On the calculation of transcallosal conduction time using transcranial magnetic stimulation.

Transcallosal conduction time (TCT), based on the results of transcranial magnetic stimulation studies, is currently calculated as a function of the ipsilateral silent period (iSP) and of the motor evoked potential (MEP) obtained from a target muscle (TCTcurrent = iSP latency - MEP latency). We argue that this measure overestimates TCT and may lead to a bias in statistical group comparisons. We propose an alternative measure, TCTproposed, which we defined as TCTproposed = iSP latency - cSP latency, where cSP is the contralateral silent period. We report our results on the comparison of the two measures in twenty healthy individuals and provide a theoretical basis for TCTproposed.

Identification of echocardiographic indices for the early detection of left-ventricular systolic dysfunction in beta-thalassaemia via Self-Organizing Maps: a data-exploration study.

Congestive heart failure (CHF) remains the primary cause of death in patients suffering from beta-thalassaemia major. Its early detection allows the prompt initiation of aggressive chelation therapy, when the condition can still be reversed. We aimed at identifying echocardiographic indices for the early detection of left ventricular (LV) systolic dysfunction, the physiological abnormality underlying CHF, in these patients. We used Self-Organizing Maps (SOMs)--an artificial neural network--for identifying novel correlations within our Electronic Healthcare Record (EHCR) database on beta-thalassaemia. We sought echocardiographic parameters that are correlated to future deterioration of the LV ejection fraction and therefore constitute early signs of LV systolic dysfunction. At the same time, we evaluated SOMs as tools for exploring clinical datasets and make recommendations on the setup of the SOM algorithm that is appropriate for such tasks. We found that high values of the LV end-systolic diameter index and of the E/A ratio are early indications of LV systolic dysfunction. From a technical point of view, zero-mean unit-variance normalization of the input data, a large initial neighbourhood radius and a rectangular SOM grid produced optimal maps for the purpose of detecting clinical correlations. We have successfully used SOMs for exploring a clinical dataset and for creating novel medical hypotheses. A clinical study has been launched to confirm these hypotheses, and initial results are encouraging.

Cardiovascular adaptation to chronic anemia in the elderly: an echocardiographic study.

OBJECTIVE: To study the effects of chronic severe anemia on the aging heart. METHODS: We studied 41 elderly patients (mean age 69.8 yr, standard deviation [SD] 3.9 yr) suffering from chronic severe anemia (mean hemoglobin 6.3, SD 0.5 g/dL) with no history of cardiac disease, along with 63 healthy age- and sex-matched controls. Assessment included physical examination, electrocardiogram and Doppler echocardiography. RESULTS: Although heart rates were similar between patients and controls, arterial blood pressures were significantly lower in patients (mean pressure 92.7 mm Hg, SD 7.9, v. mean 102.1 mm Hg, SD 3.5; p < 0.001). No patient was found to have congestive heart failure. Patients with chronic anemia had larger diameters of the left (end-systolic 35.28, SD 4.20, v. 33.73, SD 2.08 mm, p < 0.05; end-diastolic 53.33, SD 4.55, v. 50.37, SD 2.10 mm, p < 0.001) and right ventricles (30.76, SD 3.98, v. 29.04, SD 2.04 mm; p < 0.05), and greater left-ventricular mass (277.64, SD 62.85, v. 212.91, SD 24.87 g; p < 0.001). Fractional shortening did not differ significantly (0.33, SD 0.04, v. 0.33, SD 0.03). The load-independent end-systolic index was lower in patients (2.67, SD 0.56, v. 3.87, SD 0.49 kdyn x m2/cm5; p < 0.001) along with end-systolic stress and total systemic resistance (p < 0.001) than controls, whereas the cardiac index was higher (4.31, SD 1.29, v. 2.73, SD 0.51 L/min/m2; p < 0.001). Differences between the 2 groups in diastolic function indices and pulmonary arterial pressures were not statistically significant. INTERPRETATION: Chronic severe anemia is well tolerated by the aging heart. Neither congestive heart failure nor clearly evident left-ventricular dysfunction were encountered. The heart exhibited an adaptive potential through remodelling by means of the Frank-Starling mechanism and afterload reduction. However, the lower end-systolic index in patients suggests that ventricular performance was marginally compromised. This state of high output was achieved mainly by increased stroke volume, with little contribution from heart rate.