Author(s): CITHERLET, T., MANFERDELLI, G., RABERIN, A., BOURDILLON, N., MILLET, G., Institution: UNIVERSITY OF LAUSANNE, Country: SWITZERLAND, Abstract-ID: 379

INTRODUCTION:
Breathing is a critical pillar of physiological homeostasis and there is a growing public interest in breathing techniques, with trends such as mouth taping and nasal dilators. Nevertheless, the specific cardiorespiratory consequences of nasal versus oral breathing remain under-explored, particularly under environmental stressors like hypoxia and hypercapnia, which could exacerbate their physiological impact.
METHODS:
Twenty-three young adults participated in a randomized cross-over study. Participants performed 6-min trials of nasal, oral, and free breathing under three resting conditions: normoxia, poikilocapnic hypoxia (FiO₂ = 12%), and normoxic hypercapnia (FiCO₂ = 5%). We continuously monitored pulmonary gas exchange breath-by-breath using a metabolic cart, cardiac hemodynamics (cardiac output, heart rate, stroke volume) via impedance cardiography, and oxygen saturation (SpO₂) using pulse oximetry. Baroreflex sensitivity (BRS) and blood pressure were assessed using finger photoplethysmography and an automated cuff, respectively.
RESULTS:
In normoxia, breathing mode had minimal effects, though oral breathing was associated with reduced BRS compared to free breathing (P=0.04). In hypoxia, oral breathing elicited a higher respiratory frequency compared to free breathing (15.7 ± 2.8 vs 14.9 ± 2.8 breaths/min; P<0.01). Conversely, nasal breathing mitigated hypoxic tachycardia, maintaining a significantly lower heart rate compared to free breathing (70 ± 13 vs 74 ± 13 bpm; P=0.01). In hypercapnia, nasal breathing significantly reduced the metabolic cost of breathing (V̇O₂) compared to free breathing (324 ± 69 vs 360 ± 58 mL/min; P=0.02). Additionally, oral breathing in hypercapnia was associated with increased diastolic blood pressure compared to free breathing (75 ± 5 vs 72 ± 5 mmHg; P<0.01).
CONCLUSION:
The physiological impact of breathing mode is negligible at rest in normoxia but becomes significant under environmental stress (hypoxia/hypercapnia). Nasal breathing improves autonomic regulation and ventilatory efficiency, mitigating hypoxic tachycardia and reducing the metabolic cost of breathing in hypercapnia, whereas oral breathing alters cardiorespiratory control. These findings suggest that nasal breathing serves as a potent tool for optimizing health, enhancing cardiorespiratory stability, especially during contexts such as altitude exposure.