Nasal resistance to respiratory airflow: a plethysmographic alternative to the face mask.

Nasal airflow resistances were measured simultaneously by face mask and "head-out" body plethysmograph and compared. Computer averaging of transnasal pressure and flow signals digitized at 50Hz during 5 breath sequences was employed to determine a ratio of pressure to flow as an index of nasal resistance to breathing. The mean value of ten plethysmograph measurements differed by only 2.0% from that of ten face mask measurements which were made simultaneously. Coefficients of variation of plethysmograph resistance measurements averaged less than 6% in twenty subjects (ten measurements/subject) aged 7-68 years over an intersubject resistance range of 1 to 7 cms H2O/l/sec (0.1-0.7 Pa/cm3/sec). Voluntarily altered minute ventilations from 8-28 l/min in a subject at rest increased this variation to 10%. The "head-out" body plethysmograph is a versatile and reliable instrument for assessment of nasal respiratory airflow resistance.