10.14639/0392-100X-N1503
Objective. Positional Obstructive Sleep Apnoea Syndrome (POSAS) is a sub-type of Obstructive Sleep Apnoea Syndrome (OSAS) in which obstructive apnoeas occur mainly in the supine sleeping position. In clinical practice, information on sleep posture is generally gathered by polysomnographic exam (PSG). The current trend in positional therapies consists of position trainers which help to avoid the supine position. The aim of this study is to detect the reliability of different devices on assessing sleeping position, comparing the data with objective evaluation by an infra-red camera. Methods. We compared the positional results of 4 healthy volunteers obtained from a type III PSG and with a neck-worn sleep position trainer (Night Shift - NS). Results. Data showed that NS is a good tool to assess the position of the trunk, with high rate of agreement with PSG, but in some conditions there are limitations, especially in detecting the real head and neck position and low accordance between NS data and information recorded by infra-red camera. Conclusions. Our study confirmed that more information about body position during sleep is needed, underling the necessity of developing new technologies that are able to better identify reciprocal body positions.
text/xml
1827-675X
1503
en
Andrea Marco Minetti
http://creativecommons.org/licenses/by-nc-nd/4.0
ACTA Otorhinolaryngologica Italica
devices
Can sleeping position be correctly identified by OSAS studies?
Text.Serial.Journal
https://www.actaitalica.it/
41
OSAHS
2021-12-21
2021-02-22
2021-12-22
2021-12-22
550-557
1
Andrea Marco Minetti
2021/12/21
10.14639/0392-100X-N1503
550
ENT MD freelancer, doctoral school in OSAS-EOS DRS, Milan, Italy
1827-675X
devices
557
Can sleeping position be correctly identified by OSAS studies?
https://www.actaitalica.it/article/download/1503/720
41
ACTA OTORHINOLARYNGOLOGICA ITALICA 2021;41:550-557; doi: 10.14639/0392-100X-N1503




OSAHS


Can sleeping position be correctly identified
by OSAS studies?
Siamo capaci di identificare correttamente la posizione del sonno negli studi
su OSAS?
Luca Cerritelli1, Luigi Marco Stringa1, Giulia Bianchi1, Henry Zhang2, Giovanni Cammaroto3, Claudio Vicini1,3,
Stefano Pelucchi1, Andrea Marco Minetti4
1
 Ear-Nose-Throat & Audiology Unit, University of Ferrara, Ferrara, Italy; 2 Department of Otolaryngology, Head and Neck, Royal
London Hospital, London, UK; 3 Department of Head-Neck Surgery, Otolaryngology, Head-Neck and Oral Surgery Unit, Morgagni
Pierantoni Hospital, Forlì, Italy; 4 ENT MD freelancer, doctoral school in OSAS-EOS DRS, Milan, Italy


SUMMARY
Objective. Positional Obstructive Sleep Apnoea Syndrome (POSAS) is a sub-type of Ob-
structive Sleep Apnoea Syndrome (OSAS) in which obstructive apnoeas occur mainly in
the supine sleeping position. In clinical practice, information on sleep posture is generally
gathered by polysomnographic exam (PSG). The current trend in positional therapies con-
sists of position trainers which help to avoid the supine position. The aim of this study is to
detect the reliability of different devices on assessing sleeping position, comparing the data
with objective evaluation by an infra-red camera.
Methods. We compared the positional results of 4 healthy volunteers obtained from a
type III PSG and with a neck-worn sleep position trainer (Night Shift - NS).
Results. Data showed that NS is a good tool to assess the position of the trunk, with high
rate of agreement with PSG, but in some conditions there are limitations, especially in de-       Received: February 22, 2021
tecting the real head and neck position and low accordance between NS data and informa-           Accepted: August 3, 2021
tion recorded by infra-red camera.
Conclusions. Our study confirmed that more information about body position during sleep           Correspondence
is needed, underling the necessity of developing new technologies that are able to better         Luca Cerritelli
identify reciprocal body positions.                                                               Ear-Nose-Throat & Audiology Unit, University of
                                                                                                  Ferrara, via A. Moro 8, loc. Cona, 44124 Ferrara,
KEY WORDS: OSAS, POSAS, sleep position, obstruction, devices                                      Italy
                                                                                                  E-mail luca.cerritelli.bo@gmail.com
RIASSUNTO
                                                                                                  Funding
Obiettivo. La sindrome delle apnee ostruttive notturne posizionali (POSAS) è un sottotipo
                                                                                                  None.
della sindrome delle apnee ostruttive notturne (OSAS) nella quale le apnee si verificano
prevalentemente in posizione supina. Nella pratica clinica, le informazioni sulla posizione
                                                                                                  Conflict of interest
nel sonno sono acquisite grazie a un polisonnigrafo (PSG). Attualmente le terapie posizio-        The Authors declare no conflict of interest.
nali utilizzano correttori di posizione che aiutano a evitare la posizione supina. L’obietti-
vo dello studio è quello di individuare la correlazione fra diversi rilevatori di posizione,
confrontando i dati con una valutazione oggettiva fornita da una telecamera a infrarossi.           How to cite this article: Cerritelli L, Stringa
Metodi. Abbiamo confrontato i dati ottenuti da 4 volontari sani mediante un PSG di tipo III         LM, Bianchi G, et al. Can sleeping position
e un dispositivo di terapia posizionale applicato al collo (Night Shift - NS).                      be correctly identified by OSAS studies? Acta
                                                                                                    Otorhinolaryngol Ital 2021;41:550-557. https://
Risultati. I dati hanno mostrato che il NS è uno strumento efficace e altamente correlabile
                                                                                                    doi.org/10.14639/0392-100X-N1503
al PSG per valutare la posizione del tronco. Tuttavia i dati raccolti hanno evidenziato una
bassa correlazione tra il NS e la telecamera a infrarossi per quanto concerne l’individua-
                                                                                                  © Società Italiana di Otorinolaringoiatria
zione della reale posizione di testa e collo.                                                     e Chirurgia Cervico-Facciale
Conclusioni. Il nostro studio ha confermato la necessità di elaborare nuove tecnologie per
ottenere ulteriori informazioni sulla posizione del corpo durante il sonno.                                      OPEN ACCESS
PAROLE CHIAVE: OSAS, POSAS, posizione nel sonno, ostruzione, dispositivi                          This is an open access article distributed in accordance with
                                                                                                  the CC-BY-NC-ND (Creative Commons Attribution-Non-
                                                                                                  Commercial-NoDerivatives 4.0 International) license. The
                                                                                                  article can be used by giving appropriate credit and mentio-
                                                                                                  ning the license, but only for non-commercial purposes and
                                                                                                  only in the original version. For further information: https://
                                                                                                  creativecommons.org/licenses/by-nc-nd/4.0/deed.en




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                                                                            Can sleeping position be correctly identified by OSAS studies?




Introduction                                                     These different placements can potentially generate a bias
                                                                 between body posture registered by the PSG (position de-
Positional Obstructive Sleep Apnoea Syndrome (POSAS)             tector is always on the thorax) and by sleep position trainer
is a sub-type of Obstructive Sleep Apnoea Syndrome (OS-          (position detector may be on the neck). In this view, the
AS) in which obstructive apnoeas occur mainly in the su-         results of positional treatment can be affected by important
pine sleeping position.                                          bias.
Many classifications of POSA patients have been pub-             Prior to evaluate efficacy of any positional therapy, it is
lished 1-5 since its introduction by Cartwright in 1991 6.       mandatory to know if the recording systems are reliable in
The most recent, and in our opinion most comprehensive, is       correctly detecting sleeping position.
the APOC classification 7. This classification system strati-    The aim of this study is to detect the reliability of different
fies patients into 3 categories according to the possibility     devices on assessing sleeping position, comparing the re-
of being cured or not by positional therapy (respectively        sults obtained in the same subject with objective evaluation
APOC-1, 2, 3).                                                   by an infra-red camera.
Positional therapy refers to a group of devices with the aim     We compared the positional data obtained from a modern
of avoiding the supine sleeping position.                        type III PSG (cardiorespiratory monitoring device, Nox
New evidence 8 suggested that positional therapy can be          T3) and a sleep position trainer (Night Shift - NS) during
treated with other therapies, like surgery 9-11, ventilatory     the same night.
therapy or oral device 12, and improve the overall outcome.
In clinical practice, information on sleep posture is general-
ly achieved by data collected from polysomnographic exam         Materials
(PSG). All PSGs are able to detect body position thanks to       Subjects
an accelerometer positioned within the instrument. These         We recruited 4 young and healthy Italian volunteers, aged
devices are generally fixed on the trunk of the patient, so      between 29-32 years, 3 males and 1 female. There was no
that the posture recorded refers to the trunk position. In       previous clinical history of snoring or OSAS. The partici-
fact, accelerometers inside PSG are not able to record the       pants were non-obese subjects (mean BMI 24.6 kg/m2).
position of all parts of the body, for example head or neck      The subjects agreed to participate to the study, and consent
position. This is a remarkable limit of PSG studies, because     was given according to local ethical approval.
previous studies have shown that the position of head and
neck can play a key role during the genesis and release of       Neck worn device
the apnoeic and hypopnoeic events. Zhu et al. 13 reported        NS Sleep Positioner (Advanced Brain Monitoring, Carls-
that head rotation alone can be sufficient, in mild cases,       bad, CA) is composed of a plastic device fastened on the
to treat POSA, despite the supine trunk position: they re-       back of the neck with an adjustable rubber strap secured by
ported a 27% of resolution of apnoeas when OSAS patients         a magnetic clasp (Fig. 1).
turn their head sideways. Ono et al. demonstrated that the       Neck positions are reported as upright, supine, lateral left,
Apnoea-Hypopnoea Index (AHI) with the head rotated, de-          lateral right and prone. Upright is assigned when the neck
spite the supine trunk position, is better than AHI with head    angle is ≥ 60° around the horizontal axis 18. Supine is as-
supine 14.                                                       signed when the neck angle to the left/right is < 43° around
It is also widely demonstrated that not only head rotation,      the vertical axis. Lateral left or right is assigned when the
but also head extension can have a positive effect on the        neck angle exceeded 47° around the vertical axis. The NS
airway in OSA patients 15-17.                                    assumes the patient has remained in the previously as-
The current trend in positional therapies consists of using      signed position when the neck angle falls between 43° and
sleep position trainers. These are devices worn during sleep     47° around the vertical axis. Prone is the mirrored position
that can recognise the patient’s position by the use of an       of supine with the additional requirement that the Z-axis is
accelerometer. These sleep position trainers produce vibra-      < -15°. See Figure 2 for more details.
tions if the supine position is detected, and the intensity
of vibration increases until the patient rotates into a non-     Polygraphic recording
supine position, in order to avoid the supine position. They     Polygraphic recording was performed by NOX-T3 cardi-
also have a role in diagnostics by recording the sleeping        orespiratory monitoring (Nox Medical, Reykjavik, Iceland).
position. Sleep position trainers vary in types and styles,      It consists of different sensors: nasal cannula, thoraco-ab-
each with its own positioning on the patient’s body, e.g.        dominal straps, pulse oximeter and accelerometer. The na-
neck, thorax or head.                                            sal cannula detected the nasal airflow. Thoraco-abdominal



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L. Cerritelli et al.




 A
                                                                                                      B




                                                                                                                                             C




 D




                                                                           E




Figure 1. (A) example of how to wear Night Shift Positioner. Note the position behind in the neck; (B) how to place the NOX T3 device with clips to the thorax;
(C) Infra-red camera; (D) image of combination of NS +PSG. Note the position of the NOX-T3 on the thorax and the neck worn device (NS). (E) Nocturnal view from
the infra-red video-recording.


                                                                                  Video recording
                                                                                  A video recording was performed by two high resolution
                                                                                  infra-red cameras (Dahua IPC-A35, 3.6 mm lens, 3 MP,
                                                                                  20 fps/1080 pixels). The cameras recorded an mp4 file of
                                                                                  the entire night session.

                                                                                  Methods
Figure 2. Superior view, patient lying supine. Note the vertical axis, which is   The inclusion criteria were:
orthogonal in comparison to the patient’s plane.                                  1. age > 18 years old;
                                                                                  2. BMI < 30 kg/m2.
                                                                                  The exclusion criteria were the presence of any factor that
straps monitor the thoraco-abdominal movement by RIP                              could affect body sleeping position, such as:
(respiratory impedance plethysmography). A pulse-oximeter                         1. neck or shoulder pain;
detected heart rate and oxygen saturation. The plastic device                     2. previous orthopaedic surgery (e.g. arm or leg fractures,
is fastened on the thorax to the patient’s shirt with clips. It                      arthroprosthesis);
contains an accelerometer inside, which is able to detect                         3. pregnancy;
body position and the patient’s movements. In this way,                           4. use of hypnotic drugs or alcohol consumption;
NOX-T3 is able to identify the position of the thorax.                            5. previous clinical history of snoring, apnoeas, daily sleepiness.



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                                                                                         Can sleeping position be correctly identified by OSAS studies?




Patients spent one night sleeping in their bed in their own                   placed on the thorax, and a sleep position trainer (NS),
home, wearing simultaneously the neck worn device (NS)                        placed on the neck.
and a cardiorespiratory monitoring device (NOX-T3).                           To obtain an objective assessment of the patient’s sleeping
The NOX-T3 was fully equipped with nasal cannula, thora-                      position, we simultaneously recorded a video using the two
co-abdominal straps, pulse oximeter and accelerometer in                      infra-red cameras, both synchronised with the other two de-
order to record the cardio-respiratory parameters of the                      vices (NS and NOX-T3).
subjects during night.                                                        The cameras were placed respectively on one side (left con-
To record body position, we used different devices: a poly-                   ventionally) and at the foot of the patient with a 90° angula-
somnography (NOX-T3, cardio-respiratory-monitoring),                          tion compared with the vertical and longitudinal axis of the
                                                                              patient, as seen in Figure 3.
                                                                              Patients were advised not to cover their head, neck or tho-
                                                                              rax with a blanket, in order to ensure good visualisation by
                                                                              the infra-red cameras.
                                                                              All devices (NS, PSG and video cameras) were switched
                                                                              on manually and simultaneously by the patients themselves
                                                                              while going to bed.
                                                                              The recording time was impressed on the video tape to
                                                                              compare, time after time, body position identified by the
                                                                              video with the data from the other two devices.
                                                                              We synchronised the time of all devices, in order to analyse
                                                                              the data obtained simultaneously. To better relate the data
                                                                              obtained, we manually set the degrees in which the PSG
                                                                              detects sleeping position according to the data set on the
                                                                              NS.
                                                                              NS was used in diagnostic mode. This means that the de-
                                                                              vice does not vibrate if patients were lying supine, but was
                                                                              able to collect data about sleeping position.
                                                                              The NS, being placed around the neck, could give informa-
                                                                              tion about the head and neck segment.
                                                                              The data was downloaded from NS with its specific soft-
                                                                              ware, which was able to illustrate the body position dur-
                                                                              ing time and assessing the percentual time spent in supine
                                                                              position. Figure 4 shows the NS report. The first line shows
Figure 3. Disposition of cameras. One camera is positioned on one side, and
one camera at the foot of the patient. Each camera has a 90° angle in rela-   patient’s night movements, with a different height of the
tion to the patient.                                                          line proportionally to its intensity. The second shows the




Figure 4. Night shift data report.



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L. Cerritelli et al.




patient’s position (supine, left, right, prone). The last shows                           Each sleeping time was divided into epochs. An epoch is
the loudness of snoring expressed in decibel (dB). Under                                  the period of time between two body movements recorded
the graph, there is time of night in which the events occur.                              by PSG, NS and/or video.
Figure 4 also shows that NS is able to detect movements                                   From each period we reported the position of the head
of the patients and the noise (expressed in decibel dB) of                                and neck region and the trunk (for example supine, left,
snoring.                                                                                  prone, right) seen in the video and we compared it with
The comparison between two of the three method of posi-                                   the position recorded by PSG and NS in these periods.
tion recording (PSG, NS and video camera) allows to eval-
uate the reciprocal position of two different body segment                                Results
(“thorax” and “head and neck”) and to compare the efficacy
                                                                                          The PSG analysis confirmed that subjects were not OSAS
of the single device realted with the secure position data
                                                                                          patients: mean AHI was 2.8/h (range 4.9-0.3/h), mean ODI
from the camera.
                                                                                          2,5/h (range 0.2-5.8/h), mean supine AHI 2.6/h (range
All possible comparisons are listed in the Table I.
                                                                                          0-5.2/h), non-supine AHI 2.9/h (range 0.4-5.1/h).
The study was approved by the Institutional Ethical Com-
mittee and was conducted according to the principles stated                               Mean supine time
in the Declaration of Helsinki “Ethical Principles for Medi-                              The mean supine time recorded by NS and PSG was, re-
cal Research Involving ‘Human Subjects”.                                                  spectively 39.5 and 37.8%.
                                                                                          The PSG revealed a mean right sided sleeping of 21.55%
Data analysis                                                                             of total sleep time, a left sided sleeping time of 24.1% and
Downloaded data from NOX-T3 were analysed with the                                        a prone sleeping of 16.4%.
software Noxturnal version 5.1.220294. Standard 2012                                      Table II shows, subject by subject, the differences between
AASM criteria 19 were used to score apnoea and hypopnoea                                  supine recording time by PSG and NS.
events on the PSG.
Downloaded data from NS were analysed with the specific                                   Epoch by epoch
software (Advanced Brain Monitoring 2016 – Posas Soft-                                    The concordance between the position recorded by NS
ware).                                                                                    and PSG in each epoch between two body movements was
Sleep reports from NS and NOX-T3 were compared to                                         87%, as seen ** in Table III. This concordance was high-
each other and the video recording.                                                       er in 3 subjects (mean 95.6% range 0.91-1.00). Subject 4


Table I. Clinical meaning of comparison between the different methods.
 Comparison                             Methods                                                           Clinical meaning of the comparison
 Mean supine time                 NS                     PSG                         Do they (NS and PSG) agree evaluating the average supine time position?
 Epoch* between 2                 NS             Head and neck (video)                   Does NS give correct information about head and neck position?
 body movements                 NS                  Thorax (video)                           Does NS give correct information about thorax position?
                                NS                       PSG                       Do they (NS and PSG) agree evaluating the supine time position time by time?
                               PSG               Head and neck (video)                   Does PSG give correct information about head and neck position?
                               PSG                  Thorax (video)                           Does PSG give correct information about thorax position?
                            Head (video)            Thorax (video)                 In which proportion do head & neck and thorax behave as a single segment?
* An epoch is a single time body position, expressed by time between two body movements recorded by PSG, NS and/or video.



Table II. Supine time (%) for each subject recorded by NS and PSG and its concordance rate.
                               Supine time (%) recorded by NS           Supine time (%) recorded by PSG                               Concordance rate
 Subject 1                                         40                                              41.5                                        -0.96*
 Subject 2                                         34                                              27.9                                         0.82
 Subject 3                                        72.8                                             70.7                                         0.97
 Subject 4                                        11.3                                             11.1                                         0.98
 Mean                                             39.5                                             37.8                                         0.93
* In this case there is a negative concordance, because supine time % recorded by PSG is bigger than supine time % recorded by NS.




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                                                                                              Can sleeping position be correctly identified by OSAS studies?




Table III. This table shows for each epoch, subject by subject, the concordance rate between the different methods of position recording.
 Concordance            PSG/trunk        NS/head & neck          Head & neck/        NS/PSG     NS/ trunk VIDEO        PSG/head & neck       Supine time
 epoch by epoch           video               video               trunk video                                                 video            PSG/NS
 Subject 1                 1                   0,28                  0.28             1                1                     0.32                -0.96
 Subject 2                0.92                 0.87                  0.75            0.96             0.96                   0.79                 0.82
 Subject 3                0.87                 0.43                  0.48            0.91             0.96                   0.39                 0.97
 Subject 4                  1                   0.5                  0.31            0.63             0.63                   0.56                 0.98
 AVERAGE                  0.95                 0.52                  0.50           0.87**            0.88                   0.52                 0.93
** p < 0,005.



showed a low concordance rate (63%). This subject spent                         tector is always on the thorax) and sleep position trainer
a lot of time in the prone position, with a higher grade of                     (position detector may be on the neck).
rotation of his head seen by the video recording while lying                    This is the first study to evaluate sleeping position recorded
in prone position. In this case, while the PSG with his sen-                    simultaneously by a diagnostic device (PSG) and a thera-
sor placed on the chest detected the prone position, the NS                     peutic positional device. As control, we recorded the entire
applied on the posterior part of the neck recorded right or                     night with two infrared cameras.
left rotation of the head and neck segment. This bias did not                   NS was mainly chosen as a sleep positional trainer for its
influence supine sleeping time, because these (head rotated                     ability to also work in diagnostic mode, in order to record
and prone) are non-supine types: concordance between NS                         the body’s position without producing any vibration in the
and PSG according to supine position was nonetheless the                        supine position. Its effectiveness in POSA treatment has
highest (0.98) in subject 4.                                                    been demonstrated 18.
Lying in the prone position, it is very difficult not to one’s                  Prior to evaluating the efficacy of positional therapy, it is
rotate head because of the impossibility to breathe through                     mandatory to know if the recording systems available are
a pillow. The grade of rotation of the head was higher than                     reliable in correctly detecting sleeping position. For this
in supine position.                                                             reason, we decided to recruit healthy young volunteers,
The agreement between the position of the head (according                       without a previous history of snoring or OSAS.
to the video) and the trunk seen in the video was 46%: this                     We performed a cardiorespiratory monitoring for one night
means that rarely while patients were lying on their back                       while patients were sleeping in their bed to confirm the
was the head supine too, in only 46% of epochs.                                 absence of OSAS. We decided not to remove the sensors
The grade of rotation of the head was, in these cases, lower                    in order to simulate the footprint of the full device and its
than in prone position, and the NS recorded the supine po-                      impact on sleeping.
sition, despite the mild grade of rotation of the head.                         Despite the presence of cardiorespiratory data, the aim of
The agreement between the head position recorded by vid-                        this study was not to evaluate the efficacy of positional
eo and NS was 52%. This was similar to the agreement                            therapy, but rather correct assessment of sleeping position
between PSG and head position seen in the video.                                by different devices.
                                                                                Healthy, young volunteers were recruited to exclude any
                                                                                potential bias due to BMI, OSAS and muscle-skeletal pa-
Discussion
                                                                                thology.
In clinical practice, information about sleep posture is gener-                 Our results show that NS is a good tool to assess the posi-
ally collected by PSG. All PSGs are able to detect body position                tion of the trunk, with a high rate of agreement with PSG
thanks to an accelerometer positioned within the instrument.                    (epoch by epoch 95.6%, supine time 93%), even if it’s po-
These devices are generally fixed on the trunk of the patient, so               sitioned around the neck.
the posture recorded refers only to the trunk position.                         Nevertheless, if patients spend a lot of time in the prone po-
Positional therapy refers to a group of devices with the aim                    sition, NS makes mistakes: concordance between NS and
of avoiding the supine sleeping position.                                       PSG, in this case, was lower (e.g. subject 4, 62%).
There are different kinds of sleep position trainers, each                      Fortunately, because the aim of NS is to avoid the supine
with its own positioning on the patient’s body, which can                       position, these mistakes do not impact the outcome of the
be the neck, thorax, or head.                                                   device: and prone position is a non-supine position.
These different placements can potentially generate a bias                      Consequently, NS can be used to avoid a supine position
between body posture registered by the PSG (position de-                        of the trunk in its therapeutic modality. Many studies have



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L. Cerritelli et al.




demonstrated its efficacy 18. However, despite the fact that     force patients lying on their side the whole night, when
it is a neck worn device, it is not able to detect the actual    maybe simple head rotation could resolve the apnoea? Posi-
position of the head and neck segment (Tab. II). Previous        tional therapy can be effective, but shoulder complications
studies have reported that head rotation can be sufficient,      are a common and unpleasant side effect of this therapy 25.
in mild cases, to treat POSA, despite the supine trunk posi-     With this study we could not assess the efficacy of NS on
tion: Zhu et al. 13 reported 27% of resolution of apnoeas in     apnoeas, but our data show that, even if NS is a neck worn
OSAS patients when the head is rotated laterally.                device, its information is in agreement with the thoracic
Van Kesteren et al. 20 demonstrated that, especially in PO-      device.
SA patients, head position has a fundamental role in the         The greatest limitation of our study is some subjectivity in
genesis of apnoeas. Simply with head rotation, the antero-       visual position assessment of the overnight video record-
posterior collapse of the tongue due to gravity forces can be    ing. At times it was difficult to determine if head position
avoided and the airway can be stiffened. AHI with the head       was greater than or less than 45° from the vertical plane.
rotated, despite the supine trunk position, is better than AHI   Another limitation of this study is the fact that we evalu-
with head supine 14. Our population consisted of healthy         ated head rotation, but not flexion or extension, considering
subjects, so that we could not assess the contribution of        its potential role in the genesis of apnoeas 16. Choi et al. 15
head and trunk position on apnoeas.                              demonstrated that neck flexion significantly increases air-
Other studies suggested, on the contrary, the predominant        way resistance in patients with OSA, maintaining the head
role of the position of the thorax in worsening sleep apneas.    in extension preserves airway patency.
Joosten S.A. and colleagues 21 demonstrated a 13% func-          In contrast with the previous study, Skinner et al. 17 sug-
tional residual capacity (FRC) decrease in the OSA group         gested that any potential effect attributable to neck flexion
when moving from lateral to supine. This reduction of FRC        would be smaller than reducing in the negative effect of
influences upper airway collapsibility with resultant chang-
                                                                 gravity on the upper airway with an elevated posture.
es in upper airway pressure 22,23. A loss of lung volume can
                                                                 Further studies should evaluate head position, considering
raise upper airway collapsibility (Pcrit) so much that this
                                                                 the wide range of possible movements and its correlation
triggers upper airway obstruction in a vulnerable airway.
                                                                 with apneas.
In addition, a reduced lung volume increases the loop gain
                                                                 In the literature, a new plug-in accelerometer module for
of the ventilatory control system during sleep by reducing
                                                                 the PSG system that is able to detect head position is avail-
lung oxygen and carbon dioxide stores that may therefore
                                                                 able 26, but in our opinion it does not work with all the PSGs
contribute to breathing instability in the supine sleeping po-
                                                                 used in common clinical practice.
sition 24.
The PSG accelerometer, due to its position on the thorax,        In our opinion, the integration of a system like this, even
cannot assess the head or neck position. Standard PSGs do        if it could be improved upon, can give useful information
not include head position to differentiate between head and      about the reciprocal position of head and neck, which is
trunk position in POSA patients. For this reason, we tried to    necessary to correctly treat POSA patients.
associate NS and PSG, thinking that the former could pro-        The next step would be to apply these devices to the OSAS
vide adjunctive information about neck and, consequently,        population, if good indications have been obtained from
head position.                                                   healthy subjects.
Nevertheless, the agreement between the position recorded
by NS and head/neck position (seen in the video recording)       Conclusions
was very low (52%).
                                                                 This pilot study confirmed that more information about
In 46% of cases, the head and trunk were not in the same
                                                                 sleeping body position is needed, especially in POSA pa-
position; in other words, if NS would be active with vibra-
                                                                 tients in which positional therapy can have potentially good
tion, patients would be forced to rotate to one side, even if
they already had rotation of the head, potentially curative      outcomes. We hope that the results of this study will high-
of their apnoeas.                                                light the need to develop new sensors that are able to identi-
Further studies might develop and investigate new devices        fy head, neck and thorax positions. This technical develop-
that are able to detect both head and trunk position. POSA       ment is needed to better diagnose and treat POSA patients.
therapy has to be tailored to PSG findings, but usually these
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