Deflation flow-volume curve analysis is a pulmonary function test sensitive to small airways dysfunction that is suitable for use in infants and children who are intubated. This test relies upon deflation flow-volume (DFV) curve analysis, which is a technique to obtain maximal expiratory flow-volume curves (MEFV) by forced deflation of the lungs in infants who are intubated. The method mimics the voluntary forced flow-volume curves that adults and older children undertake. We studied 10 anesthetized male Rhesus monkeys of the same weight as human infants but developmentally equivalent to older children. We reviewed the effects on forced deflation vital capacity (DVC) and flows at various subdivisions of vital capacity (PEF, MEF50, MEF25, MEF10) of systematically varying the required inspiratory and deflation pressure during the course of 56 consecutive deflation maneuvers. Inflation pressures of +40 and +50 cm H2O caused a marked but transient bradycardia along with a (probably spurious) short-lasting fall to 89% mean arterial oxygen saturation (SaO2). Increasing positive and negative pressures increased DVC and expiratory flows. The highest mean DVC was 75.6 +/- 1.3 ml/kg, PEF was 128.0 +/- 3.5, MEF50 was 85.9 +/- 2.2, MEF25 was 74.3 +/- 1.9, and MEF10 was 38.5 +/- 2.9 ml/kg/s, all obtained at the pressure gradient of 90 cm H2O (+50/-40 cm H2O) at the start of the deflation maneuver. At this gradient, the intraindividual coefficients of variation were: DVC = 0.8%, PEF = 3.1%, MEF50 = 2.2%, MEF25 = 2.1%, MEF10 = 5.4%.(ABSTRACT TRUNCATED AT 250 WORDS)