apnea on inhalation or exhalation

Midwestosa: Same as me! If I don't use my APAP, just as I'm dropping off to sleep, I feel like a valve shuts off and I can't breathe out; I then become alert and find myself blowing out very forcefully through my mouth - and then the cycle starts again.... and again .... and again - when I do manage to sleep I am often aroused and aware of this "blowing out" during the night but often not - and hubby tells me about it in the morning! I get it sometimes even with my machine, which worries me.
Also: you say the treatment is the same using cpap/bipap - I don't know anything about bipap (or how it differs from APAP) but are you in agreement with the moderator on Apnea Support Forum who says "the algorithms for all APAPs are designed to detect inhalatory apneas and air flow decreases. The algorithm will not work properly in your case where your issue is during exhalation. Maintaining a constant pressure will."??
(she was replying to a chap with Catathrenia)
McSleepy: do you not agree with above statement? - or are you saying that and APAP but with advanced breathing pattern tracking might help? Do you know if the Resmed S9 is one such machine.
Please excuse my ignorance but all this is way above my head (I don't really know what a algorithm actually is!) - but I'm following the gist and learning fast!
Many, many thanks
Y.

bouncer wrote:Can anyone tell me if it is it common to have apneas on exhalation, as I do? I gather (maybe incorrectly) that most people cannot breathe in and wake up snorting air in but I have trouble breathing out and wake up with sharp mouth exhalation; or is it all the same type of apnea? Hoping that someone can clear up my confusion!

On one hand there is more than enough theoretical discussion in the literature to answer "yes", assuming that the question was posed in the right context. Why would you expect inhalation to be more critical than exhalation? In other words whether in the multi-functional aspects of sleep apnea your critical issue is mechanical airflow and pressure differences, or the chemistry of O2 - CO2 exchange and pH during a full breath cycle, or the vascular constriction regulating airflow through the nose, or neural control, etc.
It is more complex to discuss what one particular patient, or one CPAP machine vs. another can do about it.

Here are some extracts that may be useful. I don't have definitive answers, just some information to share for discussion:

1. from a text on breathing physiology: Lungs: a primary source of our energy... extract O2 from the air we breathe primarily on the exhale. Nostrils: smaller than the mouth, so air exhaled through the nose creates back pressure when one exhales. It slows the air escape so lungs have more time to extract O2. Wit proper O2-CO2 exchange, the blood will maintain a balanced pH. If CO2 is lost too quickly via mouth breathing, O2 absorption is decreased.

2. paper by Petrosyan: Exhaled breath markers in OSA (2007): ... Oxidative stress & inflammation of the respiratory tract can be non-invasively monitored by measuring exhaled breath markers... can lead to nasal inflammation in the presence of CPAP

3. paper by Lojander: Nasopharyngeal symptoms and nasal CPAP therapy in OSAS (1999): ... frequency of nasopharyngeal symptoms before and during nCPAP treatment ... difficulty in exhaling (29%) and a sensation of suffocation (26%) were also problems associated with nCPAP treatment.

4. if you follow and believe in some of Dr. Park's comments http://www.medhelp.org/posts/Sleep-Apne ... how/789327 (in reading them I couldn't resist comparing the push-pull of the respiratory muscles to unclogging one's kitchen drain pipe with a plunger ): ... pressure sensors inside SA patients reveal that every time an apnea occurs, a tremendous vacuum effect is created inside the chest & throat, suctions normal stomach juices into your esophagus & throat… in some cases … reach your nose to cause nasal congestion and inflammation, which can aggravate tongue and soft palate collapse by creating a vacuum effect downstream. Ultimately, it’s a vicious cycle.

5. verbal information from a sleep doctor: breathing stop is more connected to CO2 exhalation (chest suction) than O2 inhalation.

6. book by Randerath Sleep Apnea, Current dx and Treatment (2007), Chapter on the Physiology of Breathing during Sleep talking about CO2 expiration irregularity: Tonic drives are affected by sensory inputs from O2, CO2 and pH needs. Hypercapnia increases the phasic activation of airway muscles … under certain circumstances this may foster mixed and obstructive apnea. In healthy subjects the sleep-related changes are adequately compensation, bold gases remain within normal. In a handicapped respiratory system the compensatory efforts are less effective.

You could also search this forum, or the published literature on keywords like "expiration, exhalation, exhalatory, exhale".
Re a CPAP machine's ability to detect flow limitations and predict imminent apneas: there is an interesting discussion on the thread
viewtopic.php?f=1&t=62947&p=588912#p588912
ResMed S9 users talking about the Forced Oscilation Technique, exhalation, Expiratory Pressure Relief.

Y., to answer your question: I would not like to get into discussing automatic-pressure CPAP machines as I don't think they can help me, and I don't think they are any good, in general, at least from my experience. They might work for the typical cases but tend to balk at the slightest challenge. The two APAP machines I tried - a Respironics System One, and my current VPAP Auto 25, failed miserably in trying to determine the optimal pressure. In fact, they were quite unusable, as the former had a vicious algorithm where it would start with a pressure support (PS) of 2cm H2O (and I need at least 5cm) and would take it from there (except, it couldn't get it right); the latter would allow PS to be set, but it would not adjust it, only vary the total pressure. Regardless, I am focusing on bi-level pressure machines, which have worked for me quite well. I know the latest S9 series did not include any such machines (last time I checked was a few months ago), so your machine must be constant pressure.

Having said that, note that I am not trying to diagnose your problem and recommend any action - even a doctor would not do that in an Internet forum. I believe that the information we get from the Internet is useful to give us some ideas, which we could then process to make up our minds, and then talk to our doctors, and try and convince them to do something about our problems. This has worked for me quite well. I would recommend studying the various technologies used in CPAP machines and then possibly considering any changes that could help you. It is so disappointing that the sleep professionals, who are supposed to have taken care of all that, seem to rarely be of much help (judging from my own experience and from the existence of forums like this one).

I will just provide a bit to get you started. This is from the manual of my machine:

Operating Information
These VPAP devices use internal pressure and flow sensors in the air path to respond reliably to patient flow rates even in the presence of most normal leaks in the patient circuit.
Bilevel Pressures
VPAP assists spontaneous breathing by cycling between two pressures in response to the patient flow or a preset fixed time. The inspiratory positive airway pressure (IPAP, or the sum of EPAP and the pressure support level) assists inspiration. The lower expiratory positive airway pressure (EPAP) eliminates exhaled air through the mask exhaust vent. This facilitates exhalation comfort while providing a splint to maintain an open upper airway. The difference of the two pressures—pressure support level—contributes to improved patient ventilation.

Apneas and Hypopneas
An apnea is when the respiratory flow decreases by more than 75% for at least 10 seconds. A hypopnea is when the respiratory flow decreases to 50% for at least 10 seconds. The accuracy of apnea and hypopnea logging will be degraded by high mask leak. The Apnea Index (AI) and Apnea Hypopnea Index (AHI) is calculated by dividing the total number of events that occurred by the total mask-on duration in hours.

These descriptions, albeit not strict algorithm definitions, give you an idea how apneas are detected. Note that there is no mention of doing that only during inhalation, although it is not out of the question.

I also wanted to comment that if you feel the urge to exhale through your mouth when you get startled while trying to fall asleep, then you probably don't t have an obstruction, but might instead be simply bothered by the pressure resistance. Exactly the way I would be bothered with constant pressure, or with any pressure support less than 5 cm. You would really need to work on accurately diagnosing your problems before you take any action.

McSleepy

bouncer wrote:the algorithms for all APAPs are designed to detect inhalatory apneas and air flow decreases. The algorithm will not work properly in your case where your issue is during exhalation. Maintaining a constant pressure will

That's poor advice, IMO.

Exhalation apenas can occur for a wide range of physical reasons, and it clear enough from the literature about them that xPAP approaches will treat some of those reasons quite satisfactorily.... again it depends on the physiology of the exhalation apnea event(s).

Cheers,

Bill

bouncer wrote:Can anyone tell me if it is it common to have apneas on exhalation, as I do? I gather (maybe incorrectly) that most people cannot breathe in and wake up snorting air in but I have trouble breathing out and wake up with sharp mouth exhalation; or is it all the same type of apnea?
Hoping that someone can clear up my confusion!
Thanks
Bouncer

I also experience the same problem occasionally, I don't know if it occurred because I was under stress? I just started a new job and perhaps I felt a little under stress? I'm afraid to go to sleep because when it happens it is hard for me to fall back to sleep again.