1,721,076 research outputs found
Does Circumferential Stress Help to Explain Flow-Mediated Dilation?
No full textINTRODUCTION: Despite its potential, the validity of the flow-mediated dilation (FMD) test has been questioned because of lack of normalization to the vasodilatory stimulus. The hemodynamic conditions inside blood vessels lead to the development of superficial stress near the vessel walls, which can be divided into 2 categories: (1) circumferential stress (CS) and (2) shear stress (SS). Although SS is thought to be the primary governing stimulus, to the best of our knowledge, the degree to which CS contributes to FMD has not been reported in the literature.
PURPOSE:
The purpose of this study was to determine the importance of CS to FMD. We defined FMD as the SS-diameter dose-response slope.
METHODS:
Fourteen physically active, young [mean (SD) age, 26 (5) years], male subjects were tested. Progressive forearm heating and handgrip exercise elicited steady-state increases in shear rate. Hierarchical linear modeling was used to estimate change in diameter with repeated measures of SS and CS nested within each subject.
RESULTS:
Circumferential stress was found to positively promote FMD in addition to SS (β = 0.019, P = 0.019). However, the variance explained by CS was less than 1%.
CONCLUSIONS:
The physiologic significance of CS to FMD was minimal. However, physically active, young men were recruited; it remains to be determined whether CS has a more pronounced effect in subjects exhibiting cardiovascular risk factors
Effect of home-based, overground robotic-assisted gait training on vascular health in people with chronic stroke
Full text linkOverground robotic-assisted gait training (O-RAGT) has been shown to improve clinical functional outcomes in people living with stroke. The purpose of this study was to identify whether a home-based O-RAGT program, in combination with usual care physiotherapy, would demonstrate improvements in vascular health in individuals with chronic stroke, and, whether any changes in vascular outcomes would be sustained 3 months after completing the program. Thirty-four participants with chronic stroke (between 3 months and 5 years post-stroke) were randomized to either a 10-week O-RAGT program in combination with usual care physiotherapy, or to a usual care physiotherapy only control group. Participants’ pulse wave analysis (PWA), and regional (carotid-femoral pulse wave analysis [cfPWV]) and local (carotid) measures of arterial stiffness were assessed at baseline, post-intervention, and 3-month post-intervention. Analysis of covariance demonstrated a significant reduction (improvement) in cfPWV between BL and PI for O-RAGT (8.81 ± 2.51 vs 7.92 ± 2.17 m/s, respectively), whilst the control group remained unchanged (9.87 ± 2.46 vs. 9.84 ± 1.76 m/s, respectively; p0.05). A significant increase in physical activity, as determined by the time spent stepping, was observed for O-RAGT between baseline and post-intervention assessments (3.2 ± 3.0 to 5.2 ± 3.3 %, respectively) but not for CON (p < 0.05). The improvement in cfPWV, in combination with an increase in physical activity whilst wearing the O-RAGT and concomitant reduction in sedentary behaviour, are important positive findings when considering the application of this technology for ‘at home’ rehabilitation therapy for stroke survivors. Further research is needed to determine whether implementing ‘at home’ O-RAGT programs should be a part of the stroke treatment pathway. Clinical trial registration number; NCT03104127; https://clinicaltrials.gov/ct2/show/NCT0310412
Reliability of pulse waveform separation analysis: effects of posture and fasting
Full text linkObjective: Oscillometric pulse wave analysis devices enable, with relative simplicity and objectivity, the measurement of central hemodynamic parameters. The important parameters are central blood pressures and indices of arterial wave reflection, including wave separation analysis (backward pressure component P b and reflection magnitude). This study sought to determine whether the measurement precision (between-day reliability) of P b and reflection magnitude: exceeds the criterion for acceptable reliability; and is affected by posture (supine, seated) and fasting state.
Methods: Twenty healthy adults (50% female, 27.9 years, 24.2 kg/m2) were tested on six different mornings: 3 days fasted, 3 days nonfasted condition. On each occasion, participants were tested in supine and seated postures. Oscillometric pressure waveforms were recorded on the left upper arm.
Results: The criterion intra-class correlation coefficient value of 0.75 was exceeded for P b (0.76) and reflection magnitude (0.77) when participants were assessed under the combined supine-fasted condition. The intra-class correlation coefficient was lowest for P b in seated-nonfasted condition (0.57), and lowest for reflection magnitude in the seated-fasted condition (0.56). For P b, the smallest detectible change that must be exceeded in order for a significant change to occur in an individual was 2.5 mmHg, and for reflection magnitude, the smallest detectable change was 8.5%.
Conclusion: Assessments of P b and reflection magnitude are as follows: exceed the criterion for acceptable reliability; and are most reliable when participants are fasted in a supine position. The demonstrated reliability suggests sufficient precision to detect clinically meaningful changes in reflection magnitude and Pb
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Validity of single-point assessments for determining leg pulse wave velocity in sitting and supine positions
No full textThere has been a great deal of interest into the effects of prolonged sitting on lower limb vascular function. However, most studies use flow-mediated dilation which is technically challenging. A simpler technique is pulse wave velocity (PWV) which can be estimated at any single arterial site of interest using a number of different calculations (Bramwell-hill [PWVBH ], β-stiffness index [PWVβ ] and blood flow [PWVBF ]). Findings from this technique would be better inferred if they compare to a standard criterion 2-point PWV assessment. The current study used ultrasound to determine which estimation of single-point PWV is most valid. The criterion was traditional ECG-gated 2-point (superficial femoral [SF]-posterior tibialis [PT]) PWV. Single-point estimates were calculated at the SF and PT arteries in both supine and seated positions. Single-point PWV was considered valid if the aSEE was <1.0 m·s. Findings show that for both postural positions, the absolute standard error of estimates (aSEE) criterion of <1.0 m·s was not achieved in either the PT or SF arteries using any of the single-point PWV calculations. However, single-point calculations consistently demonstrated the lowest error at the SF artery using PWVβ in both supine (SF aSEE = 1.7 vs. PT 2.7 m·s) and seated (SF aSEE = 1.5 vs. PT 3.0 m·s) positions. All single-point ΔPWV (supine - seated) calculations were higher in sitting, with PWVβ having the closest agreement (ΔSF aSEE 1.7 m·s) to the 2-point criterion. Single-point PWV calculations do not directly reflect regional 2-point PWV. However, they are sensitive to change when moving from supine to seated positions.</p
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Reliability of Pulse Waveform Separation Analysis Responses to an Orthostatic Challenge
Full text linkCardiovascular autonomic nervous system function can be assessed by using an orthostatic challenge to induce arterial wave reflection. While arterial reflection is typically estimated using central augmentation index, a superior estimation can be obtained using pulse wave separation analysis to estimate the aortic backward pressure wave (Pb). However, to be of value in a clinical or research setting, an assessment tool must be precise (reliable). Therefore, this study sought to determine the measurement precision of Pb responses to a modified tilt-table test.
[The full abstract is available to download in PDF format as it contains characters that cannot be accurately reproduced here.
Acute effects of exercise posture on executive function in transient ischemic attack patients
Full text linkIn patients with stroke or transient ischaemic attacks (TIA), a decline in executive function may limit an individual’s ability to process motor tasks and re-learn motor skills. The purpose of this study was to assess the acute effect of exercise posture (seated vs. supine cycle ergometry) on executive function and prefrontal cortex perfusion, in patients with TIA. Eleven TIA patients (65±10y) and 15 age-matched, healthy-controls (HC; 62±7y) completed two graded exercise tests to maximal functional capacity (1 x seated; 1 x supine) and two 30-minute sub-maximal exercise tests (1 x seated, 1 x supine). Executive function was assessed prior-to and following (1.5-min Post, 15-min Post) the submaximal exercise tests using a Stroop Task. Prefrontal cortex perfusion (total hemoglobin) was continuously recorded using near infrared spectroscopy. There was no Posture (seated, supine) by Group (TIA, HC) interaction for the Stroop task (P > .05). HC completed Stroop tasks significantly faster than TIA (51.9[10.3] vs. 64.2[8.5] s, respectively); while Stroop completion time significantly improved between Baseline and 1.5-min Post (61.3[10] vs. 58.1[9.4] s, respectively) and 1.5-min Post and 15-min Post (54.8[8.9] s). Posture and Group had no significant influence on prefrontal cortex perfusion (P > .05). In conclusion, executive function improves to a similar extent in TIA and age-matched, healthy-controls following an acute bout of exercise, regardless of exercise posture (seated vs. supine). As acute improvements in executive function were maintained for 15 minutes, there could be an important window of opportunity for assigning executive tasks following exercise rehabilitation for patients with TIA
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