Biomedical subjects

H Stodkilde-Jorgensen

Publications and source records attributed to H Stodkilde-Jorgensen.

6 recordsLinked to original sources

PubMed2004

Reading with the ears.

We studied the cortical networks of Morse code reading with functional magnetic resonance imaging (fMRI). Four expert radio telegraphists performed two closely matched reading experiments, one in binaurally presented high speed Morse code and one in print. Performance was equal for both conditions. Reading single nouns in Morse code resulted in predominantly left-sided activation of the frontal and temporal perisylvian language areas, prefrontal cortex, and premotor cortex. In a within-subject comparison between reading Morse code and reading print, the activation pattern in the left temporoparietal association cortex was similar for both forms of reading, suggesting that reading Morse code shares part of its cortical networks with reading print.

Acoustic Stimulation↗

PubMed1999

High-resolution assessment of velocity fields and shear stresses distal to prosthetic heart valves using high-field magnetic resonance imaging.

BACKGROUND AND AIM OF THE STUDY: Complications after replacement of diseased heart valves with mechanical prostheses have been shown to be related to the hemodynamics distal to the valve. For this reason, the velocity patterns have been disclosed in vitro with a variety of different techniques. This study introduces a magnetic resonance imaging (MRI) -based technique, which entails easy acquisition of fluid velocity field data with a high accuracy and spatial resolution. METHODS: A high-field magnetic resonance scanner equipped with short echo time phase-contrast velocity measurement software was applied in a detailed mapping of the axial velocity profile across the entire vessel area at two positions downstream of a bileaflet valve prosthesis inserted in a pulsatile flow system in vitro. The laminar shear forces were calculated from the fluid velocity field data. RESULTS: The velocity profiles very close to the valve reflected the bileaflet design as also shown in previous studies, but the extent and velocities of the jet emanating from the slit between the leaflets were clearly better visualized. However, one diameter downstream of the valve the central jet was completely dispersed and the hemodynamic complexity was significantly reduced. Recirculation and retrograde flow regions that might be relevant for understanding typical long-term complications after implantation were observed close to the valve. CONCLUSIONS: In one scan experiment the presented method provides information on flow characteristics that previously required application of different types of experiment. Thus, the method seems promising as a new technique for detailed and extensive mapping of the velocities and laminar shear stresses downstream of prosthetic heart valves in vitro.

Blood Flow Velocity↗

PubMed1997

Cortical sites of sustained and divided attention in normal elderly humans.

Human brain mechanisms subserving attention have been assigned to prefrontal, midfrontal, and posterior parietal cortices, as well as to the anterior cingulate and the thalamus. To map these mechanisms in the brain, most studies have used selective attention tasks; few studies have mapped the brain under sustained or divided attention. The present study was designed to create maps of regional activity associated with sustained and divided attention using two different sensory modalities: visual checkerboard stimulation and vibrotactile stimulation of the right hand. Five cerebral PE-tomograms of 15O-labeled water uptake were acquired from 16 elderly healthy subjects during sustained or divided attention to the frequency of stimulation. To locate active brain regions, the t-statistic map of relative changes in cerebral blood flow was coregistered to the subjects' averaged brain MR images and to the standard Talairach brain coordinate system. Attention was associated with activity in two sites, the right middle frontal gyrus (Brodmann area 46) and the right inferior parietal lobule (Brodmann area 40). The frontal site was more active when the subjects attended to the visual stimulus and when the attention was divided, while the parietal site was more active during attention to the vibrotactile stimulus and during simple sustained attention. Our observations are consistent with the hypotheses (1) that the right posterior parietal attention center subserves attention to several sensory modalities and (2) that a cortical network of specific neuronal sites subserves both sustained and divided attention. These hypotheses must be tested in further studies.

Aged↗

PubMed1996

Effects of brain death and glucose infusion on hepatic glycogen and blood hormones in the pig.

We wished to study the effects of intravenous glucose/ insulin infusion to brain-dead pigs on the hepatic glycogen content. Four groups of 40-kg pigs were studied: brain-dead and control pigs given isotonic saline or glucose/insulin (7.5 mg glucose/kg/min, 1.25 mU insulin/kg/ min) (n = 5 to 10 in each group). Brain death was induced by inflating a balloon placed in the epidural space. In brain-dead pigs given saline, liver glycogen decreased from 45 +/- 11 mmol/g DNA (mean +/- SEM) to 7 +/- 3 mmol/ g DNA after 6 hours. Thereafter, it increased to 28 +/- 9 mmol/g DNA after 9 hours (P = .05 compared with the 6-hour measurement). These changes were accompanied by transient increases in plasma adrenaline, glucose, free fatty acids (FFA), and glucagon. Following glucose/ insulin infusion, hepatic glycogen increased steadily and was approximately double after 12 hours (P < .01) in both brain-dead and in non-brain-dead pigs. In brain-dead pigs, the increases in the aforementioned blood measurements were smaller following glucose/insulin infusion than following saline infusion. However, studies of longer duration will be needed to examine these effects on a time scale that is relevant to human organ donors. In conclusion, the decrease in hepatic glycogen content after brain death could be prevented by intravenous glucose/insulin infusion probably because of a reduction of the adrenaline response to the induction of brain death.

Animals↗

PubMed1988

The four-electrode impedance technique: a method for investigation of compliance in luminal organs.

A probe for measurement of related values of cross-sectional area (CA) and pressure has been developed to record characteristics of the walls in luminal organs. The aim of this study was to test the probe in vitro. CA was measured in the range 0.17 to 7.07 cm2 by means of the field gradient principle. Pressure was measured in the range 0 to 20 kPa (150 mmHg) by external transducers. After calibration both the pressure and the CA measuring system did measure the parameters adequately. The CA measuring system was dependent on the temperature and electrolyte concentration of the fluid, but was not affected by the size and form outside the excitation electrodes. The upper frequency limits for recordings of CA and pressure were 15.7 and 0.44 Hz, respectively. These in vitro results indicate that the tube assembly has characteristics sufficient for simultaneous measurement of CA and pressure in sphincter regions. These two variables can be used to describe mechanical wall properties such as compliance, hysteresis and creep.

Animals↗

PubMed1987

Three-dimensional visualization of axial velocity profiles downstream of six different mechanical aortic valve prostheses, measured with a hot-film anemometer in a steady state flow model.

Hot-film anemometry was used for in vitro steady-state measurements downstream of six mechanical aortic valve prostheses at flow rates 10, 20 and 30 l.min-1. Three-dimensional visualizations of velocity profiles at two downstream levels were made with the valves rotated 0 and 60 degrees in relation to the sinuses of valsalvae. The velocity fields downstream of the disc valves were generally skew with increasing velocity gradients and laminar shear stresses with increasing flow rates. Furthermore, increased skewness of the velocity profiles was noticed when the major orifices of the disc valves were towards the commissure than when approaching a sinus of valsalvae. The velocity profiles downstream of the ball valve were generally flat but with considerably more disturbed flow, consistent with the findings in turbulent flow.

Aortic Valve↗