Abstract
Background: Cough is a defensive behavior that can be initiated in response to a stimulus in the airway (reflexively), or on command (voluntarily). There is evidence to suggest that physiological differences exist between reflex and voluntary cough; however, the output (mechanistic and airflow) differences between the cough types are not fully understood. Therefore, the aims of this study were to determine the lung volume, respiratory kinematic, and airflow differences between reflex and voluntary cough in healthy young adults.Methods: Twenty-five participants (14 female; 18–29 years) were recruited for this study. Participants were evaluated using respiratory inductance plethysmography calibrated with spirometry. Experimental procedures included: (1) respiratory calibration, (2) three voluntary sequential cough trials, and (3) three reflex cough trials induced with 200 μM capsaicin.Results: Lung volume initiation (LVI; p = 0.003) and lung volume excursion (LVE; p < 0.001) were significantly greater for voluntary cough compared to reflex cough. The rib cage and abdomen significantly influenced LVI for voluntary cough (p < 0.001); however, only the rib cage significantly impacted LVI for reflex cough (p < 0.001). LVI significantly influenced peak expiratory flow rate (PEFR) for voluntary cough (p = 0.029), but not reflex cough (p = 0.610).Discussion: Production of a reflex cough results in significant mechanistic and airflow differences compared to voluntary cough. These findings suggest that detection of a tussigenic stimulus modifies motor aspects of the reflex cough behavior. Further understanding of the differences between reflex and voluntary cough in older adults and in persons with dystussia (cough dysfunction) will be essential to facilitate the development of successful cough treatment paradigms.
Highlights
Cough is a sensorimotor airway protective mechanism that functions to expel foreign or endogenously produced material from the lower airways (Loudon and Shaw, 1967; Harris and Lawson, 1968; Macklem, 1974)
lung volume initiation (LVI) and lung volume excursion (LVE) were significantly greater for voluntary cough compared to reflex cough (Figure 2)
The results of this prospective study increase our understanding of the mechanistic and airflow differences between voluntary and reflex cough in healthy young adults. These differences likely resulted from a combination of increased respiratory and laryngeal muscle co-contraction, along with possible inhibition of inspiration secondary to a strong UTC that is associated with reflex cough as opposed to voluntary cough
Summary
Cough is a sensorimotor airway protective mechanism that functions to expel foreign or endogenously produced material from the lower airways (Loudon and Shaw, 1967; Harris and Lawson, 1968; Macklem, 1974). Voluntary cough is initiated on command (Lee et al, 2002; Eccles, 2009; Hegland et al, 2012; Mazzone et al, 2013), whereas reflex cough is initiated secondary to the stimulation of peripheral sensory receptors (Mazzone, 2005; Widdicombe and Singh, 2006; Canning and Chou, 2009). The neural differences have been relatively well studied, the airflow and kinematic differences between reflex and voluntary cough are not as well understood, leaving a significant gap in our understanding of the important differences (or similarities) between the two cough types. The aims of this study were to determine the lung volume, respiratory kinematic, and airflow differences between reflex and voluntary cough in healthy young adults
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