Extubation force depends upon angle of force application and fixation technique: a study of 7 methods

BACKGROUND: Endotracheal tubes are frequently used to establish alternate airways. Precise placement of the tubes must be maintained to prevent serious complications. Several methods for fixation of endotracheal tubes are available. Available methods vary widely in form and functionality. Due to the unpredictable and dynamic nature of circumstances surrounding intubation, thorough evaluation of tube restraints may help reduce airway accidents such as tube dislodgement and unplanned extubation. METHODS: Seven different tube-restraint combinations were compared against themselves and one another at a series of discrete angles (test points) covering a hemisphere on the plane of the face. Force values for tube motion of 2 cm and 5 cm (or failure) were recorded for 3 pull tests, at each angle, for each method of tube fixation. RESULTS: All methods showed variation in the force required for tube motion with angle of force application. When forces were averaged over all test points, for each fixation technique, differences as large as 132 N (30 lbf) were observed (95% CI 113 N to 152 N). Compared to traditional methods of fixation, only 1 of the 3 commercially available devices consistently required a higher average force to displace the tube 2 cm and 5 cm. When ranges of force values for 5 cm displacement were compared, devices span from 80–290 N (18–65 lbf) while traditional methods span from 62–178 N (14–40 lbf), highlighting the value of examining forces at the different angles of application. Significant differences in standard deviations were also observed between the 7 techniques indicating that some methods may be more reproducible than others. CONCLUSIONS: Clinically, forces can be applied to endotracheal tubes from various directions. Efficacies of different fixation techniques are sensitive to the angle of force application. Standard deviations, which could be used as a measure of fixator reliability, also vary with angle of force application and method of tube restraint. Findings presented in this study may be used to advance clinical implementation of current methods as well as fixator device design in an effort to reduce the incidence of unplanned extubation

Persistence of Albunex (ALB) Ultrasound Contrast Agent – Invitro Study of the Effects of Pressure and Acoustic Power on Particle-Size, and the Duration of Contrast and Doppler Enhancement

LV contrast intensity after intravenous ALB injection varies with the cardiac cycle, raising questions about the pressure related stability of the particle. We explored pressure stability and the influence of acoustic power on ALB effect in an in-vitro pulsatile model at receiving chamber (RC) pressures between 10-160 mmHg. Ultrasound imaging was performed at 5MHz along with 3.5MHz color Doppler at maximal and minimal levels of acoustic power output on a VingMed CFM scanner. We also studied the effects of static RC pressure on particle size and survival using a new phase shift laser Doppler device (Dantec). An inverse relationship existed between RC mean pressure and the duration of both echo and Doppler enhancement (r-0.95 and r-0.94, respectively). At 40-80 mmHg RC pressures, contrast persistence determinations were shorter at the higher compared to the lower acoustic power output (p- <0.05). On laser Doppler study, particle size decreased as RC pressure increased prior to particle disruption. Higher RC pressures com· press the ALB micro particle and decrease its half-life. Increased acoustic output may also shorten ALB effect

SBC2007-175993 MEASUREMENT OF IN-VIVO PULMONARY VASCULAR IMPEDANCE IN TWO ANIMAL MODELS OF PULMONARY HYPERTENSION

INTRODUCTION Pulmonary vascular input impedance has been increasingly promoted as an important diagnostic for pulmonary arterial hypertension (PAH) The human studies noted above have understandably not examined detailed associations between impedance and vascular behavior and structure, since the latter data are obtainable only through focused drug studies or ex-vivo measurements. Mechanical changes to a vascular network should be reflected in its input impedance; thus, such investigation should be useful in determining how impedance varies with changes in vascular condition, such as chronic stiffening due to vascular remodeling or acute stiffening due to smooth muscle cell response and/or pressure-induced strain-stiffening. Naturally, clinical identification of such stiffness changes on a routine basis could greatly impact diagnosis. Here, we demonstrate simple-toimplement impedance measurements in two animal models as part of a larger effort to establish said links between clinically-viable diagnostics, such as impedance, and physiological changes that occur to the vasculature as part of the progression of PAH. METHODS Animal Preparation: The two animal models examined here develop PAH due to chronic exposure to a hypoxic environment. The first model consisted of 10 male Sprague-Dawley rats (300-400g), half exposed to hypoxia via hypobaric chamber for 3-4 weeks (barometric pressure ≈ 410 mmHg) and half retained at standard conditions in Denver, CO (barometric pressure ≈ 630 mmHg). The second model utilized 4 male Holstein calves (70-110lb), again with half exposed to hypoxia for two weeks (barometric pressure ≈ 460 mmHg) and the other half remaining normoxic. Both models were exposed to a 12:12-h light-dark cycle, and water and appropriate food were made available ad libitum. Animal care and use committees at both the University of Colorado Health Science Center (rat) and Colorado State University (calf) approved all protocols and procedures. Animal Data Collection and Analysis: The measurements obtained from each animal are identical; the main differences between collection methods are equipment size and type. For all measurements, rats are anesthetized with ketamine hydrochloride (40 mg/kg) and xylazine (10 mg/kg) intraperitoneally, while cows remain conscious. Right jugular access is then obtained in each animal, and a fluid filled catheter, consisting of PV1 tubing for the rat or a commercial Swan-Ganz catheter for the calf, is inserted into the main pulmonary artery (MPA) for pressure measurements. During collection of MPA pressure, blood velocity at the midline of the MPA is obtained with pulse-wave Doppler echocardiography using an FPA probe on a commercial ultrasound scanner (Vivid 5, GE Medical Systems Inc). The imaging depth dictates the probe frequency

Circulating miRNAs in Pediatric Pulmonary Hypertension Show Promise as Biomarkers of Vascular Function

Background/Objectives. The objective of this study was to evaluate the utility of circulating miRNAs as biomarkers of vascular function in pediatric pulmonary hypertension. Method. Fourteen pediatric pulmonary arterial hypertension patients underwent simultaneous right heart catheterization (RHC) and blood biochemical analysis. Univariate and stepwise multivariate linear regression was used to identify and correlate measures of reactive and resistive afterload with circulating miRNA levels. Furthermore, circulating miRNA candidates that classified patients according to a 20% decrease in resistive afterload in response to oxygen (O2) or inhaled nitric oxide (iNO) were identified using receiver-operating curves. Results. Thirty-two circulating miRNAs correlated with the pulmonary vascular resistance index (PVRi), pulmonary arterial distensibility, and PVRi decrease in response to O2 and/or iNO. Multivariate models, combining the predictive capability of multiple promising miRNA candidates, revealed a good correlation with resistive (r=0.97, P2−tailed<0.0001) and reactive (r=0.86, P2−tailed<0.005) afterloads. Bland-Altman plots showed that 95% of the differences between multivariate models and RHC would fall within 0.13 (mmHg−min/L)m2 and 0.0085/mmHg for resistive and reactive afterloads, respectively. Circulating miR-663 proved to be a good classifier for vascular responsiveness to acute O2 and iNO challenges. Conclusion. This study suggests that circulating miRNAs may be biomarkers to phenotype vascular function in pediatric PAH

Injectable Carbon Nanotube-Functionalized Reverse Thermal Gel Promotes Cardiomyocytes Survival and Maturation

The ability of the adult heart to regenerate cardiomyocytes (CMs) lost after injury is limited, generating interest in developing efficient cell-based transplantation therapies. Rigid carbon nanotubes (CNTs) scaffolds have been used to improve CMs viability, proliferation, and maturation, but they require undesirable invasive surgeries for implantation. To overcome this limitation, we developed an injectable reverse thermal gel (RTG) functionalized with CNTs (RTG-CNT) that transitions from a solution at room temperature to a three-dimensional (3D) gel-based matrix shortly after reaching body temperature. Here we show experimental evidence that this 3D RTG-CNT system supports long-term CMs survival, promotes CMs alignment and proliferation, and improves CMs function when compared with traditional two-dimensional gelatin controls and 3D plain RTG system without CNTs. Therefore, our injectable RTG-CNT system could potentially be used as a minimally invasive tool for cardiac tissue engineering efforts

Shape Memory Polymers Containing Higher Acrylate Content Display Increased Endothelial Cell Attachment

Shape Memory Polymers (SMPs) are smart materials that can recall their shape upon the application of a stimulus, which makes them appealing materials for a variety of applications, especially in biomedical devices. Most prior SMP research has focused on tuning bulk properties; studying surface effects of SMPs may extend the use of these materials to blood-contacting applications, such as cardiovascular stents, where surfaces that support rapid endothelialization have been correlated to stent success. Here, we evaluate endothelial attachment onto the surfaces of a family of SMPs previously developed in our group that have shown promise for biomedical devices. Nine SMP formulations containing varying amounts of tert-Butyl acrylate (tBA) and Poly(ethylene glycol) dimethacrylate (PEGDMA) were analyzed for endothelial cell attachment. Dynamic mechanical analysis (DMA), contact angle studies, and atomic force microscopy (AFM) were used to verify bulk and surface properties of the SMPs. Human umbilical vein endothelial cell (HUVEC) attachment and viability was verified using fluorescent methods. Endothelial cells preferentially attached to SMPs with higher tBA content, which have rougher, more hydrophobic surfaces. HUVECs also displayed an increased metabolic activity on these high tBA SMPs over the course of the study. This class of SMPs may be promising candidates for next generation blood-contacting devices

An Implantable Transit-Time Aortic Flow Probe Using Capacitive Micromachined Ultrasound Transducers: Design and Optimization

Monitoring cardiac output continuously post-surgery for children with congenital heart disease is an important part of post-operative recovery, especially given the potential for large changes in vascular pressure as a side-effect of pharmaceutical agents given to help recovery. Current methods to monitor cardiac output are limited by the requirement for invasiveness (cuff-type flow probes), or do not provide continuous monitoring (ultrasound Doppler). Using a combination of analytical and finite element modeling, we explore the design and optimization of a unique ultrasonic transit-time flow probe that extends the capability of current devices by providing greater miniaturization, better sensitivity, and lower cost through the use of capacitive micromachined ultrasound transducer (cMUT) technology.</jats:p