AUTOMATIC TOURNIQUET FOR EMERGENCY OR SURGERY

Abstract

An inflatable tourniquet system for arterial blood occlusion of a leg or arm, e.g. after injury or for surgery. A tourniquet (TQ) is to be manually fastened around the limb by a user, e.g. a first aid helper, e.g. an untrained person. A manual inflator (B) is used to inflatable the tourniquet to apply pressure for occlusion of arterial blood flow to the limb. An electric circuit (CC) measures an electrical input from a length sensor (C), e.g. an electric conductor, and to determine a value (R), e.g. electric resistance, indicative of circumference of the limb accordingly, when the tourniquet has been fastened around the limb. A blood pressure measuring circuit (BP) automatically determines a systolic blood pressure (SBP) in response to input from a pressure sensor (PS) arranged to measure a pressure (PR) of the tourniquet. A processor (P) is programmed to operate according to a control algorithm which calculates a target pressure (AOP, OAOP) in response to the measured SBP, and the value (R) indicative of circumference of the limb. Then, the processor monitors input from the pressure sensor (PS) and compares the sensed pressure with the calculated target pressure (AOP, OAOP). Visual and/or audible feedback (FB) is give to the user, when the pressure (PR) of the tourniquet (TQ) is within an interval of the target pressure (AOP, OAOP). In some embodiments, the manual inflator (B) process may be used to provide energy harvesting for electric powering the system.

Claims

1. An inflatable tourniquet system for arterial blood occlusion of a limb, the system comprising a tourniquet (TQ) arranged to be manually fastened around a limb by a user, a manual inflator (B) connected to an inflatable chamber (CH) of the tourniquet (TQ), so as to allow application of a pressure for occlusion of arterial blood flow to the limb, upon inflation of the inflatable chamber (CH) by manually operating the manual inflator (B), a length sensor (C), an electric circuit (CC) arranged to measure an electrical input from a length sensor (C) and to determine a value (R) indicative of circumference of the limb accordingly, when the tourniquet (TQ) has been fastened around the limb, a pressure sensor (PS) arranged to measure a pressure (PR) of the inflatable chamber (CH), a blood pressure measuring circuit (BP) arranged to automatically determine a measure of a systolic blood pressure (SBP) in response to input from a pressure sensor (PS), a feedback device (FBD) arranged to provide a feedback (DB) to the user, and a processor (P) arranged for connection to the blood pressure measuring circuit (BP), the pressure sensor (PS), said electric circuit (CC), and the feedback device (FBD), wherein the processor (P) is programmed to operate according to a control algorithm being arranged: to calculate a target pressure (AOP, OAOP) in response to the measured SBP, and said value (R) indicative of circumference of the limb, to monitor input from the pressure sensor (PS) and comparing a sensed pressure (PR) by the pressure sensor (PS) with the calculated target pressure (AOP, OAOP), and to control the feedback device (FBD) to provide feedback (FB) to the user, when input (PR) from the pressure sensor (PS) indicates that pressure (PR) of the inflatable chamber (CH) is within an interval of the target pressure.

2. The inflatable tourniquet system according to claim 1, wherein the processor (P) is arranged to calculate the target pressure (AOP, OAOP) as a sum of a first value representing the measure of systolic blood pressure using (SBP) and a second value calculated in response to said value (R) indicative of circumference of the limb.

3. The inflatable tourniquet system according to claim 1, wherein the feedback device (FBD) comprises at least one of: a visual indicator, and an audible indicator.

4. The inflatable tourniquet system according to claim 1, wherein the processor (P) calculates a target pressure interval in response to the calculated target pressure.

5. The inflatable tourniquet system according to claim 4, wherein the processor (P) is arranged to control the feedback device (FBD) to provide at least three different feedbacks (FB) to the user in response to input from the pressure sensor (PS), so as to indicate whether the pressure (PR) is: below, within, or above the calculated target pressure interval, respectively.

6. The inflatable tourniquet system according to claim 1, comprising an electric conductor (C) arranged in the tourniquet (TQ), so as to allow measurement of an electrical resistance (R) of a part of the electric conductor (C) corresponding to a circumference of the limb, when the tourniquet (TQ) has been fastened around the limb, wherein the electric conductor (C) is connected to an electric circuit (CC) arranged to generate a measure of said electrical resistance (R) of said part of the electric conductor (C) corresponding to the circumference of the limb.

7. The inflatable tourniquet system according to claim 6, wherein the electrical conductor (C) is mounted in a lining or sleeve of the tourniquet (TQ).

8. The inflatable tourniquet system according to claim 1, wherein calculation of the target pressure (AOP, OAOP) involves calculating a value indicative of a tissue padding coefficient of the limb in response to the value (R) indicative of circumference of the limb, and a value from a prestored table.

9. The inflatable tourniquet system according to claim 1, wherein the manual inflator (B) comprises a bulb inflator (B) arranged for being squeezed by the user in order to inflate the inflatable chamber (CH).

10. The inflatable tourniquet system according to claim 1, comprising a clock arranged to determine a time of application of the tourniquet (TQ) on the limb, and wherein the system is arranged to provide a feedback in response to said time of application of the tourniquet (TQ).

11. The inflatable tourniquet system according to claim 1, comprising an electric energy harvesting device arranged to generate electric energy to power at least the processor (P) in response to manual operation of the manual inflator (B).

12. The inflatable tourniquet system according to claim 11, comprising an electric energy storage element arranged to store electric energy generated by the electric energy harvesting device.

13. The inflatable tourniquet system according to claim 1, wherein the processor (P) is arranged inside a casing attached to a part of the tourniquet (TQ).

14. A method for determining feedback to a user of an inflatable tourniquet for arterial blood pressure occlusion of a limb, the method comprising receiving (R_R) a value indicative of a circumference of the limb (R), receiving (R_SBP) a value indicative of systolic blood pressure (SBP) determined in response to a pressure measured in an inflatable chamber of the inflatable tourniquet, calculating (C_TPR) a target pressure in response to the value indicative of systolic blood pressure (SBP), and the value indicative of a circumference of the limb (R), monitoring (MN_PR) pressure of the inflatable chamber and comparing the pressure of the inflatable chamber of the tourniquet with the calculated target pressure, and providing (P_FB) feedback to the user, indicating that the pressure of the inflatable chamber has reached the calculated target pressure.

15. A computer program product comprising computer readable program code which, when executed on a processor, causes the processor (P) to perform the method according to claim 14.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

[0049] FIG. 1 illustrates a sketch of elements of an inflatable tourniquet system, and

[0050] FIG. 2 illustrates steps of a method embodiment.

DESCRIPTION OF EMBODIMENTS

[0051] FIG. 1 shows an inflatable tourniquet system embodiment. The system is suitable for arterial blood occlusion of a limb, and it is suitable in emergency situations where even untrained users can operate the system, e.g. to provide a fast helping action to stop a bleeding from an injured limb.

[0052] The system has a tourniquet TQ arranged to be manually fastened around a limb by a user. The tourniquet TQ has a built in inflatable chamber CH in connection with a manual inflator B, e.g. a squeezable bulb, so as to allow application of a pressure for occlusion of arterial blood flow to the limb, upon inflation of the inflatable chamber by manually operating the manual inflator B. The inflatable tourniquet TQ may be similar to those known in the art with respect to its structure, size and closing mechanism etc. However, the tourniquet TQ has an electric conductor C arranged in or on its structure, which allows measurement of an electrical resistance R of a part of the electric conductor C corresponding to a circumference of a limb, when the tourniquet TQ has been fastened around the limb. The electric conductor C may be formed by e.g. copper, aluminium, steel, or other conducting material with known resistivity, preferably the electric conductor C is provided inside an insulating material. E.g. the electric conductor C is a wire. The electric conductor C is connected to an electric circuit CC which can generate a measure of the electrical resistance R of the part of the electric conductor C corresponding to a circumference of the limb. The electrical circuit CC is connected to the electrical conductor C, so as to allow electrical contact with respective ends of the part of the electrical conductor which corresponds to a circumference of the limb. Especially, the electric conductor C can be arranged along the length of the tourniquet TQ, and wherein the fastening mechanism of the tourniquet TQ (not shown) is used to provide electric connection to a part of the electric conductor C which corresponds to the circumference of the limb, thereby allowing the measuring resistance to reflect the circumference of the limb. As seen, the electric conductor C is shown to have a zig-zag or square wave pattern with conducting parts parallel with a length direction of the tourniquet, so as to indicate a preferred type of electric conductor C which allows measuring an electric resistance value varying with lateral strain as the tourniquet TQ is wrapped around the limb. In this way, the electric conductor C in accordance with the principle of a strain gauge. The electric conductor C may be mounted, e.g. integrated, in a sleeve of the tourniquet TQ.

[0053] A blood pressure measuring circuit BP is arranged to automatically determine a measure of a systolic blood pressure SBP in response to input from a pressure sensor PS arranged to measure a pressure of the inflatable chamber CH. Such automatic blood pressure measuring circuit BP is known in the art, e.g. it may operate according to an oscillometric method as known in the art. Especially, the blood pressure measuring circuit may start operating once the pressure sensor PS senses a pressure exceeding a preset value.

[0054] A feedback device FBD serves to provide a feedback FB to the user, e.g. a visible and/or audible feedback. Especially, the feedback device FBD may comprise an LED array or a similar arrangement to provide feedback FB to the user applying the tourniquet and indicate when the tourniquet pressure is above, below or within the optimal range.

[0055] A processor P, or preferably a processor system including memory etc., is arranged for connection to the blood pressure measuring circuit BP, the pressure sensor PS, the electric circuit CC, and the feedback device FBD. The processor P is programmed to operate according to a control algorithm, preferable with its executable program code stored in read-only memory. The control algorithm serves:

1) to calculate a target pressure in response to the measured SBP, and the electrical resistance R of the part of the electric conductor C corresponding to a circumference of the limb,
2) to monitor input PR from the pressure sensor PS and comparing a sensed pressure by the pressure sensor PS with the calculated target pressure, and
3) to control the feedback device FBD to provide feedback FB to the user, when input PS from the pressure sensor PS indicates that pressure of the inflatable chamber CH is within an interval of the target pressure. The target pressure is preferably calculated as in Eq. (1) or (2) as further explained below.

[0056] In this way, the user is provided with feedback FB about the manual inflation process and can thus stop further inflation, once the target pressure has been obtained.

[0057] In the following, the actual process involved in using a specific system embodiment will be described.

[0058] The manually operated tourniquet is tightened around the extremity, i.e. limb (arm or leg), by drawing the tourniquet material through an external housing until the limb is tightly encircled. The cuff of the tourniquet is then locked in place using a clamp on the tourniquet housing unit. When the manual inflator bulb is squeezed, and the inflation chamber of the cuff begins to inflate. This triggers a measurement of the limb circumference using an electric conducting wire (or wires) running through the tourniquet, and which form a loop beginning and ending at the external tourniquet housing. The electrical resistance of the loop is measured and from this the length of wire can be calculated, using known resistivity and diameter values for the wire. The processor (CPU chip) compares measured resistance with a look-up table of resistance values which correspond to a known length, e.g. 3 Ohms=30 cm limb circumference. The CPU chip then matches this limb circumference with a look-up table of known values to find the corresponding TPC.

[0059] As the tourniquet is tightened, the tourniquet is inflated manually by the user up to a pressure above SBP. An SBP measuresment can only be taken after inflation is complete, and during deflation of the inflatable chamber after a pressure above SBP has been achieved. Once SBP is determined, the tourniquet is then be inflated again to inflate it to the target pressure, i.e. preferably Arterial Occlusion Pressure (AOP) or Optimal AOP (OAOP). The target pressure is computed using Eq. (1) or Eq. (2), where TPC and SBP are used: Eq. (1): AOP=SBP+10/TPC, and Eq. (2): OAOP=AOP+20 mmHG. In OAOP, a safety margin of 20 mm HG is added. This safety margin may be chosen to be smaller or larger than 20 mmHG, e.g. it may be selected in the range 10 mmHG to 50 mmHG.

[0060] The CPU chip compares the pressure of the tourniquet with the optimal pressure and will give feedback to the user, to guide the user into bringing the tourniquet within the optimal pressure range. This is achieved, for example, using a red LED to signal that the tourniquet pressure is too low, green LED to signal that the pressure is correct and a flashing orange or blue LED to alert nearby emergency operators that the tourniquet pressure has risen above the optimal level. Alternatively, or additionally, feedback may be given to the user by means of a small screen e.g. an e-ink screen.

[0061] Once the optimal or target pressure range has been reached (for example, OAOP5 mmHG), the user receives positive feedback from the system and will stop squeezing the bulb. Hereby the user is quickly set free to continue other treatment of the patient. SBP is preferably automatically measured at regular intervals (e.g. every 5 minutes) to check for changes in the patient's blood pressure. The calculations of AOP and OAOP are automatically repeated each time, using the original limb circumference reading for the calculation. This method allows the system to ignore changes in limb circumference caused by the pressure of the tourniquet. If the SBP has changed such that the tourniquet pressure is now outside the optimal range, feedback will once again be given to the user to adjust the tourniquet application pressure until it falls again in the optimal range.

[0062] The typical manual cuff inflation time required is estimated to be approximately 5-20 s. Based on values reported in the literature for human energy harvesting from squeezing, it is possible to estimate the power and energy harvested during cuff inflation. Assuming a gripping force of 200-250 N (roughly half of the maximum gripping force of a 30 year old male), and application of this force over a distance of 10 mm during squeezing of the bulb at a rate of 1 Hz the following, a power of such as P=2.0-2.5 W is obtained. Hereby, the total energy harvested over the 5-20 s period may be Etot=10-50 J.

[0063] An energy harvesting calculation can also be made for a rotary alternator, used as the tourniquet material is drawn through the external housing during the tightening around the limb before inflation. Assuming that the initial tourniquet circumference is 70 cm and the system is applied to either the arm or leg of a person 20 years or older with an average build, an energy output can be calculated to be Etotal=22.4-53.2 J.

[0064] In conclusion, the energy available to harvest from either of the mentioned methods would likely be sufficient to record data for tourniquet pressure, limb circumference etc. and to then make calculations and provide user feedback with this data. This could be achieved using a (super-)capacitor to store energy harvested from the tourniquet application and a CPU chip and LED array for feedback as described previously.

[0065] FIG. 2 shows steps of an embodiment of a method for determining feedback to a user of an inflatable tourniquet for arterial blood pressure occlusion of a limb. The method comprises an initial step of inflating I_TQ the inflatable chamber of the tourniquet. By sensing that the pressure in the inflatable chamber has reached a preset minimum pressure value, the further steps can be initiated. This inflation is done by the user. The further steps include receiving R_R a value indicative of electrical resistance of a part of an electric conductor arranged in the tourniquet, when the tourniquet has been fastened around the limb, wherein the part of the conductor corresponds to a circumference of the limb. Further, the method comprises receiving R_SBP a value indicative of SBP determined in response to a pressure measured in an inflatable chamber of the inflatable tourniquet. Further, the method comprises calculating a target pressure C_TPR in response to the value indicative of SBP, and the electrical resistance of the part of the conductor corresponding to a circumference of the limb. Preferably, a targer pressure interval is calculated. Still further, the method comprises monitoring pressure MN_PR of the inflatable chamber and comparing the pressure of the inflatable chamber of the tourniquet with the calculated target pressure, and providing feedback P_FB to the user, indicating that the pressure of the inflatable chamber has reached the calculated target pressure.

[0066] To sum up, the invention provides an inflatable tourniquet system for arterial blood occlusion of a leg or arm, e.g. after injury or for surgery. A tourniquet TQ is to be manually fastened around the limb by a user, e.g. a first aid helper, e.g. an untrained person. A manual inflator B is used to inflatable the tourniquet to apply pressure for occlusion of arterial blood flow to the limb. An electric circuit CC measures an electrical input from a length sensor C, e.g. an electric conductor, and to determine a value R, e.g. electric resistance, indicative of circumference of the limb accordingly, when the tourniquet has been fastened around the limb. A blood pressure measuring circuit BP automatically determines a systolic blood pressure SBP in response to input from a pressure sensor PS arranged to measure a pressure PR of the tourniquet. A processor P is programmed to operate according to a control algorithm which calculates a target pressure in response to the measured SBP, and the value R indicative of circumference of the limb. Then, the processor monitors input from the pressure sensor PS and compares the sensed pressure with the calculated target pressure. Visual and/or audible feedback is give to the user, when the pressure of the tourniquet TQ is within an interval of the target pressure. In some embodiments, the manual inflator B process may be used to provide energy harvesting for electric powering the system.

[0067] While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems. Any reference signs in the claims should not be construed as limiting the scope.