Respiratory Laryngeal Coordination in Airflow Conservation and Reduction of Respiratory Effort of Phonation

Abstract

Objective: This study evaluates the need of airflow conservation and the effect of glottal resistance on respiratory effort of phonation under different phonation conditions.

Methods: A computational model of the pressure-volume-flow relationship of the respiratory system is developed.

Results: Simulations show that increasing the glottal resistance reduces the glottal airflow and allows phonation to be sustained for a longer breath group duration. For a given breath group duration, the reduced airflow also allows phonation to be sustained within a narrow range of lung volumes, thus lowering the overall respiratory effort.

Conclusions: This study shows that for breath group durations and subglottal pressures typical of normal conversational speech, airflow conservation or maintaining "effortless" respiratory support does not provide a stricter requirement on the glottal resistance than that required for initiating phonation. However, the need for airflow conservation and respiratory effort reduction becomes relevant when the target subglottal pressure and breath group duration increase as in prolonged speech or singing or in conditions of weakened pulmonary function. In those conditions, the glottal resistance is expected to increase proportionally with increasing subglottal pressure to conserve airflow consumption and reduce respiratory effort.

Keywords: Airflow conservation; Glottal resistance; Respiratory effort of phonation; Respiratory model; Respiratory–laryngeal coordination.

Fig. 1

a) A sketch of the respiratory model. P_exp: the net expiratory muscle pressure; P_alv: the alveolar pressure; P_pl: the intrapleural pressure; P_sub: the subglottal pressure; R_law: the lower airway resistance. b) the lung volume-relaxation pressure curve used in this study for normal lung compliance (solid line) and reduced lung compliance (dashed line).

Fig. 1

a) A sketch of the respiratory model. P_exp: the net expiratory muscle pressure; P_alv: the alveolar pressure; P_pl: the intrapleural pressure; P_sub: the subglottal pressure; R_law: the lower airway resistance. b) the lung volume-relaxation pressure curve used in this study for normal lung compliance (solid line) and reduced lung compliance (dashed line).

Fig. 2

The subglottal pressure (left) and lung volume (right) as a function of time following a 0.5-sec inspiratory phase. No respiratory muscle pressure is applied (P_exp = 0 Pa). — : Rg = 1 Pa·s/ml; – – – : Rg = 4 Pa·s/ml; … Rg = 9 Pa·s/ml. Curves in red, blue, and black colors indicate conditions with a P_ins of −0.6 kPa, −1.5 kPa, and −2.4 kPa, respectively.

Fig. 3

The expiratory muscle pressure required to maintain a target subglottal pressure (left) and the corresponding lung volume (right) as a function of time following a 0.5-sec inspiratory phase. — : Rg = 1 Pa·s/ml; – – – : Rg = 4 Pa·s/ml; … Rg = 9 Pa·s/ml. Curves in red, blue, and black colors indicate conditions with a P_ins of −0.6 kPa, −1.5 kPa, and −2.4 kPa, respectively.

Fig. 4

(Color online) Normal speech conditions. The maximum expiratory muscular pressure required to maintain a target subglottal pressure for a breath group duration of 4s (top row) and the termination lung volume (LVT) at the end of the breath group as a percentage of the VC (bottom row), as a function of the glottal resistance (GR) and the target subglottal pressure. Three inspiratory muscular pressures are considered: P_ins = 0.6 kPa (left), 1.5 kPa (middle), and 2.4 kPa (right). The red thick lines indicate phonation threshold pressure, and the thin lines indicate conditions with LVT=30%VC.

Fig. 5

(Color online) Constraints due to phonation initiation (red line), conservation of airflow (thick line) and respiratory effort (dashed line for ‘effortless’ speech) in the glottal resistance (GR)-target subglottal pressure (Ps) space. These constraints define different regimes in the GR-Ps space. Phonation is not possible in regions to the left of the phonation initiation line. For regions below the airflow constraint, one would run out of airflow and not able to finish the desired breath group duration. In regions between the thick line and the dashed line, phonation is possible for the desired breath group duration but the respiratory effort is likely high. a) normal speech; b) prolonged speech or singing; c) speech with reduced lung compliance.

Fig. 5

(Color online) Constraints due to phonation initiation (red line), conservation of airflow (thick line) and respiratory effort (dashed line for ‘effortless’ speech) in the glottal resistance (GR)-target subglottal pressure (Ps) space. These constraints define different regimes in the GR-Ps space. Phonation is not possible in regions to the left of the phonation initiation line. For regions below the airflow constraint, one would run out of airflow and not able to finish the desired breath group duration. In regions between the thick line and the dashed line, phonation is possible for the desired breath group duration but the respiratory effort is likely high. a) normal speech; b) prolonged speech or singing; c) speech with reduced lung compliance.

Fig. 5

(Color online) Constraints due to phonation initiation (red line), conservation of airflow (thick line) and respiratory effort (dashed line for ‘effortless’ speech) in the glottal resistance (GR)-target subglottal pressure (Ps) space. These constraints define different regimes in the GR-Ps space. Phonation is not possible in regions to the left of the phonation initiation line. For regions below the airflow constraint, one would run out of airflow and not able to finish the desired breath group duration. In regions between the thick line and the dashed line, phonation is possible for the desired breath group duration but the respiratory effort is likely high. a) normal speech; b) prolonged speech or singing; c) speech with reduced lung compliance.

Fig. 6

(Color online) Prolonged speech or singing. The maximum expiratory muscular pressure required to maintain a target subglottal pressure for a breath group duration of 6.5s (top row) and the termination lung volume (LVT) at the end of the breath group as a percentage of the VC (bottom row), as a function of the glottal resistance (GR) and the target subglottal pressure. Three inspiratory muscular pressures are considered: P_ins = 0.6 kPa (left), 1.5 kPa (middle), and 2.4 kPa (right). The red thick lines indicate phonation threshold pressure, and the thin lines indicate conditions with LVT=30%VC.

Fig. 7

(Color online) Speech under reduced lung compliance. The maximum expiratory muscular pressure required to maintain a target subglottal pressure for a breath group duration of 4s (top row) and the termination lung volume (LVT) at the end of the 4s as a percentage of the VC (bottom row), as a function of the glottal resistance (GR) and the target subglottal pressure. Three inspiratory muscular pressures are considered: P_ins = 0.6 kPa (left), 1.5 kPa (middle), and 2.4 kPa (right). The red thick lines indicate phonation threshold pressure, and the thin lines indicate conditions with LVT=30%VC.