Forced expirations in normal subjects. Is the shape of the flow rate curve related to existence of a wheeze?

The flow rate curve takes different shapes during forced expirations performed by normal subjects. In some cases a wheeze may exist. In this study, we examine the conditions for appearance of a wheeze, before and after the peak flow, and the relationship between the wheeze and the shape of the flow rate curve. We analyzed ten parameters in 83 forced expirations produced by 32 normal subjects (16 men and 16 women) using multidimensional scaling techniques. Among these expirations, 53 presented a wheeze. The first two axes of the analysis define a plane on which forced expirations are divided into four quadrants. Two opposite quadrants (upper right and bottom left) contain the wheezing expirations, while the two others only have the ones with no wheezing. This distribution corresponds to specific shapes of the flow rate curve. We found that wheezes are associated with two main shapes. One of them consists of a short onset until a sharp peak, followed by a fast exponential decay. The other is about triangular, with a late appearance of the wheeze, and is only produced by women.