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  • Author or Editor: Daniel J.-M. Desmecht x
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Summary

Although healthy and diseased bovine respiratory tracts have been intensively studied during the last years, to the authors’ knowledge, there have been no attempts to objectively examine the inspiratory drive from the brain to the nerves and muscles and its transformation in pressure. Such technique would be useful in assessing the possibility of altered ventilatory drive or inspiratory muscle fatigue in the context of an animal with ventilatory failure.

The relation among ventilation, airway opening occlusion pressure generated 100 milliseconds after onset of inspiration (Pawo100ms) and 6 indexes describing diaphragmatic electromyographic activity (emg di) recorded via implanted fishhooks was evaluated during free and impeded CO2 rebreathing in 6 young bulls. The best significant linear correlations (r > 0.8) with inspiratory center afferent stimulation, as judged by end-tidal CO2 concentration in expired air, were found for Pawo100ms, peak moving time average or variance emg di, and mean integrated emg di, whatever had been the respiratory impedance. However, with an inspiratory load, Pawo100ms responses systematically had greater increase for a given change in the driving emg di, implying dependence of the former not only on neural input, but also on configurational factors that determine inspiratory muscle excitation-pressure generation couplings. The reproducibility of emg di absolute values and changes was satisfactory up to 10 hours, but could not be repeated from one day to the other.

It was concluded that, provided the constancy of the electrical coupling of the recording system to the tissue being studied is ensured, specific emg di and Pawo100ms values correlate reliably with amount of CO2 during free and loaded breathing. Simultaneous collection of both values during experimentally induced pulmonary disease in calves could, therefore, produce information to help answer questions about the role of cns and inspiratory muscle dysfunction in case of ventilatory failure. Careful interpretation, however, requires additional measurements, such as end-expiratory lung volume, and some familiarity with the underlying physiologic processes that link phrenic nerve discharge to generation of negative pressure at the airway opening.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine whether a cholinergic mechanism interferes with the pulmonary response to 5-hydroxytryptamme (5-HT) in the bovine species.

Design

The protocols differed with regard to the type of pretreatment calves were given 10 minutes before administration of 5-HT (0.05 mg/kg of body weight/min, over 2 minutes). Pretreatment consisted of saline, atropine, or hexamethonium solution given IV.

Animals

6 healthy unsedated Friesian calves.

Procedure

Pulmonary function values were obtained before, during, and after 5-HT infusions.

Results

After saline pretreatment, response to 5-HT consisted of immediate and brief apnea, bradycardia, and hypotension, followed by sustained tachypnea, tachycardia, pulmonary hypertension, and hypocapnic hypoxemia. Lung dynamic compliance (CLdyn) decreased to 19% of its baseline value, and total pulmonary resistance (Rl) increased to 235%. Hexamethonium pretreatment resulted in a similar pattern of response except for the immediate and brief 5-HT-induced triad of apnea, bradycardia, and hypotension, which was suppressed. After atropine pretreatment, immediate and brief 5-HT-induced apnea-bradycardia-hypotension triad and sustained hypoxemia were abolished. In contrast, sustained tachypnea, tachycardia, pulmonary hypertension, and hypocapnia were maintained. Changes of CLdyn (59%) and Rl (138%) were significantly attenuated.

Conclusions

The initial and short-lasting response to 5-HT (ie, the apnea-bradycardia-hypotension triad) is mediated through a reflex central cholinergic pathway. The 5-HT-induced changes in Cldyn and Rl are consistent with development of diffuse bronchoconstriction. Attenuation of these changes by atropine suggests that this bronchoconstrictor response to 5-HT is partly mediated through a cholinergic postganglionic pathway. (Am J Vet Res 1996;57:896–901)

Free access
in American Journal of Veterinary Research

SUMMARY

Owing to technical and ethical limitations, a substantial part of the knowledge about the pathophysiologic mechanism of the human diaphragm has been obtained from studies in which phrenic nerve activation was usually carried out by direct surgical exposure of the nerves in the neck of deeply anesthetized, mechanically ventilated animals. Novel information has been gleaned from such studies, but the restrictive conditions under which it was collected preclude reliable extrapolation. We, therefore, addressed the question of whether accurate electrophysiologic evaluation of the phrenic nerve-diaphragm pathway can be performed in intact, nonanesthetized calves.

Transjugular phrenic activation was well tolerated, safe, specific, and able to achieve constant symmetric and supramaximal phrenic stimulations during prolonged periods. Eighteen noninvasive cutaneous and esophageal reception circuits were tested for their ability to record the diaphragmatic evoked potential. In addition, they were compared for specificity and reproducibility of the recorded potentials during prolonged periods of tidal or stimulated respiration. The best diaphragmatic potential was recorded from surface electrodes attached to the skin of the ninth and tenth intercostal spaces, using a xyphoidian reference.

We describe a method that allows easy, longterm, and reliable electrophysiologic evaluation of the phrenic nerve-diaphragm pathway in intact, conscious calves. It is hoped that such a model will produce relevant novel information regarding pathophysiology of the diaphragm.

Free access
in American Journal of Veterinary Research

Summary

A method yielding functional diaphragmatic variables in conscious animals is crucially needed to determine whether concepts and conclusions drawn from deeply anesthetized, highly instrumented clinically normal animals can be extrapolated to patients. Transdiaphragmatic pressure (Pdi) was, therefore, measured in 20 conscious calves during supramaximal transvenous bilateral stimulations of the phrenic nerves (pulse duration, 0.2 milliseconds; pulse frequency, 1, 10, 20, 30, 40, 70, and 100 Hz). Constancy of phrenic activation and precontraction length and geometry was ensured by respectively monitoring the amplitudes of right and left mass action potentials and triggering each activation train at end-expiratory lung volume against an occluded airway. Repeated phrenic activation and pressure recording procedures were well tolerated, safe, specific, and able to achieve constant and symmetric diaphragmatic tetanic contractions for prolonged periods. The Pdi increased with frequency of stimulation, so that, at 10, 20, 40, and 70 Hz, the mean ± sd generated Pdi was 33 ± 5, 65 ± 8, 82 ± 6, and 94 ± 6% of Pdi at 100 Hz, respectively. The general shape of the Pdi-frequency relation and the absolute values of the generated Pdi were reproducible at 10-hour intervals despite CO2- or resistor-induced substantial changes in breathing pattern. It is concluded that this experimental model provides a reliable assessment of diaphragm function in conscious animals and can be used to study diaphragmatic contractility.

Free access
in American Journal of Veterinary Research

Summary

Although the respiratory tract of healthy and diseased cattle has been intensively studied during the past few years, only a few attempts to detect dysfunctions of bovine inspiratory muscles have been reported. Such technique would be useful in assessing the possibility of inspiratory muscle fatigue in the context of ventilatory failure. Fatigue in skeletal muscle is associated with characteristic changes in the electromyographic power spectrum. Power spectral analysis was therefore applied to cattle diaphragmatic electromyograms (emg di) to precisely determine the exact influence of motion and ecg artifacts, describe its basic frequency content, and extract a spectral index capable of providing an accurate warning of fatigue.

The emg di was recorded via intramuscularly placed fishhook electrodes in 5 healthy young bulls during resting and stimulated respiration. The emg di and egc signals were analyzed by use of power spectral density analysis after band-pass filtering (20 to 1,800 Hz). The emg di spectrum was concentrated in the band width 20 to 530 Hz. Electrode motion artifacts were absent, and it was always possible to find an electrode pair giving ecg-free emg di. Of the 12 power and frequency values used to quantitate the spectrum, the most stable was the centroid frequency. It was reproducible within and between calves and was only minimally altered by changing inspiratory load.

Though the clinical relevance of fatigue in the respiratory musculature in case of ventilatory failure is currently unknown, the method described here constitutes a possible approach to detection of such phenomenon in cattle.

Free access
in American Journal of Veterinary Research

Summary

Effects of iv and aerosol administration of 5-hydroxytryptamine (5-ht) on ventilation, pulmonary mechanics values, pulmonary arterial pressure, and heart rate were investigated in healthy unsedated Friesian calves.

Minute volume increased significantly, mainly because of an increase in respiratory rate. Except for total pulmonary resistance after bolus injection, continuous administration of 5-ht given by either route caused significant alterations of lung dynamic compliance and total pulmonary resistance, the former decreasing to one-fifth of its baseline value and the latter increasing twofold. Pulmonary arterial pressure increased significantly, whatever the speed or route of administration. Administration of a bolus did not affect heart rate, whereas continuous iv administration of 5-ht as well by perfusion or by aerosol resulted in sustained tachycardia.

It was concluded that 5-ht induces reversible bronchoconstriction and pulmonary vasoconstriction in healthy unsedated calves, 5-ht-induced functional alterations depend on the speed of administration, and excess of 5-ht production or depression in uptake by the lungs during bovine respiratory tract diseases could contribute to pulmonary dysfunction.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To characterize the cardiovascular response to IV administration of serotonin (5-hydroxytryptamme [5- HT]) in calves.

Animals

5 healthy unsedated Friesian calves.

Procedure

41 5-HT administrations were performed: 11 slow infusions (duration, 5 minutes) and 30 bolus infusions (duration, 5 seconds). Cardiovascular function values were recorded before, during, and after the infusions.

Results

Slow infusion of 5-HT first resulted in a brief period of severe bradycardia, then in sustained tachycardia with a concomitant increase in cardiac output. Systemic blood pressure response to 5-HT was triphasic, with initial hypotension concomitant with bradycardia, then a pressor phase associated with an increase in systemic vascular resistance, and finally, a long-lasting hypotensive phase associated with decreased systemic vascular resistance. Pulmonary hypertension was associated with increased pulmonary vascular resistance, reflecting intense pulmonary vasoconstriction. Bolus infusion at increasing dosages resulted in dose-dependent bradycardia and systemic hypotension, followed by dose-dependent systemic hypertension. Unlike with slow infusion, neither the second tachycardic nor the third systemic hypotensive phases were evident.

Conclusions

5-HT induces dose-dependent cardiovascular responses, including a reflex response followed by pulmonary and systemic vasoconstriction, in healthy calves.

Clinical Relevance

Determining the type of serotonergic receptors responsible for these responses may help to determine whether 5-HT is involved in the mechanisms underlying brisket disease in cattle. (Am J Vet Res 1996; 57:731–738)

Free access
in American Journal of Veterinary Research

Abstract

Objective—To determine the contribution of MX dynamin, oligoadenylate synthetase (OAS), and double-stranded RNA-dependent protein kinase R (PKR) to the antiviral effects of type 1 interferons (IFNs) against bovine parainfluenza-3 virus (PI-3V) infection of Vero cells.

Sample Population—Vero cell cultures.

Procedures—PI-3V yield was first compared between control and transfected type 1 IFNs– incompetent Vero cells expressing recombinant OAS or MX proteins. Afterwards, phosphorylation of eukaryotic initiation factor 2 α (eIF2α) was used to scale the degree of PKR activation upon infection of Vero cells by PI-3V.

Results—Overexpression of OAS did not result in significantly decreased viral replication. Phosphorylated eIF2α forms, the hallmark of PKR activation, were not increased in IFNα-primed infected Vero cells. Although human MXA contributed to partial blockade of replication of bovine PI-3V, the antiviral effect was not as strong as that of IFNα.

Conclusions and Clinical Relevance—The powerful anti-Paramyxovirus activity of type 1 IFNs is mediated by noncanonic pathways.

Full access
in American Journal of Veterinary Research

SUMMARY

The purpose of this study was to investigate the mechanism by which 5-hydroxytryptamine (5-ht) modifies respiratory function, specifically, hyperventilation, diffuse bronchoconstriction, and pulmonary arterial hypertension in cattle. We determined whether the IV response to 5-ht in calves was attributable to stimulation of 5-ht2 receptors.

Six healthy unsedated young bull calves of the Friesian (n = 4) and of the Belgian White and Blue (n = 2) breeds were used. A specific 5-ht2 antagonist (metrenperone, 0.05 mg/kg of body weight) was administered IM 30 minutes before the cattle were given a 5-minute IV 5-ht infusion. Pulmonary function values were registered before, during, and after the 5-ht challenge infusion. Minute volume increased significantly, because of an increase in respiratory rate. Conversely, lung dynamic compliance, total pulmonary resistance, and pulmonary arterial pressure were not changed.

We concluded that in cattle, 5-ht-induced ventilatory response is not mediated through activation of 5-ht2 receptors. However, the 5-ht2 receptors are involved in 5-ht-induced broncho- and pulmonary vasoconstriction.

Free access
in American Journal of Veterinary Research