1Īrterial pulse pressure respiratory variation (ΔPp) has greater specificity and sensitivity for detecting cardiovascular responsiveness to volume expansion than ΔPs. As arterial systolic pressure and plethysmographic systolic component variations (ΔSpleth) could change similarly, ΔSpleth has been proposed as a useful tool for determining recruitable preload in the absence of invasive pressure monitoring. Varying the arterial pressure through arterial lines during mechanical ventilation has been recommended for testing cardiovascular responsiveness during volume replacement in critically ill patients. Changes in intra-thoracic pressure interfere with venous return and cardiac output.