SmartPill Monitoring for Assessment of GI Function in SCI

Total Transit Time Total transit time (TTT) is simply the amount of time (hours) it takes for a meal to travel from the mouth, through the digestive tract and for its waste by-products to be eliminated through a bowel movement. Inter-individual TTT can vary greatly due to dietary habits, age, climate, exercise habits, immobility, medications and other lifestyle variables. Due to these multiple variables, a general TTT for the public cannot be determined. It is clear however, that a healthy person should have a total transit time ranging from 8 to 14 hours, resulting in one to three loose bowel movements every 24 hours. People who are in good physical condition, consume fiber-rich diets, and take no constipating medications are most likely to have a normal TTT. Colonic transit time (CTT) is the amount of time it takes for a partially digested meal to travel from the terminal ileum, through the large bowel and for its waste by-products to be eliminated through a bowel movement.

There are several ways to measure TTT. Each requires ingesting a tracking device or a tracer that can be monitored as it moves throughout the digestive system.

Total transit time has been traditionally measured using radiopaque markers1. This technique is simple and inexpensive and can be performed in any radiology department. Several other methods have been suggested, including the single-marker bolus technique (ingestion of markers on a specific day followed by several x-rays until all markers are passed) or multiple-marker bolus technique (ingestion of markers each day for several days followed by single or multiple abdominal x-rays). Radiopaque markers have been widely used to measure total transit. This technique provides valuable clinical information and has been proven to be reliable and reproducible.

Scintigraphy can be used as an alternative to the radiopaque marker technique for measuring TTT. The tagged material is surrounded by a substance that dissolves once it arrives at the colon. Another technique widely used in the past is the Hydrogen Breath Test which measures the transit time of the meal from the mouth to the cecum. The meal reaching the colon is indicated by a rise in the relative hydrogen content in exhaled air2,3. While many valid GI assessment techniques exist, many are invasive and impose many inconveniences for patients.

A relatively new device, the SmartPill, offers the ability to assess many GI variables including temperature, pressure, pH, and transit time while minimizing the invasive nature of investigation. The SmartPill is a small wireless capsule that is ingested by the patient. Values for pressure, temperature, and pH are transmitted continuously from the capsule to a receiver carried by the patient until the capsule is excreted during normal evacuation. This information is then downloaded onto a master computer and expressed graphically for comparative purposes.

Purpose of measuring TTT Measuring TTT is useful in evaluating patients with constipation, abdominal bloating, and refractory irritable bowel syndrome. It provides quantitative information about total transit, enables the identification and characterization of transit abnormalities, and allows assessment of the severity of the problem as well as the response to therapy.

Disorders Affecting TTT Intestinal Motility Disorder (IMD) may be due to primary or secondary causes depending on endogenous or exogenous etiologies. This would include several asymptomatic conditions, such as maldigestion, achalasia, or alkaline bile reflux from the duodenum to the stomach. Intestinal pseudo-obstruction (Ogilvie syndrome), irritable bowel syndrome (IBS), fecal incontinence, and constipation are all conditions related to disordered intestinal motility. Many common drugs (tricyclic antidepressants, diuretics, laxatives, lithium salts, vinca alkaloids, chemotherapy agents, etc.) may interfere with intestinal motility on the receptor level or by interfering with the parasympathetic nervous system, which largely controls GI motility. Drugs such as benzodiazepines, lithium salts, laxatives, and codeine cause secondary stasis4. The latter can produce narcotic bowel syndrome, which is usually observed in patients who abuse opiates for chronic pain. Endocrine disorders, such as myxedema, can also cause gastrointestinal obstruction due to the decrease in the thyroid hormone level as well as an imbalance in sodium and potassium metabolism.

CTT in SCI patients The magnitude of bowel dysfunction in spinal cord injury patients has been documented in several studies. Spinal cord injury affects colorectal motility, transit times, and bowel emptying, often leading to constipation, fecal incontinence or a combination of the two. Although these symptoms are not life-threatening, they may negatively impact quality of life as well as increase levels of anxiety and depression5.

Abnormal bowel function is one of the most bothersome problems in patients with SCI. While it is known how bowel dysfunction affects quality of life, research examining the pathophysiological causes of bowel dysfunction are limited. Moreover, most studies have provided only partial information on bowel dysmotility, focusing on only CTT or anal dysfunction, rather than identifying a comprehensive neurogenic bowel pattern according to different neurological abnormalities and clinical manifestations.

Constipation, obstructive defecation, and fecal incontinence are known to be frequent complications in SCI. However, their presence and severity are not homogeneous in all patients and depend on the integration of mechanisms such as abdominal compression, colorectal motor activity, and anal sphincter function as well as digitalization for bowel evacuation. Paralleling these complications, CTT is increased in SCI subjects when compared with the normal populations. Recent clinical studies of individuals with SCI have identified prolonged CTT in 57% of the subjects6. While these studies investigated the correlation between intestinal symptoms and the level of SCI, the relationship between intestinal symptoms and the changes in CTT were not evaluated. While several studies have identified prolonged CTT in SCI patients, other investigations have not produced consistent findings7, 8.

The present study aims to evaluate multiple variables of GI function in both patients with SCI and able-bodied controls using the SmartPill device. In comparing values for TTT, CTT, pH, temperature, and pressure in patients with SCI to healthy, able-bodied controls, the SmartPill device may provide valuable insight into the pathophysiological implications of SCI on GI function.