube 25 by a condenser
point. The rate at which this charge on con
2|’. The signals ampli?ed in the two sections
denser I4 leaks off through resistor I5 determines
of tube 25 are applied differentially to a meter 75 the length of time during which this control
/
/
2,409,749
6
5
with the blades 39, 40 and 4| in their upper posi
tion, the resistors 43 and '42 are connected in
action with respect to undesired signals is main
tained. The circuit is preferably proportioned so
that the condenser charges very quickly and dis
charges relatively slowly. A bias for tube I3 is
therefore developed from the signal translated
which vis effective to stabilize the positive peaks
of the signal translated at the zero grid-voltage
series in that order between the terminals A and
B. It will also, be seen that, with the blades 39,
4c, M in the lower position, the resistors 42 and
133 are connected in series in that order between
terminals A and B. The arrangement of Fig. 2,
therefore, provides a convenient means for vary
point on the characteristic of the triode section
ing the effect of tap 43, thereby to provide addi
of tube l3. In this manner the undesired low
amplitude components mentioned above are 10 tional ?exibility in adjusting the system. In
other words, by this arrangement more ?exibil
caused to fall below the cut-off point of tube I3
ity is provided for balancing the signals trans
and are not translated thereby, In this manner
lated by the upper section of tube 25 against the
the effect of the undesired components mentioned
signals translated by the lower section thereof.
above is eliminated or very much reduced.
It will be readily apparent to those skilled in
Resistor 32 is provided across meter 3| for ad
the art that the diode of tube l3 can be omitted
justing the sensitivity thereof, while, if desired,
and the operationof the circuit otherwise main
switch 3;’; may be operated to include condenser
‘ tained, providing sumcient grid current is drawn
34 across the terminals of meter 3|, thereby effec
by tube iii to charge condenser M in the manner
tively reducing the effective overall band width
of the signal components being considered.
20
required.
As stated above, the circuit is preferably so ad
iusted that condenser 22 will pass 100 per cent. of
the signals translated by the triode section of
tube l3, whereas the smaller condenser 26 will
In summary, therefore, it will be seen that the
system disclosed is suitable for indicating the rel
ative content of a predetermined characteristic
in two predetermined frequency spectrums, one
attenuate a portion of the low frequencies. ’ By
' of which is substantially contained within the
using condensers of different capacities, the ?lter
other.
action of condensers 2.2. and 25 can be varied to
suit the particular use to which the system is to
utilized to indicate the relative energy content
of the sound components of an adequate sample
of an entire heart spectrum and of a portion of
this spectrum. The ?lter means including con~
denser 22 and resistor 23 thus comprises means
for deriving and translating a ?rst electrical sig
nal corresponding to the content of one of the
be put. The potential divider provided by re
sistor 24 enables the strength of the two signals
translated by the individual channels to be ‘made
equal, thus to balance the meter. This resistor
may be provided with a scale which indicates the
As speci?cally described, the system is
above-mentioned spectrums, speci?cally corre
percentage of total energy which must be passed
by the condenser 22 to balance the energy pass 35 sponding to the content of the entire spectrum
of the sample of heart sounds. The filter means
ing through the channe1 including condenser 25
including condenser 26 and resistor 21 comprises
and therefore gives directly the ratio
means for deriving and translating a second elec
trical signal corresponding to the content of the
Sound energy passing filtersX100
Total ampli?ed sound energy
The frequency spectrum of normal heart sounds
other of the . above-mentioned spectrums, spe
ci?cally corresponding to the frequency spec
trum containing the higher-frequency compo~
nents of the sample of heart sounds. The upper
contains most of its energy in the very low fre
section of tube 25 comprises a means, coupled to
quencies. With a proper choice of circuit values,
which derives and trans
the meter 3! can be made to balance approxi 45 the ?lter means 22,
mately at the mid-scale point thereof or at any
other pointv desired. The system is particularly
lates the above-mentioned ?rst signal, for deriv~
ing a third signal varying in accordance with the
content of the above~mentioned predetermined
useful in the study of heart sounds and the man
characteristic in the ?rst electrical signal. Spe
ner in which they are affected by exercise, dis
ease, therapeutic agents, industrial exposure to 50 ci?cally, a signal is derived which varies in ac
cordance with the entire energy content of the
chemicals, malnutrition, etc.
sample of the heart sounds or in accordance with
The arrangement of Fig. 1 may be modi?ed, if
the average amplitude of the frequency compo
desired, to include the circuit of Fig. 2 by sub
nents of the above-mentioned ?rst electrical
stituting the circuit of Fig. 2 for the portion indi
cated in the dotted rectangle 38 of Fig. 1. In 55 signal. The lower section of tube 25 comprises
means, coupled to the ?lter means 26, El which
making this substitution, terminals marked .A,
derives and translates the above-mentioned sec—
B and C of Fig. 1 are connected to correspondingly
ond signal, for deriving a fourth signal varying
marked terminals of Fig. 2. The circuit of Fig. 2
in accordance with the content of the above
comprises a three-pole double-throw switch hav-'
ing blades 39, ‘4b and 4!, blade 39 being connected 60 mentioned predetermined characteristic in the
second electrical signal. Speci?cally, a signal is
to terminal A, and blade 4!} being connected to
derived which varies in accordance with the en~
terminal B. (Switch blade at is connected to one
ergy content of the frequency spectrum including
terminal of a resistor 42', the other terminal of
resistor 42 being connected to the upper station
the higher frequency components of the sample
ary contact for blade ti] and to the lower sta
of heart sounds or in accordance with the average
tionary contact for blade 39. An additional re
amplitude of the components included in the
sistor G3 is provided'and is connected between
above-mentioned second electrical signal. Meter
the upper contact for blade 39 and the lower
3!, therefore, is differentially responsive to the
contact for blade Ml, a tap thereon being con
above-mentioned
third and fourth signals for
nected to terminal 0‘. The upper contact for 70 indicating the relative content desired.
blade Al is connected to the lower contact for
While applicants do not intend to limit the in
blade til, while the upper contact for blade 39 is
vention
to any particular circuit constants. the
connected to the lower contact for blade M.
following circuit constants are given as illustra
In considering the operation of the circuit of
tive of ‘those which have been found to be of par
Fig. 2 in the system of Fig. 1, it will be seen that,
2,409,749
7
8
ticular utility in a system of the type under con
signals for indicating said relative energy con
tent.
3. A cardiometer for indicating the relative
sideration:
Tube
Tube
Tube
Tube
ll ____________________ __
l3 ____________________ __
l8 ____________________ __
25 _____________________ __
Type
Type
Type
Type
average amplitude of signals in two predeter
1N 5-GT
1H 5-GT
1G 6-G
1G 6-G
mined frequency spectrums of heart sounds one
of which is substantially contained within the
other comprising, means for deriving and trans
lating a ?rst electrical signal corresponding to
Condenser I4 _______________ __ 0.25 microfarad
Condenser 22 _______________ __
Condenser 26 _______________ __
Condenser 34 _______________ __
Resistor l5 _________________ __
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
Resistor
23 _________________ __
24 _________________ __
2'! _________________ __
28 ___________________ _.
29 _________________ __
30 _________________ __
32 __________________ __
42 __________________ _.
43 __________________ _.
0.25 microfarad
0.10 microfarad
one of said spectrums of heart sounds, means in
10 cluding a series condenser and a shunt resistor for
40 microfarads
3megohms
500,000 ohms
deriving and translating a second electrical signal
corresponding to the other of said spectrums of
heart sounds, means coupled to said means for
deriving and translating said ?rst signal for deriv
15 ing a third signal varying in accordance with the
average amplitude of said ?rst electrical signal,
307,000 ohms
500,000 ohms
50,000 ohms
12,000 ohms
50,000 ohms
10,000 ohms
107,000 ohms
200,000 ohms
While there have been described what are at
present considered to be the preferred embodi
ments of this invention, it will be obvious to those
skilled in the art that various changes and modi
?cations may be made therein without departing
from the invention, and it is, therefore, aimed
in the appended claims to cover all such changes
and modi?cations as fall within the true spirit 30
and scope of the invention.
What is claimed is:
l. A cardiometer for indicating the relative
content of a predetermined characteristic in two
predetermined frequency spectrums of heart 35
sounds one of which is substantially contained
within the other comprising, means for deriving
and translating a ?rst electrical signal corre
sponding to the content of one of said spectrums
of heart sounds, means including a series con 40
denser and a shunt resistor for deriving and
means coupled to said means for deriving and
translating said second signal for deriving a
fourth signal varying in accordance with the
average amplitude of said second electrical sig
nal, and means differentially responsive to said
third and fourth signals for indicating said rela
tive average amplitude.
ll._A cardiometer for indicating the relative
amplitude of sound signals contained in two pre
determined frequency spectrums of heart sounds
one of which is substantially contained within the
other comprising, means including a series con
denser having a value of the order of 0.25 micro
farad and a shunt resistor for deriving and
translating a ?rst electrical signal correspond
ing to the sound content of one of said spectrums,
means including a series condenser having a value
of the order of 0.10 microfarad and a shunt re
sistor having a value of the order of the value of
said ?rst-named resistor for deriving and
translating a second electrical signal correspond
ing to the sound content of the other of said
spectrums, means coupled to said means for deriv
ing said ?rst signal for deriving a, third signal
varying in accordance with the average amplitude
of said ?rst electrical signal, means coupled to
said means for deriving said second signal for
deriving a fourth signal varying in accordance
with the average amplitude of said second elec
trical signal, and means differentially responsive
to said third and fourth signals for indicating
said relative amplitude.
5. A cardiometer for indicating the relative
content of a predetermined characteristic in two
translating a second electrical signal correspond
ing to the content of the other of said spectrums
of heart sounds, means coupled to said means
for deriving and translating said ?rst signal for 45
deriving a third signal varying in accordance
with the content of said predetermined charac
teristic in said ?rst electrical signal, means
coupled to said means for deriving and translat
ing said second signal for deriving a fourth signal 50
varying in accordance with the content of said
predetermined frequency spectrums of heart
predetermined characteristic in said second elec
sounds one of which is substantially contained
trical signal, and means differentially responsive
within the other comprising, means for deriving
to said third and fourth signals for indicating
and translating a ?rst electrical signal corre
said relative content.
sponding to the content of one of said spectrums
2. A cardiometer for indicating changes in the
of heart sounds, means including a, series con
relative energy content in two predetermined
denser and a shunt resistor for deriving and
frequency spectrums of heart sounds one of which
translating a second electrical signal correspond
is substantially contained within the other com
ing to the content of the other of said spectrums
prising, means for deriving and translating a ?rst 60 of heart sounds, means coupled to said means
electrical signal corresponding to the energy con
for deriving and translating said ?rst signal for
tent of one of said spectrums of heart sounds,
deriving a third signal varying in accordance with
means including a series condenser and a shunt
the content of said predetermined characteristic
resistor for deriving and translating a second
in said ?rst electrical signal, means coupled to
electrical signa1 corresponding to the energy con 65 said means for deriving and translating said
tent of the other of said spectrums of heart
second signal for deriving a fourth signal vary
sounds, means coupled to said means for deriving
ing in accordance with the content of said pre
and translating said ?rst signal for deriving a
determined characteristic in said second electrical
third signal varying in accordance with the aver
signal, and means for adjusting the relative am
age amplitude of said ?rst electrical signal, means 70 plitude of said third and fourth signals and for
coupled to said means for deriving and translat
diiferentially combining them to indicate said
ing said second signal for deriving a fourth signal
relative content.
.
varying in accordance with the average amplitude
6. A cardiometer for indicating the relative con
of said second electrical signal, and means dif
tent of a predetermined characteristic in two pre
ferentially responsive to said third and fourth 75 determined frequency spectrums of heart sounds
2,409,749
10
'sponding to the content of one of said spectrums
one of which is wholly contained within the other
of heart sounds, means including a series con
comprising, means for deriving and translating
denser and a shunt resistor for deriving and
a ?rst electrical signal corresponding to the con
translating a second electrical signal correspond
tent of the wider of said spectrums of heart
sounds, band-pass selector means including a Cl ing to the content of the other of said spectrums
of heart sounds, means having a fast response
series condenser and a shunt resistor coupled to
and a slow recovery for reducing the e?ect of
said last-named means for deriving therefrom
undesired components of relatively low amplitude
and for translating a second electrical signal cor
such as sound components due to breathing and
responding to the content of the other of said
muscle tremors on said ?rst and second electri
spectrums of heart sounds, means coupled to said
cal signals, means coupled to said means for de
means for deriving and translating said ?rst sig
riving and translating said ?rst signal for de
nal for deriving a third signal varying in accord
riving
a third signal varying in accordance with
ance with the content of said predetermined char
the content of said predetermined characteristic
acteristic in said ?rst electrical signal, means
in said ?rst electrical signal, means coupled to
coupled to said band-pass selector for deriving
said means for deriving and translating said sec
a fourth signal varying in accordance with the
ond signal for deriving a fourth signal varying in
content of said predetermined characteristic in
accordance with the content of said predeter
said second electrical signal, and means differen
mined characteristic in said second electrical sig
tially responsive to said third and fourth signals
for indicating said relative content.
20 nal, and means differentially responsive to said
third and fourth signals for indicating said rela—
'7. A cardiometer for indicating the relative
tive content.‘
'
content of a predetermined characteristic in two
9. A cardiometer for indicating the. relative
predetermined frequency spectrums of heart
content of a predetermined characteristic in two
sounds one of which is substantially contained
predetermined frequency spectrums of heart
within the other comprising, means for deriving
sounds one of which is substantially contained
and translating a ?rst electrical signal corre
within the other comprising, means for deriving
sponding to the content of one of said spectrums
of heart sounds, means including a series con
denser and a shunt resistor for deriving and
and translating a ?rst electrical signal corre
sponding to the content of one of said spectrums
of heart sounds and including a series condenser
translating a second electrical signal correspond
and a shunt resistor for deriving and translat
ing to the content of the other of said spectrums
ing a second electrical signal‘ corresponding to
of heart sounds, means for reducing the effect of
the content of the other of said spectrums of
undesired components of low amplitude such as
heart sounds, amplifying means comprising a grid
sound components due to breathing and muscle
current recti?er in said ?rst-named means for
tremors on said ?rst and second electrical sig
reducing the eifect of undesired components of
nals, means coupled to said means for deriving
relatively low amplitude such as sound com
and translating said ?rst signal for deriving a
ponents due to breathing, and muscle tremors on
third signal varying in accordance with the con
said ?rst and second electrical signals, means
tent of said predetermined characteristic in said
?rst electrical signal, means coupled to said means 40 coupled to said amplifying means for deriving a
third signal varying in accordance with the con
for deriving and translating said second signal
tent of said predetermined characteristic in said
for deriving a fourth signal varying in accord
?rst electrical signal, means coupled to said am
ance with the content of said predetermined char
plifying means for deriving a fourth signal vary
acteristic in said second electrical signal, and
ing in accordance with the content of said pre
means differentially responsive to said third and
determined characteristic in said second electri
fourth signals for indicating said relative content.
cal signal, and means differentially responsive
8. A cardiometer for indicating the relative con
to said third and fourth signals for indicating
tent of a predetermined characteristic in two
said relative content.
predetermined frequency spectrums of heart
JOHN H. FOULGER.
sounds one of which is substantially contained 50
PAUL E. SMITH, JR.
within the other comprising, means for deriving
and translating a ?rst electrical signal corre
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