Chapter 18 Heidelberg pH Capsule Gastric Analysis
Proper digestion is a prerequisite for optimum health, and incomplete or disordered digestion can be a major contributor in the development of many diseases. The problem is not only that ingestion of the best nutritional substances may be of little benefit when breakdown and assimilation are inadequate, but also that incompletely digested macromolecules can be inappropriately absorbed into the systemic circulation. This process can lead to various immune complex deposition diseases and is now theorized to be an integral part of the etiology of food allergies.
Adequate gastric hydrogen chloride (HCl) is also necessary for protection of the gastrointestinal tract from ingested pathogens and for the maintenance of proper bowel flora. A healthy flora is known to be important for proper immune function, vitamin absorption, and the prevention of opportunistic infections such as Candida albicans in the gut.
The Heidelberg gastric analysis technique was developed to measure the hydrogen ion concentration (pH) of the digestive tract and determine the acid secretory ability of the parietal cells. Its use of radiotelemetry allows the gathering of this important information in a convenient and accurate manner.
The Heidelberg pH capsule system had its origin about 50 years ago at Heidelberg University in Germany. In research sponsored by Telefunken, a West German electronics firm, the inventor H.G. Noeller studied gastric acidity in 10,000 people. Since then, about 140 studies, according to a PubMed inquiry, have used the Heidelberg system to investigate various aspects of digestion.1–7 Physicians and researchers now use this technique for measuring the pH of the digestive system.
Physiology of Digestion in the Stomach
The epithelium of the stomach contains many gastric glands. These tubular glands consist of parietal, chief, and mucous cells. The antral portion of the stomach produces the digestive hormone gastrin, the release of which is stimulated by the following:
• The physical bulk of the ingested food distending the stomach
After gastrin is absorbed into the bloodstream, it is carried to the gastric glands, where it stimulates the parietal cells to produce HCl acid and, to a lesser extent, the chief cells to produce digestive enzymes (such as pepsin and intrinsic factor). With adequate stimulation, the parietal cells increase their production of HCl by as much as eightfold.
When the pH of the stomach reaches about 2, the gastrin mechanism becomes blocked and feedback causes the parietal cells to decrease production of HCl. This concentration of hydrogen ions (by a factor of 100,000) is an energy-dependent process.
Dietary protein is composed of amino acids held together by peptide linkages. Pepsin A, the major gastric protease, cleaves these in the stomach and is most active at pH values of between 2 and 3. It is inactive at a pH of 5 and above. Consequently, to have any significant digestive effect in the stomach, the gastric juices must be acidic.
Trypsin (a protein-splitting enzyme secreted by the pancreas) completes the process, yielding amino acids and dipeptides. The biochemical messenger that stimulates this pancreatic secretion is the acidic bolus of food moving from the stomach into the duodenum.
The Heidelberg system consists of the following equipment:
• Radiotelemetry capsule—a hard plastic capsule (about 2 cm long × 0.8 cm in diameter) that contains a miniature radio transmitter, a pH sensing device, and a saline-activated battery.
• Waistband antenna—receives the signal from the capsule and relays it to the receiver.
• Receiver/recorder—receives and translates the signal. The pH reading is displayed on a meter and recorded by a continuous printer for a permanent record. The receiver also contains a calibration probe used to calibrate each capsule with known pH 1 and 7 solutions.
• Heater block—maintains the calibrating solutions at 37o C.
The test can be conducted in two ways: the tethered capsule repeat challenge and the flow-through method. Each gives different information and has its advantages and disadvantages. For both procedures, the test begins after the patient has fasted (food and liquid) for 8 hours.
The Tethered Capsule Repeat Challenge
In this procedure, the capsule is tethered so that it remains in the stomach while the stomach is challenged by the ingestion of a saturated sodium bicarbonate solution (i.e., baking soda).8 The challenge solution triggers a rise in stomach pH and a subsequent attempt by the parietal cells to reestablish appropriate acidity. The majority of people have a normal initial pH of between 1 and 2.3. Abnormalities of stomach secretions are usually found only after the stomach is challenged. (A more involved protocol can be found in Wright.8)
1. The waistband antenna is fastened around the patient’s waist and the receiver/recorder is turned on and calibrated.
2. The patient swallows the capsule, which is attached to a 1-meter long, thin cotton thread (a small amount of distilled water is allowed). The pH reading typically starts at 7 and falls toward 1. After about 5 minutes, the capsule reaches the bottom of the stomach (which normally displays a pH of between 1 and 2) and the remaining thread is taped to the cheek to prevent movement of the capsule out of the stomach and into the intestine.
3. If the fasting pH is normal, the patient swallows the first challenge of 5 mL of the alkaline solution. Within 30 seconds, the pH normally rises to 7 and the patient is asked to lie down on his or her left side (to keep the stomach contents in as long as possible).
4. If stomach function is normal and acid is secreted sufficiently in response to the alkali challenge, the pH returns to normal (between 1 and 2) within 20 minutes.
5. The challenge is repeated up to four times, as long as the response time is within 20 minutes.