[Hemodynamic side effects of high-frequency jet ventilation as a function of lung volume. Impedance spirometric studies]

Abstract

In five patients with acute respiratory insufficiency the changes in tracheal pressure (P), lung volume (V) and transthoracic electric impedance TEI (Z) were measured during delayed expiration all over the inspiratory capacity (IC) from TLC to FRC. The quasi-static V/Z- and Z/P-curves were two-dimensionally displayed, and the Z/P-curve was volume-calibrated on the Y-axis (Z) using the linear V/Z-relationship. During high-frequency jet ventilation (HFJV, 200/min), the Z- and P-excursions were displayed on the "frozen" Z/P-curve as flat discs. By well-aimed increase in driving pressure and I/E-ratio the unknown FRC was enhanced in 4 stages (I-IV) by 0.33 IC, 0.5 IC, 0.66 IC and 0.75 IC, to measure haemodynamic reactions 10 minutes later (Swan-Ganz catheter). The pulmonary vascular resistance remained unchanged between stage I and II. It changed moderately in stage III (+14%) and was found to be markedly increased in stage IV (+45%). The increase in PVR was well parabolically correlated (r = 0.88) to the fraction of IC by which FRC was expanded. In a previous study a very similar function could be documented by us for the end-inspiratory lung volume during conventional PEEP ventilation. Concomitant to the increase in PVR the CI fell linearilly (r = 0.95). We conclude from our results: 1. TEI may be of value in monitoring HFJV. It offers the possibility to measure the increase in lung volume ("PEEP effect") and to titrate it deliberately within the usable volume range IC. 2.(ABSTRACT TRUNCATED AT 250 WORDS)