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M M Claessens

Publications and source records attributed to M M Claessens.

3 recordsLinked to original sources
PubMed2001

Quantitative NMR microscopy of osmotic stress responses in maize and pearl millet.

The effect of osmotic stress (-0.35 MPa) on the cell water balance and apical growth was studied non-invasively for maize (Zea mays L., cv. LG 11) and pearl millet (Pennisetum americanum L., cv. MH 179) by (1)H NMR microscopy in combination with water uptake measurements. Single parameter images of the water content and the transverse relaxation time (T(2)) were used to discriminate between the different tissues and to follow the water status of the apical region during osmotic stress. The T(2) values of non-stressed stem tissue turned out to be correlated to the cell dimensions as determined by optical microscopy. Growth was found to be strongly inhibited by mild stress in both species, whereas the water uptake was far less affected. During the experiment hardly any changes in water content or T(2) in the stem region of maize were observed. In contrast, the apical tissue of pearl millet showed a decrease in T(2) within 48 h of stress. This decrease in T(2) is interpreted as an increase in the membrane permeability for water.

Adaptation, Physiological↗
PubMed2001

Supernormal left ventricular diastolic function in triathletes.

We studied the structural and functional heart adaptations of 52 male triathletes compared with those of 22 active, nonathletic men, by 2-dimensional Doppler echocardiography. Left ventricular diastolic function was evaluated by recording transmitral flow velocities. To exclude the influences of preload, left atrial pressure, and aortic pressure, left ventricular diastolic function was also evaluated by pulsed Doppler tissue imaging. Significant differences in cardiac structure and function were observed between the 2 groups. In the triathletes, the left ventricular diastolic function was completely normal, despite signs of mixed eccentric and concentric left ventricular hypertrophy, and this function was better than that in the control group. We measured 2 aspects of the late passive diastolic filling period in the triathletes: ASEAC value (the amplitude of excursion of the interventricular septal endocardium at the end of left ventricular diastole just after atrial contraction); and the time between onset of the P wave on the electrocardiographic tracing and onset of systolic septal movement on M-mode echocardiography. Pulsed Doppler tissue imaging confirmed these results. The E/A ratios (peak early left ventricular diastolic motion velocity divided by the peak atrial systolic motion velocity), measured by pulsed Doppler tissue imaging, yielded even more evidence for supernormal left ventricular diastolic function in the triathletes. Left ventricular relaxation and filling properties were measured along the longitudinal and transverse axes by pulsed Doppler tissue imaging, which was useful for evaluating left ventricular diastolic function. We determined that triathletes may develop supernormal left ventricular diastolic function with increased diastolic reserves.

Adult↗