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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
 
Pediatr Res. Author manuscript; available in PMC 2012 August 1.
Published in final edited form as:
PMCID: PMC3210911
NIHMSID: NIHMS296638

Significance of Gastroesophageal Refluxate in Relation to Physical, Chemical and Spatio-temporal Characteristics in Symptomatic ICU Neonates

Abstract

GERD (gastroesophageal reflux disease) is a frequent consideration in ICU neonates. We tested the hypothesis that symptoms in GERD are dependent on the spatio-temporal and physico-chemical characteristics of reflux events by evaluating the symptom sensitivity index (SSI) and symptom index (SI) in relation to the refluxate characteristics. Thirty symptomatic neonates (30.7±0.8 wk gestation) were evaluated using manometry and pH-Impedance methods. During 704.3 hr of recordings, 2,063 GER (gastroesophageal reflux) were observed; 54% of the GER were associated with symptoms. Defined by physical characteristics, there were 51.3% liquid, 29.1% gas, and 19.6% mixed GER. Defined by chemical characteristics, there were 48.5% acid- and 51.5% non-acid GER. Defined by most proximal extent, 79.2% were supra-UES (upper esophageal sphincter), 20.8% were infra-UES. Higher SSI was noted with pH-only events (P<0.0001 vs. pH-Impedance events). Higher SI was noted with movement symptoms (vs. sensory, P=0.04). In a subset analysis, the frequencies of GER events, acid clearance time, and SSI were all greater in chronic lung disease vs. none (P<0.001). In conclusion, clinical significance of symptoms as measured by SSI and SI and characterization of spatial-temporal-physical-chemical nature of GER events as defined by pH-impedance methods clarifies the definition of GERD.

BACKGROUND

Gastroesophageal reflux disease (GERD) is a frequent consideration in infants at-risk of life threatening events, chronic lung disease (CLD) and dysphagia. Concern of GERD in neonates is evident by the frequent use of acid suppressive medications (1), and prokinetics (2) that are commonly prescribed to alter gastric acidity or gastro-prokinetic functions. Furthermore, practices in the NICU attribute aero-digestive symptoms to the injurious effects of acid reflux events (ARE). However, the composition of the refluxate varies depending on the composition of the gastric contents, i.e., acid, enzymes, food, gas, bile, swallowed material; albeit, all of these have a common factor, i.e., volume. Suppression of gastric acid alone may have been beneficial or associated with side-effects (1) and therapies targeted to modify gastroesophageal reflux (GER) and gut motility have noxious consequences (3).

Using pH-impedance techniques, classification of acid reflux events (ARE) in relation to symptom characteristics in CLD has been determined by us (4). Traditionally, esophageal pH<4 is considered ARE, and all others as non-acid reflux events (NARE) (5). However, significance of measurable characteristics of refluxate such as ARE, NARE, gas, mixed, liquid, high or low reflux events in relation to symptoms in symptomatic NICU neonates remaining unclear. Therefore, this study was undertaken to: 1) classify the physico-chemical and spatio-temporal characteristics of GER events, 2) characterize the frequency and distribution of symptoms, 3) define the relationship of symptoms with the characteristics of GER using symptom sensitivity index (SSI) and symptom index (SI), and 4) perform subset analysis among a) those with CLD and those without, and b) differences in symptom distribution within the NARE group in response to pH change vs. none.

METHODS

Subjects

Thirty neonates (median (IQR)) of 30.6 (7.0) wk gestation, 1.4 (1.4) kg at birth were evaluated for suspected GERD at 43.6 (5.6) wks postmenstrual age (PMA) and weighed 3.6 (1.7) kg. None were receiving acid suppressive medications or prokinetics. At assessment, subjects were receiving full enteral nutrition via intragastric feedings or oral feedings and standard respiratory management at the Nationwide Children’s Hospital NICU. CLD was defined as the need for supplemental oxygen requirement beyond 36 wks PMA. Informed written consent was obtained before the start of the study and the protocol was approved by the IRB at The Research Institute of Nationwide Children’s Hospital.

Manometric Methods

We used the same manometric technique previously utilized by our group to characterize the esophageal motility waveforms and to define the distance from nares to the upper esophageal sphincter (UES) and the lower esophageal sphincter (LES) (4, 68). Briefly, the catheter assembly (Dentsleeve International, Mui Scientific, Ontario, Canada) was passed nasally in the supine lying infant and pull through techniques were adopted to ensure appropriate positioning (9). The catheter was withdrawn at 0.5 cm intervals with a pause of at least 20 s in each station, until the high pressure zone of the LES or UES were identified by the presence of a constant increase in the pressure above baseline. Change in LES pressure with breathing and swallow induced changes in UES and LES relaxations were observed to ensure proper positioning.

pH-Impedance Methods

Twenty-four hour pH-impedance studies were done using the pH-MII probe, model ZIN-S61C01E, (Sandhill Scientific Inc, Highlands Ranch, Colorado, USA) that had 6 impedance channels (7 impedance rings) and one pH channel (4). After calibration, the probe was securely set at 87% of the distance from the nares to the upper border of the LES, such that the location of the pH sensor was in the distal esophagus (10). Based on the manometric definitions, the esophageal body length varied between 5.1 and 9.9 cm (median, 7.8cm) and the pH-impedance probe was of adequate size to use in infant esophageal lengths up to 15 cm.

Documentation of Symptoms

Trained nurse assistants, who were blinded to the recordings, documented the symptoms/caring events upon occurrence. The nurses were well trained to recognize the symptoms objectively. Event markers were placed directly using the touch screen interface for: 1) respiratory symptoms (cough, grunting, gagging, bradycardia, and desaturation), 2) sensory symptoms (irritability, arching, grimace, cry or pain) and 3) physical movement (stretching of limbs). Irritability was characterized by neck extension and arching; and pain in neonates was recognized as grimace, eye convergence, frown or folds on the forehead or cry.

Data analysis

Manual analysis was performed to document GER by observing the change in impedance by >50% with retrograde bolus movement (11, 12). GER was classified based on the physical property into gas, liquid and mixed refluxate. Gas reflux was defined as a rapid rise (50% from pre-episode mean impedance value) simultaneously in at least two consecutive impedance channels without any evidence of swallowing. Liquid reflux was defined as a 50% drop from pre-episode mean impedance value with retrograde bolus movement starting distally and propagated to at least 2 more proximal channels. Mixed reflux was defined as combination of liquid and gas reflux (13). GER was also classified based on the chemical property into (a) ARE, (fall of pH to <4 for >5 seconds or when the pH decrease of at least 1 pH unit for >5 s if pH was already <4 during liquid presence as determined by MII), and (b) NARE (no decrease in pH to <4 during liquid presence as determined by MII; subset analysis was also performed based on the presence or absence of a pH change of >1 unit for each NARE) (5). Gas reflux was classified into ARE and NARE depending on the association of fall in pH. Spatial characteristics of the GER events were identified by the proximal extent of the refluxate into supra-UES or infra-UES based on the manometric definitions. Temporal characteristics were determined by the duration of the dwell of the refluxate (clearance) within the esophageal column. Bolus clearance time (BCT) was measured from the onset at which impedance drops below 50% of the baseline to the offset at which impedance returns to 50% of the baseline value. Acid clearance time (ACT) was defined as the time taken for the esophageal pH to normalize to pH ≥4.0 for ≥5.0 s. Artifacts and meal periods were excluded. Symptom-reflux relationships were applied in each of these nine GER characteristics (ARE, NARE, gas, liquid, mixed, high, low, and pH-only events). Any GER was labeled as symptomatic if a symptom presented during the GER and for 2-min after the reflux duration. The same symptom would only be counted once following the GER to overcome the overlap of the same symptom associated with consecutive GER time windows. The SI was calculated {(number of symptoms with reflux events/total number of symptoms in 24 hr) × 100} (12, 14). We also calculated the SSI {(number of reflux events associated with symptoms/total number of reflux events in 24 hr) × 100} (4, 12, 14, 15).

Statistical analysis

The physical, chemical characteristics and most proximal extent within the esophagus were tested for association with the symptoms. SSI and SI were calculated. Multinomial mixed models or linear mixed models were used to study the association between BCT and ACT and GER characteristics. In these models a statement for repeated-effect was included to account for the correlation within subjects. These models were fit using PROC GENMOD or PROC MIXED in SAS (SAS v.9.1. Institute Inc., Cary, NC, USA). Since data are not normally distributed, values are shown as median (IQR) or as % unless stated otherwise. Log transformation was performed to achieve normality for the statistical analyses (mixed models). P-value <0.05 was considered significant.

RESULTS

Participant Characteristics

Demographic comparisons between CLD and non-CLD are stated (Table-1). At evaluation, 11 (36.7%) infants were oral-fed and the rest via nasogastric tube; and 7 (39%) in the CLD group and 4 (33%) in the non-CLD group received continuous tube feeding (P=NS). At discharge, 15 (50%) were oral-fed exclusively, 7 (23%) were oral and gastrostomy-fed, and 8 (27%) were gastrostomy-fed exclusively.

Table 1
Participants characteristics

Classification of GER events: physical, chemical and spatial characteristics

Overall, 2,063 GER events were recognized by combined MII-pH recordings; of which, 1,969 (95.4%) were pH-impedance events and 94 (4.6%) were pH-only events. False pH-refluxes caused by pH-fluctuations or electrode drift were ruled out. Physical characteristics of GER revealed that 1,010 (51.3%) were liquid, 574 (29.1%) were gas, and 385 (19.6%) were mixed. Chemical characteristics revealed that 954 (48.5%) were ARE, 1015 (51.5%) were NARE. Spatial characteristics were based on the manometric definitions in each patient, and 1559 (79.2%) supra-UES GER and 410 (20.8%) infra-UES GER were identified by the most proximal extent of the refluxate.

Bolus clearance time in relation to physico-chemical and spatial characteristics

Each patient spent median 27.4 (12.5) s per event in bolus clearance of liquid or mixed GER events. Characteristics of BCT per GER event per individual subject data are summarized (Fig-1A). Prolonged BCT was noted with mixed GER compared to liquid GER by 1.5-fold, (P=0.0002), and supra-UES GER compared to infra-UES GER by 1.2-fold, (P<0.0001). Similar BCT was noted between ARE and NARE. Subgroup analysis on median BCT per event per subject was similar between patients with CLD (26.1 (10.5) s) and without CLD (32.9 (9.3) s, P=0.2).

Fig. 1
Duration of average BCT and average ACT per patient per GER event

Acid clearance time in relation to acid pH-impedance events and pH-only events

The median ACT per acid pH-impedance events per subject was 234.8 (208.8) s, and with pH-only events was 335.9 (624.6) s (P<0.0001, Fig-1B). Similarities was noted between patients with and without CLD for acid pH-impedance events (294.2 (221.5) vs. 215.5 (191.2), P=0.1) and pH-only events (364.0 (1076.1) vs. 304.9 (512.8), P=0.2).

Physico-chemical property of refluxate proximal extent: supra-UES or infra-UES

There were 1559 supra-UES and 410 infra-UES events. Liquid GER events were greater in infra-UES (vs. supra-UES, P<0.0001, Fig-2A). Chemical composition of GER among the infra-UES was different (vs. supra-UES, P<0.0001, Fig-2B) in that more ARE were seen when the maximal height was infra-UES, and more NARE were seen when the maximal height was supra-UES.

Fig. 2
Physico-chemical composition of GER defined as supra-UES or infra-UES

Prevalence of symptoms based on physico-chemical characteristics

The distribution of the individual SI and SSI values is shown in Fig-3. In 6 (20%) patients, the SI was >50%. An SSI of >10% was observed in 29 (96.7%) patients. The highest SSI encountered was 95%. Discordance between the SI and SSI was observed in a substantial proportion of the patients (Fig-3).

Fig. 3
Distribution of SI and SSI

Overall, 2146 symptoms were noted in 1031 pH-impedance events and 938 (47.7%) GER events were unassociated with symptoms. The SSI for composite symptoms per pH-impedance event (occurrence of any combination of symptoms per GER event) was 52.4% (1031/1969). Out of the 94 pH-only events, 82 (87.3%) were associated with 249 symptoms. The SSI for composite symptoms per pH-only event was 87.3% (82/94). However, only 56.5% acid pH-impedance events were associated with symptoms (P<0.0001 vs. pH-only events).

We analyzed the relationship between the physico-chemical characteristics of the pH-impedance events and symptoms (composite symptoms, respiratory symptoms, sensory symptoms, or physical symptoms) (Table-2). The occurrence of symptoms with GER was similar among physical and chemical characteristics (all P=NS). However, the distribution of respiratory symptoms, sensory symptoms, and physical symptoms was different in relation to physical and chemical characteristics (Fig-4). Gas GER events were associated with more sensory symptoms than liquid and mixed refluxate. Compared to non-acid GER, acid GER were associated with more physical symptoms and less sensory symptoms.

Fig. 4
Symptom distribution based on physico-chemical characteristics
Table 2
Symptom Sensitivity Index (SSI) based on the properties of reflux

Out of 7118 symptoms, only 2395 were associated with pH-impedance events or pH-only events. SI was calculated as 2395/7118=33.7%. The distribution of reflux associated movement-symptoms was greater (P=0.04 vs. sensory, P=0.1 vs. respiratory, Table-3). Similarly, whenever a symptom was present, the odds of having a liquid reflux event was 2-fold higher than the odds of having a gas reflux or a mixed reflux event.

Table 3
Symptom Index (SI) based on the properties of reflux

Subgroup analysis did not show any difference among the group of patients with and without CLD in symptom distribution with pH-impedance events. Conversely, the occurrence of symptom-associated pH-only reflux events was higher with CLD patients compared to non-CLD patients, 94.3% vs. 78.0%, (P=0.03). Specifically, the odds of CLD patients having a pH-only events resulting in sensory symptoms was 3.6 times higher than the odds of non-CLD patients having a sensory symptom-associated pH-only events (P=0.0001). Relation between symptoms and physico-chemical characteristics of pH-impedance events was similar between CLD and non-CLD.

Out of the 1015 NARE, only 225 (22.2%) were associated with a change in pH by > 1. The frequency of symptom-associated GER were similar regardless of the change in pH (>1 pH unit, 43.1% vs. none, 50%, P=NS). However, only 19.7% of the symptomatic non-acid GER were associated with change in pH by >1.

Prevalence of symptoms based on spatio-temporal characteristics

Out of 1559 supra-UES GER, 821 were associated with a total of 1686 symptoms (SSI=821/1559=52.7%); and out of 410 infra-UES GER, 210 were associated with 460 symptoms (SSI=210/410=51.3%). Whenever a symptom occurred, the odds of supra-UES GER (SI=1686/7118=23.7%) was 3.6 times higher than the odds of infra-UES GER (SI=460/7118=6.5%).

We next examined the relationship between symptom frequency and the duration of bolus and acid clearance. Symptomatic ARE, including both acid pH-impedance events and pH-only events, were associated with longer ACT (P=0.001, Fig-5A); similarly, the association between symptomatic pH-impedance events and longer BCT was also noted (P=0.01, Fig-5B).

Fig. 5
Relationship of symptoms/reflux with esophageal ACT and BCT

The association between ACT and symptom frequency among patients with and without CLD was examined. Each ARE, including both acid pH-impedance events and pH-only events, was categorized based on symptoms. Prolonged ACT were associated with symptomatic AREs in CLD (all P<0.05, Table-4); such association was absent in non-CLD (all P=NS, Table-4). Prolonged ACT was noted in CLD vs. non-CLD for symptomatic AREs, (all P<0.05, Table-4).

Table 4
The association of acid clearance time (sec) and symptomatic AREs.

DISCUSSION

The definition of GERD in neonates/infants remains controversial and debates continue about the use and abuse of anti-reflux medical and surgical interventions (1, 16). Given the complexity of refluxate composition and inability to distinguish symptoms due to physiological from pathological GER in the NICU infant, there is little recourse than to define GERD in an individualized setting. Establishing objective evidence of GER events and the relationship of symptoms with the physical or chemical composition of the refluxate is essential to characterize GERD.

Several important findings were observed with GER events in this study: 1) NARE are of equal frequency as ARE (1719), and majority of events spread proximally above the UES; 2) average BCT was prolonged with mixed vs. liquid, with supra-UES vs. infra-UES; 3) ACT per acid pH-impedance event was lesser than pH-only events; 4) infra-UES GER was correlated with higher percentage of ARE compared to supra-UES GER, and supra-UES GER were associated with greater proportion of NARE; 5) 54% of GER events documented by pH-impedance were associated with symptoms, and over 87% of the pH-only events were associated with symptoms; 6) the occurrence of symptoms was similar among different physico-chemical characteristics, although the distribution of respiratory symptoms, sensory symptoms, and physical symptoms was different in relation to physico-chemical characteristics; 7) subgroup analysis did not show any difference among the group of patients with and without CLD in symptom distribution, although the occurrence of symptom-associated pH-only reflux events was higher with CLD patients and that the sensory symptoms were greater in this group than non-CLD patients; 8) symptomatic ARE were associated with longer ACT; 9) prolonged acidity was associated with symptomatic ARE in CLD patients unlike non-CLD patients.

In this study we categorized chemical GER events into ARE and NARE, as used before (8). We did not consider NARE to be synonymous with weakly alkaline reflux events, as we did not technically measure the degree of alkalinity (pH>7).

It is clear from this study that symptoms can occur with varying physico- chemical properties of refluxate or of its varying ascent. Some infants are more sensitive in reacting with symptoms (as in CLD) than others (without CLD). It is also clear why the management of GERD based on symptoms only is controversial, as there are ‘reflux-type symptoms’ in the absence of GER. Management of GERD based on the frequency of GER is also controversial as a substantial proportion of GER were not associated with symptoms. Therefore, clinical trials based on symptom profiles only in neonates cannot offer definitive conclusions about GERD management. Similarly, clinical trials that have been based on the frequency of acid GER cannot offer definite conclusions about GERD management. The value of NARE and other background disease characteristics may have been ignored in such trials. Anti-reflux prophylactic medical therapies have been associated with necrotizing enterocolitis when given within the first weeks of life in premature infants, digestive problems, alteration of aero-digestive flora (20), abnormalities of calcium absorption and osteopenia (3). Furthermore, aspirates of gastric juice in those treated with acid suppressants can be deleterious to the bronchial airway, and inflammatory reaction induced by bacteria and endotoxins have been reported in those CLD patients who were managed on proton pump inhibitors for GERD (21). Anti reflux surgical therapies have been reported to be associated with early satiety, dyspepsia, and inability to vomit, fundoplication break-up, and GI dysmotility (3).

Interestingly, in our study, the prolonged acid clearance and its association with increased symptom frequency supports the hypothesis that chemosensitive stimulation and prolonged dwell of the acid GER in the esophagus activates visceral, somatic and sensory aero-digestive pathways resulting in the generation of symptoms (irritability and arching, grimace, cry, cough, gagging, stridor, physical movement, etc). Indeed all these symptoms involve nerve-muscle interaction at various levels, and these phenomena may support sensitization of esophageal afferents. Prolongation of ACT may be due to alteration of clearance mechanisms, esophageal dysmotility, or decreased acid neutralization or larger volume of refluxate. Furthermore sensitization may be greater in CLD infants as the SSI was greater in these infants compared to those with non-CLD infants. It is still unclear as to the best choice of symptom indices (SI, SSI, SAP) regardless of the age spectrum. In neonate this association may be even more challenging owing to multiplicity of symptoms and non-verbal nature of subject. Future studies must address the complexity of neonatal symptoms and best predictors in relation to GERD. The discordance between the SI and SSI is noted, and may be due to the chance of the SI being higher in the presence of many GER episodes and the SSI tends to be higher in the presence of many symptoms. From our study, useful conclusions can be drawn based on discordant indices, in that, the combination of a high SSI and a low SI indicates that the patient’s esophagus is sensitive to reflux but causes other than reflux are likely to contribute to the symptoms (22, 23). Although there were multiple symptoms belonging to different classifications, i.e., respiratory, sensory or physical, a given symptom was counted only once to overcome the overlap. However, each symptom may have different sensory-motor basis for its occurrence. This study lends support to the activation of esophageal-airway reflexes in the genesis of symptoms. For example, in pH-only reflux events, where there was no ascending spread of the refluxate, the ACT was longer and SSI was of increased frequency. The reasons why pH-only events occur are not entirely clear, and have been reported by others (12). Such events may happen because of swallow-related GER events, transient LES relaxation or incomplete LES relaxation reflex. During such scenarios, activation of esophageal vagal afferents and airway and supra-UES efferents can result in aero-digestive defensive reflexes and symptoms, thus forming the basis for esophago-glottal closure and pharyngo-glottal closure reflexes (24, 25). These protective reflexes prevent the refluxate from reaching the airway.

This study also lends support to the association of symptoms not only with acid events but also with non-acid, gas, liquid or mixed events. Esophageal clearance of a bolus depends on multiple factors involved with esophageal motility, i.e., sensory-motor characteristics of the peristaltic reflexes (Deglutition reflex response, secondary peristalsis), upper esophageal sphincter contractile reflex, lower esophageal sphincter relaxation reflex (9, 26). We have shown recently that the recruitment of esophageal and airway defensive reflexes increases with volume dependent provocation, chemosensitive stimulation, or graded volumes of esophageal distention. Thus, treatment strategies based on modification of gastric acidity alone can be ineffective as acid is not the lone provoking agent.

GER may therefore be an important co-morbidity factor especially in NICU neonates (4, 27). Although GER (physiologic form) may be more frequent in neonates, distinction from GERD (pathologic form) can be difficult. As such, there are no definite standards to aid in the diagnosis of GERD, or of symptom recognition, or with the management of GER among NICU neonates. Lack of clarity with diagnosis and therapeutic targets for neonatal GERD can lead to empiric therapies with resultant consequences (3). Recent Pediatric GERD guidelines from NASPGHAN/ESPGHAN offer little evidence on the evaluation and management of suspected GERD in neonates, and the expert committee recognized lack of quality evidence that supports a) the diagnosis of GERD, b) medical therapies or c) life style changing surgical therapies (3).

In conclusion: 1) The current study is the first study to have attempted classification of the GER and symptom indices based on physico-chemical and spatio-temporal attributes of the refluxate in neonates. 2) Given the complexity of the composition of refluxate in the definition of GERD, the relationship of symptoms vs. the physic-chemical composition of the refluxate is essential, so that therapeutic targets can be appropriate. 3) Infants with intractable CLD merit evaluation for alternate pathophysiology. 4) Locus of esophageal provocation may influence aero-digestive symptoms. 5) The occurrence of respiratory symptoms regardless of spatio-temporal distribution of refluxate suggests the activation of esophago-airway and pharyngeal-airway reflex interactions. 6) Clinical significance as measured by SSI and SI and characterization of spatial-temporal-physical-chemical nature of GER events as defined by pH-impedance methods clarifies the definition of GERD, i.e., GER with increased frequency of respiratory, sensory or movement symptoms.

Acknowledgments

Statement of financial support: This study is supported in part by grant funding from NIH grant RO1 DK 068158 to S.R.J..

ABBREVIATIONS

ACT
acid clearance time
ARE
acid reflux event
BCT
bolus clearance time
CLD
chronic lung disease
GER
gastroesophageal reflux
GERD
gastroesophageal reflux disease
NARE
non-acid reflux event
SI
symptom index
SSI
symptom sensitivity index
UES
upper esophageal sphincter
LES
lower esophageal sphincter

References

1. Malcolm WF, Gantz M, Martin RJ, Goldstein RF, Goldberg RN, Cotten CM. Use of medications for gastroesophageal reflux at discharge among extremely low birth weight infants. Pediatrics. 2008;121:22–27. [PubMed]
2. Barney CK, Baer VL, Scoffield SH, Lambert DK, Cook M, Christensen RD. Lansoprazole, ranitidine, and metoclopramide: comparison of practice patterns at 4 level III NICUs within one healthcare system. Adv Neonatal Care. 2009;9:129–131. [PubMed]
3. Vandenplas Y, Rudolph CD, Di Lorenzo C, Hassall E, Liptak G, Mazur L, Sondheimer J, Staiano A, Thomson M, Veereman-Wauters G, Wenzl TG. North American Society for Pediatric Gastroenterology Hepatology and Nutrition, European Society for Pediatric Gastroenterology Hepatology and Nutrition. Pediatric gastroesophageal reflux clinical practice guidelines: joint recommendations of the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN) and the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) J Pediatr Gastroenterol Nutr. 2009;49:498–547. [PubMed]
4. Jadcherla SR, Gupta A, Fernandez S, Nelin LD, Castile R, Gest AL, Welty S. Spatiotemporal characteristics of acid refluxate and relationship to symptoms in premature and term infants with chronic lung disease. Am J Gastroenterol. 2008;103:720–728. [PubMed]
5. Vela MF, Camacho-Lobato L, Srinivasan R, Tutuian R, Katz PO, Castell DO. Simultaneous intraesophageal impedance and pH measurement of acid and nonacid gastroesophageal reflux: effect of omeprazole. Gastroenterology. 2001;120:1599–1606. [PubMed]
6. American Gastroenterological Association. American Gastroenterological Association medical position statement: guidelines on the use of esophageal pH recording. Gastroenterology. 1996;110:1981. [PubMed]
7. Jadcherla SR, Duong HQ, Hofmann C, Hoffmann R, Shaker R. Characteristics of upper oesophageal sphincter and oesophageal body during maturation in healthy human neonates compared with adults. Neurogastroenterol Motil. 2005;17:663–670. [PubMed]
8. Gupta A, Jadcherla SR. The relationship between somatic growth and in vivo esophageal segmental and sphincteric growth in human neonates. J Pediatr Gastroenterol Nutr. 2006;43:35–41. [PubMed]
9. Jadcherla SR, Hoffmann RG, Shaker R. Effect of maturation of the magnitude of mechanosensitive and chemosensitive reflexes in the premature human esophagus. J Pediatr. 2006;149:77–82. [PubMed]
10. Jadcherla SR, Rudolph CD. Gastroesophageal reflux in the preterm neonate. NeoReviews. 2005;6:e87–e98.
11. Wenzl TG, Silny J, Schenke S, Peschgens T, Heimann G, Skopnik H. Gastroesophageal reflux and respiratory phenomena in infants: status of the intraluminal impedance technique. J Pediatr Gastroenterol Nutr. 1999;28:423–428. [PubMed]
12. Rosen R, Nurko S. The importance of multichannel intraluminal impedance in the evaluation of children with persistent respiratory symptoms. Am J Gastroenterol. 2004;99:2452–2458. [PubMed]
13. Zerbib F, des Varannes SB, Roman S, Pouderoux P, Artigue F, Chaput U, Mion F, Caillol F, Verin E, Bommelaer G, Ducrotte P, Galmiche JP, Sifrim D. Normal values and day-today variability of 24-h ambulatory oesophageal impedance-pH monitoring in a Belgian-French cohort of healthy subjects. Aliment Pharmacol Ther. 2005;22:1011–1021. [PubMed]
14. Wiener GJ, Richter JE, Copper JB, Wu WC, Castell DO. The symptom index: a clinically important parameter of ambulatory 24-hour esophageal pH monitoring. Am J Gastroenterol. 1988;83:358–361. [PubMed]
15. Lam HG, Breumelhof R, Roelofs JM, Van Berge Henegouwen GP, Smout AJ. What is the optimal time window in symptom analysis of 24-hour esophageal pressure and pH data? Dig Dis Sci. 1994;39:402–409. [PubMed]
16. Mousa H, Caniano DA, Alhajj M, Gibson L, Di Lorenzo C, Binkowitz L. Effect of Nissen fundoplication on gastric motor and sensory functions. J Pediatr Gastroenterol Nutr. 2006;43:185–189. [PubMed]
17. Mousa H, Woodley FW, Metheney M, Hayes J. Testing the association between gastroesophageal reflux and apnea in infants. J Pediatr Gastroenterol Nutr. 2005;41:169–177. [PubMed]
18. Condino AA, Sondheimer J, Pan Z, Gralla J, Perry D, O’Connor JA. Evaluation of infantile acid and nonacid gastroesophageal reflux using combined pH monitoring and impedance measurement. J Pediatr Gastroenterol Nutr. 2006;42:16–21. [PubMed]
19. van Wijk MP, Benninga MA, Omari TI. Role of the multichannel intraluminal impedance technique in infants and children. J Pediatr Gastroenterol Nutr. 2009;48:2–12. [PubMed]
20. Srinivasan R, Asselin J, Gildengorin G, Wiener-Kronish J, Flori HR. A prospective study of ventilator-associated pneumonia in children. Pediatrics. 2009;123:1108–1115. [PubMed]
21. Mertens V, Blondeau K, Vanaudenaerde B, Vos R, Farre R, Pauwels A, Verleden G, Van Raemdonck D, Dupont L, Sifrim D. Gastric juice from patients “on” acid suppressive therapy can still provoke a significant inflammatory reaction by human bronchial epithelial cells. J Clin Gastroenterol. 2010;44:e230–e235. [PubMed]
22. Bredenoord AJ, Weusten BL, Smout AJ. Symptom association analysis in ambulatory gastro-oesophageal reflux monitoring. Gut. 2005;54:1810–1817. [PMC free article] [PubMed]
23. Sengupta JN. Electrophysiological recording from neurons controlling sensory and motor functions of the esophagus. Am J Med. 2001;111:169S–173S. [PubMed]
24. Jadcherla SR, Gupta A, Coley BD, Fernandez S, Shaker R. Esophago-glottal closure reflex in human infants: a novel reflex elicited with concurrent manometry and ultrasonography. Am J Gastroenterol. 2007;102:2286–2293. [PubMed]
25. Jadcherla SR, Gupta A, Wang M, Coley BD, Fernandez S, Shaker R. Definition and implications of novel pharyngo-glottal reflex in human infants using concurrent manometry ultrasonography. Am J Gastroenterol. 2009;104:2572–2582. [PMC free article] [PubMed]
26. Pena EM, Parks VN, Peng J, Fernandez SA, Di Lorenzo C, Shaker R, Jadcherla SR. Lower esophageal sphincter relaxation reflex kinetics: effects of peristaltic reflexes and maturation in human premature neonates. Am J Physiol Gastrointest Liver Physiol. 2010;299:G1386–G1395. [PubMed]
27. Jadcherla SR, Wang M, Vijayapal AS, Leuthner SR. Impact of prematurity and co-morbidities on feeding milestones in neonates: a retrospective study. J Perinatol. 2010;30:201–208. [PMC free article] [PubMed]