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Biomedical subjects

J Malak

Publications and source records attributed to J Malak.

9 recordsLinked to original sources

Leishmania donovani invasion of the blood in a child with dermal leishmaniasis.

Cutaneous leishmaniasis is highly endemic in eastern Mediterranean countries. The causative organisms are Leishmania tropica or Leishmania major but, further west, variants of Leishmania infantum frequently cause cutaneous leishmaniasis. We report a young girl from Beirut with an acute cutaneous leishmaniasis in whom the causative organism was cultured from both the skin lesion and the blood in the absence of any signs or symptoms typical of systemic involvement. The parasite was found to have a zymodeme typical of organisms belonging to the L. donovani complex. With the negative past history and in the absence of anti-Leishmania antibodies in her serum, post-kala-azar dermal leishmaniasis is an unlikely possibility, especially in view of the rarity of the complication in this part of the world. The infection was probably acquired during a recent visit to Aleppo, where cutaneous leishmaniasis is hyperendemic as similar cases have not been reported in Beirut. This case indicates the need to consider L. infantum strains in addition to L. tropica in cutaneous disease in Aleppo. This case also demonstrates that L. infantum can spread by the haematogenous route, even in a child without evidence of the immunosuppression, which usually predisposes to such spread.

Animals↗

Otic rosacea.

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Ear Canal↗

A modelized distribution of actomyosin interactions in the vertebrate cardiac muscle.

Preliminary assumption of this model is that interactions between actin and myosin presupposes an exact three-dimensional geometrical correspondence between sites, due to the very short time constants present under physiological conditions. Only small and controlled torsions of the actin filaments are accepted. The model uses geometrical information concerning orientations and dimensions of myosin crossbridges and actin monomeres to modelize the distribution of their inter-actions. An orientation map of actin sites in the cross-section perpendicular to the filament axis is proposed, adapted to the specific filament array of vertebrate muscle. Orientation of myosin crossbridges follows Luther's rules. According to the model, any interaction between actin and myosin implies the superimposition of their respective cross-sectional planes. The axial length of actin monomere is 55 A; the distance between two crossbridges along the myosin filament axis is 143 A. The following properties are derived: 1) The shortening step of the sliding actin filament must be a multiple of 11 A (highest common factor). Taking into account the staggered disposition of the two actin strands and the presence of two heads for each cross-bridge, the most probable value for this shortening step is equal to 99 A. A specific scheme is proposed to describe the shortening process. The behavior of the modelized crossbridge does not need any elastic structure--2) Planes situated at 715 A (lowest common multiple) of actin and myosin coinciding planes are also in coincidence. In a hemi-sarcomere the maximal number of these planes, referred to as simultaneously activable planes, is 10 (20 if both myosin heads are considered). The proportion of interactions authorized by the site orientations is 1/12. In the model, the concept of randomly recruited crossbridges is replaced by a discretized recruitment, based on geometrical properties at an ultrastructural level. The proposed distribution is homogeneous: it can be extended radially in the sarcomere and authorizes the actin filament sliding in the whole physiological range under the control of a dual activation function, reproducing Ca++ temporal and spatial distribution.

Actins↗

Relations between posterior wall kinetics during diastole and left ventricular filling.

M-mode echocardiography reveals an abrupt change between early and late left ventricular posterior wall kinetics during relaxation. No attempt has been previously made to relate this wall kinetic change and transmitral flow rate. In 25 normal subjects, 14 patients with dilated cardiomyopathy (Group 1) and 17 patients with hypertrophic cardiomyopathy (Group 2), M-mode echocardiographic studies were performed on the posterior wall and mitral valve. Transient values of mitral orifice area were calculated and transmitral flow velocities were recorded: area and velocity data yielded transmitral flow rates. Time intervals were determined from mitral opening to peak early area, velocity and flow rate and to posterior wall slope change. An additional group included five patients with a mitral prosthesis. The posterior wall slope change was present when part of the myocardial structures were almost akinetic or when mitral chordae tendineae were absent; slope change appeared as a regional phenomenon in the free wall. In the normal subjects, close values were found for the four time intervals. In the patients with dilated and hypertrophic cardiomyopathy, peak early velocity (95.7 +/- 16.7 and 146.2 +/- 31.4 ms, respectively), peak flow rate (84.7 +/- 18.2 and 137.4 +/- 29.5 ms) and time to slope change (91.4 +/- 18.6 and 133.6 +/- 32.7 ms) were significantly delayed (p less than 0.001) in comparison with peak area (56.6 +/- 9.5 and 84.3 +/- 22.5 ms). Slope change does not indicate the end of the early filling phase but, rather, its transition from acceleration to deceleration. Time to peak velocity or time to peak filling rate must be considered in a relaxation analysis.

Blood Flow Velocity↗

[Normalization of the dimensions of the left ventricle as measured by echocardiography].

An M mode echocardiographic study was performed, of left ventricular dimensions and wall thickness in two series of normal (N1, N2) and pathological (P1, P2) subjects. In the more recent series (N2 = 40, P2 = 17) data acquisition was facilitated by tests deduced from the technique of ultrasound transit time. The parameters compared were based on: 1) the proportionality between fractional shortening and fractional thickening (N1: not significant; N2: p less than 0.001), 2) the relationship between systolic radius and wall thickness (linear correlation, r = 0.95, between N2 and P2). The slope seemed to be related to the initial condition of contraction, the ratio of end diastolic wall thickness/radius (N1: p less than 0.01). There are several ways of normalising myocardial surface of section in adults and children; the normal surface is related to body surface area (r = 0.87; p less than 0.001 between calculated and predicted values for a N2 mean of 9.3 +/- 0.06 cm2/m2). The end diastolic diameters and wall thicknesses correlated with body surface area but the coefficients were not as statistically significant due to physiological variations in chamber filling. The indexed myocardial surface was increased (p less than 0.001) in the pathological series. The introduction of these tests improves the reliability of echocardiographic data. The use of several measurements simultaneously allows normalisation of body surface area and increases the diagnostic efficacy.

Echocardiography↗