Non-invasive real-time measurements of cardiac vagal tone in dogs with cardiac disease

In dogs with spontaneous heart disease, an electronically generated measurement of cardiac vagal tone, the cardiac index of parasympathetic activity, was a sensitive, simple and inexpensive measure of the severity of heart failure. Dogs with cardiac disease and an index score less than 3 were at 15.8 (95 per cent confidence interval 2.9 to 87.2) times the risk of dying within a year than those with a score of 3 and over. The measurement of the index provided an objective and reliable beat-by-beat measurement of cardiac vagal tone, which was prognostically useful in dogs with heart disease.     

Intragastric gavage with denatonium benzoate acutely induces neuronal activation in the solitary tract nucleus via the vagal afferent pathway

Natural toxic substances have a bitter taste and their ingestion sends signals to the brain leading to aversive oral sensations. In the present study, we investigated chronological changes in c-Fos immunoreactivity in the nucleus tractus solitarius (NTS) to study the bitter taste reaction time of neurons in the NTS. Equal volumes (0.5 mL) of denatonium benzoate (DB), a bitter tastant, or its vehicle (distilled water) were administered to rats intragastrically. The rats were sacrificed at 0, 0.5, 1, 2, 4, 8, or 16 h after treatment. In the vehicle-treated group, the number of c-Fos-positive nuclei started to increase 0.5 h after treatment and peaked 2 h after gavage. In contrast, the number of c-Fos-positive nuclei in the DB-treated group significantly increased 1 h after gavage. Thereafter, the number of c-Fos immunoreactive nuclei decreased over time. The number of c-Fos immunoreactive nuclei in the NTS was also increased in a dose-dependent manner 1 h after gavage. Subdiaphragmatic vagotomy significantly decreased DB-induced neuronal activation in the NTS. These results suggest that intragastric DB increases neuronal c-Fos expression in the NTS 1 h after gavage and this effect is mediated by vagal afferent fibers.     

Suspected vagal reflex and hyperkalaemia inducing asystole in an anaesthetised horse

A 10-year-old 466 kg mustang gelding presented to an equine referral hospital for surgical repair of nasal, frontal and lacrimal bone fractures from an unknown trauma. Surgical repair was performed under general anaesthesia, including a right-sided maxillary regional anaesthetic block with mepivacaine hydrochloride. Progressive hyperkalaemia was documented perianaesthetically (T-3 mins; 134 mins after induction; potassium 6.4 mmol/L (ref 3.5-5.1 mmol/L). Perianaesthetic bradycardia was attributed to alpha −2 agonist infusion administration, and other characteristic ECG changes (flattened P waves, narrow T waves of increased amplitude, prolonged QRS complex) were not documented. Asystole occurred 137 min after induction of anaesthesia; however, a review of the available literature suggests the degree of hyperkalaemia documented was unlikely to be the primary cause of asystole but may have been a contributing factor. It is hypothesised that a trigeminocardiac reflex was the primary contributory factor to asystole in the described case, and may represent a maxillomandibulocardiac reflex that has not been previously described in the horse.     

Use of vagal nerve stimulation as a treatment for refractory epilepsy in dogs

OBJECTIVE: To evaluate safety and efficacy of vagal nerve stimulation in dogs with refractory epilepsy. DESIGN: Placebo-controlled, double-masked, crossover study. ANIMALS: 10 dogs with poorly controlled seizures. PROCEDURE: A programmable pacemaker-like device designed to deliver intermittent stimulation to the left cervical trunk of the vagus was surgically implanted in each dog. Dogs were assigned randomly to two 13-week test periods, 1 with nerve stimulation and 1 without nerve stimulation. Owners recorded data on seizure frequency, duration, and intensity, as well as adverse effects. RESULTS: No significant difference in seizure frequency, duration, or severity was detected between overall 13-week treatment and control periods. During the final 4 weeks of the treatment period, a significant decrease in mean seizure frequency (34.4%) was detected, compared with the control period. Complications included transient bradycardia, asystole, and apnea during intraoperative device testing, and seroma formation, subcutaneous migration of the generator, and transient Horner's syndrome during the 14-day period between surgery and suture removal. No adverse effects of stimulation were detected, and most owners were satisfied with the treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Vagal nerve stimulation is a potentially safe approach to seizure control that appears to be efficacious in certain dogs and should be considered a possible treatment option when antiepileptic medications are ineffective.     

Effect of verapamil on cardiac chronotropic response to vagal stimulation in neonatal pigs

The effects of verapamil on the chronotropic response to vagal stimulation in young pigs anesthetized with sodium pentobarbital (30 mg/kg of body weight, intraperitoneally) was evaluated. After bilateral vagotomy, the administration of verapamil (loading dose of 100 micrograms/kg, followed by 2 micrograms/kg/min infusion) resulted in a significant (P less than 0.05) reduction in heart rate (HR) and mean arterial blood pressure. Cardiac frequency responses to vagal stimulation were obtained by stimulating the distal end of the right vagus nerve at selected frequencies (5, 10, 15, and 20 Hz) with supramaximal voltage (10 to 15 V) and constant duration (2 ms). The HR was measured after 15 s at each level of stimulation. The slopes of decrease in HR to the frequency of vagal stimulation were significantly (P less than 0.05) reduced after verapamil as compared with its controls. After atropine (0.5 mg/kg), the vagally induced tachycardia was partially attenuated by verapamil, but was completely eliminated by beta blockade with propranolol (1 mg/kg). These findings indicated that verapamil may influence the parasympathetic control of the heart in young pigs.     

Effect of adrenalectomy on cholecystokinin-8-induced Fos-like immunoreactivity in myenteric neurons and the dorsal vagal complex in rats

OBJECTIVE: To investigate the effect of adrenalectomy on cholecystokinin-8 (CCK-8)-induced Fos-like immunoreactivity (Fos-LI) in the myenteric neurons of the dorsal vagal complex (DVC) in rats. ANIMALS: 16 male Sprague Dawley rats. PROCEDURES: Rats were allocated to 1 of 2 groups and underwent adrenalectomy or a sham adrenalectomy procedure. Rats were challenged with a supraphysiologic dose of CCK-8 (40 microg/kg) or physiologic saline (0.9% NaCl) solution (0.5 mL) administered IP; after 90 minutes, rats were euthanized, and Fos-LI was quantified in the DVC (at the levels of the area postrema, nucleus tractus solitarii, and dorsal motor nucleus of the vagus) and the myenteric neurons of the duodenum and jejunum by use of a diaminobenzidine reaction enhanced with nickel. The Fos-LI-positive cells were counted by use of an automated system and manually in the DVC and intestinal samples, respectively. Counts of Fos-LI in the different hindbrain levels and myenteric neurons were compared between the adrenalectomy--and shamtreated groups and between the CCK-8- and saline solution-treated groups. RESULTS: After adrenalectomy, CCK-8-induced Fos-LI was attenuated only in the myenteric neurons of the duodenum. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that the adrenal gland has a role in the activation of myenteric neurons by CCK-8 in rats.     

Use of ocular compression to induce vagal stimulation and aid in controlling seizures in seven dogs

Ocular compression (OC) was used to treat 7 dogs with seizures. Treatment was accomplished by use of digital pressure applied to one or both eyes by veterinarians, hospital staff, or owners. The OC was believed to exert an effect through stimulation of the vagus nerve. Use of OC appeared to be efficacious for aborting seizures in 3 dogs, decreasing heart rate and causing muscle relaxation in 1 dog, and preventing onset of seizures in 2 other dogs. In 1 dog, rhythmic application of OC caused onset of rhythmic facial twitches. Administration of OC may be beneficial in treating seizuring dogs.     

Dysphagia caused by focal guttural pouch mycosis: mononeuropathy of the pharyngeal ramus of the vagal nerve in a 20-year-old pony mare

A 20-year-old pony mare was presented to the equine hospital with a ten-day history of dysphagia, regurgitation and coughing. An obstruction of the oesophagus was excluded via endoscopy, but the proximal oesophagus appeared to be distended and circular contractions were missing. A guttural pouch endoscopy revealed a single, black-mottled plaque on the pharyngeal ramus of the vagus nerve in the left guttural pouch, causing a local swelling of this nerve. The pharyngeal ramus seemed to be atrophic distal to the lesion. A biopsy was taken from the lesion and histopathological findings proved the reasonable suspicion of a guttural pouch mycosis with a high degree of purulent-necrotic inflammation and invasion of fungal hyphae. There were no signs of neoplasia, such as melanoma. Daily guttural pouch irrigations with a clotrimazole emulsion (20 g Canesten^® Gyn⁴ solved in 500 ml water), led to a good recovery of the mucosa above the nerve. Periodic endoscopic examination of the left guttural pouch showed that local thickening and distal atrophy of this pharyngeal ramus did not improve, neither did the clinical symptoms. Due to progressive weight loss, acute respiratory distress and aspiration pneumonia, the 20-year-old pony mare unfortunately had to be euthanized three weeks after discharge. This case report emphasizes the enormous importance of a single nerve for the realization of the swallowing process. The one-sided loss of function of the pharyngeal branch of the vagal nerve cannot be compensated neither by the remaining ipsilateral nerves nor by the contralateral normal functioning glossopharyngeal and vagal nerves and thus inevitably leads to severe dysphagia.     

Effects of vagal maneuvers on heart rate and Doppler variables of left ventricular filling in healthy cats

BackgroundEvaluation of left ventricular (LV) diastole is clinically important in cats with heart disease. Diastolic dysfunction is a main characteristic of feline cardiomyopathy and is associated with clinical signs and poor outcome. Numerous echocardiographic indices characterizing LV diastole exist, of which Doppler variables of transmitral flow and mitral annular motion are used most often. However, rapid heart rate (HR), a common finding in cats examined in the veterinary hospital environment, may cause summation of flow waves limiting interpretation of diastolic function.ObjectiveTo evaluate the effects of vagal maneuvers (gentle eyeball pressure and nasal planum massage) on HR and Doppler variables of LV diastolic filling.AnimalsTwenty-four healthy client-owned cats with summated transmitral flow waves at baseline.MethodsProspective observational study. Transthoracic echocardiography was performed and Doppler transmitral and mitral annular tissue Doppler velocities recorded both before and during vagal maneuvers. Data were compared using a paired t-test.ResultsApplication of vagal maneuvers temporarily decreased HR in all cats (mean reduction ± SD; 42 ± 22 bpm). The duration of HR reduction (<5 s, 5–10 s, and >10–15 s) was evenly distributed among groups (8 cats in each). Summated Doppler transmitral flow and mitral annular tissue velocity waves were separated during vagal maneuvers in 71% and 72% of cats, respectively. No adverse effects were observed.ConclusionsVagal maneuvers may be utilized as a simple non-pharmacologic tool in the Doppler evaluation of LV diastolic function in healthy cats.     

Etiology, forms, and prognosis of gastrointestinal dysfunction resembling vagal indigestion occurring after surgical correction of right abomasal displacement

The objectives of this study were to determine the etiology and types of vagal indigestion (VI) occurring after right displacement of the abomasum or abomasal volvulus (RDA/AV), and the prognosis for each type. Data of cows presented for RDA/AV from a retrospective (n = 288) and a prospective (n = 132) study were used. Vagal indigestion occurred in 39 and 22 cows in each study, respectively. A necropsy was performed in 29 cases. Gastric compartment dilation compatible with VI type III or IV occurred in 23 cases. An abnormal gastric wall was detected in 22 cases. Peritonitis was present in 18 cows. Vagal nerve lesions were present in 5 out of 13 cases studied. Clinical, hematological, and necropsy results suggested a classification of VI with respect to presence or absence of peritonitis. Gastric wall damage, peritonitis and vagal nerve lesions appear important in the etiology. Considering peritonitis occurrence, antimicrobial therapy appears necessary in the treatment of RDA/AV.