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Biomedical subjects

J G Miller

Publications and source records attributed to J G Miller.

At least 163 records · Page 9Linked to original sources
PubMed1979

The relationship between collagen and ultrasonic attenuation in myocardial tissue.

The relationship between ultrasonic attenuation and collagen content is examined in hearts from normal dogs and in hearts from dogs subjected to ischemic injury by coronary occlusion as an approach toward elucidating the physical mechanisms responsible for the attenuation of soft tissue. Increased ultrasonic attenuation is shown to correlate well with increased collagen concentration determined biochemically in regions of ischemic injury studied 2, 4, and 6 weeks following occlusion. Extrapolation of experimentally determined relationship between attenuation and collagen concentration suggests that collagen is responsible for not more than 15% of the attenuation observed in normal myocardium. These results indicate that collagen appears to be the principal determinant of the elevated attenuation detected in regions of myocardial infarction, but is apparently not the primary determinant of the attenuation of normal myocardium.

Animals↗
PubMed1979

Changes in ultrasonic attenuation indicative of early myocardial ischemic injury.

This study was designed to determine whether quantitative alterations in ultrasonic attenuation are associated with myocardial changes occurring after acute ischemic injury. Five hundred seventeen regions of myocardium from 41 dogs were studied in vitro at five intervals after coronary occlusion: 15 min, 1 h, 6 h, 24 h, 3 days, and 6 wk. Quantitative indices of ultrasonic attenuation were determined from the measured frequency dependence of the ultrasonic attenuation coefficient characterizing each myocardial region over the range 2-10 MHz. Independent definition of regions of ischemic injury was provided by either creatine kinase depletion or colloidal carbon dye distribution. Results of this study indicate that ischemic myocardial regions investigated 15 min to 24 h after coronary occlusion demonstrated ultrasonic attenuation significantly decreased from nonischemic regions (P less than 0.05). In contrast, ultrasonic attenuation was significantly increased in zones of ischemia or infarction investigated at 3 days and 6 wk after coronary occlusion (P less than 0.05 and P less than 0.01, respectively). These results indicate that altered attenuation of transmitted ultrasound by myocardium in vitro is an early manifestation of ischemia.

Animals↗
PubMed1977

Ultrasonic attenuation of myocardial tissue: dependence on time after excision and on temperature.

The ultrasonic attenuation coefficient of myocardium over the frequency range 2-10 MHz has been measured in vitro as a function excision and as a function of temperature. Results indicate that the attenuation coefficient was approximately independent of time for 4 h following excision at 19.5 degrees C, but increased by about 20% over a 4-h interval at 35 degrees C. The attenuation coefficient decreases approximately linearly with increasing temperature over the range 20.5 degrees -37 degrees C, with the value at 37 degrees C being about 20% lower than at 20.5 degrees C.

Animals↗
PubMed1977

Detection of myocardial infarction in vitro based on altered attenuation of ultrasound.

This study was designed to determine whether attenuation of ultrasound by myocardium is potentially useful in detecting and quantifying infarction. Accordingly, we analyzed 44 regions of myocardium from 11 dogs 4-10 weeks after coronary occlusion. Attenuation of ultrasound in each region was assessed by transmitting a broadband pulse through the tissue in vitro and carefully gating the appropriate pulse into a spectrum analyzer for Fourier analysis (frequency range, 2-9.5 MHZ). An ultrasonic index of attenuation was derived from the slope of the best-fit line relating attenuation and frequency obtained from the Fourier transform. Acquistion of ultrasonic data was improved with the use of a specially designed small diameter receiving transducer. Myocardial creatine kinase content was assayed in each region to provide an independent index of regional injury. Results obtained from ultrasonic and biochemical analyses correlated with a correlation coefficient between the two of 0.80 in 24 regions of myocardium from the six dogs studied 4-5 weeks after infarction, and 0.72 in 20 regions from the five dogs studied 9-11 weeks after infarction. These findings indicate that regional infarction is associated with quantitative changes in ultrasonic attenuation.

Animals↗
PubMed1976

Revascularization of the heart through the coronary veins.

Fifty-six dogs were used in a study to evaluate perfusion of the left anterior descending vein by the internal mammary artery in hearts with normal coronary arteries and those with ligated desending coronary arteries. Perfusion of the myocardium with arterial blood through the cardiac veins offers minimal immediate protection from infarction, as evidenced by light and electron microscopy studies. This protection is of short duration due to intimal fibrosis and luminal stenosis or obstruction of the perfused veins. Nineteen animals in which the coronary vein was perfused and the corresponding coronary artery was not ligated died within sixty hours from the time of operation. Pathological examination revealed patent grafts in all the animals. There was marked congestion of the myocardium with petechial hemorrhages over the surface of the heart. No evidence of myocardial infarction was found.

Animals↗
PubMed1976

Continuous detection of microemboli during cardiopulmonary bypass in animals and man.

A device that continuously and accurately detects solid and gaseous microemboli (75-100 muM) during cardiopulmonary bypass is described. A continuous ultrasonic standingwave field was generated between two parallel piezoelectric crystals. Extremely high sensitivity to small changes in ultrasonic attenuation was achieved with a transmission oscillator ultrasonic spectrometer (TOUS). The device was relatively insensitive to variations in flow rate, gradual temperature changes, hematocrit, protein content, and pressure. The system was tested with 100, 200, and 300 muM microspheres. Animal perfusions demonstrated high initial counts that were markedly reduced by an arterial line filter. Furthermore, high cardiotomy suction rates, use of nitrogen, and physical disturbances of the oxygenator increased the microemboli rate. Of 30 clinical perfusions, 15 had complete data for analysis. There was a statistically significant difference (P less than 0.01) in the total number of microemboli between the first 10 minutes (4398 +/- 1132) versus the second 10 minutes of perfusion (2739 +/- 1195). It is concluded that an accurate device that continuously measures the number of microemboli may provide data that will lead to significant improvements in the quality of extracorporeal circulation in the future.

Animals↗
PubMed1973

Fowler mcCormick.

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History, 20th Century↗
PubMed1972

Living systems.

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Biochemical Phenomena↗
PubMed1971

Odor incongruity and chirality.

The enantiomers R-(-)- and S-(+)-carvone are the organoleptic constituents in oil of spearmint and caraway, respectively. Their odor distinctiveness has been unambiguously demonstrated by chemical interconversion, independent synthesis, and resolution. Odor differences between other chiral isomers were also firmly established.

Isomerism↗