Flowmetric comparison of respiratory inductance plethysmography and pneumotachography in horses

Respiratory inductance plethysmographic (RIP) and pneumotachographic (Pn) f lows were compared dynamically in horses with bronchoconstriction. On a bre ath-by-breath basis, RIP was normalized to inspiratory volume from Pn, and peak [peak of subtracted final exhalation waveform (SFEmax)] and selected a rea [integral of subtracted final waveform during first 25% of exhaled volu me (SFEint)] differences between RIP and Pn flows during early expiration w ere measured in three settings: 1) healthy horses (n = 8) undergoing histam ine bronchoprovocation; 2) horses with naturally occurring lower airway obs truction (AO) (n = 7); and 3) healthy horses (n = 6) given lobeline . HCl t o induce hyperpnea. In setting 1, histamine challenge induced a dose-depend ent increase in SFEmax and SFEint differences. A test index of airway react ivity (interpolated histamine dose that increased SFEmax by 35%) closely co rrelated (r(s) = 0.93, P = 0.001) with a conventional index (histamine dose that induced a 35% decrease in dynamic compliance). In setting 2, in horse s with AO, SFEmax and SFEint were markedly elevated, and their absolute val ues correlated significantly (P < 0.005) with pulmonary resistance and the maximum change in transpulmonary pressure. The effects of bronchodilator tr eatment on the SFEmax and SFEint were also highly significant (P < 0.0001). In setting 3, hyperpnea, but not tachypnea, caused significant (P < 0.01) increases in SFEmax but not in SFEint. In conclusion, dynamic comparisons b etween RIP and Pn provide a defensible method for quantifying AO during tid al breathing, without the need for invasive instrumentation.