Optimal timing of simethicone administration prior to upper endoscopy: A multicenter, single-blind, randomized controlled trial.

Background and study aims Simethicone is useful as premedication for upper endoscopy because of its antifoaming effects. We aimed to evaluate the effect of timing of simethicone administration on mucosal visibility. Patients and methods In this multicenter, randomized, endoscopist-blinded study, patients scheduled for upper endoscopy were randomized to receive 40 mg simethicone at the following time points prior to the procedure: 20 to 30 minutes (early group), 0 to 10 minutes (late group) or 20 mg simethicone at both time points (split-dose group). Images were taken from nine predefined locations in the esophagus, stomach, and duodenum before endoscopic flushing. Each image was scored on mucosal visibility by three independent endoscopists on a 4-point scale (lower scores indicating better visibility), with adequate mucosal visibility defined as a score ≤ 2. Primary outcome was the percentage of patients with adequate total mucosal visibility (TMV), reached if all median subscores for each location were ≤ 2. Results A total of 386 patients were included (early group: 132; late group: 128; split-dose group: 126). Percentages of adequate TMV were 55%, 42%, and 61% in the early, late, and split-dose group, respectively ( P < 0.01). Adequate TMV was significantly higher in the split-dose group compared to the late group ( P < 0.01), but not compared to the early group ( P = 0.29). Differences between groups were largest in the stomach, where percentages of adequate mucosal visibility were higher in the early (68% vs 53%, P = 0.03) and split-dose group (69% vs 53%, P = 0.02) compared to the late group. Conclusions Mucosal visibility can be optimized with early simethicone administration, either as a single administration or in a split-dose regimen.

The effects of art therapy on anxiety, depression, and quality of life in adults with cancer: a systematic literature review.

PURPOSE: While there is increasing evidence for the effectiveness of psychosocial support programs for cancer patients, little attention has been paid to creativity or art as a way of addressing their psychological problems and improving quality of life. This review provides an overview of interventional studies that investigate the effects of art therapy interventions on anxiety, depression, and quality of life in adults with cancer. METHODS: We conducted a literature review with a systematic search. The databases PubMed/MEDLINE, PsycINFO, and EMBASE were searched for articles on art therapy among adult (18 years and above) cancer patients, published between September 2009 up to September 2019. Search terms were established for each database specifically. A total of 731 publications was assessed for relevance by title and abstract. The remaining 496 articles were examined using three inclusion criteria: interventions were guided by an artist or art therapist, participants were actively involved in the creative process, and anxiety, depression, and/or quality of life were included as outcome measures. Methodological quality of the included studies was appraised using specific checklists. RESULTS: Seven papers met the inclusion criteria. Data was extracted from three non-randomized intervention studies and four randomized controlled trials. All studies used a quantitative design with validated outcome measures. Four articles described positive effects of art therapy on anxiety, depression, or quality of life in adults with cancer. CONCLUSION: Art therapy could possibly help decrease symptoms of anxiety and depression, and improve quality of life in adult cancer patients. However, because of the heterogeneity of the interventions and limited methodological quality of the studies, further research using stringent methods is needed.

Note: Laser-cut molybdenum grids for a retarding field energy analyzer.

A retarding field energy analyzer (RFEA) with grids created by laser-cutting a honeycomb mesh in a 50 µm thick molybdenum foil is presented. The flat grids span an area of 1 cm2 and have high transmission (20 µm wide walls between 150 µm wide meshes). The molybdenum grids were tested in a 3-grid RFEA configuration with an analyzer depth of 0.87 mm.

Coaching Reduced the Radiation Dose of Pain Physicians by Half during Interventional Procedures.

The increased use of C-arm fluoroscopy in interventional pain management has led to higher radiation exposure for pain physicians. This study investigated whether or not real-time radiation dose feedback with coaching can reduce the scatter dose received by pain physicians. Firstly, phantom measurements were made to create a scatter dose profile, which visualizes the average scatter radiation for different C-arm positions at 3 levels of height. Secondly, in the clinical part, the radiation dose received by pain physicians during pain treatment procedures was measured real-time to evaluate (1) the effect of real-time dose feedback on the received scatter dose, and (2) the effect of knowledge of the scatter dose profile and active coaching, on the scatter dose received by the pain physician. The clinical study included 330 interventional pain procedures. The results showed that real-time feedback of the received dose did not lead to a reduction in scatter radiation. However, visualization of the scatter dose in a scatter dose profile and active coaching on optimal positions did reduce the scatter radiation received by pain physicians during interventional pain procedures by 46.4% (P = 0.05). Knowledge of and real-time coaching with the scatter dose profile reduced the dose of pain physicians by half, caused by their increased awareness for scatter radiation and their insight into strategic positioning.

Concentrations of venlafaxine and its main metabolite O-desmethylvenlafaxine during pregnancy.

WHAT IS KNOWN AND OBJECTIVE: Depression during pregnancy is common and includes risks for mother and child. Pharmacokinetics of venlafaxine may be changed during pregnancy. This study aimed to describe changes in metabolic ratios and concentrations of venlafaxine and its main metabolite O-desmethylvenlafaxine during and after pregnancy. METHODS: To study this, we used data from our study of compliance to Antidepressants During Pregnancy (the ADAP study) to investigate the course of venlafaxine and O-desmethylvenlafaxine concentrations during pregnancy and in the period post-partum. RESULTS AND DISCUSSION: We found that the venlafaxine concentration significantly changed during pregnancy when compared to the post-partum period (P = 0·028). The median concentration of venlafaxine in the first trimester was 98·9% (54·2-292·0%), the second 100·0% (46·5-264·0%) and the third trimester 87·0% (61·5-217·2%). We did not found differences in O-desmethylvenlafaxine concentrations in the different trimesters of pregnancy compared with the post-partum period, P = 0·565. Also the ratio of O-desmethylvenlafaxine/venlafaxine concentrations increased significantly from 76·9% (range 32·8-142·0%) in the first trimester to 196·7% (range 83·3-427·6%) in the third trimester compared with the post-partum period, P = 0·004. Further, three of seven patients had concentrations below the therapeutic reference range (100-400 µg/L) in any period of pregnancy, whereas no one had subtherapeutic concentrations in the post-partum period. WHAT IS NEW AND CONCLUSION: Venlafaxine concentrations decreases during pregnancy, and the ratio of the concentrations of O-desmethylvenlafaxine/venlafaxine increases during pregnancy. Pregnant women using venlafaxine are at risk for subtherapeutic concentrations, therefore routine monitoring of concentrations venlafaxine and O-desmethylvenlafaxine is recommendable during pregnancy.

Admission time is associated with outcome of upper gastrointestinal bleeding: results of a multicentre prospective cohort study.

BACKGROUND: It has been suggested that patients presenting with upper gastrointestinal bleeding (UGIB) during the weekend have a worse outcome compared with weekdays, with an increased risk of recurrent bleeding and mortality. AIM: To investigate the association between timing of admission and adverse outcome after UGIB. METHODS: We prospectively collected data from patients presenting with symptoms suggestive of UGIB to the emergency room of eight participating hospitals. Using standard descriptive statistics and logistic regression analyses, differences in 30-day mortality, rebleeding rate, and need for angiography and surgical intervention were assessed for week- and weekend admissions and time of admission. Moreover, patient- and procedure-related factors were identified that could influence outcome. RESULTS: In total, 571 patients were included with suspected UGIB. Patient admitted during the weekend had a higher mortality rate than patients admitted during the week [9% vs.3%; adjusted odds ratio 2.68 (95%CI 1.07-6.72)]. Weekend admissions were not associated with other adverse outcomes. Patients admitted during the weekend presented more often with bleeding and had a significantly lower systolic and diastolic blood pressure. No differences were found in procedure-related factors. Time of admission was not associated with an adverse outcome, although patients admitted during the evening had a significantly longer time to endoscopy (15, 22 and 16 h for day, evening and night admissions respectively, P < 0.01). CONCLUSION: Although quality of care did not appear to differ between week/weekend admissions, patients with suspected upper gastrointestinal bleeding admitted during the weekend were at higher risk of an adverse outcome. This might be due to the fact that these patients have more severe haemorrhage.

Prediction scores in gastrointestinal bleeding: a systematic review and quantitative appraisal.

BACKGROUND AND STUDY AIMS: Several algorithms predicting outcomes in acute gastrointestinal bleeding have been developed over the past three decades. These algorithms differ substantially and therefore the aim of the current study was to conduct a systematic review to compare their predictive performance and methodological quality in gastrointestinal bleeding. METHODS: A PubMed literature search was performed up to 1 July 2011. All studies reporting prediction scores in gastrointestinal bleeding were included. Studies were analyzed for predictive performance, and a quality appraisal of these rules was performed for which a score range of 0 (lowest) to 29 (highest) was used. RESULTS: A total of 372 studies were identified, of which 16 were eligible for inclusion. The studies evaluated different outcomes: mortality (n = 5), rebleeding (n = 2), intervention required (n = 2), or a combination (n = 7). The predictive performance of the identified prediction scores varied between an area under the curve of 0.71 - 0.92 (if given). The mean overall quality rating was 17 (SD 4.0, range 9 - 25). Major methodological shortcomings were the absence of validation and absence of impact analyses. Eight of 16 scores (50 %) were determined "easy to use," and five scores (31 %) reported some type of action based on the results. CONCLUSION: Substantial heterogeneity in outcomes and results was seen in the 16 identified prediction scores. Moreover, the methodological quality was suboptimal in most studies. However, we suggest that clinicians should use the "best available" scores according to performance and quality, which are the Blatchford score to assess the need for intervention, and the scores of Villanueva et al. for poor outcome, Guglielmi et al. for rebleeding, and Chiu et al. for mortality risk.

Test-re-test reliability of walking speed, step length and step width measurement after traumatic brain injury: a pilot study.

PRIMARY OBJECTIVE: Assess the test-re-test reliability of walking speed, step length and step width measurement in people with traumatic brain injury (TBI). RESEARCH DESIGN: Repeated measures (two test occasions). METHODS: Thirteen people with TBI completed four comfortable and four fast-paced walking trials of the 10 m walk test and two trials of the 6-minute walk test (6MWT). Walking speed, step length and step width were measured during the 10 m walk test and walking distance and average speed were measured during the 6MWT. The tests were repeated 1-week later. MAIN RESULTS: Walking speed and distance showed excellent test-re-test reliability, with an intra-class correlation coefficient (ICC) of 0.95-0.96. Reliability was also high for step length and width measurement (ICC 0.91-0.98). CONCLUSIONS: This test-re-test reliability means that walking speed and distance and step length and width can be used by physiotherapists to monitor improvements in walking after TBI.

Inter-rater reliability and concurrent validity of walking speed measurement after traumatic brain injury.

OBJECTIVE: To assess the inter-rater reliability and concurrent validity of walking speed measurement after traumatic brain injury. DESIGN: Twelve subjects each completed five comfortably paced and five fast-paced walking trials. Walking speed was measured simultaneously by five observers using a stopwatch (clinical procedure) and by infrared timing gates (gold standard). SETTING: Brain injury rehabilitation unit. SUBJECTS: People with traumatic brain injury who could walk independently and were participating in a rehabilitation programme. MAIN OUTCOME MEASURES: Walking speed over a 10-metre distance. RESULTS: The inter-rater reliability of walking speed measured using a stopwatch was very high, with an intraclass correlation coefficient of at least 0.998 for both comfortable and fast-paced tests. Concurrent validity was excellent for comfortable and fast tests, with perfect correlations between the stopwatch and infrared timing gate measurement procedures. CONCLUSIONS: Physiotherapists can use a stopwatch as a reliable and valid measurement tool to quantify walking speed over a short distance at both comfortable and fast paces in people who have sustained traumatic brain injuries.

Inter-rater reliability and concurrent validity of step length and step width measurement after traumatic brain injury.

PURPOSE: To determine the inter-rater reliability and concurrent validity of step length and step width measurement after traumatic brain injury. METHOD: Twelve people with traumatic brain injury completed six comfortable and six fast paced walking trials over a 10 m distance. Step length and step width were measured by five observers using two procedures. First, using pens taped on the subjects' heels which marked the floor at each heel strike and a tape measure. Second, by videotaping the subjects' feet as they walked on a mat marked with 5 cm grids and using a computer program to digitize foot position and calculate step length and width. RESULTS: The inter-rater reliability of step length and width measurements was very high, with intraclass correlation coefficients between 0.94 and 1.00, for both procedures. Concurrent validity was excellent, with correlations between the procedures ranging from 0.93 to 1.00. However, attaching pens to the heels did cause a slight reduction in right step length and walking speed when walking at a fast or comfortable pace, respectively. CONCLUSIONS: Assessing step length and width using pens taped to the subjects' heels and a tape measure is a reliable and valid clinical measure after traumatic brain injury.

The influence of eye muscle surgery on shape and relative orientation of displacement planes: Indirect evidence for neural control of 3D eye movements.

Is Listing's law a consequence of 2D control of eye positioning, where eye torsion is determined by the biomechanical properties of the orbit, or is it a reflection of full 3D neuronal control? This was investigated by observing the influence of a change in mechanical properties of the eye socket on 3D eye movements. The shape and relative orientation of displacement planes were measured using scleral search coils before and after operation of five patients with strabismus. The operation influenced the shape of displacement planes in both eyes of all patients. After the operation, most patients obeyed Listing's law more accurately: a monocular, surgically induced, orbital change caused binocular improvements of torsional control. The relative orientation of planes also changed, but no clear relationship was found between the type of operation and the direction of rotation. The results suggest that Listing's law is not just a result of the biomechanical properties of the eye socket, but has a neural basis.

Listing's law in strabismus and amblyopia: a preliminary report.

We investigated whether Listing's law applies in patients with diminished or no stereopsis due to strabismus or amblyopia. Eye movements of normal subjects and patients with strabismus and/or amblyopia were recorded during monocular and binocular fixation; from these data the shape and relative orientation of displacement planes were calculated. In normal subjects, monocular or binocular fixation did not influence the thickness and relative orientation of displacement planes. No differences were found between normals and the patient with amblyopia due to anisometropia. In one patient with strabismus but without amblyopia, the orientation of displacement planes depended on the fixation conditions; a coupling between horizontal vergence effort and plane orientation was observed. Patients with amblyopia and strabismus showed abnormally shaped and/or abnormally orientated displacement planes, which depended on the fixation conditions. Differences between both eyes in the shape of the planes were also observed. These results show that normal Listing behavior can be present in subjects with diminished stereopsis. They also show that normal stereopsis does not necessarily mean normal Listing behavior, suggesting that Listing's law is mainly a result of motor strategy.

Multiresidue analysis of beta2-agonist in human and calf urine using multimodal solid-phase extraction and high-performance liquid chromatography with electrochemical detection.

Various beta2-agonists are used as illegal growth promoters in man and in animals. We developed a multiresidue procedure for the analysis of four beta-agonists in human and calf urine. The sample was pre-extracted with an Extrelut column at alkaline pH. The beta-agonists were eluted with a mixture of tert.-butylmethyl ether and hexane. Then the extract was further cleaned with a mixed mode SPE column, or with a combination of immunoaffinity chromatography (IAC) and the mixed mode SPE column. The IAC column contained antibodies against salbutamol, which were suitable for multiresidue extractions. The extract was then brought onto a mixed mode SPE column at an acidic pH. The column was washed with 70% methanol in water. Thereafter, the beta-agonists were eluted with ammoniated ethanol-hexane. The extract was analysed with an HPLC method with electrochemical detection. The beta-agonists were separated on a reversed-phase column using a mobile phase buffered at pH 5.5 and containing an ion-pair reagent. Recoveries were higher when the IAC procedure was not performed (90-105% vs. 65-75%), but the extracts were cleaner when the latter step was included. Detection limits in human and calf urine were in the low ng/ml range. The study indicated that beta2-agonists can be analysed in human and calf urine without the selectivity of a mass spectrometer, but that comprehensive clean-up is required to avoid the interference of urine matrix components.

The influence of visual input on the vestibulo-ocular reflex.

In order to stabilise a fixation target on the retina, eye movements have to compensate for head movements. During slow head movements visual feedback can control these eye movements. During fast movements of the head, mainly the vestibulo-ocular reflex (VOR) controls eye movements, as visual feedback is too slow. However, visual feedback is an important factor in controlling the VOR; e.g. the gain of the VOR depends on the distance of the target. This study investigates the influence of retinal image position during fast head movements. The experiments were carried out in five human subjects using scleral search coils. The adaptation of each eye individually to a change of retinal position of a target was examined during head shaking. The change in visual input was carried out by placing Fresnel prisms of different strengths in front of both eyes, thus inducing a change in retinal image position without changing the retinal slip. The results show, that both eyes make the appropriate corrections when the visual input changes, even during fast head-movements. These corrections did not influence the gain of the VOR. From these results we conclude, that retinal image position besides retinal slip has a major influence on the monocular eye movements even at high head rotation frequencies.

Insulin increases the processing efficiency of messenger ribonucleic acid-S14 nuclear precursor.

Feeding a lipogenic diet increases transcription and enhances processing of the rat hepatic messenger RNA (mRNA)-S14 gene. To determine the separate roles of insulin and increased glucose in these processes, we used the streptozotocin-induced diabetic rat model. Diabetes caused a reduction in mature mRNA-S14 in chow- and lipogenic diet-fed animals (P < 0.006 and P < 0.001, respectively). Insulin restored these levels to normal. Despite the known effects of insulin and carbohydrate on the transcription of this gene, we were unable to demonstrate significant changes in the nuclear proteins that bind to carbohydrate response regions. Yet, insulin restored the content of the mRNA by increasing the ratio of mature to precursor mRNA-S14. Insulin significantly increased this ratio (P < 0.0001) independent of diet and diabetes, further supporting the action of insulin on increasing processing from precursor to mature mRNA. The mechanism of the enhanced processing was studied by ribonuclease mapping and primer extension analysis. Ribonuclease mapping showed that lipogenic diet feeding increases the efficiency of processing at a step before formation of the branched form of the precursor mRNA. Taken together, our data demonstrate for the first time that insulin significantly enhances the efficiency of processing of a pre-mRNA.

The influence of adenosine on red blood cell flow cessation in skeletal muscle.

The observed positive correlation between cessation of red blood cell flow in capillaries at low perfusion pressures and the oxygen tension (PO2) in the superfusion solution may be due to oxygen-dependent arteriolar constriction. To test this hypothesis, we investigated capillary flow cessation during aortic occlusion and concomitant changes in diameters of terminal arterioles and capillaries in normal and vasodilated vascular beds of rabbit tenuissimus muscle (n = 15) by means of video intravital microscopy. In the vasodilated bed, arteriolar tone was eliminated by local application of 10(-4) M adenosine (ADO). The PO2 in the superfusate was varied locally, i.e., in the solution between objective lens and muscle surface. At a local PO2 of 40 mm Hg without ADO, flow ceased in about 50% of the capillaries during aortic occlusion while the arterioles dilated to 118% of control (median; p < 0.001). Addition of ADO led to an increase in arteriolar and capillary diameter to 220% (median; p < 0.001) and 121% (median; p < 0.05), respectively. Under ADO, the incidence of capillary flow cessation was reduced (p < 0.05) to about 20%. Elevation of the local PO2 from 40 to 100 mm Hg in the presence of ADO did not lead to a significant change in the incidence of flow cessation, nor to changes in arteriolar or capillary diameter. In the presence of ADO, median arteriolar and capillary diameters during aortic occlusion were 96% (p < 0.001) and 7% (p < 0.05) larger than their control diameters without ADO, respectively. In summary, it is suggested that the incidence of flow cessation may depend on both the arteriolar and the capillary diameter. Of these two factors, capillary diameter may be the most important one, because its changes affect the interaction between red blood cells and the vessel wall in the narrow capillaries, and, hence, the resistance to flow. In the presence of ADO, at elevated local PO2 levels flow cessation still occurs in about 20-30% of the capillaries, suggesting that arteriolar contraction is only in part responsible for the incidence of flow cessation.

Local application of adenosine induces an increase of capillary diameter in skeletal muscle of anesthetized rabbits.

The effects of locally applied adenosine (ADO) and/or femoral artery pressure reduction (induced by complete aorta occlusion) on capillary diameter were investigated in the tenuissimus muscle of anesthetized rabbits. Capillaries were visualized by means of intravital video microscopy. Diameters were measured using an image shearing device. During control femoral artery pressure (median: 83 mm Hg) and without ADO, median capillary diameter was 4.3 microns (range: 3.2-5.3 microns; 27 capillaries in 7 animals). Complete aorta occlusion (median femoral artery pressure: 18 mm Hg) resulted in a reduction of capillary diameter to 3.9 microns (2.7-4.7 microns; p < 0.0001). Subsequent reactive hyperemia resulted in an increase in diameter to 5.2 microns (3.7-6.0 microns; p < 0.0001). Locally applied ADO (10(-4) M) probably led to complete vasodilation of the arterioles, because their diameters did not further increase during reactive hyperemia after complete occlusion. ADO (10(-4) M) induced an increase of control capillary diameter to 5.5 microns (4.1-6.4 microns; median relative increase: 27%; p < 0.0001), resulting in a decrease of capillary resistance by 61%. In the presence of ADO, aorta occlusion resulted in a capillary diameter decrease to 4.7 microns (3.4-6.1 microns); p < 0.0001). Subsequent reactive hyperemia resulted in an increase to maximally 5.6 microns (4.3-6.4 microns; p < 0.0001). This diameter was approximately the same as the control diameter during ADO. During occlusion in the presence of ADO, capillary diameter was significantly larger (11%; p < 0.0001) than during control without ADO. The capillary diameter changes induced by the various interventions were mainly passive, i.e., proportional to capillary transmural pressure changes. However, capillary diameter was larger during aortal occlusion in the presence of ADO than during control femoral artery pressures without ADO, even though capillary pressure was probably higher in the latter case. It is proposed that the prolonged increase in transmural capillary pressure due to ADO may induce changes in capillary wall configuration, leading to larger diameters.

Capillary diameter changes during low perfusion pressure and reactive hyperemia in rabbit skeletal muscle.

Capillary diameter changes were studied in the tenuissimus muscle of 29 urethan-anesthetized New Zealand White rabbits. Capillaries were visualized with transillumination bright-field microscopy (saltwater lens, x 50; resolution approximately 0.3 microns). Median capillary diameter during the control period was 4.4 microns (range 3.2-6.9 microns). Complete aortic occlusion resulted in a reduction of median femoral arterial pressure to 17 mmHg (range 4-22 mmHg). During 2 min of occlusion, capillary diameter decreased by 6%, with greater change on the arteriolar side of the capillary than on the venular side. During reactive hyperemia after release of the occluder, capillary diameter maximally increased by 12% compared with the control period, with a larger response at the arteriolar end of the capillary than at the venular end. Median capillary resistance was estimated to increase by 27% during occlusion and to decrease by 36% during peak reactive hyperemia. The observed diameter changes are compatible with the idea that capillaries change their diameter relative to changes in transmural pressure.

Oxygen- and pressure-dependent functional capillary density in rabbit tenuissimus muscle.

Perfusion of capillaries was investigated in the tenuissimus muscle of young anesthetized New Zealand White rabbits during control conditions, complete aorta occlusion, and reactive hyperemia at various local oxygen tensions. Capillaries were visualized with bright-field microscopy. The number of capillaries perfused under experimental conditions was compared with that during control conditions. Capillary diameter was measured to assess whether the interventions caused changes in luminal diameter. During control conditions at a local pO2 of about 20 mm Hg, capillary perfusion fluctuates; instantaneous capillary density is smaller than anatomical capillary density. When the aorta is (partially) occluded, capillary perfusion becomes continuous and instantaneous capillary density equals anatomical capillary density. The latter is also observed during the early phase of reactive hyperemia, prior to the reappearance of flowmotion. Capillary diameter is not invariant during these interventions, but decreases by 8% during occlusion and increases by 12% during reactive hyperemia. The concomitant change in perimeter and cross-sectional area should be factored in with functional capillary density, when tissue exchange surface area or volume flow are considered. When during control conditions, the muscle becomes locally (under the microscope lens) exposed to a higher oxygen tension, capillary diameter does not change. However, the relative number of capillaries perfused at complete aorta occlusion is unity at low local oxygen, and diminishes with increasing local oxygen to become 0 at an oxygen tension of about 70 mm Hg. In preparations in which capillary diameter is not invariant under the experimental conditions, functional capillary density can only be used to compare the number of perfused capillaries with the number of capillaries anatomically present. Capillary diameter has to be factored in when tissue perfusion or exchange surface area are considered.

Red blood cell flow cessation and diameter reductions in skeletal muscle capillaries in vivo - the role of oxygen.

When perfusion pressure is reduced, red blood cell flow in the capillaries of skeletal muscle ceases at a positive pressure difference across the vascular bed, while arterioles dilate and venules are not constricted. This flow cessation (i.e., cessation of red blood cell flow) and luminal diameter changes in capillaries following femoral arterial pressure reduction were investigated in the rabbit tenuissimus muscle in situ (n = 42) using intravital video microscopy. Arterial pressure was reduced by occlusion of the aorta distal to the renal arteries. During the experiments, leg and muscle were placed in a sealed box. The muscle was exposed to low PO2 by leading a gas mixture deprived of O2 through the box. Locally at the muscle surface, i.e., under the microscope objective, PO2 was varied by varying the PO2 in the superfusion solution. In all experiments, the remainder of the muscle was kept at low (< 20 mm Hg) PO2. The incidence of flow cessation was virtually zero at low local (< 20 mm Hg) PO2 and became almost 100% at local values above 70 mm Hg. Initial equivalent capillary diameters were 3.1-5.8 microm (median 4.0 microm) and did not correlate with local O2 tension. During aorta occlusion, capillary diameters significantly (P < 0.0001) decreased by a median value of 8% at all local PO2 values; in 14 out of 54 capillaries local diameter became less than 2.8 microm. The extent of diameter reduction did not correlate with PO2. In the 14 capillaries in which the diameter became less than 2.8 microm flow cessation occurred in only four cases. The minimal diameter reached was always at the site of an endothelial nucleus. The capillary diameter reductions are probably due to passive recoil. In the 48 capillaries in which flow ceased, only in four cases did a red blood cell stop at the site of the nucleus. We conclude that capillary diameter reductions (local and generalized) lead to a considerable increase in capillary resistance which contributes to the occurrence of flow cessation but cannot solely explain it.