EVALUATION OF NASAL PRONGS FOR ESTIMATING NASAL FLOW

Nasal prongs (NP) connected to a pressure transducer have been suggest ed as a useful alternative for measuring nasal flow in sleep apnea/hyp opnea patients. However, flow measured with NP is expected to be nonli near. The aim of the present study was to analyze and correct the nonl inearity of nasal flow measurements with NP (VNP). Nasal flow was simu ltaneously measured with a pneumotachograph (PNT; V) and (NP; VNP) in six healthy subjects during 60 s of breathing at different tidal volum es. Nonlinearity of VNP was assessed by fitting separately, for inspir ation and expiration, a Rorher-modeI equation (VNP X K-1 X V + K-2 X V -2). In addition, we fitted the data to a simpler nonlinear quadratic model (P = K x V-2). The main findings were: (1) an excellent fit of t he Rorher equation to measured data in all cases; (2) although differe nces in the Rorher equation coefficients between inspiration and expir ation were observed, they were not statistically significant; (3) a su bstantial intersubject variability was found; and finally, (4) the squ are root of VNP acceptably fitted the nasal flow data measured by PNT (V) in most cases. We conclude that in order to quantitatively assess nasal flow with NP, data should be corrected for their nonlinear press ure-flow relationships and, that the square root of the flow signal me asured with NP is the simplest method of correcting for the observed n onlinearity.