PERCUTANEOUS TRANSVENOUS MITRAL COMMISSUROTOMY IMMEDIATELY RESTORES QUICK RESPONSE OF VO2 TO MILD EXERCISE DESPITE INSIGNIFICANT INCREASES IN PEAK VO2

Percutaneous transvenous mitral commissurotomy (PTMC) increases peak o xygen uptake (VO2) chronically, but not acutely, despite early symptom atic improvements. Analysis of transient VO2 responses to submaximal e xercise (an exercise regimen more comparable to the patients' daily ac tivities than that provided by maximal exercise testing), may be sensi tive in detecting the acute hemodynamic benefits of PTMC. Since no met hods are available to accurately estimate the transient response of VO 2, we developed a new technique, using random exercise. In 15 patients who underwent successful PTMC, we repeated the conventional maximal e xercise test and the random exercise test before and within a few days after PTMC. For the random exercise test, we intermittently imposed u pright 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 VO 2 response to a hypothetical step increase in exercise. Despite improv ements in resting hemodynamics and New York Heart Association (NYHA) C lass, peak VO2 improved insignificantly (952 +/- 271 vs 1,029 +/- 342 ml/min, P = 0.063) shortly after successful PTMC. In contrast, the amp litude of the VO2 step response increased significantly in the early-t o-mid portion (28-76 s; P < 0.01-0.05). The remaining portion was unch anged. Consequently, the time constant shortened from 64 +/- 26 to 48 +/- 22 s (P < 0.05). The maximal Borg scale value during random exerci se decreased significantly (13.1 +/- 1.8 vs 11.4 +/- 1.1; P < 0.01). W e conclude that the VO2 step response, using the random exercise test, is more sensitive than peak VO2 in detecting the functional improveme nt that is coupled with the hemodynamic improvement immediately after PTMC.