Volume feedback during cough in anesthetized cats, effects of occlusions and modulation summary

Effect of various modes of tracheal mechanical stimulation on the cough motor pattern

The relationship between the level (rate) of stimulus and the characteristics of the cough response was studied on 15 spontaneously breathing anesthetized cats. Three modes of stimulation were used to elicit cough. 'High' vs. 'low' level of stimulation was accomplished: 1st mode by 1 vs. 4 penetrations of the soft catheter through the trachea (approximately 10 cm), 2nd mode by 2 penetrations with the soft catheter equipped with 4 fine cross nylon fibers vs. 4 penetrations by the stimulator with 8 fibers, and 3rd mode by a similar stimulator with 4 cross fibers probing 4 cm of the trachea either right below the larynx or deeper under the upper part of the sternum (data were pooled) vs. stimulating both areas at the same time. 'High' stimulation rate in each stimulation mode resulted in a higher number of coughs, increased cough efforts, and shortened several temporal cough features. Mechanical stimulation resulting in higher cough afferent drive induces more vigorous coughing with shorter temporal cough characteristics. Modulation of cough afferent input affects both spatial and temporal components of the cough motor pattern, representing a crucial point in cough management.

Peripheral antitussives affect temporal features of tracheobronchial coughing in cats

The influence of peripheral antitussive drugs on spatiotemporal features of coughing has not been reported. We hypothesized that this class of compounds would alter the cough motor pattern, in part, by lengthening cough phases. Peripherally acting antitussives, 3-aminopropylphosphinic acid (3APPi, 5 mg/kg) and levodropropizine (Levo, 3 mg/kg) were injected intravenously in anesthetized spontaneously breathing cats (13 males, 2 females; 4.38 ± 0.19 kg). Spatio-temporal analysis of cough induced by mechanical stimulation of the trachea showed significant reductions in cough number and expiratory cough efforts after the administration of each drug. A significant reduction in inspiratory cough efforts occurred after Levo. Both drugs induced temporal changes in the cough motor pattern, including prolongations of inspiratory phase, inspiratory-expiratory transition, total cough diaphragm activity, and total cough cycle duration. Levo also significantly lengthened the expiratory phase of cough. A shortening of the overlap between diaphragm and abdominal activity and cough abdominal electromyogram (EMG) activity was observed after the administration of 3APPi. No significant changes in cardiorespiratory data were seen, with the exception of prolonged expiratory phase after 3APPi and lower blood pressure after Levo. Peripherally induced cough suppression is accompanied with changes in cough temporal characteristics that are not observed after the administration of centrally acting antitussives. The motor output produced by the cough central pattern generator differs significantly when coughing is perturbed by peripherally and centrally acting antitussives.NEW & NOTEWORTHY In a study on anesthetized cats, peripherally acting antitussives 3-aminopropylphosphinic acid (3APPi) and levodropropizine (Levo) significantly reduced cough number and expiratory efforts, with Levo also reducing inspiratory efforts. Both antitussives altered the cough motor pattern, extending various cough phases. 3APPi shortened diaphragm-abdominal activity overlap, whereas Levo decreased the respiratory rate. These changes contrast with those induced by centrally acting antitussives.

Airway mechanics alters generation of cough motor pattern

Effects of sequential increase in airway resistance: no, low (5 kPa.s/l), high (24 kPa.s/l), and complete block in the inspiratory or expiratory phase of mechanically induced cough on the cough motor pattern were studied in 16 anesthetized (pentobarbital) spontaneously breathing cats (3.70±0.15 kg, 11♂, 5♀). Esophageal pressure and electromyographic activities of the diaphragm during inspiration and abdominal muscles during expiration were analyzed. No significant changes in the number of coughs occurred. Inspiratory occlusion caused a prolongation of cough inspiratory phase, cough inspiratory diaphragm activity, and all cough-related activity. Inspiratory occlusion along with high resistance increased inspiratory esophageal pressure amplitude, total cough cycle duration and the time between maximum activity of the diaphragm and abdominal muscles. High expiratory resistance and occlusion resulted in increased cough expiratory esophageal pressure amplitude, a longer active portion of cough expiration, and cough abdominal activity. Expiratory occlusion also prolonged cough expiratory phase, all cough activity, and total cough cycle. Significantly increased airway resistance and occlusion induce secondary, in addition to mechanical, changes in cough by significantly modulating the generated cough motor pattern. A certain level of resistance appears to be successfully compensated, resulting in minimal changes in coughing characteristics, including expiratory airflow and the rising time of the airflow. Afferent feedback from the respiratory tract, particularly volume feedback, represents a significant factor in modulating cough, mainly under various pathological conditions in the respiratory system.

Modeling and simulation of vagal afferent input of the cough reflex

We employed computational modeling to investigate previously conducted experiments of the effect of vagal afferent modulation on the cough reflex in an anesthetized cat animal model. Specifically, we simulated unilateral cooling of the vagus nerve and analyzed characteristics of coughs produced by a computational model of brainstem cough/respiratory neuronal network. Unilateral vagal cooling was simulated by a reduction of cough afferent input (corresponding to unilateral vagal cooling) to the cough network. All these attempts resulted in only mild decreases in investigated cough characteristics such as cough number, amplitudes of inspiratory and expiratory cough efforts in comparison with experimental data. Multifactorial alterations of model characteristics during cough simulations were required to approximate cough motor patterns that were observed during unilateral vagal cooling in vivo. The results support the plausibility of a more complex NTS processing system for cough afferent information than has been proposed.