Tidal Displacements Research Articles

Inferring the Mean Thickness of the Outer Ice Shell of Enceladus From Diurnal Crustal Deformation

AbstractThe thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here, we show that observations of tidally driven diurnal surface displacements can constrain the mean ice shell thickness, . Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite‐element model of Enceladus to calculate diurnal tidal displacements for a range of values in the presence of such structural heterogeneities. Consistent with results from prior studies, we find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing—such as Tiger Stripes on Enceladus—their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of that assume spherical symmetry a priori can deviate from the true value by as much as ∼41% when structural heterogeneities are present. Additionally, we show that crustal heterogeneities near the South Pole produce differences of up to 35% between Love numbers evaluated at different spherical harmonic orders. A ∼41% range in estimates of from Love numbers is smaller than that found with approaches relying on static gravity and topography (∼250%) or analyzing diurnal libration amplitudes (∼85%) to infer at Enceladus. As such, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring mean crustal thickness.

Evaluation of Tidal Effect in Long-Strip DInSAR Measurements Based on GPS Network and Tidal Models

A long-strip differential interferometric synthetic aperture radar (DInSAR) measurement based on multi-frame image mosaicking is currently the realizable approach to measure large-scale ground deformation. As the spatial range of the mosaicked images increases, the nonlinear variation of ground ocean tidal loading (OTL) displacements is more significant, and using plane fitting to remove the large-scale errors will produce large tidal displacement residuals in a region with a complex coastline. To conveniently evaluate the ground tidal effect on mosaic DInSAR interferograms along the west coast of the U.S., a three-dimensional ground OTL displacements grid is generated by integrating tidal constituents’ estimation of the GPS reference station network and global/regional ocean tidal models. Meanwhile, a solid earth tide (SET) model based on IERS conventions is used to estimate the high-precision SET displacements. Experimental results show that the OTL and SET in a long-strip interferogram can reach 77.5 mm, which corresponds to a 19.3% displacement component. Furthermore, the traditional bilinear ramp fitting methods will cause 7.2~20.3 mm residual tidal displacement in the mosaicked interferograms, and the integrated tidal constituents displacements calculation method can accurately eliminate the tendency of tidal displacement in the long-strip interferograms.

Migration and apparent survival of post-spawning alewife (Alosa pseudoharengus) in Minas Basin, Bay of Fundy

The anadromous alewife is a commercially fished clupeid in Atlantic Canada, whose oceanic migration is poorly understood. Migration of alewives is presently investigated from the lower reaches of Gaspereau River into Minas Basin, Bay of Fundy. Seventy-five post-spawning adults were tagged on their downstream migration; within two days of being tagged, most alewives had left Gaspereau River and 57 entered into the Southern Bight of Minas Basin. Thirty-one alewives were detected in Minas Passage and their average time from tagging to final detection was 28 days with standard deviation of 11 days. None of the alewives were detected in Minas Passage until day 20 after the start of tagging. After day 20, the residence timescale in Minas Basin was only 8.8 days with 95% CI of 8.4–9.3 days. Fast tidal currents prevail in much of the study area, and alewives travelled many large tidal excursions in Minas Basin and Minas Passage. Separation distances between pairs of alewives increased greatly after day 20, indicating tidal mixing over large distances within the study area. Offshore movement was associated with seasonal warming, with alewives moving down the spatial temperature gradient and into deeper waters. Offshore, larger tidal displacements widely dispersed tagged alewives through Minas Basin and to Minas Passage. During transit of Gaspereau River, 18 ± 2 alewives were lost with corroborating evidence of mortality for 4 of these. By day 20, the apparent mortality within Minas Basin was ≤ 10 alewives. Individual alewives were observed to make many transits through Minas Passage during their migration, where they may become exposed to in-stream tidal turbines.

Internal Tide Structure and Temporal Variability on the Reflective Continental Slope of Southeastern Tasmania

AbstractMode-1 internal tides can propagate far away from their generation sites, but how and where their energy is dissipated is not well understood. One example is the semidiurnal internal tide generated south of New Zealand, which propagates over a thousand kilometers before impinging on the continental slope of Tasmania. In situ observations and model results from a recent process-study experiment are used to characterize the spatial and temporal variability of the internal tide on the southeastern Tasman slope, where previous studies have quantified large reflectivity. As expected, a standing wave pattern broadly explains the cross-slope and vertical structure of the observed internal tide. However, model and observations highlight several additional features of the internal tide on the continental slope. The standing wave pattern on the sloping bottom as well as small-scale bathymetric corrugations lead to bottom-enhanced tidal energy. Over the corrugations, larger tidal currents and isopycnal displacements are observed along the trough as opposed to the crest. Despite the long-range propagation of the internal tide, most of the variability in energy density on the slope is accounted by the spring–neap cycle. However, the timing of the semidiurnal spring tides is not consistent with a single remote wave and is instead explained by the complex interference between remote and local tides on the Tasman slope. These observations suggest that identifying the multiple waves in an interference pattern and their interaction with small-scale topography is an important step in modeling internal energy and dissipation.

Deformed state of viscoelastic bodies in one problem of tidal interaction

In our previous articles we considered the motion of two viscoelastic bodies in the gravitational field of a massive material point. We studied the evolution of the bodies, stationary solutions and their stability. We solved the equations of translational-rotational motion of the bodies together with the equations of their deformed state, using the method proposed by V G Vil’ke for the systems with infinite numbers of degrees of freedom. In our manuscript we continue our research and our aim is to get the global characteristics of the bodies, deformed by tidal forces: their shape, moments of inertia, the tidal lag angle, the relationship between the viscosity coefficient and the lag angle, tidal torques, internal material properties, depending on elastic constant and viscosity coefficient. It is very important for study of an evolutional motion of the celestial bodies, since tides affect this. In order to achieve this goal we use the tidal potential perturbation and displacements of each point of the bodies. The formulation of the problem, goal set and used methods are the novelty of our research. We applied our theory to the Earth, and it was found that the Earth’s substance (in global) behaves like an auxetic.

Frequency Shift of Near-Inertial Waves in the South China Sea

AbstractDespite sufficient wind forcing, internal waves in the South China Sea do not exhibit the strong near-inertial wave (NIW) peak that is typical in most of the world oceans. Using data from 10 contemporaneous moorings deployed in summer 2011, we show that strong isopycnal vertical tidal displacements transfer most of the near-inertial (NI) kinetic energy (KE) to frequencies higher than the inertial frequency in an Eulerian reference frame. Transforming to an isopycnal-following reference frame increases the KE at NI frequencies, suggesting the presence of NIWs. However, the projection onto a semi-Lagrangian coordinate system still underestimates the expected NI peak. To fully resolve NIWs requires the use of time-dependent vertical wavenumber–frequency spectra because the intrinsic frequency of the NIWs varies substantially, owing to Doppler shifting by lateral mesoscale flows. Here, we show NIW intrinsic frequency variations of ±0.2 cpd within few days, of similar magnitude as the observed variations of relative vorticity associated with the meandering Kuroshio.

Prospects for measuring Mercury’s tidal Love numberh2with the BepiColombo Laser Altimeter

Context.The Love numberh2describes the radial tidal displacements of Mercury’s surface and allows constraints to be set on the inner core size when combined with the potential Love numberk2. Knowledge of Mercury’s inner core size is fundamental to gaining insights into the planet’s thermal evolution and dynamo working principle. The BepiColombo Laser Altimeter (BELA) is currently cruising to Mercury as part of the BepiColombo mission and once it is in orbit around Mercury, it will acquire precise measurements of the planet’s surface topography, potentially including variability that is due to tidal deformation.Aims.We use synthetic measurements acquired using BELA to assess how accurately Mercury’s tidal Love numberh2can be determined by laser altimetry.Methods.We generated realistic, synthetic BELA measurements, including instrument performance, orbit determination, as well as uncertainties in spacecraft attitude and Mercury’s libration. We then retrieved Mercury’sh2and global topography from the synthetic data through a joint inversion.Results.Our results suggest thath2can be determined with an absolute accuracy of ± 0.012, enabling a determination of Mercury’s inner core size to ± 150 km given the inner core is sufficiently large (>800 km). We also show that the uncertainty ofh2depends strongly on the assumed scaling behavior of the topography at small scales and on the periodic misalignment of the instrument.

Calculation of Tidal Displacements and Tilts for a Nonelastic Rotating Earth

A technique for calculating tidal displacements and tilts for the Earth both with the ocean and without it is presented in this work. This technique mainly follows the technique described in the International Earth Rotation Service Conventions and differs from it in small corrections in formulas for the calculation of displacements for diurnal (21) and semidiurnal (22) waves, as well as in an another set of usual and load Love numbers. Values of the gamma factors for the Earth without the ocean are also presented. Our results can be used for the processing of GNSS and tilt-measuring observations. The obtained results are compared with works by other authors, and the calculation technique is implemented in the new version of the ATLANTIDA3.1_2017 program for predicting parameters of Earth tides.

Numerical Characterization of Viscous Heat Dissipation Rate in Oscillatory Air Flow

Abstract The effect of viscous heat dissipation (VHD) in raising the temperature field of incompressible oscillatory air flow is studied numerically. A threshold is established for when the viscous heat dissipation term in the thermal energy equation changes or does not change the temperature field for the case of oscillatory air flow in a tube connecting two reservoirs. This new criterion has not been specified clearly in earlier oscillatory flow research. According to the defined threshold and when VHD is important, the effect of dissipative bulk heating can be described by a proposed correlation in terms of Womersley number (Wo) and axial tidal displacement (ΔZ) of the oscillatory fluid. These results are determined using two-dimensional (2D) numerical simulations of laminar oscillatory air flow (Pr = 0.7) for different adiabatic unconductive tube-reservoirs' systems configurations over a wide range of oscillatory frequencies and tidal displacements. It is found that the low amount of fluid kinetic energy, which is converted into internal energy, is not sufficient to significantly heat up the fluid at a low rate of the viscous work. Therefore, the effect of viscous heat dissipation in oscillatory air flow can be ignored only below a specific limit of unsteadiness depending on Womersley number and axial tidal displacement. Also, the results showed that the VHD becomes more significant with increasing (Wo) and (ΔZ).

Accurate Evaluation of Vertical Tidal Displacement Determined by GPS Kinematic Precise Point Positioning: A Case Study of Hong Kong.

Global Positioning System (GPS) kinematic precise point positioning (KPPP) is an effective approach for estimating the Earth’s tidal deformation. The accuracy of KPPP is usually evaluated by comparing results with tidal models. However, because of the uncertainties of the tidal models, the accuracy of KPPP-estimated tidal displacement is difficult to accurately determine. In this paper, systematic vector differences between GPS estimates and tidal models were estimated by least squares methods in complex domain to analyze the uncertainties of tidal models and determine the accuracy of KPPP-estimated tidal displacements. Through the use of GPS data for 12 GPS reference stations in Hong Kong from 2008 to 2017, vertical ocean tide loading displacements (after removing the body tide effect) for eight semidiurnal and diurnal tidal constituents were obtained by GPS KPPP. By an in-depth analysis of the systematic and residual differences between the GPS estimates and nine tidal models, we demonstrate that the uncertainty of the tidal displacement determined by GPS KPPP for the M2, N2, O1, and Q1 tidal constituents is 0.2 mm, and for the S2 constituent it is 0.5 mm, while the accuracy of the GPS-estimated K1, P1, and K2 tidal constituents is weak because these three tidal constituents are affected by significant common-mode errors. These results suggest that GPS KPPP can be used to precisely constrain the Earth’s vertical tidal displacement in the M2, N2, O1, and Q1 tidal frequencies.

Experimental and numerical investigation of axial heat transfer enhancement by oscillatory flows

In the current study, axial heat transfer enhancements by laminar oscillatory flow between cold and hot reservoirs connected by a bundle of tubes are examined experimentally and numerically. The dimensionless frequency parameter, Womersley number Wo, ranged from 0.1 to 100 with different tidal displacements. Exceeding its molecular counterpart by about five orders of magnitude, the oscillatory thermal conductivity was enhanced with quadratic scaling on the tidal displacement or pressure-gradient amplitude, and the square root of the frequency of oscillation. Two correlations were suggested for the oscillatory thermal conductivity enhancement as a function of Wo and tidal displacement. The correlations showed that the axial heat transfer rate scaled in proportion to Wo1.62 for Wo > 3 and behaves exponentially for low Wo with different scales depending on pressure gradient amplitude. The study has proposed a classification for the oscillatory flow by partitioning the flow into four different regions varying from low tidal displacement to bulk convective exchange. The results also showed that for unsteady flow the unsteady axial conduction is negligible for Wo > 3, but becomes significant as it goes below Wo = 3. This criterion invalidates the previous studies’ assumption for Wo < 3 by ignoring the unsteady axial conduction. Finally, more than ten times of enhancement in axial heat transfer rate was observed in tubes with sufficient wall thickness. This non-zero thermal diffusivity at the interface between the fluid and the tube wall has improved the storage-release process through the Stokes layer.

Tidal Love Numbers of Degrees 2 and 3

In the coming years, the high-precision processing of large arrays of modern observational data from the Global Satellite Navigation System (GNSS) will require knowledge of the theoretical values of the tidal numbers h and l of degrees 2 and 3 with a relative error no worse than 10–4. This will make it possible to predict vertical and horizontal tidal displacements of the earth’s surface at the modern level. The paper presents the values of Love numbers h, k, and l of degrees 2 and 3 calculated for an inelastic ellipsoidal self-gravitating rotating earth without an ocean. Twelve different models are considered that differ from each other by the inclusion or exclusion of individual factors that affect the result. In particular, two different versions of the earth’s structure model are used, corrections for the relative and Coriolis accelerations are considered, and the values of the Love numbers are determined considering their latitude dependence. Lame elastic parameters were recalculated for the periods of semidiurnal and diurnal tidal waves using the logarithmic creep function to account for dissipation. The normalization of the obtained values of the Love numbers corresponds to International Earth Rotation and Reference Systems Service (IERS) Conventions regarding the calculation of tidal displacements of the earth’s surface. The values are compared with the results of widely known works of other authors. Currently, the results are used to develop a new version of the ATLANTIDA3.1 software for predicting earth tides.

Effects of unmodelled tidal displacements in GPS and GLONASS coordinate time-series

This study demonstrates the effect of unmodelled (sub-)daily tidal displacement on GLONASS (GLObalnaya NAvigatsionnaya Sputnikovaya Sistema) coordinate time series in comparison with GPS (Global Positioning System). More than two propagated periodic signals appear in GPS and GLONASS coordinate time series in the presence of an unmodelled M2 /O1 tidal displacements. The propagation mechanism of Stewart et al. (2005) explains well most of the periodic signals. At a fortnightly period, an unmodeled M2 tidal displacement propagates into two long-period signals at 13.6x (x is a positive integer) and 14.76 days for GPS, while only a significant propagated periodic signal at 14.76-day is discernible for GLONASS. Similarly, significant propagated periodic signals at 13.6x and 14.19 days for GPS and only at 14.19-day for GLONASS are evident as a result of an unmodeled O1 tidal displacement. However, an unmodeled Mf (long-period) results in a strong power of similar magnitude at 13.6x-day (∼13.66-day) for both GPS and GLONASS solutions. The appearance of different periodic signals but as a result of the same unmodelled tidal displacement is attributed to the different ground repeat periods of the constellations, which is one of the factors of the propagation mechanism from Stewart et al. (2005). The latter explains the reason why the 13.6x-day fortnightly is present only for GPS solutions. Comparing the powers of the M2 aliased periodic signals at 13.6x-day and 14.76-day from a stacked spectra over all stations, the amplitude of the former is larger than the latter by an order of magnitude. The results of this study may infer that the 13.6x-day periodic signal in GPS/GNSS (Global Navigation Satellite System) derived products of the IGS (International GNSS Service) is a joint contribution of the propagation of unmodelled (sub-)daily tidal displacements and errors at longer periods with the former appearing to contribute more. We also demonstrated that significant reduction of the propagated periodic signals can be achieved from combined-system solutions.

Viscosity and elasticity: a model intercomparison of ice-shelf bending in an Antarctic grounding zone

ABSTRACTGrounding zones are vital to ice-sheet mass balance and its coupling to the global ocean circulation. Processes here determine the mass discharge from the grounded ice sheet, to the floating ice shelves. The response of this transition zone to tidal forcing has been described by both elastic and viscoelastic models. Here we examine the validity of these models for grounding zone flexure over tidal timescales using field data from the Southern McMurdo Ice Shelf (78° 15′S, 167° 7′E). Observations of tidal movement were carried out by simultaneous tiltmeter and GPS measurements along a profile across the grounding zone. Finite-element simulations covering a 64 d period reveal that the viscoelastic model fits best the observations using a Young's modulus of 1.6 GPa and a viscosity of 1013.7 Pa s (≈ 50.1 TPa s). We conclude that the elastic model is only well-constrained for tidal displacements &gt;35% of the spring-tidal amplitude using a Young's modulus of 1.62 ± 0.69 GPa, but that a viscoelastic model is necessary to adequately capture tidal bending at amplitudes below this threshold. In grounding zones where bending stresses are greater than at the Southern McMurdo Ice Shelf or ice viscosity is lower, the threshold would be even higher.

Experimental investigation of heat transfer enhancement factors in the oscillating flow heat exchanger using Kurzweg’s and Nishio’s correlations

In the present work, an experimental investigation of heat transfer enhancement parameters of the oscillating flow heat exchanger using Kurzweg’s and Nishio’s correlations is carried out. An oscillatory axial movement of fluid is established within the flow tube using piston cylinder mechanism. The experiments are carried out for seven different frequencies, five tidal displacements and four heat fluxes. It is observed that at a constant tidal displacement (S), experimental effective thermal conductivity (keff) increases progressively with frequency (f) up to a maximum and then decreases. The frequency corresponding to peak keff is an optimum frequency. In addition to this, it is also observed that with increase in S, the point of peak keff is shifted towards lower frequency. A similar trend is observed for axial heat flux (qa) and convective heat transfer coefficient (h). Based on the dimensional analysis and experimental data, an empirical correlation is obtained for experimental effective thermal diffusivity (αeff) as a function of the Womersley number (Wo) and the transition number (β). Finally the result shows that, in the oscillating flow heat exchanger, f, S, Prandtl number (Pr) of fluid, fluid thermal properties to wall thermal properties, and the ratio of length of cooling tube in heat sink (Lc) to S are primary influencing parameters.

Ocean tide loading displacements in western Europe: 1. Validation of kinematic GPS estimates

AbstractGPS has been extensively used to estimate tidal ground displacements, but the accuracy of this has not been systematically verified. Using more than 20 sites distributed across western Europe, we show that postprocessed kinematic precise point positioning GPS with appropriately tuned process noise constraints is capable of recovering synthetic tidal displacements inserted into real data, with a typical accuracy of 0.2 mm depending on the time series noise. The kinematic method does not result in erroneous propagation of signals from one coordinate component to another or to the simultaneously estimated tropospheric delay parameters. It is robust to the likely effects of day‐to‐day equipment and reference frame changes, and to outages in the data. A minimum data span of 4 years with at least 70% availability is recommended. Finally, we show that the method of reducing apparent coordinate time series noise by constraining the tropospheric delay to values previously estimated in static batch GPS analysis, in fact, results in the suppression of true tidal signals. Using our kinematic GPS analysis approach, periodic displacements can be reliably observed at the 0.2 mm level, which is suitable for the testing and refinement of ocean tide and solid Earth response models.

Internal tidal energy fluxes in the South China Sea from density and velocity measurements by gliders

Internal tidal energy fluxes were obtained from June 2011 to August 2011 using underwater gliders in the South China Sea. Spray gliders profiled every ∼2 h to 500 m, which is deep enough given the shallow thermocline to compute mode‐1 fluxes from vertical mode fits to tidal displacements and currents. Westward, mode‐1 diurnal and semidiurnal fluxes exceeded 40 and 30 kW m−1. To our knowledge, these flux observations are the first from both velocity and density measurements by gliders. Fluxes compare well with a mooring near a generation site in southern Luzon Strait and a regional model. Furthermore, the zonal‐depth structure of the internal tide is obtained by binning measurements, which cover four spring‐neap cycles and over 100 km along 20°39′N. Westward phase propagation is found for currents and displacements, while roughly constant phase is found along beams. Both these features of the phase suggest a narrow‐banded internal tide. Semidiurnal energy density is largest along a raypath which coincides with generation sites on both the eastern and western ridges in Luzon Strait. Diurnal energy density is surface‐intensified consistent with relatively shallower diurnal raypaths emanating from the eastern ridge.

The tidal displacement field at Earth's surface determined using global GPS observations

AbstractWe investigate the 3‐D tidal displacement field on Earth's surface recorded globally by 456 continuous global positioning system (GPS) stations of IGS spanning 1996–2011, for eight principal diurnal and semidiurnal tidal constituents. In‐phase and quadrature amplitudes of the residual tidal displacements, after removal of an a priori body tide model, are estimated using the precise point positioning (PPP) technique on the daily GPS data; the resultant daily estimates are combined to derive final estimates for each tide at each station. The results are compared with the predictions of eight recent global ocean tide models, separately for coastal (307) and inland (149) stations. We show that GPS can provide tidal displacement estimates accurate to the level of 0.12 mm (horizontal) and 0.24 mm (vertical) for the lunar‐only constituents (M2, N2, O1, and Q1) and less favorably for solar‐related tidal constituents (S2, K2, K1, and P1), although improved by ambiguity resolution. Most recent ocean tide models fit the GPS estimates equally well on the global scale but do not agree well between them in certain coastal areas, especially for the vertical displacements, suggesting the existence of model uncertainties near shallow seas. The tidal residuals for the inland stations after removing both body tides and ocean tidal loading (OTL) furthermore show clear continental‐scale spatial coherence, implying deficiencies of the a priori body tide modeling in catching lateral heterogeneity in elastic as well as inelastic properties in the Earth's deep interior. We assert that the GPS tidal displacement estimates now achieve sufficient accuracy to potentially provide constraints on the Earth's structure.

Distribution of lung tissue hysteresis during free breathing

To characterize and quantify free breathing lung tissue motion distributions. Forty seven patient data sets were acquired using a 4DCT protocol consisting of 25 ciné scans at abutting couch positions on a 16-slice scanner. The tidal volume of each scan was measured by simultaneously acquiring spirometry and an abdominal pneumatic bellows. The concept of a characteristic breath was developed to manage otherwise natural breathing pattern variations. The characteristic breath was found by first dividing the breathing traces into individual breaths, from maximum exhalation to maximum exhalation. A linear breathing drift model was assumed and the drift removed for each breath. Breaths that exceeded one standard deviation in period or amplitude were removed from further analysis. A characteristic breath was defined by normalizing each breath to a common amplitude, aligning the peak inhalation times for all of the breaths, and determining the average time at each tidal volume, keeping inhalation and exhalation separate. Breathing motion trajectories were computed using a previously published five-dimensional lung tissue trajectory model which expresses the position of internal lung tissue, X, as: X(v,f:X0)=X0+α(X0)v+β(X0)f, where X0 is the internal lung tissue position at zero tidal volume and zero airflow, the scalar values v and f are the measured tidal volume and airflow, respectively, and the vectors α and β are fitted free parameters. In order to characterize the motion patterns, the trajectory elongations were examined throughout the subject's lungs. Elongation was defined here by generating a rectangular bounding box with one side parallel to the α vector and the box oriented in the plane defined by the α and β motion vectors. Hysteresis motion was defined as the ratio of the box dimensions aligned orthogonal to and parallel to the α vector. The 15th and 85th percentile of the elongation were used to characterize tissue trajectory hysteresis. The 15th and 85th percentile bounding box elongations were 0.090 ± 0.005 and 0.083 ± 0.013 in the upper left lung and 0.187 ± 0.037 and 0.203 ± 0.053, in the lower left lung. The 15th and 85th percentiles for the upper right lung were 0.092 ± 0.006 and 0.085 ± 0.013, and 0.184 ± 0.038, and 0.196 ± 0.043 in the lower right lung. Both percentiles were calculated for tidal volume displacements between 5 and 15 mm. In the left lung, the average elongations in the upper and lower lung were ζ=0.120 ± 0.064 and ζ=0.090 ± 0.055, respectively. The average elongations in the upper and lower right lung were ζ=0.107 ± 0.060 and ζ=0.082 ± 0.048, respectively. The elongation varied smoothly throughout the lungs. The hysteresis motion was relatively small compared to the volume-filling motion, contributing between 8% and 20% of the overall motion. Statistically significant differences were observed in the range of hysteresis contribution for upper and lower lung regions. The characteristic breath process provided an excellent method for defining an average breath. The characteristic breath had continuous tidal volume and airflow characteristics when the breath was continuously repeated,useful for generating patterns representative of realistic motion for breathing motion studies.

Transient decrease in PaCO2 and asymmetric chest wall dynamics in early progressing pneumothorax

Diagnosis of pneumothorax (PTX) in newborn infants has been reported as late. To explore diagnostic indices for early detection of progressing PTX, and offer explanations for delayed diagnoses. Progressing PTX was created in rabbits (2.3 ± 0.5 kg, n = 7) by injecting 1 ml/min of air into the pleural space. Hemodynamic parameters, tidal volume, EtCO(2), SpO(2), blood gas analyses and chest wall tidal displacements (TDi) on both sides of the chest were recorded. (Mean ± SD): A decrease in SpO(2) below 90 % was detected only after 46.6 ± 11.3 min in six experiments. In contrary to the expected gradual increase of CO(2), there was a prolonged transient decrease of 14.2 ± 4.5 % in EtCO(2) (p < 0.01), and a similar decrease in PaCO(2) (p < 0.025). EtCO(2) returned back to baseline only after 55.2 ± 24.7 min, and continued to rise thereafter. The decrease in CO(2) was a mirror image of the 14.6 ± 5.3 % increase in tidal volume. The analysis of endotracheal flow and pressure dynamics revealed a paradoxical transient increase in the apparent compliance. Significant decrease in mean arterial blood pressure was observed after 46.2 ± 40.1 min. TDi provided the most sensitive and earliest sign of PTX, decreasing on the PTX side after 16.1 ± 7.2 min. The TDi progressively decreased faster and lower on the PTX side, thus enabling detection of asymmetric ventilation. The counterintuitive transient prolonged decrease in CO(2) without changes in SpO(2) may explain the delay in diagnosis of PTX encountered in the clinical environment. An earlier indication of asymmetrically decreased ventilation on the affected side was achieved by monitoring the TDi.