1,721,146 research outputs found
Estimating the autonomic function from heart rate variability in mechanically ventilated patients after spinal cord injury
No full textAssessing the convolutedness of multivariate physiological time series
No full textA feature of time-series variability that may reveal underlying complex dynamics is the degree of "convolutedness". For multivariate series of m components, convolutedness can be defined as the propensity of the trail of the time-series samples to fill the m-dimensional space. This work proposes different convolutedness indices and compare them on synthesized and real physiological signals. The indices are based on length L and planar extension d of the trail in m dimensions. The classical ones are: the L/d ratio, and the Mandelbrot's fractal dimension (FD) of a curve: FDM =log(L)/log(d). In this work we also consider a correction of the Katz’s estimator of FDM, i.e., FDKC =log(N)/(log(N)+log(d/L)), with N the number of samples; and FDMC, an estimator of FDM based on FDKC calculated over a shorter running window Nw
Low compliance of orthosis locomotion : selection criteria based on energy expenditure
No full textOxygen consumption (V̇O2), heart rate (HR) and cost of locomotion (C, energy required to cover 1 m per unit of transported mass) were measured in 14 paraplegics (age 19-59 yrs, BW 48-100 Kg, injury level C7-T11), during both wheelchair (Whch) and orthosis-assisted locomotion at 2-4 speeds, up to exhaustion (peak value, p). Subjects were divided into three groups; the HIP Guidance Orthosis Orlau Parawalker (PW, n=4), the Reciprocating Gait Orthosis (RGO, n=6) and the RGO with functional neuromuscular stimulation (RGO+FNS, n=4). Alms of the study were: a) to find out indicators of the poor long-term compliance (all but 2 RGO withdrawals in 5 yrs) on the basis of cost of locomotion and physical fitness; b) to assess selection criteria for the assignment of the different type of orthoses; c) to estimate whether electrical stimulation improves locomotion reducing fatigue. In RGO+FNS walking the slope difference of HR/V̇O2 curves between Whch and orthosis (ΔslHR/V̇O2) is significantly lower than in the other groups (=0 beats-l-1 for RGO+FNS vs 39 and 61 beats-I-1, for RGO and PW, respectively). Neither C, nor V̇O2P or ΔslHR/V̇O2 correlates with ortnosis length of use. C was higher (p<0.05) in RGO+FNS at low speeds (0.4-0.7 Km/h), but for medium to high speeds (0.7-1 Km/h) C was similar for the 3 orthoses, averaging 0.9*0.1 mlO2·m-1·Kg-1. It appears that: a) the poor long-term compliance for orthosis use depends on mechanisms (presumably psychological) apparently not related to fitness level; b) only those subjects who can deambulate at higher speeds might be suitable for electrical-stimulated types of orthosis. Hypothesis is made that adequate psychological and specific muscular training may improve compliance
Fractal analysis of heart rate variability reveals alterations of the integrative autonomic control of circulation in paraplegic individuals
Full text linkThe autonomic nervous system plays a major role in the integrative control of circulation, possibly contributing to the 'complex' dynamics responsible for fractal components in heart rate variability. Aim of this study is to evaluate whether an altered autonomic integrative control is identified by fractal analysis of heart rate variability. We enrolled 14 spinal cord injured individuals with complete lesion between the 5th and 11th thoracic vertebra (SCIH), 14 with complete lesion between 12th thoracic and 5th lumbar vertebra (SCIL), and 34 able-bodied controls (AB). These paraplegic subjects have an altered autonomic integrative regulation, but intact autonomic cardiac control and, as to SCILindividuals, intact autonomic splanchnic control. Power spectral and fractal analysis (temporal spectrum of scale coefficients) were performed on 10 min tachograms. AB and SCILpower spectra were similar, while the SCILfractal spectrum had higher coefficients between 12 and 48 s. SCIHindividuals had lower power than controls at 0.1 Hz; their fractal spectrum was morphologically different, diverging from that of controls at the largest scales (120 s). Therefore, when the lesion compromises the autonomic control of lower districts, fractal analysis reveals alterations undetected by power spectral analysis of heart rate variability
The G1456 to T mutation in the thrombomodulin gene is not frequent in patients with venous thrombosis
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EFFECTS OF AUTONOMIC TONE ON SHORT VERSUS LONG DISTANCE PERFORMANCES IN SWIMMERS
No full textWhatever the swimming specialty, swim training programs generally consist of high volume, which may shifts the heart rate (HR) autonomic control towards vagal predominance. Although it is accepted that an enhanced parasympathetic tone may improve performance on long distances, it is poorly known whether it may affect performance on short distances. PURPOSE. To evaluate resting autonomic tone and swimming performance on short and long distances in highly trained swimmers. METHODS. Two groups of national–level swimmers (all males, crawl specialists) were evaluated: short (S: 50-100 m; n=13; 24±3 yrs) and long (L: 1500 m; n=9; age 19±1 yrs) distance specialists. All swimmers belonged to the same team and were similar for training level. Beat-by-beat HR was recorded at rest in the morning, in supine position, by a HR monitor for 15 minutes. HR variability indexes were calculated from time (RMSSD, pNN50, indexes of vagal tone) and frequency (LF, Low Frequency and HF, High Frequency as absolute values and in normalized units (nu); LF/HF ratio, index of sympathovagal balance) domains. The anaerobic threshold was evaluated by an incremental swimming test with lactate measurements. RESULTS. The percentage of swimmers who showed resting bradycardia tended to be higher in L (78%) than in S (54%) group. HRV indexes did not significantly differ between groups: RMSSD 67±23 vs 66±11 ms, pNN50 40±17 vs 48±10%, LFnu 62.3±12.3 vs 54.4±14.8, HFnu 37.6±12.3 vs 45.6±14.8, LF/HF 2.1±1.9 vs 1.5±1.0 (S vs L group, respectively). In S group, 50 m best time correlated positively (p<0.05) with RMSSD (r=0.64), pNN50 (r=0.73) and absolute HF power (r=0.64), and negatively with LFnu (r=-0.56), but not with anaerobic threshold. On the contrary, in L group 1500 m did not correlate with RMSSD, pNN50 and absolute HF power (although negative trends were perceived), negatively correlated with absolute LF power (r=-0.65 p=0.05), positively correlated to LFnu (r=0.72, p=0.02), and tended to increase with anaerobic threshold. CONCLUSION. L swimmers were not more hypervagotonic than S swimmers, and such adaptation tended to be positively associated with anaerobic threshold. Conversely, high vagal tone appeared somehow detrimental on short swimming performance, as it negatively predicts performance on 50 m events, whereas anaerobic threshold did not
Cardio-respiratory adjustments and cost of locomotion in school children during backpack walking (the Italian Backpack Study).
No full textThe use of a school backpack is one of the possible causes of back pain in children. Oxygen consumption (VO2), pulmonary ventilation, and heart rate (fc) were measured in 35 pre-pubertal subjects [17 girls and 18 boys, mean (SD) age 11.3 (0.6) years]. They took part in a four-step experiment: (1) standing for 5 min, (2) walking at 3 km.h(-1) for 7 min, (3) walking at 3 km.h(-1) for 7 min carrying a school backpack weighing 8 kg, and (4) walking at 7 km.h(-1) for 5 min with no load. The occurrence of back pain in the last 2-3 years and during the last 15 days was assessed for the subjects by means of a questionnaire. Mean (SD) standing VO2, was 215 (45) ml.min(-1) during walking at 3 km.h(-1), 503 (101) ml.min(-1) during walking without a load, and increased to 541 (98) ml.min(-1) during walking with a load (P<0.01). Carrying a backpack increased fc only minimally. The energy cost of walking at 3 km.h(-1) without the backpack was 10.0 (2.0) ml O2.m(-1), and with the backpack was 10.8 (1.9) ml O2.m(-1) (P< 0.01). The net energy cost of locomotion was 0.129 (0.032) ml.kg body mass(-1).m(-1) for the unloaded condition and slightly lower, at 0.123 (0.025) ml.kg body mass(-1).m(-1) during loaded walking (P < 0.05). Ventilation did not change significantly between unloaded and loaded conditions. When the data were assessed according to the occurrence of back pain, the fc/VO2 slope was significantly lower in children without back pain, even though the net energy cost of locomotion was similar. Overall, these data suggest that the cardiovascular effortrequired for locomotion while carrying a backpack is minimal. However, fatigability and back pain are more likely to take place in less physical performing subjects. Thus, the occurrence of back pain in schoolchildren during locomotion while carrying a backpack may improve with an improvement in their level of fitness
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