Pattern of Systemic Venous Return during Negative Pressure Ventilation with Pneumowrap: A Pulsed Wave Doppler Study in Patients with COPD

Abstract

Intermittent negative pressure ventilation (INPV) has been suggested as decreasing the fatigue of inspiratory muscles and the severity of respiratory failure in patients with obstructive pulmonary disease². However, it is still not clear whether and to what extent the respiratory muscles are rested during INPV applied by means of cuirass and pneumowrap ventilators. The reliable data on the presence or absence of spontaneous contractions of the respiratory muscles would be important not only from the point of view of the effectiveness of muscular rest. By creating different changes in pleural and abdominal pressures INPV with and without active contribution of inspiratory muscles may differently affect both preload and afterload of the ventricles. Better understanding of the mechanical function of the diaphragm during INPV might be of help in explaining the contradictory results of studies addressing hemodynamic effects of this kind of respiratory support³ (Ambrosino, unpublished information). EMGdi is not considered a fully reliable marker of the mechanical function of the diaphragm during supported ventilation. We attempted to identify active contractions of the diaphragm through their effect on the blood flow velocity in the inferior vena cava (IVC). We assumed that contracting the diaphragm should increase cranial flow velocity in IVC by a simultaneous increase in abdominal pressure and decrease in pleural pressure.