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. 2016 Aug;6(3):35-43.
doi: 10.4236/ojmip.2016.63004. Epub 2016 Aug 22.

Cough modulation by upper airway stimuli in cat - potential clinical application?

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Cough modulation by upper airway stimuli in cat - potential clinical application?

Poliacek Ivan et al. Open J Mol Integr Physiol. 2016 Aug.

Abstract

The modulation of mechanically induced tracheobronchial cough was tested by applying various stimuli and the elicitation of other airway protective behaviors in pentobarbital anesthetized cats. Capsaicin and histamine were injected in the nose, and mechanical nylon fiber and / or air puff stimulation was applied to the nose and nasopharynx. Reflex responses of cough, sneeze, aspiration reflex and expiration reflex were induced mechanically. Swallow was initiated by the injection of water into oropharynx. Subthreshold mechanical stimulation of nasopharyngeal and nasal mucosa, as well as water stimulation in the oropharynx and larynx, with no motor response, had no effect on rhythmic coughing. Cough responsiveness and excitability increased with capsaicin and air puff stimuli delivered to the nose. Vice versa, the number of cough responses was reduced and cough latency increased when aspiration reflexes (>1) occurred before the cough stimulus or within inter-cough intervals (passive E2 cough phase). The occurrence of swallows increased the cough latency as well. Cough inspiratory and / or expiratory motor drive was enhanced by the occurrence of expiration reflexes, swallows, and sneezes and also by aspiration reflex within the inspiratory phase of cough and by nasal air puff stimuli. Complex central interactions, ordering and sequencing of motor acts from the airways may result in the disruption of cough rhythmic sequence but also in the enhancement of cough. Our data confirm that number of peripheral stimuli and respiratory motor responses significantly alters cough performance. We propose developing and testing stimulation paradigms that modify coughing and could be employed in correcting of inappropriate or excessive coughing.

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Figures

Figure 1
Figure 1. Schematics of stimulations, related stimulation sites and induced airway motor behaviors
Capsaicin initially inducing the sneeze reflex and histamine were injected to the nose, air-puff pressure pulses directed from the naspharynx to the nose and mechanical continuous stimulations inducing and not-inducing the sneeze reflex were applied in the nose. Mechanical tactile stimulation and air puff (some at subthreshold pressure with no motor response) eliciting aspiration reflex were delivered to the nasopharynx. Injection of water in oropharynx elicited swallow. Presence of water in pharynx and larynx was without motor response. Individual tactile mechanical stimuli to the glottis induced expiration reflex. Cough was produced by repetitive mechanical stimulation in the lower trachea.
Figure 2
Figure 2
Water in oropharynx (water) induced swallows (depicted by a burst of geniohyoid muscle activity – GH and slight depression immediately followed by a burst of cricopharyngeus muscle = upper esophageal sphincter activity - UES) resulted in prolonged inter-cough intervals (latency to the following cough response) and increased cough motor drives. The number of cough efforts, however, was not significantly altered. Int, integrated activity (moving average); EP, esophageal pressure; ABD, abdominal muscle activity; PS, parasternal muscle activity
Figure 3
Figure 3. An example of aspiration reflexes within the expiratory phase of cough
They temporarily interrupt the course of cough expulsion - see breaks in the expiratory part of EP and ABD waveforms, however, without significant changes in cough spatiotemporal characteristics. For more details see [8]. EP, esophageal pressure; DIA, integrated (moving average) EMG activity of the diaphragm; ABD, integrated (moving average) EMG activity of the abdominal muscles
Figure 4
Figure 4. An example of effect of expiration reflexes (ExpRs) induced within the inter-cough intervals on the cough reflex on the right hand side (ExpRs – cough)
Control cough stimulation is on the left hand side. BP, arterial blood pressure; EP, esophageal pressure; DIA, integrated (moving average) EMG activity of the diaphragm; ABD, integrated (moving average) EMG activity of the abdominal muscles

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