Early effects of acetazolamide on hemoglobin mass and plasma volume in chronic mountain sickness at 5100 m

INTRODUCTION AND OBJECTIVES

Chronic Mountain Sickness (CMS) syndrome, combining excessive erythrocytosis and clinical symptoms in highlanders, remains a public health concern in high-altitude areas, especially in the Andes, with limited therapeutic approaches. The objectives of this study were to assess in CMS-highlanders permanently living in La Rinconada (5100-5300 m, Peru, the highest city in the world), the early efficacy of acetazolamide (ACZ) and atorvastatin to reduce hematocrit (Hct), as well as the underlying mechanisms focusing on intravascular volumes.

MATERIALS AND METHODS

Forty-one males (46±8 years of age) permanently living in La Rinconada for 15 [10-20] years and suffering from CMS were randomized between ACZ (250 mg once-daily; N = 13), atorvastatin (20 mg once-daily; N = 14) or placebo (N = 14) uptake in a double-blinded parallel study. Hematocrit (primary endpoint) as well as arterial blood gasses, total hemoglobin mass (Hb_mass) and intravascular volumes were assessed at baseline and after a mean (±SD) treatment duration of 19±2 days.

RESULTS

ACZ increased PaO₂ by +13.4% (95% CI: 4.3 to 22.5%) and decreased Hct by -5.2% (95% CI: -8.3 to -2.2%), whereas Hct remained unchanged with placebo or atorvastatin. ACZ tended to decrease Hb_mass (-2.6%, 95% CI: -5.7 to 0.5%), decreased total red blood cell volume (RBCV, -5.3%, 95% CI: -10.3 to -0.3%) and increased plasma volume (PV, +17.6%, 95% CI: 4.9 to 30.3%). Atorvastatin had no effect on intravascular volumes, while Hb_mass and RBCV increased in the placebo group (+6.1%, 95% CI: 4.2 to 7.9% and +7.0%, 95%CI: 2.7 to 11.4%, respectively).

CONCLUSIONS

Short-term ACZ uptake was effective to reduce Hct in CMS-highlanders living at extreme altitude >5,000 m and was associated with both an increase in PV and a reduction in RBCV.

[Physiological and pathological responses to altitude]

Hypobaric hypoxia, the hallmark of a high altitude environment, has important physiological effects on both the cardiovascular and respiratory systems in order to maintain a balance between oxygen demand and supply. This dynamic of acclimatization is influenced both by the level of altitude and the speed of progression, but is also very individual with a wide spectrum of responses and sensitivities. This wide range of responses is associated with nonspecific symptoms characterising acute mountain sickness and high-altitude cerebral or pulmonary oedema. This article reviews the current knowledge about both the acclimatization processes and specific diseases of high-altitude.

[Cardiac dysfunction and the obstructive sleep apnoea syndrome]

INTRODUCTION

Cardiac insufficiency affects nearly 2% of the population with increased morbidity/mortality despite advances in therapeutic management. The sleep apnoea syndrome (SAS) is a risk factor for, and cause of aggravation of, myocardial dysfunction.

BACKGROUND

SAS is found in 70% of patients with chronic cardiac failure, 65% of patients with refractory hypertension, 60% of patients with cerebro-vascular accidents and 50% of patients with atrial fibrillation. The associated cardiovascular mortality is multiplied by a factor of 2 to 3. The pathophysiological mechanisms are intermittent nocturnal hypoxia, variations in CO₂ levels, variations in intrathoracic pressure and repeated arrousals from sleep, concurrent with sympathetic hyperactivity, endothelial dysfunction and systemic inflammation.

CONCLUSIONS

SAS and cardiological management in patients presenting with myocardial dysfunction should be combined. It is necessary to pursue the scientific investigations with the aim of determining a precise care pathway and the respective places of each of the cardiological and pulmonary measures.

[Place of the exercise stress test at the sportsman]

Is the stress test still part of the useful examinations in the detection of risk heart disease in sports subjects? Should we continue to use it as a surveillance examination in coronary sports patients? Meta-analysis, considering a ST subshift of more than 1mm as a criterion for positivity, underline the low prevalence of abnormal examinations and a significant rate of false-positives. But for the diagnosis of coronary artery disease, it is mainly the evolution of the ST segment to effort or recovery and the occurrence of stress arrhythmias that detect true positivity. When coronary risk is more important (presence of risk factors, resumption of sport, intense and prolonged efforts), it seems lawful to recommend such a review on a regular basis among men over 40 years of age with two risk factors but Also among veterans taking up sport after a period of prolonged inactivity. For the asymptomatic coronary athlete the stress test remains at the centre of the final decision for the resumption of a sport in competition irrespective of the method of revascularization. Of course the stress test, even inevitable, remains flawed in the detection of coronary artery disease in the asymptomatic athlete. However, it provides additional information on the condition of being maximal, and attaching importance to arrhythmias, the tensional profile and the maximum power developed in addition to the ST segment's only study.

Physiological responses to hypoxic constant-load and high-intensity interval exercise sessions in healthy subjects

PURPOSE

The aim of this study was to assess the acute cardiorespiratory as well as muscle and cerebral tissue oxygenation responses to submaximal constant-load (CL) and high-intensity interval (HII) cycling exercise performed in normoxia and in hypoxia at similar intensity, reproducing whole-body endurance exercise training sessions as performed in sedentary and clinical populations.

METHODS

Healthy subjects performed two CL (30 min, 75% of maximal heart rate, n = 12) and two HII (15 times 1-min high-intensity exercise-1-min passive recovery, n = 12) cycling exercise sessions in normoxia and in hypoxia [mean arterial oxygen saturation 76 ± 1% (clamped) during CL and 77 ± 5% (inspiratory oxygen fraction 0.135) during HII]. Cardiorespiratory and near-infrared spectroscopy parameters as well as the rate of perceived exertion were continuously recorded.

RESULTS

Power output was 21 ± 11% and 15% (according to protocol design) lower in hypoxia compared to normoxia during CL and HII exercise sessions, respectively. Heart rate did not differ between normoxic and hypoxic exercise sessions, while minute ventilation was higher in hypoxia during HII exercise only (+ 13 ± 29%, p < 0.05). Quadriceps tissue saturation index did not differ significantly between normoxia and hypoxia (CL 60 ± 8% versus 59 ± 5%; HII 59 ± 10% versus 56 ± 9%; p > 0.05), while prefrontal cortex deoxygenation was significantly greater in hypoxia during both CL (66 ± 4% versus 56 ± 6%) and HII (58 ± 5% versus 55 ± 5%; p < 0.05) sessions. The rate of perceived exertion did not differ between normoxic and hypoxic CL (2.4 ± 1.7 versus 2.9 ± 1.8) and HII (6.9 ± 1.4 versus 7.5 ± 0.8) sessions (p > 0.05).

CONCLUSION

This study indicates that at identical heart rate, reducing arterial oxygen saturation near 75% does not accentuate muscle deoxygenation during both CL and HII exercise sessions compared to normoxia. Hence, within these conditions, larger muscle hypoxic stress should not be expected.

Hypoxic conditioning and the central nervous system: A new therapeutic opportunity for brain and spinal cord injuries?

Central nervous system diseases are among the most disabling in the world. Neuroprotection and brain recovery from either acute or chronic neurodegeneration still represent a challenge in neurology and neurorehabilitation as pharmacology treatments are often insufficiently effective. Conditioning the central nervous system has been proposed as a potential non-pharmacological neuro-therapeutic. Conditioning refers to a procedure by which a potentially deleterious stimulus is applied near to but below the threshold of damage to the organism to increase resistance to the same or even different noxious stimuli given above the threshold of damage. Hypoxic conditioning has been investigated in several cellular and preclinical models and is now recognized as inducing endogenous mechanisms of neuroprotection. Ischemic, traumatic, or chronic neurodegenerative diseases can benefit from hypoxic conditioning strategies aiming at preventing the deleterious consequences or reducing the severity of the pathological condition (preconditioning) or aiming at inducing neuroplasticity and recovery (postconditioning) following central nervous system injury. Hypoxic conditioning can consist in single (sustained) or cyclical (intermittent, interspersed by short period of normoxia) hypoxia stimuli which duration range from few minutes to several hours and that can be repeated over several days or weeks. This mini-review addresses the existing evidence regarding the use of hypoxic conditioning as a potential innovating neuro-therapeutic modality to induce neuroprotection, neuroplasticity and brain recovery. This mini-review also emphasizes issues which remain to be clarified and future researches to be performed in the field. Impact statement Neuroprotection and brain recovery from either acute or chronic neurodegeneration still represent a challenge in neurology and neurorehabilitation. Hypoxic conditioning may represent a harmless and efficient non-pharmacological new therapeutic modality in the field of neuroprotection and neuroplasticity, as supported by many preclinical data. Animal studies provide clear evidence for neuroprotection and neuroplasticity induced by hypoxic conditioning in several models of neurological disorders. These studies show improved functional outcomes when hypoxic conditioning is applied and provides important information to translate this intervention to clinical practice. Some studies in humans provide encouraging data regarding the tolerance and therapeutic effects of hypoxic conditioning strategies. The main issues to address in future research include the definition of the appropriate hypoxic dose and pattern of exposure, the determination of relevant physiological biomarkers to assess the effects of the treatment and the evaluation of combined strategies involving hypoxic conditioning and other pharmacological or non-pharmacological treatments.

Muscle phosphorylase kinase deficiency: a neutral metabolic variant or a disease?

OBJECTIVE

To examine metabolism during exercise in 2 patients with muscle phosphorylase kinase (PHK) deficiency and to further define the phenotype of this rare glycogen storage disease (GSD).

METHODS

Patient 1 (39 years old) had mild exercise-induced forearm pain, and EMG showed a myopathic pattern. Patient 2 (69 years old) had raised levels of creatine kinase (CK) for more than 6 months after statin treatment. Both patients had increased glycogen levels in muscle and PHK activity <11% of normal. Two novel pathogenic nonsense mutations were found in the PHKA1 gene. The metabolic response to anaerobic forearm exercise and aerobic cycle exercise was studied in the patients and 5 healthy subjects.

RESULTS

Ischemic exercise showed a normal 5-fold increase in plasma lactate (peak 5.7 and 6.9 mmol/L) but an exaggerated 5-fold increase in ammonia (peak 197 and 171 μmol/L; control peak range 60-113 μmol/L). An incremental exercise test to exhaustion revealed a blunted lactate response (5.4 and 4.8 mmol/L) vs that for control subjects (9.6 mmol/L; range 7.1-14.3 mmol/L). Fat and carbohydrate oxidation rates at 70% of peak oxygen consumption were normal. None of the patients developed a second wind phenomenon or improved their work capacity with an IV glucose infusion.

CONCLUSION

Our findings demonstrate that muscle PHK deficiency may present as an almost asymptomatic condition, despite a mild impairment of muscle glycogenolysis, raised CK levels, and glycogen accumulation in muscle. The relative preservation of glycogenolysis is probably explained by an alternative activation of myophosphorylase by AMP and P(i) at high exercise intensities.

[Hepatopulmonary syndrome characteristics in hepatic cirrhosis associated with COPD]

AIM

To evaluate specific features of hepatopulmonary syndrome (HPS) in patients with cirrhosis and cirrhosis associated with chronic obstructive pulmonary disease (COPD).

MATERIAL AND METHODS

We made a retrospective analysis of case histories of 75 patients with hepatic cirrhosis (HC) of different etiology. The patients were divided into two groups: 23 patients with HC and COPD (group 1); 52 patients with HC without COPD (group 2). The patients were examined with spirography, gasometry. Single-breath carbon monoxide diffusion capacity (Dlco), TCO and TCO/VA were estimated. Transthoracic contrast-enhanced echocardiography was conducted for detection of intrapulmonary bypass in AaDO2 > 15 mm Hg.

RESULTS

COPD stage I and II were diagnosed in 14 of 23 and 9 of 23 patients of group 1, respectively. TCO and TCO/VA had a trend to lowering in group 1 (p > 0.05). PaO2 was lower (p < 0.05) while AaDO2 was higher (p < 0.05) in group 1. Four patients of group I had intrapulmonary bypasses: of the first degree (2 patients with hypoxemia) and of the first and second degree (2 patients with normoxemia). In group 2 three patients had intrapulmonary bypasses: of the fourth degree in 1 patient with hypoxemia and of the first and second degree in 2 patients with normoxemia.

CONCLUSION

HC patients with COPD had more severe hypoxemia. Mild and moderate HPS were registered in both groups. In COPD the risk of HPS is 3 times higher.

Does circulating BNP normalize after heart transplantation in patients with normal hemodynamic and right and left heart functions?

BACKGROUND

Increased brain natriuretic peptide (BNP) in cardiovascular disease is thought to be a compensatory protective mechanism allowing to delay the occurrence of terminal heart failure. Heart transplantation should normalize the neuroendocrine balance but BNP remains elevated in stable heart-transplant recipients (Htx). Such increase has been related to persistent endothelial and cardiac dysfunctions. The purpose of this study was to determine whether selected Htx, presenting with normal hemodynamic and cardiac systolic and diastolic functions on both side of the heart, show a normalization of their BNP plasma values.

METHODS

Of a cohort of well-being 26 Htx, we selected 12 patients with normal hemodynamics and left and right heart systolic and diastolic functions and compared their circulating BNP, cyclic guanosine monophosphate (cGMP) (the BNP second messenger) and endothelin-1 (ET) values with that of 12 age-, body mass index- and mean arterial pressure-matched controls. Cardiac function determination by echodoppler included cardiac filling pressures assessment using tissue Doppler imaging. Blood samples for biological and hormonal determinations were drawn at rest, within 15 min before echocardiography.

RESULTS

As selected, hemodynamic and left and right heart systolic and diastolic functions were located in the normal range in Htx. Plasma ET value was also similar in Htx and controls (20.7 +/- 0.9 vs. 19.6 +/- 0.9 fmol/mL). However, circulating BNP, like cGMP, was still significantly increased after heart transplantation, when compared with controls (33.8 +/- 8.5 vs. 4.0 +/- 0.9 pg/mL, p = 0.002 and 8.2 +/- 1.1 vs. 4.4 +/- 0.3 nmol/L, p = 0.003) for BNP and cGMP, respectively, in Htx and controls. Interestingly, the sole correlation observed was between BNP and cGMP (r = 0.85, p < 0.0001) after heart transplantation.

CONCLUSIONS

After heart transplantation, BNP remained increased despite the normalization of hemodynamic and cardiac systolic and diastolic functions. This suggests that such endocrine heart stimulation should not be viewed only as a hemodynamic marker in Htx. Further studies will be useful to investigate the role of pro-inflammatory cytokines and whether elevated BNP still possesses antifibrotic properties, further supporting the interest of enhancing its activity after heart transplantation.

Relationship Between Very High Physical Activity Energy Expenditure, Heart Rate Variability and Self-Estimate of Health Status in Middle-Aged Individuals

In middle-aged persons, moderate physical activity energy expenditure (PAEE) has been shown to be associated with increased vagal-related heart rate variability (HRV) indexes and better health status. The purpose of this study was to determine whether a very high PAEE has greater effect on vagal-related HRV indexes and self-estimates of well-being in middle-aged subjects having distinct long-term physical activity profiles. Forty-four subjects were divided into three groups on the basis of the sport score of the Modified Baecke Questionnaire for Older Adults: sedentary (SED, n = 15), moderately-trained (MT, n = 16), and highly-trained subjects (HT, n = 13). PAEE was estimated by triaxial accelerometry during one week. Time and frequency domain HRV indexes were determined during quiet periods in the morning on 5-min R-R interval segments under controlled breathing. Quality of life was evaluated using the SF-36 health survey questionnaire. PAEE was significantly different for each group (374.5 +/- 13.8, 616.8 +/- 22.4, and 1086.6 +/- 43.2 kcal . day (-1) for SED, MT, and HT, respectively, p < 0.001). MT presented significantly higher vagal-related HRV indexes than SED and HT (p < 0.05). None of the HRV indexes was significantly greater in HT than in SED. MT and HT had similar health status scores, which were significantly higher than for SED. These results indicate that in middle-aged subjects, habitual moderate PAEE is associated with greater vagal tone and self-estimates of well-being compared to low PAEE. In contrast, very high PAEE is associated with similar vagal-related indexes as low PAEE, despite better overall health status.

Chronic L-Arginine Supplementation Enhances Endurance Exercise Tolerance in Heart Failure Patients

The purpose of the study was to determine the potential beneficial effect of six weeks oral L-arginine supplementation (LAS) on endurance exercise, an important determinant of daily-life activity in patients with chronic stable heart failure (CHF). After an initial incremental maximal exercise test, CHF patients performed an identical thirty-minute interval endurance exercise test before and after six weeks with (L-arginine group; ARG) or without LAS (control group; CTL). Hemodynamic, respiratory, and metabolic parameters were determined at rest, during exercise, and during recovery. Mean heart rate decreased throughout exercise and recovery after LAS (- 8.2 +/- 1.4 b x min(-1); p = 0.003 and - 6.7 +/- 1.6 b x min(-1); p < 0.001, respectively), systemic blood pressure and respiratory parameters remaining unchanged. Resting L-argininaemia increased from 102 +/- 11 to 181 +/- 37 micromol x l(-1) (p < 0.004) and exercise-induced peak increase in plasma lactate was blunted after LAS (4.13 +/- 0.75 vs. 3.13 +/- 0.39 mmol x l(-1); p = 0.02). No significant change was observed in the control group. In heart failure patients, six weeks oral LAS enhances endurance exercise tolerance, reducing both heart rate and circulating lactates. This suggests that chronic LAS might be useful as a therapeutic adjuvant in order to improve the patient's physical fitness.

Acute myocardial ischaemia induces specific alterations of ventricular mitochondrial function in experimental pigs

AIMS

As cardiac metabolic flexibility is crucial, this study examined whether acute ischaemia can induce specific qualitative alterations of the mitochondrial metabolic pathways as well as energy transfer systems.

METHODS

Left descending coronary artery ligation was performed after sternotomy in eight pigs and the heart was excised after 45 min of ischaemia. Maximal O2 uptake (V(max), micromol O2 min(-1) g(-1) dry weight) of saponin-skinned myofibres were measured from ischaemic and non-ischaemic area of ventricular myocardium.

RESULTS

V(max) decreased by approximately 20% in ischaemic myocardium with both glutamate-malate (18.1 +/- 1.3 vs. 22.1 +/- 1.7 in control, P < 0.05) and pyruvate substrates (19.3 +/- 1.0 vs. 23.3 +/- 2.0 in control, P < 0.05) whereas no difference was observed with palmitoyl carnitine (15.6 +/- 1.8 vs. 16.6 +/- 0.9 in control). The K(m) of mitochondrial respiration for ADP decreased in ischaemic heart by 24% (679 +/- 79 vs. 899 +/- 84 microm of ADP in control, P < 0.05). Moreover, the mitochondrial creatine kinase efficacy (K(m) without creatine/K(m) with creatine), representative of the coupling of oxidative phosphorylation process with the mitochondrial creatine kinase, was reduced in ischaemic heart (11.6 +/- 2.5 in ischaemic vs. 18.0 +/- 2.2 in control, P < 0.05).

CONCLUSIONS

These findings argue for specific mitochondrial impairments at the level of pyruvate oxidation and creatine kinase channelling system after an acute period of in vivo ischaemia, whereas the lipid mitochondrial oxidation pathway seems to be preserved. Such a loss of metabolic flexibility following acute ischaemia could become an early feature of metabolic dysregulation of the heart.

Effect of Acute Hypoxia on Heart Rate Variability at Rest and During Exercise

The purpose of this study was to investigate sympathovagal balance as inferred from heart rate variability (HRV) responses to acute hypoxia at rest and during exercise. HRV was evaluated in 12 healthy subjects during a standardized hypoxic tolerance test which consists of four periods alternating rest and moderate exercise (50 % V.O (2)max) in normoxic and hypoxic conditions. Ventilatory responses were determined and HRV indexes were calculated for the last 5 min of each period. In well-tolerant subjects, hypoxia at rest induced a decrease of root-mean-square of successive normal R-R interval differences (RMSSD) (p < 0.05) and of absolute high frequency (HF) power (p < 0.001). All absolute HRV indexes were strongly reduced during exercise (p < 0.001) with no further changes under the additional stimulus of hypoxia. A significant increase (p < 0.05) in the HF/(LF+HF) ratio (where LF is low frequency power) was found during exercise in hypoxia compared to exercise in normoxia, associated with similar mean changes in ventilation and tidal volume. These results indicate a vagal control withdrawal under hypoxia at rest. During exercise at 50 % V.O (2)max, HRV indexes cannot adequately represent cardiac autonomic adaptation to acute hypoxia, or possibly to other additional stimuli, due to the dominant effect of exercise and the eventual influence of confounding factors.

Abnormal heart rate variability in a subject with second degree atrioventricular blocks during sleep

OBJECTIVE

We compare the profiles of heart rate variability (HRV) during sleep stages in 9 healthy controls and one subject with second degree atrioventricular blocks (AVB), investigating the role of sympathovagal balance in such pathology.

METHOD

Sleep and cardiac records were taken for one night in 9 male subjects from 21:00 to 07:00 h and for two nights in a male subject with AVB. Time and frequency domain indexes of HRV were calculated over 5 min-periods.

RESULTS

In one subject without any daytime heart disease, 253 and 318 AVB of type 2 (Mobitz 2) were observed during the two experimental nights, predominantly during rapid eye movement (REM) sleep and the surrounding sleep stage 2 in the second half of the night. In the 9 control subjects, absolute HRV indexes and low frequency (LF)/(LF+high frequency, HF) (where LF and HF are low frequency and high frequency power) were low during slow wave sleep, and significantly increased during REM sleep and the preceding sleep stage 2. In the subject with AVB, these HRV indexes were abnormally low during all sleep stages, with a predominant increase in parasympathetic activity as inferred from low LF/(LF+HF). During wake, however, LF/(LF+HF) normally increased, and the tachycardia observed with the arousal that terminates SWS was preserved in the subject with AVB.

CONCLUSION

These results suggest that in the subject with second degree atrioventricular blocks, sleep processes, particularly during REM sleep, create a specific neurological background that prevents an increase in sympathetic tone and triggers cardiac pauses.

Mechanisms of renal hyporesponsiveness to ANP in heart failure

The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure.

L-arginine reduces exercise-induced increase in plasma lactate and ammonia

To investigate the effect of L-arginine supplementation (L-ARG) on physiological and metabolic changes during exercise, we determined in a double-blind study the cardiorespiratory (heart rate, oxygen consumption (VO(2)) and carbon dioxide production (VCO(2)) and the metabolic (lactate and ammonia) responses to maximal exercise after either an intravenous L-ARG hydrochloride salt or placebo load in 8 healthy subjects. Exercise-induced increases in heart rate, VO(2) and VCO(2) were not significantly different after L-ARG or placebo. By contrast, peak plasma ammonia and lactate were significantly decreased after L-ARG load (60.6 +/- 8.2 vs. 73.1 +/- 9.1 micro mol x l(-1), p < 0.01 and 7.1 +/- 0.7 vs. 8.2 +/- 1.1 mmol x l(-1), p < 0.01, for ammonia and lactate, respectively). Plasma L-citrulline increased significantly during exercise only after L-ARG load, despite a concomitant decrease in plasma L-ARG. Furthermore, a significant inverse relationship was observed between changes in lactate and L-citrulline concentrations after L-ARG load (r = -0.84, p = 0.009). These results demonstrate that intravenous L-ARG reduces significantly exercise-induced increase in plasma lactate and ammonia. Taken together, the specific L-citrulline increase and the inverse relationship observed between L-citrulline and plasma lactate after L-ARG might support that L-ARG supplementation enhances the L-arginine-nitric oxide (NO) pathway during exercise.

Non-invasive cardiac output evaluation during a maximal progressive exercise test, using a new impedance cardiograph device

One of the greatest challenges in exercise physiology is to develop a valid, reliable, non-invasive and affordable measurement of cardiac output (CO). The purpose of this study was to evaluate the reproducibility and accuracy of a new impedance cardiograph device, the Physio Flow, during a 1-min step incremental exercise test from rest to maximal peak effort. A group of 12 subjects was evaluated to determine the reproducibility of the method as follows: (1) each subject performed two comparable tests while their CO was measured by impedance cardiography using the new device (COImp1, COImp2), and (2) in a subgroup of 7 subjects CO was also determined by the direct Fick method (COFick) during the second test. The mean difference between the values obtained by impedance (i.e. COImp1-COImp2) was -0.009 l.min-1 (95% confidence interval: -4.2 l.min-1, 4.2 l.min-1), and CO ranged from 3.55 l.min-1 to 26.75 l.min-1 (n = 146). When expressed as a percentage, the difference (COImp1-COImp2) did not vary with increasing CO. The correlation coefficient between the values of COImp and COFick obtained during the second exercise test was r = 0.94 (P < 0.01, n = 50). The mean difference expressed as percentage was -2.78% (95% confidence interval: -27.44%, 21.78%). We conclude that COImp provides a clinically acceptable evaluation of CO in healthy subjects during an incremental exercise.