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- Author or Editor: Pierre M. Lekeux x
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Abstract
Objective—To characterize the accuracy of an ultrafine 99m-technetium-labeled carbon dry aerosol for use in assessment of regional ventilation in calves with pulmonary dysfunction.
Animals—7 Belgian White and Blue calves.
Procedure—The ultrafine aerosol was assessed by comparing deposition (D) images with ventilation (V) images obtained by use of 81m-krypton (81mKr) gas via D-to-V ratio (D:V) image analysis in calves during spontaneous breathing (SB) and during experimentally induced pulmonary dysfunction (ePD).
Results—Mismatching index (LrTot) calculated on the D:V images revealed a good match (LrTot, 0.96 ± 0.01) between D and V distribution patterns in calves during SB. Calculation of the ultrafine aerosol penetration index relative to 81mKr (PIRel) revealed preferential distribution of the ultrafine aerosol in lung parenchyma (PIRel, 1.13 ± 0.11). In ePD, heterogeneity in the D:V distribution was observed (LrTot, 0.78 ± 0.10) as a result of ultrafine aerosol particles impaction in airways as indicated by PIRel (0.66 ± 0.16) and a proportion of pixels more radioactive in D images, compared with V images, that was located in the central part of the lung (47.5 ± 7.7% in ePD vs 32.8 ± 5.7% in SB). However, this central deposition did not prevent visual examination of the entire ventilated lung.
Conclusions and Clinical Relevance—The ultrafine aerosol appears suitable for use in examination of ventilated parts of lungs of cattle, even those with impaired pulmonary function. However, airway impaction of ultrafine aerosol particles impedes the quantification of regional ventilation in cattle with abnormal lung function. (Am J Vet Res 2001;62: 1881–1886)
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)
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.
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.
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.
Abstract
Objective—To compare sensitivity of the impulse oscillometry system (IOS) with that of the conventional reference technique (CRT; ie, esophageal balloon method) for pulmonary function testing in horses.
Animals—10 horses (4 healthy; 6 with recurrent airway obstruction [heaves] in remission).
Procedure—Healthy horses (group-A horses) and heaves-affected horses (group-B horses) were housed in a controlled environment. At each step of a methacholine bronchoprovocation test, threshold concentration (TC2SD; results in a 2-fold increase in SD of a value) and sensitivity index (SI) were determined for respiratory tract system resistance (Rrs) and respiratory tract system reactance (Xrs) at 5 to 20 Hz by use of IOS and for total pulmonary resistance (RL) and dynamic lung compliance (Cdyn), by use of CRT.
Results—Bronchoconstriction resulted in an increase in Rrs at 5 Hz (R5Hz) and a decrease in Xrs at all frequencies. Most sensitive parameters were Xrs at 5 Hz (X5Hz), R5Hz, and R5Hz:R10Hz ratio; RL and the provocation concentration of methacholine resulting in a 35% decrease in dynamic compliance (PC35Cdyn) were significantly less sensitive than these IOS parameters. The TC2SD for Xrs at 5 and 10 Hz was significantly lower in group-B horses, compared with group-A horses. The lowest TC2SD was obtained for X5Hz in group-B horses and R5Hz in group-A horses.
Conclusions and Clinical Relevance—In contrast to CRT parameters, IOS parameters were significantly more sensitive for testing pulmonary function. The IOS provides a practical and noninvasive pulmonary function test that may be useful in assessing subclinical changes in horses. (Am J Vet Res 2003;64:1414–1420)
Abstract
Objective
To assess sensitivity of scintigraphic alveolar clearance rate as an indicator of alveolar epithelium damage in horses.
Animals
5 healthy horses (group A) and 5 with chronic obstructive pulmonary disease (COPD; group B).
Procedure
Horses underwent clearance rate (k [%/min]) determination. Clearance rate of group-B horses was determined after remission of the disease following 2 months at pasture (remission 1), stabling in a controlled environment (remission 2), and during crisis induced by exposure to moldy hay and straw. Methacholine challenge test was performed at each investigation period to determine nonspecific pulmonary airway hyperresponsiveness. Pulmonary function tests (PFT) also were performed, and cell populations in bronchoalveolar lavage (BAL) fluid were determined on another occasion.
Results
Group-B horses had significantly faster mean clearance rate during crisis (k = 4.30 ± 0.95%/min), compared with that for remission 1 (k = 1.98 ± 0.55%/min), which did not differ from the rate in group-A horses (k = 1.95 ± 0.33%/min). Despite lack of clinical signs of COPD during remission when stabled in a controlled environment, an intermediate value was found (k = 3.20 ± 0.72%/min).
Conclusions
This technique allowed grading of lung damage induced by COPD, whereas use of PFT and determination of BAL fluid cell populations failed to differentiate between remission 1 and remission 2.
Clinical Relevance
Determination of alveolar clearance rate by use of scintigraphy is a sensitive indicator of lung damage. A modified clearance rate was found despite the lack of clinical and functional changes. (Am J Vet Res 1999;60:495-500)
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)
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.
