Patent Publication Number: US-2021178062-A1

Title: Tube diameter recognition

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to medical fluid-delivery devices, and specifically to medical fluid-delivery devices that pump fluid to a subject by pressing on a conduit. 
     BACKGROUND 
     Pumps are often used in the medical industry for delivering fluids, e.g., drugs, or diagnostic fluids, to subjects. One type of medical pump is an infusion pump, used to infuse a fluid into a subject&#39;s circulatory system via infusion tubing. Some infusion pumps pump fluid through the infusion tubing by repeatedly pressing, i.e., squeezing, the tubing. 
     SUMMARY OF THE INVENTION 
     Typically, parameters of a pumping mechanism, e.g., pumping cycle rate, of a fluid-delivery device, e.g., an infusion pump, are calibrated for a given delivery flow rate based on a diameter of the infusion tubing. For example, in an infusion pump where fluid is pumped to the subject by repeatedly squeezing the tubing with a pressing surface, the volume of fluid that is displaced during each intake/delivery cycle of the pumping mechanism is affected by the tube size. For infusion tubing of different sizes, parameters such as a speed at which the pressing surface squeezes the tubing, a wait-time between each pumping cycle in order to let the tube refill with fluid from a fluid source (e.g., an IV bag), upper and lower limits of each pressing surface stroke, and/or parameters of a pressure sensing mechanism within the fluid-delivery device, will vary for different desired delivery flow rates. 
     The inventors have realized that a volume of fluid displaced within the infusion tubing for each squeeze is dependent on a relationship between (a) how far the tube is squeezed from a first position to a second position (i.e., the difference in height of the tube before and after the tube is squeezed), and (b) the unsqueezed, fully-round, outer diameter of the tubing. In order to deliver fluid at a given flow rate, the pumping cycle rate of the pumping mechanism is calibrated based on the volume of fluid displaced within the infusion tubing for each squeeze, i.e., for each pumping cycle. Thus, in order to calibrate the pumping mechanism for a given flow rate, the fully round outer diameter of the tube should be known. 
     Therefore, in accordance with some applications of the present invention, apparatus and methods are presented for measuring the outer diameter of a conduit, e.g., infusion tubing, within a fluid-delivery device, e.g., an infusion pump. The fluid-delivery device measuring an outer diameter of any conduit received within it allows for a “tube-agnostic” system that is not limited to only receiving a conduit of a specific diameter, but, instead, may self-calibrate parameters such as pressing surface speed, pumping cycle rate, and/or pressure mechanism parameters, based on measuring the outer diameter of the conduit within the fluid-delivery device. 
     There is therefore provided, in accordance with some applications of the present invention, a method for measuring a size of a fluid-filled conduit in a fluid-delivery device, the method including: 
     (A) isolating a segment of the fluid-filled conduit by occluding a first site of the fluid-filled conduit and a second site of the fluid-filled conduit, the isolated segment being between the first and second sites; 
     (B) iteratively increasing pressure within the isolated segment, by incrementally squeezing a portion of the isolated segment of the fluid-filled conduit; 
     (C) for each iteration of squeezing the portion of the isolated segment of the fluid-filled conduit, measuring an increase in force exerted by the isolated segment of the fluid-filled conduit, associated with a respective pressure change during that incremental squeezing; and 
     (D) measuring an indication of the size of the conduit when an increase in force exerted by the isolated segment, measured in response to an incremental squeezing of the portion of the isolated segment of the fluid-filled conduit, passes above a threshold value. 
     For some applications, measuring the increase in force includes, using a force sensor, measuring the increase in force exerted, on the force sensor, by the isolated segment of the fluid-filled conduit, during each incremental squeezing. 
     For some applications: 
     incrementally squeezing a portion of the isolated segment includes using a pressing surface to incrementally squeeze the isolated segment, and 
     measuring the increase in force includes, using a force sensor coupled to the pressing surface, measuring the increase in force exerted, on the pressing surface, by the fluid-filled conduit, during each incremental squeezing. 
     For some applications, measuring the indication of the size of the conduit includes measuring an indication of an outer diameter of the conduit. 
     For some applications, the method further includes inhibiting the start of fluid-delivery to a subject if the measured indication of size of the conduit indicates that the size of the conduit is not within a predetermined range of sizes. 
     For some applications, measuring the indication of the size of the fluid-filled conduit includes measuring the indication of the size of the fluid-filled conduit using a size sensor. 
     For some applications, measuring the indication of the size of the fluid-filled conduit using the size sensor includes measuring the indication of the size of the fluid-filled conduit using a size sensor that is maintained in contact with the isolated segment of the fluid-filled conduit. 
     For some applications, the size sensor is maintained in contact with the isolated segment of the fluid-filled conduit by a spring, the spring causing the size sensor to exert a force on the isolated segment of the fluid-filled conduit prior to the squeezing. 
     For some applications, measuring the increase in force includes using the size sensor to measure the force exerted, on the size sensor, by the isolated segment of the fluid-filled conduit, during the squeezing. 
     For some applications, measuring the indication of the size of the conduit using the size sensor includes measuring the indication of the size of the conduit using a size sensor that does not contact the conduit. 
     For some applications, measuring the indication of the size of the conduit using the size sensor that does not contact the isolated segment of the fluid-filled conduit includes measuring the indication of the size of the conduit using an optical sensor. 
     For some applications, the method further includes regulating a parameter of the fluid-delivery device in response to the measured indication of the size of the conduit. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating a pumping cycle rate of the fluid-delivery device. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating an upper limit and a lower limit of a stroke of the pressing surface of each pumping cycle. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating a wait-time between consecutive pumping cycles. 
     There is further provided, in accordance with some applications of the present invention, a method for measuring a size of a fluid-filled conduit in a fluid-delivery device, the method including: 
     (A) isolating a segment of the fluid-filled conduit by occluding a first site of the fluid-filled conduit and a second site of the fluid-filled conduit, the isolated segment being between the first and second sites; 
     (B) iteratively increasing pressure within the isolated segment, by incrementally squeezing a portion of the isolated segment of the fluid-filled conduit; 
     (C) for each iteration of squeezing the portion of the isolated segment of the fluid-filled conduit, measuring an increase in size of the isolated segment of the fluid-filled conduit, associated with a respective pressure change during that incremental squeezing; and 
     (D) measuring an indication of the size of the conduit when an increase in size of the isolated segment, measured in response to an incremental squeezing of the portion of the isolated segment of the fluid-filled conduit, passes below a threshold value. 
     For some applications, measuring the indication of the size of the conduit includes measuring an indication of an outer diameter of the conduit. 
     For some applications, the method further includes inhibiting the start of fluid-delivery to a subject if the measured indication of size of the conduit indicates that the size of the conduit is not within a predetermined range of sizes. 
     For some applications, the method further includes regulating a parameter of the fluid-delivery device in response to the measured indication of the size of the conduit. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating a pumping cycle rate of the fluid-delivery device. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating an upper limit and a lower limit of a stroke of the pressing surface of each pumping cycle. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating a wait-time between consecutive pumping cycles. 
     There is further provided, in accordance with some applications of the present invention, a method for measuring a size of a fluid-filled conduit in a fluid-delivery device, the method including: 
     isolating a segment of the fluid-filled conduit by occluding a first site of the fluid-filled conduit and a second site of the fluid-filled conduit, the isolated segment being between the first and second sites; 
     squeezing a portion of the isolated segment of the fluid-filled conduit; 
     measuring a force exerted by the isolated segment of the fluid-filled conduit during the squeezing; and 
     when the measured force passes above a threshold value, measuring an indication of a size of the conduit. 
     For some applications, measuring the indication of the size of the conduit includes measuring an indication of an outer diameter of the conduit. 
     For some applications, the method further includes inhibiting the start of fluid-delivery to a subject if the measured indication of size of the conduit indicates that the size of the conduit is not within a predetermined range of sizes. 
     For some applications, measuring the force includes, using a force sensor, measuring the force exerted, on the force sensor, by the isolated segment of the fluid-filled conduit, during the squeezing. 
     For some applications: 
     squeezing a portion of the isolated segment includes using a pressing surface to squeeze the isolated segment, and 
     measuring the force includes, using a force sensor coupled to the pressing surface, measuring the force exerted, on the pressing surface, by the fluid-filled conduit, during the squeezing. 
     For some applications, the method further includes regulating a parameter of the fluid-delivery device in response to the measured indication of the size of the fluid-filled conduit. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating a pumping cycle rate of the fluid-delivery device. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating a pumping cycle rate of the fluid-delivery device. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating an upper limit and a lower limit of a stroke of the pressing surface of each pumping cycle. 
     For some applications, regulating the parameter of the fluid-delivery device includes regulating a wait-time between consecutive pumping cycles. 
     For some applications, measuring the indication of the size of the fluid-filled conduit includes measuring the indication of the size of the fluid-filled conduit using a size sensor. 
     For some applications, measuring the indication of the size of the fluid-filled conduit using the size sensor includes measuring the indication of the size of the fluid-filled conduit using a size sensor that is maintained in contact with the isolated segment of the fluid-filled conduit. 
     For some applications, the size sensor is maintained in contact with the isolated segment of the fluid-filled conduit by a spring, the spring causing the size sensor to exert a force on the isolated segment of the fluid-filled conduit prior to the squeezing. 
     For some applications, measuring the force includes using the size sensor to measure the force exerted, on the size sensor, by the isolated segment of the fluid-filled conduit, during the squeezing. 
     For some applications, measuring the indication of the size of the conduit using the size sensor includes measuring the indication of the size of the conduit using a size sensor that does not contact the conduit. 
     For some applications, measuring the indication of the size of the conduit using the size sensor that does not contact the isolated segment of the fluid-filled conduit includes measuring the indication of the size of the conduit using an optical sensor. 
     There is further provided, in accordance with some applications of the present invention, apparatus for delivering a fluid to a subject, the apparatus including: 
     a fluid-delivery device configured to receive a conduit, the fluid-delivery device including:
         a pressing surface configured to squeeze the conduit;   an upstream valve located upstream of the pressing surface and configured to reversibly occlude the conduit upstream of the pressing surface;   a downstream valve located downstream of the pressing surface and configured to reversibly occlude the conduit downstream of the pressing surface;   a force sensor positioned so as to measure an increase in force exerted by the conduit on the force sensor when the pressing surface is driven to squeeze an isolated segment of the conduit while the upstream and downstream valves are occluding the conduit on respective sides of the isolated segment; and   a size sensor configured to measure an indication of a size of the conduit when the measured increase in force passes above a threshold value.       

     For some applications, the size sensor is configured to measure an indication of an outer diameter of the conduit. 
     For some applications, the force sensor is positioned such that, when the conduit is received within the fluid-delivery device, the force sensor is preloaded against the isolated segment of the conduit. 
     For some applications, the fluid-delivery device is configured to receive a conduit having an outer diameter selected from a predetermined range of outer diameters. 
     For some applications, the predetermined range of outer diameters includes, at least, 3-6 mm. 
     For some applications, the size sensor is positioned such that, when the conduit is received within the fluid-delivery device, the size sensor is in contact with the isolated segment of the conduit. 
     For some applications, the apparatus further includes a spring coupled to the size sensor such that the size sensor is maintained in contact with the isolated segment of the fluid-filled conduit by a compression force that (a) compresses the spring and (b) is caused by the conduit being received within the fluid-delivery device. 
     For some applications, the size sensor is configured to measure the indication of the size of the conduit when the measured increase in force passes above a threshold value that is greater than the compression force. 
     For some applications, the size sensor is configured to measure the indication of the size of the conduit without contacting the conduit. 
     For some applications, the size sensor is an optical sensor. 
     There is further provided, in accordance with some applications of the present invention, apparatus for delivering a fluid to a subject, the apparatus including: 
     a fluid-delivery device configured to receive a conduit, the fluid-delivery device including:
         a pressing surface configured to squeeze the conduit;   an upstream valve located upstream of the pressing surface and configured to reversibly occlude the conduit upstream of the pressing surface;   a downstream valve located downstream of the pressing surface and configured to reversibly occlude the conduit downstream of the pressing surface; and   a sensor positioned so as to
           (a) measure an increase in force exerted by the conduit on the sensor when the pressing surface is driven to squeeze an isolated segment of the conduit while the upstream and downstream valves are occluding the conduit on respective sides of the isolated segment, and   (b) measure an indication of a size of the conduit when the measured increase in force passes above a threshold value.   
               

     For some applications, the sensor is configured to measure an indication of an outer diameter of the conduit. 
     For some applications, the fluid-delivery device is configured to receive a conduit having an outer diameter selected from a predetermined range of outer diameters. 
     For some applications, the predetermined range of outer diameters includes, at least, 3-6 mm. 
     For some applications, the sensor is positioned such that, when the conduit is received within the fluid-delivery device, the sensor is maintained in contact with the isolated segment of the fluid-filled conduit. 
     For some applications, the apparatus further includes a spring coupled to the sensor such that the sensor is maintained in contact with the isolated segment of the fluid-filled conduit by a compression force that (a) compresses the spring and (b) is caused by the fluid-filled conduit being received within the fluid-delivery device. 
     The present invention will be more fully understood from the following detailed description of applications thereof, taken together with the drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-B  are schematic illustrations of a fluid-delivery device, a segment of fluid-filled conduit disposed within the fluid-delivery device and isolated by an upstream valve and a downstream valve, a pressing surface for squeezing the conduit, a force sensor preloaded against the conduit, and a size sensor in contact with the conduit, in accordance with some applications of the present invention; 
         FIGS. 2A-B  are schematic illustrations of a fluid-delivery device, a segment of fluid-filled conduit disposed within the fluid-delivery device, and isolated by an upstream valve and a downstream valve, a pressing surface for squeezing the conduit, a force sensor, and a size sensor not in contact with the conduit, in accordance with some applications of the present invention; 
         FIG. 3  is a schematic illustration of a fluid-delivery device, a segment of fluid-filled conduit disposed within the fluid-delivery device isolated by an upstream valve and a downstream valve, a pressing surface for squeezing the conduit, and a sensor configured to measure both force and displacement, in accordance with some applications of the present invention; 
         FIGS. 4 and 5A -B are flowcharts showing different respective methods for measuring a size of a fluid-filled conduit in a fluid-delivery device, in accordance with some applications of the present invention; and 
         FIGS. 6-7  are graphs corresponding, respectively, to the flowcharts of  FIGS. 4 and 5A -B. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is now made to  FIGS. 1A-B , which are schematic illustrations of a fluid-delivery device  20 , a segment  22  of fluid-filled conduit  24  disposed within fluid-delivery device  20  and isolated by an upstream valve  26  and a downstream valve  28 , a pressing surface  30  for squeezing conduit  24 , a force sensor  32 , and a size sensor  34  in contact with conduit  24 , in accordance with some applications of the present invention. For some applications, fluid-delivery device  20  receives a conduit  24  having a fully-round diameter D, e.g., outer diameter D of conduit  24 , selected from a predetermined range of outer diameters. For example, standard outer diameters of infusion tubing may range from 3-6 mm, with the internal diameter typically being 0.8 mm to 2 mm smaller than the outer diameter. Upstream valve  26  and downstream valve  28  may be activated to reversibly occlude conduit  24 . An isolated segment  22  of conduit  24  is defined when both upstream valve  26  and downstream valve  28  are occluding conduit  24  at the same time. Typically, prior to isolating segment  22  of conduit  24 , conduit  24  is filled with fluid, e.g., liquid, such that the contents of conduit  24  are generally incompressible. Thus, pressing surface  30  may be used to squeeze a portion of isolated segment  22 , which in turn causes other portions of isolated segment  22  that are not being squeezed by pressing surface  30  to inflate. 
     Force sensor  32  is positioned so as to measure an increase in force exerted by conduit  24  on force sensor  32  as pressing surface  30  is driven to squeeze isolated segment  22  of conduit  24 , such as is shown in  FIG. 1B . For some applications, pressing surface  30  is driven to iteratively squeeze isolated segment  22 , thereby incrementally increasing pressure within isolated segment  22 . For each incremental increase in pressure, due to each incremental squeeze, force sensor  32  measures an increase in force exerted by conduit  24  on force sensor  32 . When the increase in force exerted by conduit  24  on force sensor  32  for each incremental squeeze passes above a threshold value, it can be assumed that an outer diameter of the now-inflated portions of isolated segment  22  represents fully-round outer diameter D of conduit  24 . Once the now-inflated portions of isolated segment  22  are fully inflated, i.e., have reached fully-round outer diameter D, the wall of conduit  24  starts to provide stronger resistance against further inflation of isolated segment  22 . This causes the change in pressure within isolated segment  22  per each incremental squeeze to suddenly increase, defining the threshold value (further described hereinbelow with reference to  FIG. 6 ). Thus, when the increase in force passes above the threshold value, size sensor  34  measures an indication of size, e.g., an indication of outer diameter, e.g., the diameter, of conduit  24 . Typically, force sensor  32  is positioned so as to be preloaded against isolated segment  22  of conduit  24  so as to increase sensitivity of the force measurement, such as is shown in  FIG. 1A . 
     For some applications, force sensor  32  measures an absolute value of force exerted by conduit  24  on force sensor  32 , and when the value of the measured force is high enough, i.e., once the force reaches the predetermined threshold value, it can be assumed that an outer diameter of the now-inflated portions of isolated segment  22  represents fully-round outer diameter D of conduit  24 . Thus, when the measured force exerted on force sensor  32  reaches the threshold value, size sensor  34  measures an indication of size, e.g., an indication of outer diameter, e.g., the outer diameter, of conduit  24 . Typically, force sensor  32  is positioned so as to be preloaded against isolated segment  22  of conduit  24  so as to increase sensitivity of the force measurement, such as is shown in  FIG. 1A . 
     For some applications, size sensor  34  may be a contact sensor  36 , positioned so as to be in contact with isolated segment  22  of conduit  24  when conduit  24  is received within fluid-delivery device  20 . For some applications, contact sensor  36  may comprise a spring  38  that is coupled to contact sensor  36  so as to maintain contact sensor  36  in contact with isolated segment  22  of conduit  24 , regardless of the size of the conduit received within fluid-delivery device  20 . For example, spring  38  may bias contact sensor  36  towards a lower surface  40 , against which conduit  24  is braced when received within fluid-delivery device  20 . As shown in  FIG. 1A , due to spring  38  biasing contact sensor  36  towards lower surface  40 , contact sensor  36  itself slightly squeezes conduit  24 . Thus, when conduit  24  is received within fluid-delivery device  20 , conduit  24  causes a compression force that compresses spring  38  a first compression distance. Now-compressed spring  38  ensures maintained contact between contact sensor  36  and isolated segment  22  with a compression force. Typically, a larger-sized conduit  24  will cause a larger compression force than a compression force caused by a smaller-sized conduit  24 . 
     For some applications, contact sensor  36  measures the indication of the size of conduit  24 , e.g., the indication of fully-round outer diameter D of conduit  24 , by measuring a height H of the top of outer wall  42  of isolated segment  22  with respect to lower surface  40 . Alternatively, contact sensor  36  may be calibrated so as to measure the indication of fully-round outer diameter D by measuring a height of some other reference point on conduit  24  with respect to lower surface  40 . For some applications, when conduit  24  is received within fluid-delivery device  20 , contact sensor  36  may measure a height H of the top of outer wall  42  of isolated segment  22 , based on the first compression distance of spring  38 , prior to isolated segment  22  being squeezed by pressing surface  30 . As shown in  FIG. 1A , prior to isolated segment  22  being squeezed by pressing surface  30 , height H of the top of outer wall  42  of isolated segment  22  is therefore typically less than fully-round outer diameter D. Subsequently, during the squeezing of isolated segment  22 , the inflation of isolated segment  22  causes a vertical displacement of contact sensor  36 , which in turn causes further compression of spring  38 . The further compression distance of spring  38  corresponds to a displacement of contact sensor  36  during the squeezing, the displacement of contact sensor  36  being indicative of the now-inflated height H of the top of outer wall  42  of isolated segment  22 . Spring  38  is typically compliant enough so as to allow the inflation of isolated segment  22  to compress spring  38  with relative ease. 
     As described hereinabove, during the squeezing of isolated segment  22  it can be assumed that (a) an outer diameter of the now-inflated portions of isolated segment  22  represents a fully-round outer diameter D of conduit  24  when (b) the force being measured by force sensor  32  reaches a threshold value. Thus, when the measured force reaches the threshold value, it may be assumed that the measured displacement of contact sensor  36  during the squeezing, which is indicative of the now-inflated height H of the top of outer wall  42  of isolated segment  22 , is indicative of the fully-round outer diameter D of conduit  24 . 
     Reference is now made to  FIGS. 2A-B , which are schematic illustrations of fluid-delivery device  20 , segment  22  of fluid-filled conduit  24  disposed within fluid-delivery device  20  and isolated by upstream valve  26  and downstream valve  28 , pressing surface  30  for squeezing conduit  24 , force sensor  32 , and size sensor  34  not in contact with conduit  24 , in accordance with some applications of the present invention. For some applications, size sensor  34  may be a non-contact size sensor that does not contact isolated segment  22  of conduit  24 .  FIG. 2A  shows pressing surface  30  in starting position, and  FIG. 2B  shows pressing surface  30  squeezing conduit  24 . In the absence of size sensor  34  pressing against conduit  24  (such as is shown in  FIGS. 1A-B ), the difference in height H of the top of outer wall  42  of isolated segment  22  before and after conduit  24  is squeezed is typically small, e.g., on the order of magnitude of microns, and is therefore not portrayed in the progression from  FIG. 2A  to  FIG. 2B . For some applications, the difference in height H of the top of outer wall  43  of isolated segment  22  before and after conduit  24  is squeezed may be larger due to parameters such as elasticity of the conduit, distance between the upstream and downstream valves, length of pressing surface  30 , and depth of the pressing surface stroke. 
     For example, size sensor  34  may be an optical sensor  44 . Optical sensor  44  typically measures height H of the top of outer wall  42  of isolated segment  22  relative to a reference point that is determined during an initial calibration of fluid-delivery device  20 , e.g., during production of fluid-delivery device  20 . The reference point may be lower surface  40  against which conduit  24  is braced when conduit  24  is received within fluid-delivery device  20 . Alternatively or additionally, the reference point may be a different surface within fluid-delivery device  20 , whose distance from optical sensor  44  is determined during initial calibration. As described hereinabove, once the force exerted by conduit  24  on force sensor  32  reaches the predetermined threshold value, optical sensor  44  may measure height H of the top of outer wall  42  of isolated segment  22 , and it can be assumed that the now-inflated height H represents fully-round outer diameter D of conduit  24 . 
     Reference is now made to  FIG. 3 , which is a schematic illustration of fluid-delivery device  20 , segment  22  of fluid-filled conduit  24  disposed within fluid-delivery device  20  and isolated by upstream valve  26  and downstream valve  28 , pressing surface  30  for squeezing conduit  24 , and a sensor configured to measure both force and displacement, in accordance with some applications of the present invention. For some applications, instead of a separate force sensor and a separate size sensor, contact sensor  36  may be used to measure (a) the force exerted by conduit  24  on contact sensor  36  during the squeezing, and (b) the indication of the size of conduit  24 , e.g., of fully-round outer diameter D of conduit  24 , when the measured force reaches the predetermined threshold value. 
     As described hereinabove, spring  38  of contact sensor  36  may be coupled to contact sensor  36  so as to maintain contact sensor  36  in contact with conduit  24  when conduit  24  is received within fluid-delivery device  20 . As pressing surface  30  squeezes isolated segment  22  of conduit  24 , contact sensor  36  is vertically displaced causing compression of spring  38 . This compression is converted to a measurement of the force exerted by conduit  24  on contact sensor  36 . When the measured force reaches the predetermined threshold, as described hereinabove, it may be assumed that the displacement of contact sensor  36  during the squeezing is indicative of fully-round outer diameter D of conduit  24 , and as such, the same compression of spring  38  that resulted in the measured force reaching the threshold value is converted to a displacement measurement. Thus, the inflated height H of the top of outer wall  42  of isolated segment  22  is measured, the inflated height H being indicative of fully-round outer diameter D of conduit  24 . 
     For some applications, force sensor  32  may also be coupled to, e.g., mounted on, pressing surface  30 , such that as pressing surface  30  squeezes isolated segment  22  of conduit  24 , the force sensor measures the force exerted by conduit  24  on pressing surface  30 . For example, force sensor may be mounted on the side of pressing surface  30 , or between pressing surface  30  and conduit  24 . As described hereinabove, when the measured force reaches the predetermined threshold value, size sensor  34  measures the indication of the size, e.g., fully-round outer diameter D, of conduit  24 . 
     It is noted that in  FIGS. 1B, 2B, and 3 , isolated segment  22  of conduit  24  is shown as having reached its fully-round outer diameter D due to the squeezing, at which point height H of the top of outer wall  42  of isolated segment  22  is equal to fully round outer diameter D of conduit  24 . Thus, height H of the top of outer wall  42  of isolated segment  22  appears in the figures to be the same as fully-round outer diameter D. 
     Additionally, it is noted that while the description above, with reference to  FIGS. 1A-B  and  FIG. 3 , relates to compression of spring  38 , the scope of the present invention includes spring  38  being positioned within fluid-delivery device  20  such that spring  38  is attached to the conduit  24 , e.g., looped around conduit  24 , in a way that would cause spring  38  to stretch (rather than compress) upon inflation of conduit  24 . 
     Reference is now made to  FIG. 4 , which is a flowchart depicting a method  50  for measuring the size, e.g., fully-round outer diameter D, of fluid-filled conduit  24 , in accordance with some applications of the present invention. For some applications, as described hereinabove with reference to  FIGS. 1-3 , method  50  is based on a measurement of an increase in force exerted by conduit  24  on an element external to conduit  24 , as conduit  24  is squeezed. In a first step  52  of method  50 , segment  22  of conduit  24  is isolated by occluding a first site of conduit  24  and a second site of conduit  24 , for example using upstream valve  26  and downstream valve  28  respectively, such that isolated segment  22  is between the first and second sites. Pressure within isolated segment  22  is then incrementally increased by incrementally squeezing a portion of isolated segment  22  (step  54 ) so as to inflate portions of isolated segment  22  that are not being squeezed. 
     For each incremental squeezing of isolated segment  22 , an increase in force exerted by isolated segment  22  of conduit  24  associated with the increase in pressure during the incremental squeezing is measured (step  56 ). For some applications, the increase in force may be measured with a dedicated force sensor, such as force sensor  32  as described with reference to  FIGS. 1A-B  and  FIGS. 2A-B . Alternatively, for some applications, there may not be a sensor dedicated to only measuring force, and the force may be measured using the same sensor that is used to measure the size of conduit  24 , such as size sensor  34 , e.g., contact sensor  36 , as described with reference to  FIG. 3 . Optionally, a force sensor may be coupled to pressing surface  30 , and the force exerted by conduit  24  on pressing surface  30  during the squeezing is measured directly by pressing surface  30  as it squeezes conduit  24 . 
     As described hereinabove, when the measured increase in force passes above a predetermined threshold value (as depicted by decision diamond  58  in  FIG. 4 , and as further described hereinbelow with reference to  FIG. 6 ), an indication of the size, e.g., fully-round outer diameter D, of conduit  24  is measured (step  60 ). The indication of the size, e.g., fully-round outer diameter D, of conduit  24  may be measured by a size sensor that contacts conduit  24 , e.g., contact sensor  36  as described with reference to  FIGS. 1A-B  and  3 , or alternatively by a size sensor that is not in contact with conduit  24 , e.g., optical sensor  44  as described with reference to  FIGS. 2A-B . 
     For some applications, a parameter of fluid-delivery device  20  may be regulated (step  62 ) in order to obtain a desired flow rate in response to the measured indication of the size of conduit  24 . For some applications, the upper and lower limits of the pressing surface stroke are fixed, and a pumping cycle rate of the fluid-delivery device may be regulated in order to obtain a desired flow rate in response to the measured indication of size conduit  24 . Alternatively, the pressing surface stroke may be adjustable, e.g., pressing surface  30  may be controlled by a lead screw and gear, and the upper and/or lower limits of each pressing surface stroke may be regulated in order to obtain a desired flow rate in response to the measured indication of size of conduit  24 . For some applications, a wait-time between each pumping cycle, e.g., in order to let the tube refill with fluid from a fluid source (e.g., an IV bag), may be regulated in response to the measured indication of size of conduit  24 . For some applications, parameters of a pressure sensing mechanism within the fluid-delivery device may vary based on desired flow rate, and thus may be regulated in response to the measured indication of size, e.g., fully-round outer diameter D, of conduit  24 . 
     Reference is now made to  FIG. 5A , which is a flowchart depicting a method  64  for measuring the size, e.g., fully-round outer diameter D, of fluid-filled conduit  24 , in accordance with some applications of the present invention. Alternatively to method  50 , which is based on force measurement, method  64  is based on watching an increase in the value indicative of the size, e.g., fully-round outer diameter D, of conduit  24 , during the squeezing. In a first step  66  of method  64 , segment  22  of conduit  24  is isolated by occluding a first site of conduit  24  and a second site of conduit  24 , for example using upstream valve  26  and downstream valve  28  respectively, such that isolated segment  22  is between the first and second sites. Pressure within isolated segment  22  is then incrementally increased by incrementally squeezing a portion of isolated segment  22  (step  68 ), and an increase in size of conduit  24  associated with the increase in pressure during the incremental squeezing is measured (step  70 ). 
     As the portion of isolated segment  22  is squeezed, the portions of isolated segment  22  not being squeezed begin to inflate, as described hereinabove. At first the inflation is rapid, however as the inflated height H of isolated segment  22  nears fully-round outer diameter D, the increase in size of isolated segment  22  measured in response to an incremental squeezing of isolated segment  22  starts to slow down due to the increase in resistance from the wall of conduit  24 , i.e., as the inflated height H of isolated segment  22  nears fully-round outer diameter D, the increase in size of isolated segment  22  for each incremental squeeze is reduced (as further described hereinbelow with reference to  FIG. 7 ). Thus, steps  68  and  70  may be iteratively repeated until the measured increase in size of conduit  24 , measured in response to an incremental squeezing of the portion of isolated segment  22 , passes below a threshold value. At that point it can be assumed that the now-inflated height H of the top of outer wall  42  of isolated segment  22  represents fully-round outer diameter D of conduit  24 , and thus an indication of the size, e.g., fully-round outer diameter D, of conduit  24  is measured (step  74 ). 
     For some applications, the indication of the size, e.g., fully-round outer diameter D, of conduit  24  may be measured by a size sensor that contacts conduit  24 , e.g., contact sensor  36  as shown in  FIGS. 1A-B , and  3 . Alternatively, for some applications, the indication of the size, e.g., fully-round outer diameter D, of conduit  24  may be measured by a sensor that is not in contact with conduit  24 , e.g., optical sensor  44  as shown in  FIGS. 2A-B . 
     Reference is now made to  FIG. 5B , which is a flowchart depicting a method  94  for measuring the size, e.g., fully-found outer diameter D, of fluid-filled conduit  24 , in accordance with some applications of the present invention. Method  94  is a combination of method  50  and method  64 , and is based on watching (a) the force measurement and (b) an increase in the value indicative of the size, e.g., fully-round outer diameter D, of conduit  24 , during squeezing. In a first step  96  of method  94 , segment  22  of conduit  24  is isolated by occluding a first site of conduit  24  and a second site of conduit  24 , for example using upstream valve  26  and downstream valve  28  respectively, such that isolated segment  22  is between the first and second sites. Pressure within isolated segment  22  is then incrementally increased by incrementally squeezing a portion of isolated segment  22  (step  98 ). During the incremental squeezing (a) an increase in size of conduit  24  associated with the increase in pressure is measured (step  100 ) and (b) an increase in force exerted by isolated segment  22  of conduit  24  associated with the increase in pressure during the incremental squeezing is measured (step  102 ). The increase in force may be measured using the same techniques as described hereinabove with reference to  FIG. 4 . 
     In contrast to method  50  and method  64 , each of which relies on one threshold being met in order to determine when the size measurement of conduit  24  should be taken, method  94  relies on both (a) the increase in size threshold and (b) the increase in force threshold, being met. Thus, when (a) the measured increase in size of conduit  24 , measured in response to the incremental squeezing of the portion of isolated segment  22 , passes below a threshold value, and (b) the measured increase in force, measured in response to the incremental squeezing of the portion of isolated segment  22 , passes above a predetermined threshold value (as depicted by decision diamond  104  in  FIG. 5B ), an indication of the size, e.g., fully-round outer diameter D, of conduit  24  is measured (step  106 ). 
     For some applications, a parameter of fluid-delivery device may be regulated (step  108 ) in response to the measured indication of the size of conduit  24 , as described hereinabove. 
     Reference is now made to  FIG. 6 , which is a graph corresponding to the method depicted in  FIG. 4 , in accordance with some applications of the present invention. Curve  78  on the graph represents a model of the pressure P within isolated segment  22  as pressing surface  30  incrementally squeezes, i.e., indents by a distance x, isolated segment  22 . The slope of curve  78  represents the rate of change of pressure P within isolated segment  22  as pressing surface  30  incrementally squeezes isolated segment  22 . Thus, the slope of curve  78  can be described as dP/dx. 
     The slope of segment  80  of curve  78  represents the rate of change in internal pressure before the now-inflated portions of isolated segment  22  reach fully-round outer diameter D, and the slope of segment  82  of curve  78  represents the rate of change in internal pressure once the now-inflated portions of isolated segment  22  reach fully-round outer diameter D. As described hereinabove, once the now-inflated portions of isolated segment  22  are fully inflated, the wall of conduit  24  starts providing increased resistance against further inflation, typically causing a relatively sharp increase in the rate of change of pressure within conduit  24  per each further incremental squeeze. Thus, as depicted in the graph of  FIG. 6 , the slope of segment  80  represents a first rate of change of internal pressure (dP1/dx), and the slope of segment  82  represents a second rate of change of internal pressure (dP2/dx). The threshold value for assuming that the now-inflated portions of isolated segment  22  have now reached fully-round outer diameter D is typically when dP/dx increases from dP1/dx to dP2/dx, represented by dashed line  84 . 
     Reference is now made to  FIG. 7 , which is a graph corresponding to the method depicted in  FIG. 5 , in accordance with some applications of the present invention. Curve  86  on the graph represents a model of the inflated height H of isolated segment  22  as pressing surface  30  incrementally squeezes, i.e., indents by a distance x, isolated segment  22 . The slope of curve  86  represents the rate of change of inflated height H of isolated segment  22  as pressing surface  30  incrementally squeezes isolated segment  22 . Thus, the slope of curve  86  can be described as dH/dx. 
     The slope of segment  88  of curve  86  represents the rate of change in inflated height H before inflated height H of isolated segment  22  nears fully-round outer diameter D, and the slope of segment  90  of curve  86  represents the rate of change in inflated height H once inflated height H of isolated segment  22  reaches fully-round outer diameter D. As described hereinabove, as the inflated height H of isolated segment  22  nears fully-round outer diameter D, the increase in size of isolated segment  22  measured in response to an incremental squeezing of isolated segment  22  starts to slow down and becomes somewhat asymptotic. Thus, as depicted in the graph of  FIG. 7 , the slope of segment  88  represents a first rate of change of inflated height H (dH1/dx), and the slope of segment  90  represents a second rate of change of inflated height H (dH2/dx). The threshold value for assuming that the now-inflated portions of isolated segment  22  have now reached fully-round outer diameter D is typically when dH/dx decreases from dH1/dx to dH2/dx, represented by dashed line  92 . For some applications, the threshold value for assuming that the now-inflated portions of isolated segment  22  have now reached fully-round outer diameter D may be when the rate of change in inflated height H reaches approximately zero, i.e., dH/dx˜0. 
     For some applications, a parameter of fluid-delivery device  20  may be regulated (step  76 ) in response to the measured indication of the size of conduit  24 , as described hereinabove. 
     For some applications, fluid-delivery device  20  may inhibit delivery of fluid to a subject if the measured indication of size of conduit  24  indicates that conduit  24  is not within a predetermined range of sizes. For example, if an infusion tube placed into fluid-delivery device  20  is measured to be either too small (e.g., less than 3 mm in outer diameter) or too large (e.g., greater than 6 mm in outer diameter), e.g., not within 3-6 mm in outer diameter, then fluid-delivery device  20  will not start a treatment of fluid-delivery to the subject. 
     It will be appreciated by persons skilled in the art that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description.