Normal standards for single breath tests of ventilatory capacity in children.

Tests of ventilatory capacity based on the recording of a maximum forced expiration after a full inspiration are becoming increasingly widely used. They are quicker to perform and require less cooperation and effort on the part of the subject than the conventional maximum breathing capacity estimation, and the results are more informative because three indices of ventilatory capacity, each of different significance, are derived from the recording of this simple manoeuvre. These indices are: (1) the forced vital capacity, (2) the volume of gas expired over a given time interval (usually the first second or half second), and (3) the percentage of the vital capacity (or forced vital capacity) expired within the same time period (that is, 2 as a percentage of 1). In this department the procedure has been found most appropriate in paediatric work; the children learn it readily and can repeat it frequently with, in my experience, greater consistency than the maximum breathing capacity test. Adequate normal standards are available for the vital capacity (Turner and McLean, 1951; Jones, 1955), and this paper provides data relating to the percentage of the vital capacity expired in the first second and half second of a forced expiration.