Biomedical subjects

H Reutenauer

Publications and source records attributed to H Reutenauer.

15 recordsLinked to original sources

PubMed2002

Regional response of cerebral blood volume to graded hypoxic hypoxia in rat brain.

BACKGROUND: The response of cerebral blood flow to hypoxic hypoxia is usually effected by dilation of cerebral arterioles. However, the resulting changes in cerebral blood volume (CBV) have received little attention. We have determined, using susceptibility contrast magnetic resonance imaging (MRI), changes in regional CBV induced by graded hypoxic hypoxia. METHODS: Six anaesthetized rats were subjected to incremental reduction in the fraction of inspired oxygen: 0.35, 0.25, 0.15, and 0.12. At each episode, CBV was determined in five regions of each hemisphere after injection of a contrast agent: superficial and deep neocortex, striatum, corpus callosum and cerebellum. A control group (n = 6 rats) was studied with the same protocol without contrast agent, to determine blood oxygenation level dependent (BOLD) contribution to the MRI changes. RESULTS: Each brain region exhibited a significant graded increase in CBV during the two hypoxic episodes: 10-27% of control values at 70% SaO2, and 26-38% at 55% SaO2. There was no difference between regions in their response to hypoxia. The mean CBV of all regions increased from 3.6 (SD 0.6) to 4.1 (0.6) ml (100 g)-1 and to 4.7 (0.7) ml (100 g)-1 during the two hypoxic episodes, respectively (Scheffé F-test; P < 0.01). Over this range, CBV was inversely proportional to SaO2 (r2 = 0.80). In the absence of the contrast agent, changes due to the BOLD effect were negligible. CONCLUSIONS: These findings imply that hypoxic hypoxia significantly raises CBV in different brain areas, in proportion to the severity of the insult. These results support the notion that the vasodilatory effect of hypoxia is deleterious in patients with reduced intracranial compliance.

Animals↗

PubMed1997

[Skeletal muscle abnormalities in chronic obstructive lung disease with respiratory insufficiency. Value of P31 magnetic resonance spectroscopy].

31P magnetic resonance spectroscopy (31P MRS) is a non-invasive method to evaluate high energy compounds [adenosine triphosphate (ATP), phosphocreatin (PCr), inorganic phosphates (Pi)] and intracellular pH (pHi) of skeletal muscle during exercise and recovery. It is a clinically applicable method of investigation for severe COPD patients with respiratory failure since exercise is limited to a single group of muscle (calf). Pronounced alterations of muscular metabolism have been shown in these patients: (1) reduced aerobic capacity (as reflected by the ratio of Pi/PCr as a function of power and changes in recovery kinetics of PCr after exercise and (2) increased anaerobic metabolism (reflected by a decrease in intracellular pH). Four different studies reveal similar abnormalities. Acute oxygen administration partially improves these parameters, suggesting that other factors in addition to hypoxaemia may contribute to the metabolic impairment. The effect of increased physical activity on these abnormalities deserve further investigations.

Adenosine Triphosphate↗

PubMed1994

Standardisation of 31phosphorus-nuclear magnetic resonance spectroscopy determinations of high energy phosphates in humans.

A procedure is described for standardising the determination of adenosine 5'-triphosphate and phosphocreatine concentration ([ATP] and [PC], respectively, in absolute arbitrary units) in human muscle by nuclear magnetic resonance (NMR) spectroscopy. The individual 31phosphorus (31P)-NMR spectra obtained on equal hemispherical tissue volumes (muscle plus skin and fat) were corrected for the thickness of the skin and of the subcutaneous fat. The volumes investigated were standardised using an external reference. The procedure described made possible the comparison of high energy phosphate concentrations among different subjects. It was applied to the assessment of [ATP] and [PC] in four groups of sedentary subjects (children, and adults aged 20-35, 35-50 and over 50 years), and in a group of athletes (volleyball players). The [ATP] and [PC] were not statistically different in the groups investigated.

Adenosine Triphosphate↗

PubMed1994

Determinants of peak muscle power: effects of age and physical conditioning.

The relationships between absolute peak muscle power (Wpeak), muscle cross sectional area (CSAtot, i.e. the sum of both thigh and calf CSA) and muscle high energy phosphate concentration (adenosine 5'-triphosphate [ATP] and phosphocreatine concentrations [PC]) were studied in 47 subjects classified into five groups: A, 10 sedentary (S) subjects aged 20-35 years; B, 9 S aged 35-50 years; C, 9 S aged more than 50 years; D, 13 children aged 8-13 years; and E, 6 athletes (top level volleyball players) aged 24 (SD 3) years. The Wpeak was measured during a maximal vertical high jump off both feet on a force platform. The CSAtot was measured anthropometrically. The [ATP] and [PC] were determined by 31Phosphorus nuclear magnetic resonance spectroscopy. The Wpeak decreased with age, was 65% lower in D than in A, and 43% higher in E than in A. The CSAtot did not vary with age, was 45% smaller in D than in A, and 15% greater in E than in A. The [ATP] and [PC] were essentially the same in all groups. The changes observed in Wpeak were only partially accounted for by changes in CSAtot. Therefore, in addition to the variables investigated, other factors appear to have been involved in the determination of Wpeak with increasing age and training. An important role may be played by hormonal, particularly at puberty, and neural factors.

Adenosine Triphosphate↗

PubMed1993

Muscular metabolism during oxygen supplementation in patients with chronic hypoxemia.

The effects of supplemental oxygen (O2) versus air on working calf muscle metabolism were studied in seven patients with stable chronic obstructive pulmonary disease (COPD) and chronic hypoxemia (PaO2 = 57 +/- 3 SE mm Hg) and seven age-matched control subjects. Oxygen and air were randomly administrated at 24-h intervals, and O2 flow rate was adjusted to correct hypoxemia (PaO2 = 87 +/- 4 mm Hg) in the COPD group. The relative concentrations of ATP, phosphocreatine (PCr), inorganic phosphate (Pi), phosphomonoesters (PME), and the intracellular pH (pHi) were determined with 31P magnetic resonance spectroscopy at rest, during a graded standardized and localized exercise protocol (360 active plantar flexions), and during recovery. In resting muscle no significant effect of added O2 was demonstrable in each group with regard to pHi, Pi/PCr, and ATP/(PCr+Pi+PME) ratios. Mechanical data were similar between the two groups and between the two tests during the whole exercise. The indices of muscular oxidative metabolism (Pi/PCr and pHi at the end of exercise and recovering PCr resynthesis rate) were impaired in the COPD group compared with that in the control group during air (all p < 0.05). All these parameters were significantly improved with added O2 in the COPD group (p < 0.05), whereas no similar effects were observed in the control group. However, these beneficial effects were incomplete since the exercising Pi/PCr ratio remained higher in the COPD group than in the control group during added O2. This energetic muscular impairment could correspond to tissular damage related to chronic hypoxemia.

Aged↗

PubMed1993

Discrimination between cross-country and downhill skiers by pulmonary and local 31PNMR evaluations.

The purpose of the present study was to correlate data on calf muscle metabolism using 31P nuclear magnetic resonance spectroscopy with measurements of whole body maximal oxygen consumption and maximal power output, and to determine whether the combination of these data could be used to predict athletic ability. Experiments were performed in a 2.35 Tesla, 35 cm diameter electromagnet on the leg muscle of sedentary human subjects (N = 6) and groups of athletes trained for endurance (cross-country skiers, N = 7) or strength performance (downhill skiers, N = 5). The exercise protocol consisted of successive plantar flexions performed at graded fractions of the maximal voluntary contraction (MVC). The results obtained from NMR investigation (changes in content of inorganic phosphate: Pi, phosphocreatine: PC and muscle ATP, and intracellular pH) were then compared with those of maximal O2 consumption (VO2max) and maximal power (MP). When the data on athletes were compared with those obtained on sedentary subjects, the curves illustrating the relationship between the imposed load and the Pi/PC ratio were significantly shifted toward high output power for a given Pi/PC value. It also appeared from this study that specific training in force development (downhill skiing) induced a slighter decrease in PC level than for endurance (cross-country skiers) despite improvement in physical performance. A slight but significant intracellular acidification was observed in the muscles of sedentary subjects and downhill skiers for contraction at, respectively, 50% and 80% of MVC, but not in the skeletal muscles of cross-country skiers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1992

Muscle bioenergetics in skiers: studies using NMR spectroscopy.

Sedentary human subjects (n = 6) and two homogeneous groups of athletes, trained for down-hill skiing (n = 5) and cross-country skiing (n = 7), were subjected to cardiorespiratory testing and to evaluation of the bioenergetics of calf muscles by means of Phosphorus Nuclear Magnetic Resonance Spectroscopy. The exercise consisted of successive plantar flexions performed at graded fractions of the maximal voluntary contraction force. It appears from this study that the decrease in phosphocreatine level induced by exercise at 80% of maximal voluntary contraction, was smaller in the muscles of athletes who trained for cross-country skiing, than in the muscles of down-hill skiers and control subjects. Intracellular acidosis was virtually absent in cross-country athletes. The rate of restitution of phosphocreatine, after the exercise, was higher in both groups of skiers, compared to sedentary subjects. The maximal oxygen consumption and the maximal alactic power were higher in athletes than in sedentary subjects. NMR data and mechanical measurements are used in consideration with functional systemic indexes to characterize the capabilities of skiers.

Adult↗

PubMed1992

Metabolism and aerobic capacity of skeletal muscle in chronic respiratory failure related to chronic obstructive pulmonary disease.

The calf muscle energy metabolism of 8 stable chronic obstructive pulmonary disease (COPD) patients with chronic respiratory failure (arterial oxygen tension (Pao2) 7.7 +/- 0.4 kPa or 58 +/- 3 mmHg) was studied, using 31-phosphorus magnetic resonance spectroscopy (31P MRS). MRS spectra were acquired at rest and during the course of 360 pedal movements at 20, 35 and 50% of the maximal voluntary contraction (MVC) and during recovery. Eight healthy age-matched subjects served as the control group. No significant differences between groups were observed in resting muscle, as regards intracellular pH, Pi/PCr ratio (Pi: inorganic phosphate; PCr: phosphocreatine) and the relative ATP expressed as the ratio beta ATP/PCr + Pi + PME (PME: phosphomonoester). Although effective power outputs were similar for both groups at each work level, COPD patients exhibited a higher Pi/PCr ratio than health controls (3.34 +/- 0.89 vs 0.49 +/- 0.05 at 50% MVC; p less than 0.01) and a lower pHi (6.65 +/- 0.11 vs 7.06 +/- 0.02 at 50% MVC; p less than 0.01). PCr resynthesis during recovery was slower in patients than in control subjects (t1/2 PCr 1.27 +/- 0.26 min vs 0.47 +/- 0.05 min; p less than 0.05). These results suggest impairment of aerobic capacity in a non-ventilatory working muscle, which may be due to hypoxaemia in patients with chronic respiratory failure.

Aged↗

PubMed1992

Exertional heatstroke and muscle metabolism: an in vivo 31P-MRS study.

An impairment of muscle energy metabolism has been suggested as a predisposing factor for, as well as a consequence of exertional heatstroke (EHS). Thirteen young men were investigated 6 months after a well-documented EHS using 31Phosphorus Magnetic Resonance Spectroscopy (31P-MRS). The relative concentrations of ATP, phosphocreatine (PCr), inorganic phosphate (Pi), phosphomonoesters (PME), and the intracellular pH (pHi) were determined at rest, during a graded standardized exercise protocol (360 active plantar flexions) and during recovery. Also the leg tissue blood flow was determined by venous occlusion plethysmography during the MRS procedure. Sixteen age-matched healthy male volunteers served as control group. In resting muscle, there were no significant differences between the groups as regards pHi, Pi/PCr, and ATP/PCr+Pi+PME ratios. During steady state exercise conditions, effective power outputs were similar for both groups at each level of exercise: 20, 35, and 50% of maximal voluntary contraction (MVC) of the calf muscle. No significant differences were shown between the two groups in Pi/PCr, pHi, or changes of leg blood flow at each level of exercise. At 50% MVC, Pi/PCr was 0.48 +/- 0.08 vs 0.47 +/- 0.05 (P = 0.96), pHi was 6.94 +/- 0.03 vs 6.99 +/- 0.02, respectively (P = 0.13). Finally, the rate of PCr resynthesis during recovery was not significantly different between the two groups: t1/2 PCr = 0.58 +/- 0.07 vs 0.50 +/- 0.05 min, respectively (P = 0.35). Therefore, no evidence of an impairment of muscle energy metabolism was shown in the EHS group during a standardized submaximal exercise using 31P-MRS performed 6 months after an EHS.

Adenosine Triphosphate↗

PubMed1991

Impairment of muscular metabolism in chronic respiratory failure. A human 31P MRS study.

The calf muscle metabolism of 7 patients with stable chronic respiratory failure (PaO2 below 65 Torr) was studied using 31P NMR spectroscopy. NMR spectra were acquired at rest, during the course of 360 pedal movements at 20, 35 and 50% of the maximal voluntary contraction (MVC) and during recovery. Eight normal aged-matched subjects served as a control group. In resting muscle, no significant differences were observed between both groups as regards intracellular pH, inorganic phosphate/phosphocreatine (Pi/PCr) and beta-ATP/PCr + Pi + phosphomonoester (PME) ratios. Although effective power outputs were similar for both groups at each work level, patients exhibited a higher Pi/PCr ratio than healthy controls (3.19 +/- 1.01 vs 0.49 +/- 0.05 at 50% MVC; p less than 0.01) and a lower pHi (6.65 +/- 0.11 vs 7.06 +/- 0.02 at 50% MVC; p less than 0.01). Moreover, PCr resynthesis during recovery was slower in patients than in control subjects (t1/2 PCr = 1.26 +/- 0.30 vs 0.47 +/- 0.05 min; p = 0.01). These results suggest impairment of aerobic capacity in a non-ventilatory working muscle, probably due to hypoxemia in patients with chronic respiratory failure.

Adenosine Triphosphate↗

PubMed1991

Phosphorylated compounds and function in isolated hearts: a 31P-NMR study.

The potential role of phosphorylated compounds in the control of myocardial cell respiration was investigated by means of 31P-nuclear magnetic resonance (NMR) spectroscopy. Isolated isovolumic rat hearts, perfused with a 9 mM glucose, 2 mM pyruvate medium at a constant beating rate (6 Hz) and temperature (37 degrees C), were subjected to changes in work load by varying the calcium concentration ([Ca2+]) in the perfusion fluid from 0.5 to 1.0, 1.5, or 2.0 mM. Each change in left ventricular developed pressure (LVDP) induced by the [Ca2+] change was accompanied by alterations in the inorganic phosphate-to-creatine phosphate ratio ([Pi]/[PCr]), with the ATP level remaining constant. The relationship between [Pi]/[PCr] and LVDP followed a Michaelis-Menten pattern with an apparent Michaelis constant (Km) of 0.09 and a maximal LVDP of 91 mmHg. This Km corresponded to intracellular concentrations of 1.2 mM for Pi and 13.0 mM for PCr. The calculated [ADP] and phosphorylation potential corresponding to these values were 44 microM and 151,000 M-1, respectively. All these values are close to those estimated under in situ physiological conditions. These results support the assumption that in the rat heart, as in skeletal muscle, mitochondrial activity could be controlled by changes in phosphorylated compound concentrations under normoxic conditions.

Adenosine Triphosphate↗

PubMed1987

[MRI of the cervical spine. Creation of a surface coil. Technical and clinical results].

Cervical myelopathy represents a good indication for study by Magnetic Resonance Imaging (MRI). The MRI examination may be performed without hospitalisation and without any pain or risk for the patient. It often gives sufficient information to decide whether to proceed with surgical intervention, after imaging on standard plain films and ever before cervical myelography. An efficient study of the cervical spinal cord requires special surface coils adapted to this region. We have developed a surface coil, working as a receiver, inductively coupled, tuned and matched all at once, and easy to use. The concave form of this coil has been studied so as to be comfortable for all patients. It can be directly connected to our Thomson CGR machines (Magniscan 5000). In continuous routine use for 6 months, without any problems, it has been found to be very reliable. We present here some results on different types of myelopathy and discuss methodological aspects concerning the choice of acquisition parameters in the examinations. The simplicity of its realisation and the low cost leads us to believe that it will be possible to construct other surface coils convenient on many other parts of the body.

Cervical Vertebrae↗

PubMed1987

Disruption of muscle energy metabolism due to intense ischaemic exercise: a 31P NMR study in rats.

This study uses 31P NMR as a tool for the study of the capacity of recovery of the rat skeletal muscle after an exercise performed during an acute state of ischaemia. The leg muscle of a rat submitted to a 20 minute exercise period one hour after irreversible femoral artery ligation, manifested a dramatic (75%) decrease in phosphocreatine (PC) content, a less pronounced (30%) decrease in ATP, an accumulation of inorganic phosphate (Pi) and an increase in the phosphomonoester (PME) resonances, in addition to acidosis to pH 6.4. An investigation over a 40 minute post-exercise period using 31P NMR and biochemical analysis led to the following observations: 1. The PC and Pi contents of the muscle experienced no further significant changes, remaining at the level reached by the end of the exercise. 2. The ATP content similarly remained at the level reached at the end of this period, the adenylate charge being 0.91 (controls 0.93). 3. The IMP accumulated during ischaemic exercise remained at its high level. It seems likely that this compound contributes in a large part to the resonances in the PME region of the spectra. 4. Intracellular acidosis persisted despite a decrease in lactate content. The most important finding from this study is that the situation created by ischaemic exercise--as revealed by the NMR spectra--is characterized by a blocking of the main biochemical processes (phosphorylations, purine nucleotide cycle, pH regulation). Such a condition, which does not seem to entail lethal cell injury, could thus be used as a basis for the study via 31P NMR of the therapeutic effect of various treatments.

Adenine Nucleotides↗

PubMed1987

[Phosphorus-31 NMR spectrometry of the calf muscles in patients with arterial claudication. Preliminary results].

Phosphorus NMR spectrometry allows non-invasive exploration in vivo of certain aspects of muscle energy metabolism. A study was conducted in 10 healthy volunteers and 12 patients with lower limb affections (stage II claudication) to define a precise methodology and to discuss perspectives offered by this new method, in the light of preliminary findings. Changes with time of amplitude of peaks of phosphocreatine (Pcr), inorganic phosphorus (Pi) and ATP, and of intracellular pH, showed that recovery of 80% of resting value of the ratio Pcr/Pi + Pcr after quantified exercise is a very discriminatory parameter correlated with severity of arteriographic findings in patients with claudication.

Energy Metabolism↗

PubMed1987

[Effects of acute arterial occlusion on muscle energy metabolism. An experimental model using phosphorus NMR spectroscopy in the rat].

Phosphorus-31 MR spectroscopy allows non-invasive evaluation of the energy state of a tissue and was used to study effects of acute ischemia in rat skeletal muscle. Male Wistar rats were anesthetized with pentobarbital (50 mg.kg-1) and the femoral artery ligated on leaving the abdominal cavity. Animals were then set inside a superconducting magnet (Bruker 2.35 T) and a circular coil (15 mm diameter) placed on leg facing gastrocnemius muscle. Pulse lengths were chosen in such a may that the sensitive zone would include mainly gastrocnemius muscle. Signals were accumulated over 2 or 18 minutes. One hour after insertion of ligature muscular exercise was provoked over 20 minutes by electrical stimulation of sciatic nerve (4 Hz, 2 to 5 V). Muscles were removed at different stages of the test for biochemical assays. Figure 1 includes spectra at 2 and 18 minutes showing the effects of ischemic when compared with normoxic muscle exercise. Figure 2, showing phosphocreatine (PC) and ATP levels, illustrates the accentuation under the effect of ischemia of degradation in PC during muscular exercise and its subsequent slow reconstitution. Table I lists more precise MR data obtained during 18 minutes and compares them with biochemical findings. Ischemic exercise appears also to induce significant degradation of ATP, accumulation of inorganic phosphate (Pi) and phosphomonoesters (PME) as well as persistent intracellular acidosis (pH 6.5 as against 7.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗