Precision and accuracy of Morgan ventilometers at continuous and sinusoidal flows.

The P.K. Morgan Mark II Ventilometer comprises a turbine transducer and a control/readout unit, which contains either a VENTX5A or VENTX6A programme. This equipment is used to measure minute ventilation during oxygen consumption tests. The precision and accuracy of six of these devices (a VENTX5A with two turbines, and two VENTX6As each with two different turbines) were examined during continuous and pulsatile flows; accuracy was affected by the syringe rate during the calibration procedure. The reference standard was a 350 l Collins chain-compensated gasometer. At continuous flows, the two VENTX5A devices showed accuracies of 99.5-100.5% over the range 60-160 l.min-1 whereas those for the four VENTX6As were 99.3-102.1% over the range 60-200 l.min-1. The mean accuracies of sinusoidal flows for the VENTX5A ranged between 96.1-101.3% for minute volumes spanning 15-200 l.min-1; comparable data for the VENTX6As were 95.9-98.9%. These mean accuracies improved to 98.1-101.3% for the VENTX5A at measured minute volumes > 80 l.min-1. Omission of the two lowest tidal volumes (1 and 1.5 l) for the VENTX6As narrowed the range of accuracy to 96.9-98.5%. The coefficients of variation for five trials at each minute ventilation were 0-0.2%. We conclude that, while the P.K. Morgan Mark II Ventilometer has excellent precision, its accuracy is dependent on the calibration syringe rate, minute ventilation and program.