The absence of sawtoothing in any patient with OSA was surprising and may be related to our insistence upon the strict criteria for sawtoothing defined by others, by the blinding of our test interpreters to the diagnosis of OSA, or by insensitivity of our pulmonary (unction apparatus in detecting small oscillations in the flow-volume relationship. We believe that the latter explanation best accounts for our disparate results, as other studies reporting the sawtooth pattern in OSA have used pulmonary function testing equipment different from ours. Differences in electronic filtering of flow signals from spirometry may account for the wide range of prevalence of sawtoothing in OSA. Pulmonary (unction testing systems that attenuate the signal response may “filter out” the sawtooth appearance of the flow-volume loop in patients with OSA.
Our study confirms previous reports demonstrating significant inverse relationships between PFTs and the severity of sleep-disordered breathing. We found that the frequency of abnormal breathing events during sleep was inversely related to several lung volumes (FRC and percentage of predicted values for FVC and TLC), PIF, and MW (percent predicted). In patients with OSA alone, AHI was strongly related to FRC (rs = – 0.74; p<0.01). All of these relationships were dependent upon obesity (but not age), becoming insignificant when BMI was controlled. The relationships between apnea/hypopnea frequency and percentage of predicted values for both FVC and TLC were also dependent upon FRC, becoming insignificant when FRC was controlled. Controlling for ERY which is inversely related to the degree of obesity in both normal subjects and patients with OSA, also rendered these relationships insignificant. Thus, obesity, reflected as BMI, appears to explain the inverse relationship between PFTs (FRC, other lung volumes, MW, and PIF) and the frequency of sleep-disordered breathing events. tadalis sx
Others have suggested that reduction in FRC may be related to the severity of sleep-disordered breathing. The reasons for this association are speculative, but our data suggest that obesity is responsible. It is known that the efficiency of the diaphragm as a generator of pressure is enhanced at low lung volumes. In obese individuals a longer diaphragm at a low FRC might generate more negative inspiratory pressures in the thorax and upper airway during contraction than a shorter diaphragm at a higher FRC, predisposing the pharynx to collapse.
We found only one relationship between PFTs and sleep-disordered breathing events to be independent of BMI. In patients with OSA, the relationship between the AI and MW (percent predicted) was significant (rs= —0.77; p<0.01) and remained so when partial correlation analysis accounted for BMI. This inverse relationship between the frequency of apneas during sleep and M W (percent predicted) in OSA has not previously been reported and is difficult to explain. Obesity and age do not weaken the significance of the relationship. We speculate that poor performance of the M W maneuver by patients with OSA occurs as a result of the suppressive effects of sleep apnea on motivation, effort, or respiratory muscle strength. The latter explanation is attractive because of strong correlations between MW (percent predicted) and FVC, a test which is in part dependent on respiratory muscle strength (for all subjects, rs = 0.73 and p<0.001; for patients with OSA, rs = 0.77 and p<0.01). Acute respiratory muscle fatigue may account for the poor MW values in those with the most severe OSA, but this seems unlikely, as the M W maneuver was carried out for only 12 s. We did not measure peak inspiratory pressure or maximum transdiaphragmatic pressure in our study, two measurements that possibly would clarify the observed relationship between the AI and MW (percent predicted). Chronic respiratory muscle fatigue cannot be excluded as a cause of this relationship.
Limitations of our study include a relatively small number of patients and control subjects. We did not measure FRC in the supine position, which is lower than in the sitting position in patients with OSA. We also did not obtain flow-volume loops in the supine position, which may increase their sensitivity in OSA. cialis 10 mg
We conclude that patients with OSA who have smaller oropharyngeal dimensions have higher values for FEF50%/FIF50%. Significant inverse relationships exist between several PFTs and the frequency of sleep-disordered breathing events. Obesity may in general account for the strength of these relationships. Our study confirms that conventional PFTs, including the flow-volume loop, are normal in overweight men with OSA.