Left Ventricular Pressure-Volume and Frank-Starling Relations in Endurance Athletes Implications for Orthostatic Tolerance and Exercise Performance

Background. Endurance athletes have a high incidence of orthostatic intolerance. We hypothesized that this is related to an abnormally large decrease in left ventricular end-diastolic volume (LVEDV) and stroke volume (SV) for any given decrease in filling pressure. Methods and Results. We measured pulmonary capillary wedge (PCW) pressure (Swan-Ganz catheter), LVEDV (two-dimensional echocardiography), and cardiac output (C2H2 rebreathing) during lower body negative pressure (LBNP,-15 and-30 mm Hg) and rapid saline infusion (15 and 30 ml/kg) in seven athletes and six controls (Vo2max, 68±7 and 41±4 ml/kg/min). Orthostatic tolerance was determined by progressive LBNP to presyncope. Athletes had steeper slopes of their SV/PCW pressure curves than nonathletes (5.5+2.7 versus 2.7+1.5 mI/mm Hg, p<0.05). The slope of the steep, linear portion of this curve correlated significantly with the duration ofLBNP tolerance (r=0.58, p=0.04). The athletes also had reduced chamber stiffness (increased chamber compliance) expressed as the slope (k) of the dP/dV versus P relation (chamber stiffness, k=0.008±0.004 versus 0.031±0.004, p<0.005; chamber compliance, l/k=449.8+283.8 versus 35.3+±4.3). This resulted in larger absolute and relative changes in end-diastolic volume over an equivalent range of filling pressures