10 individuals aged 18-60 who have sustained an acute traumatic SCI (above T2 spinal level) less than 72 hours prior will be recruited over a period of 2 years. Recruitment will be isolated to those individuals who already have a central venous catheter and arterial line as part of standard clinical care (which actually occurs in most patients). In addition to standard clinical lines, an esophageal Doppler probe will be placed to measure aortic outflow on which beat-by-beat systolic cardiac function (i.e., stroke volume, cardiac output, ejection fraction) can be estimated. During a 120 min monitoring period, beat-by-beat dependent cardiac indices will be recorded and a modified Starling curve will be constructed by examining relationships between central venous pressure (i.e., an index of venous return) and aortic flow (i.e., an index of cardiac output). After 1hr of monitoring (Part A), a 250ml bolus of intravenous crystalloid will be infused over a 5 min period and measure beat-by-beat central venous pressure and aortic flow (stroke volume) responses (Part B). The primary outcomes are daily resting stroke volume and ejection fraction, change in stroke volume and central venous pressure (CVP) in response to fluid challenge. The secondary outcome is the slope of the Starling curve