RESPIRATORY OSCILLATION MECHANICS IN INFANTS WITH BRONCHIOLITIS DURING MECHANICAL VENTILATION

The aim of the study was to describe the pattern of respiratory oscill ation mechanics and responses to positive end-expiratory pressure (PEE P) in bronchiolitis. Six infants were studied during the course of mec hanical ventilation. A 20 Hz sinusoidal pressure variation was applied at the endotracheal tube where flow was measured with a pneumotachogr aph. Resistance and reactance obtained from the complex pressure-flow ratio were separated during inspiration (R-rs,R-i; X-rs,X-i) and expir ation (R-rs,R-e; X-rs,X-e), and the differences between R-rs,R-i and R -rs,R-e (Delta R-rs) and X-rs,X-i and X-rs,X-e (Delta X-rs) were calcu lated. The data were corrected for the mechanical characteristics of t he endotracheal tube. The measurements were repealed while PEEP was va ried between 0 and 8 hPa. Two infants were found to have normal R-rs a nd near-zero X-rs and both parameters exhibited little change within t he respiratory cycle or with varying PEEP. Four infants had high R-rs at zero PEEP. In two, R-rs,R-i was markedly elevated (108.5 and 85.2 h Pa.s/L, respectively), and X-rs,X-i was markedly negative (-25.0 and - 22.5 hPa.s/L, respectively) at zero PEEP, while Delta R-rs and Delta X -rs were small. R-rs,R-i and the absolute value of X-rs,X-i decreased with increasing PEEP. This pattern of oscillation mechanics was consis tent with low lung volumes and atelectasis, being reversed by increasi ng PEEP. In the remaining two subjects, R-rs,R-i was moderately elevat ed (57.8 and 53.6 hPa.s/L, respectively) and X-rs,X-i moderately negat ive (-12.5 and -7.7 hPa.s/L, respectively) at zero PEEP. Delta R-rs (- 59.8 and -56.5 hPa.s/L, respectively) and Delta(rs) (28.1 and 48.7 hPa .s/L, respectively) were large, but were dramatically reduced by incre asing PEEP. These patterns were consistent with expiratory airflow lim itation. Measurements of respiratory impedance are, therefore, informa tive in regard to the pathophysiological mechanisms occurring in bronc hiolitis during mechanical ventilation, and they may be helpful in set ting the level and assessing the effect of PEEP. (C) 1998 Wiley-Liss, Inc.