Hypercapnia Enhances the Development of Coughing during Continuous Infusion of Water into the Pharynx

Abstract

We investigated the effects of increasing CO2 ventilatory drive on the coordination of respiration and reflex swallowing elicited by continuous infusion of distilled water into the pharynx (2.5 ml/min) in 11 normal subjects. Ventilation was monitored using a pneumotachograph and swallowing was recorded by submental electromyogram. The CO2 ventilatory drive was increased by addition of external dead space, while ventilation, the frequency of swallows, and the timing of swallows in relation to the phases of the respiratory cycle were measured at steady-state conditions. We found that the CO2 ventilatory response is not influenced by continuous reflex swallowing but that hypercapnia influences the timing and frequency of these swallows. Signs of aspiration were never observed during continuous infusion of water at eucapnia, but seven of 11 subjects showed laryngeal irritation and/or pending aspiration during hypercapnia, and the incidence of laryngeal irritation was higher the greater the PCO2. Detailed analysis of laryngeal irritations consisting of single coughs in seven subjects revealed that the majority of laryngeal irritations occurred when swallows coincided with expiratory-inspiratory transition or when swallows coincided with inspiration, whereas laryngeal irritation after an expiratory swallow was never observed. These results suggest that the automatic respiratory control system is not influenced by continuous swallowing but that the coordination of swallowing and respiration may be compromised during hypercapnia.

Effect of a tracheostomy speaking valve on breathing–swallowing interaction

“…However, in COPD patients, the abnormalities in swallow timing within the respiratory cycle [25] are similar to those in neuromuscular patients [19]. In addition, studies in healthy individuals established that the occurrence of inspiration after swallows was increased by hypercapnia [26] or the application of an inspiratory elastic load [27], suggesting that poor breathing-swallowing coordination might be a non-specific sign of respiratory difficulty. Therefore, there is no reason our results would not apply to other populations with respiratory failure.…”

Effects of withdrawal of phasic lung inflation during normocapnia and hypercapnia on the swallowing reflex in humans

“…Considering that the swallowing reflex functions as a protective reflex, it is likely that the swallowing reflex interacts with background chemical ventilatory drive. In fact, our previous study [4] showed that hypercapnia not only decreased the frequency of the repetitive swallowing induced by continuous infusion of water into the pharynx but also changed the timing of swallows in relation to the phase of the respiratory cycle.…”

Physiological and Pathophysiological Implications of Upper Airway Reflexes in Humans.

“…8), whereas a decrease in CO 2 ventilatory drive has the opposite effect [56]. In addition, it has been reported in a recent study on conscious subjects that the CO 2 ventilatory response is not influenced by continuous reflex swallowing but hypercapnia decreases the frequency of swallows and increases the incidence of laryngeal irritation during continuous infusion of water into the pharyngeal cavity [57]. These observations suggest that the function of protecting the airway subserved by upper airway reflexes may be compromised during hypercapnia or hypoxia.…”