Objective
To investigate whether electrical impedance tomography (EIT) is capable of monitoring regional lung recruitment and lung collapse during a positive end-expiratory pressure (PEEP) trial.
...Design
Experimental animal study of acute lung injury.
Subject
Six pigs with saline-lavage-induced acute lung injury.
Interventions
An incremental and decremental PEEP trial at ten pressure levels was performed. Ventilatory, gas exchange, and hemodynamic parameters were automatically recorded. EIT and computed tomography (CT) scans of the same slice were simultaneously taken at each PEEP level.
Measurements and results
A significant correlation between EIT and CT analyses of end-expiratory gas volumes (
r
= 0.98 up to 0.99) and tidal volumes (
r
= 0.55 up to
r
= 0.88) could be demonstrated. Changes in global and regional tidal volumes and arterial oxygenation (PaO
2
/FiO
2
) demonstrated recruitment/derecruitment during the trial, but at different onsets. During the decremental trial, derecruitment first occurred in dependent lung areas. This was indicated by lowered regional tidal volumes measured in this area and by a decrease of PaO
2
/FiO
2
. At the same time, the global tidal volume still continued to increase, because the increase of ventilation of the non-dependent areas was higher than the loss in the dependent areas. This indicates that opposing regional changes might cancel each other out when combined in a global parameter.
Conclusions
EIT is suitable for monitoring the dynamic effects of PEEP variations on the regional change of tidal volume. It is superior to global ventilation parameters in assessing the beginning of alveolar recruitment and lung collapse.
Electrical isolation of the pulmonary veins (PVs) has been established in clinical routine as a curative treatment for atrial fibrillation (AF). While catheter ablation carries procedural risks, ...radiosurgery might be able to non-invasively induce lesions at the PV ostia to block veno-atrial electrical conduction. This porcine feasibility and dose escalation study determined the effect of radiosurgery on electrophysiologic properties of the left atrial-PV junction.
Eight adult Goettingen mini-pigs underwent electrophysiological voltage mapping in the left atrium and the upper right PV. Radiation was delivered with a conventional linear accelerator. A single homogeneous dose ranging from 22.5 to 40 Gy was applied circumferentially to the target vein antrum. Six months after radiosurgery, electrophysiological mapping was repeated and a histological examination performed. Voltage mapping consistently showed electrical potentials in the upper right PV at baseline. Pacing the target vein prompted atrial excitation, thus proving veno-atrial electrical conduction. After 6 months, radiation had reduced PV electrogram amplitudes. This was dose dependent with a mean interaction effect of -5.8%/Gy. Complete block of atrio-venous electrical conduction occurred after 40 Gy dose application. Histology revealed transmural scarring of the targeted PV musculature with doses >30 Gy. After 40 Gy, it spanned the entire circumference in accordance with pulmonary vein isolation.
Pulmonary vein isolation to treat AF can be achieved by radiosurgery with a conventional linear accelerator. Yet, it requires a high radiation dose which might limit clinical applicability.
To perform a proof-of-principle dose-escalation study to radiosurgically induce scarring in cardiac muscle tissue to block veno-atrial electrical connections at the pulmonary vein antrum, similar to ...catheter ablation.
Nine mini-pigs underwent pretreatment magnetic resonance imaging (MRI) evaluation of heart function and electrophysiology assessment by catheter measurements in the right superior pulmonary vein (RSPV). Immediately after examination, radiosurgery with randomized single-fraction doses of 0 and 17.5-35 Gy in 2.5-Gy steps were delivered to the RSPV antrum (target volume 5-8 cm(3)). MRI and electrophysiology were repeated 6 months after therapy, followed by histopathologic examination.
Transmural scarring of cardiac muscle tissue was noted with doses ≥32.5 Gy. However, complete circumferential scarring of the RSPV was not achieved. Logistic regressions showed that extent and intensity of fibrosis significantly increased with dose. The 50% effective dose for intense fibrosis was 31.3 Gy (odds ratio 2.47/Gy, P<.01). Heart function was not affected, as verified by MRI and electrocardiogram evaluation. Adjacent critical structures were not damaged, as verified by pathology, demonstrating the short-term safety of small-volume cardiac radiosurgery with doses up to 35 Gy.
Radiosurgery with doses >32.5 Gy in the healthy pig heart can induce circumscribed scars at the RSPV antrum noninvasively, mimicking the effect of catheter ablation. In our study we established a significant dose-response relationship for cardiac radiosurgery. The long-term effects and toxicity of such high radiation doses need further investigation in the pursuit of cardiac radiosurgery for noninvasive treatment of atrial fibrillation.
Purpose To assess the changes in corneal hysteresis (CH) as measured by the Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, New York, USA) to describe the influence of clear ...corneal cataract surgery on corneal viscoelastic properties and intraocular pressure (IOP) measured by noncontact tonometry (NCT) and Goldmann applanation tonometry (GAT). Design Retrospective, interventional, comparative study. Methods One hundred and one eyes of 101 consecutive patients who underwent routine clear corneal cataract surgery were evaluated. CH, NCT, and central corneal thickness (CCT) were measured by ORA before surgery and at postoperative day 1. A control group of 48 pseudophakic eyes (surgery >3 months previously) was included. Results CCT increased from 556.82 ± 32.5 μm before surgery to 580.26 ± 45.5 μm after surgery ( P < .001; control, 555.16 ± 42.33 μm). Mean CH decreased from 10.35 ± 2.5 mm Hg before surgery to 9.20 ± 1.9 mm Hg after surgery ( P < .001; control, 10.47 ± 1.63 mm Hg). NCT values rose from 17.85 ± 3.8 mm Hg before surgery to 20.10 ± 6.3 mm Hg after surgery. GAT values were 14.85 ± 2.8 mm Hg before surgery and 15.24 ± 4.1 mm Hg after surgery ( P = .52). There was no significant difference of CCT or CH between the preoperative values and the values of the control group (CCT, P = .986; CH, P = .166), in contrast to the difference between postoperative values and the values of the control group (CCT, P = .005; CH, P = .031). Conclusions At day 1 after clear corneal cataract surgery, CH is diminished, whereas CCT is increased significantly. Postoperative corneal edema leads to a change of corneal viscoelastic properties, resulting in a lower damping capacity of the cornea. It is supposed that GAT and NCT measurements are significantly different because of postoperative changes in viscoelastic properties of the cornea.
In this paper, the authors propose an on-line signal processing algorithm which is capable to significantly improve the performance. After characterizing the dynamic behavior of the sensor system, a ...properly designed deconvolution filter is used to reduce response time and signal noise. They also provide an example of this algorithm for a novel electrochemical sensor for the measurement of the anesthetic agent propofol in exhaled air. For this application, the acceleration is prerequisite for the measurement chain to be of practical use in a clinical setting. The goals, to establish measurement dynamics to record the physiologic parameter and to reduce non-physiological disturbances, were achieved with additional reserves. As an example, they present propofol monitoring in breath of one patient in order to demonstrate the performance of the introduced algorithm in a real clinical application. They proved that the electrochemical sensor, associated with the provided algorithm, is capable for real-time monitoring in a clinical setting.
The transit of ethanol from blood to breath gas is well characterised. It is used for intraoperative monitoring and in forensic investigations. A further substance, which can be measured in breath ...gas, is the phenol propofol. After a simultaneous bolus injection, the signals (time course and amplitude) of ethanol and propofol in breath gas were detected by ion molecule reaction–mass spectrometry (IMR-MS) and compared. After approval by the regional authorities, eight pigs were endotracheally intubated after a propofol-free induction with etomidate. Boluses of ethanol (16 μg/kg) and propofol (4 or 2 mg/kg) were infused alone and in combination. For both substances, breath gas concentrations were continuously measured by IMR-MS; the delay time, time to peak and amplitude were determined and compared using non-parametric statistic tests. IMR-MS allows a simultaneous continuous measurement of both substances in breath gas. Ethanol appeared (median delay time, 12 vs 29.5 s) and reached its peak concentration (median time to peak, 45.5 vs 112 s) significantly earlier than propofol. Time courses of ethanol and propofol in breath gas can be simultaneously described with IMR-MS. Differing pharmacological and physicochemical properties of the two substances can explain the earlier appearance and time to peak of ethanol in breath gas compared with propofol.
As shown previously in goats, clenbuterol increased the power of electrically conditioned skeletal muscle ventricles (SMVs) of clinically relevant size (150 mL), which were constructed around a mock ...system. They pumped against a pressure of 60 to 70 mm Hg immediately during surgery and up to several months after, finally at >1 L/min. SMVs without clenbuterol administration failed. Thus, we expected that clenbuterol-supported SMVs might become integrated into the circulation by a 1-step operation instead of the 2-step procedure required up to now.
In adult Boer goats (n=5), latissimus dorsi muscle was wrapped around a polyurethane chamber of 150 mL that was connected to the descending aorta. This muscular flow-through pumping chamber containing a stabilizing inner layer (called a biomechanical heart BMH) was formed and immediately made to work against a systemic load with the support of clenbuterol (5x150 microg/wk). During surgery, the mean stroke volume of BMHs was 53.8+/-22.4 mL. One month after surgery, in peripheral arterial pressure, the mean diastolic (P(MD)) and minimal diastolic (P(min)) pressures of BMH-supported heart cycles differed significantly from unsupported ones (P(MD)=+2.9+/-1.1 mm Hg P<0.04, P(min)=-2.4+/-0.9 mm Hg P<0.04). After BMH-supported heart contractions, the subsequent maximal rate of pressure generation, dP/dt(max), increased by 20.5+/-8.1% (P<0.02). One BMH, catheterized 132 days after surgery, shifted a volume of 34.8 mL per beat and 1.4 L/min with a latissimus dorsi muscle of 330 g. Depending on duration of training, the percentage of myosin heavy chain type 1 ranged between 31% and 100%.
Under support of clenbuterol, BMHs of a clinically relevant size can be trained effectively in the systemic circulation after a 1-step operation and offer the prospect of a sufficient volume shift and probably unloading of the left ventricle.
PDF
