In situ continuous monitoring of dissolved gases (N2, O2, CO2, H2) prior to H2 injection in an aquifer (Catenoy, France) by on-site Raman and infrared spectroscopies: instrumental assessment and geochemical baseline establishment.

The establishment of a baseline of gases from an aquifer appears to be an essential prerequisite for monitoring and securing underground storage operations such as the storage of carbon dioxide (carbon capture and storage: CCS), methane or hydrogen. This study describes an innovative metrological technique dedicated to the in situ and continuous quantification of dissolved gases (CO2, O2, N2, CH4 and H2) in a shallow aquifer, on the site of Catenoy (Paris Basin) with a water table at a depth of 13 m. Monitoring was carried out from May 7, 2019 to November 19, 2019, before the simulation of H2 injection. Gases as vapors were collected from the aquifer through a nine-meter long, half-permeable polymer membrane positioned below a packer in a 25-meter deep well. Collected gases were analyzed simultaneously at the surface by fiber Raman (CO2, O2, N2, CH4 and H2) and infrared sensors (CO2). Gas concentrations were determined from Raman and infrared data, and then converted into dissolved concentrations using Henry's law. The dissolved gas concentrations were about constant over the 6 months period with average values of 31-40 mg L-1 (CO2), 8 mg L-1 (O2), 17 mg L-1 (N2), and 0 mg L-1 (H2, CH4) indicating a very low variability in the aquifer. This is believed to allow for rapid detection of any possible abnormal concentration variation, in particular linked to an accidental arrival of gases such as hydrogen. Such an online gas measurement system can be deployed as is on any site type of underground storage without any need for adaptation.

Human vertical optokinetic nystagmus and after-response, and their dependence upon head orientation with respect to gravity.

Characteristics of human vertical optokinetic nystagmus (VOKN) and afternystagmus (VOKAN) were examined by electro-oculography in 18 normal human subjects by means of the analysis of slow phase velocity (SPV) and area under the regression curve of the VOKAN decay. Under normal gravity, subjects were tested in upright and left ear down (90 degrees roll) positions, respectively, using a hemisphere onto which stripes were projected at a velocity of 40 degrees/s in left, right, up and down directions. Analysis of the VOKN and VOKAN revealed a significant asymmetry of vertical eye movements in the subjects' sagittal plane, ie, stronger upward SPV than downward in both VOKN and VOKAN decay. This asymmetry became even more prominent when the head was in the 90 degrees roll position. It is postulated that the asymmetry of VOKN and VOKAN in humans, as in animals, is due to the asymmetrical storage capability of the vertical velocity storage mechanism which mainly contributes to upward eye movements. In addition, it is postulated that the vertical storage mechanism is modified by the action of gravity on the otolith organs. However, only two out of our 18 subjects demonstrated cross-coupling, as reported in animals, from the horizontal to the vertical mode of storage when the head was tilted away from the spatial vertical.

The use of confirming x-rays to verify tip position for peripherally inserted catheters.

The tips of long-line peripherally inserted catheters may be positioned in the superior vena cava (SVC), subclavian vein, or axillary vein. Based on current standards of practice, catheters with tips placed in the SVC are central lines that require a confirming x-ray; catheters with tips terminating in the subclavian or axillary vein are noncentral and do not require confirming x-rays. Several authors follow this standard; others, however, suggest that radiographic examination should be performed on catheters with tips lying in locations other than SVC unless numerous specific criteria are met. In this study, x-rays were obtained for 42 patients in a hospital setting to determine tip location and position. Radiographic examination revealed that six were looped and five were positioned in a branch or tributary off the axillary vein. To eliminate the complications associated with catheter tip malposition (i.e., thrombus, occlusion), x-ray confirmation should be performed on all lines placed in or beyond the axillary vein to ensure correct tip position.

Stimulus velocity dependence of human vertical optokinetic nystagmus and afternystagmus.

Stimulus velocity dependence of human VOKN and VOKAN was investigated using 20 degrees, 40 degrees, 60 degrees, and 80 degrees/s optokinetic stimulation. In our experimental conditions, 40 degrees/s was found to be the most appropriate stimulus velocity for inducing reliable VOKN and VOKAN based on the analysis of SPV, gain, and the area under the VOKAN decay curve. There was a clear trend toward up/down asymmetry of VOKN gain, with higher upward OKN SPV than downward at 40 degrees/s. VOKAN with both short and long time constant components was induced in 5 of 11 subjects, but only when the stimulus was upgoing. Stimulation at 20 degrees/s in either direction produced a decay with only a short time constant. VOKN-SPV and the area under VOKAN decay curve at 40 degrees/s showed no significant difference from the corresponding values at 60 degrees/s or 80 degrees/s, indicating that following and the velocity storage mechanism had saturated at 40 degrees/s. However, the gain at 60 degrees/s and 80 degrees/s became low and eye movement regularity was poor. Stimulation at 20 degrees/s may activate mainly the vertical pursuit mechanism, as it did not produce up/down asymmetry. It is proposed that, as in the horizontal case, two kinds of mechanisms are involved in vertical stripe-following eye movements, which represent smooth pursuit and optokinetic systems respectively.

Multisensory integration in the human vestibular velocity storage mechanism?

To test the hypothesis that auditory inputs can interact with the optokinetically or vestibularly-charged human VSM, we examined the effects of sound on rotational nystagmus and HOKAN. Subjects were rotated at 60 degrees/s, in either clockwise (CW) or counterclockwise (CCV) direction, for a total of 3 min. After 1 min of constant rotation, the optokinetic surround (7 ft dia., 2 degrees stripes at 18 degrees intervals) was illuminated for 60 s and the ensuing HOKAN was recorded for 60 s (standard DCEOG). The chair was stopped 60 s later and the post-rotatory nystagmus (PRN) was recorded. The acoustic stimulus (4/s, 10 ms pulses) was presented to the subject by a loudspeaker in 4 randomized test conditions: (1) fixed to the surround-on during OKN, off during OKAN (2) fixed to the surround-off during OKN, on during OKAN (3) rotating with the subject-on during OKN, off during OKAN (4) rotating with the subject-off during OKN, on during OKAN. In all conditions, the sound was on during per- and post-rotatory nystagmus. Each test was performed on a different day and consisted of 4 randomized control and test trials (CW and CCW). Under none of the above conditions was the rotatory or optokinetic decay affected by the presence of stationary or rotating sound. This absence of alteration of PRN by sound cues contradicts that reported by Kollar et al. (1988). Our evidence that neither HOKAN nor post rotatory nystagmus decay is affected by sound cues supports the conclusion that, under our conditions, multisensory interaction does not occur in the human VSM.

Suppression of optokinetic velocity storage in humans by static tilt in pitch.

The effects of static tilts about the pitch axis on human horizontal optokinetic after-nystagmus OKAN (HOKAN) were examined. Static tilts in pitch produced tilt-dependent HOKAN suppression. The slow decay (indirect pathway) component (coefficient C and long time constant 1/D) of the two-component model for OKAN was significantly reduced, while the short decay (direct pathway) component (coefficient A and short time constant 1/B) remained invariant as angle of tilt was increased. These results provide further evidence that otolith organ activity can couple to horizontal velocity storage in humans, in accordance with models proposed in the literature.

Suppression of optokinetic velocity storage in humans by static tilt in roll.

The effects of static tilts about the roll (anterior-posterior) axis on human horizontal optokinetic afternystagmus (HOKAN) were examined. Static tilts in roll, with subjects lying on their left side, produced significant tilt-dependent HOKAN suppression. Only the slow (indirect pathway) component time constant (1/D) of the double exponential model for human HOKAN decreased with angle of roll tilt. The effect was direction specific in that suppression occurred only following a leftward-going stimulus. These findings provide further support for the postulate that otolith-organ-mediated activity can couple to the horizontal velocity storage mechanism in humans. A slight trend towards a tilt-dependent reduction of coefficient A (initial slow phase velocity of fast component decay) was revealed, suggesting the possibility that otolith-organ-mediated activity could couple to direct (pursuit-mediated?) pathways as well. No horizontal-to-vertical cross-coupling occurred, indicating that this aspect of the 3-dimensional model for velocity storage proposed by Raphan & Cohen (1988) may not completely apply to humans.

Effect of active head movements about the pitch, roll, and yaw axes on human optokinetic afternystagmus.

Effects of active head movements about the pitch, roll, or yaw axes on horizontal optokinetic afternystagmas (OKAN) were examined in 16 subjects to test the hypothesis that otolith organ mediated activity induced by a change in head position can couple to the horizontal velocity storage in humans. Active head movements about the pitch axis, forwards or backwards, produced significant OKAN suppression. Pitch forward head movements exerted the strongest effect. Active head movements about the roll axis towards the right also produced OKAN suppression but only if the tilted position was sustained. No suppression was observed following sustained yaw. However, an unsustained yaw left movement after rightward drum rotation significantly enhanced OKAN. Sustained head movement trials did not significantly alter subsequent control trials. In contrast, unsustained movements about the pitch axis, which involve more complex interactions, exerted long-term effects on subsequent control trials. We conclude that otolith organ mediated activity arising from pitch or roll head movements couples to the horizontal velocity storage in humans, thereby suppressing ongoing OKAN. Activity arising from the horizontal canals during an unsustained yaw movement (observed mainly with yaw left), following drum rotation in a direction contralateral to the movement, may also couple to the velocity storage, resulting in increased activity instead of suppression.

Human optokinetic afternystagmus. Charging characteristics and stimulus exposure time dependence in the two-component model.

The dependence of human optokinetic afternystagmus (OKAN) velocity storage (charging) and optokinetic nystagmus (OKN) characteristics on optokinetic (OK) stimulus exposure time was investigated, using the two-component double exponential model for OKAN decay. Results are compatible with our previously proposed concept of two velocity storage integrators, one responsible for the short time constant decay (pursuit-mediated) and the other for the long time constant decay (OK system-mediated). The dependence of the long time constant integrator of OKAN on stimulus exposure time was clearly demonstrated. The short time constant integrator appeared to be independent of stimulus exposure time within the range studied. We conclude that the charging time-course of each component is distinct from that of the other. The time constants of each component decay were found to be invariant. A left-right asymmetry observed in both OKN and OKAN responses suggests that the integrators are direction sensitive.

Human optokinetic afternystagmus. Stimulus velocity dependence of the two-component decay model and involvement of pursuit.

The dependence of human OKAN characteristics on optokinetic (OK) stimulus velocity was examined using the two-component double exponential model for OKAN decay. Drum velocities studied were between 10 degrees and 70 degrees deg/sec over a constant exposure period of 60 sec. Results reveal two distinct types of response: a 'low'-level response at lower drum velocities (10 degrees, 20 degrees, 30 degrees/sec) and a 'high'-level response at higher drum velocities (40 degrees, 60 degrees, 70 degrees /sec). These findings support our previous proposal that OKAN decay is a two-component process, and extend it by demonstrating that these two components have differing stimulus velocity sensitivities, as would be predicted if it were assumed that they represented direct (pursuit) and indirect (non-pursuit) pathways respectively.

Human optokinetic afternystagmus. Effects of repeated stimulation.

Normal human subjects were exposed to repeated optokinetic afternystagmus (OKAN) testing in either one direction or alternating directions of stripe movement. Sessions were conducted at intervals of either one week or several weeks. Repeated exposure to OKAN stimulation in one direction produced significant response decrements in cumulative displacement, short time constant, long time constant, and the coefficient of the long time constant component (C). The data suggest that the decrease in C and cumulative displacement occurred most noticeably between trials 3 and 4 of the first session. Retesting after 1 week, and up to 8 weeks later revealed no recovery. Repeated exposure to alternating leftward and rightward stimuli resulted in response decrement in both cumulative displacement and C. Responses to leftward stimuli were indistinguishable from responses to rightward stimuli.

Human optokinetic afternystagmus. Slow-phase characteristics and analysis of the decay of slow-phase velocity.

Events following the extinction of lights after 1-minute exposures of naive, normal subjects to an optokinetic stimulus at 40 deg/sec have been closely examined and quantified. Mean eye displacement in each slow phase decreased from 10.12 +/- 1.61 deg during optokinetic nystagmus (OKN) to 3.36 +/- 2.32 deg during optokinetic afternystagmus (OKAN). Slow-phase duration increased from 0.26 +/- 0.03 sec during OKN to 0.45 +/- 0.195 sec during OKAN. Eye displacement per slow phase remained fairly constant during OKAN, suggesting a spatial reference for the resetting of gaze. OKAN decay is a two-component process which can be closely approximated by a sum of two exponentials, one with a short time constant of 1.15 sec and the other with a long time constant of 48.8 sec. OKAN decay commenced at a time after lights out which depended upon the presence and timing of an intervening fast phase. When a fast phase intervened, OKAN decay commenced about 230 msec after it, and about 460 msec after lights out. When lights out occurred during the fast phase, OKAN decay commenced about 340 msec later.