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Biomedical subjects

Bui-Mong-Hung

Publications and source records attributed to Bui-Mong-Hung.

At least 19 recordsLinked to original sources
PubMed1984

A simulation method for the study of laser transillumination of biological tissues.

The Monte-Carlo method is employed to simulate the illumination of a blood slab by a continuous laser. It is assumed that the geometry of the medium is bidimensional and that scattering or absorption takes place only when a photon strikes a red blood cell. The parameters involved in the calculations concern the photons free path lengths between two collisions, the scattering angles and the absorption probability at collision. These parameters are assessed according to experimental or literature data. Fortran programs allow the computation of diffuse and collimated transmittances (Td and Tc, respectively), of transmittance measured with an optic fiber Tf and of reflectance R. The variations of Tc and Tf with blood thickness are in accordance with established laws. Moreover, measured and computed reflectances change with hematocrit ratio in a similar way. This work demonstrates that the Monte-Carlo method is a simple reliable tool which can be used to provide a realistic model of laser penetration in complex biological structures. Moreover, this method will permit investigations in laser tomo-spectrometry by providing a useful simulation of the interaction of ultrashort light pulses with biological media.

Animals↗
PubMed1984

Imaging mammalian tissues and organs using laser collimated transillumination.

Images of mammalian organs were built up using a Laser collimated transillumination device equipped with a bidirectional scanning setup. A microcomputer was used to run the scanning process, acquisition of detected signals and images restitution. The images featured a satisfactory resolution of optical discontinuities on both sample surfaces. Light scattering within biological tissues restricted the spatial discrimination encountered with geometrical selection approach. By combining space and time resolution at various wavelengths, the production of an efficient tomospectroscopy could be envisaged.

Animals↗
PubMed1984

Overall myocardial energetics in physiological conditions and in acute volume overloading.

Left ventricular heat production (PH,lv) was compared with myocardial O2 consumption (P met O2) and mechanical parameters in intact anaesthetized dogs before and after acute volume overload induced by a perfusion of LMW dextran. From myocardial blood flow and coronary arterio-venous temperature differences, the coronary heat loss was determined. Thermodilution techniques were used to estimate the ratio between heat carried away by the coronary system and total heat production as the left ventricular volumes. Compared with P met O2, PH,lv bore a linear correlation. Heat production per beat was highly correlated to mean systolic wall force, midwall circumferential length, midwall fibre shortening and mean circumferential shortening rate (MCSR). Mechanical efficiency computed from heat production (EH) appeared to be very close to the efficiency computed from oxygen consumption (EO). Acute overload was characterized by a very large increase in both stroke volume and MCSR. The dramatic increase observed in heart external power was accompanied by a moderate increase in PH,lv and mechanical efficiency. Nevertheless, the changes in efficiency appeared to be strongly dependent upon the changes observed in heart rate (HR). When HR was increased, the heat production per beat was moderately decreased and efficiency was drastically improved. Conversely, dogs in which HR remained stable exhibited a marked increase in the energetic cost of each beat, with efficiency being practically unmodified. Thus, since myocardial energetics is involved in acute volume overload, two possible means of adaptation may be considered: (a) tachycardia may alleviate the energetic cost of each beat, thus improving heart mechanical efficiency and (b) conversely, if HR remains stable, it may do so at the expense of the energetic cost of the myocardium for each beat, with efficiency not actually being enhanced.

Animals↗
PubMed1982

A hybrid device for measurement of left ventricular heat production.

The presented hybrid system allows precise temperature measurements in various sites of the circulation, from the acquisition and preprocessing of dilution curves. From haemodynamic data and left ventricular heat production, an in situ estimate of left heart efficiency is made available. A simplifying hypothesis allows the determination of total left ventricular heat production from three data inputs: (1) the coronary sinus blood flowrate, (2) the thermal coronary veno-arterial difference, (3) the ratio of thermodilution curves areas recorded in the aortic root and the coronary sinus, following a rapid injection in the left ventricular cavity of cold isotonic glucose. Experiments were performed on anaesthetized, artificially ventilated, closed-chest dogs, into which five catheters and probes had been inserted.

Animals↗
PubMed1981

Determination of left ventricular heat production in working dog heart.

1 degree Total left ventricular heat production was reliably estimated from the coronary blood flow, the coronary arteriovenous thermal difference and the thermodilution curve areas recorded in aortic root and in coronary sinus after injection of cold glucose solution into the left ventricular cavity. The assumption was made that the distribution of a cold solution, purposely introduced into the coronary arteries, obeys the same law as the heat generated by the myocardium. 2 degrees Temperature measurements were achieved with thermistors and a linear ohmmeter. Experiments were performed on thoracotomized dogs, allowing the utilization of an ultrasonic method for determination of the entire coronary sinus blood flow diverted through a cannula positioned in the coronary sinus. The spontaneous changes in acid-base balance and hemodynamic state, which were not systematically avoided, provided a fairly large interval of variation for coronary flow and myocardial oxygen consumption. 3 degrees Within the power interval of 0.5-2.2 watts per 100 g of left ventricular weight, there was a good linear correlation between left ventricular oxygen consumption and the sum of left ventricular heat production and external pressure power. 4 degrees These results suggest that the proposed method is a valuable approach for determination of the cardiac energetics in the in situ working heart. This method permitted repeated determinations of left myocardial heat production and may lead to a practical approach for measuring the left ventricular efficiency in intact animals.

Animals↗
PubMed1976

Biochemical heterogenity of the left ventricular myocardium: transmural and base-apex gradients on H.E.P. contents of the well oxygenated perfused dog heart.

An investigation into the contents (mumol/g w.w.) of the creatine phosphate (CP) and adenosine triphosphate (ATP) of various myocardial regions was performed on the empty beating isolated blood perfused dog heart. Across the myocardial wall, CP concentration was higher in the outer portion (9.03 +/- 0.18) than in the inner portion (8.59 +/- 0.20) (P less than 0.05). In addition to this transmural gradient, a longitudinal gradient was found: tissue contents of both CP and ATP decrease significantly from the base (CP: 9.70 +/- 0.28, ATP: 5.84 +/- 0.20) to the apex (CP: 8.69 +/- 0.27, ATP: 5.57 +/- 0.17) (P less than 0.01 and P less than 0.05 respectively). The gradients of metabolites in the well oxygenated empty beating heart suggest that a permanent metabolic adaptation to less adequate regional O2 reserves is physiologically operating in the subendocardial layer and the apex region of the left ventricle.

Adenosine Triphosphate↗