ID: 127: DECREASED CPAP ADHERENCE IN NON-OBESE OSA PATIENTS WITH REVERSIBLE UPPER AIRWAY OBSTRUCTION

Rationale

Upper airway resistance is critical to the pathophysiology of obstructive sleep apnea (OSA). We have previously characterized a subset of patients with OSA who have evidence of reversible upper airways resistance as measured by spirometry. Specifically, these patients have an increased FEF50/FIF50 ratio which decreases with administration of a short acting bronchodilator. On average these patients had a lower BMI (average 27) compared to OSA patients as a whole suggesting the possibility of unique upper airway pathophysiology among this group. In the current study, we identify additional patients with OSA who have reversible upper airways obstruction on spirometry and characterize their compliance with CPAP therapy as compared to a traditional OSA population.

Methods

We retrospectively evaluated patients who had a sleep screen suggestive of OSA in the last 2 years. Patients who also had spirometry in the previous 5 years were identified for further analysis. Those patients with either normal spirometry or fixed obstructive defects who had a decrease in the FEF50/FIF50 ratio after administration of a short acting inhaled beta agonist (albuterol) were then characterized. We then measured objective CPAP adherence using data downloaded from the positive airway pressure device with adherence defined as CPAP use >4 hrs more than 70% of nights over a 30 day period.

Results

We identified 70 patients with positive sleep screens who also had spirometry demonstrating normal of fixed lower expiratory obstruction with evidence of upper airways obstruction as demonstrated by a decreased FEF50/FIF50 ratio. Of these, 45 had a decrease in the FEF50/FIF50 ratio of more than 20% following administration of inhaled albuterol. Overall, CPAP adherence between those with reversible upper airways obstruction and those without was similar (23/45=51% vs 14/26=54%). However, subgroup analysis revealed a lower adherence rate among non-obese patients (BMI<30) with reversible airways obstruction (6/16=36%).

Conclusion

The identification of a subset of patients with OSA who have evidence of decreased upper airway resistance in response to inhaled bronchodilator suggests unique pathology in this group. Decreased adherence to traditional OSA therapy with CPAP among these patients is additional evidence of differential pathophysiology requiring novel treatments. Specifically, treatment with a long acting beta agonist (LABA) prior to sleep may reduce upper airway obstruction and be better tolerated than CPAP.

Basic principles for evaluation of less deformable erythrocyte subpopulations with the Microfiltrometer

The Microfiltrometer consists of a filtration system for diluted erythrocyte suspensions, through a filter containing 30 cylindrical micropores, 5 microm in diameter, under the influence of a driving pressure. A feeding sinusoidal alternating current of 40 kHz, 300 microA is delivered to the filter. The change in impedance is collected for each temporary flow of erythrocytes through a given micropore. Two main parameters are measured for individually explored erythrocytes: the entry time tau in the micropore and the maximal variation of impedance deltaZ occurring for the transitory flow. The slope deltaZ/tau defines the velocity of pore blockage. A "Microfiltrometer Deformability Index" (MDI) is established by using this slope. When MDI > or = 1, the erythrocyte is considered to be deformable and, conversely, when MDI < 1, the erythrocyte is considered to be undeformable. Using this procedure, less than 2% undeformable erythrocytes in healthy blood samples are identified, with a specificity of 99% and a sensitivity of 97.5%.

A comparison of 15N proline and 13C leucine for monitoring protein biosynthesis in the skin

The tracers L 15N-proline and L(1-13C)-leucine were used to explore the synthesis of skin proteins in vivo in rabbits. They orally received a single dose containing an equimolecular mixture of L(1-13C)-leucine and L 15N-proline. The changes in the amounts of these tracers in blood and skin were monitored for a total of 8 h. The data showed the appearance of the two tracers in blood within 15 min and their clearance in 8 h. They were both rapidly (15 min) incorporated into skin proteins, but more proline was incorporated than leucine. We therefore consider L 15N-proline to be a better tracer than L(1-13C)-leucine for studying protein metabolism in the skin.