Our results confirm the data of others and show that the response of the MiniWright peak flowmeter is a function of the square root of actual flow through the meter. Flow rate measurements from such a meter could be easily corrected by altering the scale on the meter itself to reflect this relationship.
With use, the MiniWright meters become less accurate and begin to significantly overestimate actual flow. This problem is not seen with the Assess meters after 200 uses, but it might be expected after extended periods of active use.
Conclusions
The Assess peak flowmeter is more accurate than the MiniWright peak flowmeter over clinically relevant peak flow ranges. After limited use, the accuracy of the MiniWright peak flowmeter is markedly diminished. We were unable to show any significant difference in durability between the Assess and MiniWright peak flowmeters. The old Healthscan meters are unreliable, out of production, and should not be used. Mechanical portable peak flowmeters do not necessarily retain accuracy over time and usage. We therefore recommend that the accuracy of such devices be checked by comparison to a reliable standard periodically. The optimal interval for rechecking remains to be determined.