Assessment of Gastric Emptying Using Gamma Scintigraphy

Journal of Clinical Pharmacy and Therapeutics(1987) 12,343-346.

ASSESSMENT OF GASTRIC EMPTYING USING GAMMA SCINTIGRAPHY D. Harris, J. T. Fell,H. L. Sharma,* and D. C. Taylor? Department of Pharmacy, *Department of Medical Biophysics, University of Manchester, and tZC1 Pharmaceuticals, Alderley Park, Macclesjield, U.K.

SUMMARY

Gamma scintigraphy was used to measure the gastric emptying rates of three test meals in human volunteers. Emptying rates were determined for solid and liquid materials alone, and for liquid in the presence of solid material. It was shown that the emptying of solids from the stomach was significantly slower than that of liquid, whether liquid alone or liquid in the presence of solid material. It was concluded from these results that, in the case of a solid test meal from which radio-label could be eluted, the free label would empty considerably faster than the remaining solid material. The emptying rate observed scintigraphically would not, therefore, be a true estimate of the solid emptying rate.

INTRODUCTION The emptying of liquids from the stomach is a function of the intragastric pressure (1) and, as such, bears a first-order relationship to time (2). Particles of solid are selectively retained by the pylorus until they have been sufficiently reduced in size (3): solids therefore empty more slowly than liquids, and do so in a linear manner with time (2). Information on the emptying rates of solid and liquid materials can be of use in the investigation of a number of disease conditions, and in the evaluation of certain surgical procedures. Using gamma scintigraphy, and by selectively radio-labelling a particular component of a test meal, it is possible to investigate the different emptying rates of various solid and liquid materials. In order for investigations of this kind to be valid, however, the radiolabel must remain associated with the relevant component of the test meal for the duration of the study (4). Studies have been carried out using a labelled solid material from which there can be some elution of radio-label into solution ( 5 ) . Under these circumstances, the observed emptying rate would be the result of both solid and liquid emptying processes. The aim of this study was to determine whether this type of test meal can be used to estimate the gastric emptying rate of solids. 343

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The test meals used in this study were as follows. (a) 230 g ‘Readybrek’, containing 100 mg of an insoluble ion-exchange resin (Dowex 1-X8, BDH Chemicals, Poole, U.K.), labelled with 50 pCi 99 m-Tc (1.9 MBq); (b) 200 ml orange juice labelled with 50 pCi 99 m-Tc-DTPA (Pentetate-11, Amersham, U.K.); (c) 115 g unlabelled ‘Readybrek’, followed by 100 ml labelled orange juice. 99 m-Tc-DTPA (Diethylenetriaminepenta-aceticacid) is a reliable liquid marker, since it is stable and it is not absorbed from the gastro-intestinal tract (6). Ion-exchange resins are suitable solid-phase markers, since they are inert, insoluble, and show permanent binding of the radio-label (7). Four informed, healthy, male volunteers participated in the study. After an overnight fast, the subjects ingested one of the above test meals. Each subject received each test meal once, with the exception of one subject who was investigated only with the solid test meal (a). After ingestion of the test meal, the subject lay under a gamma-camera (NE-8960, Nuclear Enterprises, Edinburgh, U.K.) which was fitted with a parallel-hole collimator. 60 one-min frames were collected, and the data was accumulated by an on-line computer system (MAPS-2000, Link Systems, High Wycombe, U.K.). At the end of the study, a ‘region of interest’ was defined around the stomach. For each frame, the number of counts within this region was calculated and the results corrected for radioactive decay. The activity that remained at each time interval was expressed as a percentage of the initial activity.

RESULTS

In vitro tests showed that there was no significant release of radio-label from the ionexchange resin in (a), and there was no detectable absorption or adsorption of TcDTPA by the solid components in (c). Regression lines were fitted to each emptying profile: a zero-order model was fitted to the solid-emptying data (test meal (a)), and a mono-exponential model to the liquidemptying data (test meals (b) and (c)). Emptying profiles of the three test meals in one subject are shown in Figs 1 and 2. From these regression lines, T-half values were calculated for each investigation (the time taken for half the radio-label present initially to leave the stomach). These T-half values are shown in Table 1.

DISCUSSION Table 1 shows that there was no significant difference between the emptying rates of liquid alone, (b), and liquid in the presence of solid, (c). In both of these cases, liquids emptied significantly faster than did the solid meal, (a). Where there is radio-label associated with both solid and liquid phases of a test meal, this label will be emptied from the stomach by a combination of solid and liquid emptying processes. These results show that the liquid component of such a meal will empty

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Time ( m i d

Fig. 1. Gastric emptying profile of solid test meal.

i 50

'0

10

20

30 40 Time (rnin)

60

Fig. 2. Gastric emptying of liquid and mixed test meals. (0)Liquid meal; (W) liquid componentof mixed meal.

Table 1. Mean T-half values determined for each test meal Test meal (a) Labelledsolid meal (b)Labelled liquid meal (c) Labelled liquid component of mixed meal

T-half ( fSD) 81 (26) 23 (4)

30(10)

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considerably faster than the solid component. Where the proportion of free radio-label is significant, the emptying rate observed scintigraphically will be markedly greater than the true solid emptying rate. Test meals from which radio-label can be eluted, as used by some workers (3, cannot therefore be used to assess solid emptying. REFERENCES 1 . Strunz, U.T. & Grossman, M.I. (1978) Effect of intragastric pressure on gastric emptying and secretion: roles of proximal and distal stomach. American Journal of Physiology, 235, E552-E555. 2 . Heading, R.C., Tothill, P., McLoughlin, G.P. & Shearman, D.J.C. (1976) Gastric emptying rate measurement in man. Gastroenterology, 71,4550. 3. Kelly, K.A. (1980) Review: Gastric emptying of liquids and solids. American Journal of Physiology, 239, G71476. 4. Christian, P.E., Datz, F.L., Sorensen, Y.A. & Taylor, A. (1983) Editorial. Technical factors in gastric emptying studies. Journal of Nuclear Medicine, 24,264-268. 5 . Gannon, M.X., Pears, D.J., Chandler, S.T., Fielding, J.W.L. & Baddeley, R.M. (1985) The effect of gastric partitioning on gastric emptying in morbidly obese patients. British JournaZ of Surgery, 72, 952-954. 6. Chaudhuri, T.K. (1974) Use of 99m-Tc-DTPA for measuring gastric emptying time. Journal of Nuclear Medicine, 15,391-395. 7. Hunter, E. (1980) The in-vivo assessment of oral solid dosage forms in the gastrointestinal tract using external scintigraphy. Ph.D. thesis, University of Manchester.