TRANSESOPHAGEAL ECHOCARDIOGRAPHIC EVALUATION DURING NEGATIVE-PRESSUREVENTILATION USING THE HAYEK OSCILLATOR

Objectives: To evaluate the effects of negative-pressure ventilation ( NPV) on hemodynamics using the Hayek oscillator (Breasy Medical Equipm ent, London, UK) and to determine whether the oscillation frequency ca n modify the hemodynamics, assessed by transesophageal echocardiograph y (TEE). Design: A prospective study. Setting: A university hospital. Participants: Eleven American Society of Anesthesiologists class I pat ients undergoing orolaryngeal surgery. Interventions: The ultrasound p robe was inserted under general anesthesia. After baseline measurement s were determined during spontaneous breathing, the frequency was chan ged from 30 to 60 to 120 cycles/min, consecutively. The left ventricul ar end-diastolic area (LVEDA), end-systolic area (LVESA), fractional a rea change (LVFAC), and end-systolic wall stress (ESWS) were determine d. The velocities of the pulmonary artery (PA) flow, pulmonary venous (PV) flow, and transmitral flow were measured by pulsed Doppler techni ques. Measurements and Main Results: PaO2 increased and PaCO2 decrease d significantly. NPV caused a significant increase in the LVEDA, where as it did not significantly change the PA velocity. ESWS, an index of afterload, remained unchanged.Conclusion:The authors conclude that NPV using the Hayek oscillator induces an increase in the LVEDA without a ny changes in PA velocity, suggesting increased transmural pressure ra ther than increased preload, and that the three different frequencies do not modify the effects on the hemodynamics. Copyright (C) 1998 by W .B. Saunders Company.