Reflex activities of the upper airway muscles during experimental nasal occlusion in anesthetized dogs

Reflex responses of the upper airway muscles during experimental nasal and tracheal occlusions were studied in 21 anesthetized dogs breathing through the nose or a tracheostomy (tracheal cannula). Out of them, five animals were examined for maintained negative and positive pressures applied to the isolated upper airway. When the nose was occluded at end-expiration during three consecutive breathings, the electromyographic (EMG) activity of alae nasi (AN) and posterior cricoarytenoid (PCA) muscle markedly increased. The upper airway was subjected to negative pressure, -2.41 approximately -3.04 kPa (n = 34) by these nasal occlusions. The activity of upper airway muscles was also increased by tracheal occlusions. However, such augmentation of PCA activity was much less in tracheal occlusions than nasal occlusions, whereas there was the smaller difference in AN activity between both occlusions. During nasal occlusions, a prolongation of the inspiratory time (TI) was observed. Furthermore, maintained negative pressure applied to the isolated upper airway provoked an augmentation of PCA activity. Such an augmented EMG activity of PCA and the prolongation of TI were largely diminished by sectioning the superior laryngeal nerves. These results proves that the upper airway muscles play an important role to protect the upper airway from collapsing by nasal occlusions. In addition, it is suggested that a lack of lung volume feedback is substantially concerned with the activation of AN, while negative pressure in the upper airway is essential to stimulate PCA.     

Vagal afferent activities and respiratory reflexes during drug-induced bronchoconstriction in the guinea pig.

Vagal afferent activities and respiratory reflexes during drug-induced bronchoconstriction were studied in 31 anesthetized, spontaneously breathing or artificially ventilated guinea pigs. Histamine (5, 10, 20 micrograms/kg), ACh (10, 20, 40 micrograms/kg) and endothelin-1 (2 micrograms/kg) were intravenously injected to the animals in order to induce the bronchoconstriction. In spontaneously breathing and vagi intact animals, a considerable respiratory change characterized by rapid-shallow breathing was elicited by histamine. Such respiratory change was abolished by bilateral vagotomy, indicating that the vagal pathway fairly participated in the respiratory change during bronchoconstriction. Indeed, recordings of electrical activities of single vagal afferent nerve fibers from pulmonary stretch and irritant receptors elucidated that the bronchoconstriction by the three drugs markedly influenced these receptor activities. The response of stretch receptors to bronchoconstriction was grouped into four types: two of those types showed a marked increase in their activities and the other two a decrease or no change. Such uneven response was assumed to be derived from heterogenous contraction and aeration among the intrapulmonary small airway. On the other hand, irritant receptors were invariably stimulated by increased transmural pressure during bronchoconstriction. Administration of isoproterenol (20 micrograms/kg) which inhibited the smooth muscle contraction abolished stimulatory effect of the drugs to irritant receptors, suggesting that the effect was due to indirect action through the muscle contraction rather than their direct action to the nerve endings.     

Nasal sensory receptors responding to capsaicin, water and tactile stimuli in sevoflurane-anesthetized dogs.

Responses of nasal receptors to capsaicin and water were studied from afferent recordings of the posterior nasal nerve (PNN) in 12 anesthetized dogs. Out of 12 non-respiration-modulated nasal receptors, 7 responded only to capsaicin, 3 responded to both water and capsaicin, and 2 to neither of them. All the fibers showed a rapid adaptation to mechanical probing of the nasal mucosa. These results indicate that the presence of sensory receptors responding to capsaicin and water are involved in PNN afferents of the dog.     

Relationship between clinical signs and lung function in horses with recurrent airway obstruction (heaves) during a bronchodilator trial

During a trial to determine the dose response to the beta2-adrenergic agonist pirbuterol, we judged the severity of airway obstruction by use of a clinical scoring system and compared this to objective data obtained by quantitative measures of lung function. Six horses affected by recurrent airway obstruction were used in this trial. Four hundred and sixty-eight measurements of lung function and clinical scores were obtained from 13 measurement periods when horses received each of 6 doses of pirbuterol. Scores of 1-4 were assigned to degree of nasal flaring and abdominal effort and summed for a total score. The veterinarian scoring the signs did not know the dose of pirbuterol received by the horse and was unaware of the lung function data. Nasal, abdominal and total scores were significantly related to changes in lung function and changes in breathing pattern. There were significant differences between total scores greater than 5 in indices that reflected changes in breathing strategy (peak inspiratory and expiratory flow), peripheral airway obstruction (dynamic elastance), and effort of breathing (maximal change in pleural pressure). Below a total score of 5, there were fewer significant differences in lung function even though measurements of pulmonary resistance and dynamic elastance indicated considerable airway obstruction. Failure of clinical score to reflect this low-grade airway obstruction suggests that airway disease is underdiagnosed and its detection would be helped by the availability of a convenient lung function test.     

Airway responsiveness measured by barometric plethysmography in guinea pigs

Barometric plethysmography has become an increasingly used method to indirectly measure respiratory function in unrestrained freely-moving animals. This technique has been criticized because of physiological uncertainty of its major index, the enhanced pause (Penh). Moreover, a recent study raises concerns that during histamine challenges part of the Penh response could be produced by upper airways (nasal) responses. In this study we compared airway responsiveness measured by barometric plethysmography and total lung resistance (RL) in guinea pigs, and evaluated the role of upper airways during Penh measurement. Our results showed that intravenous acetylcholine or histamine caused a dose-dependent increase of the Penh values in non-anesthetized guinea pigs, which were correlated with RL values obtained in separate groups of anesthetized animals. In anesthetized but spontaneously breathing guinea pigs intravenous acetylcholine or histamine also produced a dose-dependent increment of Penh, which was similar regardless if guinea pigs breathed through the nose or through a tracheal tube. Our results suggest that, independently of the physiological meaning of Penh, this index seems to be a useful indirect measurement for evaluating airway responsiveness to intravenous agonists in guinea pigs, and that nasal passage seems not to be involved in this measurement.     

Effects of volatile anesthetics on the activity of laryngeal 'drive' receptors in anesthetized dogs.

Effects of halothane, isoflurane and sevoflurane on laryngeal drive receptor activity were studied in the afferent activity of the superior laryngeal nerve in anesthetized spontaneously breathing dogs. Of 40 single units recorded, most of them (65%) responded to the volatile anesthetics applied to the isolated larynx at a concentration of 5%. The exposure to the anesthetics resulted in either an inspiratory increase (15%), both inspiratory and expiratory decrease (54%), or both inspiratory increase and expiratory decrease (31%) responses. The average discharge frequency of the receptors tended to be decreased on inhalation of the anesthetics, where significant decreases were observed in both respiratory phases for halothane and at expiration for isoflurane, but in neither respiratory phase for sevoflurane. These results support an advantage of sevoflurane over halothane and isoflurane for induction of anesthesia to minimize the influence of the activity of laryngeal drive receptors on the breathing pattern and airway stability.     

Respiratory reflexes in response to nasal administration of halothane to anesthetized, spontaneously breathing dogs

OBJECTIVE: To characterize and determine the sensory innervation of respiratory reflexes elicited by nasal administration of halothane to dogs. ANIMALS: 10 healthy Beagles. PROCEDURE: Dogs underwent permanent tracheostomy and, 2 to 3 weeks later, were anesthetized with thiopental and alpha-chloralose administered IV. The nasal passages were functionally isolated so that halothane could be administered to the nasal passages while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to administration of halothane at concentrations of 1.25, 1.75, and 2.5 times the minimum alveolar concentration (MAC), and 5% (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of 5% halothane were also recorded following transection of the infraorbital nerve, transection of the caudal nasal nerve, and nasal administration of lidocaine. RESULTS: Nasal administration of halothane induced an inhibition of breathing characterized by a dose-dependent increase in expiratory time and a resultant decrease in expired volume per unit time. Effects were noticeable immediately after the onset of halothane administration and lasted until its cessation. Reflex responses to halothane administration were attenuated by transection of the caudal nasal nerve and by nasal administration of lidocaine, but transection of the infraorbital nerve had no effect. CONCLUSIONS AND CLINICAL RELEVANCE: Nasal administration of halothane at concentrations generally used for mask induction of anesthesia induces reflex inhibition of breathing. Afferent fibers in the caudal nasal nerve appear to play an important role in the reflex inhibition of breathing induced by halothane administration.     

Ethmoidal hematoma in nine horses

Ethmoidal hematoma was diagnosed in 9 horses by results of physical examination, endoscopy, radiography, and histologic examination of tissues. The horses had stertorous breathing (n = 4) or intermittently sanguineous nasal discharge (n = 7). All horses underwent sinusotomy and extirpation of the lesion. At reexamination 15 to 104 months after surgery (mean, 61 months), 3 horses had recurrence of ethmoidal hematoma, and 1 horse had ethmoidal hematoma involving the contralateral ethmoturbinates. One of the horses with recurrence of ethmoidal hematoma also developed a contralateral lesion; both lesions recurred and additional surgeries were performed.     

Nasal Septum Resection in the Horse

The nasal septum was surgically removed from 22 horses with upper airway obstruction caused by thickening and/or deviation of the septum. The most common presenting complaints were a low-pitched, snoring, respiratory noise and respiratory difficulty during exercise, which usually occurs in young horses. Abnormalities of the septum were most commonly congenital defects or caused by trauma or inflammation secondary to severe respiratory infection.
Diagnosis was made based on history, clinical signs, and results of physical examination. Radiography and endoscopy were useful adjuncts in some horses.
Under general anesthesia, the septum was removed by scalpel and osteotome (19 horses) or by obstetrical wire and osteotome (1 horse). In two horses, the rostral one third of the septum was removed by scalpel alone.
In three horses, the alar folds and floor of the nasal diverticula were removed in an attempt to relieve airway obstruction caused by flattening of the bridge of the nose following removal of the nasal septum.
Follow-up was obtained on 18 horses: persistent noise during exercise continued in 90%; however, 50% returned to usefulness.     

Abstracts: LVII Annual Meeting of the Italian Society for Veterin Ary Sciences (SISVET), Ischia 2003

The Bactrian camel is an important domestic animal in some of the desert and semi-desert areas of the world. However, there is no detailed report about the nervous supply to the nasal cavity of the Bactrian camel. In the present study, seven heads of adult Bactrian camels were collected and the nerve distribution in the nasal cavity was dissected grossly. The results demonstrated that the nerves supplying to the nasal cavity included the olfactory nerve, the ethmoidal nerve from the ophthalmic nerve, and the caudal nerve from the maxillary nerve. The general patterns of nervous distribution in the nasal cavity of the Bactrian camel corresponded with those of other domestic animals. However, the terminal nerve was not observed by this gross anatomical method in the Bactrian camel.     

Respiratory reflexes in response to upper-airway administration of sevoflurane and isoflurane in anesthetized, spontaneously breathing dogs

OBJECTIVE: To evaluate the respiratory effects occurring during administration of sevoflurane or isoflurane to the upper airway in dogs. STUDY DESIGN: A prospective, randomized study. ANIMALS: Twelve healthy adult beagles (6 males, 6 females). METHODS: At least 2 weeks after undergoing permanent tracheostomy, dogs were premedicated with acepromazine-buprenorphine, and anesthesia was induced with thiopental and maintained with alpha-chloralose. The upper airway was functionally isolated so that the inhalant could be administered to the upper airway while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to the administration of sevoflurane or isoflurane at concentrations of 1.2, 1.8, and 2.4 times the minimal alveolar concentration (MAC) (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of each anesthetic were also recorded following upper-airway administration of lidocaine. RESULTS: Respiratory reflexes elicited by upper-airway administration of each anesthetic were characterized by a dose-dependent increase in expiration time, with a resultant decrease in respiratory minute ventilation and increase in end-tidal PCO2. The magnitude of these responses was greater with isoflurane than with sevoflurane at 1.8 and 2.4 MAC. These reflexes were abolished after lidocaine nebulization into the upper airway. CONCLUSION: Isoflurane induces greater reflex inhibition of breathing than does sevoflurane when the anesthetic is inhaled into the upper airway at concentrations used for mask induction.     

Effect of commercially available nasal strips on airway resistance in exercising horses

OBJECTIVE: To determine the effect of a commercially available nasal strip on airway mechanics in exercising horses. ANIMALS: 6 horses (5 Standardbreds and 1 Thoroughbred). PROCEDURE: Horses exercised on a treadmill at speeds corresponding to 100 and 120% of maximal heart rate with and without application of a commercially available nasal strip. Concurrently, tracheal pressures, airflow, and heart rate were measured. Peak inspiratory and expiratory tracheal pressures, airflow, respiratory frequency, and tidal volume were recorded. Inspiratory and expiratory airway resistances were calculated by dividing peak pressures by peak flows. Endoscopic examination of the narrowest point of the nasal cavity (ie, nasal valve) was performed in 1 resting horse before, during, and after application of a nasal strip. RESULTS: During exercise on a treadmill, peak tracheal inspiratory pressure and inspiratory airway resistance were significantly less when nasal strips were applied to horses exercising at speeds corresponding to 100 and 120% of maximal heart rate. Application of the nasal strip pulled the dorsal conchal fold laterally, expanding the dorsal meatus. CONCLUSIONS AND CLINICAL RELEVANCE: The commercially available nasal strip tented the skin over the nasal valve and dilated that section of the nasal passage, resulting in decreased airway resistance during inspiration. The nasal strip probably decreases the amount of work required for respiratory muscles in horses during intense exercise and may reduce the energy required for breathing in these horses.     

Excision of Tumors in the Nasal Vestibule of Two Dogs

Two dogs with tumors in the left nasal vestibule were treated by surgical excision of the affected part of the nose. Radiation and chemopotentiation were used in one dog, which remained tumor-free after 12 months. When recovering from anesthesia, the second dog developed respiratory distress associated with upper airway obstruction and failure to mouth breathe. The dog was successfully treated by temporary tracheostomy and remained tumor-free after 3 months. Surgery preserved the function of the right nostril and gave an acceptable cosmetic result in both cases.     

Effects of stylopharyngeus muscle dysfunction on the nasopharynx in exercising horses

REASONS FOR PERFORMING STUDY: Nasopharyngeal collapse has been observed in horses as a potential cause of exercise intolerance and upper respiratory noise. No treatment is currently available and affected horses are often retired from performance. OBJECTIVE: To determine the effect of bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction on nasopharyngeal function and airway pressures in exercising horses. METHODS: Endoscopic examinations were performed on horses at rest and while running on a treadmill at speeds corresponding to HRmax50, HRmax75 and HRmax, with upper airway pressures measured with and without bilateral glossopharyngeal nerve block. RESULTS: Bilateral glossopharyngeal nerve block caused stylopharyngeus muscle dysfunction and dorsal nasopharyngeal collapse in all horses. Peak inspiratory upper airway pressure was significantly (P = 0.0069) more negative at all speeds and respiratory frequency was lower (P = 0.017) in horses with bilateral glossopharyngeal nerve block and stylopharyngeus muscle dysfunction compared to control values. CONCLUSIONS: Bilateral glossopharyngeal nerve anaesthesia produced stylopharyngeus muscle dysfunction, dorsal pharyngeal collapse and airway obstruction in all horses. POTENTIAL RELEVANCE: The stylopharyngeus muscle is probably an important nasopharyngeal dilating muscle in horses and dysfunction of this muscle may be implicated in clinical cases of dorsal nasopharyngeal collapse. Before this information can be clinically useful, further research on the possible aetiology of stylopharyngeus dysfunction and dysfunction of other muscles that dilate the dorsal and lateral walls of the nasopharynx in horses is needed.     

Expression of vasoactive intestinal peptide, calcitonin gene-related peptide, substance P, and intermediate neurofilaments in nasal mucosal nerve fibers of horses without nasal disease

OBJECTIVE: To determine the distribution of nerve fibers containing calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal peptide (VIP), and intermediate neurofilaments in nasal mucosa of horses. ANIMALS: 6 horses without evidence of nasal disease. PROCEDURE: Full-thickness nasal tissue specimens were obtained from the rostral portion of the nasal septum at necropsy, and fluorescence immunohistochemistry was performed to assess mucosal distribution of nerve fibers. RESULTS: Nerve fibers with CGRP-like immunoreactivity (CGRP-Li) formed a dense subepithelial network, and a large number of fibers were found coursing between epithelial cells. Fibers with CGRP-Li were also associated with blood vessels and mucous glands. Fibers with SP-like immunoreactivity (SP-Li) had a similar distribution and density. In contrast, there were few fibers with VIP-like immunoreactivity. Fibers containing intermediate neurofilaments were prominent and appeared as large nerve fiber bundles mainly adjacent to the nasal septum but also close to mucous glands and within the lamina propria. Intermediate neurofilaments were also identified in single nerve fibers at all sites, but the density of fibers with intermediate neurofilaments did not match that of fibers with CGRP- or SP-Li. CONCLUSIONS: The density and distribution of nerve fibers containing SP- or CGRP-Li in nasal mucosa of horses was similar to that reported for other species. However, expression of VIP in nerve fibers was low. Antibodies against intermediate neurofilaments identified many nerve fibers in nasal mucosa of horses but did not appear to identify small diameter fibers expressing SP or VIP.     

Nasal swelling due to plasma cell infiltrate in a cat without plasma cell pododermatitis

A cat with an upper respiratory infection was presented for examination. Close examination of the face revealed a firm, haired rounded swelling on the bridge of the nose. Serum protein electrophoresis demonstrated a mild hypergammaglobulinaemia. The cat tested negative for feline immunodeficiency virus. Skin biopsy of the nasal lesion revealed nodular angiocentric infiltrates in the deep dermis and subcutis. The mixed infiltrate had numerous plasma cells. Presence of calicivirus antigen could not be demonstrated within the skin lesion by immunohistochemical staining. The cat was treated for upper respiratory infection and 1 month later the nasal lesion had resolved. A firm and rounded swelling over the bridge of the nose may be a feline cutaneous plasmacytic reaction pattern.     

Attempts to restore abduction of the paralyzed equine arytenoid cartilage. III. Nerve anastomosis.

The purpose of this project was to attempt restoration of abduction of a recently denervated left dorsal cricoarytenoid muscle in the horse by anastomosing the first cervical nerve to the abductor branch of the left recurrent laryngeal nerve. Ten horses were used in the study. In six horses the left recurrent laryngeal nerve was transected and ligated while the ventral branch of the left first cervical nerve was anastomosed to the abductor branch of the left recurrent laryngeal nerve. The remaining four horses also had the left recurrent laryngeal nerve transected and ligated but had no nerve anastomosis performed. Each horse was evaluated preoperatively, and at one week, three and six months after surgery, by endoscopy and determination of upper airway resistance. The endoscopy was performed with the horses breathing room air and while breathing 10% carbon dioxide. All ten horses showed endoscopic signs of complete laryngeal hemiplegia immediately postoperatively. Starting at three months postoperatively clonic movements of the left arytenoid cartilage were observed in four of the six reinnervated horses but not in the sham operated horses. At the sixth postoperative month five reinnervated horses had clonic movements of the left arytenoid cartilage. The comparison of upper airway resistance measurements before surgery and at one week, three and six months after surgery showed no significant differences in either control or experimental horses. Following euthanasia at six months postoperatively, the left and right dorsal crioarytenoid muscles were compared for evidence of reinnervation. No significant difference in weight was noted in the reinnervated horses but the left dorsal cricoarytenoid muscle weighed less than the control horses.     

Headshaking in horses: possible aetiopathogenesis suggested by the results of diagnostic tests and several treatment regimes used in 20 cases

Twenty mature horses with typical headshaking of 2 week-7 year duration were studied. Clinical examinations included radiography of the head and nasopharyngeal endoscopy. All were assessed at rest and at exercise, both before and after fitting an occlusive nasal mask, application of tinted contact lenses and the perineural anaesthesia of the infraorbital and posterior ethmoidal branches of the trigeminal nerve. Infraorbital anaesthesia had no effect in 6/7 cases but 11/17 (65%) cases showed a 90-100% improvement following posterior ethmoidal nerve anaesthesia. Tinted contact lenses had no apparent long-term benefit, although 2 cases showed a transient improvement. We found no other evidence to suggest a photic aetiology in the current series of cases. Treatment regimens based on the results of the diagnostic investigative methods included sclerosis of the posterior ethmoidal branch of the trigeminal nerve. This was effective in some cases but the benefits were temporary. Cyproheptadine alone was ineffective but the addition of carbamazepine resulted in 80-100% improvement in 80% of cases. Carbemazepine alone was effective in 88% of cases but results were unpredictable at predefined dose rates. The positive response to carbamazepine, combined with the clinical features is consistent with involvement of the trigeminal nerve, particularly the more proximal branches such as the posterior ethmoidal nerve. Headshaking has some clinical features in common with trigeminal neuralgia in humans. As a result of the findings detailed in this paper, we conclude that a trigeminal neuritis or neuralgia may be the basis of the underlying aetiopathology of equine headshaking. Initial observations of the positive response of headshakers to carbamazepine therapy is encouraging. However, future studies will include a more detailed investigation of dosages, duration of effectiveness (in some cases it appears short-lived) and other effects. In practice there is a realistic possibility of controlling but not curing headshaking with carbamazepine therapy at the present time. Other future investigations will include details of the functional anatomy of the trigeminal nerve and the role of the P2 myelin protein in headshaking and other neurological disease.     

Equine paranasal sinus cysts: a report of 15 cases

The clinical and radiographic features of 15 cases of paranasal sinus cysts are described. Breed, sex and side frequency were unremarkable but two distinct categories of age incidence emerged. Onset of signs had occurred before one year of age in three cases, while all but two of the remaining 12 animals were older than nine years. The most common clinical signs were nasal airway obstruction, facial swelling and nasal discharge, often occurring in combination. Radiographic changes were recorded in all horses. Sinus opacification was a consistent finding and in several cases the bone surrounding the sinus had increased in thickness. Increase in intra-maxillary sinus pressure was demonstrated by septal displacement on ventro-dorsal radiographs in almost half the cases. Less common signs included expansion, free fluid accumulation within the affected sinus, dental distortion and displacement and mineralisation. Two horses were destroyed without treatment but in 13 animals surgical exploration was performed. Two of these were destroyed, one at the time of surgery and one five days postoperatively. In the remaining 11 cases, all accessible parts of the cyst were removed through a facial flap and drainage to the nasal meati was established. All these horses recovered satisfactorily and were followed up for periods between three months and six years without evidence of recurrence. Thirteen cysts arose in the caudal maxillary sinus and one each in the frontal and rostral maxillary compartments. Histopathological examination of portions of the cyst walls suggests that, like ethmoidal haematomas, they may originate from episodes of haemorrhage beneath the upper respiratory tract mucosa.