Dynamic Structures and Materials (United States)

Polyelectrolytes with ionic domains screened by bulkyhydrophobicsegments form processable, hydrophobic complexes called “compleximers”.Ionic liquids, which are chemically similar, further plasticize compleximers,yet the mechanisms behind their plasticization effects and distributionwithin the complexes remain unclear. This study examines the relaxationdynamics of plasticized compleximers across multiple length scalesusing rheology, fluorescence recovery after photobleaching (FRAP),and broadband dielectric spectroscopy (BDS). The incorporation ofionic liquids into compleximers reduces their glass transition temperature(Tg), accelerates diffusive processes,increases segmental motion, and leads to a small decrease in activationenergy associated with these relaxation processes. However, the activationenergies vary substantially between techniques, probing differentphysical processes: approximately 200 kJ/mol in rheology, 50 kJ/molin FRAP, and 90 kJ/mol in BDS. These variations suggest that collectivedynamics strongly influence the compleximer rheology, making the mobilization(and activation) of polymer chains distinct from the local movementof ionic segments.

The development of epoxy resin formulations from renewable feedstocks has been thoroughly explored in the chemical literature. A simple one-pot chemical reaction involving sustainable phenolic molecules and epichlorohydrin results in the production of renewable epoxy monomers. These monomers can be cured with amines or anhydrides to yield cross-linked thermosetting resins. Although a wide variety of recipes exist, there is a notable gap in the application of these sustainable resin formulations to engineering contexts. This gap is primarily due to the lack of comprehensive, standardized analyses of these resin recipes, which impede their potential use in advanced composite applications. In this study, we reveal a high-performance resin formulation utilizing epoxidized phloroglucinol derived from brown algae in combination with an aerospace-grade amine hardener. The resin processing and thermomechanical properties are investigated using ASTM standard tests including tensile strength, flexural strength, fracture toughness, and interlaminar shear strength. Given the detailed comparative analysis, the partially renewable resin recipe outperforms petroleum derived analogues.

Abstract Review: 116 refs.

To revise and update the Acute Physiology and Chronic Health Evaluation (APACHE) model for predicting intensive care unit (ICU) length of stay. Observational cohort study. One hundred and four ICUs in 45 U.S. hospitals. Patients included 131,618 consecutive ICU admissions during 2002 and 2003, of which 116,209 met inclusion criteria. None. The APACHE IV model for predicting ICU length of stay was developed using ICU day 1 patient data and a multivariate linear regression procedure to estimate the precise ICU stay for randomly selected patients who comprised 60% of the database. New variables were added to the previous APACHE III model, and advanced statistical modeling techniques were used. Accuracy was assessed by comparing mean observed and mean predicted ICU stay for the excluded 40% of patients. Aggregate mean observed ICU stay was 3.86 days and mean predicted 3.78 days (p < .001), a difference of 1.9 hrs. For 108 (93%) of 116 diagnoses, there was no significant difference between mean observed and mean predicted ICU stay. The model accounted for 21.5% of the variation in ICU stay across individual patients and 62% across ICUs. Correspondence between mean observed and mean predicted length of stay was reduced for patients with a short (< or =1.7 days) or long (> or =9.4 days) ICU stay and a low (<20%) or high (>80%) risk of death on ICU day 1. The APACHE IV model provides clinically useful ICU length of stay predictions for critically ill patient groups, but its accuracy and utility are limited for individual patients. APACHE IV benchmarks for ICU stay are useful for assessing the efficiency of unit throughput and support examination of structural, managerial, and patient factors that affect ICU stay.

When assessing the effectiveness of home-based geriatric exercise programs in rural communities, some environments preclude using an indoor gymnasium when administering the 6-minute walk component of the Senior Fitness Test. Parking lots or neighborhood sidewalks are often more accessible. PURPOSE To determine the comparability of the 6-minute walk test indoors and outdoors on different surfaces and varying numbers of right angle turns. METHODS Twenty eight chronically exercising adults ≥ age 65 walked outdoors on a paved concrete surface in a 20 yd. by 5 yd. rectangle (i.e., 50 yd. perimeter) following the Senior Fitness Test Manual protocol (Rikli & Jones, 2001). The same individuals also walked indoors on an oval track with a resilient surface (circumference 144.3 yds). Distances walked were measured with a distance measuring wheel. RESULTS Scores for the two methods of administering the test were internally consistent (Cronbach's α = .96). The participants walked farther on the oval track than around the rectangle (647 ± 21 vs. 585 ± 19 yds, p<0.001). Responses to the standard rectangular layout could be predicted from the oval layout by the equation [51.9 yds + 0.840(continuous walking distance), R2 = .85]. CONCLUSION Within participant responses are similar across both versions of the six-minute walk. The walking course layout affects the distance walked, but a simple equation makes the 2 layouts used here readily comparable. Supported by NIH Grant R01 AI49956

Stress testing is integral to evaluate patients with heart disease. However, few data are available regarding safety of stress testing in patients with implantable cardioverter defibrillators (ICDs). Some exercise laboratories consider maximal exercise stress testing and pharmacologic stress testing with dobutamine contraindications in patients with ICDs and some laboratories inactivate ICDs prior to stress testing. PURPOSE The aim of this retrospective study was to assess the safety and feasibility of exercise and pharmacologic stress testing (PST) in patients with ICDs. METHODS Patients with ICD implantation and subsequent stress testing were included in this analysis. Chart review was performed. Primary end-points were occurrence of malignant ventricular arrhythmias (MVAs), onset of burst pacing or ICD firing, cardiopulmonary resuscitation (CPR) or death during stress testing. Secondary end-points were need for urgent coronary revascularization based on stress testing results and hospital readmissions for MVAs. RESULTS From January 1999 to December 2003, 1734 patients underwent ICD implantation or generator replacement. A total of 84 patients subsequently underwent 107 stress tests at William Beaumont Hospital, Royal Oak. Mean age was 67±12 years and 76% were men. Indications for ICD implantation were dilated cardiomyopathy (51%), sustained ventricular tachycardia (39%), sudden cardiac death (8%) and long QT syndrome (1%). 41% underwent exercise stress testing and 59% underwent PST utilizing dobutamine (21%) or dipyridamole (38%). Left ventricular ejection fraction was 32±20. 71% had fixed defects and 22% had reversible perfusion defects as determined by myocardial perfusion imaging. None of the ICDs were inactivated prior to stress testing. Heart rate at peak stress averaged 92±27 beats per minute. 83% were on beta-receptor antagonists. Although 4% of patients had self-terminating, non-sustained ventricular tachycardia at peak stress, none had sustained ventricular tachycardia precipitating burst pacing, ICD shock, CPR or death. One patient underwent urgent coronary angiography, but was found to have non-critical coronary disease. There were no hospital readmissions for MVAs. CONCLUSIONS These preliminary findings suggest that stress testing can be performed safely in patients with ICDs. MVAs requiring emergent treatment are rare occurrences during stress testing. Knowledge of programmed ventricular tachycardia and ventricular fibrillation zones may help predetermine maximal heart rates on stress testing and preclude routine inactivation of ICDs prior to testing.

575 HISTORY - A 78-year-old healthy woman agreed to wear a Holter monitor during her second skydive. The dive was performed in tandem with an instructor and included a brief period of free fall. She had no history of heart disease or cardiovascular symptoms and was only using Timoptic for glaucoma. Heart rate and blood pressure measurements were obtained at baseline, immediately prior to jumping, shortly after landing, and after a recovery period. She reported no symptoms during the jump. She activated the event marker immediately before jumping. Her average resting heart rate was 73 bpm and resting blood pressure 160/84; after touch down her blood pressure was 160/104. Her maximum recorded heart rate during the jump was 147 bpm five seconds prior to jumping. This was equivalent to 89.1% of the maximum heart rate achieved on subsequent exercise stress testing. She exercised using the Bruce protocol for 8.5 minutes and achieved a maximum heart rate of 165 bpm, corresponding to 116% of her age predicted maximal heart rate. Resting blood pressure (BP) was 140/86 mm Hg and the maximum BP was 180/90 mm Hg at peak treadmill exercise. No ST segment displacement was noted. PHYSICAL EXAMINATION - Resting blood pressure was 140/86 mm Hg and the heart rate was 72 bpm. She was a healthy appearing elderly woman who looked younger than her chronologic age. The jugular veins were nondistended, lungs were clear, and the heart had a regular rate and rhythm with no murmurs or gallops. DIFFERENTIAL DIAGNOSIS: Sinus tachycardia secondary to apprehension and catecholamine discharge (i.e., hyperadrenergic response). Tachyarrhythmia. TESTS AND RESULTS: Manual analysis of the Holter recordings confirmed sinus tachycardia. A rapid acceleration of heart rate occurred just before skydiving, approximating 147 bpm which represents 89.1% of her actual maximal heart rate. Thirty-six premature atrial contractions and one ventricular contraction occurred during the 3.6 hours of Holter monitoring. An isolated PVC occurred less than a minute prior to her jump, while no ectopy occurred during the free fall. Infrequent atrial premature contractions occurred during exercise testing. FINAL WORKING DIAGNOSIS: Physiologic sinus tachycardia secondary to apprehension. Dynamic stress testing revealed a maximum heart rate that was considerably higher than that predicted for age; thus, she achieved 89.1% of the peak heart rate attained during maximal exercise testing prior to and during skydiving. The cardiovascular demands of marked apprehension should be considered when counseling elderly patients contemplating engaging in such activities.

1713 Although the potential for cardiac rehabilitation programs (CRP) to attenuate the progression of coronary artery disease (CAD), reduce symptoms, and decrease fatal and nonfatal cardiac events in women (♀) has been documented, <5% of all eligible ♀ with CAD currently participate. Methods: To clarify those variables that facilitate enrollment in CRP, as well as perceived barriers to participation, we retrospectively surveyed (via questionnaire) 297 ♀ who were discharged from a tertiary care hospital in 1998 with a diagnosis of myocardial infarction, balloon angioplasty, bypass surgery, or combinations thereof. Results: 106 ♀ responded (36%), whose ±SD age was 66.6±11.9 yrs. Although the majority of ♀ (78%) were aware of available CRP, only 34% were formally enrolled, suggesting a far lower utilization of these programs among the entire population surveyed (n=297). The primary motivators to participate were physician referral (39%), and the desire to prevent future cardiac events (27%). On the other hand, barriers to participation included the lack of physician encouragement (48%), activity-limiting co-morbidities (36%), a functional capacity deemed sufficient for daily activities (18%), travel difficulties (11%), and suboptimal insurance reimbursement (10%). Interestingly, 31% of the respondents believed that their heart disease had been "cured" by revascularization. Conclusion: The strength of the physician's recommendation appears to be the most powerful predictor of CRP entry. Nearly a third of ♀ surveyed believed their revascularization circumvented the need for a CRP.

Systolic blood pressure (SBP) normally decreases during the recovery phase of graded exercise testing (GXT). In some patients, however, post exercise values of SBP may exceed (>10 mmHg) peak exercise values. To clarify the significance of this observation, we compared 51 subjects ([horizontal bar over]x ± SD age = 66.6 ± 10.5 yrs) who demonstrated this unusual hemodynamic response with a matched control group (n = 51; 62.1 ± 8.7 yrs) who also underwent myocardial perfusion imaging (MPI) with Technetium 99m sestamibi (93% specificity, 90% sensitivity) during GXT. Significant ST-segment depression (ST↓), angina pectoris, and reversible defects by MPI for normal and abnormal SBP responders were: Table Normal and abnormal responders achieved similar age-predicted maximal heart rates (HRmax), 85 and 86% HRmax, respectively; however, the former demonstrated higher MET levels (8.6 ± 2.3 vs. 7.6 ± 2.6; p<0.05). Patients with a recovery SBP > peak exercise SBP were more likely to demonstrate ≥2 indices of myocardial ischemia (p <0.005).Conclusion: An abnormal increase in SBP during the recovery phase of GXT may suggest exercise-induced myocardial ischemia and left ventricular impairment.