Dear Dr. Gebien,

Currently, the AASM scoring procedure for apneas delineates three criteria:

While Obstructive Sleep Apnea (OSA) events are characterized by disturbed or absent indication of airflow by the thermocouple, instead, Central Sleep Apnea (CSA) events show no indication of both airflow and respiratory effort. The latter case is the rarest and depends on dysfunctions of the NCS that translated into reduced/absent muscle activity of both the diaphragm and inspiratory/expiratory muscles at the rib cage level.

"[...] there are no movements of the chest or abdominal sensors [...]" is a correct assumption but it is not sufficient to state the presence of CSA.

It should be checked if the event matches the aforementioned criteria and if it leads to a drop in oxygen saturation of at least 4%.

Hope my answer may help clarify your doubts,

Have a nice day,

Nicolò La Porta

Nicolò La Porta Thank you for your response!

Your answer, while helpful, doesn't quite answer the question of whether polysomnography can detect peripheral respiratory pump arrest (i.e. intermittent diaphragm pausing leading to apneas).

My fear is that apneas being diagnosed as secondary to "central apnea" are not truly central in origin. Also, is phrenic nerve electrical activity ever monitored to truly confirm a central cause?

Dov Jordan Gebien, you're welcome.

Sorry if I did not catch immediately your question. Your clarification enlightens your point. AASM divides sleep diagnostic devices into four types:

The first system collects at least seven among the following bio-parameters [1]:

• EEG (C4-A1 or C3-A2).
• EOG.
• chin EMG.
• ECG.
• Oronasal airflow.
• Respiratory effort (Respitrace at abdominal and thoracic level)
• Oxygen saturation (Photoplethysmography)

and monitors also:

• leg movements through leg EMG
• Body position through inertial sensor (IMU)

As you can see from the above lists, the only way PSG can detect peripheral respiratory pump arrest (i.e. intermittent diaphragm pausing is through the respitrace and the airflow.

"[...] My fear is that apneas being diagnosed as secondary to "central apnea" are not truly central in origin [...]"

Therefore, your hypothesis is legitimate, but with the technologies involved in type I PSG evaluations it is not possible to distinguish the latter case because of the nature of the technology used to collect the signals (e.g. impedance plethysmography for the respitrace) which is not sensitive to this fine-grained difference.

"[...] Also, is phrenic nerve electrical activity ever monitored to truly confirm a central cause? [...]"

Up to my current knowledge phrenic nerve electrical activity is not monitored during PSG but phrenic nerve electric stimulation is a possibility of treatment for patients who are not compliant to air pressure treatments such as CPAP, NEPAP, BiPAP, ASV...

Hope my answer may help clarify your doubts,

Have a nice day,

Nicolò La Porta

[1] Ferber, R., Millman, R., Coppola, M., Fleetham, J., Friederich Murray, C., Iber, C., ... & Williams, A. (2018). Portable recording in the assessment of obstructive sleep apnea. Sleep, 41(9), zsy134.

No, typical PSG does not measure the diaphragm directly. However, D-EMG has been done by Luo (2008 and 2009*), and which determined many apneas thought to be central were in fact obstructive. MAIN POINT: Diaphragm spasm could represent a novel form of apnea, a peripheral one. Also, it could mimic obstructive apneas on PSG.

*Luo YM, Tang J, Jolley C, Steier J, Zhong NS, Moxham J, Polkey MI. Distinguishing obstructive from central sleep apnea events: diaphragm electromyogram and esophageal pressure compared. Chest. 2009 May;135(5):1133-1141. doi: 10.1378/chest.08-1695. Epub 2008 Dec 31. PMID: 19118271.