Effect of altitude on hand-held peak flowmeters.

ABSTRACT

OBJECTIVE: To quantify the effect of altitude on the operational characteristics of hand-held peak flowmeters. DESIGN: Altitude simulation within a hypobaric chamber combined with five constant simulated peak flows delivered from a computerized pump were used to test commercially available peak flowmeters. SETTING: F.G. Hall Hyperbaric/Hypobaric facilities located at Duke University School of Medicine. MEASUREMENTS Two each of nine models of commercially available hand-held peak flowmeters and a volume spirometer were tested at six simulated altitudes (100, 500, 1,000, 1,500, 2,000, and 3,000 m) using five target peak flows. Each peak flow was injected into each meter twice. Forward stepwise regression was used to check for nonlinear relationships between altitude and peak expiratory flowmeter readings. Linear regression equations were fit to the data at each target flow across altitude. Effect of absolute peak flow was tested by analysis of covariance. RESULTS: For these altitudes, linear relationships were found between altitude and measured peak flow. For all meters tested, the average decrease in peak flow ranged from -8.7% at the lowest target flow (123 L/min) to -6.5% at the highest target flow (702 L/min) for each 100 mm Hg decrease in barometric pressure (PB). Individual meters ranged from -12.3% at the lowest target flow to -4.4% at the highest target flow for 100 mm Hg decrease in PB. The spirometer had no significant changes associated with changes in PB. In all cases, the magnitude of the altitude effect, measured by percent change, decreased with increasing peak flow. CONCLUSIONS: Peak expiratory flowmeters underread PEF as a function of both increasing altitude and increasing target peak flow.