Effects of pulmonary rehabilitation on cardiac magnetic resonance parameters in patients with persistent dyspnea following pulmonary embolism.

Background: Persistent dyspnea and reduced exercise capacity is common in pulmonary embolism (PE) survivors. Although improved right ventricular function after pulmonary rehabilitation has been demonstrated in chronic thromboembolic pulmonary hypertension, it is still unknown whether a similar effect also occurs in other patients with dyspnea after pulmonary embolism. Purpose: The aim of this study was to explore potential effects of a pulmonary rehabilitation program on cardiac structure and function as assessed with cardiac magnetic resonance (CMR). Material and methods: Twenty-six PE survivors with persistent dyspnea were included. Right and left ventricular assessment with CMR was performed before and after an eight-week pulmonary rehabilitation program. Results: Dyspnea as measured by the Shortness of Breath Questionnaire improved significantly after rehabilitation: 15 (IQR: 7-31) versus 8 (IQR: 3-17). Absolute right ventricular global longitudinal strain by CMR was reduced from 19% to 18% (95% CI of difference: 0-3 percent points), and absolute RV lateral strain from 26% to 24% (95% CI of difference: 1-4 percent points). Right ventricular mass was reduced after rehabilitation from 49 g to 44 g (95% CI of difference: 2-8 g). Conclusion: Although there was a substantial improvement in dyspnea after rehabilitation, we found only a minor reduction in absolute right ventricular longitudinal strain and right ventricular mass. No other CMR parameter changed. We therefore suggest that rehabilitation effect of in this patient group was not primarily mediated by cardiac adaptions.

Aqueductal Stroke Volume: Comparisons with Intracranial Pressure Scores in Idiopathic Normal Pressure Hydrocephalus.

BACKGROUND AND PURPOSE: Aqueductal stroke volume from phase-contrast MR imaging has been proposed for predicting shunt response in normal pressure hydrocephalus. However, this biomarker has remained controversial in use and has a lack of validation with invasive intracranial monitoring. We studied how aqueductal stroke volume compares with intracranial pressure scores in the presurgical work-up and clinical score, ventricular volume, and aqueduct area and assessed the patient's response to shunting. MATERIALS AND METHODS: Phase-contrast MR imaging was performed in 21 patients with probable idiopathic normal pressure hydrocephalus. Patients were selected for shunting on the basis of pathologically increased intracranial pressure pulsatility. Patients with shunts were offered a second MR imaging after 12 months. Ventricular volume and transverse aqueductal area were calculated, as well as clinical symptom score. RESULTS: No correlations between aqueductal stroke volume and preoperative scores of mean intracranial pressure or mean wave amplitudes were observed. Preoperative aqueductal stroke volume was not different between patients with shunts and conservatively treated patients (P = .69) but was correlated with ventricular volume (R = 0.60, P = .004) and aqueductal area (R = 0.58, P = .006) but not with the severity or duration of clinical symptoms. After shunting, aqueductal stroke volume (P = .006) and ventricular volume (P = .002) were reduced. A clinical improvement was seen in 16 of 17 patients who had shunts (94%). CONCLUSIONS: Aqueductal stroke volume does not reflect intracranial pressure pulsatility or symptom score, but rather aqueduct area and ventricular volume. The results do not support the use of aqueductal stroke volume for selecting patients for shunting.

Determination of genuine diffusivities in heterogeneous media using stimulated echo pulsed field gradient NMR.

Pulsed field gradient (PFG) NMR diffusion measurements in heterogeneous media may lead to erroneous results due to the disturbing influence of internal magnetic field gradients. Here, we present a simple theoretical model which allows one to interpret data obtained by stimulated spin echo PFG NMR in the presence of spatially varying internal field gradients. Using the results of this theory, the genuine self-diffusion coefficients in heterogeneous media may be extrapolated from the dependence of the apparent diffusivities on the dephasing time of the simulated echo PFG NMR sequence. Experimental evidence that such extrapolation yields satisfactory results for self-diffusion of hexadecane in natural sediments (sand) and of n-octanol in doped MgO pastes is provided.

NMR studies of water diffusion and relaxation in hydrating slag-based construction materials.

The NMR relaxation properties of hydrating blast-furnace slag cements have recently been shown to be dominated by the effect of water self-diffusion in internal magnetic field gradients in the pastes. While this was suggested on the basis of NMR relaxometry and magnetic susceptibility data, we report here the results from first direct studies of the water self-diffusion in the hydrating paste using a specialized PFG sequence and very intensive magnetic field gradient pulses.

Cation diffusion in cartilage measured by pulsed field gradient NMR.

In this study, the pulsed field gradient (PFG) nuclear magnetic resonance (NMR) technique was used for the investigation of (1) concentration and compression effects on cation self-diffusion, and (2) restricted diffusion of cations in cartilage. Since physiologically relevant cations like Na+ are difficult to investigate owing to their very short relaxation times, the cations tetramethylammonium (TMA) and tetraethylammonium (TEA) were employed for diffusion studies in samples of explanted cartilage. Results indicated that the diffusion of monovalent cations shows strong similarities to observations already made in studies of the diffusion of water in cartilage: with increasing compression, i.e. decreasing water content, the diffusion coefficient of the cation decreases concomitantly. The diffusion coefficients also showed a decrease with increasing cation concentrations, basically reflecting the corresponding decrease in the water content. Both results could be explained by the well-established model of Mackie and Meares. This, together with the similarity of the diffusion coefficient D in cartilage relative to free solution (about 50%) for both cations, is consistent with the view that the water content and not the charge is the most important determinant of the intratissue diffusivity of monovalent cations. Diffusion studies with increasing observation times showed strong evidence of restricted diffusion, allowing the estimation of the geometry of barriers within cartilage.