1,720,978 research outputs found
A beat-by-beat analysis of cardiovascular responses to dry resting and exercise apnoeas in elite divers.
No full textPURPOSE:
Cardiovascular responses during resting apnoea include three phases: (1) a dynamic phase of rapid changes, lasting at most 30 s; (2) a subsequent steady phase; and (3) a further dynamic phase, with a continuous decrease in heart rate (HR) and an increase in blood pressure. The interpretation was that the end of the steady phase corresponds to the physiological apnoea breaking point. This being so, during exercise apnoeas, the steady phase would be shorter, and the rate of cardiovascular changes in the subsequent unsteady phase would be faster than at rest.
METHODS:
To test these hypotheses, we measured beat-by-beat systolic (SBP), diastolic, and mean blood pressures (MBP), HR, and stroke volume (SV) in six divers during dry resting (duration 239.4 ± 51.6 s) and exercise (30 W on cycle ergometer, duration 88.2 ± 20.9 s) maximal apnoeas, and we computed cardiac output ([Formula: see text]) and total peripheral resistance (TPR).
RESULTS:
Compared to control, at the beginning of resting (R1) and exercising (E1) apnoeas, SBP and MBP decreased and HR increased. SV and [Formula: see text] fell, so that TPR remained unchanged. At rest, HR, SV, [Formula: see text], and SBP were stable during the subsequent phase; this steady phase was missing in exercise apnoeas. Subsequently, at rest (R3) and at exercise (E2), HR decreased and SBP increased continuously. SV returned to control values. Since [Formula: see text] remained unchanged, TPR grew.
CONCLUSIONS:
The lack of steady phase during exercise apnoeas suggests that the conditions determining R3 were already attained at the end of E1. This being so, E2 would correspond to R3
A new interpolation-free procedure for breath-by-breath analysis of V’O2 in exercise transients
No full textIntroduction. Interpolation methods circumvent poor time resolution of breath-by-breath oxygen uptake (VO2) kinetics at exercise onset. We report an interpolation-free approach to the improvement of poor time resolution in the analysis of VO2 kinetics.
Methods. Noiseless and noisy (10% Gaussian noise) synthetic data were generated by Monte Carlo method from pre-selected parameters (Exact Parameters). Each data set comprised 10 O2-on transitions with noisy breath distribution within a physiological range. Transitions were superposed (no interpolation, None), then analysed by bi-exponential model. Fitted model parameters were compared with those from interpolation methods (average transition after Linear or Step 1-sec interpolations), applied on the same data. Experimental data during cycling were also analysed. The 95% confidence interval around a line of parameters’ equality was computed to analyse agreement between exact parameters and corresponding parameters of fitted functions.
Results. The line of parameters’ equality stayed within confidence intervals for noiseless synthetic parameters with None, unlike Step and Linear, indicating that None reproduced Exact Parameters. Noise addition reduced differences among pre-treatment procedures. Experimental data provided lower phase I time constants with None than with Step.
Conclusion. In conclusion, None revealed better precision and accuracy than Step and Linear, especially when phenomena characterized by time constants of less than 30 sec are to be analysed. Therefore, we endorse the utilization of None to improve the quality of breath-by-breath VO2 data during exercise transients, especially when a double exponential model is applied and phase I is accounted for
An analysis of performance in human locomotion
No full textThis paper reports an analysis of the principles underlying human performances on the basis of the work initiated by Pietro Enrico di Prampero. Starting from the concept that the maximal speed that can be attained over a given distance with a given locomotion mode is directly proportional to the maximal sustainable power and inversely proportional to the energy cost of locomotion, we discuss the maximal powers (and capacities) of anaerobic (lactic and alactic) and aerobic metabolisms and the factors that limit them, and the factors affecting the energy cost of various locomotion modes. Special attention is given to the role of air resistance and frictional forces. Finally, computation of performance speed is discussed along the approach originally developed by di Prampero
Vagal blockade suppresses the phase I heart rate response but not the phase I cardiac output response at exercise onset in humans
Full text linkPurpose: We tested the vagal withdrawal concept for heart rate (HR) and cardiac output (CO) kinetics upon moderate exercise onset, by analysing the effects of vagal blockade on cardiovascular kinetics in humans. We hypothesized that, under atropine, the φ1 amplitude (A1) for HR would reduce to nil, whereas the A1 for CO would still be positive, due to the sudden increase in stroke volume (SV) at exercise onset. Methods: On nine young non-smoking men, during 0–80 W exercise transients of 5-min duration on the cycle ergometer, preceded by 5-min rest, we continuously recorded HR, CO, SV and oxygen uptake (V ̇ O2) upright and supine, in control condition and after full vagal blockade with atropine. Kinetics were analysed with the double exponential model, wherein we computed the amplitudes (A) and time constants (τ) of phase 1 (φ1) and phase 2 (φ2). Results: In atropine versus control, A1 for HR was strongly reduced and fell to 0 bpm in seven out of nine subjects for HR was practically suppressed by atropine in them. The A1 for CO was lower in atropine, but not reduced to nil. Thus, SV only determined A1 for CO in atropine. A2 did not differ between control and atropine. No effect on τ1 and τ2 was found. These patterns were independent of posture. Conclusion: The results are fully compatible with the tested hypothesis. They provide the first direct demonstration that vagal blockade, while suppressing HR φ1, did not affect φ1 of CO
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
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
Effects of acceleration in the Gz axis on human cardiopulmonary responses to exercise
Full text linkThe aim of this paper was to develop a model
from experimental data allowing a prediction of the
cardiopulmonary responses to steady-state submaximal
exercise in varying gravitational environments, with
acceleration in the Gz axis (ag) ranging from 0 to 3 g. To
this aim, we combined data from three different experiments,
carried out at Buffalo, at Stockholm and inside the
Mir Station. Oxygen consumption, as expected, increased
linearly with ag. In contrast, heart rate increased non-linearly
with ag, whereas stroke volume decreased non-linearly:
both were described by quadratic functions. Thus, the
relationship between cardiac output and ag was described
by a fourth power regression equation. Mean arterial
pressure increased with ag non linearly, a relation that we
interpolated again with a quadratic function. Thus, total
peripheral resistance varied linearly with ag. These data led
to predict that maximal oxygen consumption would
decrease drastically as ag is increased. Maximal oxygen
consumption would become equal to resting oxygen consumption
when ag is around 4.5 g, thus indicating the
practical impossibility for humans to stay and work on the
biggest Planets of the Solar System
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
