Journal of Pediatric Gastroenterology & Nutrition:
Neonatal Respiratory Research Unit, Department of Pediatrics and Physiology, Université de Sherbrooke, Sherbrooke, Quebec, Canada.
Address correspondence and reprint requests to Djamal-Dine Djeddi, MD, PhD, Departments of Pediatrics and Physiology, Université de Sherbrooke, Sherbrooke, QC J1H 5N4, Canada (e-mail: email@example.com).
Received 5 March, 2012
Accepted 7 June, 2012
Supplemental digital content is available for this article. Direct URL citations appear in the printed text, and links to the digital files are provided in the HTML text of this article on the journal's Web site (www.jpgn.org).
D.D. was supported by the Department of Pediatrics, Amiens University Hospital, France. The study was also supported by grants from the Canadian Institutes of Health Research, the Canada Foundation for Innovation, and the Canada Research Chair in Neonatal Respiratory Physiology allocated to J.P.P. J.P.P. is a member of the FRSQ-funded Clinical Research Center Étienne-Le Bel, Sherbrooke University Hospital.
ABSTRACT: We aimed to determine whether the newborn lamb at term is a valid model for studying gastroesophageal reflux. Seven bottle-fed lambs, ages 2 to 3 days, underwent esophageal multichannel intraluminal impedance-pH monitoring (MII-pH). A total of 196 reflux episodes were recorded, including 73% alkaline and 27% weakly acidic. No acid refluxes were observed. Median bolus clearance time was 4 seconds (3; 5.5), and proximal reflux extent was 35% (26). This first report of MII-pH in the newborn mammal sets the foundations for future studies with physiological and clinical relevance to human neonates.
Gastroesophageal reflux (GER) is a physiological process, which is virtually universal in newborns. It is considered pathological (GER disease, GERD) when it causes excessive symptoms or complications such as esophagitis, apneas, or apparent life-threatening events (1). Although transient lower esophageal sphincter relaxation is the predominant mechanism of GER in preterm and term infants, characterization of neonatal esophageal motor function remains largely incomplete (2).
To our knowledge, there is no animal model of neonatal GER. Meanwhile, ovine models have been used for studying numerous physiological processes and pathological conditions in the neonatal period for >1 century (3), including simulated reflux laryngitis by local repeated gastric juice surrogate injection (4). Previous in vivo studies have demonstrated similarities between the ovine and human esophagus with respect to thickness and histological structure (5). In addition, during the first 2 weeks of life, the preruminant lamb is essentially monogastric, the milk being digested in the abomasum, while the reticulum and the rumen are bypassed (6). The aim of the present study was to test the hypothesis that the newborn lamb is a relevant model for studying neonatal GER using esophageal multichannel intraluminal impedance-pH monitoring (MII-pH).
Seven full-term lambs ages 2 to 3 days and weighing 3.3 kg (0.7) were involved in the study. The study was approved by the ethics committee for animal care and experimentation of the University of Sherbrooke. The nonsedated lambs underwent a 24-hour MII-pH monitoring while freely moving in a Plexiglas chamber and able to bottle-feed with ewe milk ad libitum. Positioning of the catheter 3 cm above the cardioesophageal junction was confirmed by x-ray and verified at necropsy. MII-pH recordings were analyzed with the MMS software and visually verified. Definitions of refluxes and their characteristics have been described previously (7). Tracings were analyzed during preprandial (30 minutes before feeding), feeding, and postprandial (30 minutes after feeding) periods. Further details on the methodology are available in the online-only supplemental data file (http://links.lww.com/MPG/A148). Descriptive statistical analyses were performed using Prism software version 5.04 (GraphPad Software, San Diego, CA). Data are presented as mean (standard deviation) or median (Q25; Q75).
A mean of 7 (2) milk feedings was noted during the 24-hour recordings. An example of a recording is given in Fig. 1, and results for the 7 lambs are shown in Table 1. Overall, esophageal pH was >4 and >7 during 100% and 91% (12) of recording time, respectively. Most refluxes (55% ) were purely liquid.
Although the mean number of refluxes was identical during pre- and postprandial periods (0.5 [0.6] and 0.5 [0.5], respectively), weakly acid refluxes were predominantly observed in postprandial periods and alkaline refluxes in fasting periods. Only 10 refluxes (8 gaseous and 2 mixed) were observed in perprandial periods. Further results are available in the online-only supplemental data file (http://links.lww.com/MPG/A148).
Results from the present study lead us to propose the preruminant newborn lamb as the first animal model to study neonatal GER. Indeed, we show that 24-hour MII-pH recordings can be easily performed in freely moving, nonsedated newborn lambs; and aside from the absence of acid refluxes, the many recorded refluxes present a morphology and a migration up to the proximal esophagus bearing striking similarities with refluxes in human infants.
The most significant difference between newborn lambs and the human newborn is the absence of acid refluxes in lambs. The higher esophageal pH in lambs is probably related to the low amount of hydrochloric acid secreted by the abomasum at birth; this amount dramatically increases in the first weeks of life owing to the increased number of parietal cells (8). Of note, because of their frequent feedings, human newborns also have prolonged periods with buffered gastric contents, leading to a higher proportion of weakly acid (or even alkaline) refluxes (73%) than acid refluxes (27%) (9). Hence, the scope of the pathological consequences of neonatal reflux is still widely debated and mainly concerns non–acid reflux–related complications such as apnea. Our newborn ovine model can serve to clarify this controversy.
An extensive review of the literature reveals that there are only a few published animal models for studying GER (rats, dogs, cats, pigs) mostly in nonphysiological conditions and during short-term measurements (mostly < 1 hour) (10–12). An exception is the adult rat, which has been used for studying the consequences of chronic reflux related lung aspirations (13). In addition, there are no animal models of GER in newborns. The temperament and size of the lamb make it especially suitable for research involving chronic catheterization and prolonged studies in ambulatory animals. Obviously, our present observations will have to be completed by manometric studies, especially to characterize low esophageal sphincter tone and transient low esophageal sphincter relaxations in the lamb.
In conclusion, the newborn lamb appears as a useful model for investigating neonatal GER physiology and GERD pathogenesis in various conditions such as apneas-bradycardias, hypoxia, nasal respiratory support, as well as for assessing the effects of future medications against GER; however, although promising, further physiological studies need to be done to establish this lamb model as a validated model for studying neonatal reflux.
The authors gratefully acknowledge the MMS Company (Enschede, Holland) for the gracious loan of the MII-pH monitoring equipment.
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