1647 FREQUENCY DEPENDENT IMPEDANCE OF THE RESPIRATORY SYSTEM IN PARALYZED, INTUBATED INFANTS

Abstract

Theory predicts that the mechanical efficiency of high frequency ventilation should depend on the impedance of the respiratory system (Z_rs). We therefore measured Z_rs in 9 paralyzed, intubated infants with respiratory distress syndrome to determine magnitude of Z_rs as a function of frequency and also the resonant frequency of the respiratory system. Infant gestational ages ranged from 31 to 36 weeks and weights from 1.6 to 2.3 kg. All were from 1 to 7 days old. Forced oscillation measurements were made between 4 and 40 Hz with the speaker plethysmograph method of Jackson and Vinegar (J Appl Physiol: 47, 1979). The studies were conducted during brief interruption of conventional ventilation while monitoring the infant's P_tcO₂ and pulse rate. Resonant frequencies ranged from 11 to 23 Hz and at resonance Z_rs was 33 to 71 cm H₂O/L/sec. Both below and above resonant frequency, Z_rs increased, rising by 20% at 6 Hz below (range 4-8 Hz) and 8 Hz above (range 5-13 Hz) resonance. One infant exhibited little frequency dependence of Z_rs. For these patients, we conclude that a region of frequencies surrounding resonance exists where Z_rs changes little and therefore the mechanical efficiency of high frequency ventilation should change little.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD