Nasal versus Buccal Breathing and Non-Invasive Indices of Vascular Function in Healthy Young Adults: An Observational Crossover Study

Purpose: To compare the effects of nasal versus buccal breathing on non-invasive indices of vascular function under standardized resting conditions. Methods: This observational crossover study included 45 young healthy Caucasian male volunteers (mean age 21.3 ± 2.3 years). Each participant completed two breathing protocols: nasal breathing (NB) and buccal breathing (BB), in randomized order, separated by a washout period. Vascular responses were assessed using several non-invasive methods: Digital Plethysmography (DP) and UltraSound Flow-Mediated Dilation (US-FMD). Pulse Propagation Time (PPT) and Reflection Index (RI) were derived from DP, while brachial artery diameter was measured with US-FMD at rest and following each breathing condition. Results: Nasal breathing significantly increased PPT (6.35% ± 1.51) and reduced RI (4.6% ± 1.25) compared with buccal breathing, indicating changes consistent with increased vascular relaxation (p < 0.05). Ultrasound assessment demonstrated a significant increase in brachial artery diameter (4.46% ± 0.05) during nasal breathing (p < 0.001), an effect absent during buccal breathing. These findings indicate that nasal breathing is associated with enhanced vasodilation and differences in non-invasive vascular indices compared with buccal breathing. Conclusion: In healthy young adults, nasal and buccal breathing were associated with distinct patterns in non-invasive indices of vascular function. These findings highlight the physiological relevance of breathing route under resting conditions and warrant further investigation.