Reversal of Soleus Muscle Atrophy in Older Adults: A Non-Volitional Exercise Intervention for a Changing Climate.

The World Health Organization recommends that older adults undertake at least 150 minutes of moderate intensity physical activity over the course of each week in order to maintain physical, mental, and social health. This goal turns out to be very difficult for most community dwelling older adults to achieve, due to both actual and perceived barriers. These barriers include personal health limitations, confinement issues, and self-imposed restrictions such as fear of injury. Climate change exacerbates the confinement issues and injury fears among the elderly. To assist older adults in obtaining the benefits of increased physical activity under increasingly challenging climate conditions, we propose a targeted non-volitional intervention which could serve as a complement to volitional physical activity. Exogenous neuro-muscular stimulation of the soleus muscles is a non-invasive intervention capable of significantly increasing cardiac output in sedentary individuals. Long-term daily use has been shown to improve sleep, reduce bone loss, and reverse age-related cognitive decline, all of which are significant health concerns for older adults. These outcomes support the potential benefit of exogenous neuro-muscular stimulation as a complementary form of physical activity which older adults may find convenient to incorporate into their daily life when traditional forms of exercise are difficult to achieve due to barriers to completing traditional physical activities as a result of in-home or in-bed confinement, perceptual risks, or real environmental risks such as those arising from climate change.

Pulsed shortwave electromagnetic field therapy increases quality of life in canines with symptoms of osteoarthritics.

BACKGROUND: Joint stiffness, lameness and reduced activity levels are common inflammatory responses observed in canines and have significant impact on quality of life (QOL). The symptoms are often ascribed to osteoarthritis (OA), for which the standard treatment is systemic anti-inflammatories, but pharmacologic intervention can have significant short-term and long-term side effects. OBJECTIVES: Test the efficacy of a Food and Drug Administration (FDA)-cleared pulsed shortwave therapy (PSWT) device as a means to modulate vagus nerve activity and initiate a systemic anti-inflammatory response to determine its ability to improve functionality and the QOL of canines with inflammatory symptoms commonly associated with OA. METHODS: A randomized, double-blinded, placebo-controlled 14-day study of 60 dogs with a presumptive prior diagnosis of OA in at least one limb joint. Two outcomes assessing changes in the dog's QOL and functionality were measured: subjectively determined changes in eight behaviours associated with discomfort and objectively determined changes in passive range of motion (PROM). The device was secured near the cervico-thoracic region of the dog's spine. PROM measures were taken at baseline and at the end of study. Behavioural measures were taken daily. RESULTS: Forty-nine animals completed the study. No negative side effects were reported. Average subjective discomfort scores for the treatment group (N = 26) were reduced from 3.74 to 2.10 (44%), compared to no improvement in the placebo group (N = 23) over the study period (p = 0.0001). Average PROM scores increased by 5.51 (4.59-6.23) degrees relative to the placebo group (p < 0.01). Ninety-six per cent of the treatment group showed either increased PROM or improved behavioural changes or both, compared to 4% for the placebo group (p < 0.01). Most changes occurred within the first 8 days of treatment. CONCLUSIONS: PSWT applied at the level of the cervico-thoracic spine to target the vagus nerve may have the potential to improve QOL in dogs manifesting behaviours commonly associated with OA.

Reversal of cognitive impairment in a hypotensive elderly population using a passive exercise intervention.

BACKGROUND: Cognitive decline in the elderly is strongly associated with cerebral hypoperfusion, a condition that can be reversed with exercise. Adhering to a traditional exercise regimen, however, is challenging for this population. OBJECTIVE: In a pilot clinical study, we evaluated the ability of a "passive" exercise regimen (noninvasive calf muscle pump stimulation) to normalize blood pressure in a chronically hypotensive elderly population and enhance cognitive function. PARTICIPANTS AND METHODS: Ten elderly (82.5±7.5 years) men and women volunteers, residing in a senior living facility in upstate New York, were divided into control (N=5) and intervention (N=5) groups based on initial diastolic blood pressure (DBP); participants with initial DBP <65 mmHg became intervention participants, and those with initial DBP >65 mmHg enrolled in the control group. Body mass, blood pressure, and executive function (using incongruent Stroop and Trailmaking B test) were evaluated weekly for 4 months. RESULTS: At initiation of the study, time to complete the executive function tests in the hypotensive group was almost twice that of the control group. Daily calf muscle pump stimulation (passive exercise) for 1 hour/day, or less, was found to be sufficient to normalize DBP and significantly improve performance on the executive function tests.

Postural Hypotension and Cognitive Function in Older Adults.

Background: Cognitive decline in the elderly is associated with chronic cerebral hypoperfusion. While many forms of exercise can slow or reverse cognitive decline, compliance in unsupervised exercise programs is poor. Objective: We address whether passive exercise, that is, muscle stimulation, is capable of reversing postural hypotension in an older adult population sufficiently to significantly improve cognitive function as measured by executive function tests. Subjects and Methods: In this study, 50- to 80-year-old women underwent cognitive testing, long-duration cardiac hemodynamic recordings during quiet sitting, and 60 min of soleus muscle stimulation with continued hemodynamic recording. Results: Two thirds of our subjects were hypotensive (diastolic blood pressure [DBP] < 70 mmHg) after 30 min of quiet sitting. Cognitive performance was significantly better in individuals with higher DBPs (0.79 s per 1-mmHg increase in DBP). Soleus muscle stimulation resulted in an average increase in DBP of 6.1 mmHg, which could translate into a 30% or greater improvement in cognitive performance. Conclusions: Incongruent Stroop testing provides high statistical power for distinguishing differential cognitive responses to resting DBP levels. These results set the stage to investigate whether regular use of calf muscle pump stimulation could effectively reverse age-related cognitive impairment.

Association of Calf Muscle Pump Stimulation With Sleep Quality in Adults.

Prevention of lower extremity fluid pooling (LEFP) is associated with improved sleep quality. Physical activity and compression stockings are non-invasive methods used to manage LEFP, but both are associated with low adherence. Calf muscle pump (CMP) stimulation is an alternative and more convenient approach. Convenience sampling was used to recruit 11 participants between ages 45 and 65 with poor sleep quality. A within-person single-group pre-test-post-test design was used to evaluate changes in sleep quality, daytime sleepiness, and functional outcomes sensitive to impaired sleep as measured by the Pittsburgh Sleep Quality Index (PSQI), Functional Outcomes of Sleep Questionnaire, and Epworth Sleepiness Scale after 4 weeks of CMP stimulation. Statistical analysis included effect size (ES) calculations. After daily use of CMP stimulation, participants demonstrated improvement in overall sleep quality (ES = -.97) and a large reduction in daily disturbance from poor sleep (ES = -1.25). Moderate improvements were observed in daytime sleepiness (ES = -.53) and functional outcomes sensitive to sleepiness (ES = .49). Although causality could not be determined with this study design, these results support further research to determine whether CMP stimulation can improve sleep quality. © 2016 Wiley Periodicals, Inc.

Calf muscle pump stimulation as a means to reduce symptoms of fibromyalgia syndrome.

Fibromyalgia (FM) is a debilitating chronic condition that often affects women in midlife with widespread pain that interrupts attempts to exercise. The purpose of this pilot study was to test the efficacy of calf muscle pump (CMP) stimulation as an adjuvant therapy for FM by (1) assessing the correlation of the level of symptoms, as measured by the revised Fibromyalgia Impact Questionnaire (FIQR), and blood pressure (BP), (2) measuring change in mean FIQR scores for subjects who use a CMP-stimulation device for 12 weeks, and (3) measuring the correlation of total device usage and the level of symptoms as measured by the FIQR. The 29 male and female participants (mean age = 47.3 years) were screened using the Widespread Pain Index (WPI), Symptom Severity (SS) score, and the FIQR. Participants were contacted weekly, and progress was assessed using the WPI, SS score, and the FIQR as well as general questions regarding responses to CMP stimulation. The attrition rate was high, which is not uncommon in studies of patients with FM. We found that diastolic BP was significantly inversely correlated with baseline FIQR scores during quiet sitting. Further, 12 weeks of CMP stimulation was associated with significant improvement in average FIQR scores at a rate of approximately -1.5 points per week (R (2) = .9; p ≤ .0001). Total device usage was strongly and inversely correlated with baseline FIQR scores (R (2) = .43; p = .02). These findings suggest that CMP stimulation may provide an additional treatment option for individuals with FM who are challenged to perform traditional forms of exercise.

Feasibility of treatment of lower limb edema with calf muscle pump stimulation in chronic heart failure.

BACKGROUND: Persons with chronic heart failure may exhibit a decrease in functional ability related to lower extremity edema in spite of optimal diuretic therapy and salt restrictions. AIM: The aim of this pilot prospective clinical study was to test the feasibility of using exogenous calf muscle pump stimulation to decrease lower leg edema and thus improve functional status and quality of life. METHODS: Six subjects entered into this study and agreed to use the intervention 30 min/day for one month. DXA was used to assess lower extremity composition. RESULTS: Device use averaged approximately 1 h/day and resulted in a reduction in the lean mass of the legs of 0.5 kg (range = 0.08-1.0 L; p = 0.03). Linear regression analysis of reduction of lower limb edema against daily usage suggests that increased utilization of calf muscle pump stimulation was associated with increased water losses, although this trend was not significant (R(2 = 0.4, p = 0.18). CONCLUSION: This pilot indicates that exogenous calf muscle pump stimulation could be a useful and safe addition to the patients' treatment regimes, but further studies testing a more typical population with heart failure is warranted.

Influence of seated rocking on blood pressure in the elderly: a pilot clinical study.

Patients with Alzheimer's disease (AD) who rock for 1-2 hr per day in a rocking chair demonstrate significant improvements in depression, anxiety, and balance and a decrease in pain medication usage; however, the underlying basis for their responses remains unclear. Rocking with plantar flexion uses the calf muscles, enhancing lower limb fluid return to the heart, which should increase blood pressure (BP) and may, then, also increase cerebral perfusion. Accordingly, we tested the efficacy of rocking activity for increasing BP in healthy, older persons. In a pilot laboratory study of 24 healthy, White men and women aged 55-87 years, we observed that 30 min of steady rocking led to an average 12 mmHg increase in systolic blood pressure (SBP, p < .001) and a 3.6 mmHg average increase in diastolic blood pressure (DBP, p < .001). To determine the effect of using this intervention in a nonclinical setting, we tested a similar group of 7 participants at a senior center. In this setting, we observed an average increase in SBP of 27 mmHg (p < .001) and in DBP of 2.5 mmHg (p < .001) after 30 min of rocking. In a subgroup (n = 8) of hypotensive individuals (SBP < 110 mmHg after sitting quietly for 30 min) extracted from both settings, rocking raised the average SBP from <100 mmHg to approximately 120 mmHg. These results are consistent with the hypothesis that rocking can increase BP and, therefore, may enhance cerebral perfusion. This observation may play a fundamental role in designing nursing interventions focused on improvement of symptoms associated with AD.

Enhancing hemodialysis efficacy through neuromuscular stimulation.

Beat-to-beat blood pressure monitoring was used to assess the efficacy of reflex-mediated, calf muscle pump stimulation to enhance cardiovascular refilling in subjects in the supine and seated positions, with extension of this stimulation technology to dialysis evaluated in 2 dialysis patients. Micromechanical stimulation (50 mum at 45 Hz) of the plantar surface was found to significantly increase both the rate and volume of cardiovascular refilling relative to that observed for subjects in the supine position. During hemodialysis, calf muscle pump stimulation permitted significantly increased ultrafiltrate removal, specifically from 78 to 96% of clinical goal, while serving to maintain both blood pressure and blood volume.

Prevalence and etiology of delayed orthostatic hypotension in adult women.

OBJECTIVE: To evaluate the contributing roles of venous status, microvascular filtration, and calf muscle pump activity in the etiology of delayed orthostatic hypotension (OH). DESIGN: Unblinded within-subjects trial. SETTING: Academic clinical research center. PARTICIPANTS: Convenience sample of healthy adult women (N=30) with an age range of 30 to 65 years. INTERVENTION: Plantar micromechanical stimulation applied at a 45-Hz frequency and a 50-microm amplitude for a duration of 30 minutes during upright sitting. MAIN OUTCOME MEASURE: Diastolic blood pressure (DBP). RESULTS: White women (mean age, 51.8+/-1.3 y) were recruited and screened for delayed OH. About one quarter (9/33) of the screened subjects showed delayed OH as determined by a significant decrease in blood pressure after at least 15 minutes of quiet sitting. Air plethysmographic assessment provided no evidence of venous insufficiency (venous filling index, >2.5 mL/s; venous volume, >80 mL) or excessive microvascular filtration in the affected subjects, whereas activation of the calf muscle pump (CMP) through plantar-based micromechanical stimulation consistently resulted in a significant increase in systolic blood pressure (SBP) (DeltaSBP=22.8+/-3.9 mmHg, P=.003) and DBP (DeltaDBP=20.9+/-3.3 mmHg, P=.002). CONCLUSIONS: About 25% of the adult women studied showed delayed OH during quiet sitting and the proximate cause appears to be neuromuscular in origin, specifically inadequate calf muscle tone, because venous and microvascular filtration status is normative in the delayed OH subpopulation and CMP stimulation reverses the hypotension.

Reversal of lower limb edema by calf muscle pump stimulation.

BACKGROUND: Peripheral edema (PE) is commonly coupled with heart failure, restrictive cardiomyopathy, nephrotic syndrome, renal failure, and hypoproteinemia. Diuretics and/or limb elevation, although commonly prescribed to treat PE, are often insufficient to remove sufficient fluid to prevent complications. We assessed the ability of the calf muscle pump (CMP) stimulation to reverse PE. METHODS: Fluid volume was evaluated by air plethysmography in the right legs of 54 adult women (mean age 46.7 +/- 1.5 years) following venous status assessment. Change in calf volume was assessed during 30 minutes of quiet sitting, followed by 30 minutes of sitting with CMP stimulation via micromechanical stimulation of the plantar surface. RESULTS: Leg volume changes demonstrated a bimodal distribution. Leg volume decreased during quiet sitting in 56% of the study group, whereas in 44% of the group, significant lower leg fluid pooling was evident (increase in calf volume of 14.0 +/- 0.3 mL/h). CMP stimulation reversed the fluid pooling in the edematous group (-2.7 +/- 0.1 mL/h) and was able to accelerate fluid removal in the nonedematous group. CONCLUSIONS: Approximately two fifths of adult women experience substantial pooling when their lower limbs are maintained in a dependent position. Lower-extremity edema exhibited by these women may primarily be due to inadequate calf muscle tone because exogenous stimulation of the CMP was sufficient to halt and reverse fluid pooling. Whether CMP stimulation would provide a means to treat PE in individuals with edema-related health complications, such as congestive heart failure, merits further investigation.

Calibration of the continuous glucose monitoring system for transient glucose monitoring.

BACKGROUND: Oral glucose tolerance testing (OGTT) remains the gold standard for diagnosis of diabetes and is used commonly in the research laboratory. The Medtronic MiniMed (North-ridge, CA) Continuous Glucose Monitoring System (CGMS Gold), developed for long-term monitoring of glycemic levels, could provide a convenient means for tracking OGTT results during research protocols; however, the sensor demonstrates glucose and time dependencies that preclude direct application of the company-provided conversion algorithm in the first 12-24 h after sensor insertion. Here, we propose an alternative conversion algorithm that permits utilization of the CGMS monitor for glucose monitoring during this time. METHODS: Healthy female participants underwent CGMS monitoring during OGTT or fasting sessions in combination with finger-stick blood glucose measurements. Logarithmic transformations and multiple regression analysis were used to quantify the time and glucose dependence of the sensors. RESULTS: Sensor performance, as characterized by sensitivity (ratio of sensor current to capillary blood glucose levels), was shown to vary logarithmically with glucose levels as well as time after sensor insertion. A conversion algorithm developed on the basis of these observations was tested on 17 subjects during OGTT. A mean absolute relative difference between capillary blood glucose and CGMS values of 11.6 +/- 6.5% for the new algorithm was seen, compared to 20.6 +/- 5.9% with the Medtronic Solutions version 3.0c algorithm. CONCLUSIONS: Incorporation of the glucose and time dependence in CGMS sensor data yields an improved mean absolute difference between actual and estimated blood glucose values compared to the Medtronic-supplied algorithm in the immediate time period following sensor insertion.

Cardiovascular systemic regulation by plantar surface stimulation.

UNLABELLED: The decreased blood pressure and flow rates associated with orthostasis have been implicated in the etiology of numerous clinical conditions, including deep vein thrombosis, chronic fatigue syndrome, and more recently osteoporosis. Here, we investigate the potential of low-magnitude vibration, applied at the plantar surface, to inhibit the cardiovascular responses of adult women to the orthostatic stress associated with quiet sitting. METHODS: Thirty healthy women, aged 22-82 years, were exposed to a plantar-based vibration immediately after taking a seated position. Seven stimulus frequencies (0, 15, 22, 44, 60, 90, and 120 Hz, all at 0.2g) were tested on each subject, and cardiovascular responses were followed for 20 minutes. Each subject experienced only a single test frequency on any day. Pre- and poststimulus blood pressures and continuous electrocardiogram results were obtained, from which mean arterial pressure (MAP) and heart rate variability (HRV) were calculated. RESULTS: In the per-protocol study population (n = 25), 20 minutes of quiet sitting was associated with an average depression of 8.95 mm Hg in systolic pressure and of 1.9 mm Hg in diastolic blood pressure, corresponding to an average decrease in MAP of 5.15 mm Hg. These orthostasis-based changes in blood pressure were significantly reduced by exposure to plantar vibration, in a frequency-dependent manner, with essentially complete suppression of the drop in MAP achieved with plantar stimulation at 44 Hz (P < or = . 01). In the orthostatically hypotensive subpopulation (n = 15), both the 9.3-mm Hg depression in MAP and the decline in HRV were eliminated by exposure to plantar vibrations in the 40- to 60-Hz range (P = .01 and P = .03, respectively). These results are consistent with the hypothesis that the plantar vibration may be stimulating type IIA muscle fiber activity in the leg, which is critical for effective skeletal muscle pumping in the absence of locomotion. CONCLUSIONS: Our findings lead us to suggest that noninvasive, low-level, plantar-based vibration in the regime of 30-60 Hz can significantly inhibit the effects of the orthostatic stress of quiet sitting on the cardiovascular system.

Vibromyographic quantification of voluntary isometric contractile force in the brachioradialis.

This study investigated the ability of vibromyography (VMG) to accurately represent voluntary forearm muscle contractile force during attempted-isometric contraction of the brachioradialis. VMG signals were collected from the brachioradialis of healthy adult men (mean age, 26.6+/-9.8 years, N=24) during attempted-isometric contraction over a force range of 4.45 N to maximum sustained load. The VMG signals were decomposed using wavelet packet analysis techniques, and the corresponding wavelet packets were utilized in a multiple regression model for parameter reduction and identification of signal components which best correlated to muscle force. It was observed that just two wavelet components were sufficient to accurately predict muscle force (R2=0.984, P<0.0001). The signal force relationship observed is monotonic, though quadratic in form. More importantly, the wavelet data was able to predict absolute force output of the brachioradialis without normalization or prior knowledge of a subject's maximum voluntary force. These data show that VMG recordings are capable of providing a monotonic relationship between VMG signal and muscle force. Moreover, in contrast to EMG technology which can only provide relative force levels, VMG appears to be capable of reporting absolute force levels, an observation which is expected to lead to numerous applications in medicine and rehabilitation.

Reversal of lower limb venous and lymphatic pooling by passive non-invasive calf muscle pump stimulation.

Our preliminary data indicate that exogenous plantar micromechanical stimulation at 45 Hz applied at the plantar surface can prevent tachycardia and blood pressure depression associated with immobility, consistent with improvement in venous and lymphatic fluid return delivered by increased calf muscle activity. In this study, instantaneous beat-to-beat systolic blood pressure of thirty four healthy adult women participants (n=34; age range: 35-78 years) were assessed non-invasively using servo-controlled infra-red finger arterial plethysmography, for 30 minutes in the supine position, followed by 30 minutes in the seated position without plantar stimulation, and lastly for 30 minutes in the seated position with the application of a 45 Hz plantar stimulus (50 microm, p-p). Thirty minutes of supine rest resulted in an average increase of 15 mmHg in systolic pressure. During the 30 minutes of upright sitting regimen, two distinct sub-populations were observed. One group (n=18; "hypotensives") experienced a depression of approximately 15 mmHg in systolic pressure, while the other group (n=16; "normotensives and hypertensives") experienced an elevation in the systolic pressure by approximately 8 mmHg. The subsequent 30 minute application of plantar stimulus reversed the pressure drop in hypotensives and elevated the systolic pressure by approximately 20 mmHg in all the subjects. Plantar-based exogenous micromechanical vibration may be an effective approach for reversal of blood pressure depression associated with the physical stress of immobility over a long term, consistent with enhanced venous and lymphatic fluid return delivered via improved calf muscle contractility.

Effect of plantar micromechanical stimulation on cardiovascular responses to immobility.

OBJECTIVE: We investigated the cardiovascular responses of adult women to the influence of extended quiet sitting and the extent to which these responses may be reversed by micromechanical stimulation of the plantar surface. DESIGN: The cardiovascular responses of 20 healthy adult women (mean age, 55.9 +/- 4.45 yrs) were observed during quiet sitting with and without exposure to a plantar-based micromechanical stimulation. Beat-to-beat heart rate via electrocardiogram was acquired along with preexposure and postexposure blood pressures, from which heart rate variability and mean arterial pressure were determined. Seven stimulus frequencies (0, 15, 22, 44, 60, 90, and 120 Hz, all at 0.2 x g, peak to peak) were tested on each subject. RESULTS: Over one-half of the women tested (11/20) exhibited a significant resting tachycardia (mean, 8.3 +/- 0.5 beats/min) with a corresponding decline in their systolic blood pressure (9.45 +/- 1.8 mm Hg) after 20 mins of quiet sitting. Plantar stimulation at 44 Hz (25 mum, peak to peak) was able to completely reverse the effect of immobility in this group, resulting in a heart rate decline of 2.5 beats/min (P < 0.0001) and a decrease of only 1 mm Hg in systolic pressure (P = 0.006). CONCLUSION: We interpret these results to suggest that the immobility of quiet sitting has a profound effect on the cardiovascular systems in a large fraction of otherwise healthy women, perhaps due to inadequate muscle tone leading to venous insufficiency. Simple external stimulation of the plantar surface seems to be capable of preventing these cardiovascular stress-based responses.

Calf muscle pump stimulation as an adjunct to orthopaedic surgery.

Management of patients following extensive orthopaedic surgery, and in particular, joint replacement surgery, represents a continuing challenge. The associated bed rest burdens a broad range of physiologic functions, exacerbating vascular, venous, and lymphatic conditions, as well as cardiovascular conditions and glucose regulation in the hyperglycemic or diabetic patient. Most of these problems arise from a lack of mobility/exercise during recuperation. In a recent series of clinical studies, non-invasive micromechanical stimulation (MMS) of the plantar surface has been demonstrated to significantly enhance skeletal muscle pump activity in the lower limbs of patients, which results in improved blood and lymphatic flow in the lower body. These studies demonstrate efficacy in both the supine and upright positions, suggesting the potential of MMS technology to significantly improve post-surgical patient care. Moreover, evidence is increasing that sustained skeletal muscle pump activity helps to maintain normal fluid flow in bone tissue, such that MMS may provide a non-drug treatment for maintaining bone mass during bed rest, or possibly increasing bone mass following extended bed rest.

Plantar vibration improves leg fluid flow in perimenopausal women.

Recent studies have indicated that plantar-based vibration may be an effective approach for the prevention and treatment of osteoporosis. We addressed the hypothesis of whether the plantar vibration operated by way of the skeletal muscle pump, resulting in enhanced blood and fluid flow to the lower body. We combined plantar stimulation with upright tilt table testing in 18 women aged 46-63 yr. We used strain-gauge plethysmography to measure calf blood flow, venous capacitance, and the microvascular filtration relation, as well as impedance plethysmography to examine changes in leg, splanchnic, and thoracic blood flow while supine at a 35 degrees upright tilt. A vibrating platform was placed on the footboard of a tilt table, and measurements were made at 0, 15, and 45 Hz with an amplitude of 0.2 g point to point, presented in random order. Impedance-measured supine blood flows were significantly (P = 0.05) increased in the calf (30%), pelvic (26%), and thoracic regions (20%) by plantar vibration at 45 Hz. Moreover, the 25-35% decreases in calf and pelvic blood flows associated with upright tilt were reversed by plantar vibration, and the decrease in thoracic blood flow was significantly attenuated. Strain-gauge measurements showed an attenuation of upright calf blood flow. In addition, the microvascular filtration relation was shifted with vibration, producing a pronounced increase in the threshold for edema, P(i), due to enhanced lymphatic flow. Supine values for P(i) increased from 24 +/- 2 mmHg at 0 Hz to 27 +/- 3 mmHg at 15 Hz, and finally to 31 +/- 2 mmHg at 45 Hz (P < 0.01). Upright values for P(i) increased from 25 +/- 3 mmHg at 0 Hz, to 28 +/- 4 mmHg at 15 Hz, and finally to 35 +/- 4 mmHg at 45 Hz. The results suggest that plantar vibration serves to significantly enhance peripheral and systemic blood flow, peripheral lymphatic flow, and venous drainage, which may account for the apparent ability of such stimuli to influence bone mass.

Relation of postural vasovagal syncope to splanchnic hypervolemia in adolescents.

BACKGROUND: The mechanisms of simple faint remain elusive. We propose that postural fainting is related to excessive thoracic hypovolemia and splanchnic hypervolemia during orthostasis compared with healthy subjects. METHODS AND RESULTS: We studied 34 patients 12 to 22 years old referred for multiple episodes of postural faint and 11 healthy subjects. Subjects were studied in the supine position and during upright tilt to 70 degrees for 30 minutes and subgrouped into S+, historical fainters who fainted during testing (n=24); S-, historical fainters who did not faint during testing (n=10); and control subjects. Supine venous occlusion plethysmography showed no differences between blood flows of the forearm and calf in S+, S-, or control. Cardiac index, total peripheral resistance, and blood volume were not different. Using impedance plethysmography, we assessed blood redistribution during upright tilt. This demonstrated decreased thoracic blood volume and increased splanchnic, pelvic, and leg blood volumes for all subjects. However, thoracic blood volume was decreased in S+ compared with control volume, correlating well with the maximum upright heart rate. Splanchnic volume was decreased in the S+ and S- groups, correlating with the change in thoracic blood volume. Pelvic and leg volume changes were similar for all groups and uncorrelated to thoracic blood volume. CONCLUSIONS: Enhanced postural thoracic hypovolemia and splanchnic hypervolemia are associated with postural simple faint.

Effect of power-frequency magnetic fields on genome-scale gene expression in Saccharomyces cerevisiae.

To estimate the effect of 50 Hz magnetic-field exposure on genome-wide gene expression, the yeast Saccharomyces cerevisiae was used as a model for eukaryotes. 2D PAGE (about 1,000 spots) for protein and cDNA microarray (about 5,900 genes) analysis for mRNA were performed. The cells were exposed to 50 Hz vertical magnetic fields at 10, 150 or 300 mT r.m.s. for 24 h. As positive controls, the cells were exposed to aerobic conditions, heat (40 degrees C) or minimal medium. The 2D PAGE and microarray analyses for the positive controls showed high-confidence differential expression of many genes including those for known or unknown proteins and mRNAs. For magnetic-field exposure, no high-confidence changes in expression were observed for proteins or genes that were related to heat-shock response, DNA repair, respiration, protein synthesis and the cell cycle. Principal component analysis showed no statistically significant difference in principal components, with only insignificant differences between the magnetic-field intensities studied. In contrast, the principal components for the positive controls were significantly different. The results indicate that a 50 Hz magnetic field below 300 mT did not act as a general stress factor like heat shock or DNA damage, as had been reported previously by others. This study failed to find a plausible differential gene expression that would point to a possible mechanism of an effect of magnetic fields. The findings provide no evidence that the magnetic-field exposure alters the fundamental mechanism of translation and transcription in eukaryotic cells.