Vol. 18 • Issue 5 • Page 16
Allergy And Asthma
As an asthma patient settles in for the night, multiple biologic bed partners – inflammatory cells and mediators, hormone levels, and cholinergic tone – start tugging at the sheets. Add obstructive sleep apnea, and that bed becomes dangerously crowded.
“Sleep apnea worsens asthma at so many levels,” said Michel Alkhalil, MD, medical director of Troy Sleep Center in Troy, Mich. Current literature shows untreated OSA can result in increased airway inflammation, cardiac dysfunction?, sleep fragmentation and deprivation, gastroesophageal reflux disease, and weight gain, all of which can exacerbate breathing difficulties.1,2
Nocturnal asthma alone can be successfully treated with hypertonic saline solution and inhaled corticosteroids. But when doctors miss diagnosing OSA as a co-morbid disorder, asthma symptoms can spiral wildly out of control.
“We get into this vicious cycle where we treat their asthma with steroids, steroids cause weight gain, weight gain causes worsening sleep apnea, their worsening sleep apnea worsens their asthma, for which we give them more steroids,” explained Joanne Getsy, MD, medical director of Drexel Sleep Center of Philadelphia?.
Continuous positive airway pressure can intervene in this cycle. While CPAP therapy does not stop the airway spasms and swelling that trigger a full asthma attack, it does reduce the likelihood these symptoms will occur because it splints open the upper airway.
“Just that relief alone of opening up the upper airway allows the lower airway to have a more favorable intrathoracic? pressure,” said Dr. Getsy, also an associate professor of medicine in the division of pulmonary, critical care, and sleep medicine of the department of medicine at Drexel University College of Medicine.
What is more, the CPAP therapy restores natural sleep patterns to resolve sleep deprivation, regulates proteins tied to airway inflammation, and can reduce complaints associated with common conditions like obesity, GERD, and cardiac dysfunction that preliminary evidence shows can trigger asthma attacks.2
Research findings and future
Despite a growing body of knowledge that CPAP can ameliorate the night-time breathing difficulties experienced by nearly 75 percent of asthma patients, further research is needed.1Patients in three studies of CPAP therapy reported improved nighttime asthma symptoms. One also showed decreased nocturnal bronchodilator usage after two weeks of treatment.3-5
Other studies have reported decreased asthma attacks and improved quality of life indicators following therapy.5,6Some experts advocate using histology and measurement of inflammatory cytokines to quantify these changes.7 However, no conclusions can be drawn from the literature on CPAP therapy’s effect on more common asthma outcomes. Several small studies of pulmonary function testing values show either a significant improvement or no change pre- and post-therapy.1,3,4,8Current physiologic measurements for asthma may not be the best test to measure therapy outcomes. “The whole process of waking somebody up and asking them to take a deep breath in and perform a standardized test takes away from how they were before they woke up,” said Robert Owens, MD, research fellow in the divisions of sleep medicine, pulmonary, and critical care at Brigham and Women’s Hospital in Boston.
Changing the patient’s posture from a supine to seated position may negate some of CPAP therapy’s positive effects. Even without that physical shift, the deep inhalation required for a pulmonary function test may act as a bronchodilator, causing the test to record a smaller bronchoconstriction effect from CPAP. Using partial flow-volume loops is ?a step in the right direction, but more work is needed. “We need to come up with a better way to measure what is going on while the patient is asleep,” Dr. Owens said.
Meanwhile, researchers hypothesize that bilevel positive airway pressure therapy may build upon CPAP’s positive effects. “CPAP just tonically elevates the lung volumes but with (bilevel positive airway pressure), you actually get more of a stretch, you get more of a sighing kind of physiology,” said Susie Yim Yeh, MD, instructor of medicine, Harvard Medical School, and pulmonary, critical care, and sleep division of Brigham and Women’s Hospital.
This deeper inspiration can help ease the rigidity that develops when airway smooth muscle is not stretched and reduce the resulting airway constriction. As with CPAP, though, much research must be done before this becomes a standard of care.
For a list of references, look under the “Magazine” tab at www.advanceweb.com/respiratory.
Contact Kristen Ziegler at [email protected].
