Smart Data-Driven Optimization of Powered Prosthetic Ankles Using Surface Electromyography.

The advent of powered prosthetic ankles provided more balance and optimal energy expenditure to lower amputee gait. However, these types of systems require an extensive setup where the parameters of the ankle, such as the amount of positive power and the stiffness of the ankle, need to be setup. Currently, calibrations are performed by experts, who base the inputs on subjective observations and experience. In this study, a novel evidence-based tuning method was presented using multi-channel electromyogram data from the residual limb, and a model for muscle activity was built. Tuning using this model requires an exhaustive search over all the possible combinations of parameters, leading to computationally inefficient system. Various data-driven optimization methods were investigated and a modified Nelder⁻Mead algorithm using a Latin Hypercube Sampling method was introduced to tune the powered prosthetic. The results of the modified Nelder⁻Mead optimization were compared to the Exhaustive search, Genetic Algorithm, and conventional Nelder⁻Mead method, and the results showed the feasibility of using the presented method, to objectively calibrate the parameters in a time-efficient way using biological evidence.

Survey of Physician Perspective towards Management of Pain for Chronic Conditions in the Emergency Department.

Sickle cell disease (SCD) pain is often acute-on-chronic, likening it to other chronic acute-on-chronic pain conditions. Pain treatment of SCD was already reported as inadequate prior to the current opioid epidemic, but attitudes underlying treatment were understudied. Understanding these attitudes prior to the current epidemic would be revealing. Therefore in 1997, before the current opioid epidemic, we surveyed physicians' attitudes toward pain management and treatment preferences for acute pain exacerbations in the Emergency Department in SCD versus those of chronic pancreatitis and chronic low back pain, two other acute-on-chronic pain diseases. Thirty-nine residency trainees were surveyed in a level one triage hospital. Resident estimates of the rate of opioid addiction in SCD were higher than estimates in both chronic pancreatitis and chronic low back pain. Most residents relied on their personal clinical experience rather than external sources of data or knowledge as the most important driver when they managed chronic pain. This survey research shows that, predating the current opioid epidemic, there was both a backdrop of opioid-phobia and a bias against treating SCD pain compared to other chronic pain conditions among our sample. Repeating this survey research among current training physicians, along with surveys of other attitudes, would provide useful comparisons.

Electroencephalogram-Based Brain-Computer Interface and Lower-Limb Prosthesis Control: A Case Study.

OBJECTIVE: The purpose of this study was to establish the feasibility of manipulating a prosthetic knee directly by using a brain-computer interface (BCI) system in a transfemoral amputee. Although the other forms of control could be more reliable and quick (e.g., electromyography control), the electroencephalography (EEG)-based BCI may provide amputees an alternative way to control a prosthesis directly from brain. METHODS: A transfemoral amputee subject was trained to activate a knee-unlocking switch through motor imagery of the movement of his lower extremity. Surface scalp electrodes transmitted brain wave data to a software program that was keyed to activate the switch when the event-related desynchronization in EEG reached a certain threshold. After achieving more than 90% reliability for switch activation by EEG rhythm-feedback training, the subject then progressed to activating the knee-unlocking switch on a prosthesis that turned on a motor and unlocked a prosthetic knee. The project took place in the prosthetic department of a Veterans Administration medical center. The subject walked back and forth in the parallel bars and unlocked the knee for swing phase and for sitting down. The success of knee unlocking through this system was measured. Additionally, the subject filled out a questionnaire on his experiences. RESULTS: The success of unlocking the prosthetic knee mechanism ranged from 50 to 100% in eight test segments. CONCLUSION: The performance of the subject supports the feasibility for BCI control of a lower extremity prosthesis using surface scalp EEG electrodes. Investigating direct brain control in different types of patients is important to promote real-world BCI applications.

Effect of real-time cortical feedback in motor imagery-based mental practice training.

BACKGROUND: Mental practice using motor imagery of limb movement may facilitate motor recovery in persons who have experienced cerebrovascular accident (CVA). However, the lack of a feedback mechanism that can monitor the quality of the motor imagery affects patients' engagement and motivation to participate in the mental practice training program. OBJECTIVE: This study investigates the effect of novel real-time motor imagery-associated cortical activity feedback on motor imagery-based mental practice training. METHODS: Ten healthy volunteers were randomly assigned into intervention and control groups. Both groups participated in a five-visit motor imagery-based mental practice training program managed over a period of two months. The intervention group received mental practice training with real-time feedback of movement-associated cortical activity-beta band (16-28 Hz) event-related desynchronization (ERD) in electroencephalography (EEG), using a novel custom-made brain-computer interface (BCI) system. The control group received the mental practice training program without EEG cortical feedback. Motor excitability was assessed by measuring the frequency power magnitude of the EEG rhythmic activity associated with physical execution of wrist extension before and after the motor imagery-based mental practice training. RESULTS: The EEG frequency power magnitude associated with the physical execution of wrist extension was significantly lower (i.e. more desynchronized) after the mental practice training in the intervention group that received real-time cortical feedback (P < 0.05), whereas no significant difference in EEG frequency power magnitude associated with the physical execution of wrist extension was observed before and after mental practice training in the control group who did not receive feedback. CONCLUSIONS: The mental practice training program with motor imagery-associated cortical feedback facilitated motor excitability during the production of voluntary motor control. Motor imagery-based mental practice training with movement-associated cortical activity feedback may provide an effective strategy to facilitate motor recovery in brain injury patients, particularly during the early rehabilitation stage when full participation in physical and occupational therapy programs may not be possible due to excessive motor weakness.

Electroencephalography (EEG)-based brain-computer interface (BCI): a 2-D virtual wheelchair control based on event-related desynchronization/synchronization and state control.

This study aims to propose an effective and practical paradigm for a brain-computer interface (BCI)-based 2-D virtual wheelchair control. The paradigm was based on the multi-class discrimination of spatiotemporally distinguishable phenomenon of event-related desynchronization/synchronization (ERD/ERS) in electroencephalogram signals associated with motor execution/imagery of right/left hand movement. Comparing with traditional method using ERD only, where bilateral ERDs appear during left/right hand mental tasks, the 2-D control exhibited high accuracy within a short time, as incorporating ERS into the paradigm hypothetically enhanced the spatiotemoral feature contrast of ERS versus ERD. We also expected users to experience ease of control by including a noncontrol state. In this study, the control command was sent discretely whereas the virtual wheelchair was moving continuously. We tested five healthy subjects in a single visit with two sessions, i.e., motor execution and motor imagery. Each session included a 20 min calibration and two sets of games that were less than 30 min. Average target hit rate was as high as 98.4% with motor imagery. Every subject achieved 100% hit rate in the second set of wheelchair control games. The average time to hit a target 10 m away was about 59 s, with 39 s for the best set. The superior control performance in subjects without intensive BCI training suggested a practical wheelchair control paradigm for BCI users.

Prediction of human voluntary movement before it occurs.

OBJECTIVE: Human voluntary movement is associated with two changes in electroencephalography (EEG) that can be observed as early as 1.5 s prior to movement: slow DC potentials and frequency power shifts in the alpha and beta bands. Our goal was to determine whether and when we can reliably predict human natural movement BEFORE it occurs from EEG signals ONLINE IN REAL-TIME. METHODS: We developed a computational algorithm to support online prediction. Seven healthy volunteers participated in this study and performed wrist extensions at their own pace. RESULTS: The average online prediction time was 0.62±0.25 s before actual movement monitored by EMG signals. There were also predictions that occurred without subsequent actual movements, where subjects often reported that they were thinking about making a movement. CONCLUSION: Human voluntary movement can be predicted before movement occurs. SIGNIFICANCE: The successful prediction of human movement intention will provide further insight into how the brain prepares for movement, as well as the potential for direct cortical control of a device which may be faster than normal physical control.

A biomedical sensor system for real-time monitoring of astronauts' physiological parameters during extra-vehicular activities.

OBJECTIVE: To design and test an embedded biomedical sensor system that can monitor astronauts' comprehensive physiological parameters, and provide real-time data display during extra-vehicle activities (EVA) in the space exploration. METHODS: An embedded system was developed with an array of biomedical sensors that can be integrated into the spacesuit. Wired communications were tested for physiological data acquisition and data transmission to a computer mounted on the spacesuit during task performances simulating EVA sessions. RESULTS: The sensor integration, data collection and communication, and the real-time data monitoring were successfully validated in the NASA field tests. CONCLUSIONS: The developed system may work as an embedded system for monitoring health status during long-term space mission.

A motor imagery-based online interactive brain-controlled switch: paradigm development and preliminary test.

OBJECTIVE: To develop a practical motor imagery-based brain-controlled switch as functional as a real-world switch that is reliable with a minimal false positive operation rate and convenient for users without the need of attention to the switch during a 'No Control' state (when not to activate the switch). METHODS: Four healthy volunteers were instructed to perform an intended motor imagery task following an external sync signal in order to turn on a virtual switch provided on a computer screen. No specific mental task was required during the 'No Control' state. The beta band event-related frequency power (event-related desynchronization or ERD) from a single EEG Laplacian channel was monitored online in real-time. The computer continuously monitored the relative ERD power level until it exceeded a pre-set threshold and turned on the virtual switch. RESULTS: Subject 1 achieved lowest average false positive rate of 0.4+/-0.9% in a five-session online study during the entire 'No Control' state, whereby the subject required 6.8+/-0.6 s of active urging time or total response time of 20.5+/-1.9 s to perform repeated attempts in order to turn on the switch in the online interactive switch operation. The average false positive rate among four subjects was 0.8+/-0.4% with average active urging time of 12.3+/-4.4 s or average response time of 36.9+/-13.0 s. Offline analysis from subject 2 shows that the overall performance from 10-fold cross-validation was 96.2% with 3 consecutive epoch averaging, which was further improved to 99.0% by computationally intensive methods. CONCLUSIONS: The novel design of the brain-controlled switch using the ERD feature associated with motor imagery achieved minimal false positive rate with a reasonable active urging time or response time to activate the switch. SIGNIFICANCE: The reliability and convenience of the developed brain-controlled switch may extend current brain-computer interface capacities in practical communication and control applications.

Towards a user-friendly brain-computer interface: initial tests in ALS and PLS patients.

OBJECTIVE: Patients usually require long-term training for effective EEG-based brain-computer interface (BCI) control due to fatigue caused by the demands for focused attention during prolonged BCI operation. We intended to develop a user-friendly BCI requiring minimal training and less mental load. METHODS: Testing of BCI performance was investigated in three patients with amyotrophic lateral sclerosis (ALS) and three patients with primary lateral sclerosis (PLS), who had no previous BCI experience. All patients performed binary control of cursor movement. One ALS patient and one PLS patient performed four-directional cursor control in a two-dimensional domain under a BCI paradigm associated with human natural motor behavior using motor execution and motor imagery. Subjects practiced for 5-10min and then participated in a multi-session study of either binary control or four-directional control including online BCI game over 1.5-2h in a single visit. RESULTS: Event-related desynchronization and event-related synchronization in the beta band were observed in all patients during the production of voluntary movement either by motor execution or motor imagery. The online binary control of cursor movement was achieved with an average accuracy about 82.1+/-8.2% with motor execution and about 80% with motor imagery, whereas offline accuracy was achieved with 91.4+/-3.4% with motor execution and 83.3+/-8.9% with motor imagery after optimization. In addition, four-directional cursor control was achieved with an accuracy of 50-60% with motor execution and motor imagery. CONCLUSION: Patients with ALS or PLS may achieve BCI control without extended training, and fatigue might be reduced during operation of a BCI associated with human natural motor behavior. SIGNIFICANCE: The development of a user-friendly BCI will promote practical BCI applications in paralyzed patients.

Image-guided stereotactic body radiotherapy for lung tumors using BodyLoc with tomotherapy: clinical implementation and set-up accuracy.

We investigated the use of a BodyLoc immobilization and stereotactic localization device combined with TomoTherapy megavoltage CT (MVCT) in lung stereotactic body radiotherapy (SBRT) to reduce set-up uncertainty and treatment time. Eight patients treated with 3-5 fractions of SBRT were retrospectively analyzed. A BodyLoc localizer was used in both CT simulation for localization and the initial patient treatment set-up. Patients were immobilized with a vacuum cushion on the back and a thermoplastic body cast on the anterior body. Pretreatment MVCT from the TomoTherapy unit was fused with the planning kilovoltage CT (KVCT) before each fraction of treatment to determine interfractional set-up error. The comparison of two MVCTs during a fraction of treatment resulted in the intrafractional uncertainty of the treatment. A total of 224 target isocenter shifts were analyzed to assess these inter- and intrafractional tumor motions. We found that for interfractional shifts, the mean set-up errors and standard deviations were -1.1 +/- 2.8 mm, -2.5 +/- 8.7 mm, and 4.1 +/- 2.6 mm, for lateral, longitudinal, and vertical variation, respectively; the mean setup rotational variation was -0.3 +/- 0.7 degrees; and the maximum motion was 13.5 mm in the longitudinal direction. For intrafractional shifts, the mean set-up errors and standard deviations were -0.1 +/- 0.7 mm, -0.3 +/- 2.0 mm, and 0.5 +/- 1.1 mm for the lateral, longitudinal, and vertical shifts, respectively; the mean rotational variation was 0.1 +/- 0.2 degrees; and the maximum motion was 3.8 mm in the longitudinal direction. There was no correlation among patient characteristics, set-up uncertainties, and isocenter shifts, and the interfractional set-up uncertainties were larger than the intrafractional isocenter shift. The results of this study suggested that image-guided stereotactic body radiotherapy using the BodyLoc immobilization system with TomoTherapy can improve treatment accuracy.

Analysis of daily setup variation with tomotherapy megavoltage computed tomography.

The purpose of this study was to evaluate different setup uncertainties for various anatomic sites with TomoTherapy pretreatment megavoltage computed tomography (MVCT) and to provide optimal margin guidelines for these anatomic sites. Ninety-two patients with tumors in head and neck (HN), brain, lung, abdominal, or prostate regions were included in the study. MVCT was used to verify patient position and tumor target localization before each treatment. With the anatomy registration tool, MVCT provided real-time tumor shift coordinates relative to the positions where the simulation CT was performed. Thermoplastic facemasks were used for HN and brain treatments. Vac-Lok cushions were used to immobilize the lower extremities up to the thighs for prostate patients. No respiration suppression was administered for lung and abdomen patients. The interfractional setup variations were recorded and corrected before treatment. The mean interfractional setup error was the smallest for HN among the 5 sites analyzed. The average 3D displacement in lateral, longitudinal, and vertical directions for the 5 sites ranged from 2.2-7.7 mm for HN and lung, respectively. The largest movement in the lung was 2.0 cm in the longitudinal direction, with a mean error of 6.0 mm and standard deviation of 4.8 mm. The mean interfractional rotation variation was small and ranged from 0.2-0.5 degrees, with the standard deviation ranging from 0.7-0.9 degrees. Internal organ displacement was also investigated with a posttreatment MVCT scan for HN, lung, abdomen, and prostate patients. The maximum 3D intrafractional displacement across all sites was less than 4.5 mm. The interfractional systematic errors and random errors were analyzed and the suggested margins for HN, brain, prostate, abdomen, and lung in the lateral, longitudinal, and vertical directions were between 4.2 and 8.2 mm, 5.0 mm and 12.0 mm, and 1.5 mm and 6.8 mm, respectively. We suggest that TomoTherapy pretreatment MVCT can be used to improve the accuracy of patient positioning and reduce tumor margin.

EEG-based online two-dimensional cursor control.

This study aims to explore whether human intentions to move or cease to move right and left hands can provide four spatiotemporal patterns in single-trial non-invasive EEG signals to achieve a two-dimensional cursor control. Subjects performed motor tasks by either physical movement or motor imagery. Spatial filtering, temporal filtering, feature selection and classification methods were explored to support accurate computer pattern recognition. The performance was evaluated by both offline classification and online two-dimensional cursor control. Event-related desynchronization (ERD) and post-movement event-related synchronization (ERS) were observed on the contralateral hemisphere to the moving hand for both physical movement and motor imagery. The offline classification of four motor tasks provided 10-fold cross-validation accuracy as high as 88% for physical movement and 73% for motor imagery. Subjects participating in experiments with physical movement were able to complete the online game with the average accuracy of 85.5 + or - 4.65%; Subjects participating in motor imagery study also completed the game successfully. The proposed brain-computer interface (BCI) provided a new practical multi-dimensional method by noninvasive EEG signal associated with human natural behavior, which does not need long-term training.

Single trial detection of human movement intentions from SAM-filtered MEG signals for a high performance two-dimensional BCI.

The objective of this research is to explore whether a two-dimensional BCI can be achieved by reliably decoding single-trial magneto-encephalography (MEG) signal associated with sustaining or ceasing right and left hand movements. Seven naïve subjects participated in the study. Signals were recorded from 275-channel MEG and synthetic aperture magnetometry (SAM) was employed. The multi-class classification for four-directional control was evaluated offline from 10-fold cross-validation using direct-decision tree classifier and genetic algorithm based Mahalanobis linear distance. Beta band (15-30Hz) event-related desynchronization and event related synchronization were observed in right and left hand movement related motor areas for physical movements as well as motor imagery. The cross-validation accuracy for the proposed four-direction classification from SAM- filtered MEG signal was as high as 95-97% for physical movements and 86-87% for motor imagery. The high classification accuracy suggests that a reliable high performance two-dimensional BCI can be achieved from single trial detection of human natural movement intentions from SAM-filtered MEG signals, where user may not need extensive training.

Spatial detection of multiple movement intentions from SAM-filtered single-trial MEG signals.

OBJECTIVE: To test whether human intentions to sustain or cease movements in right and left hands can be decoded reliably from spatially filtered single-trial magnetoencephalographic (MEG) signals for motor execution and motor imagery. METHODS: Seven healthy volunteers, naïve to BCI technology, participated in this study. Signals were recorded from 275-channel MEG, and synthetic aperture magnetometry (SAM) was employed as the spatial filter. The four-class classification was performed offline. Genetic algorithm based Mahalanobis linear distance (GA-MLD) and direct-decision tree classifier (DTC) techniques were adopted for the classification through 10-fold cross-validation. RESULTS: Through SAM imaging, strong and distinct event-related desynchronization (ERD) associated with sustaining, and event-related synchronization (ERS) patterns associated with ceasing of right and left hand movements were observed in the beta band (15-30Hz) on the contralateral hemispheres for motor execution and motor imagery sessions. Virtual channels were selected from these areas of high activity for the corresponding events as per the paradigm of the study. Through a statistical comparison between SAM-filtered virtual channels from single-trial MEG signals and basic MEG sensors, it was found that SAM-filtered virtual channels significantly increased the classification accuracy for motor execution (GA-MLD: 96.51+/-2.43%) as well as motor imagery sessions (GA-MLD: 89.69+/-3.34%). CONCLUSION: Multiple movement intentions can be reliably detected from SAM-based spatially filtered single-trial MEG signals. SIGNIFICANCE: MEG signals associated with natural motor behavior may be utilized for a reliable high-performance brain-computer interface (BCI) and may reduce long-term training compared with conventional BCI methods using rhythm control.

Decoding human motor activity from EEG single trials for a discrete two-dimensional cursor control.

This study aims to explore whether human intentions to move or cease to move right and left hands can be decoded from spatiotemporal features in non-invasive EEG in order to control a discrete two-dimensional cursor movement for a potential multidimensional brain-computer interface (BCI). Five naïve subjects performed either sustaining or stopping a motor task with time locking to a predefined time window by using motor execution with physical movement or motor imagery. Spatial filtering, temporal filtering, feature selection and classification methods were explored. The performance of the proposed BCI was evaluated by both offline classification and online two-dimensional cursor control. Event-related desynchronization (ERD) and post-movement event-related synchronization (ERS) were observed on the contralateral hemisphere to the hand moved for both motor execution and motor imagery. Feature analysis showed that EEG beta band activity in the contralateral hemisphere over the motor cortex provided the best detection of either sustained or ceased movement of the right or left hand. The offline classification of four motor tasks (sustain or cease to move right or left hand) provided 10-fold cross-validation accuracy as high as 88% for motor execution and 73% for motor imagery. The subjects participating in experiments with physical movement were able to complete the online game with motor execution at an average accuracy of 85.5 +/- 4.65%; the subjects participating in motor imagery study also completed the game successfully. The proposed BCI provides a new practical multidimensional method by noninvasive EEG signal associated with human natural behavior, which does not need long-term training.

Maximal aerobic capacity and the oxygen uptake efficiency slope as predictors of large artery stiffness in apparently healthy subjects.

PURPOSE: Large artery stiffness is now recognized as an important marker of cardiovascular health. The purpose of the present investigation was to assess the relationship between large artery stiffness and the oxygen uptake efficiency slope (OUES) and to determine whether the OUES is a viable surrogate for maximal oxygen uptake (VO(2max)) in a multivariate regression analysis developed to estimate large artery stiffness. METHODS: Two hundred seventy-five apparently healthy subjects (149 men; age = 48.1 +/- 15.8 years/126 women; age = 47.0 +/- 15.3 years) participated in this study. Subjects underwent maximal cardiopulmonary exercise testing to determine VO(2max) and the OUES. The OUES was calculated using 50% and 100% of the exercise data. Measurement of aortic wave velocity (AWV in meters/second) was obtained via magnetic resonance imaging. RESULTS: Pearson product-moment correlation analysis revealed that VO(2max) (r = -0.49, P < .001), the OUES calculation using 50% of exercise data (r = -0.25, P < .001), and the OUES calculation using 100% of exercise data (r = -0.34, P < .001) were all significantly related to AWV. However, only VO(2max) was retained in a linear regression (also including age and resting systolic blood pressure) used to predict AWV. DISCUSSION: Previous research has demonstrated a relationship between VO(2max) and AWV, which was also found in the present study. While the OUES was significantly correlated with AWV, it does not appear to be an adequate replacement for VO(2max) when attempting to gauge large artery compliance.

An observational, prospective study exploring the use of heart rate variability as a predictor of clinical outcomes in pre-hospital ambulance patients.

OBJECTIVE: To explore the use of pre-hospital heart rate variability (HRV) as a predictor of clinical outcomes such as hospital admission, intensive care unit (ICU) admission and mortality. We also implemented an automated pre-analysis signal processing algorithm and multiple principal component analysis (PCA) for outcomes. MATERIALS AND METHODS: We conducted a prospective observational clinical study at an emergency medical services (EMS) system in a medium sized urban setting in the United States. Electrocardiogram (ECG) data was obtained from a sample of 45 ambulance patients conveyed to a tertiary hospital, monitored with a LIFEPAK12 defibrillator/monitor. After extracting the data, filtering for noise reduction and isolating non-sinus beats, various HRV parameters were computed. These included time domain, frequency domain and geometric parameters. PCA was performed on the hospital outcomes for these patients. RESULTS: We used a combination of HRV parameters, age and vital signs such as respiratory rate, SpO2 and Glasgow coma score (GCS) in a PCA analysis. For predicting admission to ICU, sensitivity was 100%, specificity was 48.6%, and negative predictive value (NPV) was 100%; for predicting admission to hospital, sensitivity was 78.9%, specificity was 85.7%, and NPV was 75.0%; for predicting death, sensitivity was 50.0%, specificity was 100%, and NPV was 97.4%. There was also a significant correlation of several HRV parameters with length of hospital stay. CONCLUSIONS: With signal processing techniques, it is feasible to filter and analyze ambulance ECG data for HRV. We found a combination of HRV parameters and traditional 'vital signs' to have an association with clinical outcomes in pre-hospital patients. This may have potential as a triage tool for ambulance patients.

Association of hypertensive diastolic blood pressure with dyslipidemia during exercise in apparently healthy subjects.

INTRODUCTION: Diastolic blood pressure (DBP), which is influenced by cardiac output and total peripheral resistance, normally remains stable or decreases during the transition from rest to exercise. Dyslipidemia has been shown to attenuate vasodilation, and may therefore impede the normal reduction in peripheral vascular resistance during exercise. This investigation examines differences in lipid levels between apparently healthy individuals with a normal and hypertensive DBP response to exercise. METHODS: From a pool of 275 apparently healthy subjects, 35 individuals (aged 57.8 +/- 15.0 years, 13 men and 22 women) with a normal DBP at rest (<80 mm Hg) that increased to a hypertensive level at maximal exercise (> or = 90 mm Hg) were randomly age and sex matched to 35 subjects (aged 56.5 +/- 13.4 years) with a normal DBP at rest (<80 mm Hg) that remained below a hypertensive level at maximal exercise (<90 mm Hg). RESULTS: A paired t test revealed DBP to be significantly higher in the group with an abnormal response to exercise (97.0 +/- 7.6 mm Hg vs 76.8 +/- 7.4 mm Hg; P < .001). Total cholesterol (204.2 +/- 31.2 mg/dL vs 190.6 +/- 28.9 mg/dL; P < .05) and low-density lipoprotein (126.5 +/- 30.5 mg/dL vs 109.8 +/- 25.5 mg/dL; P < .05) levels were also significantly higher in the group with an abnormal DBP response to exercise. All other variables were similar between groups. DISCUSSION: Results indicate that elevated lipid levels are associated with a hypertensive DBP response during maximal exercise in apparently healthy individuals. The abnormal DBP response to exercise observed in this study may be related to attenuated vasodilation in skeletal muscle induced by higher levels of low-density lipoprotein.

High aerobic capacity does not attenuate aortic stiffness in hypertensive subjects.

BACKGROUND: It is unknown whether increased physical fitness reduces aortic stiffness in hypertensive individuals. The purpose of this cross-sectional study was to examine, in a cohort of community-dwelling subjects with no history of cardiac events, differences in the impact of aerobic capacity on aortic stiffness between normotensive and hypertensive subjects. METHODS: The study sample included 275 subjects representing a large age range (21-85 years). Of these, 61 subjects (hypertensive cohort) were either hypertensive at enrollment or were taking antihypertensive medication. The remaining 214 subjects (normotensive cohort) had no history of hypertension. The study protocol included maximal cardiopulmonary exercise testing (determination of maximal oxygen consumption, or VO2max) and measurement of aortic wave velocity (AWV) using a novel magnetic resonance-based method. RESULTS: Overall, the hypertensive cohort exhibited significantly elevated AWV in comparison to a subset of normotensives matched for age, sex, and aerobic fitness. Each cohort was then subdivided according to the percentage of predicted VO2max achieved (< 100% = "unfit," > or = 100% = "fit"). Differences between subgroups were assessed by unpaired t test. In the normotensive cohort, AWV was significantly lower in the fit versus the unfit subgroup. However, in the hypertensive cohort, AWV was not significantly different between fit and unfit subgroups nor between treated and untreated subgroups. CONCLUSION: Unlike the situation in healthy normotensive subjects, higher peak aerobic capacity is not associated with lower aortic stiffness in hypertensive individuals.

Influence on aerobic fitness on aortic stiffness in apparently healthy Caucasian and African-American subjects.

BACKGROUND: Previous research suggests that arterial stiffness may be significantly higher in African-Americans compared to Caucasians. However, the influence of aerobic fitness on the putative difference in arterial stiffness between these groups has not been previously investigated. METHODS: Two hundred forty-eight subjects (215 Caucasian, 33 African-American) participated in this study. Within one week following enrollment, subjects underwent body mass index (BMI, kg/m2) assessment, cardiopulmonary exercise testing and measurement of aortic wave velocity (AWV, m/s) via magnetic resonance imaging. Initially, 33 Caucasian subjects were randomly age (+/-4 years) and sex-matched (10 male/23 female) to the African-American subjects. 25 Caucasian subjects were then randomly matched for age (+/-4 years), sex (7 male/18 female) and maximal oxygen consumption (VO2Max+/-7 mlO2 kg(-1) min(-1)) to the African-American subjects. Matching based upon VO2Max criteria was not possible for 8 African-American subjects. RESULTS: In the age and sex-matched analysis, Caucasian subjects demonstrated a significantly higher VO2Max (38.3+/-9.6 vs. 27.9+/-8.6 mlO2 kg(-1) min(-1), p<0.001) and lower BMI (24.5+/-3.2 vs. 29.3+/-6.2 kg/m2, p<0.001) and AWV (5.8+/-1.7 vs. 6.7+/-1.5 m/s, p=0.03). However, when subjects were matched for age, sex and VO2Max, the differences in both BMI (26.8+/-5.5 vs. 27.9+/-5.6 kg/m2, p=0.45) and AWV (6.1+/-1.8 vs. 6.5+/-1.6 m/s, p=0.77) were insignificant. CONCLUSIONS: The results of the present study suggest that previously reported differences in arterial stiffness between Caucasians and African-Americans are at least partially a consequence of a lower level of aerobic fitness in the latter group, a phenomenon that has also been previously demonstrated.