Objective: While the relationship between lung volume and laryngeal resistance (Rlaw) during phonation onset remains a subject of debate, recent studies emphasize the role of respiratory-phonatory coordination in optimizing vocal efficiency and preventing vocal strain. This study aimed to investigate how respiratory priming at different lung volume conditions influences Rlaw during phonation onset in vocally trained and untrained speakers.
Methods: Thirteen vocally healthy participants (9 females, mean age = 27.1 ± 6.1 years; 4 males, mean age = 36.0 ± 3.5 years) were categorized into vocally trained (n = 5) and untrained (n = 8) groups. After respiratory training, they were prompted to produce the sustained vowel /pi:/ in habitual lung volume (baseline, BL), high lung volume (HLV) at 90% of vital capacity (VC), and low lung volume at 40% of VC (resting expiratory level, REL). Lung volume was measured using a respiratory inductive plethysmograph while airflow and subglottal pressure were recorded to calculate Rlaw (cmH2O/l/s). Three-way analysis of variance (ANOVA) was used to analyze the effects of condition, task order, and vocal training on Rlaw.
Results: Validation analysis showed that participants correctly initiated phonation in the target conditions (BL, HLV, and REL). Significant main effects of condition (p = 0.015) and task order (p < 0.001) on Rlaw were observed. Vocal training had no significant main effect (p = 0.866), suggesting that respiratory-phonatory coupling is not significantly altered by prior training. There was a significant interaction between task order and training (p < 0.001): Mean Rlaw was higher in task order BL-REL-HLV than in BL-HLV-REL and the mean difference between the two task orders was larger for trained (p <.001) compared to non-trained (p = .008), which might indicate the role of individual physiological and behavioural variability. Rlaw was significantly higher at both REL (+7.2 cmH2O/l/s; p = 0.025) and HLV (+6.5 cmH2O/l/s; p = 0.053) relative to baseline, aligning with recent findings that low or high lung volume may increase laryngeal tension and resistance, potentially due to the need for greater neuromuscular coordination at these limits. No significant difference in Rlaw was found between REL and HLV (p = 0.990), and these findings were consistent across task orders.
Conclusions: The findings support emerging evidence that respiratory priming at low and high lung volumes increases Rlaw during phonation onset, likely due to the additional biomechanical and neuromuscular adjustments required to maintain phonatory stability. These results highlight the role of respiratory-phonatory interaction in voice production and suggest potential applications in voice training and clinical interventions for optimizing vocal efficiency and reducing phonatory effort. Future research should further explore the influence of respiratory priming on vocal performance in diverse populations.