Triggered electromyography (tEMG) in the lumbar spine It́s reliable? Correlation of tEMG with postoperative CT images in lumbar instrumentation. / Electromiografía evocada (tEMG) en la columna lumbar. ¿Es confiable? Correlación de tEMG con imágenes de TC posoperatorias en la instrumentación lumbar.

INTRODUCTION: Instrumentation with pedicle screws (PS) can compromise the adjacent neural structures. Triggered electromyography (tEMG) is a modality of intraoperative neuromonitoring, used to assist in the placement of these. The objective of the present study is to evaluate the reliability of this tool. METHOD: Retrospective review of patients underwent posterior lumbar fusions from January 2017 to December 2019, correlating postoperative CT images (postop CT) with tEMG results for each PS with a threshold of 10mA, establishing sensitivity and specificity of this tool. Diagnostic test and receiver operating characteristic curve were performed to evaluate the area under the curve. RESULT: A total of 275 PS were evaluated between L1 to S1; 5 PS showed concordance for an inadequate trajectory, while 10PS, with tEMG <10mA, were correctly positioned. The postoperative CT identified 17 pedicle gaps not noticed by the tEMG. Sensitivity and specificity were 23% (95% CI: 8-45) and 96% (95% CI: 93-98), respectively, with a PPV of 33.3% and a NPV of 93.6%. The area under the curve was 0.74 (95% CI: 0.62-0.86) with a cut-off point of 24mA, showing a sensitivity of 77% (95% CI: 0.55-0.92) and specificity of 69% (95% CI: 0.63-0.75). CONCLUSION: Given its low sensitivity, we do not recommend tEMG as the sole test in the verification of PS. We recommend using a cut-off point ≤8mA as it demonstrated the highest levels of sensitivity and specificity. We do not recommend using high thresholds to increase sensitivity.

Electromiografía evocada (tEMG) en la columna lumbar. ¿Es confiable? Correlación de tEMG con imágenes de TC posoperatorias en la instrumentación lumbar / Triggered electromyography (tEMG) in the lumbar spine Its reliable? Correlation of tEMG with postoperative CT images in lumbar instrumentation

Introducción: La instrumentación con tornillos pediculares (TP) puede comprometer las estructuras neurales adyacentes. La electromiografía evocada (tEMG) es una modalidad del neuromonitoreo intraoperatorio utilizada para asistir la colocación de estos. El objetivo del presente estudio es evaluar la confiabilidad de esta herramienta. Método: Revisión retrospectiva de pacientes intervenidos de artrodesis lumbar posterolateral instrumentada desde enero del 2017 hasta diciembre del 2019. Se correlacionaron las imágenes de TC postoperatorias (TC-postop) con los resultados de la tEMG para cada TP con un umbral de 10mA, y se establecieron la sensibilidad y especificidad de esta herramienta. Se realizó test diagnóstico y la curva característica operativa del receptor para evaluar el área bajo la curva. Resultado: Se evaluaron 275 TP entre L1 y S1; 5 TP presentaban concordancia para una trayectoria inadecuada, mientras que 10TP, con tEMG <10mA, se encontraban correctamente posicionados. La TC-postop identificó 17 brechas pediculares no advertidas por la tEMG. La sensibilidad y la especificidad fue del 23% (IC 95%: 8-45) y 96% (IC 95%: 93-98), respectivamente, con un VPP del 33,3% y un VPN del 93,6%. El área bajo la curva fue de 0,74 (IC 95%: 0,62-0,86) con punto de corte de 24mA, que mostró una sensibilidad del 77% (IC 95%: 0,55-0,92) y una especificidad del 69% (IC 95%: 0,63-0,75). Conclusión: Dada su baja sensibilidad, no aconsejamos la tEMG como prueba única en la verificación de TP. Recomendamos la utilización de un punto de corte ≤8mA, ya que ha demostrado los niveles más altos de sensibilidad y especificidad. No recomendamos el uso de umbrales elevados para aumentar la sensibilidad.(AU)

Introduction: Instrumentation with pedicle screws (PS) can compromise the adjacent neural structures. Triggered electromyography (tEMG) is a modality of intraoperative neuromonitoring, used to assist in the placement of these. The objective of the present study is to evaluate the reliability of this tool. Method: Retrospective review of patients underwent posterior lumbar fusions from January 2017 to December 2019, correlating postoperative CT images (postop CT) with tEMG results for each PS with a threshold of 10mA, establishing sensitivity and specificity of this tool. Diagnostic test and receiver operating characteristic curve were performed to evaluate the area under the curve. Result: A total of 275 PS were evaluated between L1 to S1; 5 PS showed concordance for an inadequate trajectory, while 10PS, with tEMG <10mA, were correctly positioned. The postoperative CT identified 17 pedicle gaps not noticed by the tEMG. Sensitivity and specificity were 23% (95% CI: 8-45) and 96% (95% CI: 93-98), respectively, with a PPV of 33.3% and a NPV of 93.6%. The area under the curve was 0.74 (95% CI: 0.62-0.86) with a cut-off point of 24mA, showing a sensitivity of 77% (95% CI: 0.55-0.92) and specificity of 69% (95% CI: 0.63-0.75). Conclusion: Given its low sensitivity, we do not recommend tEMG as the sole test in the verification of PS. We recommend using a cut-off point ≤8mA as it demonstrated the highest levels of sensitivity and specificity. We do not recommend using high thresholds to increase sensitivity.(AU)

Triggered electromyography (tEMG) in the lumbar spine it's reliable? Correlation of tEMG with postoperative CT images in lumbar instrumentation / Electromiografía evocada (tEMG) en la columna lumbar. ¿Es confiable? Correlación de tEMG con imágenes de TC posoperatorias en la instrumentación lumbar

Introduction: Instrumentation with pedicle screws (PS) can compromise the adjacent neural structures. Triggered electromyography (tEMG) is a modality of intraoperative neuromonitoring, used to assist in the placement of these. The objective of the present study is to evaluate the reliability of this tool. Method: Retrospective review of patients underwent posterior lumbar fusions from January 2017 to December 2019, correlating postoperative CT images (postop CT) with tEMG results for each PS with a threshold of 10mA, establishing sensitivity and specificity of this tool. Diagnostic test and receiver operating characteristic curve were performed to evaluate the area under the curve. Result: A total of 275 PS were evaluated between L1 to S1; 5 PS showed concordance for an inadequate trajectory, while 10PS, with tEMG <10mA, were correctly positioned. The postoperative CT identified 17 pedicle gaps not noticed by the tEMG. Sensitivity and specificity were 23% (95% CI: 8-45) and 96% (95% CI: 93-98), respectively, with a PPV of 33.3% and a NPV of 93.6%. The area under the curve was 0.74 (95% CI: 0.62-0.86) with a cut-off point of 24mA, showing a sensitivity of 77% (95% CI: 0.55-0.92) and specificity of 69% (95% CI: 0.63-0.75). Conclusion: Given its low sensitivity, we do not recommend tEMG as the sole test in the verification of PS. We recommend using a cut-off point ≤8mA as it demonstrated the highest levels of sensitivity and specificity. We do not recommend using high thresholds to increase sensitivity.(AU)

Introducción: La instrumentación con tornillos pediculares (TP) puede comprometer las estructuras neurales adyacentes. La electromiografía evocada (tEMG) es una modalidad del neuromonitoreo intraoperatorio utilizada para asistir la colocación de estos. El objetivo del presente estudio es evaluar la confiabilidad de esta herramienta. Método: Revisión retrospectiva de pacientes intervenidos de artrodesis lumbar posterolateral instrumentada desde enero del 2017 hasta diciembre del 2019. Se correlacionaron las imágenes de TC postoperatorias (TC-postop) con los resultados de la tEMG para cada TP con un umbral de 10mA, y se establecieron la sensibilidad y especificidad de esta herramienta. Se realizó test diagnóstico y la curva característica operativa del receptor para evaluar el área bajo la curva. Resultado: Se evaluaron 275 TP entre L1 y S1; 5 TP presentaban concordancia para una trayectoria inadecuada, mientras que 10TP, con tEMG <10mA, se encontraban correctamente posicionados. La TC-postop identificó 17 brechas pediculares no advertidas por la tEMG. La sensibilidad y la especificidad fue del 23% (IC 95%: 8-45) y 96% (IC 95%: 93-98), respectivamente, con un VPP del 33,3% y un VPN del 93,6%. El área bajo la curva fue de 0,74 (IC 95%: 0,62-0,86) con punto de corte de 24mA, que mostró una sensibilidad del 77% (IC 95%: 0,55-0,92) y una especificidad del 69% (IC 95%: 0,63-0,75). Conclusión: Dada su baja sensibilidad, no aconsejamos la tEMG como prueba única en la verificación de TP. Recomendamos la utilización de un punto de corte ≤8mA, ya que ha demostrado los niveles más altos de sensibilidad y especificidad. No recomendamos el uso de umbrales elevados para aumentar la sensibilidad.(AU)

Women's mood at high altitude. sexual dimorphism in hypoxic stress modulation by the tryptophan-melatonin axis.

Sexual (and gender)-dimorphism in tolerance to hypobaric hypoxia increasingly matters for a differential surveillance of human activities at high altitude (HA). At low altitudes, the prevalence of anxiety and depression in women has already been found to double when compared with men; it could be expected to even increase on exposure to HA. In purposefully caring for the health of women at HA, the present work explores the potential involvement of the tryptophan (Trp)-melatonin axis in mood changes on exposure to hypobaric hypoxia. The present work highlights some already known anxiogenic effects of HA exposure. Hypoxia and insomnia reduce serotonin (5-HT) availability; the latter defect being expressed as failure of brown adipose tissue (BAT) activation and mood disorders. Rapid eye movement (REM) sleep organization and synapsis restoration that are additionally affected by hypoxia impair memory consolidation. Affective complaints may thus surge, evolving into anxiety and depression. Sex-related differences in neural network organization and hormonal changes during the menstrual cycle, and certainly also during the life cycle, underscore the possibility of 5-HT-related mood alterations, particularly in women on HA exposure. The mean brain rate of 5-HT synthesis at sea level is already 1.5-fold higher in males than in females. sexual dimorphism also evidences the overexpression effects of SERT, a 5-HT transporter protein. Gonadal and thyroid hormones, as influenced by HA exposure, further modulate 5-HT availability and its effects in women. Besides caring for adequate oxygenation and maintenance of one's body core temperature, special precautions concerning women sojourning at HA should include close observations of hormonal cycles and, perhaps, also trials with targeted antidepressants.

Delayed orexin signaling consolidates wakefulness and sleep: physiology and modeling.

Orexin-producing neurons are clearly essential for the regulation of wakefulness and sleep because loss of these cells produces narcolepsy. However, little is understood about how these neurons dynamically interact with other wake- and sleep-regulatory nuclei to control behavioral states. Using survival analysis of wake bouts in wild-type and orexin knockout mice, we found that orexins are necessary for the maintenance of long bouts of wakefulness, but orexin deficiency has little impact on wake bouts <1 min. Since orexin neurons often begin firing several seconds before the onset of waking, this suggests a surprisingly delayed onset (>1 min) of functional effects. This delay has important implications for understanding the control of wakefulness and sleep because increasing evidence suggests that different mechanisms are involved in the production of brief and sustained wake bouts. We incorporated these findings into a mathematical model of the mouse sleep/wake network. Orexins excite monoaminergic neurons and we hypothesize that orexins increase the monoaminergic inhibition of sleep-promoting neurons in the ventrolateral preoptic nucleus. We modeled orexin effects as a time-dependent increase in the strength of inhibition from wake- to sleep-promoting populations and the resulting simulated behavior accurately reflects the fragmented sleep/wake behavior of narcolepsy and leads to several predictions. By integrating neurophysiology of the sleep/wake network with emergent properties of behavioral data, this model provides a novel framework for investigating network dynamics and mechanisms associated with normal and pathologic sleep/wake behavior.

Disección carotídea en un paciente consumidor de cocaína / Carotid dissection in a cocaine-abusing patient

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Lung oxidative stress as related to exercise and altitude. Lipid peroxidation evidence in exhaled breath condensate: a possible predictor of acute mountain sickness.

Lung oxidative stress (OS) was explored in resting and in exercising subjects exposed to moderate and high altitude. Exhaled breath condensate (EBC) was collected under field conditions in male high-competition mountain bikers performing a maximal cycloergometric exercise at 670 m and at 2,160 m, as well as, in male soldiers climbing up to 6,125 m in Northern Chile. Malondialdehyde concentration [MDA] was measured by high-performance liquid chromatography in EBC and in serum samples. Hydrogen peroxide concentration [H(2)O(2)] was analysed in EBC according to the spectrophotometric FOX(2) assay. [MDA] in EBC of bikers did not change while exercising at 670 m, but increased from 30.0+/-8.0 to 50.0+/-11.0 nmol l(-1) (P<0.05) at 2,160 m. Concomitantly, [MDA] in serum and [H(2)O(2)] in EBC remained constant. On the other hand, in mountaineering soldiers, [H(2)O(2)] in EBC under resting conditions increased from 0.30+/-0.12 mumol l(-1) at 670 m to 1.14+/-0.29 mumol l(-1) immediately on return from the mountain. Three days later, [H(2)O(2)] in EBC (0.93 +/-0.23 mumol l(-1)) continued to be elevated (P<0.05). [MDA] in EBC increased from 71+/-16 nmol l(-1) at 670 m to 128+/-26 nmol l(-1) at 3,000 m (P<0.05). Changes of [H(2)O(2)] in EBC while ascending from 670 m up to 3,000 m inversely correlated with concomitant variations in HbO2 saturation (r=-0.48, P<0.05). AMS score evaluated at 5,000 m directly correlated with changes of [MDA] in EBC occurring while the subjects moved from 670 to 3,000 m (r=0.51, P<0.05). Lung OS may constitute a pathogenic factor in AMS.

Role of exercise and ascorbate on plasma antioxidant capacity in thoroughbred race horses.

During exercise, the oxygen consumption and the production of free radicals increase and can lead to oxidative stress with a deleterious effect on cellular structures involved in physical activity. To evaluate the oxidative stress produced by exercise and the role of ascorbate as an antioxidant, venous blood samples were obtained from 44 thoroughbred racehorses, before and after a 1000+/-200-m race at maximum velocity. Fourteen of these horses were treated intravenously with 5 g of ascorbate before running. Antioxidant capacity (PAOC), endogenous and exogenous ascorbate concentration, total antioxidant reactivity (TAR), urate concentration, creatine kinase activity, protein concentration and thiobarbiturate reactive substances (TBAR) as oxidative stress indicators were measured in the plasma of some of these horses. PAOC, TAR and TBAR increased after the race, while plasma ascorbate and urate concentrations remained unchanged. Total plasma protein (TPP) concentrations increased in line with antioxidant capacity. As predicted, both the plasma ascorbate concentration and PAOC increased immediately after ascorbate administration, but was not modified after the race, such as TBAR. However, in both groups plasma creatine kinase activity increased after the race. These results would suggest that the administration of ascorbate could nullify the oxidative stress produced by exercise in thoroughbred racehorses, but could not prevent muscular damage.

[Technique of abdominal ultrasonography in newborn foals and normal findings]. / Technik der Abdominalsonographie beim neugeborenen Fohlen und Darstellung von Normalbefunden.

Under field conditions, the diagnosis of foal's diseases relies almost exclusively on the physical examination. As the signs of illness in the equine neonate are frequently vage and non-localizing, the diagnosis of diseases may be problematic. This often causes misinterpretations and leads to ineffective prophylaxis and treatment. The purpose of this study was to evaluate the usefulness of diagnostic ultrasonography of the foal's abdomen under field conditions to provide an optimized technique and to describe the normal findings. Diagnostic ultrasonography of the abdomen was performed after obtaining clinical history and passing the physical examination of 25 foals without signs of abdominal problems. The foals were scanned in a stable box, being restrained by three persons in semi-lateral recumbency. Usually, sedation was not necessary. The ventral abdominal wall was clipped, a generous amount of ultrasound coupling gel was applied and massaged on the skin surface. The ultrasonographic examination was carried out using a portable sector scanner ("Microimager 2000", Ausonics) with 5.0 and 7.5-MHz transducers or a combined 5.0 and 7.5-MHz transrectal linear-array scanner ("450 Enhanced", Pie Medical). Employing the 5.0-MHz sector scanner first, the abdomen was explored from caudal to cranial in left and right semi-lateral recumbency. The 7.5-MHz scanner was used to attain higher resolution of certain structures. The sector scanner turned out to be suitable under field conditions and adequate to examine the abdominal organs. The transrectal linear-array scanner also provided the most important informations, although it was difficult to maintain a good contact area of the scan head. By ultrasonography it was possible to identify the urinary bladder, kidneys, spleen, liver and part of the gastrointestinal tract. Thus, application of ultrasound could successfully be performed on newborn foals under field conditions.

Vascular endothelial growth factor in exercising humans under different environmental conditions.

It was the aim of this study to investigate the time course of changes in the serum concentrations of vascular endothelial growth factor (VEGF) during a regular survival training programme combined with food and fluid deprivation and during a high altitude marathon run. We studied soldiers of the Austrian Special Forces performing survival training at sea-level and marathon runners of the Posta Atletica who crossed the border between Chile and Argentina at altitudes up to 4722 m. Baseline data collected before the 1-week of survival training showed that the soldiers had normal VEGF [n = 8, 246.7 (SD 118.5) pg.ml(-1)] serum concentrations which remained unchanged during the course of the study. Before the high altitude marathon the subjects showed normal VEGF serum concentrations [178 (SD 84.5) pg.ml(-1)]. After the run VEGF concentrations were found to be significantly decreased [41.0 (SD 41.6) pg ml(-1), P < 0.01]. It was concluded that prolonged physical stress during normobaric-normoxia did not alter the VEGF concentrations whereas during severe hypobaric-hypoxia decreased VEGF serum concentrations were measured, at least temporarily, after prolonged physical exercise which might have been due to changes in production, release, removal and/or binding of circulating VEGF.

Membrane lipid diffusion and band 3 protein changes in human erythrocytes due to acute hypobaric hypoxia.

Because it has been reported that hypoxia in rats may promote lipid peroxidation and other free radical reactions that could modify membrane lipids and proteins, the effect of acute hypobaric hypoxia on human erythrocyte membranes was investigated. 12-(1-Pyrene)dodecanoic acid fluorescent probe was used to assess short-range lateral diffusion status in the membrane bilayer. Membrane protein modification was detected by SDS-PAGE. Healthy young men were exposed for 20 min to the hypobaric hypoxia, simulating an altitude of 4,500 m. Under this condition, erythrocyte membrane lipids reached a state of higher lateral diffusivity with respect to normobaric conditions and membrane band 3 protein was modified, becoming more susceptible to membrane-bound proteinases. These observations suggest that acute hypobaric hypoxia may promote an oxidative stress condition in the erythrocyte membrane.

[Fat embolism--a too infrequently determined pathoanatomic diagnosis]. / Die Fettembolie--eine zu selten gestellte pathoanatomische Diagnose.

In 1993, pulmonary fat embolism occurred in 92 cases (17%) out of 527 clinical autopsies. It was found in 62% of patients who had suffered bone fractures, in 9% with soft tissue surgery and in 53% after resuscitation; non-traumatic fat embolism was present in 6% of the cases. The comparison group of 50 persons with lethal polytrauma revealed pulmonary fat embolism in 52% of the cases. Bone-marrow embolism and microthrombi accompanied fat embolism of the lungs; furthermore some of the persons with pulmonary fat embolism also expressed minor degrees of renal (55%) and cerebral (25%) fat emboli. A retrospective analysis of the clinical data revealed no specific symptoms: a so called fat embolism syndrome had not been discovered clinically in any of the cases with histologically proven fat embolism. The significance of pulmonary fat embolism as a cause of death with regard to histological and clinical findings is discussed.

Shift working in the Chilean Andes (> 3,600 m) and its influence on erythropoietin and the low-pressure system.

It was hypothesized that, in shift workers with a history of intermittent hypoxic stress (working 10 days at > 3,600 m, then resting for 4 days at sea level) for > 5 yr, the initial erythropoietin (EPO) response and the changes in central venous pressure (CVP) are different from those in Caucasian lowlanders. We studied the kitchen personnel (n = 11) of a mine (3,600 m) and a group of Caucasian lowlanders (n = 5). Blood samples were taken, and CVP was determined several times before, during, and after a typical shift. At baseline data collection (BDC) before transition, the shift workers had EPO concentrations of 5.2 +/- 2.4 mU/ml, which increased at altitude (P < 0.01) and returned to BDC values on the recovery (day 16). The Caucasians showed the same time course. Serum transferrin receptor concentrations did not change in either group. CVP values were generally higher in the shift workers than in the Caucasians. In conclusion, the hypothesis that the initial EPO response to a hypoxic stimulus is altered in these shift workers has to be refuted. Higher hemoglobin concentrations and/or CVP values in shift workers might be responsible for the rather low EPO concentrations in shift workers at BDC.

Olf-1-binding site: characterization of an olfactory neuron-specific promoter motif.

We report characterization of several domains within the 5' flanking region of the olfactory marker protein (OMP) gene that may participate in regulating transcription of this and other olfactory neuron-specific genes. Analysis by electrophoretic mobility shift assay and DNase I footprinting identifies two regions that contain a novel sequence motif. Interactions between this motif and nuclear proteins were detected only with nuclear protein extracts derived from olfactory neuroepithelium, and this activity is more abundant in olfactory epithelium enriched in immature neurons. We have designated a factor(s) involved in this binding as Olf-1. The Olf-1-binding motif consensus sequence was defined as TCCCC(A/T)NGGAG. Studies with transgenic mice indicate that a 0.3-kb fragment of the OMP gene containing one Olf-1 motif is sufficient for olfactory tissue-specific expression of the reporter gene. Some of the other identified sequence motifs also interact specifically with olfactory nuclear protein extracts. We propose that Olf-1 is a novel, olfactory neuron-specific trans-acting factor involved in the cell-specific expression of OMP.

[Quantitative 201Tl-scintigraphy of the lower limb in arterial occlusive disease]. / Quantitative 201Tl-Szintigraphie der Unterschenkel bei arterieller Verschlusskrankheit.

201Tl scintigraphy is useful in evaluating the hemodynamic consequences of arterial stenoses in arterial occlusive disease. The aim of the present study was to determine normal values for absolute Tl uptake in the lower leg, for the quotient between left and right lower leg uptake as well as for the redistribution pattern after bicycle exercise. We examined as reference 49 patients without clinical evidence of peripheral or coronary artery disease: absolute Tl uptake in the lower leg in anterior scintigraphy (acquisition time: 120 sec) was 5.02 +/- 1.70 counts/pixel (left) and 5.21 +/- 1.53 counts/pixel (right), the quotient between right and left lower leg was 0.85 +/- 0.09 and the redistribution pattern (quotient of the mean activity exercise/rest) 0.82 +/- 0.17 (left) and 0.83 +/- 0.15 (right). The arithmetic mean minus 2 standard deviations was regarded as the lower limit of normal. In 8 patients with mechanical compression of the left femoral artery before injection at least two scintigraphic parameters were abnormal, in 7 patients with angiographically proven peripheral artery disease at least one scintigraphic parameter was below normal. Quantification of Tl redistribution offers diagnostic advantages in bilateral peripheral artery disease.

[Hemolysis induced by Loxosceles laeta venom. In vitro experience]. / Estudio de la hemolisis inducida por veneno de Loxosceles laeta. Experiencia in vitro.

To study the effects of loxosceles laeta venom on red blood cells and the possible factors involved in hemolysis during arachnidism, in vitro models were designed to measure the role of loxosceles venom, calcium, complement and antibodies in the mechanism of red blood cell destruction. The degree of basal hemolysis was measured in a 5% suspension of group O, Rh (+) red blood cells in pH 7.4 buffer. In a similar suspension spider venom was added in amounts equivalent to one venom gland. After 72 hours of incubation, basal hemolysis was 5.59 +/- 2.04% which increased to 26.01 +/- 7.9% adding venom (p < 0.001). Adding calcium to the incubation medium, hemolysis increased to 88.5 +/- 7.16% (p < 0.001). Incubating red blood cells with control human serum and venom, hemolysis was 14.58 +/- 2.42%, which decreased significantly to 6.85 +/- 3.35% when serum was heat inactivated; this demonstrates an effect of the presence of complement. We did not find antivenom antibody production in patients with arachnidism 10, 15 or 30 days after the spider bite. It is thus demonstrated that loxosceles laeta venom has a direct lytic action on red blood cells that is calcium and complement dependent and is not mediated by antibodies or other substance.

Haemorheology and exercise: intrinsic flow properties of blood in marathon running.

Haemorheological and haematological parameters were studied in venous blood samples taken from 8 endurance-trained athletes before and after a marathon run. Viscometry was performed in a 20 microns glass capillary and in a Couette viscometer. Apparent blood viscosity was lower in the capillary than in the rotational viscometer, but significant differences between pre- and post-run samples were not observed in either system. This is presumably due to the absence of changes of haematocrit (pre-run [mean +/- SD]: 0.453 +/- 0.016, post-run: 0.456 +/- 0.018). Although protein concentration increased significantly from 70.8 +/- 2.1 g/l (pre-run) to 76.0 +/- 3.9 g/l (post-run), the difference of plasma viscosity was not statistically significant (pre-run: 1.26 +/- 0.03 cP, post-run: 1.30 +/- 0.07 cP). In all samples, plasma viscosity showed a significant positive correlation with total protein, globulin, albumin, but not with fibrinogen concentration. Cone-plate aggregometry and a filtration technique were used to evaluate red cell aggregation and deformability, two determinants of blood rheology which also were not different between pre- and post-run samples. The absence of viscosity changes in relation to the marathon run may be due to the relative stability of blood and plasma volume, which can be deduced from haematological parameters. Alterations of plasma composition (e.g. acidosis or hyperosmolality) seem to cause only minor, if any, changes of microrheological cell properties.