Abstract:
The present application concerns detecting catheter proximity to a blood-vessel wall and blood-vessel wall artifacts associated therewith. In one embodiment, a light source, in a catheter, can be used to project light into the blood vessel. An intensity associated with at least one light wavelength that interacted with blood can be measured. Based on the measured intensity, a determination can be made regarding blood-vessel wall artifacts due to the catheter tip proximity to a blood-vessel wall. Feedback can be provided to the clinician in order to assist the clinician in adjusting the catheter to optimize signal quality and minimize artifacts due to the blood-vessel wall.

Description:
FIELD 
       [0001]    The present application relates to detecting catheter proximity to a blood-vessel wall and/or associated blood-vessel wall artifacts. 
       BACKGROUND 
       [0002]    During the last 25 years, the art of critical care medicine has greatly changed. Specialized units for patient care, advances in technology, and a better understanding of physiology by health care practitioners have reduced morbidity and mortality. One of the earliest advances in technology that helped to drive this progress was the development of the catheter. In the early 1970&#39;s, the addition of a thermistor to the catheter allowed for rapid assessment of cardiac output. At the same time, more sophisticated monitoring systems were also being developed. As a result, more complete hemodynamic assessment could be carried out with relative ease at a patient&#39;s bedside. 
         [0003]    With advanced technology came the requirement of advanced clinicians. For hemodynamic monitoring, catheter placement by the clinician is important for accurate measurement of total hemoglobin (tHB) and oxygen saturation and other physiological parameters. If the catheter is placed incorrectly, strong artifacts can interfere with the measurements. In particular, blood-vessel walls have optical properties that include a strong scattering profile that can create unwanted artifacts significantly interfering with hemodynamic measurements. 
         [0004]    Currently, there are no known devices to assist clinicians with proper catheter placement within a blood vessel for the clearest and highest quality signals. 
       SUMMARY 
       [0005]    The present application concerns detecting catheter proximity to a blood-vessel wall and/or blood-vessel wall artifacts. Through such detection, a clinician can be provided with audio or visual feedback in order to assist the clinician in adjusting the catheter position to optimize signal quality and minimize artifacts due to the blood-vessel wall. 
         [0006]    In one embodiment, a light source coupled to a catheter, can be used to project and receive light into the blood vessel. An intensity associated with at least one light wavelength can be measured. Based on the measured intensity, a determination can be made whether the blood-vessel wall artifacts exceed a threshold due to catheter proximity to a blood-vessel wall. 
         [0007]    In another embodiment, intensities of multiple wavelengths can be measured and a ratio of the intensities can be used to determine a level of blood-vessel wall artifacts. Use of multiple wavelengths can negate differences between light sources (e.g., light source strength). 
         [0008]    In another embodiment, one or more intensities associated with the light wavelengths can be measured and compared against predetermined benchmarks to determine a level of blood-vessel wall artifacts associated with catheter location in a blood vessel. 
         [0009]    The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a block diagram according to one embodiment wherein a catheter is inserted into a blood vessel. 
           [0011]      FIG. 2  is a block diagram of an example controller that can be used in  FIG. 1 . 
           [0012]      FIG. 3  is a flowchart of an embodiment for detecting blood-vessel wall artifacts. 
           [0013]      FIG. 4  is a flowchart of a method for using an intensity ratio of multiple wavelengths. 
           [0014]      FIG. 5  is a flowchart of a method for comparing an intensity measurement to a predetermined threshold. 
           [0015]      FIG. 6  is a flowchart of an embodiment for setting a vessel-wall indicator when the catheter is too close to the blood-vessel wall. 
           [0016]      FIG. 7  is a graph illustrating filtering used in the  FIG. 6 . 
           [0017]      FIG. 8  shows catheter placement in a blood vessel and an associated graph with intensities changing based on catheter placement within a blood vessel. 
           [0018]      FIGS. 9 and 10  show alternative embodiments used for a light source. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  shows an apparatus used to detect blood-vessel wall artifacts due to catheter proximity to a blood-vessel wall. A light source  110  is coupled to a catheter  112  inserted into a blood vessel  114 . The light source  110  can be any of a variety of types, such as an LED, and typically produces light in a wavelength range between about 400 nm to about 800 nm. Other light sources can be used. Generally, the light source is turned on continuously over a discrete period of time and generates a plurality of wavelengths that are transmitted into blood  115 . The catheter  112  can also be any of a variety of types, such as a central venous catheter or a pulmonary artery catheter, and can include two parallel optical fibers  116 ,  118 . The first optical fiber  116  is a transmit fiber designed to receive light from the light source and project the light into the blood stream illuminating the blood. The second optical fiber  118  is a receive fiber capable of receiving light from the blood and delivering the light to photodetectors  122 , which can be included in a spectrometer or other instrument for measuring the properties of light. Although any photodetectors can be used, the photodetectors  122  should preferably be capable of measuring intensities within the range of between about 400 nm and 1000 nm or higher. The received light is generally a combination of reflected light, scattered light and/or light transmitted through the blood. In any event, the received light carries information used to obtain parameters needed for hemodynamic monitoring, such as total hemoglobin and oxygen saturation. Ideally, the light interacts only with the blood. But, in practice, the light interacts not only with the blood, but with other objects located in the environment in which the catheter is positioned. In particular, blood-vessel wall artifacts can dominate the received light and significantly affect the calculated parameters. Incorrectly calculated blood parameters can have serious implications on patient safety, if used without caution. 
         [0020]    A controller  130  can be coupled to the photodetectors  122  and associated instrumentation for measuring light intensity. The controller can also be coupled to the light source  110  in order to control the light source during measurements. As further described below, the controller can use the measured light intensity of at least one wavelength captured in the photodetectors  122  to determine a level of blood-vessel wall artifacts due to the proximity of the catheter tip to the blood-vessel wall. Various techniques for using light intensity to determine blood-vessel wall artifacts and catheter position are described further below. 
         [0021]      FIG. 2  illustrates a generalized example of a suitable controller  130  in which the described technologies can be implemented. The controller is not intended to suggest any limitation as to scope of use or functionality, as the technologies may be implemented in diverse general-purpose or special-purpose computing environments. 
         [0022]    With reference to  FIG. 2 , the controller  130  can include at least one processing unit  210  (e.g., signal processor, microprocessor, ASIC, or other control and processing logic circuitry) coupled to memory  220 . The processing unit  210  executes computer-executable instructions and may be a real or a virtual processor. The memory  220  may be volatile memory (e.g., registers, cache, RAM), non-volatile memory (e.g., ROM, EEPROM, flash memory, etc.), or some combination of the two. The memory  220  can store software  280  implementing any of the technologies described herein. 
         [0023]    The controller may have additional features. For example, the controller can include storage  240 , one or more input devices  250 , one or more output devices  260 , and one or more communication connections  270 . An interconnection mechanism (not shown), such as a bus or network interconnects the components. Typically, operating system software (not shown) provides an operating environment for other software executing in the controller and coordinates activities of the components of the controller. 
         [0024]    The storage  240  may be removable or non-removable, and can include magnetic disks, magnetic tapes or cassettes, CD-ROMs, CD-RWs, DVDs, or any other computer-readable media that can be used to store information and which can be accessed within the controller. The storage  240  can store software  280  containing instructions for detecting blood-vessel wall artifacts associated with a catheter position in a blood-vessel wall. 
         [0025]    The input device(s)  250  can be a touch input device such as a keyboard, mouse, pen, or trackball, a voice input device, a scanning device, or another device. The output device(s)  260  may be a display, printer, speaker, CD- or DVD-writer, or another device that provides output from the controller. Some input/output devices, such as a touchscreen, may include both input and output functionality. 
         [0026]    The communication connection(s)  270  enables communication over a communication mechanism to another computing entity. The communication mechanism conveys information such as computer-executable instructions, audio/video or other information, or other data. By way of example, and not limitation, communication mechanisms include wired or wireless techniques implemented with an electrical, optical, RF, microwaves, infrared, acoustic, or other carrier. 
         [0027]      FIG. 3  is a flowchart of an embodiment for detecting blood-vessel wall artifacts and/or catheter proximity to a blood-vessel wall. In process block  310 , light is projected into the blood vessel using a catheter as already described. The light is transmitted through the transmit fiber  116  in the catheter  112  and may include one or more wavelengths, typically in the 400 nm to 850 nm range. In process block  320 , an intensity is measured for at least one wavelength using photodetectors  122 . The “intensity” measured is meant to be a general term associated with the emitted power per unit area or power per solid angle, depending on the particular application. In process block  330 , the intensity is used to detect blood-vessel wall artifacts. Additionally, catheter position relative to the blood-vessel wall can also be estimated based on the intensity. There are a variety of techniques that can be used to detect blood-vessel wall artifacts and the present disclosure should not be considered limited to the techniques described herein. 
         [0028]      FIG. 4  shows one such technique that can be used to implement process block  330  in  FIG. 3 . In process block  410 , intensities are received by the controller  130  from the photodetectors  122  for at least two wavelengths. In process block  420 , a ratio is calculated by dividing the first intensity measurement by the second intensity measurement. Example measurements include having a first wavelength below 580 nm and the second wavelength above 720 nm. To prevent a single frequency&#39;s intensity weighting too much on the ratio, a median or mean intensity of a narrow-band region around the first and second wavelengths can be used instead. In process block  430 , the calculated ratio can be compared to one or more predetermined thresholds. For example, if the ratio exceeds a threshold, it indicates that signal quality is poor as a result of the catheter tip being within an undesirable distance from the blood-vessel wall. A multistate indicator can also be used to show different levels of signal quality. For example, different thresholds can indicate different levels of signal quality. The thresholds can be determined using bench studies and/or animal studies. 
         [0029]      FIG. 5  shows another technique that can be used to implement process block  330  in  FIG. 3 . In process block  510 , an intensity is received associated with one wavelength (or a mean or median of a range around a single wavelength). In process block  520 , the intensity is compared to one or more predetermined thresholds. If the intensity exceeds the threshold, in process block  530 , an indicator is output to signal that quality is low. As with  FIG. 4 , the thresholds can be determined using bench studies and/or animal studies. The technique of  FIG. 5  allows a calculation using only a single wavelength, as opposed to  FIG. 4 , which requires at least two wavelengths. 
         [0030]    Whatever technique is used, a clinician can be alerted through output device  260  using either a visual or audio indication that the catheter tip placement is not ideal. This immediate feedback can allow the clinician to dynamically adjust the catheter in order to maximize signal quality. Alternatively, any stored data can have a field indicating signal quality as a result of distance of the catheter tip to the blood-vessel wall. For example, a multi-state indicator can show various levels of signal quality (e.g., a level from 1 to 3.) 
         [0031]      FIG. 6  shows another embodiment of a method for detecting blood-vessel wall artifacts due to catheter proximity to a vessel wall. In process block  610 , broadband spectra are acquired and filtered to attenuate background and random noise. A variety of noise reduction filters can be used depending on the particular application, including linear or non-linear filters.  FIG. 7  provides an example graph showing data before and after using a filter. In process block  620 , a ratio is calculated using at least two wavelength intensities. As previously described, a narrow range can also be used around two wavelength intensities. In process block  630 , a vessel wall indicator is set based on the proximity of the catheter to the blood-vessel wall. Using predetermined intensity thresholds, various levels of signal quality can be output to a clinician or data file, as previously described. Additionally, catheter position can be estimated based on the intensities. 
         [0032]      FIG. 8  shows a catheter  810  in dashed lines that has a tip  812  adjacent a blood-vessel wall  814 . Light  816  illuminated from a tip  812  of the catheter is reflected from the blood-vessel wall (as shown by arrows  818 ) creating unwanted artifacts that can significantly interfere with hemodynamic measurements. As shown in the graph  820 , the spectral intensity of the light received through the catheter increases across a variety of wavelengths, particularly in the range of 400 nm to 1000 nm or higher with the catheter placed adjacent the wall  814 . In an example embodiment, a threshold  830  can be set such that if the spectral intensity exceeds the threshold, an indicator can be provided to a clinician so that the clinician has immediate feedback on catheter tip location and placement. As a result, the clinician can move the catheter to the position shown at  840  in solid lines where the light transmitted into the blood is less affected by artifacts due to the blood-vessel walls. Such immediate feedback to the clinician ensures a high-signal quality for accurate hemodynamic measurements. 
         [0033]      FIGS. 9 and 10  show other structures that can be used to implement the methods described herein. In  FIG. 9 , multiple light sources  910 , such as multiple colored LEDs can be used to provide discrete wavelengths that can be time multiplexed by sequencer control logic  920  to individually turn on at different times. The discrete signals are transmitted through an optical transmit fiber  930  located in a catheter  935  into the blood and reflected into a receive fiber  940 . The receive fiber  940  transmits the discrete reflected signals to a single photodetector of a spectrometer  950 . Multiple photodetectors may be employed to measure the special effects of the signals. A controller  960  is coupled to the photodetectors and is used to determine blood-vessel wall artifacts and/or catheter tip location, as previously described. 
         [0034]    In  FIG. 10 , single or multiple light sources  1010  may be transmitted through a wavelength filter  1012 , such as a filter wheel, to provide an alternate or additional embodiment of discrete wavelengths that may be time multiplexed. The light signals are passed through the filter  1012  and transmitted through an optical fiber  1020  located in a catheter  1025  into blood  1030  and then reflected back through a receive fiber  1040  to at least one photodetector  1050 . A controller  1060  is coupled to the photodetectors and is used to determine blood-vessel wall artifacts and/or catheter tip location, as previously described. 
         [0035]    The techniques herein can be described in the general context of computer-executable instructions, such as those included in program modules, being executed in a computing environment on a target real or virtual processor. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc., that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Computer-executable instructions for program modules may be executed within a local or distributed computing environment. 
         [0036]    Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods. 
         [0037]    Any of the disclosed methods can be implemented as computer-executable instructions stored on one or more computer-readable storage media (e.g., non-transitory computer-readable media, such as one or more optical media discs, volatile memory components (such as DRAM or SRAM), or nonvolatile memory components (such as hard drives)) and executed on a computer (e.g., any commercially available computer, including smart phones or other mobile devices that include computing hardware). Any of the computer-executable instructions for implementing the disclosed techniques as well as any data created and used during implementation of the disclosed embodiments can be stored on one or more computer-readable media (e.g., non-transitory computer-readable media). The computer-executable instructions can be part of, for example, a dedicated software application or a software application that is accessed or downloaded via a web browser or other software application (such as a remote computing application). Such software can be executed, for example, on a single local computer (e.g., any suitable commercially available computer) or in a network environment (e.g., via the Internet, a wide-area network, a local-area network, a client-server network (such as a cloud computing network), or other such network) using one or more network computers. 
         [0038]    For clarity, only certain selected aspects of the software-based implementations are described. Other details that are well known in the art are omitted. For example, it should be understood that the disclosed technology is not limited to any specific computer language or program. For instance, the disclosed technology can be implemented by software written in C++, Java, Perl, JavaScript, Adobe Flash, or any other suitable programming language. Likewise, the disclosed technology is not limited to any particular computer or type of hardware. Certain details of suitable computers and hardware are well known and need not be set forth in detail in this disclosure. 
         [0039]    Furthermore, any of the software-based embodiments (comprising, for example, computer-executable instructions for causing a computer to perform any of the disclosed methods) can be uploaded, downloaded, or remotely accessed through a suitable communication means. Such suitable communication means include, for example, the Internet, the World Wide Web, an intranet, software applications, cable (including fiber optic cable), magnetic communications, electromagnetic communications (including RF, microwave, and infrared communications), electronic communications, or other such communication means. 
         [0040]    In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope of these claims.