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  • Title: Percutaneous transvenous mitral commissurotomy immediately restores quick response of VO2 to mild exercise despite insignificant increases in peak VO2.
    Author: Takaki H, Sunagawa K, Sugimachi M, Tamai J, Okano Y, Kurita T, Aihara N, Shimizu W, Suyama K, Kamakura S.
    Journal: Heart Vessels; 1995; 10(6):323-7. PubMed ID: 8655470.
    Abstract:
    Percutaneous transvenous mitral commissurotomy (PTMC) increases peak oxygen uptake (VO2) chronically, but not acutely, despite early symptomatic improvements. Analysis of transient VO2 responses to submaximal exercise (an exercise regimen more comparable to the patients' daily activities than that provided by maximal exercise testing), may be sensitive in detecting the acute hemodynamic benefits of PTMC. Since no methods are available to accurately estimate the transient response of VO2, we developed a new technique, using random exercise. In 15 patients who underwent successful PTMC, we repeated the conventional maximal exercise test and the random exercise test before and within a few days after PTMC. For the random exercise test, we intermittently imposed upright bicycle exercise at 50 W, according to a random binary sequence, while measuring breath-by-breath VO2. After determining the transfer function relating workload to VO2, we computed the high resolution VO2 response to a hypothetical step increase in exercise. Despite improvements in resting hemodynamics and New York Heart Association (NYHA) Class, peak VO2 improved insignificantly (952 +/- 271 vs 1,029 +/- 342 ml/min, P = 0.063) shortly after successful PTMC. In contrast, the amplitude of the VO2 step response increased significantly in the early-to-mid portion (28-76s; P < 0.01-0.05). The remaining portion was unchanged. Consequently, the time constant shortened from 64 +/- 26 to 48 +/- 22s (P < 0.05). The maximal Borg scale value during random exercise decreased significantly (13.1 +/- 1.8 vs 11.4 +/- 1.1; P < 0.01). We conclude that the VO2 step response, using the random exercise test, is more sensitive than peak VO2 in detecting the functional improvement that is coupled with the hemodynamic improvement immediately after PTMC.
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