Table 17.3 Medications that affect gastrointestinal motility.
| Decreased motility or gut transit |
| Opiates |
| Anticholinergics |
| GLP‐1 receptor agonists |
| L‐dopa |
| Tricyclic antidepressants |
| Calcium channel antagonists |
| Nitrates |
| Phosphodiesterase type 5 inhibitors (e.g. sildenafil) |
| Clonidine (an α‐2 agonist) |
| Sumatriptan (a 5‐HT‐1P agonist)a |
| Increased motility or gut transit |
| Metoclopramide |
| Domperidone |
| Erythromycin (a motilin agonist)b |
| Prucalopride |
| Beta blockers |
| Selective serotonin reuptake inhibitors |
| Cholinesterase inhibitors |
| Excess thyroxine |
a Relaxes the gastric fundus and slows gastric emptying but increases oesophageal motility.
b Stimulates gastric emptying but slows small‐intestinal transit.
Scintigraphy remains the gold standard for measurement of gastric emptying,49 and the use of two isotopes allows both the solid and liquid components of a meal to be studied (Figure 17.6). Regional meal distribution can also be evaluated by defining regions of interest within the stomach. Ultrasonography and13C isotope breath tests are alternative methods of measuring gastric emptying, although the former is restricted to liquid meals. Manometry is used predominantly for research purposes to record the frequency, amplitude, and organisation of lumen‐occlusive contractions in the antrum, pylorus, and duodenum. Proximal gastric relaxation in response to a meal can be evaluated in the laboratory using an electronic barostat; the volume of air required to maintain a fixed pressure in an intragastric bag is used as an index of proximal gastric tone. Single‐photon emission computed tomography (SPECT) is a nuclear medicine technique representing an alternative means of evaluating gastric volumes. The electrical rhythm of the stomach may be recorded from cutaneous electrodes, although the clinical significance of abnormalities of this electrogastrogram (EGG) is unclear since they are not specific for particular gastrointestinal disorders.
There is little information about the effects of ageing on the mechanics of the stomach, but fasting and postprandial antral motility did not differ between patients age 18–39 and those 40–69 years who were being investigated for unexplained gastrointestinal symptoms.50 Proximal gastric compliance is unchanged in the fasting state in the healthy elderly compared to the young, but the perception of gastric distension is diminished,15 akin to the reduction in visceral sensitivity evident in the oesophagus and stomach. Moreover, proximal gastric accommodation to a meal is delayed compared with young controls, which might contribute to early satiation. Conversely, the antrum is more distended after a nutrient drink in the healthy elderly,51 and antral width correlates with satiation and satiety in both young and old subjects. EGG recordings are similar in healthy old and young subjects, with subtle differences in response to nutrients.
Figure 17.6 Scintigraphic gastric emptying study. Part of the radiolabelled meal is evident in the stomach, while some has emptied into the small intestine (bottom left). Proximal and distal gastric regions of interest are outlined.
There is some evidence for altered responses to the presence of nutrients in the small intestine in the elderly compared to the young. In particular, intraduodenal nutrients stimulate greater cholecystokinin (CCK) release in the healthy elderly, even allowing for elevated fasting concentrations of CCK in this group,52 while intraduodenal glucose is more satiating than in the young. This enhanced small intestinal feedback could contribute to both delayed gastric emptying and impaired appetite. Furthermore, there is some evidence that the higher prevalence of Helicobacter infection and atrophic gastritis in the elderly compared to the young is associated with a decline in levels of the orexigenic peptide, ghrelin.53
Small intestine
While small intestinal function is critical to good nutrition in the elderly, its motility does not appear to be substantially altered with healthy ageing but can be affected by a number of systemic illnesses.
Changes in small‐intestinal motor function related to ageing
The small intestine is more difficult to study than the oesophagus or stomach due to its length and relative inaccessibility. Like the stomach, the frequency of its contractions are linked to an underlying electrical rhythm – in this case, between 8 and 12 cycles per minute. The small intestine displays the same fasting cyclical activity as the stomach. However, small‐intestinal manometry, which is carried out in specialised laboratories, has relatively limited clinical application. Transport through the small intestine can be measured more readily by either a breath test (which detects an increase in hydrogen resulting from the breakdown of ingested non‐absorbable carbohydrate, such as lactulose, by colonic bacteria, and therefore reflects oro‐cecal transit) or by scintigraphy.
Small‐intestinal MMC periodicity was not altered in healthy elderly volunteers age 81–91 when compared with the young, using ambulatory jejunal recording, although the propagation velocity of phase III was modestly slower. In the elderly, the amplitude and frequency of pressure waves were comparable to the young during phase III of the MMC and postprandially, but more propagated clustered contractions during fasting and postprandial recordings.54 The functional significance of the latter phenomenon is unclear, but similar patterns are seen in patients with irritable bowel syndrome. Nevertheless, small‐intestinal transit in the healthy elderly seems to be comparable to that in the young, in contrast with the delayed transit characteristic of the colon.13 This is consistent with the observation that small‐bowel bacterial overgrowth is uncommon in healthy older individuals.55
Ageing is associated with an increased prevalence of conditions such as diabetes that potentially affect small‐intestinal motility as well as small intestinal diverticula. Such conditions may induce stasis of small‐intestinal contents and, together with the reduction in gastric acid secretion often seen on the elderly, predispose to bacterial overgrowth, a potential cause of malnutrition and diarrhoea.56 However, it should be noted that bacterial overgrowth is rare in the healthy elderly.57 Small bowel bacterial overgrowth may be diagnosed by culture of duodenal aspirates or by hydrogen breath tests (with glucose or xylose as a substrate), although reports as to their sensitivity and specificity
