The impact of lung transplantation on esophageal motility and inter‐relationships with reflux and lung mechanics in patients with restrictive and obstructive respiratory disease

For many patients with lung disease the only proven intervention to improve survival and quality of life is lung transplantation (LTx). Esophageal dysmotility and gastroesophageal reflux (GER) are common in patients with respiratory disease, and often associate with worse prognosis following LTx. Which, if any patients, should be excluded from LTx based on esophageal concerns remains unclear. Our aim was to understand the effect of LTx on esophageal motility diagnosis and examine how this and the other physiological and mechanical factors relate to GER and clearance of boluses swallowed.


| INTRODUC TI ON
Although advances in therapy may delay the progression of chronic lung disorders, many will continue towards progressive respiratory failure where lung transplant (LTx) remains the only option.
However, long-term survival and mortality following LTx remain poor compared with other solid organ transplants.One of the factors that is believed to drive this poor prognosis is repetitive aspiration of gastroesophageal refluxate, injuring the lung epithelium and causing chronic lung allograft dysfunction (CLAD). 1,2ophageal dysmotility and gastroesophageal reflux (GER) are common in patients with respiratory disease, thought to be linked to disease progression, and are also common following LTx.The most common esophageal motor disorders include minor disorders of peristalsis, such as ineffective esophageal motility (IEM) and esophago-gastric junction outflow obstruction (EGJOO), [3][4][5][6][7][8][9] along with Jackhammer esophagus seen in some patients, mainly post-LTx, 4,[6][7][8][10][11][12] IEM is associated with greater numbers of proximal reflux events both in respiratory disease 9 and following LTx, 8 while EGJOO is associated with significantly less GER, despite an apparent increased risk of developing CLAD post-LTx. 8 Altough studies have suggested that distal contractile integral (DCI) 4,6,7 and aperistalsis prior to LTx can improve following LTx, 13,14 it remains unclear whether certain motility diagnoses prior to LTx either remain the same or change to another diagnosis following LTx, and if this differs with type of respiratory disease.Given the differential effects that dysmotility can have on esophageal exposure to reflux, better understanding of the changes in motility diagnosis following LTx may help to explain the current lack of clarity on the effect of LTx on GER, as attested by some studies reporting a worsening 15 but others no effect.4,6,7,10 Moreover, better understanding of changes in motor diagnosis following LTx may have important implications for identifying those at an increased risk of post-LTx complications and guide specific interventions to mitigate these complications.
Other important considerations that have been shown to influence motility, GER or both include (i) disordered lung mechanics including changes in the thoraco-abdominal pressure gradient (TAPG), which can affect the amount of GER and its proximal extent, 9,16 (ii) the effect of lung volume on esophageal length (EL), which can adversely affect esophageal motor function, 7 (iii) the presence of an abnormal post-reflux swallow induced peristaltic wave (PSPW), which has been shown to associate with increased bolus clearance time and proximal extent on reflux events, along with worse disease progression in patients with idiopathic pulmonary fibrosis (IPF), 8,17 and finally (iv) the level of contraction reserve (CR), as measured using the multiple rapid swallow (MRS) test, which theoretically could impact improvement in motility post-LTx.How these associate with type of respiratory disease and are affected by LTx is uncertain.
Lastly abnormal swallowing and impaired clearance of swallowed boluses, especially in the presence of EGJOO might be an important risk factor for aspiration, lung injury and the development of o-CLAD. 8We have shown that 66% of IPF patients' exhibit incomplete transit of boluses swallowed, and that the proportion of swallows that are associated with incomplete bolus transit directly correlates with the proportion of esophageal peristaltic events that are ineffective. 9Whether LTx improves clearance of boluses swallowed remains unknown.
All these factors continue to hinder the development of consensus guidelines on whether certain patients with end-stage lung disease should be prioritized more than others to undergo LTx based on difficult to predict and requires other GI, anatomical and pulmonary factors to be taken into consideration.

| High-resolution impedance manometry
High-resolution impedance manometry (HRIM) was performed using a solid-state catheter with 36 circumferential pressure sensors spaced at 1 cm intervals and 18 impedance channels (Medtronic, Shoreview, MN).The catheter was positioned trans-nasally with the distal sensors for both pressure and impedance in the proximal stomach.Following at least a 30 s baseline to identify the upper (UES) and lower (LES) esophageal sphincter, ten 5 mL saline swallows were given at least 30 s apart with the patient supine. 18This was followed by a MRS sequence involving five 2 mL swallows every 2-3 s in the supine position. 19

| 24 h-pH/impedance
24 h-pH/impedance (Sandhill Scientific, Highlands Ranch, CO) was performed using a single antimony pH probe (5 cm above the LES) with eight impedance electrodes.Each 5 mL swallow was evaluated to determine: (i) integrated relaxation pressure (IRP), (ii) DCI, (iii) distal latency (DL), and (iv) isobaric contour (pressurization). 21Contractile pattern was classified as normal, weak, failed peristalsis, fragmented or hypercontractile swallow. 20 v4.0 diagnoses included: (i) achalasia or EGJOO, and (ii) disorders of peristalsis, such as absent contractility, distal esophageal spasm (DES), hypercontractile esophagus (single peak hypercontractile swallow, Jackhammer esophagus and hypercontractile lower esophageal sphincter) and IEM. 20 was determined from the ratio between MRS DCI and mean single non-failed swallow DCI, where a ratio of >1 is defined as the presence of CR. 19 Impedance recordings were evaluated for each swallow and bolus clearance assessed using both colorized contour functions and superimposed impedance tracings, as previous described.21 Bolus clearance was defined as "complete" or "incomplete" based on the color overlay and line-tracing modes.21 Subjects were classified as complete bolus transit when clearance was seen in ≥80% of swallows.22 Thoraco-abdominal pressure gradient (TAPG) TAPG was calculated by subtracting the intra-abdominal pressure (AP; proximal stomach 1 cm below the lower border of the LES and referenced to atmospheric pressure) from the mean intrathoracic pressure (TP; distal esophagus between 1 and 5 cm above the upper border of the LES and referenced to atmospheric pressure) during inspiration.LES pressure during inspiration, referenced to the pressure at the level of the intra-abdominal pressure (i.e., 1 cm below the lower border of the LES), was also measured, and an adjusted TAPG was calculated by subtracting lower esophageal sphincter pressure (LESP) from the TAPG during inspiration.A cut-off value of adjusted TAPG to predict the risk of reflux was set at >0 mmHg, based on the hypothesis that reflux may occur when TAPG overcomes the LESP.23

Esophageal length (EL)
Manometric EL was measured from the lower border of the UES to the upper border of the LES at the end inspiration.Esophageal length index (ELI) was calculated by dividing EL in centimeters by patient height in meters. 7

| 24 h pH-impedance (MII-pH)
Data were manually analyzed (BioVIEW Analysis software, Sandhill Scientific, CO) excluding meals for reflux episodes based on retrograde impedance decrease to 50% of baseline in at least two distal adjacent channels.Abnormalities in reflux exposure were as previously defined. 9,24

PSPW index
The PSPW index, a novel measure of esophageal clearance in pH/ impedance studies, is defined as the number of reflux episodes followed by an impedance-detected swallow occurring within 30 s of the end of the reflux episode, divided by the total number of reflux episodes. 25,26The PSPW index was considered abnormal if <61%. 26

| Statistics
Group differences were evaluated using Student's t-tests or Mann-Whitney U-tests.Tests for proportionality between groups were assessed using Chi-square or Fisher's exact tests.The relationships between variables were assessed using scatterplots and quantified using Spearman's rank (nonparametric data) tests.Significance was evaluated at the two-tailed, p-value of <0.05 taken as significant.
Of the 6 RLD patients who underwent unilateral LTx, 4 had normal motility and 2 IEM pre-LTx, with 5/6 retaining the same diagnosis post-LTx, except for one patient with IEM who acquired EGJOO in addition to IEM.
Lastly, in the total cohort, LTx was associated with an increase in DCI (p < 0.001) and DL (p = 0.002) (Table 1).Furthermore, the percentage of patients with normal UES pressure tended to increase following LTx, (p = 0.094), whilst those with a hypotensive LES increased (p = 0.030) and those with a hypertensive LES decreased (p = 0.069).Resting LES pressure tended to decrease post-LTx (p = 0.057) (Table 1).Examining patients with RLD and OLD  TA B L E 1 HRIM findings in total cohort pre-and post-LTx.
Following LTx, EL and ELI significantly decreased in OLD patients (p = 0.020 and p = 0.022, respectively), reflecting 12 (71%) of OLD patients exhibiting a decrease in EL following LTx ( Interestingly, of those OLD patients who exhibited a decrease in EL following LTx, there was a trend that more patients either remained or changed to normal motility (50%) compared with patients who did not exhibit a reduction in EL (0%; p = 0.10).
In RLD patients who had undergone unilateral LTx, there was no

| TAPG
Patients had a significantly lower intra-TP pre-compared with post-LTx (p < 0.001).There was no difference in intra-AP.Thus, the TAPG (p < 0.001) and adjusted TAPG (p = 0.023) were greater pre-compared with post-LTx (Table 1).Changes in intra-TP and TAPG following LTx were more evident in patients with RLD than OLD (Table 2).

| MRS parameters
Fifty-three percent of patients pre-LTx exhibited an abnormal augmentation ratio (AR) in response to MRS which did not significantly change post-LTx (42%; p = 0.304).Fewer RLD patients had an abnormal AR (41%) compared with OLD patients pre-LTx (80%; p = 0.0625).
Following LTx there was no significant change in percentage of RLD

| Bolus transit
Eighty-two percent of patients before LTx exhibited incomplete transit of boluses swallowed, and across the whole patient cohort, a median of 74% (IQR: 40%-100%) of swallows were incomplete (Table 1).Following LTx, there was a tendency for the percentage of patients with incomplete bolus transit (IBT) to decrease (69%, p = 0.141).No significant differences were seen between the RLD and OLD patients pre-LTx, or changes following LTx (Table 2).
Unilateral LTx in those with RLD did not affect findings.
TA B L E 2 HRIM findings in patients with restrictive (RLD) and obstructive (OLD) lung disease pre-and post-LTx.

| Mean nocturnal baseline impedance (MNBI)
MNBI increased along the length of the esophagus, particularly in the distal esophagus (i.e., 3-5 cm above LES) post-compared with pre-LTx (Table 3).This reflected an increase in MNBI, particularly in the distal esophagus of patients with RLD and not OLD, such that post-LTx, MNBI was higher in the distal esophagus of RLD than OLD patients (at 3 cm above LES, p = 0.029; at 5 cm above LES p = 0.069).

| Post-swallow peristaltic wave (PSPW)
There was no difference in either the PSPW index or proportion of patients with an abnormal PSPW before and after LTx.Likewise, no changes were seen in patients with RLD and OLD (Tables 3 and   4).Similarly, there was no difference in the PSPW index before and after LTx in the RLD patients (n = 5) who had undergone unilateral LTx (44.7 (11.8-77.6) vs. 58.6 (34.6-82.5);p = 0.333).

| DISCUSS ION
This comprehensive study has shown for the first time that patients with RLD who have normal esophageal motility pre-LTx are more likely to remain normal after transplant, and those with abnormal motility are more likely to become normal post-LTx than patients with OLD.This was despite both RLD and OLD patient sub-groups showing an increase in DCI post-LTx, which may be related in part to more patients exhibiting hyper-contractility post-LTx.However, LTx was associated with a significant reduction in peristaltic breaks in patients with CCv4 defined normal motility, such that the number of patients with completely normal peristalsis for all swallows (i.e., no breaks) doubled following LTx.Whether the improvement in esophageal peristalsis observed in patients with RLD was related to more patients (59%) having a normal augmentation ratio than those with OLD (20%) remains to be confirmed but its noteworthy that AR did not change either in RLD or OLD following LTx, suggesting the actual surgery itself had little impact on the integrity of the neuromuscular structure/function of the esophagus.Interestingly, PSPW was abnormal in approximately half of patients with RLD and OLD, and also did not improve following LTx, the reason for which remains unknown.
Patients with OLD generally have larger lung volumes stretching the esophagus resulting in increased length. 7This has been proposed to have a negative effect of esophageal motility. 7It is therefore of note that OLD patients who exhibited a decrease in EL following LTx, tended to be more likely to retain or change to normal motility than those who did not exhibit a reduction in EL.Such effects were not seen in patients with RLD, perhaps because their smaller lungs have less effect on EL.However, post-LTx EL and ELI remained significantly longer in OLD than RLD patients, maybe explaining in part why OLD patients were less likely to exhibit an improvement in esophageal function compared with RLD patients.Moreover, in OLD patients post-LTx there was an inverse correlation between EL/ELI and AR, supporting the notion that stretching of the esophagus may indeed effect the neuromuscular function of the esophagus. 7This likely could not be seen pre-LTx in OLD patients, or pre-and post-LTx in RLD patients because of smaller differences in EL between TA B L E 3 MII-pH findings in total cohort pre-and post-LTx.Abbreviations: AET, acid exposure time; MII-pH, 24-hr pH-impedance; TBET, total bolus exposure time (i.e., % of monitored time that the esophagus was exposed to reflux of any nature).
patients.Despite these differences, as previously reported, 28  Finally, we have previously shown that not only poor clearance of reflux, but also poor clearance of boluses swallowed, especially when the EGJ is obstructed, might lead to aspiration and consequently lung injury and decline. 8In the present study, the majority of patients with either RLD or OLD exhibited incomplete transit of boluses swallowed, with approximately three quarters of swallows been incomplete.This did not appear to improve following LTx, again likely because of the variation in motility diagnosis seen post-LTx, as reflected by patients with completely normal peristalsis (i.e., no breaks) having fewer swallows associated with IBT than those with CCv4 defined normal motility.Lower intra-TPs pre-LTx and high TAPGs post-LTx also appeared to hinder clearance of boluses swallowed.
Our study has strengths and limitations.A significant strength is that we have attempted to better understand the inter-relationships between motility diagnoses (including peristaltic reserve), anatomical differences (e.g., EL), lung mechanics (e.g., TAPG) and esophageal reflux exposure (e.g., nonacid, as well as acid reflux; PSPW and MNBI) in patients with RLD and OLD both before and after LTx, and have also for the first time investigated the effect of LTx on clearance of boluses swallowed.A limitation is that no explicit statistical adjustment was made for the multiple comparisons performed in this study, but the relatively high proportion of significant/borderline and consistent results obtained in our cohort of 57 patients (some of which confirming previously published findings), and their physiological inter-relationship/correlations probably excludes the possibility of finding these results by chance.Second, a few patients had the HRIM and MII-pH tests performed on acid suppressants but were not significantly different between RLD and OLD sub-groups.
Six RLD patients, one OLD patient and one patient with combined restrictive/ obstructive lung disease underwent unilateral LTx.
Interestingly, despite only six RLD patients undergoing unilateral LTx, like the whole RLD cohort, they kept the same motility diagnoses post-LTx, with both intrathoracic pressure and TAPG tending to improve post-LTx; though further studies are required.[5] Finally, this was a cross-sectional study, and thus, although technically from the point of view of the pre-and post-LTx observations, one could claim that our observations are more than an association, investigating the potential causal effects of LTx on the associations between individual parameters is not clear directionally.
In conclusion, our observations suggest that (i) patients with RLD

1 .
Patients with restrictive lung disease who have normal esophageal motility are more likely to remain normal, or if they have abnormal motility to change to normal motility post-lung transplantatation than patients with obstructive lung disease.2. Esophageal length in patients with obstructive disease is longer than patients with restrictive disease pre-lung transplantation.Obstructive disease patients who exhibited a decrease in esophageal length post-lung transplantation are more likely to show a normalisation in motility than those who do not exhibit a reduction in esophageal length post-lung transplantation.

3 .
Esophageal length inversely correlates with augmentaion ratio in response to multiple rapid swallow in obstructive disease patients post-lung transplantation, suggesting stretching of the esophagus may effect the neuromuscular function of the esophagus.4. Clearance of reflux and mean nocturnal baseline impedance improved in restrictive but not obstructive lung disease patients post-lung transplantation.5. Peristaltic breaks and thoraco-abdominal pressure gradient impact both esophageal clearnace of reflux and boluses swallowed.esophageal physiology.This can lead to patients with abnormal pHmetry and/or significant motility abnormalities prior to LTx, being excluded from transplant waiting lists, or possibly undergo high risk fundoplication or unnecessary anti-reflux therapies that do not target the specific physiologic derangement.Our aim was therefore to further our understanding of the effect of LTx on esophageal motor function, namely motility diagnosis, and examine how this and the other factors mentioned above relate to GER and clearance of boluses swallowed both before and follow-Patients This was a prospective study of 62 consecutive patients out of a possible 347 patients referred for high-resolution impedance manometry (HRIM) and 24 h pH/impedance prior to transplant and then followed up approximately 3 months after surgery at Mayo Clinic, Florida between November 2017 and January 2022.Of the remaining 285 patients, 17 patients underwent pre-and post-LTx testing but were missing one or more HRIM tests, 195 underwent only pre-LTx testing (either still awaiting LTx, died prior to LTx or refused testing) and 73 underwent only post-LTx testing (too ill to perform pre-LTx testing or refused testing).Patients who had undergone any form of foregut surgery were excluded from our analysis.Patient data included age, sex, body mass index (BMI), indication for LTx, LTx date, and post-LTx medication.The Mayo Clinic Institutional Review Board approved the study (IRB# 18-005280).No patient received compensation for taking part in this study.
are more likely to retain a normal motility diagnosis or change to a normal motility diagnosis post-LTx than patients with OLD, (ii) CR as measured using AR during MRS pre-LTx might help identify patients most suitable for LTx, especially since AR does not appear to change with LTx, as might PSPW, (iii) reduction in EL in OLD patients during transplantation might facilitate better CR and consequently DCI, (iv) because esophageal reflux exposure is not significantly affected by LTx, a more complete physiological profile of the patient is required with a combination of HRIM and MII-pH, (v) intra-TP appears to drive esophageal exposure to reflux pre-LTx whilst intra-AP is maybe more important post-LTx, suggesting LTx normalizes some of the mechanisms to be more dependent on gastric pressure as seen in GERD patients and healthy controls, and lastly (vi) incomplete transit of boluses swallowed, which is affected by both motility diagnosis and lung mechanics should be considered at least as much as GER by clinicians.While we believe these observations between esophageal motility diagnosis, contractile reserve, traditional and novel reflux parameters, and lung mechanics in the different types of lung disease adds to our knowledge in this area, they must be viewed clinically in the context of the many other factors that can lead to transplant survival.

Table 2
).There was a trend for manometric EL (p = 0.062) and ELI (p = 0.061) to slightly increase in RLD patients, but with similar percentages of patients showing either a slight increase (21, 52.5%) or no change/ decrease in EL (19, 47.5%) following LTx.Both EL and ELI remained significantly longer in OLD compared with RLD patients post-LTx.

LTx RLD post-LTx p-value OLD pre-LTx OLD post-LTx p-value
29BI significantly increased in patients with RLD but not OLD following LTx.Generally, our reflux findings support previous observations that they offer limited utility in the transplant population,29if other factors including esophageal motility and lung mechanics, are not taken into account.For example, TBET might be normal in a particular patient but with low TP, IEM, and/or low PSPW, reflux might reach the proximal esophagus and possibly aspirate into the TP, and TAPG) it is maybe not unexpected therefore that before LTx there was no differences in esophageal reflux exposure between those with RLD and OLD, with minimal changes post-LTx, except for bolus clearance time which decreased in RLD and increased in OLD.This was associated with fewer RLD patients exhibiting an abnormal MNBI but no change in numbers of patients with OLD exhibiting abnormal MNBI post-transplant.Therefore, as expected TA B L E 4 MII-pH findings in patients with restrictive (RLD) and obstructive (OLD) lung disease pre-and post-LTx.RLD pre-