CPAP Reduces GERD: How does this work?

I had to think about this for a bit before it made sense (free
registration on Medscape required):

href="http://www.medscape.com/viewarticle/547792">Does
Continuous Positive Airway Pressure Decrease Gastroesophageal Reflux in
Patients With Obstructive Sleep Apnea?



Twenty-four-hour esophageal pH monitoring was used by Spence and
colleagues[4] to determine whether continuous positive airway pressure
(C-PAP) decreases nocturnal reflux in patients with obstructive sleep
apnea. Seventeen patients were studied on 2 different nights; 12 were
overweight (body mass index: 27.3-50.8). All subjects had
moderate-to-severe sleep apnea. Eleven patients had abnormal nocturnal
esophageal acid exposure time at baseline, with 10 of 11 demonstrating
decreasing nocturnal reflux on C-PAP. Seven of 11 reached a "normal"
level of nocturnal esophageal acid exposure with C-PAP. Overall, there
was a statistically significant improvement in percent time esophageal
pH < 4 in the entire group, as well as a reduction in the number
of reflux events per hour. Sleep indices improved in all 17 patients as
measured by a standardized sleep index.

The little synopsis does not explain the mechanism, and it is too far
afield from my specialty for me to take the time to look it up, but I
am fairly sure of the answer.  



Obstructive sleep apnea occurs when the airway collapses in response to
the inspiratory effort.  This creates a partial vacuum in the
chest.  That effect is also what causes heart problems: the
partial vacuum increases the amount of venous blood that enters the
heart, beyond what is physiologically normal.  



Probably, the increase in acid reflux occurs via the same mechanism.
 The partial vacuum in the chest is what causes it.



So people with refractory GERD should consider getting a sleep study,
if there are features that suggest they also may have sleep apnea.
 If the conditions are present simultaneously, treatment of
the obstructive apnea could help with the reflux, too.