Patent Description:
In recent years, catheter systems have been developed for interventional treatment of, for example, cardiac arrhythmias and refractory hypertension. For example, in the treatment of atrial fibrillation, one type of cardiac arrhythmia, an ablation or mapping catheter may be introduced into the heart via a vein or artery to find an aberrant electrical signal position or pathway by endocardial mapping, and then apply energy at the position or pathway to ablate it to eliminate or alter undesirable electrical signals, thus achieving curative results. Another example is the treatment of refractory hypertension through renal artery ablation, in which an ablation catheter may be arterially introduced into an artery connecting the abdominal aorta and the kidney to ablate and block the parasympathetic nerve pathway to lower the blood pressure.

For ablation therapy, how strongly an electrode disposed on a distal end of the used catheter contacts the target vessel wall or tissue is considered very important. Weak contact will lead to a superficial ablation lesion, and is thus incapable of allowing effective blockage of the aberrant electrical signals or nerve conduction. However, excessively strong contact may probably lead to perforation of the tissue, i.e., an increased safety risk. In order to avoid these issues, existing catheters of this type with force sensors at the distal end can effectively sense the contact strength between the electrode and the vessel wall or tissue. For instance, magnetic position sensors may be equipped in such a catheter to sense contact strength between the distal end thereof and the target organ. However, such sensors suffer from certain limitations in practice, such as tending to give distorted results due to interference from external magnetic fields and limiting other catheter functionalities such as three-dimensional magnetic positioning due to the use of magnetic fields. There are also catheter systems using force-sensitive materials as force sensors for sensing loads on the distal end. Although such systems are good at axial load measurement, they are lack of accuracy in non-axial load measurement. There are still other catheters employing fiber-optic systems for sensing contact forces with the vessel wall or organ, but they are difficult to package and make and expensive and require external electrical signal devices.

<FIG> schematically illustrates a conventional electrophysiology catheter, with a force sensor, passing through an intracardiac guide sheath. As shown in <FIG>, a guide sheath <NUM> establishes a channel through which an electrophysiology catheter with a force sensor <NUM> can be delivered into the body to perform an associated interventional procedure. The electrophysiology catheter may be an ablation catheter, a mapping catheter or another type of electrophysiology catheter.

The electrophysiology catheter includes a distal end at which the force sensor <NUM> is disposed. The force sensor <NUM> is configured to obtain the magnitude and direction of a contact force that occurs when the distal end of the catheter is brought into contact with the surface of a vessel wall or tissue. In other words, the force sensor <NUM> is configured to measure a reaction force in response to the contact force exerted by the catheter's distal end on the vessel wall or tissue.

In practice, in order to guide such electrophysiology catheters to various target sites, distinct guide sheaths <NUM> are designed with distal ends having different curved shapes. Additionally, such a guide sheath <NUM> should be constructed to be relatively stiff in order to maintain the designed curved shape while ensuring that a respective electrophysiology catheter can reach the target site. Consequently, as the electrophysiology catheter is guided through the guide sheath <NUM>, the force sensor <NUM> tends to experience a great deformation under the action of significant forces exerted by the guide sheath <NUM>.

This requires the force sensor <NUM> to be able to withstand large bending loads. Otherwise, when impacted by a large force, the force sensor <NUM> may break, leading to failure or a shortened service life of a strain gauge therein due to a load exceeding its measuring range.

As shown in <FIG>, the conventional force sensor <NUM> may include an elastic tube <NUM> having a wall in which one or more pierced transverse slots <NUM> (i.e., slots formed by cutting though the wall of the elastic tube <NUM>) are formed in order to enhance elasticity of the elastic tube <NUM> (especially a metal tube) and amplify any deformation thereof under the action of the transverse slots <NUM>. A strain gauge on the elastic tube <NUM> may then sense the amplified deformation and outputs an electrical signal indicating the change. Preferably, multiple such transverse slots <NUM> are formed along different circumferential circles and spaced from one another circumferentially in a staggered manner. That is, orthographic projections of these transverse slots <NUM> on a single plane are preferably distributed in a circumferentially staggered pattern.

Each transverse slot <NUM> is an arc-shaped slot cut along a circumference of the wall of the elastic tube <NUM> and provided at its both opposing ends each with a longitudinal slot <NUM> for mitigating stress concentration at the opposing ends of the transverse slot <NUM> and thus increasing its tensile strength.

However, as shown in <FIG>, when the elastic tube <NUM> is stretched, the transverse slot <NUM> will axially deform at its both axial sides away from the initial positions indicated by dashed lines in the figure, which will still cause the issue of "stress concentration" at the opposing ends. In particular, when the deformation exceeds a certain limit, the transverse slot <NUM> may crack, or even break, at the opposing ends, leading to permanent failure of the strain gauge due to the excessive strain load exceeding its maximum measuring range.

<CIT> discloses an electrophysiological catheter including distal end of catheter provided with pressure transducer including elastic body and foil gauge.

<CIT> discloses a heart valve delivery catheter including outer tube assembly and an inner tube component arranged in the outer tube assembly.

It is an objective of the present invention is to provide a force sensor and an electrophysiology catheter. The force sensor can be effectively avoided from experiencing any significant impact when the electrophysiology catheter is guided through a sheath. In this way, it is maintained within a predetermined deformation range that prevents breakage of an elastic tube of the sensor and enables an extended service life of any strain gauge therein.

To achieve the above objective, the present invention provides a force sensor as defined in claim <NUM>.

Preferably, the force sensor further comprises at least one second limiting structure disposed between the opposing ends of the transverse slot, each of the at least one second limiting structure comprising a third limiting portion connected to the first wall and a fourth limiting portion connected to the second wall, and
when the transverse slot deforms axially, the third limiting portion and fourth limiting portion are able to responsively move relative to each other until being engaged with each other.

Preferably, the third limiting portion is a male portion with a third external surface and the fourth limiting portion is a female portion with a fourth external surface, the third external surface and the forth external surface being arranged opposite to each other and defining a clearance between the third external surface and the forth external surface, and wherein the third limiting portion is confined within the fourth limiting portion.

Preferably, the first limiting portion, second limiting portion, third limiting portion and fourth limiting portion are of a same shape.

Preferably, the force sensor comprises a plurality of the first limiting structures, and wherein each of the at least one second limiting structure is disposed between adjacent two of the first limiting structures, the third limiting portion is a portion between adjacent two of the first limiting portions thereof and the fourth limiting portion is a gap between adjacent two of the second limiting portions.

Preferably, an external surface of the second limiting portion and an external surface of the third limiting portion are arranged axially opposite to each other and define a clearance between the external surface of the second limiting portion and the external surface of the third limiting portion.

Preferably, the second limiting portion comprises a second vertical portion and a second horizontal portion, and the third limiting portion comprises a third vertical portion and a third horizontal portion, the second vertical portion being connected to the second wall, the third vertical portion being connected to the first wall, the second and third horizontal portions together forming an engagement.

Preferably, the male portions are trapezoidal, L-shaped or T-shaped.

Preferably, the force sensor further comprises two longitudinal slots arranged at the respective opposing ends of the transverse slot.

Preferably, the transverse slot extends in a curved shape on a circumferential surface of the elastic tube.

Preferably, the transverse slot is formed in the elastic tube by laser cutting.

Preferably, the force sensor comprises a plurality of the transverse slots and a plurality of the strain gauges, the transverse slots spaced apart from one another across the elastic tube in an axial direction of the elastic tube and staggered from one another along a circumferential direction of the elastic tube, each of the strain gauges disposed between two opposing ends of a respective one of the transverse slots.

According to the present invention, the force sensor includes an elastic tube and a strain gauge arranged on the elastic tube. A pierced transverse slot is formed in the elastic tube, and at least one first limiting structure is disposed between two opposing ends of the transverse slot. Each first limiting structure includes a first limiting portion connected to a wall of the transverse slot and a second limiting portion connected to the other wall of the transverse slot. In the event of an axial deformation occurring to the transverse slot, the first and second limiting portions will simultaneously move relative to each other. In particular, when the axial deformation reaches a certain level, the two limiting portions will engage with each other. As a result, the transverse slot is maintained within a predetermined deformation range that can avoid breakage of the elastic tube and result in a prolonged service life of the strain gauge.

Specific embodiments of the proposed force sensor and electrophysiology catheter will be described in greater detail with reference to the accompanying drawings so that the present invention will become more apparent and readily understood.

Additionally, while the present invention is described in detail with reference to the annexed schematic figures, these figures are presented only for the purpose of facilitating the detailed description of the examples rather than limiting the invention in any sense.

As used herein, the terms "proximal" and "distal" describe relative orientations, positions and directions between elements or actions, viewed by a physician operating the product. Without wishing to be limiting, a "proximal end" usually refers to an end of the product close to the physician during normal operation, while a "distal end" usually refers to an end thereof that enters the patient first. "Axial" and "longitudinal" refer to an axial direction of an elastic tube, while "circumferential" and "transverse" refer to a circumferential direction thereof.

As used in the specification, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. As used in the specification, the term "or" is generally employed in the sense including "and/or" unless the context clearly dictates otherwise.

According to the present invention, in order to enhance breakage resistance of the elastic tube, each transverse slot <NUM> is maintained within a predetermined deformation range that ensures that the elastic tube <NUM> will not break. To this end, at least one first limiting structure is added between opposing ends of each transverse slot <NUM>.

In response to an axial deformation of the transverse slot <NUM>, a relative movement will occur in the at least one first limiting structure, and when reaching a limit position, an engagement will occur, defining a maximum deformation amount of the transverse slot <NUM>. In this way, any significant impact can be effectively avoided when the electrophysiology catheter is guided through a sheath, and the elastic tube <NUM> can be maintained within a predetermined deformation range that prevents breakage of the elastic tube and enables an extended service life of a strain gauge. Generally, such a strain gauge provides a strain measurement range of ±<NUM>,<NUM> microstrains. Accordingly, the at least one first limiting structure is generally configured to limit the maximum deformation amount to be not over <NUM>,<NUM> microstrains.

According to the present invention, each first limiting structure may include a first limiting portion and a second limiting portion. The first limiting portion is connected to a first wall of the transverse slot <NUM>. Upon any axial deformation of the first wall, the first limiting portion will experience a synchronous axial displacement. Additionally, the second limiting portion is connected to a second wall of the transverse slot <NUM>. Similarly, when the second wall deforms axially, a synchronous axial displacement will responsively occur to the second limiting portion. The first wall opposes the second wall along a widthwise direction of the transverse slot <NUM>.

Thus, when the elastic tube <NUM> is stressed and stretched by a force, both the first and second walls will deform accordingly, driving the first and second limiting portions to move relative to (i.e., toward or away from) each other. When the axial load is below a predefined threshold (e.g., <NUM>), the relative movement of the first and second limiting portions will be accommodated in a preset clearance without resulting in a contact therebetween. However, when the axial load exceeds the predefined threshold, the first and second limiting portions will move toward or away from each other until the limit position is reached, where they cooperate to form a snap-fit engagement that prevents any of them from further moving. At this point, the transverse slot <NUM> deforms by a maximum allowable amount under the action of the snap-fit engagement of the first and second limiting portions.

Obviously, in order to control the maximum deformation amount of the transverse slot <NUM>, an axial clearance between the first and second limiting portions is necessary for allowing an axial relative movement between the two limiting portions while ensuring a space for compressive or tensile deformation of the elastic tube <NUM>. Therefore, the maximum deformation amount can be controlled, in general terms, below <NUM>,<NUM> microstrains by suitably setting a dimension of the clearance.

Various examples of the limiting structure according to embodiments of the present invention will be described in greater detail below with reference to <FIG>, but the present invention is not limited to these listed examples.

As shown in <FIG> and <FIG>, in a first embodiment, a transverse slot <NUM> formed in an elastic tube <NUM> has a first wall <NUM> and a second wall <NUM>, arranged along a widthwise direction of the slot. The widthwise direction is defined as an axial direction when a center axis of the transverse slot coincides with a center axis of the elastic tube. A first limiting portion <NUM> is arranged on the first wall <NUM>, while a second limiting portion <NUM> is arranged on the second wall <NUM>. The first and second limiting portions <NUM>, <NUM> are both L-shaped portions that match each other in shape. Specifically, the first limiting portion <NUM> is a female L-shaped portion with a first internal surface, while the second limiting portion <NUM> is a male L-shaped portion with a second external surface. When the elastic tube <NUM> is not stressed, the first internal surface and the second external surface oppose each other with a clearance therebetween. In this way, when the elastic tube <NUM> experiences a force, the second limiting portion <NUM> is able to move with the transverse slot <NUM> relative to (i.e., to approach or get away from) the first limiting portion <NUM> while being always confined within the first limiting portion <NUM> without dislodging therefrom.

As shown in <FIG> and <FIG>, in a second embodiment, a transverse slot <NUM> formed in an elastic tube <NUM> also has a first wall <NUM> and a second wall <NUM>. A first limiting portion <NUM> is arranged on the first wall <NUM>, while a second limiting portion <NUM> is arranged on the second wall <NUM>. In this embodiment, the first limiting portion <NUM> is a trapezoidal male portion, while the second limiting portion <NUM> is a trapezoidal female portion. Following the same principles, when the elastic tube <NUM> is stressed and stretched (as shown in <FIG>), the trapezoidal male and female portions will move away from each other until a limit position is reached where a maximum cross-sectional width of the trapezoidal male portion is greater than a minimum cross-sectional width of the trapezoidal female portion (i.e., an opening width), bringing an external surface of the trapezoidal male portion into abutment with an internal surface of the trapezoidal female portion and thus resulting in a snap fit engagement therebetween.

As shown in <FIG>, in an example not belonging to the invention, a transverse slot <NUM> formed in an elastic tube <NUM> also has a first wall <NUM> and a second wall <NUM>. A first limiting portion <NUM> is arranged on the first wall <NUM>, while a second limiting portion <NUM> is arranged on the second wall <NUM>. In this embodiment, the first limiting portion <NUM> is a major arc-shaped female portion, while the second limiting portion <NUM> is a major arc-shaped male portion. Following the same principles, when the elastic tube <NUM> is stressed and stretched (as shown in <FIG>), the major arc-shaped male and female portions will move away from each other until a limit position is reached where an external surface of the major arc-shaped male portion is brought into close abutment with an internal surface of the major arc-shaped female portion, resulting in a snap fit engagement therebetween, because the major arc-shaped male portion has at least one portion having a cross-sectional width that is greater than an opening width of the major arc-shaped female portion.

<FIG> shows another example not belonging to the invention that is similar to the one previously introduced, except that a plurality of first limiting structures are arranged on opposing ends of a transverse slot <NUM> and spaced apart from one another. For the sake of brevity, similarities between the two embodiments will not be described herein. The arrangement of the plurality of first limiting structures imparts increased impact resistance and reliability to the elastic tube <NUM>. Even when any of the first limiting structures fails, the remaining one(s) can still provide a limiting effect. In addition, the elastic tube <NUM> also obtains improved toughness and enhanced sensing ability.

The present invention further provides a fifth embodiment, The fifth embodiment is similar to the first embodiment except that, between adjacent two first limiting structures, a second limiting structure is arranged, which includes a third limiting portion <NUM> connected to the first wall <NUM> of the transverse slot <NUM> and a fourth limiting portion <NUM> connected to the second wall <NUM> of the transverse slot <NUM>. For the sake of brevity, similarities between the two embodiments will not be described herein. In response to an axial deformation of the transverse slot <NUM>, the third and fourth limiting portions <NUM>, <NUM> can move relative to each other until they are engaged with each other.

As shown in <FIG>, the third limiting portion <NUM> is a male portion with a third external surface, while the fourth limiting portion <NUM> is a female portion with a fourth internal surface that opposes the third internal surface with a clearance therebetween. Additionally, the third limiting portion <NUM> is confined within the fourth limiting portion <NUM>. In this embodiment, the first limiting portion <NUM>, second limiting portion <NUM>, third limiting portion <NUM> and fourth limiting portions <NUM> are in the same shape. In fact, the third limiting portion <NUM> is composed of a portion between the adjacent two first limiting portions <NUM>, while the fourth limiting portion <NUM> is composed of a gap between the adjacent two second limiting portions <NUM>.

More specifically, as shown in <FIG> and <FIG>, each second limiting portion <NUM> has a second vertical portion and a second horizontal portion, and the third limiting portion <NUM> has a third vertical portion and a third horizontal portion. The second vertical portion is connected to the second wall <NUM>, while the third vertical portion is connected to the first wall <NUM>. The second horizontal portion axially opposes the third horizontal portion, thus forming a snap mechanism. Here, mutually-facing surfaces of the second and third horizontal portions are referred to as their "internal surfaces", and the respective opposite surfaces as their "external surfaces". Initially, there is a clearance between the internal surfaces of the two horizontal portions (as shown in <FIG>), which allows a relative movement (generally, an approaching movement) of the two limiting portions. As an associated deformation increases, the horizontal portions of the two limiting portions will be finally engaged with each other (as shown in <FIG>). That is, the internal surfaces of the two horizontal portions are brought into engagement with each other, which prevents the two horizontal portions from further moving toward each other anymore. In other words, after an approaching movement is made from the positions shown in <FIG>, the horizontal portions of the two limiting portions <NUM>, <NUM> reach a limit position, where their internal surfaces abut against each other, thus defining a maximum deformation limit of the transverse slot <NUM>. In other embodiments, the horizontal portions of the two limiting portions <NUM>, <NUM> may also move away from each other from the positions as shown in <FIG> until the external surface of the second horizontal portion in the second limiting portion <NUM> abuts against the internal surface of the first limiting portion <NUM> (as shown in <FIG>) so that their further relative movement is again disallowed.

<FIG> shows a sixth embodiment that is similar to the fifth embodiment except that the first limiting portion <NUM>, second limiting portion <NUM>, third limiting portion <NUM> and fourth limiting portion <NUM> are all trapezoidal. For the sake of brevity, similarities between the two embodiments will not be described herein. In case of the first limiting portion <NUM>, second limiting portion <NUM>, third limiting portion <NUM> and fourth limiting portion <NUM> being of the same shape, the two male limiting structures will be identically strong, preventing either of them from earlier breakage due to lower strength. In addition, the identical shape allows a maximized contact area between them, preventing the occurrence of insufficient contact therebetween. Further, relatively speaking, the plurality of L-shaped limiting structures can provide a more secure engagement than those of other shapes such as the trapezoidal or major arc shape.

Experimental results demonstrate that, a conventional transverse slot <NUM> without any limiting structure arranged between its opposing ends can withstand a maximum bending load of <NUM> and the elastic tube <NUM> will break upon any increase in the load, as indicated by the curve s2 in <FIG>. In spite of this, when advanced through a guide sheath <NUM>, it is very likely for a force sensor <NUM> to experience a load of <NUM> or greater when the advancement is too fast or an inappropriate driving force is applied. By contrast, a maximum bending load that a transverse slot <NUM> adopting the structure of <FIG> and <FIG> can withstand is greater than <NUM>, as indicated by the curve s1 in <FIG>, undoubtedly meeting the practical requirements. <FIG> is a diagram schematically illustrating a bending load-bearing performance comparison between the elastic tubes respectively adopting the conventional transverse slot and the modified transverse slot of <FIG>, in which the horizontal axis represents the bending displacement (measured in mm) and in which the vertical axis represents the bending load (measured in gram).

In any of the above embodiments, the transverse slot <NUM> may extend in a curved shape on the circumferential surface of the elastic tube <NUM>. That is, the transverse slot <NUM> appears curved in a front view of the elastic tube <NUM>, and arc-shaped in a top view of the elastic tube <NUM>. Preferably, the transverse slot is formed in the elastic tube <NUM> by a laser cutting. The force sensor <NUM> further includes strain gauge(s) arranged on the outer wall of the elastic tube <NUM>. The number of the strain gauge(s) corresponds to the number of the transverse slot(s). Each strain gauge may be provided on either a pierced or non-pierced section of the elastic tube <NUM>. Here, the term "pierced section" refers to a portion encompassing one of the transverse slot(s) (i.e., the strain gauge can cover the transverse slot <NUM>), whereas the term "non-pierced section" refers to a portion of the elastic tube <NUM> that is not pierced. Preferably, each strain gauge is arranged on a non-pierced section of the elastic tube <NUM>. More preferably, a plurality of the transverse slots <NUM> are axially spaced apart from one another across the elastic tube <NUM> and staggered from one another along the circumferential direction thereof, with each strain gauge preferably disposed between opposing ends of the respective transverse slot.

At last, while a few preferred embodiments of the present invention have been described above, the present invention is not limited to the scope of these disclosed embodiments. For example, in case of a plurality of limiting structures being provided, all of them may have the same structure, or one or more of them may have a different structure.

Claim 1:
A force sensor (<NUM>), comprising an elastic tube (<NUM>) and a strain gauge arranged on the elastic tube (<NUM>), wherein:
the force sensor (<NUM>) further comprises a pierced transverse slot (<NUM>) formed in the elastic tube (<NUM>), the transverse slot (<NUM>) having a first wall (<NUM>) and a second wall (<NUM>);
the force sensor (<NUM>) characterised in that it further comprises at least one first limiting structure disposed between two opposing ends of the transverse slot (<NUM>), each of the at least first limiting structure comprising a first limiting portion (<NUM>) and a second limiting portion (<NUM>), the first limiting portion (<NUM>) being connected to the first wall (<NUM>), the second limiting portion (<NUM>) being connected to the second wall (<NUM>); the first limiting portion (<NUM>) is a female portion with a first internal surface and the second limiting portion (<NUM>) is a male portion with a second external surface, the first internal surface and the second external surface being arranged opposite to each other and defining a clearance between the first internal surface and the second external surface, and wherein the second limiting portion (<NUM>) is confined within the first limiting portion (<NUM>); and
when the elastic tube is stretched by a force and the transverse slot (<NUM>) deforms in an axial direction of the elastic tube (<NUM>), the first limiting portion (<NUM>) and the second limiting portion (<NUM>) are able to responsively move away from each other in the axial direction until being engaged with each other;
wherein the first limiting portion (<NUM>) and second limiting portion (<NUM>) are both L-shaped portions that match each other in shape; or the first limiting portion (<NUM>) is a trapezoidal male portion, and the second limiting portion (<NUM>) is a trapezoidal female portion.