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Introduction: Oxygen pulse is accepted as a surrogate for stroke volume (SV) and arteriovenous oxygen difference during cardiopulmonary exercise testing (CPET). It is frequently reduced in patients with pulmonary arterial hypertension (PAH) because of their inability to properly increase SV during effort. However, similar alterations can be seen in patients with abnormal oxygen extraction, such as mitochondrial myopathy (MM). We aimed to investigate whether cardiovascular responses during exercise would be able to distinguish PAH from MM. Methods: Comparison of incremental CPET of 16 patients with MM and 21 with PAH, matched for age, gender, and % predicted peak VO2 (39±14 vs 37±14yo, 85% vs 62% female, 58±12 vs 64±12%predVO2, for PAH and MM, respectively, p>0.05). Results: O2pulse at peak of exercise was similarly reduced in both diseases (70±22 vs 71±20%pred, p0.94), but ΔHR/ΔVO2 was higher in PAH (117±42 vs 94±18beats/L, p0.04). A cutoff of 120beats/L best discriminated the groups [Sensitivity 47%; Specificity 93%; Positive likelihood ratio (PLR) 7.6 (95% CI, 1.1-53)]. In addition, 15/21 (71%) PAH patients exhibited plateau or fall of O2pulse during exercise. In contrast, only 4/16 (25%) MM patients presented plateau (p Conclusion: A greater response of heart rate to oxygen consumption (ΔHR/ΔVO2≥120 beats/L) and the presence of an abnormal plateau of O2pulse during exercise are more frequently found in patients with PAH than MM. |
