The course of lung inflation alters the central pattern of tracheobronchial cough in cat-The evidence for volume feedback during cough

Abstract

The effect of volume-related feedback and output airflow resistance on the cough motor pattern was studied in 17 pentobarbital anesthetized spontaneously-breathing cats. Lung inflation during tracheobronchial cough was ventilator controlled and triggered by the diaphragm electromyographic (EMG) signal. Altered lung inflations during cough resulted in modified cough motor drive and temporal features of coughing. When tidal volume was delivered (via the ventilator) there was a significant increase in the inspiratory and expiratory cough drive (esophageal pressures and EMG amplitudes), inspiratory phase duration (CTI), total cough cycle duration, and the duration of all cough related EMGs (Tactive). When the cough volume was delivered (via the ventilator) during the first half of inspiratory period (at CTI/2-early over inflation), there was a significant reduction in the inspiratory and expiratory EMG amplitude, peak inspiratory esophageal pressure, CTI, and the overlap between inspiratory and expiratory EMG activity. Additionally, there was significant increase in the interval between the maximum inspiratory and expiratory EMG activity and the active portion of the expiratory phase (CTE1). Control inflations coughs and control coughs with additional expiratory resistance had increased maximum expiratory esophageal pressure and prolonged CTE1, the duration of cough abdominal activity, and Tactive. There was no significant difference in control coughing and/or control coughing when sham ventilation was employed. In conclusion, modified lung inflations during coughing and/or additional expiratory airflow resistance altered the spatio-temporal features of cough motor pattern via the volume related feedback mechanism similar to that in breathing.

Keywords: Airflow resistance; Cough control; Cough motor pattern; Impaired cough; Stretch receptors; Volume feedback.

Figure 1. The scheme of volume modifications during coughing and cough analysis

A: The scheme of ventilator and stimulating tool connections to the Y-cannula during ventilator controlled cough trials. B: Schemes of modified volume and/or expiratory airflow resistance (provided by the expiratory ventilator circuit). Dashed waveforms represent (expected) regular lung volume during cough; solid waveforms are (expected) ventilator controlled lung volumes during cough inspirations. Wider cross-hatch areas denote (expected) variability and prolongation of the cough expiratory phase duration due to the additional expiratory airflow resistance (ventilator output). Please, note that when fast inflation were conducted expulsion did not begin in the middle of regular CTI, even though the inspirations became shorter (see Results). C: The scheme of cough analysis. Amplitudes of EMG activities and esophageal pressure as well as temporal parameters measured on cough are depicted. CV: Cough volume; E resist: expiratory airflow resistance; V_T: tidal volume; I resist: inspiratory airflow resistance; Int: integrated moving average; DIA: diaphragm EMG (also the amplitude of diaphragm activity in C with arrow); ABD: abdominal EMG (also the amplitude of abdominal activity in C with arrow); EP: esophageal pressure; EP E: amplitude of expiratory EP; EP I: amplitude of inspiratory EP; CTtot: total cough cycle duration; TDIA: DIA activity duration; CTI: inspiratory phase duration; CTE: expiratory phase duration; Over: overlap of DIA and ABD; CTE2: quiescent expiratory period; Dif: interval between DIA and ABD maximum; CTE1: active portion of the cough expiratory phase; TABD: duration of cough ABD activity; Tactive: duration of all cough related EMG activity

Figure 2. The effects of ventilator controlled cough inflations and/or expiratory airflow resistance on coughing

A: Positive control coughs with cough volume delivered by the ventilator (expulsions through the ventilator output circuit). B: Coughs with spontaneous inspirations and expulsions diverted through the ventilator output circuit. C: Coughs with tidal volume delivered by the ventilator in the inspiratory phase of cough. D: Coughs with cough volume delivered by the ventilator during the first half of cough inspiration. E: expiration; res: airflow resistance; I: inspiration; CTI: cough inspiratory time; CV: cough volume; VT: tidal volume; CN: cough number; ABD: abdominal EMG amplitude; DIA: diaphragm EMG amplitude; EP E: expiratory esophageal pressure amplitude; EP I: inspiratory esophageal pressure amplitude; *: P<0.05; **: P<0.01; ***: P<0.001

Figure 3. The effects of inhaled tidal volume (inspiratory resistance) on coughing

Upper section: four cough trials, where the 1^st and the 4^th trial is a control, the 2^nd and the 3^rd trial is that with tidal volume delivered by the ventilator. Low cough inspiratory volume resulted in increased cough motor drive. Lower section: expanded waveforms of ventilator controlled inspiration low volume cough (on the left hand side) and control cough (on the right hand side) - in both cases the 2^nd cough was taken. Please, retain that the control is on the right. Intervals of altered temporal characteristics are depicted. The onset, maximum, and offset of cough related EMG activities determine the interval durations. Int: integrated moving average; DIA: diaphragm EMG; ABD: abdominal EMG; EP: esophageal pressure; BP: arterial blood pressure; CTtot: total cough cycle duration; TDIA: DIA activity duration; CTI: inspiratory phase duration; Tactiv: duration of all cough related EMG activity

Figure 4. The effects of cough volume delivered fast by the ventilator (early over inflation) on coughing

st half of cough inspiration (note increases in EP early in inspiratory phase of coughs). Lower section: expanded waveforms of control (on the left hand side) and early overinflated coughs (on the right hand side). Intervals of significant temporal characteristics are depicted. Int: integrated moving average; DIA: diaphragm EMG; ABD: abdominal EMG; EP: esophageal pressure; BP: arterial blood pressure; CTI: inspiratory phase duration; Over: overlap of DIA and ABD; Dif: interval between DIA and ABD maximum; CTE1: active portion of the cough expiratory phase