Biomedical subjects

Peter Bjerring

Publications and source records attributed to Peter Bjerring.

8 recordsLinked to original sources

PubMed2003

[Optical coherence tomography].

Optical coherence tomography (OCT) is a novel technique for two and three-dimensional imaging of tissues at a histological level. The technique is based on optical technology and commercially available fiber-optic components that may be adapted for use in conventional endoscopes or intravascular catheters. OCT is a non-invasive technique, which does not utilize ionizing radiation, and it may within a few seconds provide in vivo images ("optical biopsies") of tissues in cases where excisional biopsy is hazardous or impossible, or when repeated examinations are required. OCT has numerous potential clinical applications, and the technique is currently used in ophthalmology, where it may improve diagnosis and therapeutic control of various eye diseases. Detection and characterization of skin tumors and other dermatological diseases is another area where OCT has tremendous clinical potential. In the field of cardiology, intravascular OCT may be capable to contribute to early diagnosis of vulnerable atherosclerotic lesions. The OCT technique is also being developed in other clinical areas and is expected to become integrated in a range of clinical situations in the future.

Coronary Disease↗

PubMed2003

Pain and biomechanical responses to distention of the duodenum in patients with systemic sclerosis.

BACKGROUND & AIMS: Abnormalities of the small intestine have been indicated in systemic sclerosis. The aim was to use a new method to study the active-passive mechanical and sensory properties of the duodenum in these patients. METHODS: A volume-controlled ramp-distention protocol was used in the duodenum in 9 patients and 8 healthy controls. The nonpainful/painful sensations, pressure, cross-sectional area, wall tension, and strain were evaluated. Using butylscopolamine for muscle relaxation, the active (contractile muscular component) and passive (other mechanical tissue components) were computed. RESULTS: The contraction amplitude was smaller and the cross-sectional area higher in the patients (P < 0.05). Both the active and passive tension as function of strain was translated to the left in the patients, indicating a stiffer wall. The maximum active tension and the corresponding strain were 62% and 69% lower in the patients (P < 0.05). An association was found between the duration of the disease and the strain (P < 0.05). The perception score was higher as function of pressure, tension, and strain (P = 0.01, P = 0.03, and P < 0.01, respectively) in the patients than in the controls, with strain as the most sensitive variable to describe the sensory response. In 5 patients who complained of regular clinical symptoms, the referred pain area to distention was enlarged. CONCLUSIONS: Systemic sclerosis resulted in increased stiffness and impaired muscle function of the duodenum. The pain evoked by a controlled strain of the gut was increased and can explain many of the symptoms reported in the clinic.

Adult↗

PubMed2002

Dermal collagen production following irradiation by dye laser and broadband light source.

BACKGROUND: Improvement in the appearance of wrinkles has been observed following exposure to short-pulsed 585 nm laser light. The assumed effect is a specific absorption of light in the blood vessels of the superficial dermis, resulting in release of inflammatory mediators into the interstitium followed by stimulated fibroblast activity. The fibroblasts effectively initiate tissue repair mechanisms, which include enhanced new collagen production. METHODS: Quantitative measures of collagen synthesis rate in the skin can be obtained from determinations of the aminoterminal propeptide of type III procollagen level in suction blister fluid using a radioimmunoassay. RESULTS: A single laser treatment at subpurpura energy level showed that the 585 nm laser source induced an increase of 84% (p < 0.05) in the type III procollagen production rate compared with a non-treated control site. A broadband, pulsed, white light source at 4 J/cm(2) showed no measurable increase, whilst the skin area treated with 7 J/cm(2) increased the procollagen production rate by 17% (NS, p > 0.05). A second treatment 2 weeks later further improved the laser-induced increase in procollagen production rate to 148% (p < 0.05) compared with the control site. The broadband, pulsed, white light-irradiated skin sites showed that at 4 J/cm(2) the procollagen production rate was increased by 21.4% and at 7 J/cm(2) by 32.1% compared with the corresponding non-treated control site (NS, p > 0.05). CONCLUSIONS: Irradiation by the haemoglobin-specific short-pulsed 585 nm laser induced a fivefold increase in procollagen production rate compared with a biologically comparable fluence delivered in a broadband spectrum. An additional treatment after 2 weeks further increased the effect of the short-pulsed 585 nm laser to 148% of the control. Vascular-specific light/tissue interactions seem to play a key role in stimulating skin collagen production.

Adult↗

PubMed1996

The effects of isoflurane on repeated nociceptive stimuli (central temporal summation).

Central temporal summation of afferent nociceptive stimuli is involved in central hyperexcitability. This is assumed to be an important mechanism in the nociceptive system which is probably activated during surgery and trauma. The purpose of the present study was to investigate if isoflurane has a specific effect on central temporal summation in humans. Facilitation of the nociceptive reflex to repeated stimuli can be used to assess central summation in subjects unable to cooperate due to an anaesthetic procedure. The nociceptive reflex to single and repeated (5 pulses delivered at 2 Hz) electrical surface stimuli of the sural nerve were measured in 6 healthy volunteers anaesthetized with isoflurane. A reflex was defined as an EMG signal from the rectus and biceps femoris exceeding 20 microV for more than 10 msec in the 80-200 msec interval after the stimulus. The end-tidal isoflurane concentration was increased in steps of 0.25 vol% from 0.25 to 1.50 vol%. For each concentration the thresholds for the nociceptive reflex were determined as the current intensity that could just elicit a reflex response to single stimulations, and for the repeated stimulations as the current intensity that could just elicit a reflex response to the 4th and/or 5th stimuli in the train of 5 stimuli. The nociceptive reflex to single stimuli was depressed at isoflurane concentrations producing sedation or light anaesthesia (0.25-0.50 vol% end-tidal). In contrast, 2-4-fold higher isoflurane concentrations (1.00-1.50 vol% end-tidal) that normally produce surgical anaesthesia were required to depress the nociceptive reflex to repetitive stimuli. This indicates that central temporal summation in the nociceptive system is a potent mechanism, and that isoflurane has a weak potency for depressing temporal summation in humans. As such isoflurane alone is not adequate for inhibiting surgically evoked hyperexcitability.

Adult↗

PubMed1996

The effect of Ketamine on stimulation of primary and secondary hyperalgesic areas induced by capsaicin--a double-blind, placebo-controlled, human experimental study.

The non-competitive NMDA-antagonist, Ketamine, was infused (i.v.) in healthy volunteers to study the effect on central excitability with the presence of cutaneous hyperalgesia. Hyperalgesia was established experimentally on the dorsum of the foot by topical application of capsaicin (1%). Different thermal and mechanical conditioning stimuli were applied to the primary and secondary hyperalgesic areas to modulate the central nociceptive excitability monitored by the nociceptive reflex. When the elicited reflex was combined with an activation of the secondary hyperalgesic area by continuous, non-painful, electrical stimulation, a facilitation of the reflex was observed. This indicates that summation of activity in non-nociceptive and nociceptive afferents can occur under mild pathological conditions. Conditioning thermal stimuli of the primary hyperalgesic area were employed to intensify the allodynia prior to testing this interaction between tactile and nociceptive activity. The same reflex facilitation was inhibited by Ketamine. Furthermore, Ketamine decreased the pain intensity associated with the stimuli eliciting the reflex. Psychophysical measures to single and repeated electrical and thermal (laser) stimuli applied within the hyperalgesic areas were also obtained. The intensity of pain sensations produced by single, painful, electrical stimuli applied to the primary hyperalgesic region was reduced after Ketamine infusion. Finally, five repeated, electrical stimuli applied to the secondary hyperalgesic area were used to assess the temporal summation threshold. Ketamine caused an increase in the summation threshold compared to the placebo treatment. In conclusion, these results demonstrate that (1) summation of activity in non-nociceptive and nociceptive afferents occurs under hyperalgesic conditions and, (2) this summation can be inhibited by NMDA-antagonists. Therefore, the study shows an apparent involvement of NMDA-receptors in some of the central mechanisms underlying secondary hyperalgesia.

Adult↗

PubMed1992

Quantitative sensory examination in human epidural anaesthesia and analgesia: effects of lidocaine.

To characterize the sensory effects of epidural lidocaine, 2 groups each of 10 human subjects received 25 ml of 2% lidocaine at the L1-L2/L2-L3 interspace (high lumbar group) or at the L3-L4/L4-L5 interspace (low lumbar group). Twelve quantitative sensory tests in the L5 and S1 dermatomes and leg extension strength were determined every 30 min for 3 h. Sensory and motor blockade were more pronounced in the low than in the high lumbar group. Sensory functions were blocked in the following order by epidural lidocaine: warm > cold > electrical stimuli. Perception of brief localized noxious stimuli was attenuated more than perception of noxious stimuli of longer duration and involving larger stimulus areas. It is suggested that both peripheral mechanisms (differential conduction blockade of afferent fibres) and central mechanisms (temporal and spatial summation) play a role in the sensory effects of epidural lidocaine.

Adult↗

PubMed1992

Quantitative determinations of sensory and pain thresholds on human oral mucosa by argon laser stimulation.

High-energy light from an argon laser was applied to human oral mucosa in order to investigate regional pain sensitivity. Significant regional differences in sensory and pain thresholds were observed between the test sites on the hard and soft palatal mucosa, the buccal mucosa, the tongue, the lower lip, and the skin on the hand. Pain thresholds were lowest on the tip of the tongue and highest on the hard palate. Sensory and pain thresholds were influenced by different stimulus parameters: pulse duration and laser beam diameter. Blackening of the mucosa in regions with high optical reflectance, such as the hard palate, increased light absorption and, hence, reduced both thresholds significantly. Reflectance spectrophotometric measurements indicated that the hard palatal mucosa reflected argon laser light about 1.5 times more than the tip of the tongue. The different threshold values could, in part, be ascribed to different reflectance and absorption properties of the mucosal areas but also indicated substantial regional variation in pain sensitivity of the human oral mucosa. Measurement of laser thresholds is an appropriate and standardized method for investigating sensory differences in human oral mucosa and may be used to study various pain conditions, e.g., burning mouth syndrome.

Argon↗

PubMed1990

Quantitative evaluation of hypnotically suggested hyperaesthesia and analgesia by painful laser stimulation.

The ability to reduce both clinically and experimentally induced pain by hypnotic suggestion of analgesia is well known. However, the nature of hypnotic analgesia still remains uncertain. Attempts to demonstrate and identify specific psychophysiological mechanisms have, so far, been unsatisfactory. Methodological problems in inducing pain and monitoring physiological responses may be the reason for this lack of success. In the present study, we have attempted to eliminate some of these methodological problems. The sensory and pain thresholds to laser stimulation were determined, and the laser-evoked brain potentials were measured for 8 highly hypnotically susceptible subjects in 3 conditions: (1) waking state, (2) suggestion of hyperaesthesia, (3) suggestion of analgesia. The thresholds were reduced during induced hyperaesthesia and increased during analgesia. During hyperaesthesia sensations could be evoked by laser intensities which were below intensities that could be perceived in the awake state. The amplitude of the evoked brain potentials increased during hyperaesthesia and decreased during analgesia. The latency of the potential remained constant. The perception of pain during hypnosis can change very fast, indicating that slow endogenous mechanisms may play only a minor role in suggested hyperaesthesia/analgesia.

Analgesia↗