**2. Esophageal function**

The evaluation of the esophageal function is not clearly defined because its disfunction is mainly due to neuromuscular disorders, so its pathophysiology is complex.

However, esophageal manometry and 24-hour pH-impedance monitoring are two useful tests to classify the organ's disorders [2].

#### **2.1 Manometry**

Manometry is considered as the gold standard [3] to diagnose motor alterations of the esophagus. Conventional examination uses mostly water-perfused probes, with recording points placed every 5 cm along the length of the esophageal catheter, in order to measure internal contraction and pressure. However, high-resolution manometry (HRM) is nowadays the most accurate and available tool. HRM is equipped with high-resolution solid-state catheters that transmit data on the internal condition of the esophagus, which are then converted into graphs (topography plots, EPTs). The probes are placed every 1 cm, for a total of 32–36 transducers all along the organ [4].

In the standard procedure the patient is placed in a supine position in order to eliminate the gravitational effect, and a basal recording is made for 30 seconds, followed by at least 10 consecutive swallowings, during which various parameters of esophageal peristalsis are detected and recorded, the main ones being DCI (Distal Contractile Integral) and DL (Distal Latency).

The DCI represents the contractile vigor of the esophagus, i.e., amplitude x duration x length of contraction of the distal esophagus with an isobaric contour of 20 mmHg.

The DL (measured in seconds) is the interval between relaxation of the UES and the point of deflection along the 30 mmHg isobaric contour where the propulsion velocity slows (contractile deceleration point, CDP): it represents an indirect measure of post-deglutitive inhibition and thus normal peristalsis [3].

It has to be mentioned the IRP (Integrated Relaxation Pressure, in mmHg), which is defined as the mean pressure of the EGJ measured for 4 contiguous or not-relaxation seconds, during the ten seconds following deglutive relaxation of the UES [5].

The first step of the data analysis is focalized on the evaluation of the esophagogastric junction (EGJ): basal pressure of the lower esophageal sphincter (LES), IRP and crural diaphragm (CD) are evaluated, and junction subtypes are defined.

The Lyon Consensus [6] proposes to study EGJ in two different ways, from an anatomic and morphologic point of view and then from his contractility.

Morphologically, three types of junctions are described, where type 3 is associated with decreased LES pressure due to anatomical separation >3 cm between LES and CD. By the second measurement the EGJ-CI (EGJ Contractile Integral) is calculated, which measures the level of barrier provided by the junction.

The second step is about evaluating the peristalsis of the esophageal body, based on various parameters including the DCI and the interruptions of the isobaric

#### *Gastrointestinal Physiopathological Testing for Upper GI Functional Disorders DOI: http://dx.doi.org/10.5772/intechopen.97550*

contour of 20 mmHg, although with the latest Chicago classification (CC v3.0) it has been proposed to eliminate this last parameter from the assessment of esophageal contractile force, and to consider it as a descriptor of the contractile pattern [7]. So, contractile vigor can be described as absent (DCI <100 mmHg·s·cm), weak (DCI >100 but <450), inefficient (absent or weak), or hypercontractile (DCI ≥8000); contractile pattern instead can be premature (DL >4.5 sec), fragmented (interruptions >5 cm on the isobaric contour with DCI >450) or normal [3, 5].

Basing on the results obtained from the manometry, the patient is included in one of the four groups describing esophageal motility, as defined in CC v3.0 [8]:


**Figure 1.** *Chicago classification on HRM [8].*

#### **2.2 24-hour pH-impedance monitoring**

24-hour pH-impedance monitoring is today the most useful and sensitive test to study every type of reflux episode, its composition, proximal extension, duration and clearance. It is based on the simultaneous measurement of pH and endoluminal electrical impedance: a pair of electrodes correspond to an impedance segment that provides a measure of impedance (resistance): it is inversely proportional to conductivity, increasing if air is passing through the esophagus and decreasing if water/swallowed material or reflux is passing through it [9].

By combining the two measurement, the chemical nature and the physical nature of the reflux episode can be defined as acid, weakly acidic, weakly alkaline and liquid, gaseous or mixed.

Changes in pH occurred simultaneously with impedance drops of at least 50% are classified as follows:


Furthermore, a liquid episode is defined as a retrograde flux (to the proximal esophagus) capable of changing the basal impedance value by at least 50% in two consecutive channels; a gaseous episode, on the other hand, corresponds to a simultaneous increase in impedance >3000 Ω in two consecutive channels, with a channel having an absolute value >7000 Ω. Finally, a mixed episode is a gaseous reflux that occurs during or immediately after a liquid one [10].

By measuring the impedance on different levels of the esophagus the extension of reflux can be determined; it is relevant if the pH is altered at 15 cm cranially from the LES [11]. Moreover, the Acid Exposure Time (AET) can be calculated: a total exposure of less than 4% is judged normal while a value >6% is surely pathologic, and the total number of refluxes is considered normal if <54 [12]. The temporal

#### **Figure 2.**

*(A) Weakly acidic reflux episode, (B) acidic episode, (C) weakly alkaline episode, (D) superimposed episode [9].*

*Gastrointestinal Physiopathological Testing for Upper GI Functional Disorders DOI: http://dx.doi.org/10.5772/intechopen.97550*

correlation between reflux episodes and symptoms is analyzed by measuring three parameters: the Symptom Index (SI), the Symptom Association Probability (SAP) and the Symptom Sensitivity Index (SSI). Additionally, two more parameters have been recently introduced, namely the Post reflux Swallow- induced Peristaltic Wave (PSPW) index, and the Mean Nocturnal Baseline Impedance (MNBI). The former refers to a vagal reflex that is activated after reflux and consists of swallowing that raises esophageal pH. The latter reflects the permeability of the esophageal mucosa and low values are related to alterations in tight junctions1 . Thus, calculation of MNBI and PSPW together is useful in general to improve the yield of pH-impedance testing [13], and is particularly advantageous when the diagnosis of gastroesophageal reflux disease is doubtful (e.g., with normal AET and discordant SAP and SI) to distinguish patients with hypersensitive esophagus from patients with functional heartburn [14].

In conclusion, 24-hour pH-impedance monitoring is a test which is not so specific for functional disorders, but it allows to analyze multiple parameters. It allows therefore to make a diagnosis of gastroesophageal reflux disease, or to exclude it when there are doubts, as well as to distinguish the typical forms of reflux from those belonging to functional disorders (for example functional heartburn or reflux hypersensitivity).
