## 2 Materials and Methods  
One hundred unselected participants were enrolled in the study. While patients referred to the Sleep Lab were likely to suffer from snoring or other sleep-disordered breathing, we performed the tests in the absence of the known diagnosis of each individual patient.  
To determine the severity and daily variability of the sleep-disordered breathing, each patient underwent home respiratory polygraphy examinations on two consecutive nights. The minimum duration of the examinations was six hours.  
During a routine polygraphic test for sleep apnea syndrome, the first 100 consecutive patients were selected for further analysis, independently from the symptomatology and other cardio- and cerebrovascular diseases. The inclusion criteria were the two technically good polygraphic examinations on two consecutive days. Patients with less than six hours of recording and a lack of two examinations were excluded from the study.  
The enrollment period was between 1 July 2020 and 15 September 2021. Twenty-three participants were excluded during the enrollment period due to technical problems and a lack of two examinations.  
Participants were instructed to do everything in the same way (sleep timing, eating habits, medication) as on the nights without tests.  
The patients were asked to avoid alcohol consumption during the examinations. All the patients filled out a questionnaire about their former medical history and medication, including cardiovascular diseases and alcohol consumption habits.  
Since two consecutive nights of testing were performed, the possible effect of the disease profile changes on the result of the examination was not expected.  
All the sleep examinations were performed by Alice PDx polygraphs (Philips Inc., Amsterdam, The Netherlands). The recorded channels were nasal air flow with a pressure sensor, respiratory effort (both thoracic and abdominal), peripheral oxygen saturation and pulse rate with a finger clip sensor, and snoring determined by nasal airflow cannula and body position.  
The following parameters were used for further analysis: Time in bed (TIB), apnea-hypopnea index (AHI), severity rank of the result (negative, mild, moderate, and severe), the percentage of time spent with less than 90% of oxygen saturation (T90), oxygen desaturation index (ODI), and the pattern of the examination. We defined the following patterns: supine dependent, supine dominant, continuous, continuous with phasic deterioration, phasic non-supine dependent, and sporadic.  
Recordings were validated and scored manually according to the AASM standards (version 2.6, 2020, at least 10 s of airflow cessation for apnea, and 30% drop of airflow for 10 s, at least 4% of oxygen saturation decrease, without arousal) [16] by trained scorers.  
To compare the polygraphic parameters (AHI, ODI, MinO2, AveO2, TIB, etc.) of the two consecutive examinations, Pearson's correlation coefficient was used. The results of the first examination were compared with the second examination results of the same participants. Spearman and Wilcoxon tests were used to compare the ranks of severity (negative, mild, moderate, and severe), and the apnea patterns (supine, continuous, phasic, etc.) of the two examinations. The Pearson's correlation coefficients and Spearman and Wilcoxon tests were calculated using the SPSS v.22 statistical software package (SPSS, IBM Inc., Armonk, NY, USA). The results were verified by a statistician.  
The research was reviewed and approved by a local ethics committee (5332/2014, Regional and Institutional Research-Ethical Committee, University of Pecs, Hungary).