Radio-isotope gastric emptying studies represent the current standard methodology to quantify gastric emptying after a test meal. A wide range of test meals is available, and although widely available the test is poorly standardized [4]. Alternative methodologies to assess gastric emptying include use of radio-opaque markers, breath testing, and gastric ultrasound—however, these are less studied with less well-established reproducibility and clinical correlation.

The WMC provides an indirect measure of meal emptying, since it depends on the gastric housekeeping contractions to remove the indigestible capsule, the assumption being that such motor activity follows meal digestion [33]. This assumption was found to be justified, with strong correlation between meal and capsule emptying [6, 15]. In healthy controls, the WMC cleared the stomach after 97 % of the test meal had cleared the stomach [6]. When gastroparesis patients defined by symptoms and a documented delayed gastric isotope emptying test within the past 2 years, there was a strong correlation between capsule—and isotope-measured transit [15]. The methodology for defining delayed emptying with the WMC uses a 5 h cutoff to signify delayed gastric emptying [15]. However, for the isotope study, Tougas et al. [15] demonstrated that after test meal ingestion in healthy subjects, the 95th percentile gastric emptying at 4 h is >90 % of the meal [31]. Interestingly, only 44 % of gastroparesis patients had a positive repeat isotope test while 65 % had a positive WMC test. This reflects both the poor reproducibility of the isotope study as well as the fact that it measures only fasting gastric emptying, whereas WMC measures fasting and fed emptying.

There is no standard measurement modality to assess small bowel transit. Radiology contrast series provide nonrepresentative data (fasting conditions, non-physiologic “meal”) with no normal transit ranges available and exposure to ionizing radiation. Small bowel scintigraphy, breath testing and latterly MRI, have also been used to evaluate SBTT but there is poor standardization of techniques [19].

Using the pH profiling described, the WMC technology allows for determination of SBTT . A small healthy volunteer study comparing SBTT values obtained from scintigraphy with WMC reported good correlation [3, 18]. The clinical correlation of symptoms and slow small bowel transit require further determination, especially with the emerging data on the possible significance of small intestinal bacterial overgrowth in patients with IBS [26].

Of all established motility measurements, CTT is the one with a proven utility, namely in patients with chronic constipation, especially when refractory to conservative therapy [8]. Marker studies (comprising abdominal X-ray after ingestion of capsules containing tiny radio-opaque shapes) are the most widely used methodology, and this is a relatively noninvasive methodology of segmental as well as whole colonic transit. It is, however, poorly standardized (Metcalf et al. 1987). A less widely available alternative is whole gut radio-isotope scintigraphy, which can more accurately assess segmental transit time, but is hindered by expense and exposure to radiation [13].

Colonic transit data generated by the WMC correlate well with radio-opaque marker study data both in control subjects and patients with constipation [5, 23].

The existing standard for measurement of antroduodenal motility is ambulatory solid-state manometry. This is undertaken following nasal intubation of the antroduodenum with a catheter bearing multiple pressure transducers allowing simultaneous recording of contractions at multiple sites. However, it is an invasive investigation, requiring fluoroscopic screening to place the catheter, and considerable expertise to interpret the results.

The single-point measuring technology in WMC has been studied in healthy and gastroparesis subjects [12]. Overall, gastroparetics had a 35–50 % reduction in stomach and small bowel contraction frequency compared with healthy subjects. This was especially true for patients with severe gastroparesis as defined by abnormal isotope gastric emptying, possibly reflecting ineffective migrating motor complexes required to empty the capsule from the stomach [12].

Ambulatory small bowel manometry has been shown to have a role in the assessment of patients with gastroparesis [21] and in differentiating between visceral myopathy and neuropathy [29]. In essence, patients with enteric neuropathy lose the increased motility response seen after meals. Brun et al. [3] have shown that WMC measured delay in small bowel transit correlates with reduced proximal small bowel contraction frequency and amplitude.

Colonic manometry is a classical measurement, but despite being available for many years has failed to find a distinct clinical role. An ambulatory technique is deployed, involving placement of a solid-state catheter with multiple pressure ports via the anus into the colon under endoscopic or radiological guidance after bowel preparation [7]. As such the test is non-physiological.

A key potential advantage of the WMC is that it can yield a colonic pressure profile without bowel preparation . It remains to be seen whether such data can correlate with standardized motility data and symptoms. In a study of healthy controls and patients with chronic constipation (normal and slow transit) and constipation-predominant IBS (c-IBS), Hasler et al. [11] have demonstrated that colonic pressure activity was greater distally than proximally in health and all patient groups except those with slow transit. Physiologically, it is though that the distal contractions have a role in propelling stool into the rectum. The authors also noted elevated pressure amplitudes in patients with C-IBS.