U.S. patent number 3,893,451 [Application Number 05/405,049] was granted by the patent office on 1975-07-08 for pressure transmission device.
Invention is credited to Herve Durand, Theo Grandjean.
United States Patent |
3,893,451 |
Durand , et al. |
July 8, 1975 |
Pressure transmission device
Abstract
Pressure transmission tube for medical or veterinary use,
adapted to be filled with a liquid substance constituting the
pressure transmission medium. Said tube comprises along at least
one portion of its length a section having a smaller inner diameter
differing from the inner diameter prevailing along the remaining
section of its length, which ranges from 0.5 to 2.5 mm, the section
of smaller diameter corresponding to a reduction in diameter of the
order of 10 to 85 percent.
Inventors: |
Durand; Herve (95600 Eaubonne,
FR), Grandjean; Theo (1011 Lausanne, CH) |
Family
ID: |
9105489 |
Appl.
No.: |
05/405,049 |
Filed: |
October 10, 1973 |
Foreign Application Priority Data
|
|
|
|
|
Oct 11, 1972 [FR] |
|
|
72.36033 |
|
Current U.S.
Class: |
600/486;
138/44 |
Current CPC
Class: |
A61B
5/0215 (20130101) |
Current International
Class: |
A61B
5/0215 (20060101); A61B 005/02 () |
Field of
Search: |
;128/2,2R,2.5D,2.5G,2.5R,2.5Q ;73/392,395,420 ;138/44 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Howell; Kyle L.
Attorney, Agent or Firm: Striker; Michael S.
Claims
What we claim is:
1. In a device for use in measuring blood characteristics,
particularly blood pressure or the like, having a catheter tube for
insertion into the blood stream of a body and a transducer
apparatus for picking up and converting pressure variations into
proportional electrical voltage variations susceptible of
measurement, a combination comprising a pressure transmission tube
having two spaced end portions and adapted to be filled with a
substantially immobile liquid pressure transmission medium, said
end portions respectively communicating with said catheter tube and
said transducer, and said pressure transmission tube defining an
internal passage free of turbulence-producing projections and
composed of at least two communicating main sections, one of said
main sections having a constant inner diameter of between 0.5 and
2.5 mm and having a first self-resonant frequency, and the other of
said main sections having a second self-resonant frequency and
being of narrower diameter than said one main section and having a
constant inner diameter of between 10 through 85 percent of said
inner diameter of said one main section, whereby the self-resonant
frequencies of said catheter tube and said pressure transmission
tube are shifted away from the frequencies of the pressure
variation signals to be measured so as to provide error-free
measurement of the latter; and joining means forming a continuous
internal channel located intermediate said sections of said
pressure transmission tube and communicating with said internal
passage so as to accommodate said liquid medium therein in a
non-turbulent manner.
2. A device as defined in claim 1, wherein said one main section is
composed of at least two spaced portions and the other of said main
sections is located intermediate said two portions.
3. A device as defined in claim 2, wherein the other of said main
sections is the first third of the total length of said
pressure-transmission tube as measured from that one of said spaced
end portions which communicates with said catheter.
4. A device as defined in claim 1; and further comprising
constriction means for contricting said pressure-transmission tube,
said constriction means being a tubular sleeve located externally
of said pressure-transmission tube and surrounding the same, said
sleeve being of a shrinkable material and being shrunk to said
tube, so as to thereby constrict the latter to attain said inner
diameter of the other of said main sections.
5. A device as defined in claim 1, wherein the other of said main
sections adjoins said one main section.
6. A device as defined in claim 5, wherein the other of said main
sections has a length which is less than three-fourth of the total
length of said pressure-transmission tube.
7. A device as defined in claim 5, wherein the other of said main
sections has a length which is equal to three-fourths of the total
length of said pressure-transmission tube.
8. A device as defined in claim 5, wherein the length of each of
said main sections is between 30 cm and 150 cm; and wherein said
inner diameter of one of said main sections is between 1.0 and 1.5
mm., and said inner diameter of the other of said main sections is
between 0.3 and 0.8 mm.
9. A device as defined in claim 1; and further comprising support
means for supporting said joining means.
10. A device as defined in claim 9, wherein said internal channel
of said joining means evolutively communicates with said main
sections of said pressure transmission tube.
11. A device as defined in claim 1; and further comprising
connector means located at each of said spaced end portions for
respectively connecting said pressure-transmission tube to said
catheter and said transducer.
Description
The present invention relates to a pressure transmission tube for
medical or veterinary purposes, and also to all apparatus or
instruments provided with such a tube.
The assessment of cardiovascular diseases relies more and more on
intra-vascular, intra-cardiac, rachidial, renal and similar
pressure measurements, apart from the usual clinical clues and the
results of different analyses.
The blood pressure measurement method generally used consists in
introducing a catheter into the cavity to be studied, the lumen of
the catheter being previously filled with an isotonic solution: all
variations in pressure, occuring at the catheter tip are completely
transmitted by the incompressible liquid column filling the
catheter lumen. Therefore, the measurement or the recording of the
pressure variations transmitted to the external end of the catheter
lumen will disclose the pressures occurring in the cavity under
investigation. This is usually achieved by means of a so-called
pressure transducer (of the Statham or another type), which
provides an electric voltage proportional to the pressure
variation.
However, it was found fortuitously that when two catheters of
different diameters are introduced simultaneously into the same
cavity, the pressure curves recorded through each of them, may
differ significantly one from the other. In addition, the necessity
of transmitting the pressure signals obtained by means of the
catheter to a more or less distant electronic device led to
interpose a pressure transmission tube between the catheter
terminal and the pressure transducer. It was then observed that the
distortions in the pressure signals was changed but did not
subside.
A careful study of the phenomena led to the following conclusions:
like any solid, fluid, or gazeous body, a catheter designed for
transmitting pressure variations as well as the column of liquid
filling same has its own resonance. This resonance arises whenever
the hydraulic system, extending from the catheter lumen extremity
to the transducer membrane, is stressed anywhere by a mechanical
impulse or a pressure change. If no appropriate damping device is
provided the pressure variations to be measured during their
transmission to the transducer undergo significant distortions
caused by the self-resonance phenomena occurring in the catheter
and the pressure transmission tube. The self-resonance frequency of
the most usual catheter lies between 15 and 60 Hz. If the frequency
of the pressure signals to be measured nears these resonance
frequencies, these signals, during their transmission, will undergo
an erroneous amplification which may even exceed 400 percent. Even
with pressure signal of much lower frequencies, like those
occurring in the cardio-vascular system, an erroneous amplification
of course less significant, is still observed, but this constitute
a cause of measurement errors far from negligible and impossible to
estimate because appropriate calibration means are not
available.
However, in the case of a cardiac catheterization, the mechanical
impulses imposed to the catheter by the heat and its values, give
rise to hydro-mechanical artefacts, often of high amplitude, which
interfere with the pressure curves.
The pressure curves which can be recorded during a
cardiac-catheterization are necessarily altered by the
hydromechanical parasites as well as by the distortion which tends
to widen erroneously the systolic pressure pulses.
It is the primary object of the present invention to avoid the
inconveniences set forth hereinabove by providing an improved
pressure transmission tube easy to use and manufacture, which is to
be inserted between the catheter and the transducer.
This pressure transmission tube is characterized in that it
comprises along at least one fraction of its length a section
having a smaller inner diameter differring from the inner diameter
prevailing along the remaining section of its length, which ranges
from 0.5 to 2.5 mm, the section of smaller diameter corresponding
to a reduction in diameter of the order of 10 to 85 percent.
Since its inner diameter is not uniform from end to end and
comprises at least one dimensional variation, the tube of this
invention has no inherent resonance and is therefore capable of
efficiently filtering the pressure signals to be recorded while
eliminating the greater part of the distortions to which these
signals are exposed during their transmission. In fact, it is known
that the flow of liquids, the propagation of a pressure and the
production of resonance waves in tubes of relatively small diameter
constitute complex phenomena according inter alia to the laws of
Reynolds and Hagen-Poiseuille; therefore, the resonance or damping
frequencies depend on the tube length and more particularly on the
fourth power of the inner diameter of this tube. The
characteristics of the catheter selected by a practicioner for a
given investigation cannot be modified; therefore, the resonance
frequencies should be eliminated in the pressure transmission tube
by resorting to a sequence of pipe sections having mutually shifted
resonance frequencies.
According to a first form of embodiment of the pressure
transmission tube of this invention the tube has an inner diameter
of constant value, except in a section of smaller inner diameter
which consists of a neck having a relatively reduced length, within
the range of 5 to 50mm, this neck being positioned in the first
third of the total length of the pipe system, adjacent the end
connected to the member or apparatus for detecting the pressure to
be transmitted, for example a catheter.
In a modified form of embodiment the pressure transmission tube of
this invention comprises the end to end assembly of at least two
separate tube or pipe sections having inner diameters of different
values, one section having an inner diameter within the range of
0.5 to 2.5 mm, the other section having a small inner diameter, the
reduction in diameter corresponding to 10 to 85 percent of the
inner diameter of said one section. Besides, the length of the pipe
having the smaller inner diameter is equal to or less than the
three-fourths of the total length of the tube assembly.
The attached drawing illustrates by way of example typical
embodiments of the device of this invention. In the drawings:
FIG. 1 is a side elevational view of a first embodiment of a
pressure transmission tube according to this invention;
FIG. 2 is a fragmentary axial section of this tube;
FIG. 3 is a cross-section taken along the line III--III of FIG.
2;
FIG. 4 is a side elevational view of another embodiment wherein the
tube consists of a pair of pipe sections of different diameter,
disposed end to end;
FIG. 5 is a fragmentary axial section of this tube, and
FIG. 6 is a cross-section taken along the line VI--VI of FIG.
5.
In the example illustrated in FIGS. 1-3 of the drawing the pressure
transmission tube according to this invention comprises a single
tube section 1 of a length of 50 to 300 cm. The inner diameter of
this tube is within the range of 0.5 to 2.5 mm.
Advantageously, this tube consists of plastic material such as
polyethylene, polyamide, P.V.C., E.V.A., etc. At one end, this tube
carries a connector 2 for connecting the tube to a catheter adapted
to be introduced into cavities of a patient or an animal for
measuring pressures therein. At its opposite end this tube
comprises another connector for connecting the tube to a transducer
or a measuring instrument.
According to this invention, this tube comprises a neck or
constricted portion 3 where at its inner diameter is reduced by
about 10 to about 85 percent. If for instance the inner diameter of
the tube is 1.5 mm, the inner diameter at this neck portion is
reduced to 0.6 mm/. The length of this neck portion is extremely
small and lies within the range of 5 mm to 50 mm. It will be noted
that this neck portion is located in the first third of the length
of tube 1, adjacent the connector 2 for connecting same to a
catheter.
As illustrating in FIGS. 2 and 3, the neck portion 3 may
advantageously be obtained by fitting an external tubular insert 4
to the tube 1 and shrinking this insert by means of a suitable
shrinking machine. This tubular insert 4 may consist of stainless
steel, copper or aluminium.
In the form of embodiment illustrated in FIGS. 4-6 the pressure
transmission tube of this invention consists of a pair of pipe
sections having different inner diameters, which are assembled to
each other at one end, i.e. a first section 1a having an inner
diameter within the range of 0.5 to 2.5 mm and a second section 1b
having an inner diameter reduced by 10 to 85 percent with respect
to the inner diameter of said first section 1a. At this end
opposite to the second tube section 1b the first tube section 1a
carries a connector 2 for connecting the tube to a catheter. On the
other hand, the free end of the second tube section 1b carries
another connector for connecting the assembly to a transducer or
other measuring instrument. Possibly, the first section 1a may
comprise a neck 3a similar to the neck 3 of the first embodiment
shown in FIGS. 1-3.
The two tube sections 1a and 1b are assembled by means of a
connector shown generally at 5.
This connector 5 comprises a metal tube 6 having an evolutive inner
diameter corresponding exactly on the one hand to the inner
diameter of tube section 1a and on the other hand to the inner
diameter of tube section 1b, for it is essential in devices of this
character to avoid any unevennesses likely to retain air bubbles,
how small they are. This tube 6, like tube 4, may consist of
stainless steel, aluminium or other suitable material. Finally, the
reference numeral 8 designates a socket obtained by moulding a
suitable elastomer over the ends of tubes 1a and 1b, on the one
hand, and connecting tube 6, the function of this socket 6
consisting simply of reinforcing this joint between tube sections
1a and 1b of the pressure transmission tube and thus prevent any
accidental rupture at this location.
First Application
The problem consisted in making a 130 cm long pressure transmission
tube to be connected to a conventional catheter, a socalled
"Cournand's catheter" No. 5, F-SW, having a length of 125 cm and an
inner diameter of 0.66 mm. The pressure transmission tube having
equal resonance frequencies, has been obtained by joining end to
end, a first 100 cm long tube, having an inner diameter of 0.5 mm,
with a second 30 cm long tube, having an inner diameter of 1.2 mm.
These tube sections are connected as shown at 5, FIG. 5. However,
it is not deemed necessary to describe in detail the connectors
fitted to the ends of the connecting tube, since they are
manufactured by conventional methods well known to all catheter
manufacturers.
Second application
The problem consisted in making a 150 cm long pressure transmission
tube, to be connected to a 125 cm long catheter "Flexo-Pulmocath"
No. 13, having an inner diameter of 0.90 mm. The pressure
transmission tube was according to the invention, comprised of two
polyamide tube sections joined end to end: the first section was
100 cm long and had an inner diameter of 0.5 mm; the second section
was 50 cm long, and had an inner diameter of 1.3 mm.
Third application
The problem consisted in making a 180 cm long pressure transmission
tube, to be connected to a 125 cm long catheter "Flexo-Pulmocath
No. 13, having an inner diameter of 0.90 mm.
The pressure transmission tube according to the invention consisted
of two tube sections joined end to end: the first section was 90 cm
long and had an inner diameter of 0.5 mm, the second section was 90
cm long and had an inner diameter of 1.2 mm.
In actual practice, with due regard for the resonance frequencies
of the catheter in general use having an inner diameters of 0.5 to
2.0 mm, the tubes or tube sections constituting the pressure
transmission tube according to the invention may have an inner
diameter from 0.5 to 2.0 mm; however the inner diameters and
lengths of these tube sections must be selected as a function of
the catheters to be equipped with due consideration for the above
mentioned laws.
The device according to this invention, can be used whenever it is
contemplated, to observe or record a pressure existing in a cavity,
for instance, the blood-pressure, the intra-cardiac pressure, the
intra-vascular pressure, the intra-cerebral pressure, the renal
pressure, the amniotic cavity pressure, the intra-rachidial
pressure, the peritioneal cavity pressure, etc. This device can be
used in the medical and the verterinary arts, as well as in all
laboratories, for any kind of researches.
However, its specific application consists in recording the
intra-vascular and the intra-cardiac blood pressure. Of course, the
present invention also included all pressure transmission tubes,
also referred to as connecting tubes, having different inner
diameters, having or not constricted or widened sections which,
when joined end to end, permit of obtaining a composite tube having
a non-uniform inner diameter.
The present invention may also include pressure transmission tubes
made of tube sections of which the cross-sectional contour is not a
circle but any other configuration.
The present invention may also include a pressure transmission
tube, made from a tubular element having a variable or evolutive
inner diameter; this result can be obtained, during the actual
manufacture, by using an extruder having movable punch and die
members.
* * * * *