Biomedical subjects

A Capderou

Publications and source records attributed to A Capderou.

30 records · Page 2Linked to original sources

PubMed1998

Changes in lower limb volume in humans during parabolic flight.

Variations in gravity [head-to-foot acceleration (Gz)] induce hemodynamic alterations as a consequence of changes in hydrostatic pressure gradients. To estimate the contribution of the lower limbs to blood pooling or shifting during the different gravity phases of a parabolic flight, we measured instantaneous thigh and calf girths by using strain-gauge plethysmography in five healthy volunteers. From these circumferential measurements, segmental leg volumes were calculated at 1, 1.7, and 0 Gz. During hypergravity, leg segment volumes increased by 0.9% for the thigh (P < 0.001) and 0.5% for the calf (P < 0.001) relative to 1-Gz conditions. After sudden exposure to microgravity following hypergravity, leg segment volumes were reduced by 3.5% for the thigh (P < 0.001) and 2.5% for the calf (P < 0.001) relative to 1.7-Gz conditions. Changes were more pronounced at the upper part of the leg. Extrapolation to the whole lower limb yielded an estimated 60-ml increase in leg volume at the end of the hypergravity phase and a subsequent 225-ml decrease during microgravity. Although quantitatively less than previous estimations, these blood shifts may participate in the hemodynamic alterations observed during hypergravity and weightlessness.

Adult↗

PubMed1997

Non-invasive assessment of technetium-99m albumin transit time distribution in the pulmonary circulation by first-pass angiocardiography.

This study describes a non-invasive method for assessment of the lung transit time distribution of a tracer, using first-pass technetium-99m albumin angiocardiography and a model-free method of deconvolution. Ten patients received a first injection of 1 MBq kg-1 in the external jugular vein to position a gamma camera in the left anterior oblique position and two additional injections (5 MBq kg-1) to record first-pass angiocardiographic data. Right and left ventricular time-activity curves were derived from regions of interest every 0.5 s over a 1-min period. The left ventricular curve was deconvoluted by the right ventricular curve to obtain the lung transport function. The deconvolution procedure was based on a modified version of the Kalman filtering technique. The procedure was repeated at an interval of 30 min in eight patients. Two patients were re-examined up to 2 years later. Skewness, kurtosis and relative dispersion of the distributions did not change over time. We also found that the distribution, once normalized by its first moment, was independent of isolated changes in heart rate or cardiac output. Comparison of curve shapes at an interval of 30 min by point by point analysis demonstrated the reproducibility of the technique. We conclude that computation of the pulmonary transit time distribution of 99mTc-albumin from a standard angiocardiography procedure by model-free deconvolution is reliable and reproducible over time. We suggest that it may be a valuable tool for the non-invasive follow-up of the pulmonary circulation.

Adult↗

PubMed1997

Comparison of indirect calorimetry and thermodilution cardiac output measurement in children.

We validated experimentally the ability of hood indirect calorimetry to measure accurately VO2. For this purpose we compared cardiac output calculated from the Fick equation Q = VO2/(Ca(O2) - CV(O2)), in which VO2 was obtained by hood indirect calorimetry, to thermodilution cardiac output (Qth) measured simultaneously during cardiac catheterization in children (n = 16). Because FI(CO2) is a critical factor in hood indirect calorimetry calculations, we also assessed the consequence of taking into account measured FI(CO2) rather than using the usual standard value of 0.0004. We found a good agreement between Q and Qth whether we used experimentally measured FI(CO2) in ambient air (Qth = 0.89 Q + 0.39, r = 0.941) or standard FI(CO2) (Qth = 0.84 Q + 0.55, r = 0.930). However, VCO2 and R computed from standard FI(CO2) differed significantly (p < 0.001) from values derived from measured FI(CO2). This demonstrates that indirect calorimetry allows reasonable estimates of Q, VO2, VCO2, and R provided that the actual values of FI(CO2) are used.

Adolescent↗

PubMed1996

Determination of pulmonary mean transit time and cardiac output using a one-dimensional model.

In this work, we show that a one-dimensional model of the blood flow across the lungs can reproduce the evolution of a bolus versus the time. Solving the differential equation governing the bolus concentration in the framework of this model, we determine the solution which fulfills Gaussian initial boundary conditions. An effective parameter related to the ratio of a diffusion coefficient to the square of the mean speed of the flow is defined. The determination of its numerical values following a semi-empirical approach enables us to know accurately the mean transit time and the cardiac output. The results have been compared to other methods, and were found in good agreement. Such an approach could be of interest in all studies where the knowledge of flow--including micro-circulation--is needed.

Analysis of Variance↗

PubMed1988

Muscular venous blood metabolites during rhythmic forearm exercise while breathing air or normoxic helium and argon gas mixtures.

The effects of breathing normoxic helium or argon gas mixture on the local muscular metabolism during exercise were compared to those of room air in four healthy subjects. For this purpose, PO2, PCO2, pH, the concentrations of lactate (LA), glucose (Gl) haemoglobin (Hb) and K+ and osmolarity were repeatedly measured in efferent muscular venous blood during 12 min of rhythmic forearm exercise and 16 min of recovery. The time courses and magnitude of the changes in PCO2, pH, [Gl], [Hb], [K+] and osmolarity during exercise and recovery were similar for breathing both the helium and argon gas mixtures. The main finding was that during exercise, the [LA] curve reached a peak value significantly higher by 25% under normoxic helium than under room air or normoxic argon breathing. This rise in [LA] was accompanied by a slight reduction in muscular venous PO2, too small to signify muscular hypoxia. The possibility that this decline in PO2 might be due to a shift in muscular metabolism towards lipid oxidation was confirmed by the lower muscular respiratory quotient observed during helium breathing. However, such a shift did not explain why [LA] rose during this breathing. The probable explanation is that helium facilitates LA diffusion out of the myocytes.

Adult↗

PubMed1987

Automated processing of first-pass radionuclide angiocardiography by factor analysis of dynamic structures.

A method for automatic processing of cardiac first-pass radionuclide study is presented. This technique, factor analysis of dynamic structures (FADS) provides an automatic separation of anatomical structures according to their different temporal behaviour, even if they are superimposed. FADS has been applied to 76 studies. A description of factor patterns obtained in various pathological categories is presented. FADS provides easy diagnosis of shunts and tricuspid insufficiency. Quantitative information derived from the factors (cardiac output and mean transit time) were compared to those obtained by the region of interest method. Using FADS, a higher correlation with cardiac catheterization was found for cardiac output calculation. Thus compared to the ROI method, FADS presents obvious advantages: a good separation of overlapping cardiac chambers is obtained; this operator independant method provides more objective and reproducible results. A number of parameters of the cardio-pulmonary function can be assessed by first-pass radionuclide angiocardiography (RNA) [1,2]. Usually, they are calculated using time-activity curves (TAC) from regions of interest (ROI) drawn on the cardiac chambers and the lungs. This method has two main drawbacks: (1) the lack of inter and intra-observers reproducibility; (2) the problem of crosstalk which affects the evaluation of the cardio-pulmonary performance. The crosstalk on planar imaging is due to anatomical superimposition of the cardiac chambers and lungs. The activity measured in any ROI is the sum of the activity in several organs and 'decontamination' of the TAC cannot easily be performed using the ROI method [3]. Factor analysis of dynamic structures (FADS) [4,5] can solve the two problems mentioned above. It provides an automatic separation of anatomical structures according to their different temporal behaviour, even if they are superimposed. The resulting factors are estimates of the time evolution of the activity in each structure (underlying physiological components), and the associated factor images are estimates of the spatial distribution of each factor. The aim of this study was to assess the reliability of FADS in first pass RNA and compare the results to those obtained by the ROI method which is generally considered as the routine procedure.

Angiocardiography↗

PubMed1986

Time course of muscular blood metabolites during forearm rhythmic exercise in hypoxia.

O2 concentration, PO2, PCO2, pH, osmolarity, lactate (LA), and hemoglobin (Hb) concentrations in deep forearm venous blood were repeatedly measured during submaximal exercise of forearm muscles. Concentrations of arterial blood gases were determined at rest and during exercise. Experiments were conducted under normoxia and hypobaric hypoxia (PB = 465 Torr). In arterial blood, data obtained during exercise were the same as those obtained during rest under either normoxia or hypoxia. In venous muscular blood, PO2 and O2 concentration were lower at rest and during exercise in hypoxia. The muscular arteriovenous O2 difference during exercise in hypoxia was increased by no more than 10% compared with normoxia, which implied that muscular blood flow during exercise also increased by the same percentage, if we assume that exercise O2 consumption was not affected by hypoxia. Despite increased [LA], the magnitude of changes in PCO2 and pH in hypoxia were smaller than in normoxia during exercise and recovery; this finding is probably due to the increased blood buffer value induced by the greater amount of reduced Hb in hypoxia. Hence all the changes occurring in hypoxia showed that local metabolism was less affected than we expected from the decrease in arterial PO2. The rise in [Hb] that occurred during exercise was lower in hypoxia. Possible underlying mechanisms of the [Hb] rise during exercise are discussed.

Adult↗

PubMed1984

Changes in rectal and mean skin temperature in response to suggested heat during hypnosis in man.

Rectal temperature, mean skin temperature and heart rate were recorded in 7 subjects during hypnosis, induced either alone or while sensations of heat were suggested. During hypnosis alone, a fall in the heart rate of about 10 beat X min-1 was the only autonomic response observed; body temperatures were unaltered. In contrast, during hypnosis with suggestion of heat, the following changes occurred: (1) Mean rectal temperature decreased 0.20 degrees C (p less than 0.05) within 50 min. Its mean time course differed significantly from that for hypnosis alone (p less than 0.001). (2) Comparison of individual rectal temperature time sequences showed that in fact this temperature only declined in 4 subjects out of 7, and tended to form a plateau located 0.35 degrees C below the value of the preceding waking state. Despite reinforcement of heat suggestion, the plateau continued until the end of the hypnotic trance. (3) Mean skin temperature tended to rise. (4) When hypnosis with suggestion ceased, both rectal and skin temperatures very slowly returned to their levels during the preceding waking state.

Adult↗

PubMed1983

Intersubject viability in growth hormone time course during different types of work.

This study addresses the question of variability of immunoreactive human growth hormone (IRHGH) response to the following types of muscular exercise. 1) One hour of submaximal exercise with restarting for 30 min after 20 min of recovery. Three types of responses were observed: a rise of [IRHGH] occurred in response to muscular activity; [IRHGH] was maintained at rest level during the first bout and then rose in the second bout; or [IRHGH] rose during the first bout and was no longer modified by the restarting. 2) Thirty minutes of heavy exercise. In some subjects [IRHGH] change was almost linear with time, reaching very high values and dropping as soon as exercise had stopped, whereas in others peak values were similar to those of submaximal exercise but, in contrast, plateaued during recovery. 3) One hour of exercise performed either continuously or with alternate sequences of 30-s exercise and 30-s pause. In intermittent exercise, some subjects displayed a similar time course of [IRHGH] as in continuous exercise and others displayed markedly high values. 4) One hour of submaximal exercise at three different intensities carried out at ambient temperatures of 24 and 33 degrees C. At 33 degrees C, in some subjects, [IRHGH] time course at the three intensities was unchanged at 33 degrees C compared with that at 24 degrees C, whereas the maximal value increased in another subject up to 150 ng X ml-1. A significant intrasubject consistency to a given type of exercise was evident over several months. The study emphasizes that caution should be used in drawing definite conclusions from averaged results with high variability.

Adult↗

PubMed1977

Splanchnic blood flow, O2 consumption, removal of lactate, and output of glucose in highlanders.

An impairment of gluconeogenesis has been proposed to explain the low arterial blood glucose of highlanders. Therefore, we studied splanchnic blood flow, splanchnic uptake of oxygen and lactate, and output of glucose in nine normal and six anemic highlanders at an altitude of 3,750 m. Splanchnic blood flow, arteriovenous difference for oxygen, and oxygen consumption were comparable at rest in both groups and in lowlanders from the literature, whereas splanchnic output of glucose, and uptake of lactate were approximately twice those in lowlanders. After 10 min of mild exercise in 12 subjects (7 normals, 5 anemic), no significant changes in splanchnic hemodynamics and metabolism were found. During 29% oxygen breathing in 8 subjects (5 normals, 3 anemics), arterial lactate, splanchnic uptake of lactate and output of glucose fell to normal sea-level values. We concluded that splanchnic hemodynamics are similar in adapted highlanders and in lowlanders, and that there is no evidence of an impaired gluconeogenesis at the altitude of the present study.

Adaptation, Physiological↗

PubMedDate not supplied

Simultaneous ultrasonic measurement of carotid blood flow and intracerebral haemodynamics in man.

Common carotid blood flow and middle cerebral artery velocities were determined simultaneously by using a range gated Doppler velocimeter and transcranial apparatus in ten subjects. Middle cerebral artery velocities were used as an index of cerebral resistance. Different gas mixture concentrations were breathed in order to change cerebral haemodynamic conditions. In each condition there was a simultaneous modification of blood gases and cervicocerebral haemodynamics in common carotid blood flow and cerebral vascular resistance index. Carotid blood flow and the resistance index in middle cerebral artery changed also on opposite side. Acute hypercapnia in normoxia increases common carotid blood flow by 33% and simultaneously decreases cerebral resistance index by 11%. Normocapnic hyperoxia was associated with a fall in common carotid blood flow by 13% and with an increase in cerebral resistance index by 7%. There was a inter-subject statistically significant relation between common carotid blood flow and index of cerebral resistances (0.78 < r < 0.98). However there was an individual reactivity with large scatter when data from different subjects were pooled. Nevertheless the results provide evidence that changes in middle cerebral artery resistance indices are reflected by common carotid blood flow modifications.

Adult↗

PubMedDate not supplied

[Dynamics of ECG voltage in changing gravity].

Comparative analysis of the QRS voltage response to gravity variations was made using the data about 26 normal human subjects collected in parabolic flights (CNERS-AIRBUS A300 Zero-G, n=23; IL-76MD, n=3) and during the tilt test (head-up tilt at 70 degrees for a min and head-down tilt at-15 degrees for 5 min, n=14). Both the parabolic flights and provocative tilt tests affected R-amplitude in the Z lead. During the hypergravity episodes it was observed in 95% of cases with the mean gain of 16% and maximal--56%. On transition to the horizontal position, the Rz-amplitude showed a rise in each subject (16% on the average). In microgravity, the Rz-amplitude reduced in 95% of the observations. The voltage decline averaged 18% and reached 49% at the maximum. The head-down tilt was conducive to Rz reduction in 78% of observations averaging 2%. Analysis of the ECG records under changing gravity when blood redistribution developed within few seconds not enough for serious metabolic shifts still revealed QRS deviations associated exclusively with the physical factors, i.e., alteration in tissue conduction and distance to electrodes. Our findings can stand in good stead in evaluation of the dynamics of predictive ECG parameters during long-term experiments leading to changes as in tissue conduction, so metabolism.

Adaptation, Physiological↗