During infusion of 50 g/kg/min , left ventricular stroke volume increased ( from 43.2221.5 to 51.8423.6 mL ; P = 0.003 ) , with marked falls in pulmonary vascular resistance ( by 29 % ; P = 0.03 ) and right atrial pressure ( by 40 % ; P = 0.007 ) , but with only modest falls in mean arterial blood pressure ( by 4 mm Hg ; P = 0.004 ) .