Comparison of PEFR and FEV1 in Patients with Varying Degrees of Airway Obstruction: Conclusion
One possible explanation for the higher peak flow values observed in our patient population is the altitude where testing was performed (approximately 1,606 m). Recently, Lenggenhager reported that resistance to airflow was reduced as barometric pressure decreased. Our results with normal subjects in an atmospheric chamber support this finding clinically. Subjects were able to generate sequentially higher percent predicted peak flows as the altitude was increased. On the other hand, the percent predicted FEV, that could be generated did not increase significantly at the simulated altitudes tested. It has been shown that at very high altitudes the FEV, does increase proportionately with increasing altitude.
These findings support the premise that FEVi is reproducible at most locations where routine clinical testing is performed.
Predicted peak flow values for our patients averaged approximately 16 percent higher than did FEVX values. The results of the study in the hypobaric chamber suggest that the altitude of Denver (1,600 m) accounted for part of the difference (approximately 6 percent) between FEV! and PEFR seen in our patients but did not explain the total difference between the two values. In the patients tested, the difference between FEVj and PEFR was as great in those with normal FEV! as in those with depressed values. Therefore, the effect of barometric pressure on our normal volunteers should reliably reflect the effect in asthmatic patients. Additionally, patients may be able to achieve nearnormal peak flows before dynamic collapse limits flow rates. It seems, therefore, that FEV, is more likely to detect patients with significant pulmonary obstruction. Here
The FEVt value had less intrasubject variability than PEFR in our patient population. The findings of lesser variability associated with FEV, is in agreement with those of other investigators. Although FEV! was less variable than JPF and WPF throughout the range of pulmonary function, it was clearly superior in the FEVi range of 50 to 75 percent predicted where respiratory impairment may be difficult to assess.
The FEVj and the PEFR do correlate, but these values are not interchangeable. The value of FEV, tends to have less intrasubject variability, it does not vary with respect to the altitude where the testing is generally performed, and, finally, it appears more sensitive to the presence of airway obstruction than the peak flow. Therefore, in view of the consistently higher peak flow values that can be generated, the FEV! measurement would be more likely to identify patients with mild pulmonary impairment. When available, the FEVi measurement appears superior to the peak flow rate in the initial evaluation of patients with obstructive airways disease.