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Biomedical subjects

A A Laogun

Publications and source records attributed to A A Laogun.

13 recordsLinked to original sources
PubMed1997

A comparison of the dielectric behaviour of human haemoglobin SC with SS and AA in solution.

Haemoglobin (Hb) SC is one of the most prevalent sickle-cell disorders. Patients with Hb SC are known to inherit a befa(S)-globin gene from one parent and a beta(C)-globin gene from the other. The radiofrequency dielectric properties of heterozygous Hb SC have been investigated and compared with those of homozygous Hb SS and AA in solution. The relative permittivity, epsilon', the dielectric loss factor, epsilon", and the energy dissipation factor, tan delta, of the different haemoglobin samples have been measured in the frequency range 0.1-50.0 MHz using a TF1245 Marconi Q-meter working in conjunction with a TF1246 oscillator at a room temperature of 26.0 +/- 0.5 degrees C. The Hb SC samples were found to exhibit dielectric dispersions distinctly different from those of Hb SS and AA. The dielectric data were fitted to the Cole-Cole structural equation and the fitted parameters are presented. The results are discussed on the basis of the molecular structure and polymerization characteristics of the haemoglobins in solution.

Adolescent↗
PubMed1986

Dielectric properties of mammalian breast milk at radiofrequencies.

The relative permittivity and AC conductivity of breast milk have been investigated in four different mammalian species, human, cow, goat and sheep, in the frequency range 0.1-100 MHz and at a room temperature of 26.5 +/- 0.5 degrees C. The results showed that the sheep milk exhibited the largest dielectric dispersion, followed in decreasing order by milks from the goat, cow and human. The dielectric data were fitted to the Debye and Cole-Cole structural equations and the fitted parameters have been presented for the different species. The curve-fitting analysis has shown that for all the milk samples the Cole-Cole model gave a better fit to the dielectric data than the Debye model, thus suggesting heterogeneity of structure in milk. On the basis of the Cole-Cole model, the relaxation times in the mammalian milks were found to be distributed about the mean values of 162 +/- 10, 171 +/- 9, 177 +/- 14 and 192 +/- 12 ns for human, cow, goat and sheep milks, respectively.

Animals↗
PubMed1986

Effect of temperature on the RF dielectric properties of human breast milk.

The dielectric dispersion of human breast milk has been investigated by means of a resonance technique over the frequency range 0.1-100 MHz and at six temperatures from 10 to 60 degrees C. A computer analysis of the data was carried out on the basis of the Cole-Cole structural model and the fitted parameters have been presented. The dependence on temperature of both the viscosity of the human milk and its dielectric relaxation has been discussed. The heat of activation delta H of the milk, calculated in accordance with Eyring's theory of rate processes was found to be 19.5 +/- 0.6 kJ mol-1 for the dielectric relaxation process and 20.2 +/- 0.8 kJ mol-1 for viscous flow.

Calorimetry↗
PubMed1984

Dielectric properties of insulin in solution.

Values of the relative permittivity of a 5% solution of despentapeptide insulin (DPI) are given at six temperatures over a frequency range 0.2-50 MHz. The solvent was a mixture of water and ethylene glycol at pH = 3. From the dispersion curves a dipole moment of 72 +/- 1 was obtained for the insulin molecule at 25 degrees C. By combining the dielectric measurements with values of solvent viscosity the volume of the insulin molecule in solution was found to be only slightly larger than that in the crystal. This indicates that insulin possesses a markedly lower quantity of water of hydration than has been observed for globular proteins containing a higher proportion of hydrophilic groups on the surface of the molecule.

Animals↗
PubMed1983

Dielectric characteristics of packed human erythrocytes with haemoglobins F, AA, AS and SS.

The radiofrequency dielectric behaviour of packed human erythrocytes has been investigated in normal haemoglobins F and AA and also abnormal haemoglobins homozygous SS and heterozygous AS. Dielectric measurements were made in tightly packed blood cells at an average room temperature of 26.5 +/- 0.5 degrees C in the frequency range from 0.1 to 100 MHz. In agreement with previous findings in many biological molecules, all the packed erythrocytes of the different haemoglobins exhibited a decrease in dielectric constant and an increase in conductivity with frequency. However, each type has been found to show distinct dielectric dispersion with respect to the others and this has been associated with their molecular structure in addition to the polarization of cell membrane. The possible application of this technique in identifying different haemoglobins of the blood has been suggested.

Adolescent↗
PubMed1982

In vivo arterial compliance in man.

Six hundred 'normal' volunteers have been examined, ranging in age from neonates of three days to adults of 65 years. Average compliance was measured for the aortic, iliac, and leg arterial pathways using a non-invasive atraumatic Doppler ultrasound method in non-sedated subjects. No variation of compliance with mean blood pressure was found but there was a strong dependence on age and sex. At birth, leg arteries appear to be markedly more compliant than the aorta. Relative values are reversed in the first five years, after which the aorta remains more compliant, reaching a maximum value around 10 years and then decreasing sharply towards leg values until 20 years. Beyond this age aortic compliance very slowly, and aorta, iliac, and leg arteries appear to tend towards equal compliance in the sixth decade. An explanation for the significant differences between aortic compliance in males and females from menarchy to menopause is offered and implications of these compliance variations in atherogenesis are discussed.

Adolescent↗
PubMed1982

Pulse wave reflections from arterial discontinuities.

The true or characteristic velocity of pulse waves along different arterial segments in both animals and man often permits the determination of the elastic state of the vessels in health and disease. In this study, the extent to which the measured, or apparent pulse wave velocity (PWV) suffers from reflection effects is investigated. An in vitro test-rig is used to demonstrate that PWV, measured in an elastic tube model, will oscillate about the value characteristic of the vessel wall, as distance progresses close to a discontinuity-generating reflection. These variations are shown to be markedly reduced if the segment length is longer than lambda/4 for the dominant harmonics in the pulse waves. Harmonic analysis of the pulse waves recorded from the elastic tube and from two human volunteers also show that phase velocities oscillate with increasing amplitude as reflection increases.

Animals↗
PubMed1976

Anomalous iliac compliance in children with a single umbilical artery.

Arterial compliance (C) has been measured in 18 children known to have had a single umbilical artery at birth. Non-invasive ultrasonic Doppler techniques were used to measure C for the aorta, iliac, and leg arteries. Anomalous compliance was found between the two iliac vessels, and it is suggested that this is the result of haemodynamic stress-induced changes during development. The demonstration that the form of large arteries may be changed by altered haemodynamic stress and that their physiological function is thus affected, may have important implications in the pathogenesis of degenerative disease.

Aorta, Abdominal↗
PubMedDate not supplied

A Doppler ultrasound study of vessel compliance changes in occlusive arterial diseases.

This study was undertaken to investigate the extent to which the major arteries, particularly the aorta, iliac and leg arteries are involved in certain peripheral occlusive vascular disease, e.g. diabetes mellitus and sickle-cell anaemia. By using a non-invasive Doppler technique, vessel compliance (C) was measured in the aorta, iliac and leg arterial segments of 25 juvenile and adult-onset diabetics of recent diagnosis and also in seven sickle-cell subjects (sicklers) whose conditions were known to have reached crisis state. Results have been compared with values obtained from normal subjects of the same ethnic origin and age group. Abnormal aortic compliances was found in the juvenile diabetics in marked contrast with the lower than normal aortic compliance found in the adult diabetics of over 40 years of age, but also of recent diagnosis. The results further showed that some of the young sicklers (under 30 years of age) have slightly higher blood vessel compliance than normal while the older ones have lower values. These differences in compliance are discussed in the light of previous findings in animal and man.

Adolescent↗
PubMedDate not supplied

Absolute determination of ultrasonic intensity in a diagnostic Doppler ultrasound equipment.

Absolute ultrasonic intensity from pencil type Doppler-shift probes has been measured using a radiation balance technique. Accuracy and repeatability of measurement have been considered and effects of using different absorbing materials and different liquids other than degassed water on intensity measured have also been discussed. The technique is recommended for routine monitoring of intensity levels from Doppler ultrasound equipment used by clinicians for in-vivo blood flow measurements in hospitals. In conclusion, basic requirements for accurate measurement of ultrasonic intensity using this technique have been suggested.

Evaluation Studies as Topic↗
PubMedDate not supplied

Reflection effects of vaso-active drugs on arterial pulse propagation velocities measured in-vivo in a dog.

Blood-flow velocity signals have been recorded simultaneously at the proximal and distal sites of four arterial segments in an anaesthetized dog under two vaso-active conditions (vaso-dilation and vaso-constriction) using a continuous wave Doppler-shift ultrasonic technique. Spectral analysis produced sonograms of these signals. Phase delays between flow pulses in each segment were obtained from the sonograms and the variation of the resulting phase velocities with frequency has been discussed. Foot-to-foot transit time of the sonogram waveforms for each segment also gave an apparent pulse wave velocity, PWVff (Pulse wave velocity foot-to-foot) and this has been compared with the corresponding phase velocity of the higher harmonics, PWVhh in determining the true or characteristic pulse propagation velocity in the arterial pathways.

Animals↗