Relation between partial and raised volume forced expiratory flows in sick infants

Rationale The maximal expiratory flow-volume (MEFV) and the partial expiratory flow-volume (PEFV) maneuvers are interchangeably performed when testing infant lung function. In recent years, the MEFV has gained popularity over the PEFV as it offers the investigator various forced expiratory flow and volume variables in addition to the sole, maximal flow at functional residual capacity (VmaxFRC) available from the PEFV maneuver. Both types of measure are considered to provide information on airway function. Objectives To compare VmaxFRC values by PEFV to flows at low lung volumes by MEFV in infants suffering from a variety of illnesses. Methods Retrospective analysis of records of 175 infants attending a tertiary out-patient clinic (age range 2-234 weeks). Comparisons between parameters derived from the PEFV and MEFV curves were made by linear regression and by Bland-Altman plots. Measurements and Main Results VmaxFRC highly correlated with forced expiratory flows at 85% of forced vital capacity (FEF₈₅; r = 0.87, P < 0.0001) with a mean bias of 20 ml/sec, and at 75% (FEF₇₅; r = 0.83, P < 0.0001) with a greater mean bias of -72 ml/sec, but less with forced expired volume in 0.5 sec (FEV_0.5; r = 0.66, P < 0.0001) showing a much wider scatter especially in infants with more severe obstruction. Same agreement between VmaxFRC and FEF₈₅ or FEF₇₅ was seen when presented as z-scores (r = 0.77 and 0.76; respectively). Conclusions Regardless of the maneuver performed, PEFV or MEFV, VmaxFRC and FEF₈₅, and FEF ₇₅ show high agreement in sick infants. As they both describe small airways function, both maneuvers may be interchangeable.