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Since 1991, the Virtual Reality Applications Research Team (VIRART) has been specifying, building and evaluating VEs for educational applications. In the Learning in Virtual Environments (LIVE) program, the understanding of […]

Patients with heart failure frequently report that leg fatigue limits maximal exercise capacity. However, objective documentation of muscle fatigue has not been obtained in such patients. In normal subjects, muscle fatigue during constant work load exercise is associated with an increase in electrical activity generated per contraction due to use of additional muscle fibers to compensate for fiber fatigue. The present study was performed to determine if this approach can be used to document muscle fatigue in patients with heart failure. Vastus lateralis surface electromyograms were monitored in 8 ambulatory patients with nonedematous heart failure and 6 normal subjects during maximal bicycle exercise (20 W increments every 2 minutes). The electromyogram was stored on tape and subsequently analyzed for integrated root-mean-square voltage/contraction (iRMSV). At each work load, the iRMSV of the first and last 30 seconds of the work load were compared. The maximal work load achieved by patients with heart failure was significantly lower (73 [ + or - ] W) than that by normal subjects (150 [ + or - ] w; p The data indicate that the surface electromyogram can be used to detect skeletal muscle fatigue in patients with heart failure. This approach provides an objective method of assessing exertional fatigue in such patients and may be useful for assessing the efficacy of therapeutic interventions.

Patients with heart failure frequently exhibit an excessive ventilatory response to exercise, which is acutely unaltered by therapeutic interventions. To investigate whether these ventilatory responses resolve after cardiac transplantation, 15 ambulatory patients with severe heart failure underwent exercise testing with measurement of respiratory gases before and 1.4 [+ or -] 0.6 months after transplantation. Ventilatory response was also measured in 7 age-matched, sedentary control subjects. Left ventricular ejection fraction at rest and hemodynamic measurements were obtained before and after transplantation in all patients. After transplantation, ejection fraction at rest increased from 16 [+ or -] to 56 [+ or -] 10%, pulmonary capillary wedge pressure declined from 26 [+ or -] 8 to 12 [+ or -] 5 mm Hg, and cardiac index increased from 1.7 [+ or -] 0.5 to 2.8 [+ or -] 0.5 liters/min/[m.sup.2] (all p

Dobutamine is known to increase leg blood flow during exercise in patients with heart failure. However, it is uncertain whether the increased flow is delivered to working skeletal muscle. In 7 patients with heart failure, the effects of dobutamine were examined on calf phosphorus-31 magnetic resonance spectroscopy (MRS) spectra and femoral vein blood flow during rest and upright plantar flexion. During upright plantar flexion every 3 seconds, dobutamine increased femoral venous blood flow (control 1.7 [+ or -] 0.1; dobutamine 2.1 [+ or -] 1.0 liters/min; p (Am J Cardiol 1990;6S:1121-1126), Patients with heart failure are limited in their capacity for exercise. Limitations on blood flow, combined with a suspected abnormality in the coronary arteries' ability to dilate in response to increased demands, result in an underperfusion of heart muscle during exercise. One might expect, therefore, that a drug that increases cardiac output and improves peripheral blood flow might also increase tolerance for exercise. However, at least for the drug dobutamine, this is not the case. One possible explanation is that although dobutamine improves blood flow to skeletal muscle, this improvement does not directly translate into enhanced oxygen availability for the muscle tissues. To examine this possibility, phosphorus-31 magnetic resonance spectroscopy (MRS; not magnetic resonance imaging) was used. Phosphorus-31 is the naturally-occurring, non-radioactive isotope of phosphorus and is detectable by magnetic resonance spectroscopy. Furthermore, MRS is able to distinguish whether the phosphorus atoms are part of inorganic phosphate or phosphocreatine, and thus provides a noninvasive way to monitor the metabolic activity of skeletal muscle. For example, an increase in the availability of oxygen to suffocating skeletal muscle should result in the increase in phosphocreatine energy stores and a decrease in the muscle's inorganic phosphate. The effect of dobutamine was measured in seven patients with congestive heart failure. Venous blood flow from the leg and hemoglobin oxygen saturation were monitored to confirm that the dobutamine was, indeed, having its effect on blood flow and oxygen saturation. The ratio of inorganic phosphate to phosphocreatine is linearly related to the oxygen consumption, and improvements in oxygen supply should result in a lower phosphorus ratio at a given oxygen consumption. This was not observed with dobutamine, indicating that although the drug improves cardiac function and peripheral blood flow, there is little improvement in the availability of oxygen within the skeletal muscles themselves. (Consumer Summary produced by Reliance Medical Information, Inc.)