Development of a cough induction test in pigs: effects of SR 48968 and enalapril

Effects of zofenopril and ramipril on cough reflex responses in anesthetized and awake rabbits

Cough is the most common symptom reported by patients in a primary care setting and is one of the most frequent secondary effects recorded during treatment with angiotensin-converting enzyme (ACE) inhibitors. The aim of the current study was to analyze potential differences in cough induction between 2 structurally different ACE inhibitors, namely zofenopril, which has a sulphydryl moiety, and ramipril, which has a carboxyl moiety. The cough reflex was induced by chemical (citric acid) and/or mechanical stimulation of the tracheobronchial tree in awake and anesthetized rabbits. Intravenous injection of the active compounds of the 2 ACE inhibitors, zofenoprilat (288 nmol/kg) and ramiprilat (129 nmol/kg), caused similar hypotensive effects in anesthetized rabbits. None of the studied cough-related variables changed in response to ACE inhibitor administration, with the exception of the number of coughs. Ramiprilat, but not zofenoprilat, increased the cough response induced by both mechanical and chemical stimulation (1 mol/L citric acid aerosol) of the tracheobronchial tree. In awake animals, zofenoprilat- or vehicle-treated rabbits did not show any significant changes in the number of coughs induced by 1 mol/L citric acid aerosol compared to their respective basal values (from 15.2 ± 2.3 to 13.1 ± 1.3 and from 16.1 ± 4.9 to 15.8 ± 4.3, respectively). Conversely, ramiprilat resulted in a significant increase in the number of coughs (from 21.1 ± 2.6 to 34.9 ± 3.5; P < .01). These findings confirm that there are differences in the cough potentiation effect induced by different ACE inhibitors. The low rate of cough seen with zofenoprilat may be related to its ability to induce a lower accumulation of bradykinin and prostaglandins at the lung level.

Time-series analysis for online recognition and localization of sick pig (Sus scrofa) cough sounds

This paper considers the online localization of sick animals in pig houses. It presents an automated online recognition and localization procedure for sick pig cough sounds. The instantaneous energy of the signal is initially used to detect and extract individual sounds from a continuous recording and their duration is used as a preclassifier. Autoregression (AR) analysis is then employed to calculate an estimate of the sound signal, and the parameters of the estimated signal are subsequently evaluated to identify the sick cough sounds. It is shown that the distribution of just three AR parameters provides an adequate classifier for sick pig coughs. A localization technique based on the time difference of arrival is evaluated on field data and is shown that it is of acceptable accuracy for this particular application. The algorithm is applied on continuous recordings from a pig house to evaluate its effectiveness. The correct identification ratio ranged from 73% (27% false positive identifications) to 93% (7% false positive identifications) depending on the position of the microphone that was used for the recording. Although the false negative identifications are about 50% it is shown that this accuracy can be enough for the purpose of this tool. Finally, it is suggested that the presented application can be used to online monitor the welfare in a pig house, and provide early diagnosis of a cough hazard and faster treatment of sick animals.

Preclinical assessment of novel therapeutics on the cough reflex: cannabinoid agonists as potential antitussives

Cough, a reflex defense mechanism, is a common symptom of many airway inflammatory diseases. At present there are no satisfactory treatments for cough that have an acceptable side effect profile. Recent data have described the inhibitory effect of selective cannabinoid CB(2) receptor agonists on sensory nerve activity in vitro and the cough reflex in a guinea pig model. CB(2) receptor expression is limited in the central nervous system (CNS) and hence the development of selective agonists may provide a new therapeutic strategy for treatment of cough devoid of the CNS-mediated side effects that are normally associated with nonselective cannabinoid agonists.

Experimental models and mechanisms of enhanced coughing

Enhanced coughing can be produced in a variety of animal models, including the guinea pig, cat, dog and pig. Typically, airway inflammation has been produced by sensitization, exposure to cigarette smoke, sulphur dioxide or angiotensin-converting enzyme inhibitors. In some of these models, inflammatory mediators such as bradykinin and tachykinins have been shown to contribute to the enhanced coughing. While most of these studies have focussed on peripheral mechanisms, increases in central excitability of the cough reflex have been shown to occur as a result of airway inflammation. As such, we propose that enhanced coughing in pathological conditions is the result of plastic changes in both peripheral and central neural elements. Furthermore, we present a modified model of the neurogenesis of cough that takes into account peripheral and central plasticity induced by mediators of inflammation.

Objective recognition of cough sound as biomarker for aerial pollutants

A relationship among air quality, respiratory health, and comfort in man and animal is widely shown. In general, a state of respiratory discomfort is prevailed by an increase in acoustic audible symptoms. The general concept of sound analysis as an objective contactless non-invasive biomarker for aerial pollution is studied on free-field cough sound of 12 Belgian Landrace piglets. A citric-acid-induced cough sound recognition algorithm with recognition rate of 95% is applied to cough sounds registered in the presence of distinct types of aerial pollutants: irritating gas (ammonia), respirable particles (dust), and temperature. The recognition performance for all aerial pollutants was >90% and maintained 94% on average. It is concluded that sound analysis allows an effective biomarker for all three types of aerial pollution. The generality of the biomarker is hypothesized to be due to the common mechanism involved in protective cough. As a consequence, it is suggested to use sound analysis as a biomarker for respiratory state in studies of exposure to air pollutants.

Assessing the sound of cough towards vocality

The presented research positively evaluates the vocality of the cough sound by estimating the global cough fundamental frequency or pitch. The fundamental frequency was determined by autocorrelation analysis on both the original time-signal and the linear predicted time-signal. The experimental cough database was registered in the free acoustical field on respectively three pathological and nine healthy non-smoking human subjects and on two pathological and two healthy Belgian Landrace piglets. For both species differences between pitch values for cough-sounds originating from subjects suffering from a respiratory infection and healthy subjects are put forward. The retrieved pitch-difference between respectively healthy and infected subjects indicates the existence of acoustically different cough-classes in accordance with a different cause or physical condition of the respiratory system.

Role of bradykinin and tachykinins in the potentiation by enalapril of coughing induced by citric acid in pigs

Angiotensin-converting enzyme (ACE) inhibitors are among the first-choice drugs for treating hypertension and congestive heart disease. It has been reported, however, that these drugs could induce chronic cough and airway hyperresponsiveness. The aim of this work was to assess in pigs the effects of bradykinin and tachykinins on citric-acid-induced coughing after ACE inhibitor pretreatment. Coughing was induced by challenging pigs with an aerosol of 0.8 M citric acid over 15 min. Coughs were counted by a trained observer for 30 min. The animals underwent two cough induction tests two days apart (days 1 and 3), the first being taken as a control. All drugs were injected intravenously 30 min before the second challenge. In the control group, no difference was observed between days 1 and 3. The ACE inhibitor enalapril (7.5 and 15 microg/kg) caused the cough frequency to increase significantly. In contrast, a dose-related decrease was observed with Hoe140 (icatibant), a bradykinin B2 receptor antagonist (0.5 and 1 mg/kg). When both drugs were administered simultaneously (15 microg/kg for enalapril and 1 mg/kg for Hoe140), a significant increase was observed as compared with the control value obtained on day 1. When enalapril was combined with the three tachykinin receptor antagonists SR 140333 (NK1 receptor antagonist), SR 48968 (NK2 receptor antagonist) and SR 142801 (NK3 receptor antagonist), a significant decrease was observed as compared with control value obtained on day 1; the percentage of variation was also significantly different as compared with those observed in enalapril groups at both doses. These data suggest that ACE-inhibitor-induced enhancement of the cough reflex is mainly due to tachykinins and not to bradykinin in our pig model. Bradykinin, however, plays a major role in coughing induced by citric acid alone.

Role of substance P and tachykinin receptor antagonists in citric acid-induced cough in pigs

The purpose of this work was to investigate the role of tachykinins in cough induced by citric acid (0.8 M) in pigs. With this object, we have studied the effect of citric acid on substance P content in the tracheo-bronchial tree and the effects of substance P and of tachykinin receptor antagonists on citric acid-induced cough. Citric acid exposure significantly increased substance P concentration in both broncho-alveolar and tracheal lavage fluids, while it decreased significantly the substance P content in tracheal mucosa. Substance P did not elicit cough, but significantly potentiated the citric acid-induced cough frequency. Tachykinin NK(1), NK(2) or NK(3) receptor antagonists, SR 140333 (nolpitantium), SR 48968 (saredutant) and SR 142801 (osanetant), respectively, significantly inhibited citric acid-induced cough. The same inhibitory effect of tachykinin receptor antagonists was observed, when substance P was nebulised before citric acid challenge. We conclude that citric acid induces in pigs a release of substance P in the tracheo-bronchial tree, which plays a sensitising role on the cough reflex. The involvement of tachykinin NK(1), NK(2), NK(3) receptors are also demonstrated in this reflex.