PURPOSE: A cardiovascular limit to exercise is generally manifested by depressed maximum cardiac output (Qtmax) and high ventricular filling pressures. Here, we hypothesized a subset of patients with unexplained exertional symptoms has impaired exercise tolerance due to inadequate filling pressures causing a reduction of Qtmax.
METHODS: 674 consecutive clinically indicated incremental cardiopulmonary exercise tests with radial and pulmonary artery catheters and first-pass radionuclide ventriculographic scanning (FPRVS) were analyzed. Twenty-eight patients were identified with preload failure (PLF), defined as decreased exercise capacity (VO2max < 80% predicted) from reduced cardiac output (Qtmax < 80% predicted), and RAP at exercise (RAPmax) < 10 mmHg with normal biventricular ejection fractions and without pulmonary arterial (mPAPmax < 30 mmHg and PVRmax < 80 dynes•s•cm-5) or venous (PCWPmax < 20 mmHg) hypertension. They were compared to 23 normals (VO2max and Qtmax > 80% predicted, normal central hemodynamics, and FPRVS) with an unpaired t-test.
RESULTS: All patients received up to three 500 mL normal saline boluses to achieve an upright PCWP > 5 mmHg pre-exercise. PLF patients were more likely women (89% v. 57%; p = 0.01). PLF had lower VO2max (56% v. 90% predicted; p < 0.01), resting RAP (1.9 v. 3.0 mmHg; p = 0.03), RAPmax (5.4 v. 8.9 mmHg; p < 0.01), and less RAP augmentation during exercise (3.5 v. 6.0 mmHg; p = 0.01). At maximum exercise, PLF had decreased Fick SV (73 v. 101 mL; p < 0.01), mPAP (22.8 v. 28.7 mmHg; p < 0.01), PCWP (11.5 v. 15.3 mmHg; p < 0.01), and ventricular end diastolic volumes (right, 137 v. 160 mL, p < 0.01; left, 111 v. 130 mL; p = 0.01). Notably, five of six PLF patients who underwent further evaluation with tilt table testing had abnormal studies.
CONCLUSION: A symptomatic cardiovascular limit to exercise may occur due to inadequate right-sided filling pressures despite intravenous volume resuscitation and in the absence of systemic hypotension.
CLINICAL IMPLICATIONS: Preload failure should be added to the differential diagnosis of unexplained exertional intolerance.
DISCLOSURE: William Oldham, No Financial Disclosure Information; No Product/Research Disclosure Information