Low-intensity Exercise Testing Research Articles

Comparison of Performance in the Six-Minute Walk Test (6MWT) between Overweight/Obese and Normal-Weight Children and Association with Haemodynamic Parameters: A Cross-Sectional Study in Four Primary Schools.

Physical activity plays a pivotal role in preventing obesity and cardiovascular risks. The six-minute walk test (6MWT) is a tool to assess functional capacity and predict cardiovascular events. The aim of this cross-sectional study was to compare the performance and haemodynamic parameters before and after a 6MWT between obese/overweight vs. normal-weight children (average age 8.7 ± 0.7 years) participating in a project involving four primary schools in South Verona (Italy). Validated questionnaires for physical activity and diet, as well as blood drops, were collected. Overweight or obese children (OW&OB; n = 100) covered a shorter 6MWT distance compared to normal-weight children (NW, n = 194). At the test's conclusion, the OW&OB group exhibited a higher Rate Pulse Product (RPP = Systolic Blood Pressure × Heart Rate) as compared to the NW. Body Mass Index, waist-to-height ratio, fat mass by electrical impedance, and trans fatty acids showed direct correlations with pre and post-test haemodynamic parameters, such as RPP, and inverse correlations with oxygen saturation. OW&OB children demonstrated lower performance in this low-intensity exercise test, along with an elevated haemodynamic response. Excess fat in childhood can be considered a risk factor for haemodynamic stress, with potential deleterious consequences later in life. Efforts should be initiated early to break this cycle.

Sympathetic activity–associated periodic repolarization dynamics predict mortality following myocardial infarction

Enhanced sympathetic activity at the ventricular myocardium can destabilize repolarization, increasing the risk of death. Sympathetic activity is known to cluster in low-frequency bursts; therefore, we hypothesized that sympathetic activity induces periodic low-frequency changes of repolarization. We developed a technique to assess the sympathetic effect on repolarization and identified periodic components in the low-frequency spectral range (≤0.1 Hz), which we termed periodic repolarization dynamics (PRD). We investigated the physiological properties of PRD in multiple experimental studies, including a swine model of steady-state ventilation (n=7) and human studies involving fixed atrial pacing (n=10), passive head-up tilt testing (n=11), low-intensity exercise testing (n=11), and beta blockade (n=10). We tested the prognostic power of PRD in 908 survivors of acute myocardial infarction (MI). Finally, we tested the predictive values of PRD and T-wave alternans (TWA) in 2,965 patients undergoing clinically indicated exercise testing. PRD was not related to underlying respiratory activity (P<0.001) or heart-rate variability (P=0.002). Furthermore, PRD was enhanced by activation of the sympathetic nervous system, and pharmacological blockade of sympathetic nervous system activity suppressed PRD (P≤0.005 for both). Increased PRD was the strongest single risk predictor of 5-year total mortality (hazard ratio 4.75, 95% CI 2.94-7.66; P<0.001) after acute MI. In patients undergoing exercise testing, the predictive value of PRD was strong and complementary to that of TWA. We have described and identified low-frequency rhythmic modulations of repolarization that are associated with sympathetic activity. Increased PRD can be used as a predictor of mortality in survivors of acute MI and patients undergoing exercise testing. ClinicalTrials.gov NCT00196274. This study was funded by Angewandte Klinische Forschung, University of Tübingen (252-1-0).

402 Low-intensity exercise testing for assessment of ventilatory efficiency in heart failure patients under cardiac resynchronization therapy

402 Low-intensity exercise testing for assessment of ventilatory efficiency in heart failure patients under cardiac resynchronization therapy

402 Low-intensity exercise testing for assessment of ventilatory efficiency in heart failure patients under cardiac resynchronization therapy

402 Low-intensity exercise testing for assessment of ventilatory efficiency in heart failure patients under cardiac resynchronization therapy

Prolonged exercise testing in two children with a mild Multiple Acyl-CoA-Dehydrogenase deficiency

BackgroundMultiple Acyl-CoA-Dehydrogenase deficiency (MADD) is an inherited metabolic disorder characterized by impaired oxidation of fatty acids and some amino acids.MethodsWe were interested whether children with MADD could tolerate a prolonged low-intensity exercise test and if this test could have any additional diagnostic value. Therefore, we performed a maximal exercise test and a low-intensity prolonged exercise test in 2 patients with MADD and in 5 control subjects. During a prolonged exercise test the subjects exercised on a cycle ergometer at a constant workload of 30% of their maximum for 90 minutes and heart rate, oxygen uptake, fuel utilization and changes in relevant blood and urinary parameters were monitored.ResultsThe tests were tolerated well. During the prolonged exercise test the fatty acid oxidation (FAO) was quite low compared to 5 control subjects, while characteristic metabolites of MADD appeared in plasma and urine.ConclusionWe suggest that the prolonged exercise test could be of diagnostic importance and might replace the fasting test as a diagnostic procedure in some cases, particularly in patients with anamnestic signs of intolerance for prolonged exercise.

Combining low-intensity and maximal exercise test results improves prognostic prediction in chronic heart failure

ObjectivesThis study investigated the combination of maximal and low-intensity exercise testing in predicting prognosis in chronic heart failure (CHF), using one single exercise test (two-step protocol). BackgroundRisk assessment based on any single factor has limited accuracy and reproducibility. MethodsTreadmill exercise testing was performed in 202 consecutive CHF patients (174 male; mean age 52 ± 11 years) using “breath-by-breath” gas exchange monitoring. Oxygen uptake (Vo2) kinetics were defined as oxygen deficit (ΔVo2× time [rest to steady state] − Σ Vo2[rest to steady state]) and mean response time (MRT = oxygen-deficit/ΔVo2). Peak Vo2(Vo2max) was defined as the highest Vo2. Mean follow-up was 873 ± 628 days. The primary end point was cardiac mortality and the need for urgent heart transplantation. ResultsForty-four patients (22%) died and 15 (7%) were urgently transplanted. In both univariate and multivariate analyses, MRT >50 s was the most powerful predictor of the primary end point (hazard ratio [HR] 4.44), followed by predicted Vo2max <50% (HR 3.50) and resting systolic blood pressure <105 mm Hg (HR 2.49, all p < 0.001). A majority (n = 130 [64%]) had one or none of these risk factors, with a one-year event rate of only 3%. Patients with two risk factors (n = 45 [22%]) were at medium risk (one-year event rate of 33%). Twenty-seven patients (13%) had all three risk factors, with a one-year event rate of 59%. The area under the curve, using the number of risk factors, was 0.86 ± 0.04 for the primary end point at one year. These results were independent of medication, in particular, beta-blockade. ConclusionsA combination of low-intensity and maximal exercise test results improves assessment of prognosis in patients with CHF.

Effect of dietary lipid on response to exercise: relationship to metabolic adaptation.

The aim of the present study was to relate changes in muscle oxidative capacity and free fatty acid flux in response to oil supplementation to fuel utilisation during subsequent exercise of varying intensities. Following 10 weeks of oil supplementation there was an increased capacity for fat utilisation during low and moderate intensity exercise as indicated by a lower respiratory exchange ratio (RER) (P<0.05). We suggest that this was contributed to by a parallel increase in the oxidative capacity of muscle as indicated by a significant increase in the activity of muscle citrate synthase (CS) (P<0.05) and trend towards an increase in beta-Hydroxy acyl CoA dehydrogenase (beta-HAD), (P>0.05). In addition, low and moderate intensity exercise was associated with an exercise-induced increase in plasma free fatty acids (FFA) and there was an increased facility for uptake of FFA by working muscle from circulating triglycerides, as suggested by an increase in TL activity (P<0.01). The response to oil supplementation varied between individual horses and the magnitude of response, during the low intensity exercise test, in terms of difference in RER was correlated to the increase in CS activity (r2 = 0.95, P<0.05) following oil supplementation. There was no similar significant correlation with respect to FFA, TL or beta-HAD activity (P>0.05). The hypothesis in this study was that the metabolic adaptation to oil supplementation, in terms of exercise response, was related to individual increases in the activities of CS, beta-HAD or TL. However, the relationship between these parameters was unequivocal and requires further investigation, ideally with a larger group of horses.

Early Dipyridamole Imaging Predicts Post-MI Events

Low-intensity exercise testing five to seven days after acute MI is a typical noninvasive risk stratification approach. This multicenter U.S. study