The Effect of the Nasal Airflow Reducer on Parasympathetic Activity in Adults: A Pilot and Exploratory Study

Background and Objectives: Boosting parasympathetic activity may enhance both physical and mental functions. In this study, we introduced the Lin Nasal Airflow Reducer (L.NAR), a silicone device designed to reduce nasal airflow. This pilot and exploratory study aimed to investigate the effect of L.NAR on parasympathetic activity in adults. Materials and Methods: The test protocol consisted of two 16 min ECG sessions. In the first session, participants did not wear the L.NAR for the initial 8 min (Test 1) but wore it for the remaining 8 min (Test 2). Following a 30 min rest, the second session reversed the sequence, with participants wearing the L.NAR for the first 8 min (Test 3) and removing it for the final 8 min (Test 4). Time- and frequency-domain analyses and non-linear analyses were used to assess heart rate variability (HRV) for every 300 s moving by 10 s. Repeated measurement ANOVA was conducted to compare the means across the four tests. Results: A total of 49 participants were enrolled in the analysis, with a mean age of 40.3 ± 10.7 years. Male participants had a higher body mass index (BMI) than female participants (24.0 ± 3.3 vs. 21.3 ± 2.9 kg/m², p = 0.014). Participants in Test 3 and Test 4 had significantly lower heart rate values than those in Test 1. Participants wearing the L.NAR (Test 2 and Test 3) had significantly higher RMSSD values compared to those not using the L.NAR. Among the participants, 33 (67.3%) who wore the L.NAR showed significantly higher RMSSD levels compared to their pre-L.NAR levels during the first practice. This improvement was achieved after an average of 2.5 ± 2.9 sessions. Conclusions: In this study, we introduced a novel approach using the L.NAR to increase RMSSD, a key indicator of parasympathetic activity.