Biomedical subjects

V Pichot

Publications and source records attributed to V Pichot.

15 recordsLinked to original sources

PubMed2006

Heart rate variability, training variation and performance in elite swimmers.

The aim of the present study was to investigate the relationships between heart rate variability (HRV) changes and both training variations and performances in elite swimmers. A secondary purpose was to measure catecholamine urinary excretion in elite swimmers to validate the HRV indices of sympathetic activity during training. Thirteen swimmers (4 females and 9 males) were tested before and after 4 weeks of intense training (IT) and 3 weeks of reduced training (RT). At the end of each period, the swimmers participated in an official competition of their best event. Individual performances were expressed as percentage of the previous season's best performance. Spectral analysis was used to investigate RR interval variability. HRV indices failed to show any significant changes between the study periods (p>0.05). Pre-IT HF was correlated with performance (r=0.45; p=0.05) and HFnu (r=0.59; p<0.05) during RT. On the other hand, once RT was completed, HFnu was correlated positively to performance (r=0.81; p<0.01) and negatively to fatigue (r=- 0.63; p<0.03). Conversely, the indices of sympathetic activity, i.e., LFnu and LF/HF ratio were inversely related to performance (both r=- 0.81; p<0.01); total fatigue score was correlated to the changes in HFnu (r=- 0.63; p<0.03) and in the LF/HF ratio (r=0.58; p<0.05). Changes in the adrenaline/noradrenaline ratio over the follow-up period were related to the changes in the LF/HF ratio (r=0.45; p<0.03). In highly trained swimmers coping well with a training program, including 4 weeks of IT followed by 3 weeks of RT, HRV indices were unaltered. On the other hand, after the 3 weeks of RT, HFnu was positively related to performance and inversely related to the fatigue score. Thus, elevated initial HF levels could be important in the parasympathetic activity increases during taper and, hence, in swimming performance improvement.

Adult↗

PubMed2006

Effect of endurance training on muscle microvascular filtration capacity and vascular bed morphometry in the elderly.

AIM: Exercise training is a strong stimulus for vascular remodelling and could restore age-induced vascular alterations. The purpose of the study was to test the hypothesis that an increase in vascular bed filtration capacity would corroborate microvascular adaptation with training. METHODS: We quantified (1) microvascularization from vastus lateralis muscle biopsy to measure the capillary to fibre interface (LC/PF) and (2) the microvascular filtration capacity (K(f)) in lower limbs through a venous congestion plethysmography procedure. Twelve healthy older subjects (74 +/- 4 years) were submitted to a 14-week training programme during which lower-limbs were trained for endurance exercise. RESULTS: The training programme induced a significant increase in the aerobic exercise capacity of lower limbs (+11% V(O2peak); P < 0.05; +28% Citrate Synthase Activity; P < 0.01). K(f) was largely increased (4.3 +/- 0.9 10(-3) mL min(-1) mmHg(-1) 100 mL(-1) post-training vs. 2.4 +/- 0.8 pre-training, mean +/- SD; P < 0.05) and microvascularization developed as shown by the rise in LC/PF (0.29 +/- 0.06 post- vs. 0.23 +/- 0.06 pre-training; P < 0.05). Furthermore, K(f) and LC/PF were correlated (r = 0.65, P < 0.05). CONCLUSION: These results demonstrated the microvascular adaptation to endurance training in the elderly. The increase in K(f) with endurance training was probably related to a greater surface of exchange with an increased microvessel/fibre interface area. We conclude that measurement of the microvascular filtration rate reflects the change in the muscle exchange area and is influenced by exercise training.

Aged↗

PubMed2005

Hot-drawing of single and multiwall carbon nanotube fibers for high toughness and alignment.

We report a new hot-drawing process for treating wet-spun composite fibers made of single- and multiwall carbon nanotubes and poly(vinyl alcohol). As shown in previous reports, untreated composite nanotube fibers exhibit a very large strain-to-failure, and their toughness, which is the energy needed to break the fibers, exceeds that of any other known materials. However, untreated composite nanotube fibers absorb a very small amount of energy at low strain and become degraded in humid conditions. In this work, we use hot-drawing treatments, a concept inspired from textile technologies, to improve the properties of nanotube/PVA fibers. This treatment yields a crystallinity increase of the PVA and an unprecedented degree of alignment of the nanotubes. These structural modifications lead to a markedly improved energy absorption at low strain and make the fibers resistant to moisture. Hot-drawn nanotube/PVA fibers hold great potential for a number of applications such as bulletproof vests, protective textiles, helmets, and so forth.

Journal Article↗

PubMed2004

Birth prematurity determines prolonged autonomic nervous system immaturity.

Because of its multiple involvement in physiological processes, autonomic nervous system (ANS) activity, a key regulator of homeostatic control, demonstrates a progressive increase during pregnancy. The profile of its maturation, mainly in the parasympathetic arm, in premature or full term infants, may help us to better understand its pathophysiological role. We prospectively evaluated ANS maturity in a group of 23 premature (PREM) infants at their theoretical term age and in 8 full term (FT) newborns. All recordings were registered close to the theoretical full term period (from 38 to 41 weeks) for the PREM group and during the first week of life for the FT newborns. Polygraphic recordings, EEG monitoring associated with visual clinical control, and Holter ECG, were performed simultaneously. ANS indices were then calculated during quiet sleep periods, using Wavelet transform of RR (beat to beat) intervals. High frequency components were found to be significantly lower in the PREM than in the FT group (p<0.05). Furthermore, at theoretical full term age, the greater the prematurity, the lower was parasympathetic activity. Because it is easy, monitoring of parasympathetic activity may help us to understand autonomic maturation and its clinical prognostic implications.

Apgar Score↗

PubMed2004

Influence of exercise training on cardiac baroreflex sensitivity in patients with COPD.

Decreased spontaneous cardiac baroreflex sensitivity (BRS), which could lead to the onset of cardiovascular events, has been demonstrated in chronic obstructive pulmonary disease patients. This study evaluates the effects of an exercise training programme on BRS. Twenty-one chronic obstructive pulmonary disease patients (mean+/-SD age 62+/-9 yrs; forced expiratory volume in one second 43.6+/-18.1% of the predicted value) with mild hypoxaemia (arterial oxygen tension 8.96+/-1.18 kPa) were compared to 18 healthy age-matched subjects. BRS was calculated as the slope of the baroreflex sequences between spontaneous changes in systolic blood pressure and subsequent consecutive relative risk deviation length, and was measured in the supine position and following head-up tilt for sympathetic stimulation. Pulmonary function test results and blood gas levels, measured only in patients, did not change after the training programme. Exercise training increased the maximal sustained workload (16.5%) and peak oxygen consumption (20.5%). Before training, BRS was lower in patients than in controls (2.7+/-1.5 versus 7.8+/-4.9 ms x mmHg(-1)) and tilting induced a smaller reduction in BRS (13 versus 34%). After training, BRS increased to 3.4+/-2.6 ms x mmHg(-1) in patients but remained lower than in controls. The response to the tilt test remained unchanged after training. It is concluded that, in chronic obstructive pulmonary disease patients, exercise training is associated with a gain in spontaneous baroreflex sensitivity, reflecting cardiovascular benefits.

Baroreflex↗

PubMed2003

Predicting sleep apnoea syndrome from heart period: a time-frequency wavelet analysis.

Heart rate fluctuations are a typical finding during obstructive sleep apnoea, characterised by bradycardia during the apnoeic phase and tachycardia at the restoration of ventilation. In this study, a time-frequency domain analysis of the nocturnal heart rate variability (HRV) was evaluated as the single diagnostic marker for obstructive sleep apnoea syndrome (OSAS). The predictive accuracy of time-frequency HRV variables (wavelet (Wv) decomposition parameters from level 2 (Wv2) to level 256 (Wv256)) obtained from nocturnal electrocardiogram Holter monitoring were analysed in 147 consecutive patients aged 53.8+/-11.2 yrs referred for possible OSAS. OSAS was diagnosed in 66 patients (44.9%) according to an apnoea/hypopnoea index > or = 10. Using receiver-operating characteristic curves analysis, the most powerful predictor variable was Wv32 (W 0.758, p<0.0001), followed by Wv16 (W 0.729, p<0.0001) and Wv64 (W 0.700, p<0.0001). Classification and Regression Trees methodology generated a decision tree for OSAS prediction including all levels of Wv coefficients, from Wv2 to Wv256 with a sensitivity reaching 92.4% and a specificity of 90.1% (percentage of agreement 91.2%) with this nonparametric analysis. Time-frequency parameters calculated using wavelet transform and extracted from the nocturnal heart period analysis appeared as powerful tools for obstructive sleep apnoea syndrome diagnosis.

Adult↗

PubMed2001

Wavelet transform of heart rate variability to assess autonomic nervous system activity does not predict arousal from general anesthesia.

PURPOSE: The relationship between autonomic nervous system (ANS) activity and general anesthesia has been explored. Studies have demonstrated partial recovery of heart rate variability (HRV), representative of ANS activity, in the postoperative period, but the arousal period has not been precisely studied. The goals of this study were to analyze modifications of ANS activity during general anesthesia and, more particularly, around the arousal period, to look for predictors of arousal. METHODS: We analyzed HRV changes using wavelet transform, a time-frequency analysis that, in contrast to Fourier transform, is able to assess abrupt changes of ANS activity. Seventeen patients (mean +/- SD age: 40.9 +/- 16.4 yr) under general anesthesia for hip or knee surgery, were included in the study. The analysis began one hour before anesthesia, focussed on eye opening, and ended three hours after arousal. RESULTS: There was a dramatic decrease in HRV after induction, that extended throughout anesthesia and represented a decrease in global autonomic regulation with, however, a relative predominance of vagal tone. At the moment of eye opening, there was an abrupt change in HRV, representing a sudden shift of ANS balance towards the predominance of sympathetic activity, while none of these indices changed seconds before arousal. CONCLUSIONS: Wavelet analysis of HRV appears to be powerful tool to precisely assess instantaneous changes of HRV during anesthesia. Using this method, there were no identifiable precursory HRV indices of arousal.

Adult↗

PubMed2001

A practical method to statistically classify devices according to their relative accuracy.

Mathematical methods to statistically compare the relative accuracy of physiological monitoring devices to reference measurements are scarce. We developed such a method to compare any number of devices to each other as well as to reference values. This new statistical comparative procedure uses a combination of different known mathematical processes. The method allows the separation of the error of the devices into two components, the first, being systematic, can be easily amended, while the second, inherent to the technical limitations of the measuring device as well as to the physical properties of the explored phenomenon, cannot be corrected and will thus be used as the comparative criterion for statistics. That method, which is easy to implement should ease comparisons of the accuracy of any number of devices as well as comparison of other sets of physiological values, by giving an easy access to statistical results.

Equipment Design↗

PubMed2001

Chronotropic incompetence response to exercise in congestive heart failure, relationship with the cardiac autonomic status.

In chronic congestive heart failure (CHF), attenuated heart rate response to exercise, a manifestation of chronotropic incompetence (CI), contributes to limiting exercise capacity. The present study was thus conducted to evaluate the respective role of chronic attenuation of cardiac vagal tone associated with depressed baroreflex sensitivity or affected cardiac sympathetic responsiveness in CHF patients with CI. Spontaneous cardiac baroreflex sensitivity (BRS) assessed by sequence method and spectral- and time-domain analysis of heart rate variability (HRV) were analysed in 21 chronic CHF patients. All patients performed a symptom-limited exercise test with measurement of gas exchange. Chronic incompetence which was defined as failure to achieve > or =80% of the heart rate reserve (%HRR) given by (HRpeak - HRrest)/(predictive maximal heart rate - HRrest) was observed in 14 (66%) patients. There was no significant difference in age, heart rate, peak oxygen uptake or left ventricular ejection fraction between the patients with and without CI. Although there was no significant difference in BRS, low frequency power of HRV in normalized units (LFnu) and SDNN were significantly lower in CI patients. Percentage of HRR correlated significantly with LFnu on 15 min (r=0.64, P<0.005) and, with LFnu on 24 h (r=0.52, P<0.01), SDNN (r=0.48, P=0.03) and SDANN (r=0.48, P=0.03), but not BRS (r=0.04, P=NS). Autonomic nervous system derangement is a complex process in CHF. The role of basal depressed cardiac sympathetic tone seems to contribute more closely than depressed baroreflex sensitivity to the impaired heart rate response to exercise frequently observed in CHF patients.

Adult↗

PubMed2001

[Activity of the autonomous nervous system measured based on the variability of heart rate in female urinary incontinence].

OBJECTIVES: To compare the ANS activity, measured by heart rate variability (HRV) in various types of female urinary incontinence (UI). MATERIALS AND METHODS: 25 patients were included in this prospective study: 11 presented stress UI without sphincter incompetence, 9 presented mixed UI and 5 presented urge UI. UI without idiopathic detrusor instability (IDI) (n = 11) was compared to UI with IDI (N = 14.). No statistically significant difference was observed for mean age of the patients in the two groups. A 24-hour Holter ECG, under the conditions of the patient's everyday life, provided time and frequency indices (Fourier transform) of HRV, reflecting the sympathetic, parasympathetic and global ANS activity. RESULTS: The global ANS activity of the patients with either mixed UI, urge UI or UI with IDI, was statistically significantly lower (p < 0.05) than that of patients with stress UI. The sympathetic-vagal balance, heart rate, blood pressure, and Ditrovie score were not significantly different between the groups. CONCLUSIONS: This preliminary study shows that IDI is associated with a global reduction of ANS activity compared to that of patients without IDI. Modifications of sympathetic, parasympathetic and global ANS activity were also observed between the various types of female UI.

Autonomic Nervous System↗

PubMed2000

Relation between heart rate variability and training load in middle-distance runners.

PURPOSE: Monitoring physical performance is of major importance in competitive sports. Indices commonly used, like resting heart rate, VO2max, and hormones, cannot be easily used because of difficulties in routine use, of variations too small to be reliable, or of technical challenges in acquiring the data. METHODS: We chose to assess autonomic nervous system activity using heart rate variability in seven middle-distance runners, aged 24.6 +/- 4.8 yr, during their usual training cycle composed of 3 wk of heavy training periods, followed by a relative resting week. The electrocardiogram was recorded overnight twice a week and temporal and frequency indices of heart rate variability, using Fourier and Wavelet transforms, were calculated. Daily training loads and fatigue sensations were estimated with a questionnaire. Similar recordings were performed in a sedentary control group. RESULTS: The results demonstrated a significant and progressive decrease in parasympathetic indices of up to -41% (P < 0.05) during the 3 wk of heavy training, followed by a significant increase during the relative resting week of up to +46% (P < 0.05). The indices of sympathetic activity followed the opposite trend, first up to +31% and then -24% (P < 0.05), respectively. The percentage increasing mean nocturnal heart rate variation remained below 12% (P < 0.05). There was no significant variation in the control group. CONCLUSION: This study confirmed that heavy training shifted the cardiac autonomic balance toward a predominance of the sympathetic over the parasympathetic drive. When recorded during the night, heart rate variability appeared to be a better tool than resting heart rate to evaluate cumulated physical fatigue, as it magnified the induced changes in autonomic nervous system activity. These results could be of interest for optimizing individual training profiles.

Adult↗

PubMed1999

Screening of obstructive sleep apnea syndrome by heart rate variability analysis.

BACKGROUND: Enhanced nocturnal heart rate variability (HRV) has been evoked in sleep-related breathing disorders. However, its capacity to detect obstructive sleep apnea syndrome (OSAS) has not been systematically determined. Thus, we evaluated the discriminant power of HRV parameters in a first group of patients (G1) and validated their discriminant capacity in a second group (G2). METHODS AND RESULTS: In G1, 39 of 91 patients (42.8%) were identified as diseased by polysomnography, as were 24 of 52 patients (46%) in G2. Time-domain HRV variables (SD of NN intervals [SDNN], mean of the standard deviations of all NN intervals for all consecutive 5-minute segments of the recording [SDNN index], square root of the mean of the sum of the squares of differences between adjacent normal RR intervals [r-MSSD], and SD of the averages of NN intervals in all 5-minute segments of the recording [SDANN]) were calculated for daytime and nighttime periods, as well as the differences between daytime and nighttime values (Delta[D/N]). Correlations between HRV variables and OSAS status were analyzed in G1 by use of receiver-operating characteristic (ROC) curves and logistic regression analysis. By ROC curve analysis, 7 variables were significantly associated with OSAS. After adjustment for other variables through multiple logistic regression analysis, Delta[D/N]SDNN index and Delta[D/N] r-MSSD remained significant independent predictors of OSAS, with ORs of 8.22 (95% CI, 3.16 to 21.4) and 2.86 (95% CI, 1.21 to 6.75), respectively. The classification and regression tree methodology demonstrated a sensitivity reaching 89.7% (95% CI, 73.7 to 97.7) with Delta[D/N] SDNN index and a specificity of 98.1% (95% CI, 86.4 to 100) with Delta[D/N] SDNN using appropriate thresholds. These thresholds, applied to G2, yielded a sensitivity of 83% using Delta[D/N] SDNN index and a specificity of 96.5% using Delta[D/N] SDNN. CONCLUSIONS: Time-domain HRV analysis may represent an accurate and inexpensive screening tool in clinically suspected OSAS patients and may help focus resources on those at the highest risk.

Adult↗

PubMed1999

Reduced cardiac sympathetic autonomic tone after long-term nasal continuous positive airway pressure in obstructive sleep apnoea syndrome.

The increased sympathetic activation that occurs in obstructive sleep apnoea (OSA) may play an important role in associated morbidity. We investigated the effect of long-term (3 month) nasal continuous positive airway pressure (CPAP) on the autonomic nervous system assessed by heart rate variability (HRV). Fourteen patients (12 men), mean age 61.4 +/- 8.1 years, with OSA underwent continuous synchronized electrocardiographic and polysomnographic monitoring. The apnoea/hypopnoea index (AHI) decreased from 50.6 +/- 13.7 to 2.2 +/- 2.5 events h-1 after CPAP. HRV analysis showed significant decreases in low frequency (LF; from 7.12 +/- 1.06 to 6.22 +/- 1.18 ln ms2 Hz-1; P < 0.001), high frequency (HF; from 5.91 +/- 0.87 to 5.62 +/- 0.92 ln ms2 Hz-1; P < 0.05) and LF/HF (from 1.21 +/- 0.12 to 1.11 +/- 0.15 ln ms2 Hz-1; P < 0.001) when the patients were asleep. The decrease in LF/HF was prolonged into the daytime (from 1.33 +/- 0.22 to 1.24 +/- 0.21 ln ms2 Hz-1; P < 0.001). Treatment of OSA by CPAP significantly reduced the parameters of cardiac sympathetic tone, a favourable effect.

Adult↗

PubMed1999

Wavelet transform to quantify heart rate variability and to assess its instantaneous changes.

Heart rate variability is a recognized parameter for assessing autonomous nervous system activity. Fourier transform, the most commonly used method to analyze variability, does not offer an easy assessment of its dynamics because of limitations inherent in its stationary hypothesis. Conversely, wavelet transform allows analysis of nonstationary signals. We compared the respective yields of Fourier and wavelet transforms in analyzing heart rate variability during dynamic changes in autonomous nervous system balance induced by atropine and propranolol. Fourier and wavelet transforms were applied to sequences of heart rate intervals in six subjects receiving increasing doses of atropine and propranolol. At the lowest doses of atropine administered, heart rate variability increased, followed by a progressive decrease with higher doses. With the first dose of propranolol, there was a significant increase in heart rate variability, which progressively disappeared after the last dose. Wavelet transform gave significantly better quantitative analysis of heart rate variability than did Fourier transform during autonomous nervous system adaptations induced by both agents and provided novel temporally localized information.

Adrenergic beta-Antagonists↗

PubMed1997

Accuracy of an automatic and patient-triggered long-term solid memory ambulatory cardiac event recorder.

This study evaluated the R-Test Evolution, a new type of cardiac event recorder bearing both patient-triggered and automatic capabilities. Its 7-day automatic arrhythmia analysis showed promising clinical advantages, especially when investigating patients with unexplained rare events such as syncope, feeling of weakness or faintness, palpitations, stroke, or in patients inconsistent in their use of patient-triggered recordings.

Arrhythmias, Cardiac↗