PURPOSE: To test the hypothesis that cardiac output (Q) in patients with arteriovenous malformations (AVMs) is normal at rest and increases disproportionately during exercise. MATERIALS AND METHODS: Q was measured in eight patients with large peripheral AVMs and in nine healthy subjects using a noninvasive carbon dioxide (CO₂)-based differential Fick method. Subjects were tested while seated at rest and during mild exercise (repeated leg straightening while sitting). Oxygen consumption (VO₂) was monitored as an index of the degree of exercise. RESULTS: Average resting Q was similar between AVM patients and healthy subjects (7.40 L/min ± 3.29 vs 6.13 L/min ± 0.94, respectively, P = .29). During exercise, AVM patients showed a smaller increment in VO₂ (0.50 L/min ± 0.11 vs 0.78 L/min ± 0.26, P = .012) but with more apparent effort and shortness of breath compared with healthy subjects. The change in Q per unit change in VO₂ (ΔQ/ΔVO₂) was greater in AVM patients than in healthy subjects (16.00 L/min ± 6.50 vs 9.79 L/min ± 5.33, P < .045). CONCLUSIONS: Exercise intolerance in AVM patients may be due to an imbalance in ΔQ/ΔVO₂ resulting from increased shunting through the AVM. Exercise provocation may increase the sensitivity of Q in the clinical evaluation of AVM patients.
PURPOSE: To test the hypothesis that cardiac output (Q) in patients with arteriovenous malformations (AVMs) is normal at rest and increases disproportionately during exercise. MATERIALS AND METHODS: Q was measured in eight patients with large peripheral AVMs and in nine healthy subjects using a noninvasive carbon dioxide (CO₂)-based differential Fick method. Subjects were tested while seated at rest and during mild exercise (repeated leg straightening while sitting). Oxygen consumption (VO₂) was monitored as an index of the degree of exercise. RESULTS: Average resting Q was similar between AVMpatients and healthy subjects (7.40 L/min ± 3.29 vs 6.13 L/min ± 0.94, respectively, P = .29). During exercise, AVMpatients showed a smaller increment in VO₂ (0.50 L/min ± 0.11 vs 0.78 L/min ± 0.26, P = .012) but with more apparent effort and shortness of breath compared with healthy subjects. The change in Q per unit change in VO₂ (ΔQ/ΔVO₂) was greater in AVMpatients than in healthy subjects (16.00 L/min ± 6.50 vs 9.79 L/min ± 5.33, P < .045). CONCLUSIONS: Exercise intolerance in AVMpatients may be due to an imbalance in ΔQ/ΔVO₂ resulting from increased shunting through the AVM. Exercise provocation may increase the sensitivity of Q in the clinical evaluation of AVMpatients.