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Biomedical subjects

K Kvernebo

Publications and source records attributed to K Kvernebo.

At least 37 records · Page 2Linked to original sources
PubMed1998

Spectral analysis of the laser Doppler perfusion signal in human skin before and after exercise.

Spectral analysis based on wavelet transformation of the periodic oscillations of the cutaneous laser Doppler flowmetry (LDF) signal was used to analyze exercise-induced changes in flow motion in humans. The measurements were performed on the forearm skin in nine healthy, less-trained subjects before and after exercise. Periodic oscillations with frequencies of around 1, 0.3, 0.1, and 0.04 Hz were demonstrated, which are proposed to represent the influence of heart beat, respiration, intrinsic myogenic activity, and the neurogenic factors, respectively, on cutaneous blood flow. We also demonstrated oscillations with a frequency of around 0.01 Hz both before and after exercise. The mean spectral amplitude in the frequency range from 0.0095 to 2.3 Hz increased twofold (P = 0.004) in response to exercise. This increase results from a significant increase in the amplitude of oscillations of around 1, 0.3, and 0.1 Hz. The amplitude of oscillations of around 1 and 0.3 Hz increased onefold in response to exercise (P = 0.02 for both frequencies), whereas the amplitude of oscillations of around 0.1 Hz increased threefold (P = 0.008). Furthermore, to evaluate relative changes of each particular oscillation in response to exercise, the absolute amplitude of each frequency interval was divided by the mean spectral amplitude. In this way, the relative contribution of oscillations of around 0.01 and 0.04 Hz were shown to decrease significantly following exercise (P = 0.008 and P = 0.004, respectively). The relative contribution of the oscillations of around 0.1 Hz increased, although not statistically significant (P = 0.08), while the relative contribution of the oscillations of around 0.3 and 1 Hz to the total flow motion remained unchanged in response to exercise (P = 0.84 and P = 0.95, respectively). These findings indicate an increased contribution of the oscillations of around 0.1 Hz to the regulation of the cutaneous blood flow following exercise, whereas oscillations of around 0.04 and 0.01 Hz contribute less. We conclude that spectral analysis using a wavelet transformation of the LDF signal is a valuable tool for use in the evaluation of exercise-induced changes in the dynamics of cutaneous microvascular blood flow, but further studies are necessary to clarify the physiological origin of these oscillations.

Exercise↗
PubMed1998

Enhanced endothelium-dependent vasodilatation in human skin vasculature induced by physical conditioning.

Functional alterations to the endothelial cells of the vascular system may contribute to the improved circulatory performance induced by physical conditioning. We evaluated microvascular reactivity to iontophoretic application of acetylcholine (ACh) and sodium nitroprusside (SNP) through the skin and blood perfusion measurements in the same area using laser Doppler flowmetry. Whereas ACh acts on smooth muscle cells of the vascular system via the production of vasodilator substances from the endothelium, SNP is an endothelium-independent vasodilator acting on vascular smooth muscle cells directly. The study was performed using two groups of subjects with different levels of aerobic endurance, long distance runners competing at national level (n = 9) and controls (n = 9). The subjects were tested for 40 min on a treadmill before and after an exercise test at 80% of their maximal oxygen uptake. During stimulation by ACh cutaneous perfusion increased to a higher level in the athletes than in the controls (overall P<0.05), whereas an acute period of exercise abolished this difference (overall P>0.6). There was no significant difference between the athletes and the controls with respect to the SNP-induced increase in cutaneous perfusion either before (P>0.9) or after (P>0.9) exercise. The higher cutaneous perfusion responses to stimulation with ACh in the athletes than in the controls may support the hypothesis that regular exercise modifies the responsiveness of the cutaneous endothelium. The difference in ACh-induced perfusion and in unstimulated forearm perfusion between the two groups was present only at rest. This finding indicated that mechanisms were introduced during exercise, which compensated for the lower endothelial sensitivity to stimulation in the controls at rest.

Acetylcholine↗
PubMed1998

In vitro function of an adjustable temporary venous spring filter: comparison with the temporary RF02 filter and the permanent Greenfield vena cava filter.

RATIONALE AND OBJECTIVES: The authors compared in vitro function of a temporary venous spring filter with that of a temporary RF02 filter and a permanent Greenfield filter. MATERIALS AND METHODS: All three types of filters were placed in thin polyethylene tubes (diameters, 10.0-18.0 mm). Physiologic saline was substituted for flowing blood, and blood clots of three sizes (6 x 10 mm, 6 x 20 mm, 9 x 20 mm) were funneled to the filters. Clot-trapping ability of each filter and elevation of intraluminal pressure after clot trapping were assessed for each tube size. RESULTS: No statistically significant elevation in intraluminal pressure was detected immediately after placement of any filter. The clot-trapping ability of the spring filter and of Greenfield filter were slightly lower than that of the RF02 filter, but the differences were not statistically significant. After filters had trapped large clots, a high pressure gradient was detected in the 10.0-mm tube for all filters. The spring filter was associated with a higher pressure than the other filters in the 12.0-mm tube (P < .05). CONCLUSION: In vitro function of the spring filter was satisfactory in comparison with that of the RF02 filter and the Greenfield filter. For efficient filtering in the inferior vena cava, development of a larger version of the filter may be necessary.

Equipment Design↗
PubMed1998

Exercise capacity in heart transplant recipients: relation to impaired endothelium-dependent vasodilation of the peripheral microcirculation.

OBJECTIVES: The aim of this study was to examine the responses to endothelium-dependent and -independent vasodilators on the peripheral microcirculation in heart transplant recipients in relation to exercise capacity compared with that in healthy controls. BACKGROUND: Impaired endothelium-dependent vasodilation of the microcirculation may play an important role in the limitation of exercise capacity after heart transplantation. METHODS: Microvascular perfusion responses to four graded levels of iontophoretically applied 1% acetylcholine (endothelium-dependent vasodilator) and 1% sodium nitroprusside (SNP) (endothelium-independent) in the forearm skin of 42 transplant recipients and 16 age-matched controls were determined by laser Doppler perfusion measurements. Maximal exercise capacity was assessed by peak oxygen uptake (peak VO2) during progressive, symptom-limited, upright bicycle exercise. RESULTS: With similar baseline perfusion levels in transplant recipients and controls (4.2 +/- 0.4 vs 4.6 +/- 0.6 arbitrary units [AU]), the increases in perfusion to acetylcholine, but not to SNP, were significantly attenuated in the transplant recipients: 7.0 +/- 1.0 vs 11.0 +/- 2.0, 12.7 +/- 1.5 vs 21.0 +/- 2.8, 21.0 +/- 1.9 vs 32.7 +/- 2.4, and 28.0 +/- 1.6 vs 39.2 +/- 2.4 AU, respectively (all p < 0.01). Peak VO2 was significantly lower in the transplant recipients (22.4 +/- 1.0 vs 38.0 +/- 2.9 ml/kg/min; p < 0.01). Furthermore, acetylcholine responses of the transplant recipients correlated closely to their peak VO2, irrespective of level of application (r = 0.63; p < 0.001, all four acetylcholine responses taken together), whereas no such correlation was found for SNP responses. In the control group, no relation was observed in acetylcholine/SNP responses to peak VO2. CONCLUSIONS: Exercise limitation in transplant recipients appears strongly associated with attenuated endothelium-dependent vasodilation of the peripheral microcirculation.

Acetylcholine↗
PubMed1998

[How shall we set priorities among experimental treatment methods?].

There is an increasing demand from patients to have access to new and promising treatment for severe diseases. Norway has recently started ordinary public funding of large-scale clinical investigation of treatment effect and safety for new treatment modalities. The government has thus established a new principle for funding a sub-category of clinical research: investigational medicine. How should we prioritize between promising clinical protocols when resources are scarce? The article examines criteria for priority setting in investigational medicine: quality of evidence; magnitude of expected benefit from treatment; balance between risks and benefits; quality of the research protocol; cost; and size of patient population. These criteria are applied on a controversial clinical examples, high-dose chemotherapy with hematopoietic stem cell support for metastatic breast cancer.

Antineoplastic Agents↗
PubMed1998

Endothelium-dependent vasodilation of the skin microcirculation in heart transplant recipients.

Patients with heart failure demonstrate attenuated endothelium-dependent vasodilation of the peripheral circulation, while this is suggested to be reversed after heart transplantation. However, data from human subjects are limited and conflict with studies on the peripheral vasomotor tone in cyclosporine-treated animals, suggesting endothelial dysfunction. We recorded forearm skin perfusion responses following graded iontophoresis of 1% acetylcholine (endothelium-dependent) and 1% sodium nitroprusside (endothelium-independent) by laser Doppler perfusion measurements in 32 heart transplant recipients and 15 age-matched controls. In addition, the hyperemic response to 3 min of blood flow occlusion to the forearm was measured on the third finger pulp. With comparable baseline values, the increases in perfusion to the 4 applications of acetylcholine were significantly attenuated in heart transplant recipients compared with controls: 59 +/- 9 vs. 146 +/- 32, 242 +/- 39 vs. 492 +/- 77, 480 +/- 66 vs. 845 +/- 120 and 699 +/- 77 vs. 993 +/- 139% (mean +/- SEM; all p < 0.01). Peak hyperemia (134 +/- 4 vs. 153 +/- 12 arbitrary units (AU); p < 0.05)), time for the hyperemic perfusion to return to preocclusive baseline (52.4 vs. 102.9 s; p < 0.01) and hence the area under the perfusion curve (1469 +/- 244 vs. 4581 +/- 921 AU s; p < 0.01) were reduced among heart transplant recipients. The area under the perfusion curve correlated significantly with mean arterial blood pressure (r = -0.60; p < 0.01) and with the responses to iontophoresis of acetylcholine (r = 0.41; p < 0.01). Two non-invasive tests of vascular function demonstrate attenuated endothelial-dependent microvascular responses in heart transplant recipients. The relative impact of prior congestive heart failure and postoperative factors, such as treatment with cyclosporine, remains to be determined.

Acetylcholine↗
PubMed1998

[How much is the workload of surgeons in Scandinavia?].

According to figures presented at the Bianniul General Meeting of the Scandinavian Surgical Society, the mean number of operations performed per surgeon at some clinics of different sizes in Denmark, Finland, Iceland, Norway and Sweden ranged from 90 to 240 in 1996. This corresponds to 2.6 to 8.5 hours actual operating time, though figures are misleading since time spent assisting at operations, or on endoscopies, minor diagnostics and outpatient procedures, and essential pre- and post-operative tasks is not included. This level of operative activity is considered barely sufficient for training surgeons or for maintaining surgical skills. Surgeons could devote more time to surgery if a greater proportion of their non-surgical workload was taken over by other hospital staff, which would also reduce the number of surgeons required.

General Surgery↗
PubMed1997

Human en bloc double-lung transplantation: bronchial artery revascularization improves airway perfusion.

BACKGROUND: Ischemic airway complications are common after en bloc double-lung transplantation with tracheal anastomosis. The aim of this study was to evaluate the effects of a direct revascularization of the donor bronchial artery with the recipient internal thoracic artery on airway perfusion. METHODS: Seven patients undergoing double-lung transplantation with tracheal anastomosis were investigated intraoperatively and postoperatively (12 to 36 hours) with endoscopic laser Doppler flowmetry. Sixteen patients undergoing coronary artery bypass grafting served as a control group. RESULTS: Two patients who had double-lung transplantation with tracheal anastomosis died of sepsis and multiorgan failure 1 week after transplantation. In the remaining 5 patients healing of the anastomosis was excellent during the observation period of 3 to 52 months. In 5 patients clamping of the attached internal thoracic artery induced a reduction of the laser Doppler flowmetry signal from 10% to 60%. In the 2 patients with the highest graft perfusion level, no clamping effect could be detected. Compared with the control group, perfusion was significantly higher in the transplanted airways intraoperatively, at 71 versus 55 arbitrary perfusion units (p < 0.01). Postoperative transplant airway perfusion values were not significantly different from the intraoperative value. The coefficient of variation of repeated measurements was higher in the transplanted airways, with a coefficient of variation of 0.22 versus 0.17 in the control group (p < 0.01), indicating heterogeneous transplant airway perfusion. CONCLUSIONS: This study has documented that revascularization with the internal thoracic artery supplies the transplanted airway with additional oxygenated blood.

Anastomosis, Surgical↗
PubMed1997

Hypertension prophylaxis with omega-3 fatty acids in heart transplant recipients.

OBJECTIVES: This study sought to determine whether omega-3 fatty acids act as hypertension prophylaxis in heart transplant recipients and have an impact on vascular reactivity. BACKGROUND: Cyclosporine-induced hypertension is probably related to endothelial dysfunction. Suggested vasodilatory mechanisms of omega-3 fatty acids may therefore be particularly beneficial in heart transplant recipients. METHODS: Heart transplant recipients were randomized to receive either 4 g of omega-3 fatty acids (treatment group, n = 14) daily or corn oil (placebo group, n = 14) from the fourth postoperative day. Twenty-four hour blood pressure monitoring was performed at day 12 and 1,2,3 and 6 months postoperatively. Microvascular endothelium-dependent vasodilation, evaluated by skin laser Doppler perfusion measurements of postocclusive reactive hyperemia, was determined preoperatively and at the end of the study. RESULTS: With comparable characteristics at the time of randomization, blood levels of cyclosporine did not at any point differ between the groups. After 6 months, systolic blood pressure decreased 2 +/- 4 mm Hg (mean +/- SEM) in the treatment group and increased 17 +/- 4 mm Hg in the placebo group (p < 0.01), whereas diastolic blood pressure increased 10 +/- 3 and 21 +/- 2 mm Hg (p < 0.01), respectively. The decrease in systolic blood pressure was inversely proportional to increases in concentrations of serum eicosapentaenoic and docosahexaenoic acid (p = 0.01). After 6 months, five patients in the treatment group and nine in the placebo group needed additional antihypertensive treatment. Although the endothelial-dependent phase of the reactive hyperemic response remained unchanged in the treatment group, it decreased significantly in the placebo group. CONCLUSIONS: Postoperative daily administration of 4 g of omega-3 fatty acids in heart transplant recipients is effective as hypertension prophylaxis, depending on increases in serum eicosapentaenoic and docosahexaenoic acids. Preservation of microvascular endothelial function, demonstrated by a more pronounced response to forearm skin ischemia in the treatment group, may contribute to the hypotensive role of omega-3 fatty acids.

Blood Pressure↗
PubMed1997

Adjustable temporary venous spring filter: in vitro assessment.

RATIONALE AND OBJECTIVES: The authors performed an in vitro study to evaluate a temporary venous spring filter that can extend vessels of a wide range of diameters to a slit-shaped canal. MATERIALS AND METHODS: Filters were placed in thin polyethylene tubes or in porcine inferior vena cava specimens (diameter, 10.0-16.0 mm). Physiologic saline was substituted for blood flow, and blood clots of three sizes (6 x 10, 6 x 20, and 9 x 20 mm) were funneled to the filter. Clot-trapping ability was assessed by the degree of luminal extension. RESULTS: When the luminal extension was increased from 2.6r to 2.8r (where r is the original radius of the vein models), clot-trapping ability increased significantly (61.1%-87.5% in polyethylene tubes and 15.8%-77.5% in venous specimens, P < .001). When the luminal extension was increased to 3.0r, more than 90% of the clots were trapped in all tubes. After trapping the small, medium, and large clots, mean intraluminal pressure elevation was 1.0, 1.0, and 17.0 cm of saline, respectively. CONCLUSION: Despite its simple design, the spring filter proved to be an efficient filtering device.

Animals↗
PubMed1997

Erythromelalgia: a clinical study of 87 cases.

We report on aetiological factors, clinical findings and prognosis of 87 patients with erythromelalgia (EM). This is the largest material reported in the western literature. There is a 100% follow up of patients with observation period up to 11 years. There were 61 females and 26 males. About two-thirds of the patients were primary cases and around three-quarters had a chronic condition. The condition was more common in lower than in upper extremities. Over time patients with erythromelalgic syndrome gradually get worse, those with primary and secondary acute EM get better, whilst primary and secondary chronic EM remain stable.

Adult↗
PubMed1996

Spatial and temporal evaluation of locally induced skin trauma recorded with laser Doppler techniques.

The single-fiber laser Doppler flowmetry (SF-LDF) technique has been used to study perfusion within tissues. The insertion of the SF-LDF probe into human skin locally alters microcirculation for more than 70 min after positioning. In this study the SF-LDF and a newly developed laser Doppler imager (LDI) were used to describe the spatial distribution, the intensity, and the temporal course of the trauma following intracutaneous insertion of the probe. The LDI scanned a human skin area of 6 x 6 cm (36 x 36 pixels). A flexible SF-LDF probe was inserted intradermally in the same measuring region. Recordings were performed for 120 min with the two techniques simultaneously. With the SF-LDF probe maximal hyperemia was recorded after 5-30 min. After a gradual and slow decrease most of the subjects reached a steady-state level within 80-100 min. A 3-min tourniquet occlusion test was performed 120 min after SF probe positioning. A significant hyperemic response was recorded, indicating that almost no posttraumatic activity was present at this time. The area of increased perfusion recorded with the LDI had an oval to circular configuration with a maximal extension after 5-10 min (radius 1.5-2 cm, area 8.9 cm2). The zone of maximal hyperemia was distributed adjacent to the intradermal probe, gradually decreasing toward the periphery. No significant hyperemia was shown with LDI after 100 min. There was a concordance between the time courses of the hyperemic response obtained with the two techniques.

Adult↗
PubMed1996

Laser doppler-recorded reactive hyperaemia in the forearm skin during the menstrual cycle.

OBJECTIVE: By means of laser Doppler flowmetry to describe the changes in resting microvascular perfusion and post-occlusive reactive hyperaemia in skin of the forearm and finger pulp throughout the menstrual cycle. DESIGN: Prospective descriptive study. SETTING: University Hospital of Tromso, Norway. SAMPLE: Fifteen nonsmoking healthy women were studied in the follicular (days 2 to 7) and the luteal (days 19 to 24) phase of the menstrual cycle. RESULTS: Resting perfusion in forearm and finger pulp as well as post-occlusive reactive hyperaemia in finger pulp were unchanged from the follicular to the luteal phase. The peak perfusion value of the reactive hyperaemic response after 1 min of arterial occlusion was significantly reduced from the follicular to the luteal phase (P<0.01) in forearm skin. The repayment for the blood flow debt, which is the hyperaemic response in percentage of the ischaemic build-up, was also reduced (P<0.01). After 3 min of arterial occlusion, significant reductions in peak post-occlusive flow (P<0.01), recovery time, which is the total duration of the hyperaemic response (P<0.01), and the repayment (P<0.01) were observed. A significant correlation was found between the ratio serum oestradiol/progesterone and repayment after 3 min of arterial occlusion in forearm skin (r=0.71,P<0.001). CONCLUSIONS: Vascular reactivity is altered during the menstrual cycle. In the luteal phase, significant reductions in peak perfusion, repayment and recovery time were seen. The mechanisms behind these findings are unclear, but probably involve changes in both serum oestradiol and progesterone levels.

Adolescent↗
PubMed1996

Postocclusive hyperaemia in skin measured in pigs by laser Doppler: influence of site of arterial stenosis in the limb.

OBJECTIVE: To investigate how site and severity of arterial stenosis, and distance between tourniquet and measuring probe influences the postocclusive hyperaemic response in limb skin recorded by laser Doppler. DESIGN: Open study. MATERIAL: Nine Norwegian Landrace pigs. INTERVENTION: Experimental stenoses in the abdominal aorta, the external iliac and femoral arteries. The hyperaemic responses were recorded with the probe at two different distances from the tourniquet. MAIN OUTCOME MEASURES: Curve pattern, relative reduction in flux between the two peaks in double humped curves, and time to peak hyperaemic flux. RESULTS: Double humped curves were produced at all sites, but the blood pressure gradient required at the stenosis was greater the more proximal the stenosis. In distal stenoses there was a greater relative reduction in flux between the two peaks (p < 0.05). The time to peak hyperaemic flux was related to the gradient of the stenosis (mmHg) (r = 0.62, p < 0.0001), but was independent of its site. Increased distance between the tourniquet and the probe gave lower laser Doppler amplitudes and prolonged the time to peak hyperaemia in experiments with femoral artery stenosis (p < 0.05). CONCLUSION: The hyperaemic response is governed by both the severity and the site of arterial stenosis. Stenoses distal to the tourniquet seem to impair the initial reperfusion more than comparable lesions proximal to the tourniquet. Time to reach peak hyperaemia is the single variable most closely related to the severity of the stenosis.

Animals↗
PubMed1993

[Tracheal compression treated with endoluminal stents].

Tracheobronchial stenoses can be caused by growth of endoluminal tumour or by external compression. Endoluminal tumours can be treated by means of endoscopically applied lasers, while tumours in the oesophagus, thyroid gland, or lymph nodes which compress the airways connor be reached by this type of treatment. We report four cases where life-threatening compression of airways by malignant tumours was successfully relieved by stenting the trachea with a silicone stent, Endoxane. The stent was inserted through a rigid bronchoscope, and the operative procedure was uneventful in all cases. Postoperatively, the patients did not experience severe discomfort from the stent, and neither dislocation of the stent nor retention of secretions was a problem. All the patients died of cancer-related causes, but none died from suffocation. It is concluded that tracheo-bronchial stenting is a valuable supplement to irradiation in palliative treatment of airway compression of airways caused by malignant tumours.

Adult↗
PubMed1993

The significance of probe design in evaluation of colonic perfusion with laser Doppler flowmetry.

The significance of probe design for laser Doppler flowmetry measurement depth and variation was investigated by determining flux versus pressure relations and spatial variability with various probes placed on the serosal surface of porcine sigmoid colon. For two large probes (three optical fibers with diameter and center separation > or = 500 microns) the flux versus pressure relations showed autoregulation, indicating that the mucosal perfusion contributed to the flux signal. The curves were reproducible between individuals. With two smaller probes linear flux versus pressure relations were obtained, indicating a shallow measurement not influenced by the autoregulated mucosal perfusion. The spatial variation expressed as coefficients of variation of repeated recordings at each pressure level was significantly greater with the smaller probes (p < 0.001). For clinical use the larger probes should be preferred. These include all wall layers, and only 3 repeated recordings are needed to obtain a reproducible mean flux value within +/- 10%, as opposed to 10 with the smaller probes.

Animals↗
PubMed1993

Laser Doppler flux and tissue oxygen tension as indicators of colonic perfusion in pigs.

OBJECTIVE: To evaluate laser Doppler flowmetry (LDF) and tissue oximetry (TpO2) for intraoperative assessment of colonic perfusion in pigs. MATERIAL: Eight pigs weighing from 19-22 kg. INTERVENTIONS: Relationships of laser Doppler flux and TpO2 to mean arterial pressure (MAP) were measured in porcine sigmoid colon. The influence of different fractional inspired oxygen concentrations (FiO2) and the variability of the laser Doppler flux were evaluated. RESULTS: Highly significant reproducible non-linear perfusion compared with pressure relations were found with both methods (r > or = 0.9, p < 0.0001). There was a rapid decrease when MAP fell below 90 mmHg. The dependency of TpO2 on FiO2 was omitted by using the ratio TpO2:PaO2. The coefficient of variation of repeated LDF recordings of 30 second duration with the hand held probe was 0.11 (0.07-0.16) (median and 95% confidence interval). Three recordings gave a reproducible mean flux with an estimated precision of 10% either way. Simultaneous recordings with sutured and hand-held probes correlated well (r > or = 0.9, p < or = 0.01). CONCLUSION: Both methods yielded quantitative and reproducible intraoperative assessments of colonic perfusion, and are applicable for clinical use.

Animals↗