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Original Research: SLEEP MEDICINE |

Respiratory Polygraphy With Actigraphy in the Diagnosis of Sleep Apnea-Hypopnea Syndrome* FREE TO VIEW

Emilio García-Díaz, MD; Esther Quintana-Gallego, MD; Aránzazu Ruiz, MD; Carmen Carmona-Bernal, MD; Ángeles Sánchez-Armengol, MD; Georgina Botebol-Benhamou, MD; Francisco Capote, MD
Author and Funding Information

*From the Departments of Critical Care and Emergency (Dr. García-Díaz), Pneumology (Drs. Ruiz, Carmona-Bernal, Sánchez-Armengol, and Capote), and Neurophysiology (Dr. Botebol-Benhamou), Hospitales Universitarios Virgen del Rocío, Sevilla, Spain; and the Department of Pneumology (Dr. Quintana-Gallego), Hospital San Juan de Dios, Sevilla, Spain.

Correspondence to: Emilio García-Díaz, MD, Department of Critical Care and Emergency, Hospitales Universitarios Virgen del Rocío, Manuel Siurot s/n, E-41013 Sevilla, Spain: e-mail: emil800@separ.es



Chest. 2007;131(3):725-732. doi:10.1378/chest.06-1604
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Objective: To determine the utility and reliability of a respiratory polygraphy (RP) device with actigraphy (Apnoescreen II; Erich Jaeger GMBH & CoKg; Wuerzburg, Germany) in the diagnosis of sleep apnea-hypopnea syndrome (SAHS).

Design: A prospective randomized study with blinded analysis.

Patients: Sixty-two patients with suspected SAHS.

Measurements: the following two RP studies were performed: one in the sleep laboratory (sleep laboratory RP [LRP]), simultaneously with polysomnography; and the other at home (home RP [HRP]). To study the interobserver reliability of RP, two manual analyses were carried out by two different researchers.

Results: In LRP, when the respiratory disturbance index was calculated using the total sleep time estimated by actigraphy (RDI) as a denominator, the sensitivity ranged between 94.6% and 100%, and the specificity between 88% and 96.7% for the different cutoff points of the apnea-hypopnea indexes studied. When the respiratory disturbance index was calculated according to the total recording time (RDITRT), the sensitivity was slightly lower (91.6 to 96.9%) and the specificity was similar (92 to 96.7%). In HRP, the sensitivity of the RDI ranged between 83.8% and 95.8%, and the specificity between 92% and 100%, whereas, when the RDITRT was used, the sensitivity was between 83.8% and 87.5%, and the specificity was between 94.7% and 100%. With regard to interobserver reliability, the intraclass correlation coefficient for the RDI of the two analyses of the RP was 0.99 for both LPR and HPR.

Conclusion: HPR is an effective and reliable technique for the diagnosis of SAHS, although it is less sensitive than LRP. Wrist actigraphy improves the results of HRP only slightly.

Figures in this Article

One of the most widely employed alternatives to polysomnography in the diagnosis of sleep apnea-hypopnea syndrome (SAHS) is the home sleep study performed using a portable respiratory polygraph that does not measure neurophysiologic parameters (an American Academy of Sleep Medicine [AASM], formerly the American Sleep Disorders Association, type III portable device).14 Elbaz et al5 have reported that actigraphy, utilized to estimate sleep time can improve the efficacy of respiratory polygraphy (RP) in the diagnosis of SAHS. However, although there have been published validation studies3,68 comparing these devices with polysomnography performed simultaneously in the sleep laboratory, there is little experience in their use in unattended home studies. There are even fewer studies in which, in addition to the simultaneous performance of RP and polysomnography in the laboratory (ie, sleep laboratory RP [LRP]), RP was also carried out in the patient’s home (ie, home RP [HRP]), a situation that may provide information about the influence of the setting on the diagnosis.9 On the other hand, the possibility that actigraphy could improve the diagnostic yield of unattended HRP has not been examined, and there are no in-depth studies on interobserver reliability in the analysis of the data. The objective of our study was to determine the utility and reliability of an AASM type III portable device with actigraphy (Apnoescreen II [AP-II]; Erich Jaeger GMBH & CoKg; Wuerzburg, Germany) in the diagnosis of SAHS, whether employed in the patient’s home or in the sleep laboratory.

Patients

The study group included patients living in the city of Seville, Spain, who were consecutively referred to the sleep laboratory for polysomnography because of suspected SAHS. Exclusion criteria were physical or mental impairment that ruled out the use of the equipment. The following data were collected for all the patients: sex; age; personal history; symptoms of SAHS; body mass index (in kilograms per square millimeter); systolic and diastolic arterial pressure; and results of spirometry and blood gas analysis.

All the participating patients underwent two studies with a portable RP: one was LRP performed simultaneously with polysomnography; and the other was HRP. The order of the studies was randomized, and the time interval between the studies was < 15 days. In the HRP, a technician went to the patient’s home between 10:00 and 11:30 pm to set up the equipment and get it running. The patient received instructions as to how to interrupt the recording in the morning. The patients were informed that they should not consume alcohol, sedatives, or stimulants the day before the study. The study was approved by the ethics committee of the hospital, and informed consent was obtained from all participants.

Polysomnography

An all-night polysomnographic assessment was performed in every case (Somnostar 4100; SensorMedics Corporation; Yorba Linda, CA). The assessment included EEG monitoring, electrooculography, submental electromyogram, oronasal airflow measurement with a thermistor, monitoring of chest and abdominal movements using two bands (Healthdyne Technologies Inc; Marietta, GA), ECG, and determination of arterial oxygen saturation (Sao2) by pulse oximetry (sampling frequency, 5 s). The recordings were analyzed manually by a technician other than those who had read the AP-II data and blindly with respect to the results of the simplified studies. Sleep data were staged according to the system of Rechtschaffen and Kales.10Apnea was considered to be the complete cessation of oronasal airflow lasting ≥ 10 s.Hypopnea was defined as a decrease in oronasal airflow of ≥ 50% for a duration of ≥ 10 s, accompanied by desaturation (ie, a decrease in Sao2 of ≥ 4%) and/or an EEG arousal response. An arousal was defined according to the criteria of the AASM.11 The variables analyzed were total recording time (TRT), total sleep time (TST), sleep efficiency (SE), and the apnea-hypopnea index (AHI), defined as the total number of apneas and hypopneas per hour of sleep.

RP

The measurements were performed with the AP-II, with continuous monitoring of oronasal airflow (thermistor), Sao2, heart rate (digital pulse oximetry with a sampling frequency of 5 s), respiratory movements (bands), tracheal sounds, ECG, body position (mercury sensor), and wrist actigraphy. The data were then transferred to a computer in the sleep laboratory and retrieved for analysis (Matrix Sleep Analysis software package for Windows; Aequitron Medical; Minneapolis, MN). Manual analyses were performed by two different researchers, who were blinded to each other’s results as well as to those of polysomnography. The manual analyses were carried out on the computer screen in modules consisting of seven 30-s epochs. The following variables were analyzed: TRT; TST estimated by actigraphy (TSTa); SE estimated by actigraphy; the percentage of TSTa spent in the supine position; respiratory disturbance index calculated using the TSTa (RDI); and respiratory disturbance index calculated according to the TRT (RDITRT). The definition of apnea was the same as that employed for polysomnography. Hypopnea was defined as a reduction in airflow of ≥ 50% lasting for ≥ 10 s, accompanied by a decrease in Sao2 of at least 4%. The RDI and the RDITRT were defined as the number of respiratory disturbances (apneas and hypopneas) per hour of sleep estimated by actigraphy and per hour of recording, respectively. In the analysis, sleep onset was defined as the initiation of a period of 20 epochs (10 min) of inactivity or the initiation of an inactive period prior to the onset of respiratory disturbances if this period lasted for < 10 min. During recording, wakefulness was considered to refer to those periods of continuous activity that were unrelated to respiratory disturbances (ie, apneas or hypopneas) lasting for two or more epochs (1 min) plus the two epochs following the cessation of activity.

Statistical Analysis

The descriptive variables were expressed as the mean ± SD or percentages, depending on the type of variable. The paired t test was used to compare sleep parameters, estimated by actigraphy, of RP with those of the polysomnography. The diagnostic accuracy of RP was evaluated by obtaining the receiver operating characteristic curves, and by calculating the sensitivity, specificity, and positive and negative likelihood ratios (LRs), their corresponding 95% confidence intervals (CIs), and the best cutoff points of the RDI during RP for different cutoff points of the AHI during polysomnography (ie, ≥ 10, ≥ 15, and ≥ 30). The agreement between the AHI during polysomnography and the RDI during RP was also evaluated according to the method described by Bland and Altman.12 To determine the agreement between the two observers in the analysis of the RP studies, the intraclass correlation coefficients and the κ coefficients of agreement were calculated.

With the results obtained in the 62 patients finally included in the study, real differences in sensitivity of > 10% can be detected, with a statistical power (1-β) of 0.80 and a probability of error of 0.05. The statistical analysis was carried out using a statistical software package (SPSS, version 12.0.1; SPSS, Inc; Chicago, IL).

Three of the 65 patients were excluded from the study, one due to a technical failure involving the polysomnography, and the other two withdrew during the course of the study. In one case, it was necessary to repeat polysomnography and the LRP because the sleep time was < 3 h. The home study had to be repeated in two cases (3%), one due to a technical failure on the transfer of the data to the computer and the other because of the poor quality of the oronasal airflow signal. The recordings corresponding to 62 subjects were considered valid for the study (Table 1 ).

The data from polysomnography and RP, according to the different analyses, are shown in Table 2 . The mean AHI according to the polysomnography was 30.3 ± 32.9, and the incidences of sleep-related respiratory disorders in the study population, using cutoff points of ≥ 5, ≥ 10, ≥ 15, and ≥ 30, were 71%, 59.7%, 51.6%, and 38.7%, respectively.

Tables 345 show the percentages of patients who were correctly classified (identification or exclusion), and the sensitivity, specificity, LRs, and best cutoff points for the RDI during RP, according to AHI cutoff points of ≥ 10, ≥ 15, or ≥ 30 in the polysomnography. Tables 345 also show the posttest sensitivity and specificity of the best RDI cutoff points, and the sensitivity and specificity when the respiratory disturbance index was calculated using TRT as a denominator (ie, not taking into account the analysis of actigraphy). The areas under the receiver operating characteristic curve of the RDI during RP for different cutoff points of polysomnography appear in Table 6 .

Figure 1 shows the means of the differences between the AHI during polysomnography and the RDI resulting from the analysis of the two RPs for each patient according to the Bland-Altman method.12 The overall mean difference between the AHI during polysomnography and the RDI during the HRP was 3.1 ± 17 (95% CI, −1.1 to 7.5) according to the analysis of observer A and 1.6 ± 16.4 (95% CI, −2.5 to 5.8) according to the analysis of observer B. In the case of the LRP, the overall mean difference between the AHI during polysomnography and the RDI was 2.8 ± 10.5 (95% CI, 0.13 to 5.5) in the analysis of observer A and 1.03 ± 10.3 (95% CI, −1.6 to 3.6) in the analysis of observer B. With respect to the agreement in the analyses of RP carried out by observers A and B, Table 7 shows the intraclass correlation coefficients for SE estimated by actigraphy and for the RDI during the two RP studies, and the κ coefficients for the different cutoff points of the RDI.

The results of the present study show that HRP is a valid method, with a high sensitivity and specificity for the diagnosis of SAHS, after comparing it with standard polysomnography. The diagnostic accuracy of HRP was only slightly lower than that of LRP. Moreover, in our study, the interobserver reliability in the analysis of the RP recordings was very high. On the other hand, in the case of the AP-II, wrist actigraphy contributed little to improving the efficacy of RP.

In the validation carried out in the sleep laboratory, the results were very good, with high levels of sensitivity and specificity, and were in agreement with the findings in other studies in which RP equipment was tested simultaneously with polysomnography equipment.13The diagnostic accuracy was somewhat lower in the HRP than in the LRP, a circumstance that can be explained in part by the fact that the LRP was performed on the same night as the polysomnography and may have influenced the natural night-to-night variability that is associated with sleep-related respiratory disorders.1415

As can be observed in Tables 345, the performance of the study in the patient’s home resulted in a slight loss of sensitivity in comparison with those performed in the sleep laboratory. This was also observed in the study by Reichert et al9 using a similar device (NovaSom QSG; Sleep Solutions; Pasadena, MD), in which the sensitivity was 95% in the laboratory and 91% in the home, for an RDI of ≥ 15. In our study, the major factor in the loss of sensitivity was probably the fact that the recording times in the home studies were significantly longer than those in the hospital studies. As actigraphy also overestimated the sleep time (in the analyses of the RP, SE was approximately 90%, while in polysomnography it was 76.9 ± 12.5%), the RDI may have been underestimated, since the denominator used to calculate RDI was TSTa.

Another factor that may have played a role in the lower sensitivity of our study of the HRP compared to the LRP is the lower percentage of time that patients spent in the supine position during HRP (approximately 50%; LRP, nearly 70%). This difference had been observed previously by other authors1618 and appears to be related to the polysomnography unit used, probably because of the EEG monitoring, which may cause the patient to move less and remain in the supine position for a longer time.

The specificity was higher in HRP than in LRP for all the cutoff points, according to both observers. On this subject, the specificity of the HRP for a cutoff point of ≥ 15 was 96.5% and that for a cutoff point of ≥ 30 was 94.7%, with very high positive LRs in both cases. This is important since the range between these limits includes the AHI threshold utilized in the different published guidelines and recommendations2,1920 as one of the criteria that comprise the indications for treatment with continuous positive airway pressure. According to the results of our study, an RDI higher than these thresholds in HRP using the AP-II would be an indication for treatment with continuous positive airway pressure, with a small margin of error, regardless of the criteria applied.

The AP-II includes wrist actigraphy to estimate sleep time according to the analysis of the periods of movement and inactivity, based on the observation that there is less movement during sleep than during wakefulness.21 In one report from 2002, Elbaz et al5 proposed the possibility that wrist actigraphy might be useful in improving the diagnostic yield of RP in patients with SAHS. In that study,5 the benefit obtained with actigraphy was modest, being limited to a greater sensitivity in the diagnosis of severe SAHS (AHI, ≥ 30).

The criteria employed in our study to estimate sleep time using actigraphy were partly based on the adaptation of those utilized by Elbaz et al,5 taking into account the technical features of the actigraph of the AP-II and the indications of the manufacturer. In our study, the only contribution of actigraphy was a slight increase in sensitivity, and not for every cutoff point. In HRP, actigraphy did not improve the sensitivity for a cutoff point of ≥ 15 in either of the two analyses. The best discrimination in HRP was obtained in patients with an RDI of ≥ 30. These unremarkable results are probably due to the fact that actigraphy overestimated the TST and the SE. On this matter, we know that actigraphy has been shown to correlate well with polysomnography in the detection of sleep time in healthy adults, but is less precise when the amount or quality of sleep decreases and overestimates the sleep time in patients with sleep-related respiratory disturbances.2124

Some RP devices employ other techniques to evaluate sleep, in particular the NightWatch system (Healthdyne; Marietta, GA), which uses an algorithm based on eye movement and body movement to assess and stage sleep.2527 In the study by White et al,26 this method also had a slight tendency to overestimate sleep when compared with polysomnography. However, its contribution to the diagnostic accuracy of RP was not evaluated.26

The percentage of home recordings considered to be invalid for analysis was very low in our study (3%). This failure rate is similar to that reported in studies in which a technician visited the patient’s home to set up the equipment and get it running,8,2829 and was much lower than that of the studies in which the patients were trained to operate the device themselves.8,28 It is possible that the lower failure rate could counterbalance the cost/benefit ratio for home studies in which a technician goes to the patient’s home, when compared to those in which the patient learns to set up the equipment, without expenses related to the technician.8,28.

One of the limitations of validation studies of RP systems is the failure to assess the reproducibility of the data analysis.13 We have found only one study,30 published in 2004, involving laboratory-based validation in which this aspect is addressed, and in which the authors found a good correlation between the analyses carried out by two technicians. In our study, we evaluated the interobserver reliability, that is, the degree of agreement between the readings of the recordings by two observers, and obtained results that can be considered quite satisfactory. In this respect, the intraclass correlation coefficient for the RDI was 0.99% in the analyses of both the LRP and the HRP, and the κ indexes were > 0.80 for all the cutoff points studied.

One limitation of this study is the use of thermistors to detect airflow in both RP and polysomnography studies, which makes corroborative data (ie, desaturations and/or arousals) necessary to define hypopneas. Our aims were to compare the reliability and utility of RP and to determine the influence of setting on the results. The use of other more accurate methods to detect airflow (eg, nasal pressure) probably had little influence on these aspects. The study was performed in a group of patients with high pretest probability for SAHS, and thus the results pertain only to this group.

In conclusion, HRP is effective and reliable for the diagnosis of SAHS in sleep clinic populations with a high pretest probability. However, it is less sensitive than LRP. Thus, in those cases in which the results of HRP are normal but the clinical suspicion is high, polysomnography should be performed. As wrist actigraphy tends to overestimate the sleep time, it improves the results of HRP only slightly.

Abbreviations: AASM = American Academy of Sleep Medicine; AHI = apnea-hypopnea index; AP-II = Apnoescreen-II; CI = confidence interval; HRP = home respiratory polygraphy; LR = likelihood ratio; LRP = sleep laboratory respiratory polygraphy; RDI = respiratory disturbance index calculated using the total sleep time estimated by actigraphy; RDITRT = respiratory index calculated according to the total recording time; RP = respiratory polygraphy; SAHS = sleep apnea-hypopnea syndrome; Sao2 = arterial oxygen saturation; SE = sleep efficiency; TRT = total recording time; TST = total sleep time; TSTa = total sleep time estimated by actigraphy

The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Table Graphic Jump Location
Table 1. Clinical Characteristics of the Patients*
* 

Values are given as the mean ± SD or No. (%). BMI = body mass index.

 

Data were obtained from spirometry and blood gas analysis during prior evaluation in the sleep unit.

 

Systolic arterial pressure ≥ 140 mm Hg, diastolic arterial pressure ≥ 90 mm Hg, or previous antihypertensive therapy.

§ 

A history of ischemic heart disease or stroke.

Table Graphic Jump Location
Table 2. Results of Polysomnography and RP in the Patients Studied*
* 

Values are given as the mean ± SD.

 

Compared with polysomnography (difference was not significant).

 

LRP vs HRP (p < 0.001).

§ 

In RP, the TST and SE were estimated by actigraphy.

 

Compared with polysomnography (p < 0.001).

 

LRP vs HRP (difference was not significant).

Table Graphic Jump Location
Table 3. Diagnostic Properties of RP for an AHI of ≥ 10 in Polysomnography*
* 

Values in parentheses are the 95% CI. WA = without taking actigraphy into account; LR+ = positive LR; LR− = negative LR.

 

The percentage of patients in whom RP and polysomnography findings coincide (ie, identification or exclusion), considering as a cutoff point an RDI/AHI of ≥ 10.

 

Cutoff point in RP was an RDI of ≥ 10.

§ 

Cutoff point without actigraphy was an RDITRT of ≥ 10.

 

Infinite due to the 100% specificity.

Table Graphic Jump Location
Table 4. Diagnostic Properties of RP for an AHI of ≥ 15 in Polysomnography*
* 

Values in parentheses are the 95% CI. See Table 3 for abbreviations not used in the text.

 

Indicates the percentage of patients in which RP and polysomnography findings coincide (ie, identification or exclusion), considering as a cutoff point an RDI/AHI of ≥ 15.

 

Cutoff point in RP was an RDI of ≥ 15.

§ 

Cutoff point without actigraphy was an RDITRT of ≥ 15.

Table Graphic Jump Location
Table 5. Diagnostic Properties of RP for an AHI of ≥ 30 in Polysomnography*
* 

Values in parentheses are the 95% CI. See Table 3 for abbreviations not used in the text.

 

Indicates the percentage of patients in which RP and polysomnography findings coincide (ie, identification or exclusion), considering as a cutoff point an RDI/AHI of ≥ 30.

 

Cutoff point in RP was an RDI of ≥ 30.

§ 

Cutoff point without actigraphy was an RDITRT of ≥ 30.

Table Graphic Jump Location
Table 6. Area Under the Curve of the RDI During RP According to the Cutoff Points for the AHI During Polysomnography*
* 

Values in parentheses are the 95% CI.

Figure Jump LinkFigure 1. Bland-Altman plots comparing the AHI during polysomnography with RDI in the different analyses of RP. Top left, A, and top right, C: observer A. Bottom left, B, and bottom right, D: observer B. Continuous line = mean differences; broken lines = limits of agreement (ie, mean ± 1.96 SD of the differences).Grahic Jump Location
Table Graphic Jump Location
Table 7. Agreement Between the Analyses of RP Performed by Observers A and B
* 

Values are given as the intraclass correlation coefficient (95% CI).

 

Estimated by actigraphy.

 

Values are given as the κ statistic (95% CI).

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Figures

Figure Jump LinkFigure 1. Bland-Altman plots comparing the AHI during polysomnography with RDI in the different analyses of RP. Top left, A, and top right, C: observer A. Bottom left, B, and bottom right, D: observer B. Continuous line = mean differences; broken lines = limits of agreement (ie, mean ± 1.96 SD of the differences).Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1. Clinical Characteristics of the Patients*
* 

Values are given as the mean ± SD or No. (%). BMI = body mass index.

 

Data were obtained from spirometry and blood gas analysis during prior evaluation in the sleep unit.

 

Systolic arterial pressure ≥ 140 mm Hg, diastolic arterial pressure ≥ 90 mm Hg, or previous antihypertensive therapy.

§ 

A history of ischemic heart disease or stroke.

Table Graphic Jump Location
Table 2. Results of Polysomnography and RP in the Patients Studied*
* 

Values are given as the mean ± SD.

 

Compared with polysomnography (difference was not significant).

 

LRP vs HRP (p < 0.001).

§ 

In RP, the TST and SE were estimated by actigraphy.

 

Compared with polysomnography (p < 0.001).

 

LRP vs HRP (difference was not significant).

Table Graphic Jump Location
Table 3. Diagnostic Properties of RP for an AHI of ≥ 10 in Polysomnography*
* 

Values in parentheses are the 95% CI. WA = without taking actigraphy into account; LR+ = positive LR; LR− = negative LR.

 

The percentage of patients in whom RP and polysomnography findings coincide (ie, identification or exclusion), considering as a cutoff point an RDI/AHI of ≥ 10.

 

Cutoff point in RP was an RDI of ≥ 10.

§ 

Cutoff point without actigraphy was an RDITRT of ≥ 10.

 

Infinite due to the 100% specificity.

Table Graphic Jump Location
Table 4. Diagnostic Properties of RP for an AHI of ≥ 15 in Polysomnography*
* 

Values in parentheses are the 95% CI. See Table 3 for abbreviations not used in the text.

 

Indicates the percentage of patients in which RP and polysomnography findings coincide (ie, identification or exclusion), considering as a cutoff point an RDI/AHI of ≥ 15.

 

Cutoff point in RP was an RDI of ≥ 15.

§ 

Cutoff point without actigraphy was an RDITRT of ≥ 15.

Table Graphic Jump Location
Table 5. Diagnostic Properties of RP for an AHI of ≥ 30 in Polysomnography*
* 

Values in parentheses are the 95% CI. See Table 3 for abbreviations not used in the text.

 

Indicates the percentage of patients in which RP and polysomnography findings coincide (ie, identification or exclusion), considering as a cutoff point an RDI/AHI of ≥ 30.

 

Cutoff point in RP was an RDI of ≥ 30.

§ 

Cutoff point without actigraphy was an RDITRT of ≥ 30.

Table Graphic Jump Location
Table 6. Area Under the Curve of the RDI During RP According to the Cutoff Points for the AHI During Polysomnography*
* 

Values in parentheses are the 95% CI.

Table Graphic Jump Location
Table 7. Agreement Between the Analyses of RP Performed by Observers A and B
* 

Values are given as the intraclass correlation coefficient (95% CI).

 

Estimated by actigraphy.

 

Values are given as the κ statistic (95% CI).

References

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