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Biomedical subjects

G Johannsen

Publications and source records attributed to G Johannsen.

12 recordsLinked to original sources
PubMed1992

Surface changes on dental materials. II. The influence of two different dentifrices on surface roughness measured by laser reflexion and profilometer techniques.

Surface changes on eight different dental materials were investigated, using laser reflexion technique and a profilometer. The tested materials were: Acrylic veneers Isosit, Isosit N, K+B+, Multiplus and K+Bpaste Gold Sjödings C Titanium pure non-rolled titanium Ceram a potential ceramic direct filling material The materials were subjected to brushing in a brushing machine, with a toothpaste-water slurry. Two different toothpastes were used separately; Clinomyn and Colgate. The new ceramic material showed no measurable wear by the brushing. All the other materials were affected to some extent. On titanium increasing values of light intensity were obtained thus indicating a smoother surface. Among the veneer materials K+Bpaste was the most wear resistant.

Acrylic Resins↗
PubMed1989

The effect of general anaesthesia on the haemodynamic events during laparoscopy with CO2-insufflation.

Sixteen women were studied during elective diagnostic laparoscopy with CO2-insufflation to an intraabdominal pressure (IAP) of 2 kPa and Trendelenburg tilt to 30 degrees. They were allocated to either a halothane (Group I) or a balanced (Group II) anaesthesia with relaxation and controlled ventilation. Heart rate (HR), arterial pressure, stroke volume, CO2-elimination, end-tidal CO2 vol.% and total respiratory compliance (TRC) were the parameters measured, and mean arterial pressure (MAP), total peripheral resistance (TPR), stroke index (SI) and cardiac index (CI) were calculated. At maximum haemodynamic strain, SI and CI were on average reduced by 42% in both groups, without significant changes in HR and MAP. TPR increased by 50% in Group I and 100% in Group II. The reduction in SI was related to the changes in TRC. A small increment in CO2-elimination after CO2-insufflation was most pronounced in Group II. SI and CI did not reach the pre-insufflation values after return to the horizontal position and CO2-exsufflation. The haemodynamic differences between the two groups were small compared to the effects of the laparoscopy procedures.

Adolescent↗
PubMed1989

Turbulent stresses downstream of porcine and pericardial aortic valves implanted in pigs.

Because late valve-related complications such as hemolysis and thromboembolic events are considered related to flow disturbances caused by the inserted valve, velocity fields downstream of aortic valve prostheses were studied in pigs. Acute hemodynamic evaluation of size 25-mm porcine and pericardial aortic valve prostheses 1 diameter downstream of the valve ring was performed using dynamic three-dimensional visualization of velocity profiles and spatial distribution of turbulence. Point blood velocity signals obtained with a 1-mm hot-film anemometer needle probe were used to compute Reynolds normal stresses (RNS) by calculation of the turbulent velocity energy of the axial velocity component in the systole. The porcine valves caused a skewed velocity and turbulence profile revealing mean spatial systolic RNS at 70 nm-2 +/- 35 nm-2 (+/- SD). The spatial maximum RNS was 275 +/- 139 nm-2. Corresponding values for the pericardial valves were 20 +/- 11 nm-2 and 72 +/- 46 nm-2. The pericardial valves revealed plug-shaped velocity profiles and turbulent profiles with slightly higher RNS values at the stent posts. From a hemodynamic point of view, these acute studies indicate superiority of the pericardial valves compared to the porcine valves. The turbulent stresses found in this study are of a magnitude that may cause blood corpuscular and endothelial damage.

Animals↗
PubMed1989

Surface changes on dental materials. The influence of two different dentifrices on surface roughness measured by laser reflexion and profilometer techniques.

Surface changes and wear resistance were investigated on eight different dental materials, using a laser reflexion technique and a profilometer. The tested materials were: (table; see text) The materials were subjected to brushing in a brushing machine, containing a toothpaste-water slurry. Two different toothpastes were used separately; Clinomyn and Colgate. The results showed that all the materials were to some extent affected by the brushing. Titanium was the most and SR Isosit N the least wear resistant material. Clinomyn and Colgate influenced the materials in different ways depending on their abrasive properties.

Acrylic Resins↗
PubMed1988

A model for acute haemodynamic studies in the ascending aorta in pigs.

Since data on velocity fields in the ascending aorta downstream of normal aortic valves in pigs have not yet been obtained velocity profiles were visualised using a hot film anemometer needle probe before and after total cardiopulmonary bypass and cold cardioplegic arrest. Furthermore, measurements were made during increased heart rate and cardiac output. A dynamic three dimensional visualisation of velocity fields showed a skewed clockwise rotating velocity profile, developing from peak systole and continuing throughout the systolic deceleration phase. This pattern was consistent regardless of the haemodynamic state. Heart rate was increased to 180 beats.min-1 and cardiac output by a maximum of 91%. It is concluded that the pig model is valuable for haemodynamic studies in the ascending aorta before and after cold cardioplegic arrest and that the velocity profiles found in this study are important basic data for velocity field studies downstream of artificial heart valves implanted in the aortic position.

Animals↗
PubMed1988

Velocity fields and turbulent stresses downstream of biological and mechanical aortic valve prostheses implanted in pigs.

Since detailed knowledge about velocity fields downstream of heart valve prostheses obtained from in vitro studies has not been followed up by similar detailed studies in vivo a pig model for acute velocity field studies downstream of aortic valve prostheses was established. Two mechanical and two bioprosthetic valves were studied and a dynamic three dimensional visualisation of velocity fields one diameter downstream performed under different haemodynamic conditions in a total of 22 pigs. The Ionescu-Shiley pericardial valve had velocity fields very similar to the normal native porcine aortic valve. The Edwards-Carpentier porcine valve caused a jet type flow, and the valve design of the St Jude Medical and Björk-Shiley Monostrut valves was reflected in the velocity profile. Normalised (mean(SEM] systolic Reynolds normal stresses in the total cross sectional area were: native porcine 15(1.5) Nm-2; St Jude Medical 24(3.4) Nm-2; Björk-Shiley Monostrut 25(1.6) Nm-2; Edwards-Carpentier Supra-annular 51(6.6) Nm-2; Ionescu-Shiley Pericardial 19(2.0) Nm-2. Reynolds normal stresses were higher in areas of rapidly changing or constantly high velocity gradients.

Animals↗
PubMed1988

Continuous monitoring of tissue oxygen tension during hyperoxia and hypoxia: relation of subcutaneous, transcutaneous, and conjunctival oxygen tension to hemodynamic variables.

Subcutaneous, transcutaneous, and conjunctival oxygen tensions (PscO2, PtcO2, and PcjO2, respectively) were measured in anesthetized dogs subjected sequentially to normoxia, hyperoxia, and hypoxia. Intravascular pressure, hemodynamic and oxygen transport variables were measured simultaneously. PtcO2 and PcjO2 closely paralleled PaO2 during normoxia, hyperoxia, and hypoxia over a wide range of arterial oxygen tensions. PtcO2 was reliable over the widest range of PaO2, with a correlation coefficient of .94. The PcjO2/PaO2 index fell at very low PaO2. The PscO2/PaO2 index decreased at both very low and very high PaO2. Only minor changes were found in hemodynamic and oxygen transport variables during hyperoxia. During hypoxia, however, cardiac output and other central hemodynamic measurements increased, while PscO2, PtcO2, and PcjO2 fell. Oxygen delivery and oxygen consumption were maintained or only slightly changed during hypoxia. All three continuous measurements of oxygen tension are reliable indices of PaO2 over a wide range under normovolemic conditions. The instruments for measuring PscO2 and PcjO2 are unheated and therefore may have advantages for human application.

Animals↗
PubMed1985

Lustre changes on teeth. The use of laser light for reflexion measurements on the tooth surface--in vivo.

Lustre changes on teeth in vivo were studied with the use of equipment based on a helium-neon gas laser. Variations of the intensity of laser light reflected from the tooth surface were measured under different conditions of accumulation and removal of deposits, which were assumed to consist mainly of the pellicle. The possibility of using fluoride varnish as an artificial surface layer in this kind of investigation was also tested but rejected. Measurements were made after toothbrushing with water alone and with two toothpastes possessing different degrees of abrasivity. Teeth that had been left without toothbrushing for 24 hours showed statistically significant (p less than 0.05) lower light reflexion values than those recorded immediately after the teeth had been brushed with a toothpaste. During a period of seven months, persons brushing their teeth with water alone generated lower intensity values than did those brushing with the two toothpastes. The more abrasive paste yielded the highest intensity values, indicating a more polished or cleaner surface. The results suggest that the use of a toothpaste containing abrasives contributes to the cleaning effect of toothbrushing.

Adult↗
PubMed1985

The laser reflection method. Computerized analysis of speckle pattern.

The laser reflection method of remote measurements permits registration of small tooth movements. Its precision was investigated by studying the errors associated with patient repositioning in the apparatus using the computer controlled image scanner OSIRIS. Fifty repositionings of healthy subjects were evaluated. The results show that the mean error of repositioning is 2.8 micron laterally and 9.2 micron sagittally. This agrees with earlier manual-visual measurements but the higher precision due to computer evaluation of the speckle patterns gives much more reliable estimate of the repositioning error. The study confirms the fact that the laser reflection method permits accurate measurements of tooth movements.

Adult↗
PubMed1981

Lustre changes on teeth. The use of laser beams for comparative studies in vivo.

An instrument for studies of lustre changes on teeth in vivo was constructed and evaluated. The equipment was based on a helium-neon gas laser, a coordinate screen and a photocell. The intensity of light reflected from incisors of ten test subjects was measured before and after brushing with different dentifrices. The investigation showed that the instrument was useful for measuring intensity differences of laser light reflected from teeth. The intensity was found to vary within wide limits from teeth of different persons. During a test period of 70 days only few lustre changes caused by dentifrices were registered.

Adult↗