Quote:1. Flow Limitation

What is flow limitation?

A physiological change in the status of the upper airway
Causes a spectrum of closure, from subtle narrowing to partial collapse

What is the significance of flow limitation?

It usually precedes snoring and apnea. It is therefore, usually, the earliest sign of impending airway collapse3
Airway changes limit flow despite respiratory effort and in fact, cause increased respiratory effort. This may lead to arousal

How do I observe flow limitation?

The inspiratory flow time curve represents inspiratory flow limitation
The shape of the curve indicates the status of the upper airway. A normal upper airway is observed as a bell-shaped curve. The curve flattens with increasing flow limitation and airway narrowing/ closure

How does a ResMed AutoSet device measure flow limitation?
It calculates flow limitation on a breath-by-breath basis, detecting and responding to subtle changes

How does a ResMed AutoSet device respond to flow limitation?

If flow limitation is detected, AutoSet Spirit responds by gradually increasing pressure to bring the airway back to normal. Typically, this helps prevent snoring and apneas4
If no further events occur, AutoSet Spirit gently decreases the pressure, towards the minimum set pressure

(04-24-2016, 12:31 PM)Roy289 Wrote: The Autoset line probably has the same algorithm for managing pressure thru the Flow Limitation. My Flow rate has inhalation flat topping and the pressure shows little upticks (the inspir. time is flat). Assume the flow rate is being sampled but most of my inhalations are more flat than rounded so hard to see relationship to pressure adjustment. My pressure range is currently set to 7-11 (originally at 7-14) by DME). Would resetting the pressure back to 7-14 be recommended?

(04-24-2016, 03:57 PM)palerider Wrote: apneas are not flow limitations, and vice versa, just to clarify.

an apnea is a > 90% reduction in flow from the baseline for ten or more seconds.

a hypopnea is a > 30% reduction in flow from baseline for ten or more seconds.

a flow limitation does not necessarily correspond with either of the above, a flow limitation is a restriction in the airflow, making it harder to breath, which causes increased breathing effort, and can lead to arousals, however there does not have to be any reduction in total flow due to flow limitations, (thinking gulping a drink vs sipping it, you get the same amount of drink, just takes longer one way than the other)

(04-24-2016, 04:03 PM)0rangebear Wrote: Palerider
Where does you definition of an Apnea come from?

Is the formula use in SleepyHead or Rescan.

• Resmed scores a hypopnea when the flow rate is between 25%--50% of baseline for at least 10 seconds. In other words, the flow must be reduced by at least 50% for a Resmed machine to score a H. There's also some interesting information in the table that may explain why a lot of people saw their HI decrease (sometimes dramatically) when they switched from the S8 to the S9: In order to score a H, the S9 and A10 machines require "at least one obstructed breath", whereas the S8's did not have that requirement.
  
• PR scores a hypopnea when the flow rate is between 20%--60% of baseline for at least 10 seconds. In other words, the flow rate must be reduced by at least 40% for a PR machine to score an H. Interestingly, PR requires a "recovery breath" at the end of the event unless the flow rate is reduced for at least 60 seconds.
  
• DeVilbass scores an H when the flow rate is between 10%--50% of baseline for at least 10 seconds. In other wrods, the flow rate must be reduced by at least 50% for a DeVilbass machine to score an H.