Comparison of respiratory rates derived from heart rate variability, ECG amplitude, and nasal/oral airflow.

It would often be desirable to obtain the respiratory rate during everyday conditions without obtaining an additional respiratory trace. This study investigates the agreement between respiratory rate assessed from the electrocardiogram (ECG) and the reference respiratory rate derived from a nasal/oral airflow (AF). Nasal/oral airflow and a Holter ECG were recorded in 52 healthy subjects (26 males, age range: 25.4-85.4 years) during everyday conditions for at least 10 h, including night-time sleep. The respiratory rate was assessed for each 5-min epoch (1) using respiratory sinus arrhythmia (RSA), (2) utilizing the respiration induced variations of the R-wave amplitude (ECG derived respiration (EDR)). The agreement with respect to AF was quantified using the average/std and the concordance correlation coefficient rho(c). For RSA and EDR the difference with respect to AF was 0.2 cpm (std: 0.6 cpm) during sleep and -0.2 cpm (std: 1.0 cpm) during wake time. During sleep the RSA-approach performed best for subjects < or =50 years (rho(c) = 0.79) and worst for subjects >50 years (rho(c) = 0.41). The correlation of the EDR-approach was rho(c) = 0.73 for both groups. In conclusion, the respiratory rate may be assessed with reasonable agreement by both methods in younger subjects, but EDR should be preferred in the elderly.