Section: New Results
Clinical and physiological applications - Cardiovascular system
Analysis of cardiovascular and respiratory interactions in mechanically ventilated patients in intensive care [74] , [75]
Participant : Claire Médigue.
Collaboration with François Cottin (Unité de Biologie Intégrative des Adaptations à l'Exercice, INSERM 902, Génopôle, Evry), Andry Van de Louw (Service de Réanimation Polyvalente, Centre Hospitalier Sud-Francilien, Evry) and Yves Papelier.
Positive End Expiratory Pressure may alter breathing cardiovascular variability and baroreflex gain in mechanically ventilated patients. [74] During mechanical ventilation, some patients have stable cardiorespiratory phase difference and stable high frequency (HF) amplitude of heart rate high-frequency (HF) heart rate variability over time and others do not. We hypothesized that a steady pattern could reflect a blunted autonomic nervous system and that positive end-expiratory pressure (PEEP) could further alter the autonomic nervous function. We tested the effect of increasing PEEP from 5 to 10 cm H2O on the breathing variability of arterial pressure and RR intervals, and on the baroreflex. Invasive arterial pressure, ECG and ventilatory flow were recorded in 23 mechanically ventilated patients during 15 minutes for both PEEP levels. HF amplitude of RR and systolic blood pressure time series and HF phase differences between RR, SBP and ventilatory signals were continuously computed by complex demodulation. Cross-spectral analysis was used to assess the coherence and gain functions between RR and SBP, yielding baroreflex-sensitivity indices. At PEEP 10, the 12 patients with a stable pattern had lower baroreflex gain and HF RR amplitude than the 11 other patients. Increasing PEEP was globally associated with a decreased baroreflex gain and a greater stability of HF RR amplitude and cardiorespiratory phase difference over all the patients. Anyway, four of them who exhibited a variable pattern at PEEP 5 became stable at PEEP 10. At PEEP 10, a stable pattern was associated with higher organ failure score and catecholamine dosage. Thus, stable HF RR amplitude and cardiorespiratory phase difference over time reflect a blunted autonomic nervous function which might worsen as PEEP increases with a prognostic value.
Cardiorespiratory phase difference in mechanically ventilated patients: evidence for the role of central nervous mechanisms [75] Under mechanical ventilation, large inter-patient and intra-patient RR variations of the phase of respiratory sinus arrhythmia (RSA) have been described. We sought to determine whether these variations were of central nervous origin or related to the mechanical effect of positive pressure ventilation. Therefore, we compared the RSA phase between: 1) 12 control subjects enforced to breath at the same breathing frequency than the mechanically ventilated patients, 2) 23 mechanically ventilated patients without brain injury (MV group) and 3) 12 brain dead, mechanically ventilated patients, whose central nervous functions were abolished (BD group). ECG, arterial pressure and ventilatory flow were recorded during 15 minutes. High-Frequency phase difference between RR, arterial pressure and ventilatory signals was continuously computed by complex demodulation. About RR intervals, control group exhibited RSA phases between 180° and 250° whereas an opposite pattern, between 0° and 90°, was observed in the BD group. For the two groups, the phase was stable over time. By contrast, in the MV group, the RSA phases were distributed between 0° and 260°, with a greater variability over time than the two other groups. Concerning arterial pressure, the phase difference with ventilatory signal was very close to 0° in all MV and BD patients, with minimal fluctuations over time. Therefore, during mechanical ventilation, breathing arterial pressure variability is mainly mechanically mediated, whereas functional nervous centers may sometimes induce large variations of the RSA phase, not synchronous with the mechanical effect of ventilation.
Validation of a New Method for Stroke Volume Variation Assessment: a comparison with the PiCCO Technique [72]
Participants : Claire Médigue, Michel Sorine.
Collaboration with François Cottin (Unité de Biologie Intégrative des Adaptations à l'Exercice, INSERM 902, Génopôle, Evry), Andry Van de Louw (Service de Réanimation Polyvalente, Centre Hospitalier Sud-Francilien, Evry), Taous-Meriem Laleg (INRIA project-team Magique-3D) and Yves Papelier.
This new method is based on scattering transform for a one dimension Schrödinger equation and provides new parameters, related to the systolic and diastolic parts of the pressure. We aimed at assessing the first systolic invariant INVS1 , linearly correlated to the stroke volume, by comparison with a reference method, the Picco technique, using the pulse contour method. To validate this approach, a statistical comparison between INVS1 and the stroke volume measured with the PiCCO technique was performed during a 15-mn recording in 21 mechanically ventilated patients in intensive care.
