Chapter 18 (page 83)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 18 (page 83)

Chapter 18

Radionuclides in the Investigation of Gastric Emptying

Griffith et al. (l966, l968) enumerated some of the techniques which had been used up to that time in the investigation of gastric emptying. For example, a previously administered meal could be aspirated at intervals, giving an indication of the rate of emptying. This showed that fluids left the stomach in an exponential manner; however, the technique was non-physiological and inaccurate, and required repeated naso-gastric intubations.

The time taken for a radio-opaque meal to leave the stomach could also be determined. This method could give rise to inaccuracies as it was possible that radio-opaque barium could separate from the meal, or alternatively, could become adherent to the mucosa; in both instances it would leave the stomach at a rate different to that of the meal. Moreover, the rate of emptying could not be quantified, and little information was obtained about the pattern of emptying.

Griffith et al,. (l966, l968) first used radionuclides in the study of gastric emptying. A technique was described in which a standard meal of porridge and eggs was labelled with radio-active chromium (⁵¹Cr), the rate at which it left the stomach being determined by means of external gamma counting. Subjects with and without gastro- duodenal disease were examined in the supine position, care being taken to differentiate the radio-activity emanating from the stomach from that of the small bowel. It was found that most of the meal left the stomach in an exponential manner. It also appeared that the rate of emptying of the stomach was constant for any one person whether there was gastro-duodenal disease or not.

Emptying of Liquids and Solids

Heading et al. (l974) used different radio-isotopes to label the liquid and solid components of a standard meal; by this method emptying of liquids and solids could be assessed separately but simultaneously. The liquid component, consisting of cornflakes and milk, was labelled with ^113mIn DTPA chelate. The solid component consisted of small pieces of filter paper impregnated with ^99mTc sulphur colloid and coated with a thin film of perspex. In 15 normal subjects emptying of the aqueous phase approximated to a simple exponential process, but the solid phase marker appeared to empty at a constant rate. In almost all subjects this was substantially slower than emptying of the liquid phase, and there was poor correlation between the two rates.

In a review of gastric emptying tests up to that time, Sheiner (l975) pointed out that the choice of isotope used for labelling meals varied widely between workers. For the liquid component ¹¹³In-DTPA chelate was often used, while ⁵¹Cr, ¹²⁹Cs and ^99mTc-human albumin microspheres (HAM) had all been used to determine emptying of the more solid components. The gamma emission was measured by scintiscanning or by fixed detectors in a gamma camera. The results of gastric emptying studies could be expressed in diverse ways. The rate and patterns of emptying were influenced by a variety of factors such as the fluidity of the meal, the pH, osmolarity and volume of the food eaten and the specific gravity and viscosity of the more solid components.

Meyer et al. (l976) stated that previous measurements of gastric emptying of solid foods had depended on external counting of surface adsorbed isotopes, without verification that isotopic labels remained attached to the food in the stomach. It was shown that up to 90 percent of ⁵¹Cr adsorbed to scrambled eggs could become detached in the stomach. Moreover, much of the egg was dissolved by HCl and pepsin, increasing the amount of ⁵¹Cr which entered the liquid phase. A method was developed in which ^99mTc sulphur colloid was injected intravenously into chickens in vivo. The colloid was phagocytised by Kupfer cells, incorporated intracellularly and absorbed uniformly throughout the liver substance. Less than 10 percent of the tag administered in this way separated from the fed liver in the stomach. Chicken liver tagged with ^99mTc in vivo was found to be an appropriate marker of the rate of emptying of solid food. Tests showed that ^99mTc-tagged liver left the stomach in a linear, zero-order pattern. The same amount of solid appeared to be transferred into the duodenum per hour regardless of the size of the meal. By contrast, the liquid component of a meal left the stomach more rapidly, in an exponential or first-order pattern (i.e. linear on a semilogarithmic plot). Referring to the previous investigations of Griffith et al. (l966, l968), who had found that solid food left the stomach in an exponential fashion, it was stated that the discrepancy might have been due to liquefaction of the ⁵¹Cr marker used. The observations of Meyer et al. (l976) that liquids emptied faster than solids and that liquids emptied in a first-order fashion while solids emptied in a zero- order pattern, supported the concept that the human stomach handled liquids and solids by different processes.

Heading et al. (l976), using methods similar to those in their previous study (Heading et al l974), found that the posture of a patient and the composition of a meal might modify emptying patterns. In normal control subjects and duodenal ulcer patients, liquid emptying was faster than solid emptying and could be represented as a monoexponential process. Solid emptying followed a different pattern, better represented as a linear emptying with time. In patients who had undergone Billroth II partial gastrectomy there was no evidence of differential emptying of liquids and solids.