Biomedical subjects

François Carre

Publications and source records attributed to François Carre.

4 recordsLinked to original sources

PubMed2004

Cardiorespiratory adaptations during the six-minute walk test in chronic heart failure patients.

BACKGROUND: The six-minute walk test (6-MWT) is widely used to assess exercise tolerance in chronic heart failure patients (CHF). The aim of this study was to analyse cardiorespiratory parameters kinetics during the 6-MWT in CHF and in healthy subjects. METHODS: A treadmill, symptom-limited exercise test and a 6-MWT were performed by 14 CHF under optimal drug treatment (CHFD), 17 CHF with cardiac resynchronization (CHFP), and 12 healthy subjects. Cardiorespiratory responses were assessed by a validated portable system. RESULTS: All subjects exceeded their ventilatory threshold during the 6-MWT. Healthy subjects and CHF performed the 6-MWT around 75 and 90% of peak oxygen uptake (V'O2) respectively (P<0.001). In CHF, a steady state was observed only for walking speed and V'O2, with a slight delay in comparison with healthy subjects, for whom a steady state was also observed for carbon dioxide production and ventilation (V'E). During the 6-MWT, the V'E adaptation was due mainly to an increase in tidal volume (VT) in CHFD, whereas in CHFP, it was due to a similar increase in VT and breathing frequency (f). In these patients, the 6-MWT VT/f slope was lower than in CHFD (P<0.01). CONCLUSIONS: During the 6-MWT, the V'O2 steady state is slightly delayed in CHF, which could be related partly to their higher exercise intensity. Moreover, each CHF group is characterized by a specific ventilation components response during the 6-MWT.

Adaptation, Physiological↗

PubMed2003

The relationship between expired concentration of sevoflurane and sympathovagal tone in children.

UNLABELLED: In children, sevoflurane depresses parasympathetic tone during induction more than halothane. The effects of sevoflurane on parasympathetic activity could explain the difference in heart rate (HR) changes described between infants and children. In this study, we sought to determine the relationship between the end-tidal concentration of sevoflurane and sympathetic and parasympathetic tone in children by spectral analysis of RR intervals. Thirty-three children, ASA physical status I, who required elective surgery were studied. In 10 children (Group A), recordings were performed while gradually decreasing the inspired sevoflurane concentration from 8% to the beginning of clinical awakening. In 23 other children (Group B), recordings were performed while children were awake and at a steady-state of 1 and 2 minimum alveolar anesthetic concentration of sevoflurane. A time-varying autoregressive modeling of the interpolated RR sequences was performed, and spectral density in low-frequency (LF; 0.04-0.15 Hz) and high-frequency (HF; 0.15-0.55 Hz) bands was calculated. In Group A, HR slowing paralleled the decrease in expired sevoflurane concentration. Conversely, the decrease in expired concentration of sevoflurane led to an increase in systolic blood pressure (SBP), HF, LF, and LF/HF. The increase in LF/HF preceded the increase in HF. In Group B, the baseline HF power spectrum and normalized values HFnu (HFnu = HF/LF + HF) were significantly increased in children older than 3 yr. Changes in HR induced by sevoflurane were negatively correlated with baseline HF and HFnu (R(2) = 0.6; P < 0.001). These results demonstrate that withdrawal of parasympathetic tone is the main determinant for the change in HR induced by sevoflurane. IMPLICATIONS: The effects of sevoflurane on parasympathetic activity could explain the difference in heart-rate changes described between infants and children during induction. This study describes the changes in heart rate and its variability induced by sevoflurane in children and shows that these changes are related to parasympathetic tone before the induction of anesthesia.

Anesthesia Recovery Period↗

PubMed2002

Extrapolation of cardiac index from analysis of the left ventricular outflow velocities in children: implication of the relationship between aortic size and body surface area.

BACKGROUND: It has recently been reported in critically ill patients that a linear relationship exists between cardiac index (CI) measured with thermodilution and mean aortic blood flow velocity (MAFV). This hypothesis can be validated mathematically only if the aortic area (AA index) indexed to body surface area (BSA) remains constant and if the relationship between aortic diameter (PhiAo) and BSA is nonlinear. However, several other equations have described the relationship between BSA and, respectively, PhiAo and aortic area (AA) in children. The aim of this study was to determine if the relationships calculated between BSA and aortic size in children (without left ventricular outflow tract abnormality) could validate the hypothesis that MAFV and CI are well linked linearly, leading to its use to determine CI. METHODS: Two hundred and thirty-two measurements performed in 126 children and infants were retrospectively analysed. PhiAo was measured in the long axis view at the annulus using two-dimensional mode echocardiography with a 5-MHz transducer. Various linear and nonlinear relationships between BSA and, respectively, PhiAo, PhiAoindex, AA and AAindex were determined based on a nonlinear regression method with a model as follows: y=a(xc) + b. The comparisons between regressions were conducted based on the estimation error. RESULTS: The relationships between PhiAo and BSA appeared nonlinear and was well described by: PhiAo=2.96(BSA1/4) - 1.31 with a non-zero y-intercept and PhiAo=1.64(BSA1/2) with a zero y-intercept. In contrast, the relationships between AA and BSA were linear. The AAindex was not linked to BSA and can be considered as constant. The coefficient a of the equation appeared similar to those obtained mathematically with the relationship previously described between MAFV and CI. CONCLUSIONS: The hypothesis that CI can be extrapolated to the measurement of MAFV appears valid as regards the relationships calculated between aortic size and BSA in children without left ventricular outflow tract abnormality.

Adolescent↗

PubMed2001

Impedance cardiographic waveforms in children: Involvement in left ventricular ejection time determination during anesthesia.

OBJECTIVE: The physiologic basis of the impedance cardiographic (ICG) signal is still a matter of debate. An accurate determination of left ventricular ejection time (LVET) is needed to calculate stroke volume. In children, several shapes of the ICG signal are observed during anesthesia or in critical care. The aim of this study was to determine the relationship between the shape of the ICG signal and various morphologic and hemodynamic determinants obtained with Doppler echocardiography to highlight the effect of the various shapes in the accuracy of LVET determination. DESIGN: Prospective study. SETTING: Pediatric surgery in a university hospital. PATIENTS: 103 children, ASA physical status I or II. INTERVENTIONS: General anesthesia for elective surgery. Measurements: Electrocardiography, ICG, and Doppler echocardiography were recorded simultaneously. Classic hemodynamic variables, such as heart rate, LVET, stroke volume, or systemic vascular resistance, were measured or calculated. A mathematical model of the ICG signal was used to determine the shape of the ICG signal and its potential relationship to various morphologic and hemodynamic determinants. The ICG signal shape was then modeled with the normalized amplitudes (NHA) and phase (NHP) of the three harmonics of the fundamental signal. Analysis was performed with a multiple correspondence analysis. RESULTS: ICG method LVET did not significantly correlate with LVET determined with Doppler or with heart rate. NHA and NHP of the ICG signal were not significantly related to LVET determined with Doppler or to stroke volume. NHA were linked to heart rate and the relative length of the cardiac diastolic period. CONCLUSION: The absence of relationship between LVET determined with Doppler and the main variables defining the shape of the ICG signal highlight the relative limit of stroke volume determination with ICG method. The involvement of the arterial compliance in the ICG signal shape can be discussed in regard to the links between NHA and both heart rate and the relative length of the cardiac diastolic period, respectively.

Journal Article↗