From: Vital Capacity in Heart Disease, by HW Jones. British Medical Journal, May 12, 1928, page 795.

“In this investigation a simple water spirometer (Fig. 1) has been used, graduated in cubic centimeters and balanced so no effort is required to raise the cylinder. A large number of glass mouthpieces were provided, so that they could be readily disinfected between each patient without loss of time.

“It is always advisable to explain fully the working of the machine before actually taking the measurement, as it is necessary to get the patient’s whole-hearted cooperation to obtain an accurate result. Each patient was given three attempts, the highest being taken as the vital capacity. In taking the reading if there is any tendency to expire through the nose this should be closed by pinching during expiration. When patients were not confined to bed the record was always taken standing, and generally in their ordinary clothes. With regard to the patients who were confined to bed they were all able to sit up in bed when taking the reading , so that it was not necessary to correct the reading for the 5 percent diminuation in the vital capacity which has been shown by Christie and Beams and Rabinowitch to occur when the reading is taken in the recumbent position. Owing to the variability of the vital capacity according to the height, sex, age and race of the individual concerned, the simple reading of the number of cubic centimeters expired gives little indication of the deviation from normal, unless the reading is expressed in percentages of the standard vital capacity for that individual.”