Biomedical subjects

K Krauel

Publications and source records attributed to K Krauel.

10 recordsLinked to original sources

PubMed2006

Characterisation of microemulsions containing orange oil with water and propylene glycol as hydrophilic components.

The current study aims to investigate the effect of incorporation of orange oil, mainly consisting of the cyclic mono-terpene linolene, a known skin penetration enhancer, as oil component on microemulsion formation both in water and propylene glycol containing systems. Phase diagrams of pseudoternary mixtures containing orange oil, ethyloleate or a 1:1 mixture (w/w) of orange oil and ethyloleate as oil components, a 6:4 (w/w) mixture of polyoxyethylene 20 sorbitan monooleate and sorbitan monolaurate as surfactant components and water or propylene glycol as hydrophilic components were investigated. Smaller microemulsion regions were observed when orange oil was used as a substitute for ethyloleate in both water and propylene glycol containing systems. Polarising light microscopy, viscosity measurements, electrical conductivity measurements and cryo-field emission scanning electron microscopy were used to identify structural features of the microemulsions. Solution-type, w/o droplet-type microemulsions and microemulsion areas containing liquid crystals were found in varying areas in the phase diagrams of water containing systems. Liquid crystals formation occurs when the water concentration reaches 20%-22.5% (w/w). Only solution-type microemulsions were observed in propylene glycol containing systems. The dimension of solution-type microemulsion areas in the phase diagrams is likely to depend on the miscibility of components and larger microemulsion areas were found when ethyloleate was used instead of orange oil and propylene glycol was used instead of water. W/o droplet-type microemulsions of systems containing orange oil and ethyloleate as oil components appear in different areas of the phase diagrams. Incorporation of orange oil as a penetration enhancer into a topical microemulsion affects its physical characteristics. This in turn may lead to instability of the microemulsion and/or can influence the release patterns of drugs from these microemulsions when applied as topical formulations.

Administration, Topical↗

PubMed2006

Characterisation of microstructures formed in isopropyl palmitate/water/Aerosol OT:1-butanol (2:1) system.

The aim of this work was to determine the type and microstructure of microemulsion samples formed in IPP/water/AerosolOT:1-butanol (2:1) systems as a case study for the investigation of microemulsions. The concentration of the surfactant/cosurfactant mixture was kept constant while the ratio of water to oil was varied. Several techniques were used to investigate the types and phase transitions of the microemulsion formulations. The experimental methods used included visual observation cross-polarized light microscopy (PLM) appearance, conductivity, viscosity, cryo-field emission scanning electron microscopy (cryo-FESEM), differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), and fluorescence resonance energy transfer (FRET). Taken together, the results of the various techniques imply that the systems investigated are undergoing two transitions as a function of water concentration. Between 10-15%w/w of water, the systems change from headgroup hydrated surfactant solutions in oil (or possibly very small reversed micellar systems) to w/o microemulsions. These systems then change to o/w microemulsions between 25-30%w/w of water. The transitions however, appear to be gradual, as for example the DSC data indicates a transition between 15-20%w/w of water. Furthermore, for some methods the changes observed were very weak, and only with supportive data of other techniques can the phase behaviour of the microemulsion systems be interpreted with confidence. Interestingly, no indication of the presence of a bicontinuous intermediate microstructure was found. Liquid crystal formation was detected in samples containing 55%w/w of water.

1-Butanol↗

PubMed2005

Using different structure types of microemulsions for the preparation of poly(alkylcyanoacrylate) nanoparticles by interfacial polymerization.

A phase diagram of the pseudoternary system ethyloleate, polyoxyethylene 20 sorbitan mono-oleate/sorbitan monolaurate and water with butanol as a cosurfactant was prepared. Areas containing optically isotropic, low viscosity one-phase systems were identified and systems therein designated as w/o droplet-, bicontinuous- or solution-type microemulsions using conductivity, viscosity, cryo-field emission scanning electron microscopy and self-diffusion NMR. Nanoparticles were prepared by interfacial polymerization of selected w/o droplet, bicontinuous- or solution-type microemulsions with ethyl-2-cyanoacrylate. Morphology of the particles and entrapment of the water-soluble model protein ovalbumin were investigated. Addition of monomer to the different types of microemulsions (w/o droplet, bicontinuous, solution) led to the formation of nanoparticles, which were similar in size ( approximately 250 nm), polydispersity index ( approximately 0.13), zeta-potential ( approximately -17 mV) and morphology. The entrapment of the protein within these particles was up to 95%, depending on the amount of monomer used for polymerization and the type of microemulsion used as a polymerization template. The formation of particles with similar characteristics from templates having different microstructure is surprising, particularly considering that polymerization is expected to occur at the water-oil interface by base-catalysed polymerization. Dynamics within the template (stirring, viscosity) or indeed interfacial phenomena relating to the solid-liquid interface appear to be more important for the determination of nanoparticle morphology and characteristics than the microstructure of the template system.

1-Butanol↗

PubMed2000

Chemosensory event-related potentials (CSERP) as a key to the psychology of odors.

The present article gives a critical overview of how the components N1, N2, especially the mismatch negativity (MMN), and P3 have been investigated and interpreted in the context of 'chemosensory event-related potential' (CSERP) research. In order to integrate the respective CSERP results, findings and theoretical models from other modalities are briefly described for each component. It is suggested that all components found so far within the CSERP strongly depend on the psychological state of the individual. In particular the dominant positivity of the CSERP has been focused on by investigating the specificity of olfactory emotional processing in comparison to emotional and neutral stimuli from the visual modality. The results reveal that the late positive complex within the CSERP consists of two subcomponents, one of which has a frontal and the other a parietal dominance. The posterior positivity seems to reflect the features of the P3 component and varies with the valence of odors, whereas the anterior positivity seems to be similar to the Novelty-P3. A link between olfactory and emotional processing has been confirmed by the finding that the P3 elicited by visual stimuli shows similar valence effects.

Chemoreceptor Cells↗

PubMed1999

Is odor processing related to oral breathing?

This paper addresses two questions related to the inherent association between breathing and odor perception: Does central nervous processing of odors change when an artificial breathing technique (velopharyngeal closure) is introduced and secondly, does odor processing vary with the oral breathing phase (inhalation or exhalation)? Chemosensory event-related potentials (CSERP) were obtained from eight female subjects while they were smelling an odor mixture (citral, eugenol, linalool, menthol and isoamylacetate). Each subject was required to perform spontaneous mouth breathing (120 trials) as well as the velopharyngeal closure technique (120 trials). Simultaneously, a thermistor monitored the phase of the respiratory cycle. The results reveal that the central nervous correlates of odor processing change with the breathing technique but not with the oral breathing cycle. The findings that early stimulus processing is faster (N1 latency) and late stimulus processing more pronounced (P3 amplitudes) when the subjects are breathing spontaneously are discussed with regard to attentional effects. The reduction of the N1 amplitude during the spontaneous breathing condition may be caused by larger latency variations and longer stimulus rise-times. Furthermore, it is concluded that the oral breathing cycle is less important than the nasal breathing cycle for olfactory information transmission.

Adult↗

PubMed1998

Central nervous correlates of chemical communication in humans.

The recording of chemosensory event-related potentials (CSERPs) has been established as an objective method in the assessment of central odor processing in humans. In the present study CSERPs were used to investigate whether human body odor is genetically determined by the major histocompatibility complex (MHC), referred to in humans as the human leukocyte antigen (HLA). The immunological function of the MHC is the discrimination of self/nonself within the immune system. In rodents it has been shown that body odor is significantly influenced by the MHC and that it can be discriminated by members of different species. To create a sufficiently large subject pool, 144 subjects were screened for their HLA class I loci A and B. During the electroencephalography (EEG) session the subjects (n = 40/20 women) were confronted with the body odor (axillary hair) of three different donors. Two donors (d1 and d2) were HLA-similar but had a different HLA type than the third donor (d3) and the perceiving subject. The third donor and the perceiver shared a similar HLA type. Half of the perceivers received odors from donors of the same sex, the other half smelt odors from donors of the opposite sex. In the EEG session subjects were presented with 200 trials. The odors were delivered through a constant flow olfactometer non-synchronously to breathing. The odor of d1 appeared frequently (p = 0.6) whereas the odors of d2 and d3 appeared each at a rate of p = 0.2. During half the trials the subjects were instructed to respond to the odor of d2, during the other half to the odor of d3. The EEG was recorded from Fz, Cz, Pz, F3, P3, F4 and P4 in reference to linked mastoids. First results show that male perceivers show enhanced potentials in response to male donors of a similar HLA type (d3). The CSERP results of the other groups as well as valence and attractiveness ratings will be discussed.

Adult↗

PubMed1998

Attentional modulation of central odor processing.

Two studies were conducted to investigate the influence of attention on the components of the chemosensory event-related potential (CSERP). In the first study the odors linalool and eugenol were delivered to six male subjects, in the second study three male and two female subjects were presented with their own body odor (axillary hair) and the body odor of a same sex donor. In both studies the odors were presented in an oddball paradigm under ignore and attend conditions via a constant-flow olfactometer. In the ignore condition attention was diverted from the odors with a distractor task, while in the attend condition the subjects were asked to respond to the infrequently occurring odor. In both studies the allocation of attention led to a decrease in the latency of the early components (N1, P2, N2) and to an increase in the amplitude of the late positivities. The modulation of the early components suggests that attentional gating in olfaction might already be effective at an early processing level.

Acyclic Monoterpenes↗

PubMed1996

Olfactory information processing during the course of the menstrual cycle.

In the present study we examined whether olfactory information processing depends on the phase of the menstrual cycle. Five female subjects were investigated during three phases (follicular, ovulatory, luteal) of their menstrual cycle. In each session chemosensory (olfactory) event-related potentials (CSERP) were recorded and olfactory thresholds and the hedonic tone of the test stimulus (citral) were determined. Threshold values were correlated with the salivary cortisol level. The results show that olfactory perception changes during the menstrual cycle. After the first stimulus presentations in a recording session, odors were perceived as more complex or novel during the ovulatory period (enhanced amplitude of P3-1). With continued stimulation, odor processing became faster (reduced latency of NI, P2 and P3-2) around ovulation and slower during the follicular phase. Moreover, odors were described more differentially during the ovulatory period. Olfactory sensitivity was correlated positively with the peripheral cortisol level.

Adult↗

PubMed1996

The nature of the late positive complex within the olfactory event-related potential (OERP).

The olfactory event-related potential (OERP) has been described as being dependent on exogenous stimulus features, but no effort has been made to examine possible endogenous determinants. We wanted to separate exogenous and endogenous components of the OERP by using an olfactory oddball paradigm. A high concentration of citral was used as the target stimulus, and a low concentration was used as the standard stimulus. Odors were presented within a constantly flowing air stream. We found that the early components of the OERP (N1, P2) are modulated by the stimulus concentration, whereas the late positive components (P3-1, P3-2) vary depending on the subjective stimulus significance and stimulus probability. It is concluded that the positive component of the OERP, which has been formerly explained by chemical and physical stimulus features, is actually determined by endogenous processes.

Acyclic Monoterpenes↗

PubMedDate not supplied

Body odor evoked potentials: a new method to study the chemosensory perception of self and non-self in humans.

A new method will be presented which allows the perception of body odors in humans to be studied objectively. The analysis of body odor-evoked potentials was used to investigate if and how the human brain is able to differentiate self from non-self body odor for the first time. Six subjects (three females) participated in two experimental sessions. In each session, two body odors (axillary hair) were presented within an olfactory oddball paradigm. One of the odors was collected from the subject and the other from an odor donor of the same sex. In the first session the subjects' attention was distracted to a secondary task (passive paradigm), in the second session the subjects were asked to actively differentiate the odors (active paradigm). For the EEG recordings the odors were presented within a constantly flowing airstream. The results show that the subjects could hardly differentiate the body odors subjectively. However, it could be demonstrated that the central nervous processing of one's own odor was faster than the processing of the chemosensory non-self signal. Moreover, in the active paradigm, the potentials appeared to be larger when the subjects perceived their own body odor. The conclusion is reached that the measurement of chemosensory event-related potentials (CSERP) is the method of choice for the investigation of HLA-associated body odors.

Adult↗