EFFECTS OF HYPER- AND HYPOCAPNIA ON PHONATORY LARYNGEAL RESISTANCE

The larynx has a challenging dual role in the simultaneous regulation of gas flow into and out of the lungs while also establishing resistance required for vocal fold vibration in voiced communication. Particular challenges may arise when the larynx is required to alter upper airway resistance to meet respiratory demands in a way that conflicts with requirements for voice production. Little if anything is known about reciprocal relations between these functions, particularly under conditions of respiratory abnormality that affect large sectors of the population- an estimated 25% of the US population who experience respiratory abnormalities and also relies on the larynx for voiced communication. In order to address this gap, the current study investigated two specific aims in a single within-subjects experiment: Specific Aim 1 (SA1) assessed spontaneous fluctuations in phonatory laryngeal resistance during states of (a) induced hypocapnia (low arterial carbon dioxide) and (b) induced hypercapnia (high arterial carbon dioxide), in comparison to a eupneic control condition and Specific Aim 2 (SA2) investigated the reciprocal effects of laryngeal resistance modulations on respiratory homeostasis. Results of the first aim demonstrated that phonatory laryngeal resistance remained stable and did not significantly change despite manipulations of inspired gas concentrations causing significant increases and decreases in carbon dioxide (CO2) levels. For the second aim, results showed that phonation significantly increased levels of end-tidal carbon dioxide (PetCO2) in all experimental conditions, compared to PetCO2 levels during rest breathing. Findings provide support for a theory of voice motor control suggesting that phonatory laryngeal resistance may be an essential, relatively immutable control parameter in phonation (except perhaps under extreme conditions not tested herein), and provides data on the influence of phonation on respiration. The current work sets the foundation for future studies of laryngeal function during phonation in individuals with lower airway disease