Monitoring lung impedance changes during long-term ventilator-induced lung injury ventilation using electrical impedance tomography

OBJECTIVE

The target of this methodological evaluation was the feasibility of long-term monitoring of changes in lung conditions by time-difference electrical impedance tomography (tdEIT). In contrast to ventilation monitoring by tdEIT, the monitoring of end-expiratory (EELIC) or end-inspiratory (EILIC) lung impedance change always requires a reference measurement.

APPROACH

To determine the stability of the used Pulmovista 500^® EIT system, as a prerequisite it was initially secured on a resistive phantom for 50 h. By comparing the slopes of EELIC for the whole lung area up to 48 h from 36 pigs ventilated at six positive end-expiratory pressure (PEEP) levels from 0 to 18 cmH₂O we found a good agreement (range of r ² = 0.93-1.0) between absolute EIT (aEIT) and tdEIT values. This justified the usage of tdEIT with its superior local resolution compared to aEIT for long-term determination of EELIC.

MAIN RESULTS

The EELIC was between -0.07 Ωm day^-1 at PEEP 4 and -1.04 Ωm day^-1 at PEEP 18 cmH₂O. The complex local time pattern for EELIC was roughly quantified by the new parameter, centre of end-expiratory change (CoEEC), in equivalence to the established centre of ventilation (CoV). The ventrally located mean of the CoV was fairly constant in the range of 42%-46% of thorax diameter; however, on the contrary, the CoEEC shifted from about 40% to about 75% in the dorsal direction for PEEP levels of 14 and 18 cmH₂O.

SIGNIFICANCE

The observed shifts started earlier for higher PEEP levels. Changes of EELI could be precisely monitored over a period of 48 h by tdEIT on pigs.

[Influence of Macular Hole Width on Visual Acuity, Endotamponade and Closure Rate]

Background: The influence of the width of a full-thickness macular hole on preoperative visual acuity and its role for the intraoperative approach and closure rate were analysed in a prospective study. Methods: For 47 patients with a full thickness macular hole, a precise analysis of the central retina was performed with SD-OCT. An SF₆-gas-air mixture was used, with a lower concentration (15 %) for smaller holes ≤ 400 µm (group 1, n = 17) and a higher concentration (30 %) for larger holes > 400 µm (group 2, n = 30). Besides preoperative visual acuity, postoperative IOP fluctuations and closure rate were reviewed. Results: The mean hole width with SD-OCT was 419 ± 155 µm, with a significant negative correlation with preoperative visual acuity (r = - 0.56, p = 0.002). In the first group, mean early postoperative IOP was 23 mmHg and in the second group 33 mmHg (p < 0.001). Thus, for small macular holes, early postoperative IOP decompensation from gas expansion in the eye could be minimised. The closure rate was 90 %, with no significant difference between the two groups (p > 0.05). Conclusion: Determining the width of a macular hole with SD-OCT is an important indicator for the necessary endotamponade. Using a lower gas concentration (15 %) for smaller holes (≤ 400 µm) to prevent postoperative IOP fluctuations does not negatively influence closure rates.

A spiky pattern in the course of electrical thoracic impedance as a very early sign of a developing pneumothorax

A pneumothorax (PTX) is a potentially lethal condition in high-risk intensive care patients. Electrical impedance tomography (EIT) has been proven to detect PTX at the bedside. A so far not described pattern in the course of thoracic impedance at an early state of PTX was observed in a pig model of ventilator-induced lung injury (VILI) used for a more extensive study. EIT was performed at a framerate of 50 Hz. Beginning of PTX at normal ventilation, manifestation of PTX at VILI ventilation (plateau pressure 42 cm H₂ O) and final pleural drainage were documented. At ventilation with 8·6 ml kg^-1 , early PTX findings prior to any clinical deterioration consisted in a spike-like pattern in the time course of impedance (relative impedance change referred to initial end-expiratory level). Spike amplitudes (mean ± SD) were the following: 0·154 ± 0·059 (right lung) and 0·048 ± 0·050 (left lung). At this state, end-expiratory levels (mean ± SD) were still similar, -0·035 ± 0·010 (right) and -0·058 ± 0·022 (left). After application of VILI ventilation (38 ml kg^-1 ), a PTX developed slowly, being confirmed by a continuous increase in the end-expiratory level on the right side and diverging levels of +0·320 ± 0·057 (right) and -0·193 ± 0·147 (left) at full manifestation. We assume that spikes reflect a temporary change in the electrical pathway caused by leakage into the pleural cavity. This newly described phenomenon of spikes is considered to be a potentially useful indicator for a very early detection of an evolving PTX in high-risk ICU patients.

Aperture alignment in autocollimator-based deflectometric profilometers

During the last ten years, deflectometric profilometers have become indispensable tools for the precision form measurement of optical surfaces. They have proven to be especially suitable for characterizing beam-shaping optical surfaces for x-ray beamline applications at synchrotrons and free electron lasers. Deflectometric profilometers use surface slope (angle) to assess topography and utilize commercial autocollimators for the contactless slope measurement. To this purpose, the autocollimator beam is deflected by a movable optical square (or pentaprism) towards the surface where a co-moving aperture limits and defines the beam footprint. In this paper, we focus on the precise and reproducible alignment of the aperture relative to the autocollimator's optical axis. Its alignment needs to be maintained while it is scanned across the surface under test. The reproducibility of the autocollimator's measuring conditions during calibration and during its use in the profilometer is of crucial importance to providing precise and traceable angle metrology. In the first part of the paper, we present the aperture alignment procedure developed at the Advanced Light Source, Lawrence Berkeley National Laboratory, USA, for the use of their deflectometric profilometers. In the second part, we investigate the topic further by providing extensive ray tracing simulations and calibrations of a commercial autocollimator performed at the Physikalisch-Technische Bundesanstalt, Germany, for evaluating the effects of the positioning of the aperture on the autocollimator's angle response. The investigations which we performed are crucial for reaching fundamental metrological limits in deflectometric profilometry.

[Relevant Parameters of Optic Nerve Analysis from Spectral Domain OCT for Glaucoma Diagnostics]

BACKGROUND

In early diagnosis and follow-up of patients with glaucoma anatomic-diagnostic examinations have become more important in addition to static perimetry. Patients with open angle glaucoma suffer a slow visual field loss due to the loss of ganglion cells, which these examinations could detect earlier than perimetry can.

METHODS

Parameters of the optical coherence tomography (OCT) were analysed in 89 patients (175 eyes) with advanced open angle glaucoma. In a prospective study, the functional findings from static perimetry (HFA-II, 24-2-programme) and the anatomic parameters of optic nerve analysis with SD-OCT (Cirrus-OCT) were evaluated.

RESULTS

The results showed a mean deviation (MD) in perimetry of - 8.31 ± 9.76 dB and in the analysis of the optic nerve head of 71.93 ± 15.86 µm retinal nerve fibre layer (RNFL) as well as 85.54 ± 28.2 µm RNFL for the inferior quadrant, 0.95 ± 0.46 mm(2) for the rim area and 0.69 ± 0.18 for the vertical CD ratio. There was a significant correlation (p < 0.05) between MD und RNFL (r = 0.603), as well as RNFL of the inferior quadrant (r = 0.620), rim area (r = 0.552) and average CD ratio (r = - 0.551). The best correlation for the optical nerve head analysis was found between MD and vertical CD ratio (r = - 0.568).

CONCLUSIONS

There was a good correlation between functional and anatomic parameters in perimetry and OCT. In particular, the mean and inferior retinal nerve fibre layer thickness, the rim area, and the vertical CD ratio revealed to be significant parameters in glaucomatous eyes.

[Surgical treatment of chronic macular oedema with a combination therapy]

BACKGROUND

The treatment of therapy-resistent chronic macular oedema remains a challenge. Therefore a combination therapy, consisting of medical, biological and mechanical components was assessed.

METHODS

A surgical treatment was performed in 35 eyes (34 patients) with chronic and therapy-resistant macular oedema, resulting from diabetic maculopathy (n = 25), vitreoretinal traction (n = 7) or following a retinal venous occlusion (n = 3). An intravitreal injection of bevacizumab was given on the day before surgery, consisting of pars plana vitrectomy with ILM peeling with Brilliant Blue G (BBG), as well as an air tamponade combined with postoperative prone positioning. The visual function and the central retinal thickness were measured in follow-up.

RESULTS

Functionally, the visual acuity could be stabilised to an average of 0.18 and macular oedema was reduced in most patients. Anatomically, a significant reduction in central macular thickness by 193 µm (29 %), from 598 µm to 405 µm (p < 0.001), and a regression in the intraretinal cystoid changes were observed. No significant complications occurred, whereas in 6 patients additional consecutive treatment was necessary.

CONCLUSION

A stabilisation of the visual acuity and an improvement in the structural retinal situation could be achieved by an elaborate combination therapy, based on a pharmacological, a biological and a mechanical approach. Long-term follow-up and consecutive supplementary treatments are necessary to ensure the functional stability.

Ovarian hyperstimulation syndrome is correlated with a reduction of soluble VEGF receptor protein level and a higher amount of VEGF-A

BACKGROUND

Ovarian hyperstimulation syndrome (OHSS) is a potentially life-threatening condition associated with increased vascular permeability. The vascular endothelial growth factor (VEGF) system and its receptors have been identified as the main angiogenic factors responsible for increased capillary permeability and are therefore discussed as crucial for the occurrence of OHSS. Recently, a number of soluble receptors for the VEGFs have been detected (sVEGF-Rs) and it has been shown that these sVEGF-Rs compete with the membrane-standing VEGF-R to bind VEGFs.

METHODS

We analyzed the serum levels of soluble VEGF-R1, -R2 and -R3 in 34 patients suffering from OHSS and in 34 controls without this disease. In a subgroup analysis, we correlated the severity of the OHSS with the detected amounts of VEGF-R1, -R2 and -R3. In addition, we determined the amount of total VEGF-A in the samples.

RESULTS

All the three soluble VEGF receptors tended to be higher in the control group compared with that in the OHSS group but this difference only reached significance for sVEGF-R2 (mean ± SEM: 15.5 ± 0.6 versus 13.8 ± 0.5 ng/ml, respectively, P< 0.05). In the subgroup analysis, sVEGF-R2 levels decreased as the severity of OHSS increased (OHSS-I: 16.8 ± 1.9 ng/ml and OHSS-III: 12.7 ± 1.0 ng/ml, P< 0.05) Moreover, the serum levels of total VEGF-A were higher in the OHSS group than those in the controls (537.7 ± 38.9 versus 351 ± 53.4 pg/ml, respectively P< 0.05).

CONCLUSIONS

We propose that VEGF-A plays a role in the occurrence of OHSS, that the amount of biologically available VEGF-A is modulated by sVEGF-Rs and that different combinations of VEGF-A and sVEGF-R levels might contribute to the severity of OHSS.

Regulation of the angiopoietin-2 gene by hCG in ovarian cancer cell line OVCAR-3

Angiogenesis is a crucial step in growing tissues including many tumors. It is regulated by pro- and antiangiogenic factors including the family of angiopoietins and their corresponding receptors. In previous work we have shown that in human ovarian cells the expression of angiopoietin 2 (ANG2) is regulated by human chorionic gonadotropin (hCG). To better understand the mechanisms of hCG-dependent regulation of the ANG2-gene we have now investigated upstream regulatory active elements of the ANG2-promoter in the ovarian carcinoma cell line OVCAR-3. We cloned several ANG2-promoter-fragments of different lengths into a luciferase reporter-gene-vector and analyzed the corresponding ANG2 expression before and after hCG stimulation. We identified regions of the ANG2-promoter between 1 048 bp and 613 bp upstream of the transcriptional start site where hCG-dependent pathways promote a significant downregulation of gene expression. By sequence analysis of this area we found several potential binding sites for transcription factors that are involved in regulation of ANG2-expression, vascular development and ovarian function. These encompass the forkhead family transcription factors FOXC2 and FOXO1 as well as the CCAAT/enhancer binding protein family (C/EBP). In conclusion, we have demonstrated that the regulation of ANG2-expression in ovarian cancer cells is hCG-dependent and we suggest that forkhead transcription factor and C/EBP-dependent pathways are involved in the regulation of ANG2-expression in ovarian cancer cells.

Imaging pathologic pulmonary air and fluid accumulation by functional and absolute EIT

The increasing use of EIT in clinical research on severely ill lung patients requires a clarification of the influence of pathologic impedance distributions on the validity of the resulting tomograms. Significant accumulation of low-conducting air (e.g. pneumothorax or emphysema) or well-conducting liquid (e.g. haematothorax or atelectases) may conflict with treating the imaging problem as purely linear. First, we investigated the influence of stepwise inflation and deflation by up to 300 ml of air and 300 ml of Ringer solution into the pleural space of five pigs on the resulting tomograms during ventilation at constant tidal volume. Series of EIT images representing relative impedance changes were generated on the basis of a modified Sheffield back projection algorithm and ventilation distribution was displayed as functional (f-EIT) tomograms. In addition, a modified simultaneous iterative reconstruction technique (SIRT) was applied to quantify the resistivity distribution on an absolute level scaled in Omega m (a-EIT). Second, we applied these two EIT techniques on four intensive care patients with inhomogeneous air and fluid distribution and compared the EIT results to computed tomography (CT) and to a reference set of intrathoracic resistivity data of 20 healthy volunteers calculated by SIRT. The results of the animal model show that f-EIT based on back projection is not disturbed by the artificial pneumo- or haematothorax. Application of SIRT allows reliable discrimination and detection of the location and amplitude of pneumo- or haematothorax. These results were supported by the good agreement between the electrical impedance tomograms and CT scans on patients and by the significant differences of regional resistivity data between patients and healthy volunteers.

[Kinematic analysis before and after bicondylar resurfacing knee arthroplasty]

Knee joint motion appears as a hinge movement around the flexion-extension axis. Corresponding to the rolling-sliding mechanism and alternative models of knee joint kinematics, an instant center pathway must be expected. The current photogrammetric investigation aimed to analyze these pathways when assessed in the sagittal plane in patients with preoperative varus or valgus deformity. A total of 40 patients either with varus or valgus deformity (20 in each group) were examined before and 6 months after implantation of PFC-SIGMA prostheses. Apart from the influence of knee joint deformity, a so-called soft tissue ratio was investigated. Therefore, the relation of thigh and femur as well as lower limb and tibia diameters was calculated and combined in one value. The investigation unit consisted of a standardized chair with passive knee joint movement (90-0 degrees flexion) supported by an electric motor. The position of predefined skin markers was assessed by digital camera with online transmission to a PC. The instant center pathway was then evaluated applying the Reuleaux technique based on the changes of skin marker positions. Results showed the following characteristics: small values of soft tissue ratio were represented by round or oval courses of the pathway whereas increasing ratios led to triangular and slightly increased dimensions of the courses. Varus deformity was primarily combined with an increase of the pathway's dimension and in contrast, valgus deformity showed decreased pathways. In each case, dimensions normalized after prosthesis implantation. The instant center pathway of knee joint motion showed for both patient groups characteristic phenomena. They were clearly associated with constitutional and clinical features of each patient.