Introduction to next study

[split_city]

I thought I would give some background information about a study which I'm about to commence. There is lots of evidence which states that OSA is not simply caused by one characteristic and generally, a number of phenotypes are required to result in OSA. My next study will be more of an observational study i.e. observe what happens to a number of variables when OSA patients go to sleep (as this is when the airway is most vulnerable to collapse) and also preceeding, during and post apnea. Using this information, I should be able to come up with some sort of story about factors which are more likely to contribute to collapse. The variables I will be focusing on include:

1) Diaphragm position
2) Diaphragm activity
3) Genioglossus muscle activity. This muscle is just below the tongue and acts to keep the airway open when awake. The activity of this muscle drops off at sleep onset
4) Lung volume
5) Arousal threshold
*6) I also plan to evaluate what part of the respiratory cycle does the airway collapse i.e. during inspiration or expiration.

So why study these variables?

Diaphragm position --> the diaphragm is connected to a number of structures within the chest and indirectly to structures surrounding the airway. These structures are pulled downwards during inspiration, which "stretches" the airway. This helps to keep the airway open. There have been a few studies in animals which have looked at the impact of stretch on airway collapsibility. These have shown that if you increase stretch on the airway, the airway becomes less collapsible. The reverse is seen when you reduce stretch on the airway. Our group believes that the diaphragm moves upwards at sleep onset, particularly in abdominally obese males. This movement of the diaphragm may reduce stretch on the airway, making it more collapsible.

Diaphragm activity --> goes with diaphragm position. The diaphragm is generally only active during inspiration and is electrically quiet by the end of expiration i.e. has no tone. Therefore, forces acting on the diaphragm such as pressure inside the abdomen would likely push the diaphragm upwards. This partially explains the fall in lung volume when a healthy-weight individuals move from an upright position to the supine position. Therefore, one would predict a greater upwards movement of the diaphragm in obese individuals (particularly abdominally obese males) due to increased mass loading on the chest and abdomen. However, obese individuals experience little change in lung volume when moving from an upright position to the supine position. Recall that I said the diaphragm is generally only active during inspiration? This is true in healthy-weight individuals. No-one has tested whether there is activity throughout expiration in obese individials. Perhaps obese people have increased diaphragm activity during expiration which helps to maintain diaphragm position. This perhaps explains why this groud doesn't experience a fall in lung volume following a postural change. If this reflex is present, it might decrease or be lost during sleep. Subsequently, the diaphragm might move up substantially at sleep onset in the obese.

Genioglossus activity --> This muscle has been extensively studied in OSA and non-OSA individuals. It is know that this muscle is hyperactive in OSA patients during wakefulness which is thought to help keep the airway open in OSA patients. However, the activity of this muscle drops away at sleep-onset, and even more so in OSA patients. The activity of this muscle cranks up during an obstructive event which is thought to help re-open the airway. NOTE: In a majority of cases, an arousal is required for the airway to re-open.

Lung volume --> lung volume affects airway size and collapsibility. The smaller the lung volume, the smaller and more collapsible the airway. Lung volume is lower in obese people and decreases during sleep in healthy-weight individuals. No-one has assessed what happens to lung volume at sleep onset and very few groups have looked at what happens to lung volume during obstructive events in obese OSA patients. I plan to measure lung volume change in obese male OSA patients in my next study

Arousal threshold --> this is a new area of research. Arousal has is beneficial but can also believed to perpetuate sleep apnea events. Some patients have a higher arousal threshold than others.

Most people think the airway collapses during inspiration i.e. when generating negative pressure. However, there is evidence that it passively collapses at the end of expiration when muscle activity is at its lowest.

So what do I plan to do in my study? Well, it's two fold. I plan to compare changes in lung volume, diaphragm activity and diaphragm position in obese male OSA patients and healthy-weight controls. The next part of the study will involve measuring all the above variables in the sleep apnea patients at sleep onset and also preceeding, during and following an apneic event. The results will improve our knowledge about what factors contribute to sleep apnea.

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CPAPopedia Keywords Contained In This Post (Click For Definition): Arousal

[uv]

Very interesting.
I´ve been recently diagnosed with OSA and besides using a CPAP I am trying to find alternatives that may improve my condition and maybe one day rid me of this necessary but very difficult bed companion that OSA gave me.
While searching for alternatives I found a paper that concluded that fluid shift from the legs to the upper body, induced by a positive pressure, increased airflow resistance of the pharynx. The link for the study is:

http://ajrccm.atsjournals.org/cgi/conte ... 07-927OCv2

After reading this study I decided to raise the top of my bed by five degrees and had a drop of 1.5 in my Apap pressure setting.
The last few days I was wondering about the size of my beer belly (huge) and the fluid displacement/pressure that it might cause at an horizontal position, your diaphragm hypothesis seems to be a very good one.
Thanks for posting so much interesting info in both of the threads you started.
Finnaly, I bought myself a didjeribone ( a modern didgeridoo) which I intend to use as described in a study published by the British Medical Journal that showed AHI improvements in mild to moderate apnea. The link is at:

http://www.bmj.com/cgi/reprint/332/7536/266

UV

[split_city]

Yep, I have looked at the fluid shift paper. I cited that in my current manuscript (the effect of abdominal compression on upper airway collapsibility.) The abdominal compression may have increased fluid around the neck, compressed the airway (making it smaller) and therefore, more collapsible.

Posture significantly affects how collapsible your airway is. Generally, it's more collapsible when you are on your back. I have conducted a study in awake healthy-weight subjects showing this. Our group also showed the pressure at which the airway collapsed was higher (more collapsible) when OSA patients were on their back compared to when their back was raised (bed tilted 30 degrees to the horizontal position). However, this is not always true. The airway of many OSA patients collapses equally in all positions.

Interesting story about the digeridoo. I remember having a little laugh about it. I think the study should be repeated though. But give it a go and let us know the results

[uv]

"Interesting story about the digeridoo. I remember having a little laugh about it. I think the study should be repeated though. But give it a go and let us know the results."

It has become a business in Germany:

http://www.asate.ch/default.asp?ID=38&LID=en

German entrepreneurship + Aboriginal know how may improve many an AHI


Are you filming the collapses or tongue obstructions? I am curious about this. I´ll soon be evaluated for MMA and part of the exams are made, from what I understood, with the patient´s head inside a magnetic ressonance chamber, awake and asleep to find out what causes the obstruction.

UV

[split_city]

"Interesting story about the digeridoo. I remember having a little laugh about it. I think the study should be repeated though. But give it a go and let us know the results."

It has become a business in Germany:

http://www.asate.ch/default.asp?ID=38&LID=en

German entrepreneurship + Aboriginal know how may improve many an AHI

hehe...I wonder how many people have purchased them and how many have had their AHI successfully reduced?

Perhaps Australia could use this to attract OSA patients to the country

Are you filming the collapses or tongue obstructions? I am curious about this. I´ll soon be evaluated for MMA and part of the exams are made, from what I understood, with the patient´s head inside a magnetic ressonance chamber, awake and asleep to find out what causes the obstruction.

UV

No I do not plan to film upper airway collapse. While this has been done, my patients will have enough pieces of equipment attached to them. They do have to sleep!

By magnetic resonance chamber I assume you mean an MRI machine? Many studies have used such a technique visualise the upper airway and compare upper airway dimensions, fat distribution, airway length between OSA and non-OSA patients. The problem is these images were conducted whilst the subjects were awake. Therefore, the authors could only speculate what happens when patients are asleep. There has been one or two studies in which the upper airway was imaged using MRI whilst patients were alseep. However, the patients were required to be sleep deprived the night before or sedated. Both affect the upper airway.

There is a new technique using a catheter inserted nasally to assess the upper airway during wake and sleep. It emits a laser beam. I saw a video of an airway collapsing during sleep using this catheter. Very cool!

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CPAPopedia Keywords Contained In This Post (Click For Definition): video, AHI

[blarg]

So why study this variables?

To prove Snoredog wrong?

Was this study planned before our flame war here, or?

[split_city]

So why study these variables?

To prove Snoredog wrong?

hehe...no. I have moved on from Snoredog. He can go on saying whatever he likes. I'll just choose to ignore his negative comments from now on. He's only one person.

Was this study planned before our flame war here, or?

This study was planned over a year ago. However, I am only about to begin it shortly.