TSRA Content:
Author: Navid Ajabshir, MD
This is a revision and update from the previous edition of the TSRA Primer in Cardiothoracic Surgery written by Shawn Growth, MD
Esophageal physiology testing includes identifying issues with function, as well as issues with acid reflux. Manometry provides both anatomic and functional information about the upper and lower esophageal sphincters (UES and LES, respectively), total and intra-abdominal lengths, resting pressure (LESP), and swallow-induced LES relaxation. Manometry also provides information about esophageal body contractions during swallowing (i.e., distal esophageal amplitude [DEA], duration, onset velocity, and presence of aberrant contractions). Though esophageal manometry may be conducted without it, impedance provides invaluable additional information about the effectiveness of peristalsis, as well as the identification of non-acidic reflux. Lastly, pH testing can provide objective data about esophageal exposure to acidity.
High-Resolution Manometry (HRM)
In general, manometry studies are performed after having fasted for at least 6 hours, and it should be avoided if endoscopy or upper GI series were recently performed. In HRM, the catheter is lubricated and passed transnasally until the tip reaches the stomach, much like placing a simple nasogastric tube. Next, the patient is placed supine and 5 minutes of baseline recording is obtained without swallowing. Then, 10 swallows of water are performed. These consist of a period of swallowing 5 mL of water, followed by a 30-second stabilization period. This allows esophageal muscle to properly repolarize and helps contractions to be more organized and uniform on subsequent swallows. HRM has largely replaced conventional water-perfused or micro-transducer systems. As compared with conventional catheters, HRM catheters use more sensors spaced at shorter intervals (up to 36 sensors at 1 cm intervals), which allows data to be extrapolated between the sensors. Output can be expressed as conventional line plots for each sensor or as an integrated color esophageal pressure topography (EPT) plot, also known as a Clouse plot (Figure 1A). This presents swallow data more dynamically and allows precise interpretation of peristalsis. Here, movement artifact is reduced, and recognition of anatomic landmarks is simplified. Therefore, the catheter does not need to be manipulated during the study or repositioned relative to anatomic landmarks. Despite this, several variables may alter interpretation of the findings, such as anxiety/stress, coughing, gagging, Valsalva, eructation, deep inspiration, and so forth. Medications that can alter esophageal motility (i.e., nitrates, calcium channel blockers, anti-cholinergics, and promotility agents) should be held for 24 hours prior to the study. The report should include tracings of each of the ten swallows, as well as numeric data of measurements such as: LES mean integrated relaxation pressure (IRP) (a pressure > 15mmHg is considered a hypercontractile LES), mean and peak distal contractile indices (500-5000 is considered normal), and several other parameters to help identify esophageal motility pathology (Figure 1B).
Figure 1A. HRM Result Esophageal Pressure Topography Plot
Figure 1B. HRM Numeric Data
Multichannel Intraluminal Impedance-Manometry (MIIM)
The MIIM catheter is slightly different in that there is a respiratory channel (at the top), 4 esophageal body channels (4 impedance and 4 manometry tracings in the middle), and 1 LES channel (at the bottom). The esophageal body channels are in order from proximal to distal. For instance, the top impedance tracing corresponds to the same depth as the top manometry tracing (Gallery 1, Figure 2). Focus on the manometry tracings associated with the distal esophagus (e.g., the bottom 2 tracings in Figure 2) since motility disorders relevant to surgeons affect smooth muscle.
The procedure is carried out much like HRM. After calibrating, the catheter is advanced through the nose to a depth of 60 cm. First, the catheter is slowly pulled back to map the length and resting pressure of the LES. Next, the catheter is positioned with its distal sensor 3 cm above the proximal border of the LES. The esophageal resting pressure is established to serve as a baseline for measuring esophageal body contractions. The patient is then given a minimum of ten 5 mL boluses of room temperature water. Again, it is important to wait 30 seconds after dry or liquid swallows to allow the esophageal smooth muscle to repolarize and avoid the confounding effect of deglutive inhibition. Supplementing the study with ten additional swallows of a viscous solution is beneficial for assessing bolus transit. Ignore the manometry output associated with viscous swallows since its use hasn't been validated. Finally, the LESP is reassessed. For patients with striated muscle abnormalities (i.e., scleroderma), the upper esophageal sphincter can be mapped using a similar slow pull-through technique; the patient is then given 5 liquid swallows to assess striated muscle contractions.
Though many MIIM systems have built-in computer-generated analyses, the computer’s interpretations are often inaccurate. Thus, it is critical that the reviewer precisely edit the study to allow proper interpretation. Impedance tracings are an important adjunct to this physiological testing modality. Recall that impedance measures opposition to the flow of an alternating current and is inversely related to the conductivity of a substance (i.e., high impedance = low conductivity). The baseline of an impedance tracing reflects the inherent impedance of the esophageal mucosa. After a liquid swallow, there is initially an upstroke from a bolus of air (which has higher impedance [lower resistance] than the esophageal lining) that accompanies a swallow followed by a dip in the tracing from the liquid or viscous swallow (which has lower impedance [higher resistance] than the esophageal lining). By convention, bolus entry is defined by a 50% drop from baseline, and bolus clearance is defined by a return to at least 50% of baseline and maintained for seconds. For normal bolus transit, one should be able to demonstrate where the bolus enters (on the proximal tracing) and exits (on the distal tracing) (Gallery 1, Figure 2). A stepwise downward progression of the contractions should be noted from proximal (top) to distal (bottom). Other types of contractions can also be seen, including multiple peaked, non-transmitted/ineffective (amplitude <30 mmHg), non-peristaltic, spontaneous, and retrograde contractions.
pH MONITORING
pH monitoring is another important physiology study in the management of esophageal disease. It is performed in patients who experience reflux, heartburn, regurgitation, chest pain, cough, throat clearing, or nausea, without improvement in symptoms with medications. Data obtained varies depending on the modality used. Patients should fast for 4 to 6 hours before the study. To avoid misrepresentation, the following medications should be discontinued: antacids (for at least 6 hours), H2 blockers (for at least 2 days), and proton pump inhibitors (for at least 7 days). Two of the most used modalities are the Bravo™ wireless pH study and combined multiple intraluminal impedance (MII)-pH monitoring. A 24-hour probe also exists, though this will not be discussed as use has greatly been supplanted by the Bravo™ system. Testing is routinely done in an ambulatory fashion. After placement, the patient is instructed to go about his or her daily activities as if the monitoring device was not in place. The results are expressed as a composite pH (DeMeester) score, which is calculated from the following information:
- Total % time pH < 4
- Upright % time pH < 4
- Supine % time pH < 4
- Total number of reflux episodes
- Total number of reflux episodes > 5 min
- Longest reflux episode (minutes)
A diagnosis of gastroesophageal reflux disease is confirmed if the total % time pH <4 is above 4.3% or if the DeMeester score is ≥14.72.
Bravo™
This is a small capsule that is affixed to the lumen of the esophagus 5-6 cm above the squamocolumnar junction by endoscopy. It wirelessly transmits information to a small receiver that the patient must return after the procedure for interpretation of the results. The patient is instructed to indicate on the receiver when they are having meals, when they are lying down (head of bed 30 degrees or less), and when they are having symptoms of chest pain, regurgitation, or heartburn. A diary may be used as a backup. This data is then correlated to the pH input from the capsule. The capsule is passed in the stool usually 4 to 10 days after placement. Patients should avoid MRI for 30 days as a precaution. Continuous pH measurements are typically obtained for 24 to 48 hours or up to 96 hours.
MII-pH
Here, reflux is detected by changes in intraluminal resistance. It determines the presence of liquid or gas in the esophagus by alternating an electrical current between two electrodes. The probe has multiple electrodes; thus, it can measure reflux at different sites. In doing so, the benefits of MII-pH testing over a Bravo pH study include the ability to measure both acid (pH < 4) and nonacid (pH > 4) reflux (i.e., biliary, food, saliva), as well as demonstrate the proximal extent of reflux. This method is preferred for testing patients with symptoms despite PPI/H2
blocker therapy, patients with severe symptoms that cannot tolerate being off their medications, and patients with extra-esophageal symptoms, such as a chronic cough. Unfortunately, Barrett’s esophagus and esophagitis create a low impedance environment, which can alter the detection of liquid reflux.
This technique requires nasal intubation of a catheter, after which the pH probe is positioned 5 cm above the squamocolumnar junction. When the patient experiences a symptom, he or she is instructed to hit a button denoting an event on a portable monitoring system and to write down the event in a diary. After 24 hours, the catheter is removed. The output is displayed as a series of impedance tracings (going from proximal [top] to distal [bottom]) and pH tracing at the bottom of the screen. By convention, reflux is defined as retrograde bolus entry (a 50% drop in ohms) in at least 2 consecutive distal impedance channels. This is often followed by an antegrade bolus transit (from clearing the refluxate with a swallow) (Figure 3). In addition, the proximal extent of reflux (noted by the most proximal impedance tracing that demonstrates bolus entry) can be evaluated. The recordings can also be used to correlate symptoms with reflux events, known as the Symptom Index (SI). The SI is calculated by the following formula: the number of symptoms that occurred with retrograde bolus movement divided by thetotal number of times symptoms were reported, multiplied by 100. By convention, a symptom index above 50% is considered significant.