The arterial pressure waveform during acute ventricular failure and synchronized external chest compression

Methods for mechanical cardiac support by intermittent increases in the intrathoracic pressure have recently been described. In the present study the responses of the arterial pressure waveform to mechanical ventilation with and without synchronized external chest compression (SEC) in the presence of acute ventricular failure (AVF) were evaluated by measuring the systolic pressure variation (SPV). SPV, the difference between the maximal and minimal values of systolic blood during a single positive pressure breath, consists of Δup and Δdown components when systolic blood pressure during a short apnea is used as reference value. During intermittent positive pressure ventilation (IPPV) alone, AVF caused SPV to decrease significantly from 8.8 ± 4.0 to 5.7 ± 1.9 mm Hg, and further to 3.1 ± 1.1 mm Hg after volume loading (P < 0.02). The decrease in SPV was due to a significant decrease in the Δdown component, whereas the Δup became the major component of the reduced SPV. The application of SEC caused significant increases in the Δdown, Δup, and overall SPV during AVF without volume loading. However, during AVF with volume loading, SEC increased only the Δup component of the SPV, signifying a transient increase in the left ventricular stroke output. It is concluded that the disappearance of the Δdown component of the SPV is characteristic of congestive heart failure. Analysis of the arterial waveform offers a readily available monitoring tool for the differentiation of the possible effects on increased intrathoracic pressure. The appearance of a prominent Δdown signifies inadequate preload and possible reduction in cardiac output, whereas a significant Δup component is the reflection of a true mechanical cardiac support.