A force transducer for measuring dynamic force activity within the heart of a subject essentially consists of a U-shaped beam of low elastic compliance material. Two lines extend from the beams's legs and a long coil spring is attached to the beam. A strain gauge is coupled to one of the beam's legs to sense deflections thereof. The beam with the tines and most of the spring are surrounded by a flexible tube, defining a catheter, which is insertable into a subject's heart through an appropriate artery. The tines are extractable from the catheter for implantation into the myocardium by pushing on the end of the spring which extends beyond the external end of the catheter

Culler, V. H.

Feldstein, C.

Lewis, G. W.

Silver, R. H.

English

NASA Technical Reports Server

United States Patent t 191 
Fletcher et al. 
[ 11 I 3,971,364 
[451 July 27, 1976 
[541 
[ 761 
CATHETER TIP FORCE TRANSDUCER FOR 
CARDIOVASCULAR RESEARCH 
Inventors: James C. Fletcher, Administrator of 
the National Aeronautics and Space 
Administration, with respect to an 
invention of Cyril Feldstein, Sierra 
Madre; Gilbert W. Lewis, Arcadia; 
Robert H. Silver, Van Nuys; Virgil 
H. Culler, La Canada, all of Calif. 
[22] Filed: May 16, 1975 
[21] Appl. No.: 578,241 
[52] U.S. CI. ............................ 128/2 S; 128/2.05 E; 
12812.06 E; 128/418; 128/419 P; 731398 AR 
[ 5 11 Int. CI.* ............................................ A61B 5/10 
[58) Field of Search ............. 128/2, 2.05, 2.06, 418, 
128/419; 731398 
[561 References Cited 
UNITED STATES PATENTS 
3,474,776 10/1969 O’Brien ............................... 128/2 S 
3,703,099 11/1972 Rouse ......................... 128/2.05 E X 
3,710.781 1/1973 Hutchins e t  a1 ................ 128/2.05 D 
3,750,650 8/1973 Ruttgers ......................... 128/2.06 E 
I MONITORING OR I 
RECORDING 
DEVICE 
3,815.61 I 6/1974 Denniston ....................... 128/419 D 
3,83 1,588 8/1974 Rindner .......................... 128/2.05 E 
Primary Examiner-Delbert B. Lowe 
Attorney, Agent, or Firm-Monte F. Mott; Wilfred 
Grifka; John R. Manning 
ABSTRACT [571 
A force transducer for measuring dynamic force activ- 
ity within the heart of a subject essentially consists of 
a U-shaped beam of low elastic compliance material. 
Two tines extend from the beam’s legs and a long coil 
spring is attached to the beam. A strain gauge is cou- 
pled to one of the beam’s legs to sense deflections 
thereof. The beam with the tines and most of the 
spring are surrounded by a flexible tube, defining a 
catheter, which is insertable into a subject’s heart 
through an appropriate artery. The tines are extract- 
able from the catheter for implantation into the myo- 
cardium by pushing on the end of the spring which ex- 
tends beyond the external end of the catheter. The 
tines are retractable back into the catheter, prior to 
catheter removal from the subject, by pulling on the 
externally exposed spring end. 
9 Claims, 3 Drawing Figures 
21 26 12 20 15 18 350 I I 35b 35, 
27 25 I3 22 Ib II ‘14 I7 
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CATHETER TIP FORCE TRANSDUCER FOR 
CARDIOVASCULAR RESEARCH 
ORIGIN OF THE INVENTION 
The invention described herein was made in the per- 
formance of work under a NASA contract and is sub- 
ject to the provisions .of Section 305 of the National 
Aeronautics and Space Act of 1958; Public Law 
85-568 (72 Stat. 435; 42 UsC 2457). 
BACKGROUND OF THE INVENTION 
1 .  Field of the Invention: 
The present invention generally relates to a force 
transducer and, more particularly, to a force trans- 
ducer to record dynamic force activity within the heart. 
2. Description of the Prior Art: 
A major thrust of heart research at present is directed 
towards the assessment of regional myocardial me- 
chanics. For the enhancement of such research, force 
transducers, capable of recording dynamic force activ- 
ity within the heart, are needed. It is particularly desir- 
able to record such activity without having to open the 
chest. Although various force transducers are available 
none of them can be inserted into the heart to perform 
the desired measurements. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is a primary object of the present invention to 
provide a new force transducer, finding particular util- 
ity in cardiovascular research. 
Another object of the present invention is to provide 
a novel force transducer, insertable into the heart, 
without opening the chest, for recording dynamic force 
activity within the heart. 
These and other objects of the invention are achieved 
by providing a very small force transducer, consisting 
essentially of a U-shaped beam of low elastic compli- 
ance. Sharp tines are rigidly attached to the ends of the 
U-shaped beam and a silicon semiconductor sensing 
element is attached to one of the legs or sides cf the 
beam. One end of a long coil spring extends from the 
beam. The beam with the spring are placed in a hollow 
plastic tube, representing a catheter. 
In use, the catheter, which surrounds the entire beam 
and the tines extending therefrom is inserted through 
an incision made through the skin of a subject into an 
artery and manipulated into one of the heart’s cham- 
ber, e.g., the left ventricle. Once the catheter is in the 
appropriate heart chamber the beam is pushed out of 
the catheter far enough that the tines are fully im- 
planted through the endocardium into the interior fi- 
bers of the myocardium. The leads from the sensing 
element extend through the catheter’s external end 
(the end remaining outside the subject) and are con- 
nected to an appropriate recorder, e.g., an oscillo- 
graph. The beam is pushed out from the catheter, for 
insertion into the myocardium interior fibers, by push- 
ing on the spring extending from the catheter’s external 
end, while extraction of the tines from the myocardium 
and reinsertion of the beam into the catheter is 
achieved by pulling on the external cnd of the spring. 
By rotating the external end of the spring, measure- 
ments of force along different directions in the myocar- 
dium are casily attainable. 
The novel features of the invention are set forth with 
particularity in the appended claims. The invention will 
best be understood from the following description 
.- 
5 
10 
15 
20 
25 
30 
35 
40 
45 
so 
55 
60 
65 
2 
when read in conjunction with the accompanying draw- 
ings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is substantially a side view of the novel cathe- 
FIG. 2 is a diagram useful in explaining the use of the 
FIG. 3 is a diagram useful in explaining the formation 
ter; 
catheter; and 
of a U-shaped beam from a simple small needle. 
DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 
Attention is directed to FIG. 1 wherein the novel 
transducer is shown including a U-shaped beam 10 of 
low elastic compliance. The beam can be thought of as 
formed of two parallel spaced apart legs 11 and 12 
which are interconnected at one end by a cross mem- 
ber 13. The other ends of the two legs, remote from 
cross member 13, are designated by numerals 14 and 
15. Rigidly attached to the beam legs at ends 14 and 15 
are two sharp tines 17 and 18. The tines are parallel to 
one another and extend in a direction away from cross 
member 13. If desired the outer ends 14 and 15 of the 
legs may be tapered to form sharp tips and thereby 
eliminate the need for tines 17 and 18. In such a case 
the legs would function as the tines. A strain gauge 
sensing element 20 is attached to one of the legs, such 
as leg 12. Electrical leads 21 and 22 extend from oppo- 
site ends of the sensing element 20. 
Coupled to the cross member 13 of the U-shaped 
beam 10 is a long coil spring 25. The spring extends 
from an end 26, which is connected to cross member 
13 of the beam 10, to an opposite end 27. In FIG. 1, the 
electrical leads 21 and 22 are shown extending from 
the sensor element 20 through the spring 25 and there- 
from the leads extend to an appropriate monitoring or 
recording device, designated by numeral 30. The func- 
tion of the latter is to display and/or record the changes 
in resistance of sensor element 20 which are caused by 
deflections of the leg 12 due to forces applied to the 
tine 18 when the latter is inserted into a muscle, sub- 
jected to dynamic forces, as will be described hereinaf- 
ter. 
As shown in FIG. 1 the transducer also includes a 
hollow plastic tube 35, hereinafter referred to as the 
catheter, which surrounds the beam 10, the tines 17 
and 18 and practically all of the spring 25. The beam 10 
and the spring are of such small size that they can be 
inserted within a catheter of sufficiently small diame- 
ter, of the type capable of being guided through an 
artery to a selected chamber of the heart of a subject, 
used in medical research. Generally, catheters of diam- 
eters on the order of several mm are used for such 
purposes. In one embodiment actually reduced to prac- 
tice the catheter was a 7 french catheter of a diameter 
on the order of 2.3mm. The spacing between tines 17 
and 18 was on the order of 1 Smm. 
In FIG. 1 the catheter’s ends are designated by 35a 
and 35b. End 35a is the front end or distal tip which is 
inserted through the appropriate artery from an inci- 
sion of the skin of the subject to the desired heart 
chamber, while end 35b represents the catheter exter- 
nal end o r  proximal tip which remains outside the sub- 
ject. The catheter 35 is long enough, e.g., 100cm, to 
enable end 35a to exteni into the subject’s heart, while 
end 35h remains outside the subject. Similarly spring 
25 and leads 21 and 22 are long enough to extend 
3,97 1,364 
3 4 
through the entire length of the catheter as well as may be coated with epoxy to provide physical strength 
extend beyond external end 35b. The portion of the to the spring-beam interconnection. 
spring 25 extending beyond end 35b is used to manipu- From the foregoing it should thus be appreciated that 
late the U-shaped beam 10, as will be described herein- with the novel invention disclosed herein forces in the 
after. Leads 21 and 22 extend beyond end 35h to the 5 myocardium can be measured without having to open 
device 30. the chest of the subject, Le., without surgical interven- 
In use, the catheter 35 is inserted into the subject’s tion. The catheter is insertable into the heart through 
heart through an appropriate artery, with the beam 10 an artery extending from adjacent the subject’s skin to 
and tines 17 and 18 surrounded by the catheter, as the heart. Once the catheter front end is in the heart 
shown in FIG. 1. In this position the tines cannot pierce 10 near the myocardium where force measurements are to 
or otherwise injure the artery during the catheter’s be performed, tines are extracted from the catheter and 
insertion. Verification of the catheter’s positioning penetrate the myocardium, by pushing on a coil spring 
near the endocardium of the heart at the appropriate which is surrounded by the catheter and extends be- 
location, where measurements are to be made, is yond its external end or proximal tip. After measure- 
achieved by fluoroscopy. Once the catheter is at the 1.5 ments are made the tines are retracted back into the 
desired position the beam 10 together with the tines 17 catheter by pulling on the spring before the catheter is 
and 18 are pushed foward so that the tines 17 and 18 removed from the subject. 
extend beyond catheter end 3sa and are implanted It should be appreciated that although the invention 
through the endocardium into the interior fibers of the has been described in connection with measuring 
myocardium; as shown in FIG. 2. Although not neces- 20 forces in the myocardium of a subject the invention is 
sary, if desired, the entire beam 10 may be pushed out not intended to be limited thereto. For example, the 
or withdrawn of the catheter through fron end 3sa. transducer may be inserted into a subject’s stomach to 
Dynamic forces in the myocardium deflect tine 18 and measure forces in the stomach wall. In general the 
therefore leg 12 to which element 20 is connected. Its invention can be used to measure forces in any internal 
change in resistance which is proportional to the dy- 25 muscle which can be reached from the subject’s skin 
without resort to surgery. namic forces is transmitted via leads 21 and 22 to de- It should be apparent that the small size U-shaped vice 30 for monitoring or recording, in a manner well beam 10 may be machined from a block of metal or known in the art. fabricated in any other conventional manner to form 
30  legs 11 and 12 connected by cross-member 13. In one The extraction or removal of the tines from the cath- 
embodiment, actually reduced to practice, the U- eter is easily achieved in the novel transducer of the 
shaped beam consisted of a portion of a sewing needle, present invention by pushing the portion of spring 25 which extends beyond the catheter external end 3Sb .. 
toward the catheter, thereby compressing the spring. 
The compressional force is transmitted through the 
spring coils to the beam 10 which is in turn pushed 
forward toward tip 35a, thereby exposing the tines 
which penetrate the myocardium through the endocar- 
dium. After performing the force measurement the 
tines are easily retracted back into the catheter by 
pulling on the externally exposed portion of the spring. 
With the novel transducer of the present invention 
measurements of forces along different directions 
within the myocardium can be accomplished. After one 
measurement is made in which the tines are aligned in 
a first direction the spring is pulled back to extract the 
tines from the myocardium. Then the spring is rotated 
to align the tines in a different, second direction and 
thereafter the spring is pushed in to cause the tines to 
penetrate the myocardium, while being aligned in the 
second direction. Thus, the spring is most useful for the 
removal of the tines from the catheter for implanting 
into the myocardium, for retracting the tines back into 
the catheter after all measurements are made, as well as 
to align the tines so as to measure forces along different 
directions within the myocardium. 
It  should be pointed out that by using tines 17 and 18, 
beam 10 as well as the spring 25 all of which are of 
electrically conductive metals, the transducer can be 
used as an internal electrode for an electrocardiogram. 
Clearly, to this end spring end 26 need be attached to 
beam 10 and tines 17 and 18 need be attached to the 
beam’s legs by means of electrically conductive joints 
such as by soldering or welding. To prevent electrical 
shock of the subject the leg 12 to which element 20 is 
attached may be covered by a layer of insulating mate- 
rial, such as epoxy. Also, the cross member 13 of beam 
10 and one or more loops of the spring 25 near end 26 
designated in FIG. 3 by numeral 40, which was cut off 
along lines 41 and 42. Thus, the U-shaped beam 10 
Although particular embodiments of the invention 
have been described and illustrated herein, it is recog- 
nized that modifications and variations may readily 
occur to those skilled in the art, and, consequently, it is 
40 intended that the claims be interpreted to cover such 
modifications and equivalents. 
35 consisted of a portion of the needle’s eye 43. 
What is claimed is: 
1. A transducer for measuring forces in an internal 
muscle of a living subject without surgical intervention 
first means including a plurality of substantially par- 
allel spaced apart tines with tapered outer ends for 
penetrating an internal muscle of a subject; 
strain gauge means coupled to said first means to 
provide an output related to the low compliance 
deflection of one of said tines; 
an elongated flexible member having a first end cou- 
pled to said first means remote from said tines and 
extending to a second end; and 
an elongated flexible hollow tube, definig a catheter, 
having a first working end and an opposite second 
end, said catheter being adapted to be inserted into 
said subject so that its first end is substantially 
adjacent an internal muscle of said subject and the 
second end remaining external thereof, said cathe- 
ter surrounding said first means with the tines adja- 
cent and directed toward the catheter first end, and 
said elongated flexible member, except for a por- 
tion thereof, extending beyond said catheter sec- 
ond end, at least portions of said tines being ex- 
tractable from said catheter first end for implanta- 
tion in said muscle by pushing on the portion of the 
flexible member extending beyond said catheter 
45 comprising: 
50  
55 
6 0  
65 


Catheter tip force transducer for cardiovascular research

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