Influence of Training Load and Altitude on Heart Rate Variability Fatigue Patterns in Elite Nordic Skiers.

We aimed to analyse the relationship between training load/intensity and different heart rate variability (HRV) fatigue patterns in 57 elite Nordic-skiers. 1063 HRV tests were performed during 5 years. R-R intervals were recorded in resting supine (SU) and standing (ST) positions. Heart rate, low (LF), high (HF) frequency powers of HRV were determined. Training volume, training load (TL, a.u.) according to ventilatory threshold 1 (VT1) and VT2 were measured in zones I≤VT1; VT1VT2, IV for strength. TL was performed at 81.6±3.5% in zone I, 0.9±0.9% in zone II, 5.0±3.6% in zone III, 11.6±6.3% in zone IV. 172 HRV tests matched a fatigue state and four HRV fatigue patterns (F) were statistically characterized as F(HF-LF-)SU_ST for 121 tests, F(LF+SULF-ST) for 18 tests, F(HF-SUHF+ST) for 26 tests and F(HF+SU) for 7 tests. The occurrence of fatigue states increased substantially with the part of altitude training time (r2=0.52, p<0.001). This study evidenced that there is no causal relationship between training load/intensity and HRV fatigue patterns. Four fatigue-shifted HRV patterns were sorted. Altitude training periods appeared critical as they are likely to increase the overreaching risks.

Thermal and metabolic responses of military divers during a 6-hour static dive in cold water.

BACKGROUND: Human thermal responses during prolonged whole-body immersion in cold water are of interest for the military, especially French SEALS. This study aims at describing the thermo-physiological responses. METHODS: There were 10 male military divers who were randomly assigned to a full immersion in neutral (34 degrees C), moderately cold (18 degrees C), and cold (10 degrees C) water wearing their operational protective devices (5.5 mm wetsuit with 3.0 mm thick underwear) for 6 h in a static position. Rectal temperature (T(re)) and 14 skin temperatures (T(sk)), blood analysis (stress biomarkers, metabolic substrates), and oxygen consumption (Vo2) were collected. RESULTS: At 34 degrees C, there were no significant modifications of the thermo-physiological responses over time. The most interesting result was that rates of rectal temperature decrease (0.15 +/- 0.02 degrees C x min(-1)) were the same between the two cold stress experimental conditions (at 18 degrees C and 10 degrees C). At the final experiment, rectal temperature was not significantly different between the two cold stress experimental conditions. Mean T(sk) decreased significantly during the first 3 h of immersion and then stabilized at a lower level at 10 degrees C (25.6 +/- 0.8 degrees C) than at 18 degrees C (29.3 +/- 0.9 degrees C). Other results demonstrate that the well-trained subjects developed effective physiological reactions. However, these reactions are consistently too low to counterbalance the heat losses induced by cold temperature conditions and long-duration immersion. CONCLUSION: This study shows that providing divers with thermal protection is efficient for a long-duration immersion from a medical point of view, but not from an operational one when skin extremities were taken into account.

Enterocyte damage in critically ill patients is associated with shock condition and 28-day mortality.

OBJECTIVES: Small bowel dysfunction in critically ill patients is frequent, underdiagnosed, and associated with poor prognosis. Intestinal fatty acid-binding protein is a marker of enterocyte damage, and plasma citrulline concentration is a marker of functional enterocyte mass. Primary objective was to identify factors associated with intestinal fatty acid-binding protein in critically ill patients. Secondary objectives were to study factors associated with plasma citrulline concentration and its correlation with intestinal fatty acid-binding protein. DESIGN: Prospective observational study. SETTING: ICU in a University Hospital PATIENTS: Critically ill patients 18 years old or older with an expected length of ICU stay 48 hours or more, without pregnancy, chronic small bowel disease, or chronic renal failure. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Plasma intestinal fatty acid-binding protein and citrulline concentrations, and variables relating to prognosis and treatment, were measured at admission to the ICU. One hundred and three patients were included. Intestinal fatty acid-binding protein elevation at admission to the ICU was associated with catecholamine support, higher lactate concentration, higher Sequential Organ Failure Assessment score, and higher international normalized ratio (all p≤0.001). Plasma citrulline concentration less than or equal to 10 µmol/L at admission to the ICU was associated with higher intra-abdominal pressure, higher plasma C reactive protein concentration, and more frequent antibiotic use (all p≤0.005). There was no correlation between plasma levels of intestinal fatty acid-binding protein and citrulline. At ICU admission, Sequential Organ Failure Assessment score≥12, plasma citrulline≤12.2 µmol/L, and plasma intestinal fatty acid-binding protein concentration≥355 pg/mL were all independently associated with 28-day mortality (odds ratio, 4.39 [1.48-13.03]; odds ratio, 5.17 [1.59-16.86]; and odds ratio, 4.46 [1.35-14.74], respectively). CONCLUSIONS: In critically ill patients, enterocyte damage is frequent, and it is significantly associated with shock and 28-day mortality. The link between intestinal fatty acid-binding protein and plasma citrulline concentrations in critically ill patients needs to be further evaluated.

Detection of interstitial lung disease in systemic sclerosis through partitioning of lung transfer for carbon monoxide.

BACKGROUND: Interstitial lung disease (ILD) is a leading cause of death in systemic sclerosis (SSc). Sensitivities and specificities of the current pulmonary function tests (PFTs) for the detection of ILD in SSc are poor. OBJECTIVE: To determine whether diffusion capacity of the lungs for carbon monoxide (DLCO) partitioned into membrane conductance for CO (DmCO) and alveolar capillary blood volume (Vcap) could provide more sensitive clues to ILD than current PFTs. METHODS: DmCO and Vcap were determined in 35 consecutive SSc patients in whom a cardiac and/or pulmonary vascular abnormality had been rejected according to the recommended screening algorithm. ILD was diagnosed with high-resolution computed tomography. RESULTS: Among 35 patients [6 men; median age (first-third quartile) 61.9 years (49.5-67.7)], 22 had no ILD and 13 did. Total lung capacity (TLC), vital capacity and DLCO [percentage of predicted value (%pred)] were lower in patients with ILD [86 (82-103) vs. 106 (98-112), p = 0.01, 96 (88-112) vs. 114 (104-121), p = 0.04, and 67 (59-81) vs. 80 (71-94), p = 0.02, respectively]. DmCO (%pred) and the ratio of DmCO to Vcap were much lower in patients with ILD [54 (48-72) vs. 83 (66-92), p < 0.001, and 0.22 (0.21-0.27) vs. 0.40 (0.35-0.53), p < 0.0001, respectively]. According to receiver operating characteristic analysis, the DmCO:Vcap ratio displayed higher sensitivity and specificity than TLC, vital capacity and DLCO in identifying ILD in our study group (p < 0.01). CONCLUSIONS: These results suggest that the partitioning of DLCO might be of interest for identifying ILD in SSc patients.

Relevance of water gymnastics in rehabilitation programs in patients with chronic heart failure or coronary artery disease with normal left ventricular function.

BACKGROUND: Exercise training is included in cardiac rehabilitation programs to enhance physical capacity and cardiovascular function. Among the existing rehabilitation programs, exercises in water are increasingly prescribed. However, it has been questioned whether exercises in water are safe and relevant in patients with stable chronic heart failure (CHF), coronary artery disease (CAD) with normal systolic left ventricular function. The goal was to assess whether a rehabilitation program, including water-based gymnastic exercises, is safe and induces at least similar benefits as a traditional land-based training. METHODS AND RESULTS: Twenty-four male CAD patients and 24 male CHF patients with stable clinical status participated in a 3-week rehabilitation. They were randomized to either a group performing the training program totally on land (CADl, CHFl; endurance + callisthenic exercises) or partly in water (CADw, CHFw; land endurance + water callisthenic exercises). Before and after rehabilitation, left ventricular systolic and cardiorespiratory functions, hemodynamic variables and autonomic nervous activities were measured. No particular complications were associated with both of our programs. At rest, significant improvements were seen in CHF patients after both types of rehabilitation (increases in stroke volume and left ventricular ejection fraction [LVEF]) as well as a decrease in heart rate (HR) and in diastolic arterial pressure. Significant increases in peaks VO(2), HR, and power output were observed in all patients after rehabilitation in exercise test. The increase in LVEF at rest, in HR and power output at the exercise peak were slightly higher in CHFw than in CHFl. CONCLUSIONS: Altogether, both land and water-based programs were well tolerated and triggered improvements in cardiorespiratory function.

Hyperoxia-induced alterations in cardiovascular function and autonomic control during return to normoxic breathing.

Hyperoxia causes hemodynamic alterations. We hypothesized that cardiovascular and autonomic control changes last beyond the end of hyperoxic period into normoxia. Ten healthy volunteers were randomized to breathe either medical air or 100% oxygen for 45 min in a double-blind study design. Measurements were performed before (baseline) and during gas exposure, and then 10, 30, 60, and 90 min after gas exposure. Hemodynamic changes were studied by Doppler echocardiography. Changes in cardiac and vasomotor autonomic control were evaluated through changes in spectral power of heart rate variability and blood pressure variability. Cardiac baroreflex sensitivity was assessed by the sequence method. Hyperoxia significantly decreased heart rate and increased the high frequency power of heart rate variability, suggesting a chemoreflex increase in vagal activity since the slope of cardiac baroreflex was significantly decreased during hyperoxia. Hyperoxia increased significantly the systemic vascular resistances and decreased the low frequency power of blood pressure variability, suggesting that hyperoxic vasoconstriction was not supported by an increase in vascular sympathetic stimulation. These changes lasted for 10 min after hyperoxia (p < 0.05). After the end of hyperoxic exposure, the shift of the power spectral distribution of heart rate variability toward a pattern of increased cardiac sympathetic activity lasted for 30 min (p < 0.05), reflecting a resuming of baseline autonomic balance. Cardiac output and stroke volume were significantly decreased during hyperoxia and returned to baseline values (10 min) later than heart rate. In conclusion, hyperoxia effects continue during return to normoxic breathing, but cardiac and vascular parameters followed different time courses of recovery.

A neoprene vest hastens dyspnoea and leg fatigue during exercise testing: entangled breathing and cardiac hindrance?

Symptoms and contributing factors of immersion pulmonary oedema (IPO) are not observed during non-immersed heart and lung function assessments. We report a case in which intense snorkelling led to IPO, which was subsequently investigated by duplicating cardiopulmonary exercise testing with (neoprene vest test - NVT) and without (standard test - ST) the wearing of a neoprene vest. The two trials utilised the same incremental cycling exercise protocol. The vest hastened the occurrence and intensity of dyspnoea and leg fatigue (Borg scales) and led to an earlier interruption of effort. Minute ventilation and breathing frequency rose faster in the NVT, while systolic blood pressure and pulse pressure were lower than in the ST. These observations suggest that restrictive loading of inspiratory work caused a faster rise of intensity and unpleasant sensations while possibly promoting pulmonary congestion, heart filling impairment and lowering blood flow to the exercising muscles. The subject reported sensations close to those of the immersed event in the NVT. These observations may indicate that increased external inspiratory loading imposed by a tight vest during immersion could contribute to pathophysiological events.

Broad individual immersion-scattering of respiratory compliance likely substantiates dissimilar breathing mechanics.

Head-out water immersion alters respiratory compliance which underpins defining pressure at a "Lung centroid" and the breathing "Static Lung Load". In diving medicine as in designing dive-breathing devices a single value of lung centroid pressure is presumed as everyone's standard. On the contrary, we considered that immersed respiratory compliance is disparate among a homogenous adult group (young, healthy, sporty). We wanted to substantiate this ample scattering for two reasons: (i) it may question the European standard used in designing dive-breathing devices; (ii) it may contribute to understand the diverse individual figures of immersed work of breathing. Resting spirometric measurements of lung volumes and the pressure-volume curve of the respiratory system were assessed for 18 subjects in two body positions (upright Up, and supine Sup). Measurements were taken in air (Air) and with subjects immersed up to the sternal notch (Imm). Compliance of the respiratory system (Crs) was calculated from pressure-volume curves for each condition. A median 60.45% reduction in Crs was recorded between Up-Air and Up-Imm (1.68 vs 0.66 L/kPa), with individual reductions ranging from 16.8 to 82.7%. We hypothesize that the previously disregarded scattering of immersion-reduced respiratory compliance might participate to substantial differences in immersed work of breathing.

Intermittent versus constant aerobic exercise: effects on arterial stiffness.

Aerobic exercises (of sufficient duration and intensity) decreases arterial stiffness. However, the direct relationship between the type of aerobic exercise (i.e. constant versus interval) and the alteration in arterial stiffness has been poorly explored. We evaluated the hemodynamic responses of 11 healthy males (22.5 +/- 0.7 years, height 177.7 +/- 1.1 cm, body mass 70.5 +/- 2.4 kg) following acute constant (CE) and intermittent cycling exercise (IE). Exercise duration and intensity (mean heart rate) were matched during both exercises (142.9 +/- 2.4 bpm for CE and 144.2 +/- 2.4 bpm for IE). Heart rate (HR) and cardiac output (CO) were measured throughout the whole session, while blood pressure and pulse wave velocity (PWV) were measured during pre exercise and 30 min recovery. Arterial stiffness and cardiac autonomic control were assessed through PWV and heart rate variability, respectively. After IE, lower limb arterial stiffness was significantly and steadily decreased compared to pre exercise value (from 8.6 +/- 0.1 to m s(-1) to 7.6 +/- 0.3 to m s(-1) at 30 min) and was lower than after CE (8.2 +/- 0.3 m s(-1) at 30 min, which did not significantly change compared to pre exercise: 8.7 +/- 0.2 m s(-1)). We hypothesized that the higher HR and lower arterial stiffness after IE were likely due to variations in peripheral vascular changes during the exercise which may trigger the release of endothelial or metabolic vasoactive factors. These data appear to show that IE may result in a greater stimulus for vascular adaptations when compared to CE.

Whole body immersion and hydromineral homeostasis: effect of water temperature.

This experiment was designed to assess the effects of prolonged whole body immersion (WBI) in thermoneutral and cold conditions on plasma volume and hydromineral homeostasis.10 navy "combat swimmers" performed three static 6-h immersions at 34 degrees C (T34), 18 degrees C (T18) and 10 degrees C (T10). Rectal temperature, plasma volume (PV) changes, plasma proteins, plasma and urine ions, plasma osmolality, renin, aldosterone and antidiuretic hormone (ADH) were measured. Results show that compared to pre-immersion levels, PV decreased throughout WBI sessions, the changes being markedly accentuated in cold conditions. At the end of WBI, maximal PV variations were -6.9% at T34, -14.3% at T18, and -16.3% at T10. Plasma osmolality did not change during and after T34 immersion, while hyperosmolality was present at the end of T18 immersion and began after only 1 h of T10 immersion. In the three temperature conditions, significant losses of water (1.6-1.7 l) and salt (6-8 g) occurred and were associated with similar increases in osmolar and free water clearances. Furthermore, T18 and T10 immersions increased the glomerular filtration rate. There was little or no change in plasma renin and ADH, while the plasma level of aldosterone decreased equally in the three temperature conditions. In conclusion, our data indicate that cold water hastened PV changes induced by immersion, and increased the glomerular filtration rate, causing larger accumulated water losses. The iso-osmotic hypovolemia may impede the resumption of baseline fluid balance. Results are very similar to those repeatedly described by various authors during head-out water immersion.

Heart rate variability in preterm infants and maternal smoking during pregnancy.

OBJECTIVE: Tobacco smoke exposure increases the risk of premature birth and of dying of sudden infant death syndrome (SIDS). Prematurity significantly increases the risk of dying of SIDS, but mechanisms underlying this epidemiological finding are unclear. The cumulated effect of both prematurity and prenatal exposure to nicotine on autonomic heart rate control has not been studied. METHODS: Using coarse-graining spectral analysis, we compared heart rate variability (HRV) indices of preterm newborns at 33-34 weeks post-conceptional age from smoking (n = 19) and non-smoking (n = 21) mothers. Assessment of tobacco exposure relied on maternal reports and newborns cotinine analysis. We observed how indicators of HRV depended on gestational age at birth. RESULTS: At 33-34 weeks postconceptional age, the newborns from smoking mothers had lower HRV low frequency power normalised to the total spectral power (LF/TP) than the control group (median values: 8% vs. 15% respectively, p < 0.02). In the non-smoking group, RR-interval values and total HRV power were correlated with gestational age at birth, with a shorter RR and a lower total HRV power in lesser gestational ages (rho = 0.67, p = 0.03, rho = 0.71, p = 0.003 respectively). This correlation was not observed for RR values in the group with smoking mothers.

Increased expression of blood muscarinic receptors in patients with reflex syncope.

AIMS: Pathophysiology of reflex syncope is not fully understood but a vagal overactivity might be involved in this syncope. Previously, overexpression of muscarinic M2 receptors and acetylcholinesterase was found in particular in the heart and in lymphocytes of rabbits with vagal overactivity as well as in hearts of Sudden Infant Death Syndromes. The aim of this present study was to look at M2 receptor expression in blood of patients with reflex syncope. The second objective was to measure acetylcholinesterase expression in these patients. METHODS AND RESULTS: 136 subjects were enrolled. This monocenter study pooled 45 adults exhibiting recurrent reflex syncope compared with 32 healthy adult volunteers (18-50 years) and 38 children exhibiting reflex syncope requiring hospitalization compared with 21 controls (1-17 years). One blood sample was taken from each subject and blood mRNA expression of M2 receptors was assessed by qRT-PCR. Taking into account the non-symmetric distributions of values in both groups, statistical interferences were assessed using bayesian techniques. A M2 receptor overexpression was observed in adult and pediatric patients compared to controls. The medians [q1;q3] were 0.9 [0.3;1.9] in patients versus 0.2 [0.1;1.0] in controls; the probability that M2 receptor expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.99. Acetylcholinesterase expression was also increased 0.7 [0.4;1.6] in patients versus 0.4 [0.2;1.1] in controls; the probability that acetylcholinesterase expression was higher in patients than in controls (Pr[patients>controls]) was estimated at 0.97. Both in adults and children, the expression ratio of M2 receptors over acetylcholinesterase was greater in the patient group compared with the control group. CONCLUSION: M2 receptor overexpression has been detected in the blood of both, adults and children, exhibiting reflex syncope. As in our experimental model, i.e. rabbits with vagal overactivity, acetylcholinesterase overexpression was associated with M2 receptor overexpression. For the first time, biological abnormalities are identified in vagal syncope in which only clinical signs are, so far, taken into account for differential diagnosis and therapeutic management. Further work will be needed to validate potential biomarkers of risk or severity associated with the cholinergic system.

Cardiovascular autonomic control during short-term thermoneutral and cool head-out immersion.

BACKGROUND: Moderately cold head-out water immersion stimulates both baro- and cold-receptors, and triggers complex and contradictory effects on the cardiovascular system and its autonomic nervous control. OBJECTIVES: To assess the effects of water immersion and cold on cardiovascular status and related autonomic nervous activity. METHODS: Hemodynamic variables and indexes of autonomic nervous activity (analysis of heart rate and blood pressure variability) were evaluated in 12 healthy subjects during 3 exposures of 20 min each in the upright position, i.e., in air (AIR, 24-25 degrees C), and during head-out water immersion at 35-36 degrees C (WIn) and 26-27 degrees C (WIc). RESULTS: Plasma noradrenaline, systolic and diastolic blood pressure, and total peripheral resistances were reduced during WIn compared to AIR (263.9 +/- 39.4 vs. 492.5 +/- 35.7 pg x ml(-1), 116.5 +/- 3.7 and 65.4 +/- 1.7 mmHg vs. 140.8 +/- 4.7 and 89.8 +/- 2.8 mmHg, 14.1 +/- 1.0 vs. 16.3 +/- 0.9 mmHg x L(-1) x min, respectively) while they were increased during WIc (530.8 +/- 84.7 pg ml(-1), 148.0 +/- 7.0 mmHg, 80.8 +/- 3.0 mmHg, and 25.8 +/- 1.9 mmHg x L(-1) x min, respectively). The blood pressure variability was reduced to the same extent during WIc and Win compared to AIR. Heart rate decreased during WIn (67.8 +/- 2.7 vs. 81.2 +/- 2.7 bpm during AIR), in parallel with an increased cardiac parasympathetic activity. This pattern was strengthened during WIc (55.3 +/- 2.2 bpm). CONCLUSIONS: Thermoneutral WI lowered sympathetic activity and arterial tone, while moderate whole-body skin cooling triggered vascular sympathetic activation. Conversely, both WI and cold triggered cardiac parasympathetic activation, highlighting a complex autonomic control of the cardiovascular system.

Immersion pulmonary oedema in a healthy diver not exposed to cold or strenuous exercise.

In healthy divers, the occurrence of immersion pulmonary oedema (IPE) is commonly caused by contributory factors including strenuous exercise, cold water and negative-pressure breathing. Contrary to this established paradigm, this case reports on a 26-year-old, well-trained combat swimmer who succumbed to acute IPE during static immersion in temperate (21°C) water, while using a front-mounted counterlung rebreather. The incident occurred during repeated depth-controlled ascent practice at the French military diving school. It was discovered that the diver had attempted to stop any gas leakage into the system by over-tightening the automatic diluent valve (ADV) (25th notch of 27) during the dive, thus causing a high resistance to inspiratory flow. The ventilatory constraints imposed by this ADV setting were assessed as a 3.2 Joules·L⁻¹ inspiratory work of breathing and -5 kPa (-50 mbar) transpulmonary pressure. This report confirms the key role of negative pressure breathing in the development of interstitial pulmonary oedema. Such a breathing pattern can cause a lowering of thoracic, airway and interstitial lung pressure, leading to high capillary pressure during each inspiration. Repetition of the diving drills resulted in an accumulation of interstitial lung water extravasation, causing pathological decompensation and proven symptoms.

The Key Roles of Negative Pressure Breathing and Exercise in the Development of Interstitial Pulmonary Edema in Professional Male SCUBA Divers.

BACKGROUND: Immersion pulmonary edema is potentially a catastrophic condition; however, the pathophysiological mechanisms are ill-defined. This study assessed the individual and combined effects of exertion and negative pressure breathing on the cardiovascular system during the development of pulmonary edema in SCUBA divers. METHODS: Sixteen male professional SCUBA divers performed four SCUBA dives in a freshwater pool at 1 m depth while breathing air at either a positive or negative pressure both at rest or with exercise. Echocardiography and lung ultrasound were used to assess the cardiovascular changes and lung comet score (a measure of interstitial pulmonary edema). RESULTS: The ultrasound lung comet score was 0 following both the dives at rest regardless of breathing pressure. Following exercise, the mean comet score rose to 4.2 with positive pressure breathing and increased to 15.1 with negative pressure breathing. The development of interstitial pulmonary edema was significantly related to inferior vena cava diameter, right atrial area, tricuspid annular plane systolic excursion, right ventricular fractional area change, and pulmonary artery pressure. Exercise combined with negative pressure breathing induced the greatest changes in these cardiovascular indices and lung comet score. CONCLUSIONS: A diver using negative pressure breathing while exercising is at greatest risk of developing interstitial pulmonary edema. The development of immersion pulmonary edema is closely related to hemodynamic changes in the right but not the left ventricle. Our findings have important implications for divers and understanding the mechanisms of pulmonary edema in other clinical settings.

Conditions of autonomic reciprocal interplay versus autonomic co-activation: effects on non-linear heart rate dynamics.

The present study was aimed at investigating the autonomic nervous system influences on the fractal organization of human heart rate during sympathovagal interactions, with special emphasize on the short-term fractal organization in heart rate variability (HRV), as assessed by the scaling exponent (alpha(1)) of the detrended fluctuation analysis. Linear and non-linear HRV analyses were used to study the sympathetic and vagal modulation of heart rate in ten healthy men (mean +/- SEM; age 26 +/- 1 years) during conditions of 1) increased sympathetic activity and vagal withdrawal (head-up tilt), 2) decreased sympathetic activity and increased vagal outflow (thermoneutral upright head-out water immersion, WIn), and 3) simultaneous activation of the two arms of the autonomic nervous activity (upright head-out immersion in cold water, WIc). Hemodynamic and linear HRV results were consistent with previous reports during similar physiological conditions. alpha(1) increased significantly during head-up tilt (from 0.71 +/- 0.13 supine to 0.90 +/- 0.15 upright) and WIn (0.86 +/- 0.10) and was significantly decreased during WIc (0.61 +/- 0.15). Thus, alpha(1) increased when the cardiac autonomic interplay was altered in a reciprocal fashion, whatever the direction of the balance change. Conversely, alpha(1) decreased during the concomitant activation of both vagal and sympathetic activities. The results of linear analysis were necessary to precisely define the direction of change in autonomic control revealed by an increase in alpha(1), while the direction of change in alpha(1) indicated whether an increased vagal activity is coupled with a decreased or increased sympathetic activation. Using both linear and non-linear analysis of HRV may increase the understanding of changes in cardiac autonomic status.

Cardiovascular changes induced by cold water immersion during hyperbaric hyperoxic exposure.

The present study was designed to assess the cardiac changes induced by cold water immersion compared with dry conditions during a prolonged hyperbaric and hyperoxic exposure (ambient pressure between 1.6 and 3 ATA and PiO(2) between 1.2 and 2.8 ATA). Ten healthy volunteers were studied during a 6 h compression in a hyperbaric chamber with immersion up to the neck in cold water while wearing wet suits. Results were compared with measurements obtained in dry conditions. Echocardiography and Doppler examinations were performed after 15 min and 5 h. Stroke volume, left atrial and left ventricular (LV) diameters remained unchanged during immersion, whereas they significantly fell during the dry session. As an index of LV contractility, percentage fractional shortening remained unchanged, in contrast to a decrease during dry experiment. Heart rate (HR) significantly decreased after 5 h, although it had not changed during the dry session. The changes in the total arterial compliance were similar during the immersed and dry sessions, with a significant decrease after 5 h. In immersed and dry conditions, cardiac output was unchanged after 15 min but decreased by almost 20% after 5 h. This decrease was related to a decrease in HR during immersion and to a decrease in stroke volume in dry conditions. The hydrostatic pressure exerted by water immersion on the systemic vessels could explain these differences. Indeed, the redistribution of blood volume towards the compliant thoracic bed may conceal a part of hypovolaemia that developed in the course of the session.

Evolution of liver antioxidant status and iron implication during the development of deoxycorticosterone-saline hypertension in rats.

Hypertension is known to be associated with an oxidative stress resulting from an imbalance of antioxidant defense mechanisms in various tissues. The purpose of this study was to investigate the relationship between the increase of arterial blood pressure, measured during the gradual development of experimental hypertension in deoxycorticosterone (DOCA)-salt-treated rats, and an early imbalance of liver antioxidant status. The levels of liver oxidant/antioxidant markers and iron were studied during the induction of hypertension in 3-, 6-, and 8-wk DOCA-salt-treated Sprague-Dawley rats. Hepatic antioxidant defenses were decreased as early as 3 wk of hypertensive treatment: the decrease of peroxidase-reductase-transferase and catalase activities was associated with a significant increase of thiobarbituric acid reactive substances (TBARS) levels. Liver oxidative stress increased until 6 wk and remained stable at 8 wk of DOCA-salt treatment. Concurrently, liver iron levels were increased at 6 wk and returned to normal values after 8 wk of hypertensive treatment. Iron seems to be an inductor of liver oxidative stress and responsible for the persistent oxidative stress, most likely through secondary free-radical release. Thus, our data (1) confirm that hypertension in DOCA-salt-treated rats might be a free-radical-dependent disease where hepatic oxidant/antioxidant imbalance is obviously involved from the beginning of blood pressure elevation and (2) suggest that the use of suitable iron chelators might reverse liver oxidative stress associated with the increase of blood pressure.

Monitoring Fatigue Status with HRV Measures in Elite Athletes: An Avenue Beyond RMSSD?

Among the tools proposed to assess the athlete's "fatigue," the analysis of heart rate variability (HRV) provides an indirect evaluation of the settings of autonomic control of heart activity. HRV analysis is performed through assessment of time-domain indices, the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals (RMSSD) measured during short (5 min) recordings in supine position upon awakening in the morning and particularly the logarithm of RMSSD (LnRMSSD) has been proposed as the most useful resting HRV indicator. However, if RMSSD can help the practitioner to identify a global "fatigue" level, it does not allow discriminating different types of fatigue. Recent results using spectral HRV analysis highlighted firstly that HRV profiles assessed in supine and standing positions are independent and complementary; and secondly that using these postural profiles allows the clustering of distinct sub-categories of "fatigue." Since, cardiovascular control settings are different in standing and lying posture, using the HRV figures of both postures to cluster fatigue state embeds information on the dynamics of control responses. Such, HRV spectral analysis appears more sensitive and enlightening than time-domain HRV indices. The wealthier information provided by this spectral analysis should improve the monitoring of the adaptive training-recovery process in athletes.