Just Curious

[bluesboybob]

How does a CPAP machine distinguish between obstructive and central apneas? Since I generally have one or two of each I was looking at my Oscar charts to try to see how breathing was affected by each, but I really don't see a distinction in the data. So how does the machine know?

[Sleeprider]

The machine tests the airway with a pressure pulse (Philips) or forced oscillations of pressure (Resmed) to determine if the airway is open or obstructed. It is like taking a sounding for depth. If an echo of the pulse or oscillation is received at the sensor, then the airway is labeled obstructed, and if a weak echo or none is received the airway is labeled open. The machines have no means to measure respiratory effort which is the channel measured in PSG.

[bluesboybob]

The machine tests the airway with a pressure pulse (Philips) or forced oscillations of pressure (Resmed) to determine if the airway is open or obstructed.  It is like taking a sounding for depth.  If an echo of the pulse or oscillation is received at the sensor, then the airway is labeled obstructed, and if a weak echo or none is received the airway is labeled open.  The machines have no means to measure respiratory effort which is the channel measured in PSG.

Got it! Thanks for the clear explanation. Just what I was looking for.

[gzimmer]

Hi bluesboybob,

> So how does the machine know? 

I've been asking myself the same question...

You can see Forced Oscillations (with a Resmed) if you expend the graph.

See the little wriggles in the attached pix


(I hope that more experienced members will correct me if I'm wrong)


.....Zim

[DeepBreathing]

G'day Zim. That's exactly right - the little wriggle in the airflow graph is the forced oscillation which Resmed uses to diagnose an open v obstructive apnea.

[DeepBreathing]

I was looking at my Oscar charts to try to see how breathing was affected by each

Generally an obstructive apnea is followed by a gasp for breath, which shows as a spike in the airflow graph. With a central apnea the resumption of breathing is much gentler, with only a small spike or none at all. This is not hard and fast, but a good rule of thumb.

[OpalRose]

I very seldom get Clear Airways or Obstructives, so I went back to look at some of my graphs.

You can see on this chart a Pressure Pulse (which is what Resprionics uses)
The machine has determined it as a Clear Airway event. There is no attempt to breath, but airway is open.
Notice at the end of the event the gentle breathing pattern (small or no spikes) as Deep Breathing stated.
[attachment=12687]



This chart shows a Pressure Pulse and the machine has determined that this event is an Obstructive.  There is an attempt to breath and airway is open.
Also notice the spike or gasping for air at the end of the event.
[attachment=12688]

Also, look at the left sidebar of the graph with all the statistics. You will see Pressure Pulses listed, and they are flagged on the graph.

[bluesboybob]

Thanks so much for all of the great replies. OpalRose, your charts really helped me because I also use a Respironics machine. I was not zooming in close enough to see what was happening on my charts in those few seconds before and after an event, but with the explanations and illustrations provided and can clearly see it in my own Oscar reports now. Thanks again. Bob

[OpalRose]

Glad I could help.