Address for correspondence Radu Tutuian, MD, Division of Gastroenterology, Medical University of South Carolina, 96 Jonathan Lucas Street, Suite 210 CSB, Charleston, SC 29425, USA. Tel.: + 1 843 792 7522; e-mail: firstname.lastname@example.org
Abstract Multichannel intraluminal impedance (MII) allows assessment of intraoesophageal bolus transit. In the supine position, bolus transit is produced almost exclusively by peristaltic contractions; in the upright position, gravity also contributes to bolus transit. MII and peristaltic pressures were measured in four positions (0, 30, 60 and 90°) using ten swallows (5 cc each) of both water and viscous liquid with body position determined by random choice. Tracings were analysed for total bolus transit time: time interval between bolus entry at 20 cm above and bolus exit at 5 cm above the lower oesophageal sphincter (LOS) and contraction amplitudes at 5 and 10 cm above the LOS. Statistical comparison of mean values of all four body positions was done using anova and Bonnferoni post-test. Ten normal subjects (five females and five males, age 24–45 years) completed the study. At each body position, liquid material transited faster (P < 0.001) than viscous material. Both liquid and viscous materials transited at lower inclinations (0 and 30°) significantly slower than at higher inclinations (60 and 90°). There was an almost perfect inverse linear correlation between angle of inclination and bolus transit time for both liquid (r = −0.99) and viscous (r = −1.00) boluses (Spearman correlation r > 0.99 and P < 0.02 for both substances). Contraction amplitudes for liquid vs viscous material were not significantly different at a given degree of inclination. Mean distal oesophageal amplitude declined with increasing inclination. Combined MII–OM identifies and quantifies the effects of gravity on the dichotomy between specific pressures measured by OM and function assessed as transit measured by MII.
Oesophageal manometry (OM) was initially performed using water-perfused systems requiring the patient to be supine position in order to ensure a proper alignment with external sensors.1,2 Eliminating the effects of gravity in the supine position also maximizes the workload required from the oesophageal musculature in propelling bolus from the pharynx to the stomach.3
Introducing solid-state sensors eliminated the necessity of horizontal alignment of patients with external sensors. This breakthrough also encouraged the idea of testing oesophageal contractions in a more physiologic, upright position. Studies have shown potential misdiagnoses when upright studies were compared to supine normative data.4,5 As an alternative, a mild inclination (i.e. 30–45°) has been proposed although normative data for these positions are not readily available.
Early radiographic studies indicated liquid boluses transit the oesophagus faster than viscous boluses.6–8 Radionuclide studies also found that supine posture delayed emptying of both solid and liquid boluses9 with occasional asymptomatic trapping of non-liquid materials in the distal oesophagus.10 The influence of viscosity on oesophageal peristalsis has been documented in pervious manometric studies.11
Recently, evaluation of bolus transit without radiation became available using multichannel intraluminal impedance (MII).12 This technique uses differences in resistance to alternating current between air, bolus and oesophageal wall to determine intraoesophageal bolus transit.13 Combining MII and OM (MII–OM) allows simultaneous evaluation of oesophageal contraction and bolus transit, i.e. oesophageal function testing.14
The aim of our study was to use combined MII–OM to compare oesophageal contractions and bolus transit to test the hypothesis that oesophageal function changes at various degrees of inclination.
After local IRB approval of the protocol, ten healthy volunteers (five females and five males, age range 25–45 years) underwent oesophageal function testing using combined MII–OM with a Koenigsberg eight-channel probe (Sandhill EFT catheter; Sandhill Scientific Inc., Highlands Ranch, CO, USA). All subjects provided informed consent prior to enrolment. The catheter design has two circumferential solid-state pressure sensors at 5 and 10 cm from the tip and two unidirectional pressure sensors at 15 and 20 cm. Impedance-measuring segments, consisting of two rings placed 2 cm apart, were centred on 10, 15, 20 and 25 cm from the tip. The EFT catheter was inserted transnasally into the oesophagus up to a depth of 60 cm. Lower oesophageal sphincter (LOS) was identified using the stationary pull-through technique and the most distal sensor was placed in the high-pressure zone of the LOS. Intraoesophageal pressure sensors and impedance-measuring segments were thus located at 5, 10 and 15 cm above the LOS and 5, 10, 15 and 20 cm above the LOS, respectively (Fig. 1). Subjects were randomly assigned to each of four testing positions (0, 30, 60 and 90°) by adjusting the incline of an examination table according to a pre-established randomization scheme. In each position, subjects were given ten swallows of 5-cc liquid (water consistency) and ten swallows of 5-cc viscous (apple-sauce-like consistency) materials each 20–30 s apart. Double-swallowing disqualified swallows and these were repeated.
Manometric parameters used to characterize swallows included: (i) contraction amplitude at 5 and 10 cm above the LOS, (ii) distal oesophageal amplitude (DOA) as average of contraction amplitude at 5 and 10 cm above the LOS, and (iii) onset velocity of oesophageal contractions in the distal part of the oesophagus (i.e. between 10 and 5 cm above the LOS).
Bolus entry at a specific level was considered at the 50% point between 3-s pre-swallow impedance baseline and impedance nadir during bolus presence and bolus exit and was determined as return to this 50% point on the impedance recovery curve (Fig. 2). Impedance parameters included: (i) total bolus transit time (TBTT) as time elapsed between bolus entry at 20 cm above the LOS and bolus exit at 5 cm above the LOS and (ii) bolus head advance time as time elapsed between bolus entry at 20 cm above the LOS and bolus entry at 5 cm above the LOS.
Swallows were manometrically classified as: (i) normal if contraction amplitudes at 5 and 10 cm above the LOS were each greater or equal to 30 mmHg and distal onset velocity was less than 8 cm s−1; (ii) ineffective if any of the contraction amplitudes at 5 and 10 cm above the LOS was less than 30 mmHg; (iii) simultaneous if contractions amplitudes at 5 and 10 cm above the LOS were each greater or equal to 30 mmHg and distal onset velocity was greater than 8 cm s−1.
Swallows were classified by MII as showing: (i) complete bolus transit if bolus exit points were recorded in all three distal impedance-measuring sites (i.e. 15, 10 and 5 cm above the LOS) and (ii) incomplete bolus transit if bolus exit was not identified at any of the three distal impedance-measuring sites within 15 s.
anova (using a general linear model) with patient, substance (liquid vs viscous) and position as independent variables was used to assess differences in oesophageal amplitudes, TBTT and bolus head advance time (dependent variables). For statistical significance, alpha was set at 0.05. Post-hoc Bonferroni test were used to assess differences between positions.
All ten subjects completed 80 swallows (ten swallows each of liquid and viscous materials at four degrees of inclination: 0, 30, 60 and 90°). Of the total 800 swallows, 636 (79.5%) were manometric normal, 88 (11.0%) manometric ineffective and 76 (9.5%) manometric simultaneous; 757 (94.6%) had complete bolus transit and 43 (5.4%) had incomplete transit. In each position, over 90% of swallows had complete bolus transit while manometric effectiveness decreased from 84 to 54% with increasing inclination from 0 to 90° (Fig. 3).
DOA (mean ± SEM) of manometric normal swallows decreased significantly (P < 0.01) with inclination from 114.1 ± 3.9 (at 0°) to 89.9 ± 3.6 mmHg (at 90°) for liquid and from 121.6 ± 4.1 (at 0°) to 100.6 ± 4.0 mmHg (at 90°) for viscous material. Similarly, TBTT also decreased significantly (P < 0.001) from 7.4 ± 0.1 (at 0°) to 5.9 ± 0.1 s (at 90°) for liquid and from 8.1 ± 0.2 (at 0°) to 7.1 ± 0.1 s (at 90°) for viscous material (Fig. 4).
Both DOAs and TBTTs were significantly different for liquid and viscous boluses at all degrees of inclination (P < 0.05 with anova – GLM for position and substance). TBTT and DOA also decreased significantly (P < 0.01) with inclination. Bonferroni post-hoc test pairwise comparison indicated significant differences between 0 and 60, 0 and 90, 30 and 60, and 30 and 90°, but no significant difference between 0 and 30 and 60 and 90°.
Significant differences in DOA and TBTT were observed when comparing combined low inclinations (0 and 30°) with combined steeper inclinations (60 and 90°), but no significant difference was found between 0 and 30 and 60 and 90°.
Correlation of angle of inclination (independent variable) and mean TBTT (dependent variable) revealed a significant (P < 0.001) almost perfect negative correlation for both liquid (r = −0.99) and viscous swallows (r = −1.00). The slope of negative correlation for liquid (B = 0.02) was steeper (anova, mean TBTT liquid vs viscous, P = 0.01) than the negative correlation slope for viscous material (B = 0.01) indicating that position has less effect on bolus movement of more viscous material swallowed.
The results of this study identify and compare the influence of gravity at various degrees of inclination on oesophageal pressures and intraoesophageal bolus transit. Normal subjects completely transit more than 90% of liquid or viscous bolus materials at any degree of inclination despite the fact that contraction pressures decrease and less oesophageal contractions fulfil manometric normal criteria with increase in inclination.
Using radionuclide studies, Maddern et al.9 published a study in 25 subjects comparing oesophageal emptying of liquid and solid (marshmallow) materials. According to this study, oesophageal emptying (defined as 95% radioactivity entering the stomach) for liquids requires 10 s in the supine position and 6 s in the upright position. Our findings are very similar given the fact that in our study bolus transit between 20 and 5 cm above the LOS accounts for TBTT.
Sears et al.4 comparing upright and supine manometric findings, found that using supine normal values to interpret upright manometric studies would result in over-diagnosis of oesophageal motility abnormalities. Our results are consistent with this prior conclusion and expand it using MII to show that there is a more profound effect of body position on contraction pressures than on actual bolus transit.
Dooley et al.15 published a study in six normal volunteers comparing oesophageal contractions elicit by viscous and liquid boluses. They found that liquid boluses elicit lower contraction amplitude in the upright position compared to the supine position where viscous material presented similar contraction amplitudes in upright and supine positions. Possible explanations for the discrepancy between our results and other published results might be differences in viscosity, osmolality, pH of viscous bolus materials and equipment (i.e. water-perfused systems vs solid-state pressure transducers) used.
As the majority of swallows have complete and increasing intraoesophageal transit despite decreasing contraction amplitudes in more upright positions, our findings support a conclusion that contraction amplitudes and manometric effectiveness have less influence on bolus transit in non-supine positions.
Hewson et al.,16 combining manometry and video-fluoroscopy in 20 patients (13 of whom had manometric diagnosis of DES), found a good correlation of increased onset velocity (>6.25 cm s−1) with incomplete bolus clearance from the oesophagus (98% sensitivity and positive predictive value). In our study, the majority of swallows considered being simultaneous by velocity criteria (>8 cm s−1) in normal volunteers showed complete bolus transit. This same effect was seen in a recent multicentre study of combined OM and MII in 48 healthy volunteers.17 These observations raise important questions about the validity of current manometric definitions of simultaneous contractions and their functional importance and imply that the MII technique may help provide some clarity to the concept of what a functional oesophageal spasm is. Also, simultaneous video-fluoroscopy and combined MII–OM studies are warranted to validate the MII findings in patients with abnormal oesophageal contractions against video-fluoroscopy, currently the ‘gold standard’ in oesophageal bolus transit.
Even though contraction amplitudes required to propel viscous material were similar to those required to propel liquid material at the same degrees of inclination, bolus transit times for viscous materials were significantly longer. Viscous material also showed less gravity-dependent decrease of bolus transit compared to liquid material. These findings suggest that viscous materials may provide a greater stress and should be included when testing oesophageal function.
In addition, the ability of combined MII–OM to evaluate bolus transit studies in patients with manometric abnormalities at various degrees of inclination may help provide better understanding of the relationship of abnormal supine manometric findings to those found with more physiologic upright swallowing.
In conclusion, combined MII–OM identifies and quantifies the effects of gravity on the dichotomy between specific pressures measured by OM and function assessed as transit measured by MII.