## 4 Discussion
\begin{table}
\begin{tabular}{c c c} \hline
**Breathing Pattern** & **Guzik-Index** & **Porta-Index** \\ \hline
1:0 & 46.86 & 46.91 \\
1:2 & 46.74 & 46.50 \\
1:1 & 49.42 2 3  & 48.98 4  \\ \hline \end{tabular}
\end{table} 
Table 5: The values of Guzik and Porta indices at different breathing patterns (\(n\) = 35): single-paced (1:0), dual-paced at 1:2 and 1:1 i/e ratio. The main result of the present study substantiates that dual-paced respiration proved to be the reason for the mild, but statistically significant, increase in the PAT values, regardless of the i/e ratio. Currently, we are limited to hypotheses and further investigations are needed to explain the phenomenon. [PERSON] et al. investigated the changes in the electroencephalogram (EEG) and HRV parameters during dual-paced breathing at 10 bpm, with a 2.4 s inhalation and 3.6 s-long exhalation period [42]. They found global increases in EEG parameters by the low- and high-frequency alpha power and a locally decreased theta power at dual-paced breathing compared to spontaneous respiration, as well as a significantly increased high-frequency band in the HRV, which reflects the parasympathetic activity. Due to the increase in low-frequency alpha power, they suggested that the paced  
Figure 6: The spectral analysis of the RRIs and the corresponding PAT values of the volunteer B_B_20000627 at (**A**,**B**) single-paced, (**C**,**D**) 1:2 and (**E**,**F**) 1:1 i/e ratio. The most prominent peak is at 0.22 Hz that corresponds to the respiratory sinus arrhythmia at 4500 ms paced breathing. On the FFT of both the ECG and PAT, there are second harmonics at 0.44 Hz. These harmonics are the most prominent at 1:2 breathing ratio and nearly disappear at 1:1 ratio due to the sinusoidal shape of breathing. The Origin Pro 2021 (OriginLab Corp., Northampton, MA, USA) software was used for the spectral analysis of beat-to-beat RRIs and PAT values. breathing promotes the internal alertness, indicating a successful meditation. In our study, during dual-paced breathing, volunteers were triggered by two short beeps with different tones at the beginning of inhalation and exhalation. This is similar to the auditory oddball paradigm, in which participants have to discriminate between a standard and a target stimulus from one another and perform the action. Related to the target stimuli, a positive deviation of the electroencephalogram (EEG) signal appears at approximately 300 ms delay, known as P300, which is a component of the event-related potential. It reflects the cognitive process: attention, short-memory, stimulus evaluation and decision-making [43, 44]. Several areas of research have focused on the relationship between the autonomic nervous system and the higher-level brain controls. [PERSON] et al. [45] examined the changes in sympathetic nerve activity (SSNA) during the auditory oddball task among healthy volunteers. They found significantly higher incidences of SSNA following the target stimulus. This phenomenon was not detectable in the case of the passive oddball paradigm, during which the subjects had to ignore the auditory signal. They also observed a sympathetic skin response and the reduction of skin blood flow following the SSNA burst. The decrease in skin blood flow may also have occurred during our measurements, which could explain the consequential increase in the PAT values. In another study, the activation of the anterior cingulate cortex and the cerebellum were observed [46] during stochastic decision-making tasks. The increase in the PAT values on dual-paced respiration may indicate the presence of complex connections between the autonomic nervous system and higher-level brain areas in the explanation; however, further investigations are needed in order to clarify the role of dual-paced vs. single-paced respiration in this context. Study limitations: The low sample size (\(n=35\)) may be considered as a limitation; however, the differences were proved to be statistically significant. Another shortcoming is the lack of continuous blood pressure measurement.