Incidence and characterization of aerophagia in dogs using videofluoroscopic swallow studies

Abstract

Background

Aerophagia (ingestion of air), is a functional aerodigestive disorder in people. Criteria for diagnosis of aerophagia in dogs are >1/3 of bolus volume containing air or ingested air resulting in gastric distention (>1/3 of end gastric volume). Aerophagia is highlighted during eating and drinking. Videofluoroscopic swallow studies (VFSS) document aerophagia in dogs, but the incidence, clinical signs (CS), and associated disorders are unknown.

Objectives

Identify the incidence of aerophagia, compare CS between dogs with and without aerophagia, and identify associated and predisposing disorders using VFSS.

Animals

A total of 120 client‐owned dogs.

Methods

Sequential VFSS and associated medical records from dogs presenting to veterinary teaching hospitals at Auburn University and the University of Missouri were retrospectively reviewed. Statistical comparisons were made using Mann‐Whitney and chi‐squared tests, odds ratios (OR), and multiple logistic regression (P < .05).

Results

The incidence (95% confidence interval [CI]) of aerophagia was 40% (31.7‐48.9). Dogs with mixed CS (gastrointestinal [GI] and respiratory; P < .001, 58.3%) were more likely to have aerophagia than dogs with exclusively respiratory CS (25%). Aerophagia was significantly more common in brachycephalic dogs (P = .01; 45.8% vs 13.8%), dogs with nonbrachycephalic upper airway obstruction (P < .001; 33.3% vs 4.1%), pathologic penetration and aspiration (P‐A) scores (P = .04; 41.6% vs 23.6%), and gagging (P < .001; 25% vs 11.7%). Mixed CS (P = .01), brachycephaly (P < .001), and upper airway obstruction (P < .001) were independent predictors of aerophagia.

Conclusions and Clinical Importance

Aerophagia was common, particularly in dogs with mixed CS. Brachycephalic dogs and dogs with upper airway obstruction are predisposed. Aspiration risk was high, emphasizing overlapping upper aerodigestive pathways.

Abbreviations

AP

aspiration pneumonia

AU‐VTH

Auburn University Veterinary Teaching Hospital

BALF

bronchoalveolar lavage fluid

BCS

body condition score

BOAS

brachycephalic obstructive airway syndrome

CI

confidence interval

CS

clinical signs

EP

esophageal phase

ESP

elongated soft palate

GERD

gastroesophageal reflux disease

GI

gastrointestinal

IQR

interquartile range

LES‐AS

lower esophageal sphincter achalasia‐like syndrome

ME

megaesophagus

MPA

main pulmonary artery

MSBC

mainstem bronchial collapse

MU‐VHC

University of Missouri Veterinary Health Center

OP

oral‐preparatory phase

P‐A

penetration‐aspiration

PP

pharyngeal phase

sHH

sliding hiatal hernia

UES

upper esophageal sphincter

VFSS

videofluoroscopic swallow study

1. INTRODUCTION

Aerophagia (ingestion of air) is a functional aerodigestive disorder recognized in adults and children. ¹ , ² , ³ , ⁴ In the majority of people, aerophagia results in relatively benign clinical signs (CS) including eructation and excessive flatulence, with more severe cases being associated with nausea, vomiting, and abdominal pain. ¹ , ² , ⁴ Rarely, aerophagia has been implicated in more serious conditions including colonic volvulus, ⁵ intestinal perforation, ⁶ and pneumoperitoneum. ⁷ Additionally, in people, aerophagia is associated with gastroesophageal reflux disease (GERD) ⁸ , ⁹ and aspiration, ⁸ which are known contributors to multiple clinically relevant respiratory diseases. ¹⁰

Aerophagia is defined during a VFSS in dogs as >1/3 of bolus volume containing air or ingested air resulting in gastric distention of >1/3 of end gastric volume (Figure 1). ¹¹ , ¹² Although aerophagia frequently is mentioned in the veterinary literature in association with brachycephalic obstructive airway syndrome (BOAS), ¹³ sliding hiatal hernia (sHH), ¹⁴ gastric dilatation, and volvulus, ¹¹ , ¹⁵ , ¹⁶ it remains poorly classified. Videofluoroscopic swallow studies (VFSS) are the criterion standard for evaluation of many functional aerodigestive disorders in dogs, and in people, aerophagia has been shown to be highlighted by feeding. ¹¹ , ¹⁷ As such, VFSS have been successfully used to identify aerophagia in dogs, with pathologic aerophagia being identified in 19% to 46% of dogs presented exclusively for respiratory CS. ¹¹ , ¹⁸ However, the incidence of aerophagia, presenting CS, and associated conditions in dogs presenting for VFSS regardless of cause (eg, CS of respiratory disease, gastrointestinal disease [GI], or mixed [both respiratory and GI] CS) is unknown.

FIGURE 1.

Still image of a 6‐month‐old intact male French Bulldog with aerophagia undergoing VFSS. The head is oriented to the left and the tail to the right. The stomach (asterisk) contains gas that is >1/3 of the end gastric volume.

Our primary objectives were 3‐fold. The first aim was to identify the incidence of aerophagia in dogs undergoing free‐feeding VFSS at 2 tertiary referral centers. The second was to compare presenting CS between dogs with and without aerophagia. The third objective was to identify associated and predisposing disorders for aerophagia using VFSS. We hypothesized that aerophagia would be common in dogs undergoing VFSS, especially in those with mixed respiratory and GI CS, and aerophagia would be associated with upper airway obstruction and risk for aspiration.

2. MATERIALS AND METHODS

2.1. Case selection

One hundred twenty sequential VFSS and associated medical records from dogs presented to the veterinary teaching hospitals at Auburn University (n = 60; AU VTH) and the University of Missouri (n = 60; MU VHC) from 12/1/2022‐4/1/2023 were retrospectively reviewed. Dogs were enrolled if they had complete medical records and had successfully undergone VFSS for any reason including respiratory CS, GI CS, or a combination of these. Dogs were enrolled until 60 dogs were enrolled at each institution. The swallow studies were upright and free‐feeding as previously described. ¹⁹ Demographic data (age [years], breed, head conformation [brachycephalic, mesaticephalic, or dolichocephalic], sex, body condition score [BCS; 9‐point scale], body weight [kg]), CS at presentation (including respiratory and GI CS), respiratory rate (breaths/min), and duration of CS (months) were recorded. Dogs were determined to be in respiratory distress if they required emergency intervention at the time of initial evaluation (eg, oxygen therapy), but no dog was in respiratory distress at the time of acquisition of the VFSS. Clinical signs at the time of presentation were derived from the medical record. For brachycephalic dogs, CS associated with conformation (eg, stertor) were included if they prompted veterinary medical evaluation. All radiographs were reviewed by a board‐certified radiologist. Radiographic metrics including esophageal fluid (present or absent), esophageal gas (present or absent), bronchiectasis, and aspiration pneumonia (AP) ¹² were obtained from the radiographic reports. After enrollment, all VFSS were reviewed by a single investigator (MG) with experience interpreting VFSS. ¹¹ , ¹² , ¹⁵ , ¹⁸ Dogs were considered aerophagic if they demonstrated >1/3 of bolus volume containing air for >50% of swallows or ingested air resulting in gastric distention of >1/3 of end gastric volume based on gross visual evaluation. ¹¹ , ¹² , ¹⁸ Dogs were excluded if the entire stomach could not be visualized at the end of the study. For dogs where bolus air could not be determined because of esophageal dilatation (megaesophagus) the percentage air was evaluated at the initiation of pharyngeal swallowing. Food consistency associated with aerophagia (liquid, puree, kibble, or >1 consistency) was recorded. Penetration‐aspiration (P‐A) scoring was performed as previously described, with scores ≥3 being considered pathologic. ¹² Dogs were diagnosed with macroaspiration if they had a P‐A score ≥5. ¹² Other variables evaluated on VFSS and respiratory fluoroscopy are presented in Table 1. Other diagnostic tests including laryngeal function examinations (with doxapram), bronchoscopy, bronchoalveolar lavage fluid (BALF) cytology, and BALF culture were evaluated where available.

TABLE 1.

Summary of conformational, VFSS, and respiratory fluoroscopic abnormalities in dogs with and without aerophagia as diagnosed by VFSS.

	Aerophagic (n = 48)	Nonaerophagic (n = 72)	Total (n = 120)	P value	OR (95% CI)
Pathologic P‐A	20 (41.6%)	17 (23.6%)	37 (30.8%)	.04	2.3 (1.0‐5.1)
Brachycephalic conformation	22 (45.8%)	10 (13.8%)	32 (26.6%)	<.001	5.2 (2.2‐12.6)
Macroaspiration	12 (25%)	8 (11.1%)	20 (16.6%)	.04	2.7 (1.0‐7.1)
Upper airway obstruction (non‐BOAS)	16 (33.3%)	3 (4.1%)	19 (15.8%)	<.001	12.6 (3.4‐46.2)
Laryngeal paralysis	5 (10.4%)	2 (2.7%)	7 (5.8%)
Epiglottic retroversion	4 (8.3%)	0	4 (3.3%)
Laryngeal mass	3 (6.3%)	0	3 (2.5%)
Laryngeal collapse	3 (6.3%)	0	3 (2.5%)
Pharyngeal collapse	2 (4.2%)	1 (1.4%)	3 (2.5%)
Laryngeal paresis	2 (4.2%)	1 (1.4%)	3 (2.5%)
Cervical tracheal collapse	2 (4.2%)	0	2 (1.6%)
Nasal mass	1 (2.1%)	0	1 (.8%)
Enlarged retropharyngeal lymph nodes	1 (2.1%)	0	1 (.8%)
Nasopharyngeal foreign body	1 (2.1%)	0	1 (.8%)
Other respiratory fluoroscopy abnormalities (inclusive of BOAS)
ESP	17 (35.4%)	4 (5.6%)	21 (17.5%)	<.001	9.3 (2.9‐10)
Pharyngeal collapse	13 (27.1%)	3 (4.1%)	16 (13.3)	<.001	8.5 (2.3‐32)
MSBC	3 (6.3%)	10 (13.9%)	13 (10.8%)	.19
Intrathoracic tracheal collapse	2 (4.2%)	9 (12.5%)	11 (9.1%)
OP dysfunction	5 (10.4%)	6 (8.3%)	11 (9.1%)
PP dysfunction	12 (25%)	11 (15.3%)	23 (19.1%)	.08
Pharyngeal weakness	8 (16.6%)	11 (15.2%)	19 (15.8%)	.84
UES achalasia	5 (10.4%)	0	5 (4.1%)
Abnormal UES relaxation a	3 (6.3%)	0	3 (2.5%)
UES dyssynchrony	2 (4.1%)	0	2 (1.6%)
EP dysfunction	19 (39.6%)	30 (41.7%)	49 (40.8%)	.82
ME (diffuse hypomotility)	13 (27.1%)	21 (29.1%)	34 (28.3%)	.80
LES‐AS	5 (10.4%)	7 (9.7%)	12 (10%)
ME (idiopathic)	1 (2.1%)	6 (8.3%)	7 (5.8%)
ME (aperistaltic)	0	4 (5.6%)	4 (3.3%)
Proximal hypomotility	3 (6.3%)	0	3 (2.5%)
Pathologic reflux	21 (43.8%)	32 (44.4%)	53 (44.1%)	.71
Proximal	12 (25%)	16 (22.2%)	28 (23.3%)	.93
Middle	7 (14.6%)	9 (12.5%)	16 (13.3)	.74
Extra‐esophageal reflux	2 (4.2%)	7 (9.7%)	9 (7.5%)
Nasopharyngeal reflux	1 (2.1%)	0	1 (0.8%)
Esophago‐oropharyngeal reflux	1 (2.1%)	0	1 (0.8%)
Sliding hiatal hernia	12 (25%)	9 (12.5%)	21 (17.5%)	.08

Note: VFSS parameters were evaluated as previously described. ¹² Each dog may have more than 1 abnormality. All comparisons were made using a chi‐squared test with a P value of <.05 was considered significant. Odds ratio (OR) with 95% confidence intervals (CI) are displayed for variables reaching significance. Percentages reflect the percent of dogs displaying a particular trait/diagnosis within each category (Aerophagic [n = 48], Nonaerophagic [n = 72], Total [n = 120]).

Abbreviations: BOAS, brachycephalic obstructive airway syndrome; ESP, elongated soft palate; EP, esophageal phase; LES‐AS, lower esophageal sphincter achalasia‐like syndrome; MSBC, mainstem bronchial collapse; ME, megaesophagus; OP, oral‐preparatory; P‐A, penetration‐aspiration; PP, pharyngeal phase; UES, upper esophageal sphincter.

^a Abnormal UES relaxation, refers to spontaneous relaxation and opening of the UES independent of pharyngeal swallow or eructation (eg, during quiet breathing or panting).

2.2. Statistical analysis

Statistical analysis was performed using commercial statistical analysis software (SigmaPlot 14.5). Descriptive statistics were calculated where appropriate. Normality was evaluated using the Shapiro‐Wilk test. Data for categorical variables were presented as (n) ± percentage. Data for quantitative variables are presented as mean ± SD or median (interquartile range [IQR]) for normally and nonnormally distributed data, respectively. Between group comparisons were performed using Mann‐Whitney and chi‐squared tests. Significance was set at P < .05. Comparisons reaching significance were subjected to multiple logistic regression with aerophagia as the dependent variable. Odds ratios with a 95% confidence interval (CI) were calculated for comparisons reaching significance. To decrease type 2 error, statistical comparisons were limited to clinical, demographic, or diagnostic variables exhibited by >12 dogs. Variables exhibited by ≤12 dogs are provided descriptively.

3. RESULTS

3.1. Animals

One hundred twenty client‐owned companion dogs were enrolled: AU VTH (n = 60), MU VHC (n = 60). Forty‐one breeds were represented (Table 2). Overall median (IQR) age at presentation was 6 years (1.7‐10.0 years; range, 2.5 months‐15.6 years). Twenty dogs were <1 year of age at the time of evaluation (aerophagic, n = 10; nonaerophagic, n = 10). Sixty‐seven of 120 dogs were mesaticephalic, 32/120 were brachycephalic, and 21/120 were dolichocephalic. Sixty‐four dogs were male (25 intact [MI]; 39 castrated [MC]) and 56 were female (9 intact [FI]; 47 spayed [FS]). The median (IQR) weight was 14.5 kg (7.0‐26.8 kg; range, 2.2‐67.7 kg). Body condition scores were available in 118/120 dogs. The median (IQR) BCS was 5/9 (4‐7; range, 1‐9). Dogs were presented exclusively for respiratory CS (n = 41/120), exclusively for GI CS (n = 38/120), or with mixed [GI and respiratory] CS (n = 41/120). Reported respiratory and GI CS are presented in Table 3. Twelve dogs had reported abnormalities on neurologic examination: 4 dogs had abnormalities consistent with diffuse polyneuropathy, 2 with right head tilt, and 1 each with anisocoria, T3‐L3 myelopathy, generalized hyperesthesia, decreased gag, pelvic limb weakness, and facial nerve paralysis. Nineteen dogs had evidence of upper airway obstruction unrelated to BOAS (Table 1). The median (IQR) duration of CS was 4 months (2‐12 months; range, 2 weeks‐10 years). Twenty‐five dogs had a history of aspiration pneumonia before presentation (aerophagic [n = 11]; nonaerophagic [n = 14]).

TABLE 2.

Number (n) of dogs of various breeds undergoing sequential VFSS.

Dog (n)	Breed
21	Mixed
13	French bulldog
10	Labrador retriever
6	German shepherd dog, English bulldog
5	Miniature dachshund
4	Chihuahua, beagle, boxer
3	Golden retriever, shih tzu, Australian shepherd, pug, cockapoo
2	Havanese, Pomeranian, Yorkshire terrier, miniature poodle, rat terrier
1	Australian cattle dog, standard poodle, papillon, labradoodle, golden doodle, West Highland white terrier, English cocker spaniel, Great Pyrenees, Cavalier King Charles spaniel, husky, Airedale terrier, Portuguese water dog, English setter, Staffordshire terrier, Gordon setter, bloodhound, miniature pinscher, Weimaraner, Newfoundland, Bernese Mountain dog, Maltese

TABLE 3.

Summary of presenting clinical signs (CS) for dogs with and without aerophagia as diagnosed by videofluoroscopic swallow study.

Clinical signs	Aerophagic (n = 48)	Nonaerophagic (n = 72)	Total (n = 120)	P value	OR (95% CI)
Respiratory only	12 (25%)	29 (40.2%)	41 (34.1%)	.08
Cough	33 (68.8)	39 (54.2%)	72 (0.6%)	.17
Nasal discharge	9 (18.8%)	10 (13.9%)	19 (15.8%)	.48
Respiratory distress	11 (22.9%)	6 (8.3%)	17 (14.2%)	.29
Stertor	7 (14.6%)	2 (2.7%)	9 (7.5%)
Stridor	5 (10.4%)	4 (5.5%)	9 (7.5%)
Exercise intolerance	5 (10.4%)	2 (2.7%)	7 (5.8%)
Wheeze	6 (12.5%)	0	6 (5%)
Sneezing	0	5 (6.9%)	5 (4.1%)
Dysphonia	3 (6.3%)	1 (1.4%)	4 (3.3%)
Reverse sneezing	2 (4.2%)	0	2 (1.7%)
Collapse	1 (2.1%)	1 (1.4%)	2 (1.6%)
Sleep disordered breathing	1 (2.1%)	0	1 (0.8%)
Hacking	1 (2.1%)	0	1 (0.8%)
Snoring	0	1 (1.3%)	1 (0.8%)
GI only	9 (18.8)	29 (40.3%)	38 (31.7%)	.01	0.34 (0.14‐0.81)
Regurgitation	22 (45.8%)	30 (41.7%)	52 (43.3%)	.65
Vomiting	6 (12.5%)	9 (12.5%)	15 (12.5%)	1
Gagging	12 (25%)	2 (2.7%)	14 (11.7%)	<.001	11.7 (2.5‐55)
Hard swallowing	4 (8.3%)	2 (2.7%)	6 (5%)
Repetitive swallowing	2 (4.2%)	4 (5.6%)	6 (5%)
Ptyalism	3 (6.3%)	1 (1.4%)	4 (3.3%)
Lip licking	2 (4.2%)	2 (2.7%)	4 (3.3%)
Decreased appetite	2 (4.2%)	1 (2.7%)	3 (2.5%)
Bloating	1 (2.1%)	1 (1.4%)	2 (1.7%)
Dropping food	1 (2.1%)	1 (1.4%)	2 (1.7%)
Weight loss	0	1 (1.4%)	1 (0.8%)
Bruxism	0	1 (1.4%)	1 (0.8%)
Fly biting	1 (2.1%)	0	1 (0.8%)
Flatulence	0	1 (1.4%)	1 (0.8%)
Mixed respiratory and GI CS	28 (58.3%)	13 (18.1%)	41 (34.7%)	<.001	6.4 (2.9‐10)

Note: Clinical signs were included in the study if they were the reason for veterinary evaluation. Dogs may have had more than 1 CS. All comparisons were made using a chi‐squared test with a P value of <.05 was considered significant. Percentages reflect the percent of dogs displaying a particular trait/diagnosis within each category (Aerophagic [n = 48], Nonaerophagic [n = 72], Total [n = 120]) Odds ratio (OR) with 95% confidence intervals (CI) are displayed for variables reaching significance.

3.2. Diagnostic imaging

Videofluoroscopic swallow studies and respiratory fluoroscopy were successfully performed in all dogs (n = 120). No dogs were excluded for failure to complete the study in keeping with our inclusion criteria. Twenty‐two dogs had unremarkable VFSS. Abnormalities were identified in 98/120 dogs: oral‐preparatory phase (OP; n = 11/98), pharyngeal phase (PP, n = 23/98), and esophageal phase (EP; n = 49/98), and pathologic GERD with normal OP, PP and EP swallows (n = 17/98). Each dog may have had >1 abnormality. The incidence (95% CI) of pathologic aerophagia was 40% (31.7‐48.9; n = 48/120). Aerophagia was identified when consuming liquid alone (n = 22), puree alone (n = 2), kibble alone (n = 1), or with >1 consistency (n = 23). Pathologic P‐A (ie, P‐A score ≥3) was identified in 37/120 dogs. The median (IQR) P‐A score was 2/7 (1‐3; range, 1‐7). Thoracic radiographs were available for review in 113/120 dogs. Specific abnormalities identified on VFSS, respiratory fluoroscopy, and thoracic radiographs are presented in Tables 1 and 4.

TABLE 4.

Summary or thoracic radiographic abnormalities identified in dogs with and without aerophagia as diagnosed by VFSS.

Radiographic findings	Aerophagic (n = 45)	Nonaerophagic (n = 68)	Total (n = 113)	P value
Unremarkable	18 (40%)	23 (33.8%)	41 (36.3%)	.5
Aspiration pneumonia	6 (13.3%)	12 (17.6%)	18 (15.9%)	.62
Bronchial	6 (13.3%)	6 (8.8%)	12 (10.6%)
Megaesophagus	6 (13.3%)	6 (8.8%)	12 (10.6%)
Esophageal air	3 (6.7%)	6 (8.8%)	9 (8%)
Esophageal fluid	3 (6.7%)	5 (7.4%)	8 (7.1%)
Hypoplastic Trachea	5 (11.1%)	1 (1.5%)	6 (5.3%)
Bronchiectasis	1 (2.2%)	4 (5.9%)	5 (4.4%)
Cardiomegaly	2 (4.4%)	2 (2.9%)	4 (3.5%)
Esophageal diverticula	2 (4.4%)	2 (2.9%)	4 (3.5%)
Broncho‐interstitial	0	3 (4.4%)	3 (2.7%)
Tracheal collapse (intrathoracic)	0	3 (4.4%)	3 (2.7%)
Interstitial	0	3 (4.4%)	3 (2.7%)
Sliding hiatal hernia	1 (2.2%)	0	1 (0.9%)
Laryngeal mass	1 (2.2%)	0	1 (0.9%)
Gastric foreign body	1 (2.2%)	0	1 (0.9%)
Gravel sign	1 (2.2%)	0	1 (0.9%)
Osteomas	0	1 (1.5%)	1 (0.9%)
Pulmonary nodules	0	1 (1.5%)	1 (0.9%)
Pectus craniatum	0	1 (1.5%)	1 (0.9%)
Vertebral malformations	1 (2.2%)	0	1 (0.9%)
Enlarged MPA	0	1 (1.5%)	1 (0.9%)
Tracheal stricture (intrathoracic)	0	1 (1.5%)	1 (0.9%)

Note: Main pulmonary artery (MPA). All comparisons were made using a chi‐squared test with a P value of <.05 was considered significant. Percentages reflect the percent of dogs displaying a particular radiographic finding within each category (Aerophagic [n = 45], Nonaerophagic [n = 68], Total [n = 113]).

Other diagnostic tests included functional upper airway examinations (with doxapram; n = 18/120), bronchoscopy (n = 12/120), BALF collection (n = 12/120), and BALF culture (n = 12/120). One of 12 dogs had a positive BALF culture (ie, moderate to heavy bacterial growth). Isolated bacteria included E. coli and Mycoplasma sp. Bronchoscopy, BALF cytology and upper airway examination findings are provided in Table 5.

TABLE 5.

Summary of results from bronchoscopy, bronchoalveolar lavage fluid (BALF) cytology, and laryngeal function examinations (with doxapram).

Findings	Aerophagic (n)	Nonaerophagic (n)	Total (n)
Bronchoscopy	3	9	12
Airway hyperemia	2 (66.7%)	3 (33.3%)	5 (41.7%)
Airway mucous	2 (66.7%)	2 (22.2%)	4 (33.3%)
Bronchial collapse (static or dynamic)	0	3 (33.3%)	3 (25%)
Bronchiectasis	1 (33.3%)	0	1 (8.3%)
BALF cytology	3	9	12
Nonseptic suppurative	3 (100%)	2 (22.2%)	5 (41.6%)
Eosinophilic	0	2 (22.2%)	2 (16.6%)
Septic suppurative	0	2 (22.2%)	2 (22.2%)
Mixed inflammation	0	2 (22.2%)	2 (22.2%)
Lymphocytic inflammation	0	1 (11.1%)	1 (8.3%)
Laryngeal function examination	12	6	18
Laryngeal paralysis	5 (41.7%)	2 (33.3%)	7 (38.8%)
Laryngeal paresis	2 (16.7%)	1 (16.7%)	3 (16.7%)
Laryngeal erythema	1 (8.3%)	2 (33.3%)	3 (16.7%)
Laryngeal collapse	3 (25%)	0	3 (16.7%)
Laryngeal mass	3 (25%)	0	3 (16.7%)
Laryngeal swelling	1 (8.3%)	0	1 (5.6%)
Everted laryngeal saccules	0	1 (16.7%)	1 (5.6%)

Note: Each dog may have >1 abnormality. Percentages for each finding reflect the percent of dogs having undergone bronchoscopy, BALF cytology, and or laryngeal function examination within each category (Aerophagic, Nonaerophagic, Total).

3.3. Between group comparisons

No significant differences were detected for dogs with and without aerophagia for age (P = .62), weight (P = .58), body condition score (P = .68), duration of CS (.48), respiratory rate (P = .93), or historical AP (P = .64). No statistically significant difference was found in the number of dogs with aerophagia between institutions (AU VTH and MU VHC; P = .06). Remaining between group comparisons, including those reaching statistical significance, are provided in Tables 1, 3, and 4. Using multivariable regression brachycephaly (P < .001), nonbrachycephalic upper airway obstruction (P < .001) and mixed respiratory and GI CS (P = .01) were found to be independent predictors of aerophagia.

4. DISCUSSION

Regardless of clinical indication for dogs undergoing VFSS at 2 tertiary referral centers, the incidence of pathologic aerophagia was high at 40%. Brachycephalic and upper airway obstruction unrelated to brachycephaly were independent predictors of aerophagia. Reflecting on its role as an aerodigestive disorder, aerophagia was significantly more common in dogs with mixed CS compared with dogs with exclusively respiratory CS and was significantly less common in dogs with GI CS alone. Evaluation for aerophagia by VFSS should be considered an important diagnostic test, because few dogs with pathologic aerophagia showed substantial amounts of esophageal air on thoracic radiographs. Although our study did not find an association of aerophagia with GERD as observed in people, ⁹ reflux may have been intermittent and not captured during the captured cine loops, thus leading to underestimation. Aerophagia was more common in dogs presented for gagging, and in dogs with pathologic P‐A scores including macroaspiration. As such, aerophagia is associated with more than just nuisance behaviors (eg, flatulence and eructation), and may be a sign of or contributor to more important respiratory pathology such as upper airway obstruction or aspiration.

Aerophagia in people is considered a functional nausea and vomiting disorder ² that has substantial worldwide prevalence and associations with stress and cognitive impairment. ³ , ⁴ A metanalysis showed the pooled prevalence of aerophagia in children to be 3.66% (95% CI, 2.44‐5.12). ¹ In adults, prevalence has been reported as high as 25%. ²⁰ The incidence of aerophagia in our study was 40%, including both adult and juvenile dogs. A recent study showed that 0/15 healthy control dogs with VFSS had aerophagia, suggesting that hunger associated with overnight fasting or behavioral tendencies to eat quickly are less likely to explain the high incidence of aerophagia in our study. ¹⁸ However, differences in head conformation between humans and dogs may in part explain why aerophagia is more common in dogs, because brachycephaly was an independent predictor of aerophagia in our study. In addition to brachycephaly, other types of upper airway obstruction also were independent predictors of aerophagia. This finding is consistent with previous studies in animal models that demonstrated aerophagia and aspiration after occlusion of nasal airflow. ²¹ , ²² It was believed that the increased airway resistance and accompanying alveolar hypoventilation resulted in compensatory mechanisms to maintain alveolar ventilation. These included gasps after swallow apnea, which may contribute to air swallowing. ²¹ , ²² , ²³ , ²⁴ The phase of respiration after pharyngeal swallow also may increase the frequency of aerophagia in dogs. Although pharyngeal swallowing in people is most likely associated with the expiratory limb of the respiratory cycle, 80% of swallows in dogs occur during the inspiratory phase, which may further contribute to aerophagia in this population. ²⁵ , ²⁶ Stress is a contributor to aerophagia in people, ¹ , ⁴ but the dogs in our study had no differences in their presenting respiratory rate or presenting evidence of respiratory distress between the aerophagic and nonaerophagic groups. The high incidence of aerophagia in affected dogs in our study compared with humans also may be explained by evaluating a population for which there was a medical indication for VFSS and by combining both age groups (adults and juveniles). ¹ , ⁴ , ²⁰

In our study, dogs with aerophagia were more likely to have pathologic P‐A scores (ie, scores ≥3) and evidence of macroaspiration (ie, scores ≥5). Although neither of these were independent predictors of aerophagia, in people a positive association has been made between gastric gas accumulation and ventilator‐associated pneumonia ⁸ and between aspiration pneumonia and obstruction of the upper airway. ²⁷ , ²⁸ , ²⁹ Obstructive sleep apnea (OSA) in people is an example of increased upper airway resistance that has similarities to BOAS in dogs. ³⁰ , ³¹ People with OSA are at markedly increased risk of aspiration pneumonia. ²⁷ In breathing against increased upper airway resistance, the higher pressure gradient and vacuum pressure through the airways may increase the risk of aspirating oral contents. ³² Additionally, dogs with other forms of upper airway obstruction (eg, laryngeal paralysis), might have decreased laryngeal and pharyngeal sensitivity contributing to the increased P‐A scores and macroaspiration observed in our study. ³³ Interestingly, dogs with aerophagia were not more likely to have AP than nonaerophagic dogs. This finding has been identified previously in dogs with pathologic P‐A scores presented for CS of respiratory disease where pathologic P‐A scores were associated with airway rather than pulmonary parenchymal disease. ¹⁸

Aerophagia was more common in dogs with mixed CS and less likely in dogs with GI CS alone. This difference likely reflects the association between aerophagia and upper airway obstruction identified in our study. Some GI CS, including gag, although suggestive of dysphagia, also may suggest failure of airway protection. Gag was statistically more common in dogs with aerophagia in our study and is frequently identified in pediatric human patients where upper airway obstruction interferes with breath‐swallow coordination. ³⁴ Mixed CS also may be associated with increased gastric and intestinal gas which, in addition to causing nausea, vomiting, regurgitation, and abdominal discomfort, may inhibit diaphragmatic movement resulting in hypoventilation and exacerbation of existing respiratory CS. ³⁵ Interestingly, and contrary to the human medical literature, no association was found between GERD and aerophagia in our study. The relationship between GERD and aerophagia is well known in people, but a causal relationship has not yet been established. ⁹ , ³⁶ A limitation of VFSS to assess GERD is that GERD can be intermittent and missed during acquisition of the cine loops. Other complementary diagnostic testing (eg, wireless ambulatory pH monitoring) ³⁷ may be more sensitive for GERD diagnosis. Additional studies investigating pathologic GERD and its association with aerophagia in dogs are needed.

Our study had some limitations. Because it was a retrospective study, dogs did not undergo uniform testing. Furthermore, small numbers of dogs were presented for specific diagnostic and clinical endpoints. Because of the small numbers, not all findings could be evaluated statistically. Our study also lacked a control population, and thus the incidence of aerophagia in healthy dogs could not be determined and compared to the clinical population. However, a recent study of VFSS in dogs with respiratory signs included a control population of healthy dogs lacking respiratory and digestive clinical signs and this healthy population had no dogs with aerophagia.

5. CONCLUSIONS

In dogs evaluated by VFSS, aerophagia was common with an overall incidence of 40%. Using VFSS, dogs presenting with mixed CS were more likely to have aerophagia, dogs with primary GI signs were less likely to have aerophagia, and dogs with primary respiratory signs had no significant difference in aerophagia compared with those without aerophagia. Brachycephalic dogs and dogs with upper airway obstruction should be considered predisposed to development of aerophagia. Dogs with aerophagia should be considered at increased risk for pathologic P‐A and aspiration.

CONFLICT OF INTEREST DECLARATION

Teresa Lever is 1 of the patent holders of the kennels used for this study US Patent 9 107 385. No other authors declare a conflict of interest.

OFF‐LABEL ANTIMICROBIAL DECLARATION

Authors declare no off‐label use of antimicrobials.

INSTITUTIONAL ANIMAL CARE AND USE COMMITTEE (IACUC) OR OTHER APPROVAL DECLARATION

Authors declare no IACUC or other approval was needed.

HUMAN ETHICS APPROVAL DECLARATION

Authors declare human ethics approval was not needed for this study.

Grobman M, Reinero C, Lee‐Fowler T, Lever TE. Incidence and characterization of aerophagia in dogs using videofluoroscopic swallow studies. J Vet Intern Med. 2024;38(3):1449‐1457. doi: 10.1111/jvim.17054