Introduction: A long-known, noninvasive, and inexpensive method of stimulating efferent vagus activity is slow-paced breathing. This stimulation may result in an increase in heart rate variability (HRV) and a decrease in inflammatory activity by stimulating the efferent cholinergic anti-inflammatory pathway (primary outcome of the study). A significant effect on the trajectory of Interleukin-6 was shown. The aim of the present analysis is to investigate the direct effects of respiratory intervention on parameters of HRV.
Methods: COVID-19 inpatients with bilateral pneumonia without ventilation were randomized to the intervention group (IG) (3 x 20min app-assisted breathing at 6/min) or the control group (CG) with standard care from March - May 2021 at Ulm University Hospital (DRKS00023971). Mixed linear regression models were calculated to assess A) differences in rest between IG vs. CG over time of the following HRV parameters: standard deviation of the IBI of normal sinus beats (SDNN), the root mean square of successive differences between normal heartbeats (RMSSD), Total Power (TP), Low-frequency power (LF) and High-frequency power (HF) and B) differences in HRV parameters between rest and breathing exercise (intervention group only) using linear contrasts. All models were calculated including comorbidities, number of medication, age and sex.
Results: N=43 patients (age 55±14; 67% male; N=21 intervention group) were included in the analyses. The applied breathing protocol was feasible, oxygenation was stable, and no adverse events occurred. The resting HRV parameters did not differ over hospital stay between intervention group and control group. During the breathing intervention sessions (N=21 patients from IG), Total Power (p = 0.003, chi² = 9.15; df1), LF (p<0.001, chi² = 11.47; df1), and SDNN (p = 0.008, chi² = 7.00; df1) increased statistically significantly compared to the preceding resting period (n = 142, N = 21), but not for HF (p = 0.407, chi² = .69; df1) and RMSSD (p = 0.123, chi² = 2.37; df1).
Conclusion: Slow-paced breathing was shown to be a safe intervention in hospitalized patients with COVID-19 pneumonia and was able to increase vagal tone and reduce inflammation. A broader clinical application should be investigated.