Reliability of the Polygraphic Home Sleep Test for OSA Determined by the Severity and Pattern Changes of Two Consecutive Examinations

Abstract

Diagnosis and effective treatment of obstructive sleep apnea syndrome (OSA) in adults is an important health priority. Home respiratory polygraphy is a cost-effective alternative to polysomnography in OSA. The aim of this study was to investigate the variability of two consecutive home respiratory polygraphic examinations by comparing the severity characteristics and pattern (supine dominant, continuous, etc.) variability. We examined 100 patients with clinically suspected OSA on two consecutive nights by home respiratory polygraphy. The correlation of time in bed (TIB), apnea-hypopnea index (AHI), oxygen desaturation index (ODI), and T90 of the two examinations were compared by the Pearson test. The severity ranks and nocturnal apnea patterns of the two periods were compared using Spearman and Wilcoxon tests. Pearson’s correlations represented a strong correlation of the AHI, ODI, and T90, but only moderate for TIB. The severity-specific correlation was the highest for AHI in the severe group. Out of 100 pairs of polygraphic examinations, 25 cases showed change in the severity ranking (decreased in 11, increased in 14); 15 cases showed a change in the polygraphic pattern (supine, non-supine, etc.), with severity change in 6 cases. Therapy change based on the second examination was initiated in 6 cases. Our results revealed a good intra-individual correlation between the severity grades of the two nights, with the highest value in the severe cases. In some cases, the nightly variation in the polygraphic pattern may explain the change in the severity. From a therapeutic point of view, the low number of severity changes between moderate and severe groups revealed good reliability.

1. Introduction

Obstructive sleep apnea syndrome (OSA) is characterized by the repetitive cessation of breathing, abnormal snoring, fragmentation of sleep architecture, and consequent daytime symptoms (sleepiness, memory impairment, etc.). The prevalence of OSA is high, and the well-known consequences of the disease include cerebro- and cardiovascular disorders [1,2], hypertension [3], and cognitive impairment [4].

Reliability of the accurate severity determination of obstructive sleep apnea syndrome is essential for adequate therapy. The severity can be influenced by a number of different factors, such as gender, obesity, nightly variation of sleep architecture, and sleep position.

Sleep is an adaptive system influenced by many factors (daytime physical and mental activity, etc.). Therefore, the amount and structure of sleep are not stable and may vary from day to day. This daily variation can influence sleep-related pathophysiological processes, with the consequence of changing the severity of sleep-disordered breathing [2,5,6].

Besides the above, some other important factors—like sleep position and sleep phase dependent processes—can modify the result of sleep studies.

According to daily practice, on the basis of the sleep position and sleep phase, different patterns can be defined. These include supine-dependent [7,8], supine-dominant [9], phasic non-supine (such as REM-dependent, [10]), continuous (position- and phase-independent apneas), continuous with phasic (REM) worsening, and sporadic. The pattern and the time spent in different positions during sleep can vary from night to night and can substantially influence the severity of the breathing abnormality.

Data on changes in sleep position and pattern at night are limited due to—in most cases—the conventional diagnostic process based on a single diagnostic night.

The first-night effect of the examination can further reduce the reliability of the one-night sleep study [11].

These processes suggest that a single overnight test may not always be able to accurately describe the severity of the disease.

The gold standard for the diagnosis of sleep apnea syndrome is the overnight polysomnographic examination [12], but availability is limited and the personnel (sleep technician) requirements are high [13].

In certain circumstances, as defined by the AASM guidelines [12,14], the polygraphic examination performed in the patient’s home can be a useful tool for the diagnosis of sleep apnea syndrome. According to the AASM guideline, home sleep polygraphy is recommended if the pretest probability is high for obstructive sleep apnea syndrome [13].

There are several advantages (widespread availability, lower cost, etc.) and disadvantages (technical problems, determination of the exact sleep time, etc.) of the polygraphic examinations [15]. Due to the simplicity of this method, the repeated examination can increase the reliability of the diagnosis. Although several studies have investigated the reliability of repeated polysomnography, the current literature is limited to the night-to-night variability of the severity of OSA in home sleep polygraphy [5].

Taking together these data, the question arises about the sufficient number of sleep examinations to determine the exact severity of the sleep-related breathing abnormalities.

The main goal of the present investigation was to determine the daily variability of the severity of sleep-disordered breathing by determining its characteristic parameters (apnea-hypopnea index—AHI, Oxygen Desaturation Index—ODI, Time below 90% oxygen saturation—T90, Time In Bed—TIB) and to determine the stability of the polygraphic patterns during the two consecutive night examinations.

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 Pécs, Hungary).

3. Results

3.1. Demographic Data

The demographic characteristic of the participants included the following: of the 100 participants, 85 were male and 15 were female. This imbalanced ratio was due to the referral of the patients (which represents the characteristic distribution of the male and female patients with sleep-disordered breathing). The male patients were between the ages of 23 and 75 (mean: 48.61 years, SD: 12.16 years). The age range of female patients was between 37 and 73 years (mean: 55.4 years, SD: 10.05 years).

3.2. Severity Group–Dependent Means and SDs of the AHI, ODI, MinO2, TIB, and T90

The severity-specific descriptive values (mean, SD) of the characteristic parameters (AHI, ODI, T90, MinO2, and TIB) of the first and second polygraphic examinations were calculated and are listed in

Table 1. Severity-dependent characteristic values of the AHI, ODI, T90, MinO2, TIB, and Num. of the two consecutive polygraphic examinations.

		Negative	Mild	Moderate	Severe
		Mean SD	Mean SD	Mean SD	Mean SD
1st PG	AHI (/h)	2.41 (1.35)	9.13 (3.14)	25.51 (3.77)	51.82 (17.42)
	ODI(%)	3.81 (2.35)	14.66 (8.32)	32.81 (7.95)	56.81 (18.42)
	T90 (%)	0.05 (0.07)	7.51 (20.75)	22.27 (18.39)	31.84 (24.88)
	MinO2(%)	87.8 (4.23)	85.6 (4.40)	79.5 (6.37)	68.9 (11.83)
	TIB (min)	462.7 (71.4)	478.7 (93.7)	440.1 (91.2)	472.9 (109.3)
	Num.	8	31	25	36
2nd PG	AHI (/h)	2.81 (1.51)	9.27 (3.11)	21.64 (3.64)	54.82 (18.35)
	ODI (%)	5.36 (2.4)	14.83 (11.69)	30.95 (10.85)	51.25 (18.92)
	T90 (%)	0.3 (0.61)	8.89 (22.07)	22.02 (25.25)	33.81 (24.32)
	MinO2(%)	88.5 (2.88)	84.1 (5.67)	77.6 (5.02)	68.3 (11.69)
	TIB (min)	437.9 (102.6)	456.4 (125.4)	435.9 (100.6)	420.7 (80.2)
	Num.	10	29	21	40

Mean: average, SD: standard deviation, AHI: Apnea-Hypopnea Index, ODI: Oxygen Desaturation Index, T90: Time spent below 90% of oxygen saturation, MinO2: Minimal oxygen saturation level, TIB: Time In Bed, Num.: Number of elements in a given severity group.

.

3.3. Correlation of the AHI, ODI, T90, and TIB

To determine the overall correlation of the AHI, ODI, T90, and TIB, Pearson’s correlation was calculated for 100 pairs of examinations (first and second polygraphic recordings).

The Pearson’s correlations for the AHI, ODI, T90, and TIB are 0.9199, 0.9282, 0.8126, and 0.4993, respectively. These results represent a strong correlation in the case of AHI, ODI, and T90, but only a moderate of correlation was measured for TIB (

Table 2. Pearson’s correlation of the AHI, ODI, T90, and TIB of the two consecutive polygraphic examinations (see text).

	AHI1-2		ODI1-2		T901-2		TIB1-2
	Pearson	p	Pearson	p	Pearson	p	Person	p
Total	0.9199	0.001	0.9282	0.001	0.8126	0.001	0.4993	0.001
Negative	0.1380	0.7446	0.7005	0.053	0.3363	0.4153	0.7767	0.0234
Mild	0.6329	0.002	0.8319	0.001	0.9842	0.001	0.3720	0.0469
Moderate	0.1419	0.4823	0.4696	0.0135	0.2928	0.1383	0.5329	0.0042
Severe	0.7947	0.001	0.8465	0.001	0.8652	0.001	0.6016	0.001
Moderate and severe together	0.8634	0.001	0.8792	0.001	0.6983	0.001	0.5552	0.001

AHI1-2: Correlation of the apnea-hypopnea index of the first and second examinations. ODI1-2: Correlation of the oxygen desaturation index of the first and second examinations. T90: Correlation of the percentage of time spent below 90% oxygen saturation. Negative, Mild, Moderate, and Severe: severity ranking obstructive sleep apnea syndrome according to the AASM classification. Total: the result of all the examinations of the 100 patients. Moderate and severe: moderate and severe groups together.

and

Table 3. Results of the Wilcoxon rank test of the paired samples of the first and second examination: severity and patterns of the moderate and severe groups together and total together.

	Sample Size	Severity Rank p	Pattern p
Moderate and severe:	63	0.5619	0.1289
Total	98	1.0	1.454

p: two-tailed probability. The high p values show the lack of significant differences between the two examinations of the patients.

).

To determine the severity-range-specific relationship of the first and second polygraphic examinations, Pearson’s correlations of the AHI, ODI, T90, and TIB were calculated for each severity group. The results are presented in Table 2 and Table 3.

The correlation of AHI was good for the severe group, moderate for the mild group, and low for the moderate and negative groups. In case of the ODI, the correlation was good for the severe, mild, and negative groups, and was medium for the moderate group. In case of T90, the correlation was high for the severe and mild groups, and low for the moderate and negative groups. The values are shown in Table 2.

From a therapeutic point of view, we measured a good correlation for AHI and ODI in the moderate and severe groups (0.8634 and 0.8792, respectively) while the correlation for T90 was only moderate (0.6993) (Table 2).

The correlation of the TIB was high only for the negative examinations (0.7767) and moderate for the moderate, severe and severe and moderate groups together (0.4993, 0.5329, 0.6016 and 0.5552, respectively) (Table 2).

3.4. Severity Rank and Pattern-Specific Correlation

To determine the differences between the severity ranks and the specific patterns of the two polygraphic examinations, the Wilcoxon test was performed (groups: total examinations and—from a therapeutic point of view—the moderate and severe together).

Wilcoxon test of the two night’s severity ranks and patterns showed the absence of significant differences in both total and common moderate and severe groups (Table 3).

To determine the correlation between severity ranks and patterns of the two periods, Spearman correlation was performed, which showed strong correlation in the moderate and severe groups together and in the case of the total examinations.

3.5. Number of Changes in Severity Ranks by Categories

Out of 100 cases of repeated polygraphic examination, 25 cases showed changes in severity ranking (25%, the higher severity rank indicates a more severe disease). A decrease of the severity rank of the second session was seen in 11 cases, while an increased severity was seen in 14 cases. The severity rank changes of the second examinations are listed as follows: in the negative group, it increased in 3 cases; in the mild group, it increased in 3 and decreased in 4 cases; in the moderate group, it increased in 8 and decreased in 3 cases; and in the severe group, it decreased in 4 cases (

Table 4. Spearman correlation of the severity ranks and the predefined patterns (see text) of the two consecutive polygraphic examinations.

	Severity Rank		Pattern
	rho	p	rho	p
Moderate and severe together	0.65	0.0001	0.994	0.0001
Total	0.85	0.0001	0.916	0.0001

Moderate and Severe: severity ranking obstructive sleep apnea syndrome according to the AASM classification. Total: result of all the examinations of the 100 patients.

).

3.6. Number of Polygraphic Pattern Changes by Category

Out of 100 repetitive examinations, our results showed polygraphic pattern changes (for example: from supine to non-supine, etc.) in 15 cases. The patterns of the first examination and the change during the second are listed in

Table 5. Distribution and change of the patterns of the examinations (Total: 100).

Pattern Type	N	1.	2.	3.	4.	5.	6.	Sum
1.: Sporadic	11	-	0	1	1	0	0	2
2.: Supine dependent	11	0	-	0	0	0	0	0
3.: Supine dominant	21	0	2	-	2	0	0	4
4.: Phasic, non-positional	33	1	0	3	-	2	1	7
5.: Continuous	19	0	0	0	0	-	2	2
6.: Continuous with phasic worsening	5	0	0	0	0	0	-	0

Pattern type: 1–6 of the first examination; N: number of elements in different pattern categories; 1., 2., 3., 4., 5., 6. (represents the same pattern types as in the case of the first column of the table): number and direction of changes during the second examination; Sum: total number of changes by patterns.

. In this sample, we did not find a shift of pattern in the supine-dependent and continuous with phasic worsening groups. From these 15 cases, severity rank changes of the second examinations were seen only in 6 examinations (negative: 1, mild: 3, moderate: 2, severe: 0) (Table 5).

3.7. Number of Treatment Changes Resulting from the Difference in Severity Ranking of the Second Examination

From a therapeutic point of view, we detected six cases where the second examination modified the severity of disease and the therapeutic approach. Worsening was observed in the second recording in three primarily negative and three primarily mild cases. From the two consecutive recordings, the therapeutic approaches were determined on the basis of the more severe results (

Table 6. Severity rank, pattern, and therapy changes based on the second polygraphic examination.

Severity Rank (1st Examination)	N	Change to the 1st Examination	Pattern Change	Pattern Change with Severity Rank Change	Therapy Change as a Result of 2nd Examination Due to Worsening
Negative	8	3 increased to mild	1	1	3
Mild	31	3 increased to moderate 4 decreased to negative	6	3	3
Moderate	25	8 increased to severe 3 decreased to mild	6	2	0
Severe	36	4 decreased to moderate	3	0	0

Therapy is based on the more severe examination result from the two nights. Negative, Mild, Moderate, Severe: severity ranks; N: number of elements in a given severity group (and below the actual numbers); Numbers elsewhere: number of items in a given category with change.

).

3.8. Disease Profile of the Participants

The disease profile of the participants is summarized in

Table 7. The disease profile of the participants sorted by severity group based on the categorization of the first polygraphic examination.

Severity Rank (1st Examination)	N	Common Associated Diseases
		Hypertonia	Cardiac Arrhythmias	Coronaria Artery Disease (CAD)	Diabetes Mellitus	Ischemic Stroke
Negative	8	3	0	0	1	0
Mild	31	12	2	1	2	0
Moderate	25	13	2	0	2	2
Severe	36	21	4	2	4	3

Negative, Mild, Moderate, and Severe: severity ranks of the polygraphic results; No.: the number of participants in a given group. Top row lists the different co-morbidities. The numbers below the co-morbidities represent the number of participants with the given disease in a given severity group.

.

The data show a trend that, as the severity of the disease increased, the proportion of different types of cerebro- and cardiovascular diseases increased in the study population.

Only occasional alcohol consumption was indicated in the questionnaires, and patients were instructed not to consume alcohol during the study. Thus, alcohol consumption habits did not influence the study results (thus not shown in the table).

4. Discussion

The main goal of the present study was to investigate the stability of the severity of sleep-disordered breathing by determining the characteristic parameters and the stability of the polygraphic patterns during repetitive examinations (two nights).

The importance of a reliable, widely accessible, cost-effective examination method for sleep-disordered breathing is underlined by the data, where 80–90% of patients who suffer from OSAS are undiagnosed [17].

The question arises about the effect of daily variation of sleep-disordered breathing on the severity and therapeutic approaches. Due to the daily variation of our activity, sleep amount, etc., one night of sleep examination might be insufficient to describe the exact severity.

In addition to the former, the first-night effect of the sleep examination can also modify the result of the exact severity of the sleep-disordered breathing [11]. The first-night effect may be more pronounced for PSG due to the number of electrodes, non-home environment, and continuous monitoring by sleep technicians.

Two nightly examinations can improve the reliability of the result. Ahmadi and colleagues [18] compared one and two nights of PSG examination for the diagnosis of sleep-disordered breathing. They found a significant night-to-night variation of the polysomnographic respiratory variables and concluded that 13% of the patients might benefit from the second examination.

Similar variability was also measured in the study of Gouveris [11]. Fifteen percent of patients showed significant variation between the two nights, causing a 6% of loss of severe patients with one recording.

In contrast with the former investigations, Ma and colleagues [19] concluded, that only a mild first night effect can be found, with no effect on the diagnosis of sleep-disordered breathing.

The gold standard for the diagnosis of sleep-disordered breathing is the polysomnographic examination [12,14,20], which requires a complex technical background and polysomnographic technologist. The cost of the examination is high, and the availability is limited.

Despite the standards and guidelines, the reliability of polysomnography is questionable in some circumstances [21,22]. The investigations of Kapoor [23] revealed a negative polysomnographic examination of a patient with clinically positive symptoms, and a home sleep test proved the presence of sleep-disordered breathing.

The cost-effective form of OSAS diagnosis is the polygraph-based home sleep test. The indications and contraindications are defined by the AASM guideline [12,14,20]. Depending on the applied sensor set, many forms are used. The accuracy of the polygraphic examination can be improved by the use of an extended sensor set (including body position sensor and two belts for breathing effort) [12].

In this study, we examined the accuracy of the repetitive polygraphic examination.

Our results revealed good correlation of the AHI, ODI and T90 between the two consecutive nights for 100 examinations. Determining the severity range-specific correlations, we found the highest correlation for AHI in the severe group. The results were confirmed by the severity rank–specific statistics (Wilcoxon and Spearman). The correlation for ODI and T90 varied from moderate to high in all severity groups. This finding proves the reliability of the PG for the diagnosis of sleep apnea syndrome, especially in the severe form. Our examination provides further evidence for the appropriate diagnostic procedure for obstructive sleep apnea syndrome in the case of the severe category. In given circumstances (positive complaints, witnessed apneas, and in the presence of co-morbidities—representing the high probability of severe disease), polygraphy can be a good choice for an adequate diagnosis.

Our examination showed the night-to-night variation of the severity in 25% of examinations. Both increase and decrease of the severity rank were found during the second examination. This nearly equal and bidirectional (improvement and worsening) change ruled out the first-night effect (false negative or milder severity) of the polygraphic examination in this study and might be based on the daily variability of the sleep instead of the first-night effect.

In Ahmadi’s work [18], the difference between the two overnight tests was significant if the change in AHI between the two was greater than 5/h. This does not represent real severity changes in all cases.

In contrast, in our study, we used clinically significant change (associated with a change in therapy and a change in formal severity grade).

In Ahmadi’s work, a change was described in 13% of patients in the second study, whereas in our study, only 6 out of 100 cases had a change in severity grade (6%) that warranted a change in therapy.

We consider that clinically significant change (requiring a change in therapy) is a more useful approach for daily practice.

The majority of studies use parameters of the sleep disordered breathing (AHI, ODI, etc.), but other variables like the TIB or pattern of examination can provide further insight into the exact pathology.

In contrast with the AHI, ODI, and T90, the length of examination (TIB) revealed a moderate correlation between the two nights for all 100 pairs of examinations. The severity-specific correlation of TIB was highest in the negative group. This finding can be explained by the lack of the effect of sleep fragmentation and awakenings in the negative group. In contrast, in other severity groups, breathing pathology can modify the sleep time (TIB) day by day through sleep fragmentation and consequential awakenings.

There are only limited and controversial data about the role of the nightly pattern change on the severity of sleep-disordered breathing.

According to the examinations of Levendowski [24], the time spent in the supine position was significantly higher during the first recording. In contrast, Kukwa [25] found no differences in the supine position between the two nights. According to Kukwa’s results [25] on gender differences in this question, women recorded by polygraph spent more time in a supine position.

The examination of Metersky [26] can explain the higher number of supine positions during the polysomnographic examination. The patients spent more time in the supine position during the PSG examination compared to the recording without an extended electrode set. This result emphasizes that the polysomnographic recording can overestimate the severity of sleep-disordered breathing in some circumstances.

These examinations are based on the change in severity due to the time spent in a given—i.e., supine—position. The consequence of the more time in the supine position can be a higher respiratory disturbance index. These data highlight the importance of night-to-night variability in the pattern of sleep-disordered severity ranking.

The novelty of our study is to examine the variability of different patterns between the two recorded nights. Theoretically, the different patterns could represent different pathophysiological backgrounds. An example of this might be the pathophysiological difference between the supine-dominant (with highly anatomical origin) and REM-dependent (alteration of the regulation during REM phase) patterns.

The statistical analysis of pattern changes showed good correlation between the examination nights. Pattern changes were found in 15% of 100 examinations during the second night. According to our results, the most stable patterns are the supine-dependent and continuous with phasic worsening (its polysomnographic equivalent is the continuous with REM worsening); the former is associated with high structural pathogenesis, and the latter is regulatory in origin.

In 6 of the 15 cases, pattern changes influenced the severity of sleep-disordered breathing, with the consequence of potential therapeutic change.

As is known from previous data, both polysomnographic and polygraphic examination can overestimate (supine dominant cases) or underestimate (first night effect) the real severity of the disease, with the consequence of failure of the therapeutic decision.

The therapy of sleep-disordered breathing is based on the severity defined by the apnea-hypopnea index. According to the AASM guideline [7], moderate and severe obstructive apnea syndrome requires the same therapeutic approach, which is—in most cases—continuous positive airway pressure therapy.

Taking together our data from a therapeutic point of view, we found that the variability of the severity range during the two examinations—in most cases—did not modify the appropriate therapeutic approaches significantly. From the 100 examinations, we found only six cases with therapy change, and from these cases, the therapy was modified to CPAP only in three patients.

According to this result, the most vulnerable groups are the negative and mild categories. Based on the first examination, we did not find therapeutic change in the moderate and severe groups. These findings indicate that in the negative and mild category, the polygraphic examination can be questionable for the appropriate diagnosis and therapeutic consideration. The underestimation of the real severity and therapeutic decision can be the consequence of the unknown real sleep time, which in turn affects the determination of the exact AHI. With the increase of the AHI, the effect of real sleep time on exact AHI and on the consequential therapeutic decision will decrease.

This result revealed that besides daily severity viability, from a therapeutic point of view—in most cases—one night of examination provides reliable results for the therapeutic decision strategy.

Our examination provides further evidence about the reliability of the home sleep test with polygraph in the diagnosis of obstructive sleep apnea syndrome. According to the current guidelines, in the case of a questionable result or clinical-examinational discrepancies, polysomnographic examination should be performed.

The main limitation of the present examination is the relatively modest number of patents. However, on the basis of the literature search, the majority of examinations in this field are based on comparable cases.

In the present study, the correlation of the two tests with the age, sex, and comorbidities was not explored, as the number of possible groups would require a much larger number of items for appropriate statistical analysis. Further studies along these lines are planned in the future, and data collection is ongoing.

5. Conclusions

Polygraphy is a widely used method for the home sleep test for obstructive sleep apnea syndrome, with known limitations and advantages. It is important to determine the utility of this method due to its simplicity and high cost-effectiveness.

The good reliability of the polygraphic examination in the case of the moderate and severe categories underlines the usefulness of this cost-effective method for both diagnostic purposes and from a therapeutic point of view in obstructive sleep apnea syndrome.

In other severity categories, the decision for the repetition of the examination with polygraph or polysomnograph must be based on the clinical characteristics (complaints, concomitant diseases) of the patients.

The pattern change found in some cases of the repetitive polygraphic examinations can provide new information about the pathophysiology of obstructive sleep apnea syndrome.

Our results provide further data for the decisions on the appropriate diagnostic process for sleep-disordered breathing.