The maximal expiratory flow/volume curve in 197 healthy New Zealanders: a comparison with recent American standards.

Maximal expiratory flow/volume curves were recorded from 155 healthy, non-smoking Europeans aged seven to 71 yr and 42 Polynesian children aged nine to 11 yr. Forced vital capacity (FVC), forced expiratory volume in 1s (FEV1), FEV1/FVC, peak expiratory flow (PEF) and flow at 50 and 25% of FVC (V50 and V25) were compared with the predictions made from the equations of Schoenberg, Beck and Bouhuys, describing healthy people in Connecticut, USA. In general the equations described our subjects well; the small but significant discrepancies may reflect either technical factors or possibly a true difference in populations.

Reference values for functional residual capacity and maximal expiratory flow in young children.

To determine the relation of functional residual capacity and maximal expiratory flow at functional residual capacity to sex, age, height, and weight in healthy young children living in Portland, Oregon, we tested 37 boys and 36 girls using a modified helium-dilution technique and partial expiratory flow-volume curves. Within the age, height, and weight ranges studied, exponential or multiple regression techniques offered no substantial advantage over simple linear regression using height, weight, or age. There were no sex differences for the relationship between either variable and age, height, or weight. These techniques can readily be used in children as young as 3 years of age and may provide a method for studying lung growth and development in early childhood and a way to observe the progression of disease or the effect of treatment in the young child.

Calibration of time derivatives of forced vital capacity by explosive decompression.

A simple, portable, inexpensive device is described that simulates expiratory flow curves for calibration of spirometers. A 4-L metal cylinder filled with copper mesh is fitted with a precision manometer. The pressure is increased to twice atmospheric and released by explosive decompression through 4 easily interchangeable resistors. The ratio of forced expiratory volume in one second to forced vital capacity ranged from 0.80 to 0.25, thus encompassing the range from normal to severe obstruction. Accuracy was defined by 25 measurements of forced vital capacity that differed by no more than 0.5% from the actual cylinder volume. Repeatability was reflected by a standard deviation of at most 0.04 L/s for one-second forced expiratory volume, mid-expiratory flow, and instantaneous flows at 50 and 25% of the forced vital capacity. Peak flow was less reproducible. Calibrations of a water spirometer at increased altitude and at temperatures from 4 degrees to 37 degrees C revealed no significant changes in volume or flow rates. Standard values have remained unchanged for 2.5 yr. Three volume spirometers and 2 primary flow devices were tested extensively.

Constancy of effort and variability of maximal expiratory flow rates.

In 14 normal subjects and in 13 patients with obstructive pulmonary diseases, we studied the variability within an individual of values for the maximal expiratory flow rate (Vmax) recorded simultaneously vs expired pulmonary volume (at the mouth) and vs thoracic volume (measured with a body plethysmograph). We found that the variance of Vmax within an individual at 25, 50, and 75 percent of the expired vital capacity did not differ statistically whether pulmonary volume was the expired or the thoracic gas volume. In ten healthy subjects on two occasions (at an interval of 12 days, on the average), we measured the peak expiratory flow rate and Vmax at different levels of inflation, with respect to either expired or thoracic volume. There was no statistical differences in Vmax between the first and the last day. A larger variability of Vmax measured vs expired volume implies a change in the expiratory effort from one forced expiration to another and a different degree of compression of intrathoracic air. Since this was not the case, we conclude that muscular effort during repeated forced expirations is similar. The good reproducibility of effort explains in great measure the good reproducibility of Vmax.