Biomedical subjects

A Kastrup

Publications and source records attributed to A Kastrup.

31 records · Page 2Linked to original sources

PubMed1999

Regional variability of cerebral blood oxygenation response to hypercapnia.

In functional magnetic resonance imaging studies changes in blood oxygenation level-dependent (BOLD) signal intensities during task activation are related to multiple physiological parameters such as cerebral blood flow, volume, and oxidative metabolism, as well as to the regional microvascular anatomy. Consequently, the magnitude of activation-induced BOLD signal changes may vary regionally and between subjects. The aim of this study was to use a uniform global stimulus such as hypercapnia to quantitatively investigate the regional BOLD response in the human brain. In 10 healthy volunteers, T2*-weighted gradient echo images were acquired for a total dynamic scanning time of 9 min during alternating periods of breath holding for 30 s after expiration and self-paced normal breathing for 60 s. Hypercapnia-induced BOLD signal changes in the sensorimotor cortex, frontal cortex, basal ganglia, visual cortex, and cerebellum were significantly different (P < 0.001) and varied from 1.8 to 5.1%. The highest BOLD signal changes were found in the cerebellum and visual cortex, whereas the lowest BOLD signal increase was observed in the frontal cortex. These results demonstrate a regional dependence of the BOLD signal changes during breath hold-induced hypercapnia, indirectly supporting the notion of regional different sensitivities of BOLD responses to task activation.

Adult↗

PubMed1999

Diffusion-weighted magnetic resonance imaging: theory and potential applications to child neurology.

Magnetic resonance imaging (MRI) is an excellent tool for the investigation of neurological disorders in children. Diffusion-weighted MRI (DWI) is sensitive to the diffusion (or molecular displacement) of water in tissue. The purpose of this article is to describe briefly the basic theory behind DWI and to discuss its potential applications to neurological disorders in children. We demonstrate that DWI is a sensitive technique for the detection of acute brain injury, and that it is well suited for monitoring brain development, particularly myelination and white matter changes.

Acute Disease↗

PubMed1999

Gender differences in cerebral blood flow and oxygenation response during focal physiologic neural activity.

Using functional magnetic resonance imaging techniques CBF and oxygenation changes were measured during sustained checkerboard stimulation in 38 right-handed healthy volunteers (18 men and 20 women). The average blood oxygenation level dependent (BOLD) contrast technique signal intensity change was 1.67 +/- 0.6% in the group of male volunteers and 2.15 +/- 0.6% in the group of female volunteers (P < .05). Baseline regional CBF (rCBF) values in activated gray matter areas within the visual cortex were 57 +/- 10 mL x 100 g(-1) x min(-1) in women and 50 +/- 12 mL x 100 g(-1) x min(-1) in men, respectively (P = .09). Despite a broad overlap between both groups the rCBF increase was significantly higher in women compared to men (33 +/- 5 mL x 100 g(-1) x min(-1) versus 28 +/- 4 mL x 100 g(-1) x min(-1), P < .01). The increase of rCBF was not correlated with the baseline rCBF (mL x 100 g(-1) x min(-1)) (r(s) = 0.01, P = .9). Moreover, changes of rCBF were not correlated with changes in BOLD signal intensities (r(s) = 0.1, P = .7). Enhanced rCBF response in women during visual stimulation could be related to gender differences in visual physiology or may reflect gender differences in the vascular response to focal neuronal activation. Gender differences must be considered when interpreting the results of functional magnetic resonance imaging studies.

Adult↗

PubMed1999

Decompressive craniectomy, reperfusion, or a combination for early treatment of acute "malignant" cerebral hemispheric stroke in rats? Potential mechanisms studied by MRI.

BACKGROUND AND PURPOSE: Both early reperfusion and decompressive craniectomy have proved beneficial in the treatment of large space-occupying "malignant" hemispheric stroke. The aim of this study was to directly compare the benefit of reperfusion with that of craniectomy and to study the effects of combined treatment in a rat model of focal cerebral ischemia. METHODS: Cerebral ischemia was introduced in 28 rats. Four groups were investigated: (1) no treatment, (2) decompressive craniectomy, (3) reperfusion, and (4) reperfusion and craniectomy as treatment at 1 hour after middle cerebral artery occlusion. Perfusion- and diffusion-weighted MRI were performed serially from 0.5 to 6 hours after middle cerebral artery occlusion. RESULTS: The 6-hour DWI-derived hemispheric lesion volumes in the reperfusion group (10.2+/-3.9%), the craniectomy group (23.0+/-6.4%), and the combination group (21.8+/-12.4) were significantly smaller than that in the control group (44.1+/-5.4%) (P<0.05). Reperfusion, craniectomy, and combined treatment led to higher perfusion in the cortex compared with the control group, whereas only reperfused animals achieved significantly higher perfusion in the basal ganglia. In 5 animals, combined reperfusion and decompressive craniectomy resulted in an early contrast media enhancement. CONCLUSIONS: Early reperfusion and craniectomy were shown to be effective in decreasing infarction volume by improving cerebral perfusion. Reperfusion remains the best therapy in malignant hemispheric stroke. Combined treatment yields no additional benefit compared with single treatment, probably because of early blood-brain barrier breakdown.

Acute Disease↗

PubMed1999

Cerebral blood flow-related signal changes during breath-holding.

BACKGROUND AND PURPOSE: In the past, functional MR imaging techniques have been used successfully to determine cerebrovascular reactivity (CVR) to various stimuli, complementing the arsenal of functional brain investigations feasible with MR imaging. While previous studies have focused on blood oxygenation changes under vasodilatory stress, the aim of this study was to assess regional cerebral blood flow (rCBF) changes during breath-holding by using a flow-sensitive alternating inversion recovery (FAIR) imaging technique. METHODS: In six healthy volunteers, FAIR images were acquired during alternating periods of breath-holding and breathing at 40-second intervals after inspiration and at 30-second intervals after expiration, for a total dynamic scanning time of 10 minutes. To quantify the rCBF changes, we obtained 2.5-minute baseline samples during normal breathing. RESULTS: Repeated challenges of breath-holding induced an overall rise in rCBF. In general, rCBF changes were greatest in gray matter and were insignificant in white matter. Using the mean values of the baseline images collected before breath-holding to calculate the rCBF changes, we found that quantitative analysis yielded an rCBF increase of 47% to 87% after breath-holding. The rCBF changes clearly depended on the breath-holding duration and technique; however, for one given breath-holding paradigm the results showed relatively small interindividual variability. CONCLUSION: rCBF changes during a simple vascular challenge can be detected and quantified by means of functional MR imaging at 1.5 T. Noninvasive assessment of CVR could become a useful clinical tool to identify persons with impaired CVR.

Adult↗

PubMed1998

Cerebral blood flow and CO2 reactivity in interictal migraineurs: a transcranial Doppler study.

There is still some controversy about alterations in velocity of blood flow and in cerebral vasomotor reactivity of intracranial arteries in migraineurs during the interictal phase. By means of simultaneous bilateral transcranial Doppler ultrasonography we, therefore, assessed intracranial blood flow velocities and cerebrovascular reactivity to carbon dioxide of all three basal brain arteries in 20 migraineurs during the interictal phase and 30 nonheadache-prone control subjects. Mean blood flow velocities were higher in migraineurs than in controls in all three arteries on both sides, with a significant difference (P < 0.05) for the right anterior cerebral artery and middle cerebral artery under basal conditions and for the right posterior cerebral artery during hypercapnia. Similarly, the cerebrovascular reactivity to carbon dioxide was always higher in patients than in controls, with a significant difference for the left anterior and the right middle cerebral arteries (P < 0.05) and the right posterior cerebral artery (P < 0.01). The broad overlap of cerebrovascular blood flow velocities and CO2 reactivities in patients and controls precluded identification of values diagnostic of migraine. Nevertheless, transcranial Doppler ultrasonography offers the opportunity to noninvasively monitor cerebral blood flow parameters and, therefore, represents a valuable tool for vascular research in migraine.

Adult↗

PubMed1998

Hemodynamic sequelae of ventricular tachyarrhythmias on cerebral blood flow.

The present experiments were designed to compare the behavior of cerebral blood flow (CBF) during acute moderate and severe hypotensive episodes induced by either ventricular tachycardias (VT) or by hemorrhage. Using the microsphere method CBF was determined in 20 Sprague-Dawley rats during sinus rhythm (Group A), in 28 animals during high-rate VT (Group B) and in 10 animals after hemorrhage (Group C). According to the decrease in blood pressure and with respect to the lower threshold of cerebral autoregulation Group B was divided into 2 subgroups (B1: 80-130 mmHg; B2: 50-80 mmHg) retrospectively. While CBF remained constant in Group B1 (0.98 +/- 0.3 ml g-1 min-1 vs. 1.01 +/- 0.32 in controls, NS), CBF decreased markedly during severely hypotensive VT in Group B2 (0.52 +/- 0.2 ml g-1 min-1, p < 0.001 vs. A; p < 0.05 vs. C) and during hypovolemic hypotension in Group C (0.77 +/- 0.22 ml g-1 min-1 vs. A; NS). Cerebrovascular resistance and autoregulation indices indicated a maintenance of CBF regulation during hypovolemic hypotension and a failure during normovolemic hypotension. These findings indicate that the autoregulatory ability of the brain is substantially more stable during hypovolemic hypotension than during normovolemic hypotension. Therefore, the hemodynamic sequelae of acute hypotensive episodes on CBF depend on the underlying cause of hypotension.

Animals↗

PubMed1998

Functional magnetic resonance imaging of regional cerebral blood oxygenation changes during breath holding.

BACKGROUND AND PURPOSE: Recently, noninvasive MRI methods have been developed that are now capable of detecting and mapping regional hemodynamic responses to various stress tests, which involve the use of vasoactive substances such as acetazolamide or inhalation of carbon dioxide. The aim of this study was to assess regional cerebral blood oxygenation changes during breath holding at 1.5 T. METHODS: In 6 healthy volunteers, T2*-weighted gradient echo images were acquired for a total dynamic scanning time of 10 minutes during alternating periods of breath holding and normal breathing at 40-second intervals after inspiration, at 30-second intervals after expiration, and at 18 seconds after expiration. To quantify the relative signal changes, 2.5-minute baseline image sampling with normal breathing was carried out. RESULTS: Repeated challenges of breath holding of various durations induced an overall rise in blood oxygen level-dependent (BOLD) signal intensities. In general, BOLD signal intensity increases were greatest in gray matter and nonsignificant in white matter. Depending on the breath-holding duration and techniques, BOLD signal intensity increases of all activated pixels varied from 0.8% to 3.5%. CONCLUSIONS: The present study demonstrates that cerebral blood oxygenation changes during breath holding can be detected by means of fMRI at 1.5 T. The breath-holding test, a short and noninvasive method to study cerebral hemodynamics with fMRI, could become a useful alternative to the acetazolamide or CO2 test.

Adult↗

PubMed1998

Changes of cerebrovascular CO2 reactivity during normal aging.

BACKGROUND AND PURPOSE: During the past decade, transcranial Doppler sonography has widely been used to assess blood flow velocities in the basal intracranial arteries and cerebrovascular reactivity (CR) to various stimuli. Although numerous studies have shown a decline of cerebral blood flow velocity with age, the age dependency of CR, including cerebrovascular CO2 reactivity, however, is controversial. Recently, we have reported a significant sex-related difference in CR, stressing the need to study the relation between normal aging and CR in both sexes separately. METHODS: By means of transcranial Doppler sonography, CR was determined in 100 healthy, nonsmoking volunteers (age 20 to 70 years, 10 men and 10 women per decade). RESULTS: In men, no change of CR with increasing age could be observed (P=0.98). In contrast, CR in women declined significantly, with a step decrease from the 4th to the 5th decades (F=4.413; P<0.01) and was significantly higher in the 3rd and 4th compared with the 5th, 6th, and 7th decades (P<0.05). Information on hormone replacement therapy (HRT) in women of the 6th and 7th decades was obtained retrospectively. HRT was associated with enhanced CR (HRT, n = 7 versus non-HRT, n = 13; P<0.001), with values similar to those found in premenopausal women. CONCLUSIONS: There are no changes of CR during normal aging in men, whereas CR declines significantly from the 4th to the 5th decades in women. HRT in postmenopausal women appears to enhance CR.

Adult↗

PubMed1997

Sex dependency of cerebrovascular CO2 reactivity in normal subjects.

BACKGROUND AND PURPOSE: Cerebrovascular CO2 reactivity can be assessed easily and reliably by transcranial Doppler sonography. The objectives of the present study were to evaluate sex differences in cerebral CO2 reactivity and to specify the relation between CO2 and cerebral blood flow velocity. METHODS: CO2 reactivity of the circulation of both middle cerebral arteries was measured by bilateral transcranial Doppler sonography in 60 healthy volunteers (30 men, 30 women) aged 21 to 58 years. End-tidal carbon dioxide tensions (PETCO2) were elevated with the use of carbogene gas (95% O2, 5% CO2). In each subject the mean blood flow velocity (Vmean) was plotted as a function of PETCO2. RESULTS: The best-fit curves for the relation of Vmean/PETCO2 were exponential functions, with the following basic equation: Vmean (cm/s) = aebx, where a is a theoretical quantity representing Vmean at a PCO2 of 0 mm Hg, b is the relative slope of the curve (slope divided by the value of the function) corresponding to the definition of reactivity, and x is the PETCO2 (mm Hg). The mean value of b was 0.037 +/- 0.008 in women and 0.030 +/- 0.010 in men. ANOVA demonstrated a significant difference between men and women (P < .001). CONCLUSIONS: This study demonstrates a highly significant sex-related difference in CO2-induced cerebral vasomotor reactivity. The relation between altered carbon dioxide tensions and blood flow velocities of both middle cerebral arteries in 60 healthy volunteers was found to be exponential.

Adult↗

PubMed1995

Somatic care wanted by HIV-infected intravenous drug abusers: the patients' opinions and experiences.

The somatic care of HIV-infected intravenous drug abusers (IVDUs) is often combined with many problems. The addict is often an unpopular patient, but society must assume responsibility for him or her and it is important to solve care problems in an appropriate way. This study was undertaken in order to investigate what kind of care addicts want when they become somatically ill. A questionnaire was given to patients who acquired HIV infection due to intravenous drug abuse, who visited an outpatient clinic for HIV-infected patients at the Department of Infectious Disease, Huddinge Hospital, Stockholm, Sweden. A total of 72 of the original 78 questionnaires could be evaluated. Thirty respondents took part in the Stockholm Methadone Programme. The patients were asked to rank the importance of professional competence among the staff. The patients ranked competence in pain treatment highest followed by competence in somatic medical care. Lower ranked, but still perceived as important, was competence in psychiatric medical care and social welfare work. Experience in treatment of addiction was ranked as less important. It can be concluded that it is fruitful to ask IVDUs about their preferences concerning care.

AIDS-Related Opportunistic Infections↗

PubMed1994

Characterization of antibodies using N-terminally truncated peptides produced in an automatic protein sequencer.

Antibodies raised against short peptides coupled via their C-terminus will often be specific for the N-terminus. Peptides lacking one or two N-terminal residues seemed useful for characterization of such antibodies. A simple method for N-terminal truncation of nmol amounts of peptides is described. An automatic protein sequencer was used as a suitable reactor. The method is generally versatile, but some structural features of the peptides limited the yields. Thus, purification and careful identification of the products was needed. The specificities of several antibodies were characterized by incubation with the singly and doubly truncated versions of the peptides used for immunization and/or standards. The results disclosed dependency on the N-terminal residue(s) varying from none to more than 10(4) times reduced binding.

Amino Acid Sequence↗

PubMedDate not supplied

No effect of prophylactic treatment with metoprolol on cerebrovascular CO2 reactivity in migraineurs.

The prophylactic effect of metoprolol in the treatment of migraine is well known, but its mode of action is still unclear. In the past, increased CO2 reactivity has been reported as one pathognomic finding in interictal migraineurs. Using transcranial Doppler we assessed CO2 reactivity in 20 migraineurs before and 3 h after the first intake of 50 mg metoprolol, and subsequently twice after 1 and 8 weeks of continuous therapy with 150 mg metoprolol/d. Before initiation of therapy, migraineurs as a group had increased CO2 reactivity (p=0.07) compared to 20 age- and sex-matched volunteers. While treatment with metoprolol has been reported to affect amplitudes of increased contingent negative variation or visual evoked potentials in interictal migraineurs, it had no influence on enhanced CO2 reactivity in the present study. Moreover, the pretreatment value of CO2 reactivity did not correlate with the clinical efficacy of metoprolol after a 2-month treatment period.

Adrenergic beta-Antagonists↗