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“Closing volume” during high–frequency ventilation in anesthetized dogs
Author(s) -
Haghenberg T.,
Wendt M.,
Meyer J.,
Wrenger K.,
Lawin P.
Publication year - 1988
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1988.tb02703.x
Subject(s) - medicine , high frequency ventilation , anesthesia , ventilation (architecture) , volume (thermodynamics) , tidal volume , mechanical ventilation , respiratory system , mechanical engineering , engineering , physics , quantum mechanics
Airway closure, mean airway pressure, gas exchange and different modes of artificial ventilation were investigated in anesthetized and paralyzed dogs with clinically healthy lungs. The animals were ventilated with either intermittent positive pressure ventilation (IPPV), continuous positive pressure ventilation (CPPV, positive end–expiratory pressure (PEEP) = 0.49 kPa) or high–frequency jet ventilation (HFJV, open system) of 2 and 30 Hz with an inspiratory to expiratory (I/E) – ratio of 30/70 and 60/40. Closing volume (CV) was determined by a modified technique, submitting the lung to constant subatmospheric pressure after an inspiratory vital capacity of oxygen. Two different tests for CV were used: the foreign gas bolus (FGB) with helium as nonresident gas and the single breath nitrogen dilution technique (SBO 2 ). During conventional mechanical ventilation, CV decreased significantly ( P < 0.05) after establishing a PEEP of 0.49 kPa. During HFJV, CV increased significantly ( P < 0.01). This effect was predominantly dependent on I/E duration time ratio and to a lesser extent on ventilatory frequency. There were significant differences between CV obtained by the FGB–method (CV(helium)) and CV derived from the SBO 2 –test (CV(SBO 2 )), although both tests revealed the same proportional changes of CV during the different modes of ventilation. The elevated CV was associated with a decreasing Pao 2 and increasing Aa–Do 2 and Paco 2 , indicating substantial hypoventilation and mismatching of ventilation and perfusion. Mean airway pressure increased with both CPPV and HFJV, revealing a dissociation between airway pressure and regional FRC distribution during HFJV. It is concluded that certain modes of high–frequency ventilation lead to impaired distribution of inspired gas to dependent lung regions. This effect may contribute to pulmonary dysfunction in patients with compliant lungs and prolonged spontaneous relaxation time, and lead to overexpansion of peripheral airways.