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Left Ventricular Preload Determines Systolic Pressure Variation during Mechanical Ventilation in Acute Lung Injury

Jamie R. Mitchell, Christopher J. Doig, William A. Whitelaw, John V. Tyberg and Israel Belenkie

Background: Systolic pressure variation (SPV) predicts responsiveness to volume loading during mechanical ventilation and may be related to changes in LV preload and the resultant changes in stroke volume (SV). We, therefore, tested the relations between LV preload, output and SPV in an acute lung injury (ALI) model during mechanical ventilation.
Methods: ALI was created by oleic acidinfusion (0.07 ml/kg) in 8 anesthetized dogs. We measured LV, RV, aortic, left atrial (LA) and pericardial pressures, LV area (A_LVED) and SV during mechanical ventilation with positive endexpiratory pressures (PEEP) of 0, 6, 12 and 18 cmH₂O at LV end-diastolic pressures of 5, 12 and 18 mmHg.
Results: Throughout these ranges of PEEPs and filling pressures, SPV was inversely related to LV preload [A_LVED and transmural LV end-diastolic pressure; (P_LVEDtm)] (r = −0.87 and r = −0.89, P <0.0001 respectively). Both preload measures were closely related to SV (both r = 0.90, P <0.0001). Changes in estimated P_LVEDtm (LA end-diastolic
pressure – RV end-diastolic pressure) matched changes in P_LVEDtm (r = 0.95, P < 0.0001). Alternative measures of arterial pressure variation (pulse pressure variation, SV variation and delta down) behaved similarly when compared to SPV (r = 0.91, 0.97, and 0.78, P < 0.001, respectively).
Conclusions: The inverse relations between SPV and LV preload and output indicate that LV preload is a major determinant of SPV. An estimate of LV preload based on measurements from the flow-directed catheter (i.e., wedge pressure – right atrial pressure) may predict volume responsiveness in mechanically ventilated patients.