Acute Nasal Breathing Lowers Diastolic Blood Pressure and Increases Parasympathetic Contributions to Heart Rate Variability in Young Adults

Introduction: Interest is growing in how breathing pace, pattern, and training (e.g., device-assisted or -resisted breathing) affect prognostic cardiovascular variables (e.g., blood pressure (BP)). Nasal breathing increases bronchodilation via airway epithelium nitric oxide production, increases diaphragmatic movement, and reduces accessory inspiratory muscle recruitment. Despite these changes, the effect of nasal compared with oral breathing (i.e., breathing route) on prognostic cardiovascular variables is unclear. Hypothesis: We hypothesized that nasal compared with oral breathing would acutely lower BP and improve heart rate variability (HRV) metrics. Methods: We tested 20 young healthy adults in this study (13 Female/7 Male; age: 18 [1] years, median [IQR]; body mass index: 23 ± 2 kg•m -2 , screening systolic / diastolic BP 116 ± 12 / 67 ± 7 mmHg mean ± SD). Participants self-selected their breathing rate during a five-minute ‘run-in’ period. Using a metronome, their breathing rate was fixed during two subsequent (random order) five-minute resting periods with nasal and oral breathing while we measured brachial BP and HRV metrics via ECG. We compared data between conditions using a Wilcoxon signed-rank paired test (data presented as median [IQR]) or using paired, two-tailed t-tests (data presented as mean ± SD). We set the significance to p <0.05. Results: Nasal breathing lowered mean (nasal: 84 ± 7 vs. oral: 86 ± 5 mmHg, p =0.006, Cohen’s d =0.70) and diastolic (nasal: 68 [8] vs. oral: 72 [5] mmHg, p <0.001, Rank-biserial correlation=0.89), but not systolic (nasal: 116 ± 11 vs. oral: 117 ± 9 mmHg, p =0.48, Cohen’s d =0.16) BP. Nasal breathing also raised the High-Frequency contribution to HRV (nasal: 59 ± 19 vs. oral: 52 ± 21 %, p =0.04, Cohen’s d =0.50) and lowered the Low-Frequency to High-Frequency ratio (nasal: 0.9 ± 0.8 vs. oral: 1.2 ± 0.9, p =0.04, Cohen’s d =0.49), suggesting a greater parasympathetic contribution to HRV. There were no differences between conditions for heart rate ( p= 0.90) or time-domain HRV metrics ( ps ≥0.07; e.g., the standard deviation of NN intervals). Conclusion: These data suggest that nasal compared with oral breathing acutely lowers mean and diastolic BP as well as potentially increases parasympathetic contributions to HRV.