Acute Ventilatory and Hemodynamic Responses to Nasal versus Oral Breathing during Normoxia, Hypoxia, and Hypercapnia

Abstract

Nasal breathing is considered the primary respiratory route, yet its effects on resting cardiorespiratory function under altered inspired gas composition remain unclear. We compared ventilatory and hemodynamic responses during nasal, oral, and free breathing at rest. Twenty-one young adults completed 6-min trials of each breathing pattern during normoxia and normobaric hypoxia (F i O 2 =0.12); a randomized subsample of 11 also completed normoxic hypercapnia (F i CO 2 =0.05). Gas exchange, cardiac hemodynamics (transthoracic bioimpedance) and cardiovagal baroreflex sensitivity (BRS) were measured continuously, and each stressor was compared with its own same-day normoxic baseline. We hypothesized that nasal breathing would blunt these responses. In normoxia, breathing pattern had no consistent effect, although oral breathing lowered BRS relative to free breathing in one of the two normoxic trials (14±6 vs. 19±10 ms/mmHg; P=0.047). In hypoxia, oral breathing elicited a higher respiratory frequency than free breathing (15.7±2.8 vs. 14.9±2.8 breaths/min; P=0.008) and shortened expiratory time (P=0.005), whereas nasal breathing attenuated the hypoxic rise in heart rate (70±13 vs. 74±13 bpm; P=0.018). In hypercapnia, V̇O 2 was lower during nasal than free breathing (324±69 vs. 360±58 mL/min; P=0.026), and oral breathing increased diastolic blood pressure compared to free breathing (75±5 vs. 72±5 mmHg; P=0.038). Breathing route had minimal consequences at rest in normoxia but became physiologically relevant under chemoreflex stress, where nasal breathing lowered oxygen consumption and heart rate whereas oral breathing produced less favourable cardiovascular responses. Maintaining nasal breathing may thus support cardiorespiratory function at altitude and during hypercapnia.

The authors' abstract, as published at the source. American Journal of Physiology-Heart and Circulatory Physiology, 2026 · DOI ↗