Abstract:
An exemplary implantable device includes an emitter to emit radiation to illuminate a portion of the stomach and a detector to detect emitted radiation reflected by the portion of the stomach where a contraction of the stomach alters the reflected radiation. For example, during contraction, blood is excluded from the contracting region of the stomach and the stomach becomes less red in color. An exemplary method includes illuminating a portion of the gastrointestinal tract, detecting a change in illumination received by a detector where the change in illumination is responsive to a contraction of the gastrointestinal tract. Various other methods, devices, systems, etc., are also disclosed.

Description:
TECHNICAL FIELD 
       [0001]    Exemplary methods, devices, systems, etc., presented herein generally relate to sensing gastric contractions. 
       BACKGROUND 
       [0002]    The digestive system plays a role in a variety of endocrine disorders and metabolic disorders (e.g., anorexia, obesity, gastroparesis, diabetes, etc.). As these disorders involve complex mechanisms, medicine often uses an interdisciplinary approach. For example, a patient with anorexia may be treated by a psychiatrist and an endocrinologist and a patient with morbid obesity may be treated by a surgeon (e.g., Roux-en-Y gastric bypass). Over the past 20 years, gastric electrical stimulation or gastric pacing has emerged as another option to treat obesity. 
         [0003]    With respect to obesity, the number of patients undergoing bariatric surgery for the treatment of obesity, and the proportion of the health care budget dedicated to this health problem, is growing exponentially. Yet some believe that, as a public health measure, bariatric surgery in the United States is being pursued in a less than optimal manner. This belief supports further testing of more controllable treatment options that rely on implantable programmable electronic stimulation devices. In particular, implantable devices that deliver gastric electrical stimulation have been effective in normalizing gastric dysrhythmia, accelerating gastric emptying and improving nausea and vomiting. 
         [0004]    Gastric electrical stimulation (GES) therapies generally aim to control gastrointestinal motility. For example, GES using short duration pulses can reduce nausea and vomiting in patients with gastroparesis and GES using longer duration pulses can pace intrinsic gastric slow waves and thus normalize gastric dysrhythmia. Electrical stimulation of the small intestine, colon, or anal sphincter has also been reported for the treatment of dumping syndrome, constipation, and fecal incontinency. 
         [0005]    For treatment of obesity, a therapy known as reverse (or retrograde) gastric pacing (RGP) can impair intrinsic gastric myoelectrical activity and substantially and acutely reduce food intake. RGP with a tachygastrial frequency of 9 cycles/min delivered using a pair of submucosal gastric electrodes implanted 5 cm above the pylorus in human subjects resulted in a reduction in the consumption of water, a reduction in food intake and an increase in gastric retention of a solid meal. Reduced food intake and freedom from symptoms resulting from moderate gastric stimulation are indicative of the therapeutic potential of RGP in treating obesity. 
         [0006]    A particular form of gastric electrical stimulation is sometimes referred to as tachygastrial electrical stimulation (TES) where tachygastrial frequencies induce tachygastria and reduce normal slow waves. TES delivered at the distal antrum can reduce food intake, in a manner likely attributed to TES-induced reduction in proximal gastric tone, gastric accommodation, antral contractility and gastric emptying. 
         [0007]    As various disorders and therapies pertain to gastric motility and, more specifically, waves or contractions of the gastrointestinal tract, techniques to monitor GI physiology are useful. Various techniques are discussed herein for monitoring GI contractions as well as other GI physiology. 
       SUMMARY 
       [0008]    An exemplary implantable device includes an emitter to emit radiation to illuminate a portion of the stomach and a detector to detect emitted radiation reflected by the portion of the stomach where a contraction of the stomach alters the reflected radiation. For example, during contraction, blood is excluded from the contracting region of the stomach and the stomach becomes less red in color. An exemplary method includes illuminating a portion of the gastrointestinal tract, detecting a change in illumination received by a detector where the change in illumination is responsive to a contraction of the gastrointestinal tract. Various other methods, devices, systems, etc., are also disclosed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Features and advantages of the described implementations can be more readily understood by reference to the following description taken in conjunction with the accompanying drawings. 
           [0010]      FIG. 1  is a block diagram of a sequence of digestive phases. 
           [0011]      FIG. 2  is a plot of some physiologic measures for digestion and a diagram of a portion of the gastrointestinal tract in a relaxed state and in a contracted state. 
           [0012]      FIG. 3  is a series diagrams including a diagram for a sensor for sensing VO 2 , a diagram for a sensor for sensing contractions and a diagram for an exemplary circuit for sensing contractions. 
           [0013]      FIG. 4  is an approximate anatomical diagram that includes various portions of the gastrointestinal tract (e.g., the stomach, the duodenum and the intestines). 
           [0014]      FIG. 5  is a diagram of a portion of the gastrointestinal tract. 
           [0015]      FIG. 6  is a diagram of exemplary sensor locations shown with respect to the portion of the gastrointestinal tract of  FIG. 5 . 
           [0016]      FIG. 7  is a diagram of an exemplary arrangement for acquiring one or more physiologic measures related to digestion. 
           [0017]      FIG. 8  is a block diagram of an exemplary device for acquiring contraction information and for delivering stimulation to the gastrointestinal tract. 
           [0018]      FIG. 9  is a block diagram of an exemplary method for adjusting one or more stimulation parameters for stimulating the gastrointestinal tract and an exemplary method for assessing capture. 
           [0019]      FIG. 10  is a block diagram of an exemplary method for detecting contractions of the gastrointestinal tract and for calling for an action (e.g., related to a gastrointestinal related therapy). 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description includes the best mode presently contemplated for practicing the described implementations. This description is not to be taken in a limiting sense, but rather is made merely for the purpose of describing the general principles of the implementations. The scope of the described implementations should be ascertained with reference to the issued claims. 
       Overview 
       [0021]    Various exemplary devices, methods, systems, etc., described herein relate to measurement of gastrointestinal contractions and optionally one or more other gastrointestinal physiologic measures. A particular device includes an emitter to emit radiation and a detector to detect emitted radiation as reflected or transmitted by the gastrointestinal tract. Such a device can output a signal that varies as the gastrointestinal tract contracts and relaxes. The signal can be used for any of a variety of purposes. For example, the signal can provide feedback to a stimulation device, the signal can determine digestive phase (fasting, cephalic, gastric, intestinal, etc.), or the signal can trigger any of a variety of actions (e.g., patient alert, information transmission, etc.). 
         [0022]    Digestive phases are discussed below followed by a description of some gastrointestinal physiologic measures. Exemplary devices, systems and methods are described that can acquire one or more gastrointestinal physiologic measures, which, in turn, may be used for any of a variety of purposes. 
         [0023]      FIG. 1  shows a diagram of three digestive phases  100 . Specifically, in a cephalic phase  110 , the brain alerts the stomach that it should expect arrival of a meal and the stomach comes out of its interdigestive quiescence and begins low level motor and secretory activity. After a meal is consumed, in a gastric phase  120 , the gastric motor and secretory activity increase significantly. If the meal is at all substantial, the gastric phase  120  is periodically suppressed by signals from the small intestine or by signals generated by the stomach if gastric pH falls to very low levels. Eventually, the meal is fully liquefied and emptied to the intestine (intestinal phase  130 ), and the stomach falls back into a state of very low motor and secretory activity, where it remains until the next cephalic phase  110 . 
         [0024]    More specifically, the cephalic phase  110  involves seeing, smelling and anticipating food and the brain informing the stomach that it should prepare for receipt of a meal. Communication is composed of parasympathetic stimuli transmitted through the vagus nerve to the enteric nervous system, resulting in release of acetylcholine in the vicinity of G cells and parietal cells. Binding of acetylcholine to its receptor on G cells induces secretion of the hormone gastrin, which, in concert with acetylcholine and histamine, stimulates parietal cells to secrete small amounts of acid. Additionally, a low level of gastric motility is induced. In essence, the gastric motor is turned on and begins to idle. 
         [0025]    In the gastric phase  120 , when a meal enters the stomach several additional factors come into play, foremost among them distension and mucosal irritation. Distension excites stretch receptors and irritation activates chemoreceptors in the mucosa. These events are sensed by enteric neurons, which secrete additional acetylcholine, further stimulating both G cells and parietal cells; gastrin from the G cells feeds back to the parietal cells, stimulating it even further. Additionally, activation of the enteric nervous system and release of gastrin cause vigorous smooth muscle contractions. The net result is that secretory and motor functions of the stomach are fully turned on—lots of acid and pepsinogen are secreted, pepsinogen is converted into pepsin and vigorous grinding and mixing contractions take place. However, there is a mechanism in place in the stomach to prevent excessive acid secretion: if lumenal pH drops low enough (less than about 2), motility and secretion are temporarily suspended. 
         [0026]    In the intestinal phase  130 , as food is liquefied in the stomach, it is emptied into the small intestine. It seems to be important for the small intestine to be able to slow down gastric emptying, probably to allow it time to neutralize the acid and efficiently absorb incoming nutrients. Hence, this phase of gastric function is dominated by the small intestine sending inhibitory signals to the stomach to slow secretion and motility. Two types of signals are used: nervous and endocrine. Distension of the small intestine, as well as chemical and osmotic irritation of the mucosa is transduced into gastric-inhibitory impulses in the enteric nervous system—this nervous pathway is called the enterogastric reflex. Secondly, enteric hormones such as cholecystokinin and secretin are released from cells in the small intestine and contribute to suppression of gastric activity. 
         [0027]    Collectively, enteric hormones and the enterogastric reflex put a strong brake on gastric secretion and motility. As the ingesta in the small intestine is processed, these stimuli diminish, the damper on the stomach is released, and its secretory and motor activities resume. 
         [0028]    It may be appreciated that the above mentioned digestive phases  100  include many sub-mechanisms. For example, mastication, saliva excretion, deglutition (swallowing), etc., are all part of the digestive process. Any of a variety of such mechanisms can trigger or condition gastrointestinal activity, which may alter gastrointestinal physiology. 
         [0029]      FIG. 2  shows a diagram of physiologic measures associated with digestion  200  along with a simplified diagram of gastrointestinal contractions  230 . The measures include blood flow  210 , VO 2 (GI)  220  and contractions  230 . Variations in these measures occur over time and may be associated with specific digestive phases  110 , 120  and  130 . For example, blood flow  210 , VO 2 (GI)  220  and contractions  230  may commence at some low level during the cephalic phase  110 . As food intake occurs (time 0 hours), then blood flow  210  increases to a peak value at about  1  hour after intake. VO 2 (GI)  220  also increases and peaks around the same time as blood flow  210 . Contractions  230  occur to assist in movement of food through the digestive tract. 
         [0030]    As indicated by blood flow  210  and VO 2 (GI)  220 , the cardiovascular system responds to feeding. During the cephalic phase  110  and the initial ingestion of food, a transient increase in cardiac output, aortic blood pressure and heart rate occur, which may be accompanied by an increase in mesenteric vascular resistance. Within about 5 minutes to 30 minutes after feeding, cardiac output, heart rate and blood pressure return to normal while blood flow through the superior mesenteric artery begins to rise and continues to do so for about 30 minutes to about 90 min. These responses can be attenuated by administration of sympathetic blocking agents. Thus, as in the case of early postprandial thermogenesis, the secretion of catecholamines may play an important role in the cardiovascular changes that occur during this ingestion phase. 
         [0031]    Alterations in blood flow  210  to the absorptive site concomitant with changes in gut motility (e.g., contractions  230 ) can influence the net absorption of nutrients such as amino acids and electrolytes. A positive correlation exists between blood flow  210  and the absorption of passively and actively transported substances. Increased blood flow  210  can increase absorption by increasing O 2    220  delivery to the mucosa, altering tissue colloid osmotic pressure or increasing the removal of an absorbed nutrient, thus increasing the concentration gradient between the lumen and the blood. For example, absorption of amino acids from the jejunum was found to be directly proportional to blood flow  210  and inversely proportional to gut motility (e.g., contractions  230 ). 
         [0032]    With respect to contractions  230 , the gastrointestinal tract is highly vascularized. Oxygenated blood is red; thus, in a relaxed state, the gastrointestinal tract appears red. However, when a contraction occurs, blood is forced from the constricted region of the gastrointestinal tract and it appears white (i.e., less red) compared to relaxed portions. Such a change has an analogy in the term “white knuckles” where a driver may grip a steering wheel in a manner that constricts blood flow to the tissue around the knuckles of the hand. For the stomach, a contraction may travel as a band having a width of about a centimeter or two. Hence, a change in color occurs in association with the contraction. As described herein, various techniques measure this color change. 
         [0033]    In  FIG. 2 , blood flow  210 , VO 2    220  and contractions  230  are shown together as relationships can exist between these measures. A study of blood flow in the left gastric artery in a canine model found that, in a fasting state, gastric motility and secretion exhibited periodical changes with an average cycle interval of 115.4±9.7 minutes (Naruse et al., “Interdigestive gastric blood flow: the relation to motor and secretory activities in conscious dogs”, Experimental Physiology, 77(5), 701-708). During a quiescent period, when gastric motility and secretion were minimal, the mean blood flow was stable at 33.9±3.8 ml/minute. During a contracting phase each peristaltic contraction was coupled with a rapid fall and rise in blood flow (from 10.5±1.9 ml/minutes below to 21.2±3.8 ml/minutes above the precontraction levels) in about 20 seconds to about 30 seconds. In addition there was a sustained elevation in blood flow (58.6±6.4 ml/minutes at the peak) lasting for 29.1±2.8 minutes. This study found that the onset of sustained blood flow elevation was preceded by that of motility in 63% of the cycles and that in 23% of the cycles, blood flow started to rise before the contracting phase began. Pepsin peaks coincided with blood flow peaks in two subjects and preceded the latter in the others. Feeding abolished periodic increases in motility and blood flow. The study concluded that left gastric arterial blood flow is not steady but exhibits dynamic changes in phase with periodic motor and secretory activities of the stomach in fasting conscious canines. 
         [0034]      FIG. 3  shows a sensor for VO 2  measurement  320 , a sensor for contraction measurement  330  and an exemplary circuit  340 . As described herein, the sensor for VO 2    320  can be used to measure contractions. However, other circuits can be used to measure contraction as well (e.g., exemplary circuit  340 ). 
         [0035]    The sensor for VO 2  measurement  320  includes a lead body  321 , sensor circuitry  322  and a window  324  that allows emitted radiation to interact with the surrounding environment and for reflected radiation to be detected. The particular example of  FIG. 3  is described in detail in U.S. patent application Ser. No. 11/231,555, entitled “Implantable multi-wavelength oximeter sensor”, filed Sep. 20, 2005 and U.S. patent application Ser. No. 11/282,198, entitled “Implantable self-calibrating optical sensors”, filed Nov. 11, 2005, which are incorporated by reference herein. 
         [0036]    The sensor for VO 2    320  can include a beam combiner subassembly built into the sensor assembly where the sensor  322 , in turn, is built into an implantable lead  321 . The sensor circuitry  322  includes a photo detector and an optional application specific integrated circuit (ASIC). The lead  321  includes a compartment with a pair of end caps that can be used to hermetically seal the sensor circuitry  322 . The lead  321  tube can be made of an opaque material, such as metal (e.g., titanium or stainless steel) or ceramic, so long as it includes a window  324  to allow for interaction with the surrounding environment. The window  324  can, for example, be made of synthetic sapphire or some other appropriate material. Exemplary synthetic sapphires are marketed by Imetra, Inc. (Elmsford, N.Y.) and Swiss Jewel (Philadelphia, Pa.). 
         [0037]    The optional ASIC, which can include filters, analog-to-digital circuitry, multiplexing circuitry, and the like, controls the emitters and processes photo detector signals produced by a photo detector in any manner well known in the art. As described herein, an ASIC may provide signals indicative of the photo detector signals to an implantable device, such as an implantable monitor, pacemaker, ICD, and/or metabolic therapy device (e.g., to treat obesity, diabetes, etc.). If an ASIC or equivalent circuitry is not included within the sensor circuitry  322 , and the sensor circuitry  322  outputs analog signals, such signals can be delivered between the sensor circuitry  322  and the implantable device. 
         [0038]    In the sensor circuitry  322 , an opaque optical wall is positioned between the beam combiner subassembly and the photo detector. The various components can be attached to a substrate (e.g., by epoxy) where the substrate can be a printed circuit board (PCB). Bond wires can be used to attach the various components to the substrate, as well as to attach the substrate to terminals which extend through an insulated feedthrough in an end cap of the sensor compartment. 
         [0039]    With respect to a lead-based sensor, the size of the beam combiner is preferably about 2 millimeters (mm) or less, and the size of the sensor circuitry  322  is about 4 mm or less, and preferably about 3 mm. The length of the sensor circuitry  322 , which extends axially in the lead  321  can be somewhat larger, because the length of the lead  321  is relatively large as compared to the diameter of the lead. 
         [0040]    The lead  321  may have a transparent housing, or include its own window, opening, or the like. The lead  321  can include tines for attaching the lead  321  to a desired position; the lead  321  may include any of a variety of types of fixation means, or none at all. Additionally, the lead  321  may also include a lumen for a stylet, which can be used for guiding the lead to its desired position. 
         [0041]    The sensor  320  can include wires that provide power and possibly control signals to the sensor circuitry  322  from an implantable device, and provide pulse oximetry signals from the sensor circuitry  322  to the implantable device. 
         [0042]    As described herein, a lead may include one or more electrodes configured for delivery of energy. For example, the lead  321  may include a ring electrode and a tip electrode that are connected to an implantable device by way of wires. 
         [0043]    The sensor for contractions  330  includes various features of the sensor for VO 2    320 . For example, the sensor  330  includes a lead  331 , sensor circuitry  332  and a window  334 . In the example of  FIG. 3 , a pair of tines  336  is also shown as being capable of anchoring the lead to tissue (e.g., stomach). The sensor circuitry  332  can differ from the circuitry  322  in that emitter requirements differ. More particularly, to sense a color change, as explained with respect to  FIG. 2 , the beam combiner subassembly is not necessarily required. Instead, a single emitter that emits a single wavelength or a band of wavelengths may be used. 
         [0044]    The exemplary circuit  340  includes various features of the TRS series reflective color sensors marketed by TAOS (Texas, USA). The TRS series devices are configured to convert reflected light intensity to an output voltage that is directly proportional to the reflected light intensity on the photodiode. The devices include an integral color LED and a matching color filters on the photodiode. Various components of the TRS series device are configured as a monolithic silicon IC (e.g., photodiode, operational amplifier and feedback components). Colors include red (630 nm), green (567 nm) and blue (470 nm). The TRS series devices can be configured to be triggered such that the emitter emits radiation only when desired. Thus, an exemplary circuit may be pulsed at particular times or in response to certain events to measure reflected radiation, for example, to measure contractions of the gastrointestinal tract. 
         [0045]    The circuit  340  includes a housing or package  342  that houses an emitter  344  and a detector  346 . The housing  342  includes connection tabs ground  342 , anode  343 , supply voltage  345  and output voltage  347  for the internal circuitry, as indicated in the circuit diagram. The output voltage  347  corresponds to intensity versus time. Thus, for a sensor mounted adjacent the stomach, a contraction will cause the intensity to increase as the stomach turns from red to white. 
         [0046]      FIG. 4  shows an anatomical diagram for part of the digestive system along with exemplary sensor locations  400 . The diagram  400  includes the liver  410 , the stomach  420 , the intestines  430 , the pancreas  490  and the gall bladder  497 . The stomach  420  includes labels that identify approximate locations of the esophagus  422 , the fundus  424  and the pylorus  426 . The intestines  430  include labels that identify approximate locations of the duodenum  428 , the small bowel  432  (including the jejunum  433  and ileum  434 ) and the colon  435  (including the cecum  436 ). The appendix  439  is also identified. 
         [0047]    Exemplary sensor locations, labeled A to F, include A (the esophagus  422 ), B (the fundus  424 ), C (the pylorus  426 ), D (the distal antrum), E (the duodenum  428 ) and F (the ileum  434 /the cecum  436 ). As these portions of the gastrointestinal tract include muscles that can contract, a sensor may be positioned at one of these positions to measure contractions. For example, a sensor may be positioned to measure contractions of a particular portion of the gastrointestinal tract (e.g., a portion of the stomach). Where such a sensor further includes circuitry to measure VO 2 , then contractions and VO 2  may be measured. 
         [0048]    As already mentioned, a sensor may provide a measure or signal to an implantable device. In various examples, such an implantable device is configured to deliver GES. As an implantable device may be alternatively or additionally configured for autonomic nerve stimulation, a brief description of the vagus with respect to the digestive system follows. The vagus enters the abdomen with two trunks (the right, dorsal or posterior and the left, ventral or anterior) that track generally along the esophagus. When the vagi cross the diaphragm, in most individuals they divide into five distinctive branches: (i-ii) paired gastric branches (e.g., associated with the stomach and the proximal duodenum), (iii-iv) paired celiac branches (e.g., associated with duodenum, jejunum, ileum, cecum and colon) and (v) a single hepatic branch that originates from the ventral trunk (e.g., associated with distal antrum, duodenum, liver and gall bladder). With respect to the diagram  400  of  FIG. 4 , gastric braches of the anterior vagus include direct branches to the fundus  424  (V-direct), pyloric branches to the pylorus  426  (branches emanating from vagal supply to liver  410  that include superior pyloric nerves and inferior pyloric nerves), a hepatic branch or branches (V-hepatic) and the anterior nerve of Latarjet (V-Latarjet, principal anterior nerve of lesser curvature of the fundus  424 ). Again various branches are linked to the aforementioned Auerbach plexus and Meissner plexus. 
         [0049]    The various locations labeled A-F provide general guidance for sensor placement. With respect to specific guidance,  FIG. 5  shows gastric anatomy  500  in two cross-sectional views of a segment  505  of the gastrointestinal tract. The gastrointestinal tract is essentially a tube extending from the oral cavity to the anus. This tube is organized into a series of four distinct layers which are fairly consistent throughout its length. Proceeding from the lumen  515  (i.e., abluminally from the lumen), the layers include: 
         [0050]    Mucosa  525 , which is the innermost layer (closest to the lumen  515 ) often described as the soft, squishy lining of the tract, consisting of epithelium, lamina propria and muscularis mucosae; 
         [0051]    Muscularis circular  535 , which is an inner circular layer of smooth muscle fibers wrapped around the long axis of the tract; 
         [0052]    Muscularis longitudinal  545 , which is an outer longitudinal layer of smooth muscle fibers extending parallel to the long axis of the tract; and 
         [0053]    Adventitia/serosa  555 , which is the outermost layer, which is called either adventitia (in regions where the tube passes through the body wall) or serosa (in regions where the tube passes through body cavities). 
         [0054]    The muscularis of the stomach is often thicker than that elsewhere and the muscle fibers can be layered in more orientations (often described as assuming three layers, which are not readily distinguishable in routine sections). In the stomach, the inner layer of the muscularis forms a sphincter in the pyloric stomach (the pyloric sphincter). 
         [0055]    Muscle contractions propel matter along the gastrointestinal tract. Muscle contractions of the gastrointestinal tract can be isolated to a single muscle layer or they may occur for multiple layers in a coordinated or uncoordinated manner. Contractions for multiple layers may occur in phase or out of phase. Phase locking may occur and contractions may be sequential, for example, where circular muscle contracts followed by longitudinal muscle. Contractions for multiple layers may be synchronous or asynchronous. 
         [0056]    A study by Sarna (“Gastrointestinal longitudinal muscle contractions”,  Am J Physiol Gastrointest Liver Physiol  265; G156-164, 1993) reported for a canine model, that, in the stomach, the longitudinal muscle contracted in a 1:1 relationship with the circular muscle contractions. Sarna noted that there was no significant difference between the frequency, duration and time of onset of gastric longitudinal and circular muscle contractions and their amplitudes were significantly correlated with each other. Sarna further noted that, in the small intestine when the circular muscle contracted, the longitudinal muscle exhibited passive elongation during the fasting and the fed state without any significant difference between the onset, duration and frequency of small intestinal circular muscle contractions and the passive longitudinal muscle elongations. 
         [0057]    As described herein, an exemplary sensor can detect muscle contractions of the gastrointestinal tract and such contractions may indicate patient state or digestive phase (e.g., fasting state, fed state, cephalic phase, gastric phase, intestinal phase, etc.) and optionally degree of lumen occlusion. 
         [0058]      FIG. 6  shows some exemplary locations  600  for a sensor with respect to the anatomical diagram  500  of  FIG. 5 . As gastrointestinal tract anatomy varies, the exemplary locations  600  can be selected as appropriate to accommodate any variation. The locations  600  include axial locations  601  and radial locations  603 . The axial locations  601  include locations A, A′ and A″ as in or adjacent the adventia; locations B, B′ and B″ as being approximately between the circular layer  535  and the longitudinal layer  545 ; and locations C, C′ and C″ as being in or adjacent the mucosa  525 . The radial locations  603  include locations spaced apart by about 180 degrees. For example, a sensor may be positioned at location A and another sensor positioned at location A′ adjacent the gastrointestinal tract with an angle of about 180 degrees between the sensors. Such an arrangement can help to more accurately measure contractions and optionally degree of occlusion. 
         [0059]    As explained, multiple sensors may be implanted into the body to measure gastrointestinal contractions. As indicated in a plot  610  of intensity versus time, the axial locations A, A′ and A″ can allow for detection of contraction direction and optionally degree of luminal occlusion. Specifically, axial placement can record time of maximum intensity (i.e., contraction) and a stronger contraction can be more white (i.e., less red) and thereby cause a larger increase in intensity (i.e., amplitude) versus a weaker contraction. 
         [0060]      FIG. 7  shows an exemplary arrangement  700  for acquiring information about the digestion process  200 , as explained with respect to  FIG. 2 . In  FIG. 7 , an implantable device  701  includes a lead  702  with one or more sensors configured, for example, according to sensor configuration  703 ,  705  or  707 . The configuration  703  relies on an emitter to emit radiation and a detector to detect reflected radiation; the configuration  705  relies on an emitter to emit radiation and a detector to detect transmitted radiation; and the configuration  707  relies on an emitter to emit radiation and multiple detectors to detect the emitted radiation (e.g., reflected and/or transmitted). 
         [0061]    Depending on features of the sensor, the implantable device  701  may acquire blood flow information  210 , VO 2  information  220  and/or contraction information  230 . A signal  240  represents a digital signal generated in response to contractions (noting that an analog signal may be used or an analog signal may be converted to a digital signal). In the example of  FIG. 7 , the signal  240  shows contractions with duration and amplitude information. A more simplified approach may rely on two digital states (e.g., 0 and 1) that represent a contraction or no contraction. Hardware and/or software techniques may be used to acquire any of a variety of signal that can be used to track contractions. The device  701  optionally stores acquired information  210 ,  220 ,  230  and/or signal  240  for any of a variety of purposes. 
         [0062]      FIG. 8  shows a block diagram of the exemplary device  701 . The device  701  may be optionally configured for sensing, activating and/or blocking activity of any number of organs, muscles and/or nerves. A basic device may include a processor, memory, one or more inputs, one or more outputs and control logic stored as instructions in the memory and operable in conjunction with the processor. The device  701  includes various additional features. 
         [0063]    The exemplary device  701  includes a programmable microprocessor  710  that can implement control logic  730  and other instructional modules  734 . Information may be stored in memory  724  and accessed by the programmable microprocessor  710 . For delivery of energy, the device  701  includes one or more pulse generators  742 ,  744 . The pulse generators  742 ,  744  may rely on a switch  720  for delivery of energy via one or more connectors  725 . While a device may include one or more integral leads, in general, a device includes one or more connectors for connecting a lead or leads to the device. More particularly, the connectors  725  provide for electrically connecting one or more electrodes and/or one or more sensors to the circuitry of the device  701 . In the example of  FIG. 7 , the switch  720  may select an appropriate electrode and/or sensing configuration. An electrode configuration may include an electrode from one lead and an electrode from another lead, a case electrode and another electrode or electrodes from a single lead. 
         [0064]    The device  701  further includes one or more analog to digital converters  752 ,  754  for converting analog signals to digital signals or values. An exemplary sensor may provide a digital signal (e.g., high voltage as “1” and low voltage as “0”), for example, that corresponds to a contracted state and a relaxed state, respectively, of a portion of the gastrointestinal tract. The processor  710  may use a signal provided by one of the A/D converters  752 ,  754  to control a therapy or other process. A control signal from the processor  710  may instruct the switch  720  to select a particular electrode configuration for sensing electrical or other activity. 
         [0065]    The device  701  may include one or more physiological sensors  760 . Such sensors may be housed within a case of the device  701  (e.g., a motion sensor), include a surface mounted component, include a lead, include a remote sensor, etc. A sensor may provide a digital signal or an analog signal for use by the processor  710  or other circuitry of the device  701 . A physiological sensor may provide a signal via one or more of the connectors  725  or it may be otherwise connected to device circuitry. 
         [0066]    For purposes of communication with external or other implantable devices, the device  701  includes a telemetry circuit  770 . The telemetry circuit  770  may include one or more antennae for transmission and/or receipt of electromagnetic signals. Such a circuit may operate according to a specialized frequency or frequencies designated for medical devices. Various conventional implantable devices rely on an associated programmer, which is typically an external computing device with a communication circuit suitable for communicating with an implantable device for purposes of data transfer, status checks, software download, etc. Where the circuit  770  communicates with an implantable device or a device in electrical connection with a patient&#39;s body, then the body may be a conductive medium for transfer of information. For example, the circuit  770  may be capable of communication with a specialized wristwatch where the body is relied upon as a conductor. 
         [0067]    The device  701  further includes an impedance measuring circuit  774 . Such a circuit may rely on instructions from the processor  710 . For example, the processor  710  may instruct the circuit  774  to provide a measured impedance for a particular electrode configuration. In such an example, the processor  710  may also instruct the switch  720  to provide the circuit  774  with a particular electrode configuration. Impedance information may be used by the processor  710  for any of a variety of purposes (e.g., hardware condition, cardiac condition, edema, respiration, gastrointestinal, etc.). The processor  710  may store impedance or other information to memory  724  for later use or for transmission via the telemetry circuit  770 . 
         [0068]    The device  701  includes a power source, which is shown as a battery  780  in the example of  FIG. 8 . The battery  780  powers the processor  710  and optionally other circuitry, as appropriate. In general, the battery  780  provides power to the pulse generators  742 ,  744 . Consequently, the battery  780  provides for operation of circuitry for processing control logic, etc., and provides for energy to activate tissue. A lead-based sensor may connect to the device  701  via one or more of the connectors  725  and be powered by the battery  780  (see, e.g., the lead  702  of  FIG. 7 ). The battery  780  may be rechargeable, replaceable, etc. 
         [0069]    In  FIG. 8 , the device  701  is shown as being connected to one or more stimulation leads  790 ,  790 ′ and a sensor lead  762 . A stimulation lead may provide for GES and/or nerve stimulation. A sensor lead may be configured to delivery stimulation energy, as explained with respect to  FIG. 3 . 
         [0070]    While the device  701  includes particular features, various exemplary devices, systems, methods, etc., may use or be implemented using a different device with more or less features. 
         [0071]      FIG. 9  shows an exemplary method  1000  for adjusting one or more stimulation parameters for GES and an exemplary method  1050  for assessing GES capture. The method  1000  is optionally implemented by an implantable device such as the device  701  of  FIGS. 7 and 8 . According to the method  1000 , a delivery block  1014  delivers a stimulus to cause a gastrointestinal contraction. A decision block  1016  decides if the delivered stimulus caused a contraction. If the decision block  1016  decides that a contraction did not occur, then an adjustment block  1018  adjusts one or more stimulation parameters. However, if the decision block  1016  decides that a contraction did occur, then the method  1000  continues in block  1020  where the stimulation parameters are deemed acceptable for causing a gastrointestinal contraction. The method  1000  may be used to optimize energy expended for causing contractions. For example, the blocks  1014 ,  1016 ,  1018  and  1020  may form part of a loop used to minimize stimulation energy required to cause a gastrointestinal contraction. When implemented by an implantable device with a limited power supply, such a method can increase device longevity. 
         [0072]    The method  1050  may be performed on a scheduled basis or in response to a condition such as the “no” branch of the decision block  1016  of the method  1000 . The method  1050  commences in a call block  1054  that calls for capture assessment. In the example of  FIG. 9 , capture assessment includes responding to non-capture scenarios and optimizing one or more parameters associated with delivery of stimulation energy. Accordingly, a delivery block  1058  delivers energy to a portion of the gastrointestinal tract (e.g., a portion of the stomach). A decision block  1062  decides if a capture occurred in response to the delivered energy (e.g., based at least in part on information acquired from an exemplary sensor). If the decision block  1062  decides that capture did not occur (e.g., according to one or more criteria), then the method  1050  continues at an adjustment block  1064  to adjust one or more parameters associated with delivery of stimulation energy to a portion of the gastrointestinal tract. After adjustment, delivery of energy occurs per the delivery block  1058  and the loop continues until one or more exit criteria are met. 
         [0073]    Referring again to the decision block  1062 , if this block decides that capture occurred, then the method  1050  continues at another decision block  1066  that decides if optimization should occur to optimize delivery of energy (e.g., to conserve energy, to minimize adverse tissue response, etc.). If the decision block  1066  decides that optimization is not required (e.g., already at a minimum level of energy delivery, optimization occurred within the last X hours, etc.), then the method  1050  enters a return block  1070  to exit the capture assessment. However, if the decision block  1066  decides that optimization should occur, the method  1050  enters the adjustment block  1064 , as already explained with respect to the “no” branch for the capture decision block  1062 . 
         [0074]    Information may be recorded for any of the exemplary methods described herein. For example, for the method  1050 , information about capture, parameter values, optimization, etc., may be recorded. Recorded information may be examined by a clinician to assess patient health, operation of an implantable device, etc. 
         [0075]      FIG. 10  shows an exemplary method  1100  for detecting gastrointestinal contractions. The method  1100  detects one or more contractions in a detection block  1110 . For example, as indicated in the signal plot  1112 , an exemplary sensor may detect a contraction when radiation intensity exceeds a certain intensity threshold, I(Th). An analysis block  1114  analyzes the one or more contractions, for example, using a formula or tables  1116 . A formula may be used to analyze contraction information based on intensity, wavelength and frequency of contractions. According to the method  1100 , a decision block  1118  decides, based at least in part on the analysis, if the contraction merits further action. For example, the analysis block  1114  may provide a value (e.g., contraction index “CI”  1116 ) and the decision block  1118  may compare the value to a limit (e.g., CI Limit    1120 ). As shown in  FIG. 10 , if the value exceeds the limit, then no further action is taken and the method  1100  continues at the detection block  1110  where a subsequent contraction may be detected. However, if the value does not exceed the limit, then the method  1100  calls for action per a call block  1122 . 
         [0076]    In the example of  FIG. 10 , the call for action may be from an implantable device  1130  to an external device  1131  and/or to one or more devices  1134 ,  1136  and/or  1138  accessible by a network  1132 . For example, the wristband device  1131  may receive a signal from the implantable device  1130  and, in turn, alert a care provider by dialing a cell phone number to reach the care provider&#39;s cell phone  1136 . Where action is not urgent, information may be communicated to a computer  1134  or a database  1138 . 
         [0077]    An exemplary method may detect one or more contractions and, in response, call for a particular action. For example, certain contractions may indicate that a bowel movement is imminent (e.g., to occur within a few minutes). A sensor may sense such contractions and alert a patient. In the system of  FIG. 10 , the implantable device  1130  may alert a patient via the wearable device  1131 . An alert may occur directly for some conditions and via review by a clinician for other conditions. For example, a clinician may receive patient information acquired by the implantable device  1130  and then issue an alert that alerts a patient via the wearable device  1131 . 
       CONCLUSION 
       [0078]    Although exemplary mechanisms (e.g., implemented as or in methods, devices, systems, software, etc.) have been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described.