Endoluminal capsule monitoring (also called a radio capsule or endoradiosonde; obsolete names include intestinal sensor and intestinal radiosonde) is a non-invasive medical diagnostic procedure that uses a miniaturized, ingestible capsule containing a wireless radio transmitter to measure physiological parameters, such as pH, temperature, and pressure, within the lumen of the gastrointestinal tract, transmitting the results by radio to an external receiving and recording device.Mostafanezhad, Isar; Boric-Lubecke, Olga; Lin, Jenshan (2017-12-07). Medical and Biological Microwave Sensors and Systems. Cambridge University Press. p. 4. .Nilmini, Wickramasinghe; Eliezer, Geisler (2008-06-30). Encyclopedia of Healthcare Information Systems. IGI Global. p. 889. .
Radio capsules may be powered by an internal power source, powered externally, or may passively reflect a signal from an external source (echo-capsules). A capsule may either move freely through the gastrointestinal tract, or be attached to the mucosal lining of an organ or to a tether, from which it may later detach and continue moving freely.Babsky, E. B.; Sorin, A. M.; Davydov, S. N. Instruments for Endoradiosounding: Fundamentals of Design, Application Techniques. Moscow: Nauka, 1975. 176 pp.
Components of the measurement system The capsule itself is only one part of a larger measurement system. The signal it emits must be captured by a dedicated receiving device. Where precise localization of the capsule within the patient's gastrointestinal tract is not required, and the patient is expected to go about normal daily activities outside a clinical setting, the receiver is typically a small electronic unit carried in a pocket or worn on a belt, recording measurements as they are taken. After the procedure, the recorded data is transferred, for example, to a personal computer, for processing and analysis using dedicated software.
For studies of animal gastrointestinal tracts (for example, in cattle), the receiver may be placed at the boundary of an enclosure, with the capsule's transmitter and the receiver both requiring sufficient power and sensitivity, respectively, to maintain a usable signal.
Where the capsule's location must be determined, a single receiver is insufficient. Multiple receivers (three or more), spatially distributed, or specialized direction-finding belts, may be used to calculate the coordinates of the signal source; accurate localization generally requires the patient to remain still. Even precise coordinates, however, do not always indicate which specific anatomical segment of the gastrointestinal tract the capsule occupies at a given time.
In common usage, "developing a radio capsule" typically refers to developing the entire measurement system, the capsule, the receiver(s), and the analysis software, rather than the capsule alone.
Measured parameters According to the type(s) of biomedical sensor built into the capsule, several physiological parameters can be measured and transmitted: intraluminal pH in the esophagus, stomach, small intestine, and colon temperature intraluminal pressure transit time
A wireless motility capsule (WMC) can measure gastric emptying time to help diagnose gastroparesis or gastric dumping syndrome, and can also measure transit time through the small intestine and colon. The WMC uses pH changes to detect passage through the pyloric sphincter and the ileocecal valve, and uses a temperature sensor to detect elimination from the body."SmartPill Information for Healthcare Professionals by Medtronic". Medtronic.
Historically, the most commonly measured parameters have been intraluminal pressure, temperature, and acidity. Some capsule designs combine two or more parameters in a single device; others are produced as a series, with each capsule type carrying only one kind of sensor. Radio capsules have also been developed to measure the rate of nutrient breakdown in the gastrointestinal tract, oxygen content in the digestive organs, ionizing radiation intensity, and the presence of gastrointestinal bleeding, though these directions were not developed beyond individual prototypes or proposals.
Pressure-sensing capsules Pressure-sensing radio capsules were the first type developed. Such a capsule typically comprises a pressure sensor, a high-frequency oscillator, and an independent power source. The pressure sensor must measure pressure from 0 to 200 cm of water column and respond to changes of ±5 mm of water column. The sensor may be of inductive or capacitive type.
An inductive sensor works by changing the inductance of a coil system as pressure acting on the sensor's membrane displaces a ferromagnetic or magneto-dielectric core or armature. A capacitive sensor instead relies on the change in gap between the plates of a flat capacitor as pressure changes.
Modern manometric methods commonly used to study the motor function of the digestive organs (upper esophageal sphincter manometry, esophageal manometry, sphincter of Oddi manometry, antroduodenal manometry, and anorectal manometry) require either precise fixation of the pressure sensor at a specific point in the organ, or simultaneous measurement of pressure at several points a defined distance apart, neither of which is achievable with a freely moving radio capsule.Bordin, D. S.; Valitova, E. R. Methodology and Clinical Significance of Esophageal Manometry. Ed. L. B. Lazebnik. Moscow: MEDPRAKTIKA-M, 2009. 24 pp.Stendal, Ch. Practical Guide to Gastrointestinal Function Testing. Blackwell Science Ltd., 1997. 280 pp. .
pH-sensing capsules pH-sensing radio capsules must operate across roughly 0.8 to 8.5 pH, with a sensitivity of ±0.1–0.2 pH, and maintain stable characteristics for the 2–3 days a capsule typically spends in the digestive tract. The measuring electrode in such a sensor is typically antimony or a glass electrode, with a calomel or silver chloride electrode used as the reference.
Modern acid-related diagnostic methods rely either on simultaneous pH measurement at two or more points in the gastrointestinal tract, on fixing a pH sensor at a specific location (as with 24-hour esophageal pH monitoring, positioned 5 cm above the lower esophageal sphincter), or on measuring pH at a standardized set of points (endoscopic pH mapping), approaches not achievable with a freely moving pH capsule.Butov, M. A.; Kuznetsov, P. S. Examination of Patients with Digestive System Disorders, Part 1: Examination of Patients with Stomach Disorders. Ryazan, 2007. Currently, in practical medicine, only the Bravo capsule, attached to the esophageal epithelium, sees clinical use among this category.
Temperature-sensing capsules Temperature sensors in radio capsules must operate across a range of 34–42 °C, detecting changes as small as ±0.1–0.2 °C.
Since the first radio capsule was developed, several transducer types have been used for temperature sensing: ferroelectric ceramic or other capacitors with a strongly temperature-dependent dielectric constant inductance coils with a core whose magnetic permeability is sufficiently temperature-dependent to allow measurement thermistors diodes or transistors with a pronounced temperature dependence of collector current
Such capsules were used to measure the temperature profile of the gastrointestinal tract. Temperature-based methods are not part of the current standard set of functional diagnostic techniques in gastroenterology.
History
The development boom of the late 1950s–1960s
The first radio capsule with an independent power source was described in June 1957 in the journal Nature by researchers at the Karolinska Institute (Stockholm, Sweden), R. Stuart Mackay and Bertil Jacobson.Mackay, S.; Jacobson, B. "Endoradiosonde". Nature, vol. 179, pp. 1239–1240, 1957. This was a freely moving capsule measuring pressure and temperature in the digestive tract.
The Mackay–Jacobson paper marked the start of an international burst of "capsule engineering" activity. That same year, Science published a report on a similar American capsule.Farrar, J. T.; Zworykin, V. K.; Baum, J. "Pressure-sensitive telemetering capsule for study of gastrointestinal motility". Science. 1957 Nov 8;126(3280):975–976. PMID 13486045. The following year, 1958, saw East Germanvon Ardenne, M.; Sprung, H. B. "Simultaneous registration of pressure and position changes by means of a swallowed intestinal transmitter". Z Gesamte Inn Med. 1958 Aug 15;13(16):596–601. PMID 13593548. and West GermanNöller, H. G. "Die Endoradiosondentechnik und ihre Bedeutung für die innere Medizin". Vortr. Dtsch. Ges. innere Med., 65th Congress, Wiesbaden, 1959, p. 727. capsules appear. In 1960, in the Soviet Union, a specialized laboratory for developing radio capsules and their associated telemetric systems was established in Leningrad. In 1961, English researchers published their own work,Wolff, H. S. "The radio pill". New Scientist. 1961;16:419–421. followed by Japanese researchers in 1962.Nagumo, J. et al. "Echo-capsule for medical use — a batteryless endoradiosonde". IRE Trans. on Bio-Med. Electronics, 1962, BME-9, 3, 195.
By the late 1950s, the field was considered important enough that some of the era's most prominent inventors personally took up radio-capsule design, including Vladimir Zworykin (United States) and Manfred von Ardenne (East Germany, credited with the first pH-sensing radio capsule).von Ardenne, M.; Sprunge, H. B. "Über den verschluckbaren Intestinalsender für pH-Wert-Signalisierung". Naturwissenschaften, 1958, 45, 23, 564.
In the early 1960s, Telefunken (West Germany) provided significant funding for technical experimentation and medical research in this field.Barrie, S. A. "Heidelberg pH capsule gastric analysis". In: Pizzorno, J. E.; Murray, M. T. (eds.), A Textbook of Natural Medicine. JBC Publications, Seattle, WA, 1992.
Heidelberg capsules "Heidelberg capsules" are single-use radio capsules that measure acidity within the gastrointestinal lumen, named after Heidelberg, Germany. In the early 1960s, at the University of Heidelberg's gastroenterology department, professor of pediatrics Hans G. Nöller, with financial support from Telefunken, conducted over 1,000 studies on adult patients using such capsules over a three-year period.
The term "Heidelberg Capsule" (or "Heidelberg pH Capsule") remains more common in the United States, where Heidelberg Medical Inc. manufactures Heidelberg capsules and associated radiotelemetric systems."The Heidelberg pH Diagnostic System". phcapsule.com.
Soviet radio capsule development
In late 1960, a laboratory was established in Leningrad, within an institution of the USSR Academy of Medical Sciences, with the primary task of developing endoradiosounding equipment. Overall direction of the radio-capsule research was carried out by E. B. Babsky and A. M. Sorin. Physiological and clinical testing of the completed capsules began at the end of 1961. Radio capsules were initially used to study the digestive tract; later, they were also adopted at the Leningrad Institute for Advanced Medical Training to record uterine contractile function and study labor, under S. N. Davydov.
Development proceeded in stages: first, a series of capsules was developed, each measuring a single parameter (pressure, pH, or temperature); this was followed by capsules capable of measuring two or more parameters simultaneously. Soviet designers took the position that radio capsules should be reusable, in contrast, for example, to Hans Nöller's single-use Heidelberg capsules, coating Soviet capsules in an exterior silicone rubber sleeve that served as a replaceable cover, and subjecting them to chemical disinfection between uses.
Soviet pressure-sensing capsules The first versions of Soviet pressure-sensing radio capsules were produced in 1961–62.
Soviet pH-sensing capsules