Locomotion of electrocatalytic nanomotors due to reaction induced charge autoelectrophoresis.

Bimetallic rod-shaped nanomotors swim autonomously in hydrogen peroxide solutions. Here, we present a scaling analysis, computational simulations, and experimental data that show that the nanomotor locomotion is driven by fluid slip around the nanomotor surface due to electrical body forces. The body forces are generated by a coupling of charge density and electric fields induced by electrochemical reactions occurring on the nanomotor surface. We describe the dependence of nanomotor motion on the nanomotor surface potential and reaction-driven flux.

Pain in the elderly hospice patient.

Pain in the elderly hospice patient presents a complex clinical problem that requires special attention because of the multiple physiologic changes in the older patient. Pain in the elderly is often under-treated despite the fact that this pain can be managed effectively and safely. A basic knowledge of the physiologic changes of aging, as well as the changes in pharmacokinetics, can help the clinician and the hospice team treat pain effectively while minimizing side effects for the patient and the family.

Identification of peripheral vascular disease in elderly subjects using optical spectroscopy.

The purpose of this study was to determine the usefulness of near-infrared spectroscopy (NIRS) measurements to identify peripheral vascular disease (PVD). Usefulness was determined by the frequency of a successful test, as well as comparison with standard clinical assessments. Study subjects (N = 117, mean age = 67.8 +/- 8.1 yrs) responded to a free screening for PVD. NIRS was used to measure the relative O2 saturation of hemoglobin in the soleus muscle. The time to 1/2 recovery of O2 saturation (O2T1/2) was measured after 1 minute of repeated plantar flexions using a Cybex Eagle seated calf machine. O2T1/2 was used as many subjects had recovery curves that did not have an exponential line shape. The test was done on both legs and the worst leg was used for analysis. For comparative purposes, a clinical history and physical examination were performed by a physician or nurse practitioner, which included questions on intermittent claudication, examination of peripheral pulses, and questions to identify cardiovascular risk factors. NIRS signals were obtained on 105 of 117 subjects (89% success rate). Subjects with body mass index (BMI) values above 32 appeared to have NIRS O2T1/2 values that were less reliable than subjects with BMI values < or = 32 (77% success rate). The O2T1/2 was longer in subjects with claudication and reduced pulses than in subjects without these conditions. Sensitivity comparing O2T1/2 to claudication and reduced pulse varied from 51-76% and specificity from 65-80%, depending on the cutoff value for O2T1/2 that was used (normal value plus 1 or 2 SD). A longer O2T1/2 was significantly associated with incidence of diabetes, smoking, hypercholesterol, and coronary bypass surgery. In summary, successful NIRS O2T1/2 measurements were made in 77% of the subjects, with failure primarily occurring in obese subjects. NIRS O2T1/2 measurements showed reasonable although not strong agreements with clinical assessment of PVD, and with some risk factors for cardiovascular disease.

The application of blood flow measurements to the study of aging muscle.

Blood flow to skeletal muscle is a potentially important factor in the reduction of muscle function associated with aging (sarcopenia). The main influence of reduced blood flow capacity on muscle function is in limiting oxidative metabolism. Direct measures of blood flow include: intravital-microscopy, plethysmography, radioactive microspheres, 133Xenon washout, thermodilution, and Doppler ultrasound. Indirect measurement of blood flow includes arm-to-ankle pressure index and the rate of phosphocreatine recovery after exercise. Several new methodologies have been developed to evaluate muscle blood flow, including color-Doppler imaging, magnetic resonance imaging/angiography (MRI/MRA), and near-infrared spectroscopy (NIRS). As adaptations of traditional techniques, these methods promise more precise information under less invasive conditions. MRI is an expensive and technically challenging method able to measure vessel location, blood flow, and wall diameter in blood vessels throughout the cardiac cycle. Color-Doppler provides excellent temporal resolution blood flow throughout the cardiac cycle, along with some anatomical information. NIRS is an inexpensive and portable technology that can measure changes in oxygen saturation and provide information on tissue oxygen delivery in studies of frailer and more difficult-to-study subjects. Muscle blood flow is not thought to limit oxidative metabolism under normal conditions in young individuals. However, it is not clear what happens to muscle blood flow in healthy older individuals. Reduced capillary density, less maximal blood flow, and a slower hyperemic flow response have been reported in some, but not all, studies. Further studies with the newer methodologies are needed to re-examine age-related changes in muscle blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Injuries during the one repetition maximum assessment in the elderly.

PURPOSE: A decrease in strength, and its associated loss of functional ability is common among the elderly. Although resistance training can reverse this decline, associated injuries with frequently used strength assessments may present a greater risk. METHODS: To evaluate the injuries associated with maximal strength evaluations, 83 relatively healthy elderly subjects (40 men and 43 women, 65.8 +/- 6.2 years) with and without prior weight training experience performed 1 repetition maximum testing (1 RM) involving 5 different exercises: chest press, leg extension, abdominal curl, arm curl, and seated calf raise. Subjects were separated into three groups depending on weight training experience, Group 1 had no weight training experience (n = 32), Group 2 had < 6 months of training (n = 24), and Group 3 had > 6 months of training (n = 27). Injury assessment was made 30 minutes, 2 days, and 7 days posttesting. RESULTS: Two Group 1 subjects sustained an injury (2.4% of total subjects, 8% of Group 1). Eighty-one subjects safely completed the 1 RM assessment without injury (97.6% of total). Forty-eight of the 83 subjects complained of muscle soreness after testing (58% of total). This complaint alone was not sufficient to be categorized as an injury. CONCLUSIONS: These results indicate that 1 RM testing is an acceptable tool in strength evaluations in the elderly. Additional precautions may be needed in inexperienced, elderly individuals to prevent injury.

Physical determinants of independence in mature women.

The purpose of this study was to determine the relationship in mature women between muscle strength and whole body oxidative capacity and the ability to perform activities of daily living (ADL). Sixty-one women (mean age 69 years) without major disease or disability were recruited from either a community exercise center or a personal care facility. Physiological measurements consisted of peak oxygen consumption on a cycle ergometer (VO2peak) and one repetition maximum strength of nine muscle groups (1-RM). Ability to perform ADL was measured with a balance and gait test, "Bag Carrying Test", and ADL questionnaires. Significant correlations were found with VO2peak and calf muscle strength and ability to perform ADL, with weaker or no correlations for other muscle groups. For some relationships, it was possible to identify the minimum level of physiological functioning associated with successful performance of independence tasks. In summary, physiological capacities, particularly VO2peak and strength of the calf muscles, predicted ability to perform activities needed for functional independence in healthy mature women.

Simultaneous in vivo measurements of HbO2 saturation and PCr kinetics after exercise in normal humans.

Simultaneous measurements of phosphocreatine (PCr) and oxyhemoglobin (HbO2) saturation were made during recovery from exercise in calf muscles of five male subjects. PCr was measured using magnetic resonance spectroscopy in a 2.0-T 78-cm-bore magnet with a 9-cm-diam surface coil. Relative HbO2 saturation was measured as the difference in absorption of 750- and 850-nm light with use of near-infrared spectroscopy. The light source and detectors were 3 cm apart. Exercise consisted of isokinetic plantar flexion in a supine position. Two 5-min submaximal protocols were performed with PCr depletion to 60% of resting values and with pH values of > 7.0. Then two 1-min protocols of rapid plantar flexion were performed to deplete PCr values to 5-20% of resting values with pH values of < 6.8. Areas of PCr peaks (every 8 s) and HbO2 saturation (every 1 s) were fit to a monoexponential function, and a time constant was calculated. The PCr time constant was larger after maximal exercise (68.3 +/- 10.5 s) than after submaximal exercise (36.0 +/- 6.5 s), which is consistent with the effects of low pH on PCr recovery. HbO2 resaturation approximated submaximal PCr recovery and was not different between maximal (29.4 +/- 5.5 s) and submaximal (27.6 +/- 6.0 s) exercise. We conclude that magnetic resonance spectroscopy measurements of PCr recovery and near-infrared spectroscopy measurements of recovery of HbO2 saturation provide similar information as long as muscle pH remains near 7.0.

Exercise-induced changes in oxygen saturation in the calf muscles of elderly subjects with peripheral vascular disease.

This study noninvasively measured hemoglobin oxygen saturation in young (n = 6, 28 +/- 6 yrs), old healthy (n = 20, 68 +/- 7 yrs), and old subjects with mild peripheral vascular disease (PVD) (n = 8, 72 +/- 4 yrs). Hemoglobin oxygen saturation was measured as the difference in absorption at 760 and 850 nm light using near-infrared spectroscopy (NIRS). The lateral soleus muscle was studied after mild plantar flexion exercise. The time constant of recovery of oxygen saturation (HBO2Tc) was 21.5 +/- 8.6 s in young, 26.9 +/- 13.5 s in old healthy subjects. PVD subjects had HbO2Tc values of 104.4 +/- 41.1 s in their "bad" leg and 57.6 +/- 42.2 s in their "good" leg. The correlation between HbO2Tc and ankle-arm pressures was significant (r2 = .63, p < .001). Six younger normal, five older normal, and seven PVD subjects also performed a progressive walking test. Normal subjects completed the test without difficulty, and older normal subjects showed progressive deoxygenation. PVD subjects complained of calf pain (4 out of 5 were able to finish) and showed near-maximal deoxygenation throughout the test. In summary, NIRS measurements show promise as a method of evaluating the kinetics of oxygen saturation, particularly in patients with mild peripheral vascular disease.

Relationships between in vivo and in vitro measurements of metabolism in young and old human calf muscles.

This study compared in vivo measurements of muscle metabolism in humans with magnetic resonance spectroscopy (MRS) and in vitro analysis of biopsies. Healthy subjects [4 young males, 28.2 +/- 6.8 (SD) yr, and 6 older subjects (5 males, 1 female), 66 +/- 6.0 yr] performed a maximal cycle ergometer test, and MRS measurements of the calf muscles and needle biopsies of the lateral gastrocnemius were performed. Biopsies were analyzed for fiber type and citrate synthase (CS) activity. MRS measurements of inorganic phosphate (Pi), phosphocreatine (PCr), ATP, and pH were made using a 1.8-T 78-cm clear-bore magnet-and-spectrometer system. Two or three 5-min bouts of plantar flexion were performed against variable resistance to deplete PCr levels to 50% of resting values (mean end pH 6.99). PCr values during recovery were fit to an exponential curve, and the rate constant (PCrrate) was calculated. PCrrate was used as an index of oxidative metabolism. Older subjects had lower peak O2 uptake (VO2 peak) values (19.2 +/- 5.6 vs. 49.5 +/- 8.1 ml O2.min-1 x kg-1), CS activities (16 +/- 2.8 vs. 25 +/- 2.6 mmol.kg wet wt-1 x min-1), and PCrrate values (25.3 +/- 8. vs. 37.5 +/- 5.3 mmol PCr.kg wet wt-1.min-1) than young subjects. PCrrate correlated with CS activity, and both PCrrate and CS activity correlated with VO2 peak (P < 0.05). No correlations were found between percent fiber type and PCrrate, CS activity, and VO2 peak. These results support studies that showed decreases in muscle metabolism with age in healthy humans and show a good correlation between in vivo and in vitro measurements of oxidative metabolism.

Patterns of self-care needs and interventions related to biologic response modifier therapy: fatigue as a model.

Many patients receiving biologic response modifier (BRM) therapy experience fatigue as a significant and, at times, dose-limiting side effect. For this reason, a multiinstitutional pilot study was designed to collect data about the needs and self-care interventions of patients who had undergone at least one prior treatment with a BRM and had experienced fatigue as a symptom. Information was also obtained on the extent to which the needs and self-care interventions identified by patients compared with those perceived by their family members and nurses. Of the 16 patients who participated in the study, seven were being treated with interleukin-2 (IL-2), eight with interferon alfa (IFN-alpha), and one with tumor necrosis factor (TNF). The study found no significant correlation between the degree or duration of fatigue and the BRM or dosage administered. Not surprisingly, patient and family member responses correlated fairly well. However, in several parameters, including the degree and duration of fatigue, nurses' perceptions did not correlate at all with those of the patient. While 46% of nurse responses matched those of the patient as to useful self-care interventions, only 17% of nurses accurately identified factors or events that patients perceived as worsening fatigue. Further, there was no correlation among patient, family member, and nurse responses on interventions that could be used by others to help the patient cope with fatigue. The overall results of this pilot study indicate that nurses need to be more attuned to assessing fatigue as a side effect of BRM therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle metabolism in track athletes, using 31P magnetic resonance spectroscopy.

We tested whether preferred running event in track athletes would correlate with the initial rate of phosphocreatine (PCr) resynthesis following submaximal exercise. PCr recovery was measured in the calf muscles of 16 male track athletes and 7 male control subjects following 5 min of repeated plantar flexion against resistance. Pi, PCr, and pH were measured using phosphorus magnetic resonance spectroscopy (31P MRS) with an 8-cm surface coil in a 1.8-T magnet. During exercise, work levels were gradually increased to deplete PCr to 50-60% of the initial value. No drop in pH was seen in any of the subjects during this exercise. The areas of the PCr peaks following exercise were fit to monoexponential curves. Two or three tests were performed on each subject and the results averaged. Athletes were divided into three groups based on their primary event: sprinters running 400 m or less, middle-distance athletes running 400-1500 m, and long-distance athletes running farther than 1500 m. The maximal rates of PCr resynthesis (mmol.min-1.kg-1 muscle weight) were 64.8 +/- 8.6, for long-distance runners; 41.4 +/- 11, for middle-distance runners; 32.0 +/- 7.0, for sprinters; and 38.6 +/- 10, for controls (mean +/- SE). The faster PCr recovery rates seen in long-distance runners compared with sprinters indicate greater oxidative capacity, which is consistent with the known differences between athletes in these events.

The use of nuclear magnetic resonance to evaluate muscle injury.

Magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) are new and powerful tools to study tissue biochemistry, and to provide precise anatomical visualization of soft tissue structures. This review focuses on the use of these techniques to study exercise-induced muscle injury. MRS measurements show an increase in the ratio of inorganic phosphate to phosphocreatine (Pi/PCr) 1-7 d after eccentric exercise. This increase in Pi/PCr could be due to either increases in extracellular Pi or small increases in resting muscle metabolism. Increased Pi/PCr is also seen during training programs and may indicate persistent muscle injury. Increased resting Pi/PCr with injury was not associated with altered metabolism during exercise. Elevations in resting Pi/PCr have been used to show increased susceptibility of dystrophic muscle to exercise-induced injury. Progressive clinical deterioration in dystrophic dogs is marked by impaired muscle metabolism, and the presence of low oxidative muscle fibers not seen in normal dogs. MRI shows increased proton T2 relaxation times following eccentric exercise that last up to 80 d after injury, and can reflect muscle edema as well as longer lasting changes in the characteristics of cell water. MRI demonstrate precise localization of the injured area, with large differences in both location and degree of injury in different subjects following the same exercise protocol. Thus, MRS can provide information on the metabolic response to injury, while MRI provides information regarding the site and extent of the injury. These tools have promise in helping to understand exercise-induced muscle injury.

Low to moderate intensity endurance training in healthy older adults: physiological responses after four months.

OBJECTIVE: To determine the physiological adaptations in previously sedentary healthy older men and women (mean age = 68) to a 16-week low-to-moderate-intensity exercise program. DESIGN: Randomized, controlled trial. SETTING: An exercise facility and testing laboratory in a gerontological research institute. PARTICIPANTS: Two-hundred forty-seven community-dwelling older persons free of significant cardiovascular, pulmonary, or uncontrolled metabolic disease, anemia, electrolyte abnormality, resting BP of 165/90 or greater, or chronic disease affecting the ability to exercise on a bicycle. INTERVENTION: Subjects were randomly assigned to either an exercise (n = 166) or attention control group (n = 81). Exercisers trained thrice weekly for 40 minutes on a cycle ergometer (5-minute warm up, 30 minutes at training heart rate (THR), 5-minute cool down). THR was set at 70% of peak heart rate attained on a maximal exercise test (mean = 115 +/- 15). Control subjects attended weekly group talks. Testing took place before and after the program. RESULTS: Peak attained oxygen uptake (VO2max) increased 8.5% in exercisers and decreased slightly in controls (p less than .001) and oxygen uptake at ventilatory threshold (VeT VO2) increased by 3.5% in exercisers and decreased by 3% in controls (p less than .001). This pattern of a greater increase in VO2max than VeT VO2 is different from that seen in young and middle-aged subjects. CONCLUSION: This study demonstrated that a large scale training program is feasible for healthy older people, that physiologic improvements can be measured after 16 weeks of low-to-moderate-intensity training, and that mechanisms of adaptation to exercise may be different in elderly subjects from those in younger ones.

Effects of exercise training in the elderly on the occurrence and time to onset of cardiovascular diagnoses.

To examine the long-term effects of aerobic exercise on the occurrence and time to onset of cardiovascular diagnoses, 184 initially healthy older subjects were randomized into either a long-term exercise group (Group A, n = 80), a short-term exercise group (Group B, n = 42), or a contract control group (Group C, n = 62). After completion of two years in the study, data on new cardiovascular diagnoses and time to onset of these diagnoses in each of the three groups were compared. The occurrence rates for new onset diagnoses were as follows: Group A, 2.5%; Group B, 2%; and Group C, 13%; the average time to onset was greatest for the long-term exercisers and shortest for the contact control group (P less than or equal to .02). The results suggest that a regular program of exercise may have cardiovascular benefits for those over 60 years of age.

Benefits of exercise in old age.

Although exercise capacity declines with age, the decline appears to be slight when measured in healthy, physically active subjects. There is growing evidence that exercise has a positive influence on increasing healthy function and decreasing the impact of diseases common in the elderly. While the dose-response relationship between physical activity and health benefits continues to be studied, there is some evidence that even low- and moderate-intensity exercise programs in older people result in tangible improvements in many physical and psychologic parameters.

Ventilatory threshold: measurement and variation with age.

The purpose of this study is to present measurement of ventilatory threshold (VeT) and maximal oxygen uptake (VO2max) in a large group of predominantly older subjects using a bicycle ergometer and an automated measuring system. One hundred and twenty-seven healthy elderly subjects (mean age: 68) and 44 young and middle-aged subjects (mean age: 39) underwent a maximal exercise test with breath-by-breath measurement of ventilation and gas exchange variables. Ventilatory threshold was determined by visual inspection of the breakpoints in the VE/VO2 and PETO2 data curves. Additional measures were made in a subset of subjects to determine the reproducibility and interobserver variability of VeT and the relationship between VeT and the venous lactate threshold (LaT). Day-to-day reproducibility of VeT was good with a mean difference in VO2 at VeT on two occasions of 40.23 +/- 125 ml/min. Interobserver variability was low (intraclass correlation coefficient of r = 0.941) and VeT was found to correlate to LaT (r = 0.79, P less than 0.05) with LaT occurring a mean 2.3 min after VeT. VeT declined significantly with age in both males and females but less rapidly than VO2max. Both VO2max and VeT were found to vary with age, sex, height, and weight in a stepwise multiple-linear regression analysis. Age-associated changes in skeletal muscle composition may be in part responsible for the less precipitous decline in VeT with age compared with VO2max.

Exercise capacity in the elderly.

One of the primary manifestations of ageing is a reduced ability to respond to physiologic challenges. With aging, the ability to perform exercise and physical work declines and is reflected in the reduction in maximal oxygen consumption. Although this decline is influenced to some degree by the state of health and age, it seems that maintenance of regular physical activity significantly counteracts the loss of aerobic capacity. In healthy old age, the cardiovascular system is able to compensate for certain age-associated declines in cardiac function. A program of endurance training, even when begun in old age, can restore more youthful levels of physical fitness and results in tangible improvements in certain resting, submaximal and maximal indicators of exercise capacity. With comprehensive preexercise clinical screening, physical training can be conducted safely with minimal musculoskeletal problems in the aged. The long-term effects of exercise on morbidity, mortality and psychologic function in old age are unknown.

Particular problems of antibiotic use in the elderly.

In prescribing antibiotics for older patients it is important to recognize the side effects as they are known in both older and younger people. It is particularly important to be aware of those side effects that appear to occur earlier in older patients, and also of those that may be masked in older people, eg, some of the neurotoxic syndromes. The number of drugs prescribed for geriatric patients should be kept to a minimum and meticulous records of all side effects noted. It may be impossible to decide which side effect is due to each drug in any given person, but by careful reporting and record-keeping, we may achieve a better separation of age-related drug complications from drug-drug interactions or the effects of concomitant disease states.