Pulmonary Function in Obstructive Sleep Apnea: DISCUSSION

Our data suggest that there is an inverse relationship between FEF50%/FIF50% and mean oropharyngeal cross-sectional area in patients with OSA who have normal pulmonary function. Neither obesity nor age explains this relationship. This suggests that oropha­ryngeal dimensions influence the FEF50%/FIF50% in patients with OSA, perhaps by limiting inspiratory flow. The lower PIF observed in patients with OSA (f-test) supports this concept; however, such an expla­nation for our findings is speculative, as oropharyngeal cross-sectional area was measured at FRC in the supine position and may differ from oropharyngeal area at 50 percent of vital capacity during forced expiratory and inspiratory flow-volume testing.

We found no relationships between any of our four measures of pharyngeal size and lung volumes. This observation is intriguing in light of recent evidence that pharyngeal cross-sectional area varies directly with changes in lung volume. Our results, obtained by different methods, are not inconsistent with this finding, as we did not seek to determine whether pharyngeal size varied with different lung volumes in the same individuals.

The inverse relationship between Rp and midexpiratory flow rate is difficult to explain and may be fortuitous. This association could not be accounted for by age or BMI. We suspect that in general, there is a weak inverse relationship between pharyngeal resis­tance and expiratory airflow, individuals with high pharyngeal resistance having lower expiratory flow rates. This belief is supported by the associations we found between Rp and FVC (percent of predicted; rs= —0.37; p = 0.07), PEF (percent of predicted; rs= —0.38; p = 0.06), and FEVj/FVC (rs=-0.34; p = 0.09).
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The strong association between Rp and AHI§ (rs = 0.51; p = 0.02) is consistent with previous findings suggesting that patients with OSA have a defective ability to dilate the pharynx during tidal breathing. During forced inspiratory maneuvers, this defect may not be evident, as we found no relationship between Rp and PIF. Thus, with maximal voluntary effort, individuals may be able to overcome any impairment in pharyngeal dilator function that is present during tidal inspiration.

The present study reveals that conventional meas­urements of airflow, lung volumes, and flow-volume relationships are similar in overweight men with OSA and controls of similar age, height, and weight. Our findings are consistent with those of two other con­trolled studies showing that no single measure of airflow or lung volume distinguishes patients with OSA from control subjects.

The flow-volume loop suggested upper airway ab­normalities in only one of our patients with OSA, whose FEF50%/FIF50% was elevated. Six of seven patients with severe OSA (AHI >70) had normal ratios. Others have found elevated values for FEF50%/ FIF50% in a wide range (18 to 82 percent) of patients with OSA. Differences in pulmonary function testing apparatus, the vigor of efforts to obtain maximal inspiratory and expiratory airflow rates, or the method of selecting the expiratory and the inspiratory flow- volume curves for calculation of FEF50%/FIF50% may explain the divergent results. As observed by others, we found FEF50%/FIF50% to be unrelated to the severity of sleep-disordered breathing. These findings suggest that the FEF50%/FIF50% is insen­sitive in the detection of upper airway abnormalities associated with OSA, possibly because FEF50%/ FIF50% is highly dependent upon expiratory airflow rates. Our data indicate that Rp is superior to FEF50%/FIF50% in identifying those with OSA. canadian cialis online

Category: Health

Tags: Obstructive Sleep Apnea, Pulmonary Function

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