PURPOSE: Asthmatic children, even when symptomatic, commonly manifest normal spirometry. Forced Oscillation (FO), airway occlusion (Rocc), and airflow perturbation device (APD) measures of airflow resistance (R) are performed during normal breathing, but require bulky equipment and computers. We developed a prototype Hand-Held APD (HHAPD) to measure R by perturbing airflow at 10 Hz. Pressure and flow analyses incorporated into firmware in a 15 oz HHAPD measured R at 10 Hz (R10), to assess whether this device accurately measured R in asthmatic children compared to gold standard FO using Impulse Oscillometry (IOS).
METHODS: We developed prototype HHAPDs with nonlinear (quadratic pressure-flow) airflow sensors and lightweight pressure transducers [All-Sensors]. We used average pressure-flow calibrations for 4 sensors to pre-program look-up tables for flow measurements. We compared IOS R10 in 24 asthmatic children with HHAPD R10 and a desktop APD (Fleisch pneumotachograph and [Honeywell] pressure transducers). All children were tested during clinical followup for asthma. We correlated HHAPD R10 with IOS R10 and with desktop APD R10.
RESULTS: HHAPD R10 correlated closely with desktop APD (r = 0.89, slope = 0.73) and with IOS R10 (r = 0.89, slope = 0.63). HHAPD underestimated both IOS and desktop APD R10, when R10 exceeded 5 cm H2O/L/s.
CONCLUSION: We conclude that a prototype HHAPD using nonlinear flow sensors underestimates R10 at R10 > 5 cm H2O/L/s. The close correlation between HHAPD R10 with IOS R10 indicates that HHAPD can reflect airflow resistance measured by gold standard IOS, but improved flow calibrations are warranted.
CLINICAL IMPLICATIONS: Asthmatic children frequently manifest normal spirometry. Measurement of HHAPD R with improved flow calibration may provide useful monitoring of changes in airflow obstruction in asthmatic children. HHAPD can be conveniently used at home, without maximal forced expiratory efforts.
DISCLOSURE: Jafar Vossoughi, Product/procedure/technique that is considered research and is NOT yet approved for any purpose, Airflow Perturbation Device.