Cardiovascular changes induced by cold water immersion during hyperbaric hyperoxic exposure.

The present study was designed to assess the cardiac changes induced by cold water immersion compared with dry conditions during a prolonged hyperbaric and hyperoxic exposure (ambient pressure between 1.6 and 3 ATA and PiO(2) between 1.2 and 2.8 ATA). Ten healthy volunteers were studied during a 6 h compression in a hyperbaric chamber with immersion up to the neck in cold water while wearing wet suits. Results were compared with measurements obtained in dry conditions. Echocardiography and Doppler examinations were performed after 15 min and 5 h. Stroke volume, left atrial and left ventricular (LV) diameters remained unchanged during immersion, whereas they significantly fell during the dry session. As an index of LV contractility, percentage fractional shortening remained unchanged, in contrast to a decrease during dry experiment. Heart rate (HR) significantly decreased after 5 h, although it had not changed during the dry session. The changes in the total arterial compliance were similar during the immersed and dry sessions, with a significant decrease after 5 h. In immersed and dry conditions, cardiac output was unchanged after 15 min but decreased by almost 20% after 5 h. This decrease was related to a decrease in HR during immersion and to a decrease in stroke volume in dry conditions. The hydrostatic pressure exerted by water immersion on the systemic vessels could explain these differences. Indeed, the redistribution of blood volume towards the compliant thoracic bed may conceal a part of hypovolaemia that developed in the course of the session

KTa0.65Nb0.35O3 thin films epitaxially grown by pulsed laser deposition on metallic and oxide epitaxial electrodes

International audienceFerroelectric KTa0.65Nb0.35O3 (KTN) thin films were grown by pulsed laser deposition on Pt and LaNiO3 epitaxial electrodes, on (1 0 0) and (1 1 0) SrTiO3 substrates. The effect of the nature of the electrode on structural and microstructural quality of KTN films was investigated. While epitaxial KTN thin films were successfully obtained on both electrodes, two orientations compete on Pt, whatever the main orientation of Pt is (1 0 0) or (1 1 0). On LaNiO3 in contrast, pure (1 0 0) and (1 1 0) oriented KTN films were achieved with a high crystalline quality illustrated by narrow ω-scans (Δω = 0.56° and Δω = 0.80° for (1 0 0) and (1 1 0) KTN, to be compared to 0.048° and 0.22° for (1 0 0) and (1 1 0) LaNiO3, respectively). Electrical measurements performed in tunneling atomic force microscopy (TUNA mode) on a KTN/Pt heterostructure showed a high asymmetry of the conduction mechanisms when a positive or a negative bias is applied on the sample. In particular leakage currents appear even at very low positive applied voltage. TUNA imaging operated at a moderate negative applied voltage of −3 V shows that some areas corresponding to grain boundaries seem to be more leaky than others