The effect of the use of a mouthpiece and nose clip on heart rate variability

Abstract

Aim: The aim of this study was to determine the potential impact of breathing through a mouthpiece and nose clip assembly, such as the Hans Rudolph system used in exercise testing, on autonomic modulation of heart rate, as assessed by measures of heart rate variability (HRV) during seated rest. Methods: Ten participants (2 M and 8 F, mean age 53.5 ± 2.68 years, BMI 25.80 ± 3.29 kg/m2) sat quietly for 5 min to establish resting conditions, then breathed utilizing the mouthpiece and nose clip (MP1) for 5 min then without for five minutes (NMP1), and repeated this procedure (MP2 and NMP2). ECG was recorded continuously for the duration of the test and HRV measures of SDNN, total power, very low frequency (VLF); high frequency (HF) and low frequency (LF), LF and HF normalized values and the LF/HF ratio were later calculated using Chart 5 pro software (Adinstruments). Results: ANOVA results show heart rate averages remained within one beat per minute across conditions, while measures of SDNN, VLF and Total Power were significantly greater in the NMP2 condition than MP1 and MP2; these measures for the NMP1 condition were also greater in magnitude but did not reach significance. LF normalized values were reduced in the MP conditions (MP1 0.566 ± 0.147nu, NMP1 0.708 ± 0.155nu, MP2 0.606 ± 0.129nu and NMP2 0.765 ± 0.120nu), while HF normalized values were significantly greater in the comparison of MP1 to NMP1 (p = 0.017) and approached significance in MP2 and NMP2 (p = 0.054). The LF/HF ratio was significantly greater in both NMP1 and NMP2 than both MP1 and MP2. Conclusion: the MP condition resulted in changes in measures of HRV. These changes may be the result of alterations in breathing induced by use of the MP and/or alterations in autonomic modulation of heart rate between the two conditions. This may be of relevance in studies using HRV in exercise testing.