Chronic wound repair and healing in older adults: current status and future research.

The incidence of chronic wounds is increased among older adults, and the impact of chronic wounds on quality of life is particularly profound in this population. It is well established that wound healing slows with age. However, the basic biology underlying chronic wounds and the influence of age-associated changes on wound healing are poorly understood. Most studies have used in vitro approaches and various animal models, but observed changes translate poorly to human healing conditions. The impact of age and accompanying multi-morbidity on the effectiveness of existing and emerging treatment approaches for chronic wounds is also unknown, and older adults tend to be excluded from randomized clinical trials. Poorly defined outcomes and variables, lack of standardization in data collection, and variations in the definition, measurement, and treatment of wounds also hamper clinical studies. The Association of Specialty Professors, in conjunction with the National Institute on Aging and the Wound Healing Society, held a workshop, summarized in this paper, to explore the current state of knowledge and research challenges, engage investigators across disciplines, and identify key research questions to guide future study of age-associated changes in chronic wound healing.

Ambulatory Behavior Assessment Using Deep Learning.

This work leverages a custom implementation of a deep neural network-based object detection algorithm to detect people and a set of assistive devices relevant to clinical environments. The object detections form the basis for the quantification of different ambulatory activities and related behaviors. Using features extracted from detected people and objects as input to machine learning models, we quantify how a person ambulates and the mode of ambulation being used.Clinical relevance- This system provides the data required for clinicians and hospitalized patients to work together in the creation, monitoring, and adjustment of ambulatory goals.

Use of Real Time Clinical Video Telehealth to Home by primary care providers within the Veterans Health Administration during the first wave of the COVID-19 pandemic: variability across VA stations and with time.

Objective: Determine the extent to which use of Clinical Video Telehealth to Home (VT2H) for primary care licensed independent practitioner visits (PCLIPVs) varied over time and across the Veterans Health Administration (VA) during the first 18 months of the COVID pandemic, and if there was an association between VT2H usage and VA station characteristics. Materials and Methods: All outpatient encounters (n = 12 143 456) for Veterans (n = 4 373 638) that had VA PCLIPVs during the period of observation were categorized as conducted by VT2H, in-person, or telephone. The change over time in the percentage of total PCLIPVs conducted by VT2H was plotted and associations between VA station characteristics and VT2H usage were analyzed using simple statistics and negative binomial regression. Results: Between March 2020 and mid-August 2020, VT2H visits increased from <2% to 13% of all VA PCLIPVs. However, VT2H usage varied substantively by VA station and declined system-wide to <9% of PCLIPVs by July 2021. VA stations that serve a greater proportion of rural Veterans were found less likely to use VT2H. Discussion: The VA was successful in increasing the use of VT2H for PCLIPVs during the first phase of the COVID pandemic. However, VT2H usage varied by VA station and over time. Beyond rurality, it is unknown what station characteristics may be responsible for the variance in VT2H use. Conclusion: Future investigation is warranted to identify the unique practices employed by VA stations that were most successful in using VT2H for PCLIPVs and whether they can be effectively disseminated to other stations.

Reversal of SSRI-associated apathy syndrome by discontinuation of therapy.

OBJECTIVE: To report 6 cases of selective serotonin reuptake inhibitor (SSRI)-associated apathy syndrome. CASE SUMMARIES: In all 6 cases, the patient reported loss of motivation while being treated with an SSRI. Loss of motivation was of new onset and temporally associated with the use of the SSRI. A trial of discontinuation of the SSRI was performed in all 6 patients and 2 were started on bupropion while cross-tapering from the SSRI. During the treatment trials, depression and apathy were monitored in all patients. Each case was assessed using the Apathy Evaluation Scale, Clinician version (AES-C), and by evaluating how the patient responded to discontinuation of the SSRI. DISCUSSION: Scores on the AES-C improved significantly in all 6 cases after the SSRI was discontinued. Improvement was also seen in the motivation, novelty, and persistence subdomain scores of the AES-C. A pretreatment AES-C score was available only in the first case. Based on the Naranjo probability scale, there was a probable cause of apathy syndrome with SSRI therapy in the first case and a possible association in the rest of the cases. CONCLUSIONS: In some patients SSRIs may cause an apathy syndrome that can be reversed through discontinuation of the agent. When evaluating patients being treated with an SSRI, clinicians should have a high degree of suspicion and specifically inquire for this iatrogenic form of apathy syndrome.

Rapid conversion of Tai Chi classes from face-to-face to virtual during the COVID-19 pandemic: A quality improvement project.

PURPOSE: The purpose of this quality improvement project was to examine the feasibility of rapidly converting a Tai Chi program for older Veterans from face-to-face to virtual classes. METHODS: Eighteen Veterans attending our face-to-face Tai Chi course were invited to transition to virtual classes. Feasibility was defined as the ability of program staff and participants to successfully connect and complete the initial and subsequent classes by VA Video Connect (VVC) with little to no technical difficulties, participant ability to participate in the course without safety concerns, and favorable feedback from participants and program staff. RESULTS: Nine of 18 Veterans agreed to transition to the virtual program and attended a median (interquartile range) of 11 (4-15) classes; they were younger (62.7 + 11.5 vs. 70.5 + 7.0 years, p < .05) and more likely to have the knowledge and equipment needed to participate (78% vs. 0%, p < .01) than nonparticipants. Tai Chi instructors and participating Veterans reported being able to connect to and complete the classes virtually with only minimal technical problems. No adverse events were reported. Feedback from the instructors and Veterans was positive and included comments on ease of use and enjoyability. CONCLUSION: Results suggest that virtual Tai Chi classes via VVC are feasible for some older Veterans.

An outpatient Tai Chi program: Effects on veterans' functional outcomes.

PURPOSE: To evaluate the effectiveness of an evidence-based 12-week Tai Chi course designed to improve balance and physical function in a population of older veterans. METHODS: Community dwelling veterans of all ages with gait and balance problems were invited to participate in the Tai Chi program. Participants completed the Berg Balance Scale (BBS), the Timed Up and Go (TUG) test, and the Falls Efficacy Scale-International (FES-I) at baseline and again at the end of the program. Descriptive statistics were used to summarize study participants' characteristics. The change from baseline to the end of the 12-week program was calculated for each of the three primary outcome variables (BBS, TUG, FES-I). RESULTS: Twenty-two veterans, aged 58 years and above, with perceived gait and/or balance issues were enrolled in the program with completion by 11 veterans. Veterans who completed their final assessments showed the BBS, improved significantly (p = 0.004) from baseline to the 12-week assessment. The TUG scores improved by a median of 1.3 s (p = 0.022). There was not a significant change in the FES-I. CONCLUSIONS: Preliminary findings provide evidence of the effectiveness of a 12-week Tai Chi program to improve functional outcomes for older veterans with mild to moderate gait and balance problems.

Selective serotonin reuptake inhibitors-associated apathy syndrome: A cross sectional study.

Selective serotonin reuptake inhibitors (SSRIs), commonly used to treat depression, are associated with loss of motivation, anergy, and lack of curiosity often referred collectively as apathy. However, this association has not been systematically assessed using a specific rating scale for measuring apathy syndrome. Our objective was to study the association between SSRI use and apathy syndrome.We conducted a retrospective chart review of 125 patients enrolled in an outpatient psychiatry clinic. The prevalence of apathy syndrome and its clinical significance (based on standardized assessment) were compared between patients treated and not treated with SSRIs. Apathy was assessed using the Apathy Evaluation Scale-clinician version with a score ranging 18-72 with higher score for worse apathy. A score of greater than 30 is considered clinically significant apathy.Among 119 patients, the mean apathy scores were significantly higher in those treated with SSRIs compared to those not treated with SSRIs (42.5 ±â€Š9.2 vs 31.3 ±â€Š6, P < .0001). The SSRI group also had a significantly higher percentage of patients with clinically significant apathy (92% vs 61%, P < .0001). Use of all SSRIs was associated with the presence of apathy. Apathy was seen in all mental health diagnostic categories with highest Apathy evaluation scale-clinician version scores in those with dementia.SSRI use may be associated with higher rates of apathy syndrome. Clinicians should specifically inquire about iatrogenic apathy syndrome when evaluating patients on an SSRI if there is suspicion of loss of motivation. Limitations of this study included retrospective nature of this study, and that majority of the sample was males. Prospective studies are needed to elucidate information regarding the prevalence, etiology, and treatment response for SSRI-associated apathy syndrome.

Subject Identification Using a Depth Camera for Patient Ambulation Monitoring.

Our work identifies subjects based on their height and the distance between their joints. Using a depth sensing camera, we obtained the position of a person's joints in 3D space relative to each other. The distances between adjacent joints and height of a subject's head are used to create a vector of eight features for an individual to use for identification. Using modified KNN, full and partial feature sets were used to identify subjects. Additionally, our classifier can be utilized to assess ambulation (such as walking's velocity and distance) of subject, when identified.

Increasing the availability of Tai Chi to veterans through a training of trainers course.

PURPOSE: The purpose of this nurse-led project was to increase the number of interprofessional Tai Chi instructors for veterans through a 5-week (32 hours) training of trainers (ToT) course led by a Tai Chi master trainer. METHODS: This project was designed to evaluate the effectiveness of using the ToT model to increase the availability of Tai Chi to veterans. To understand how well the ToT course met learners' needs, a two-phase course evaluation was conducted. RESULTS: Fifteen interprofessional employees enrolled in and completed the course. Most learners were white (67%) females (67%) with a median age of 50 years. All agreed that the training provided the skills, materials, and confidence to lead Tai Chi classes. Most (93%) indicated experiencing positive health benefits from the training and none experienced any negative effects. The 3-month follow-up evaluation indicated that 10 (67%) were teaching veterans in individual or group classes with two others assisting. Twelve instructors taught more than 150 veterans. CONCLUSIONS: Overall, learners evaluated this ToT course positively and indicated their needs were met and felt prepared to teach Tai Chi despite being inexperienced. The course was a success with 80% of new instructors teaching or coteaching Tai Chi to veterans.

An Interdisciplinary Approach to Educating Medical Students About Dementia Assessment and Treatment Planning.

BACKGROUND: Many general practitioners consider dementia care beyond their clinical domain and feel that dementia assessment and treatment should be addressed by specialists, such as geriatricians, geriatric psychiatrists, or neurologists. An urgent need exists to educate all medical trainees in dementia care, regardless of their specialization interests. OBSERVATIONS: We developed a multicomponent, experiential, brief curriculum using team-based learning to expose senior medical students who rotated through the US Department of Veterans Affairs Memory Disorders Clinic at the Central Arkansas Veterans Healthcare System in Little Rock to an interdisciplinary assessment of dementia. The curriculum included didactics, clinical experience, and team-based learning. In pre- and postevaluation, students rated their perception of the role of interdisciplinary team members in assessing and managing dementia, their personal abilities to assess cognition, behavioral problems, caregiver burden, and their perception of the impact of behavioral problems on dementia care. CONCLUSIONS: Dementia knowledge gaps were prevalent in this cohort of senior medical students. Providing interdisciplinary geriatric educational experience improved students perception of their ability to assess for dementia and their recognition of the roles of interdisciplinary team members. Plans are in place to continue and expand the program to other complex geriatric syndromes.

Muscle expression of genes associated with inflammation, growth, and remodeling is strongly correlated in older adults with resistance training outcomes.

A group (n = 8) of healthy older (68 +/- 6 yr) adults participated in a 36-session progressive resistance exercise training program targeting the thigh muscles to determine the relationship between muscle gene expression and gains in muscle size and strength. Biopsies were obtained from the vastus lateralis at baseline 72 h after an acute bout of exercise and 72 h after completion of the training program. Training increased thigh muscle size (7%) and strength for the three exercises performed: knee extension (30%) and curl (28%) and leg press (20%). We quantified 18 transcripts encoding factors that function in inflammation, growth, and muscle remodeling that were demonstrated previously to be regulated by aging and acute exercise. The gain in extension strength and muscle size showed a high number of significant correlations with gene expression. These gains were most strongly correlated (P < or = 0.003, R > or = 0.89) with the baseline mRNA levels for insulin-like growth factor-1, matrix metalloproteinase-2 and its inhibitor TIMP1, and ciliary neurotrophic factor. Moreover, strength gains were inversely correlated with the change in these mRNA levels after training (P < or = 0.002 and R < or = -0.90). Changes in gene expression after acute exercise were not associated with training outcomes. These results suggest that higher baseline expression for key genes in muscle conveys an adaptive advantage for certain older adults. Individuals with lower baseline expression of these genes show less adaptation to exercise despite increased gene expression in response to training. These genes hold promise as useful predictors of training outcomes that could be used to design more effective exercise regimens for maintaining muscle function in older adults.

A comparative evaluation of inpatient rehabilitation for older adults with debility, hip fracture, and myopathy.

OBJECTIVE: To compare the functional outcomes and discharge location of older adults admitted to inpatient rehabilitation for debility, hip fracture, and myopathy. DESIGN: Retrospective cohort study from 2002 to 2003 with information from the Uniform Data System for Medical Rehabilitation (UDSMR). SETTING: United States inpatient rehabilitation facilities subscribing to the UDSMR. PARTICIPANTS: Patients 65 years or older (N=84.701) with primary diagnoses of debility (n=14,835), hip fracture (n=68,915), and myopathy (n=951). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Change in functional status, including efficiency (change in functional status divided by length of stay in days) and discharge setting. RESULTS: The efficiency of the patients with debility (1.7+/-2.1) was significantly lower than that of the patients with hip fracture (1.9+/-1.6; P<.001), but not different from the patients with myopathy (1.6+/-1.4; P=.3). Significantly more patients with debility (68%) were discharged home than the hip fracture and myopathy groups (66% and 65%, respectively; P<.001). CONCLUSIONS: Although statistical differences exist, the functional recovery and rate of discharge home of older adult patients admitted to inpatient rehabilitation with a primary debility diagnosis are essentially the same clinically as those of patients with a diagnosis of either hip fracture or myopathy. Given these findings, and given that hip fracture and myopathy are approved medical conditions according to the Centers for Medicare and Medicaid Services 75% rule, the medical condition debility warrants consideration for inclusion as a qualifying medical diagnosis under this rule. However, further research is needed to develop relatively objective criteria for the debility diagnosis, and to identify those patients with debility who are most likely to benefit from inpatient rehabilitation.

Aging alters gene expression of growth and remodeling factors in human skeletal muscle both at rest and in response to acute resistance exercise.

The purpose of this investigation was to compare expression of genes that function in inflammation and stress, cell structure and signaling, or remodeling and growth in skeletal muscle of young (32 +/- 7 yr, n = 15) and elderly (72 +/- 5 yr, n = 16) healthy subjects before and after a bout of resistance leg exercises. A real-time RT-PCR method was used to screen 100 transcripts in v. lateralis biopsies obtained before and 72 h postexercise. The screen identified 15 candidates for differential expression due to aging and/or exercise that were measured quantitatively. The median levels of four mRNAs (insulin-like growth factor-1 and its binding protein IGFBP5, ciliary neurotrophic factor, and the metallopeptidase MMP2) were significantly affected by aging and were greater (1.6- to 2.3-fold, P

Methylphenidate for Apathy in Community-Dwelling Older Veterans With Mild Alzheimer's Disease: A Double-Blind, Randomized, Placebo-Controlled Trial.

OBJECTIVE: Apathy is a common behavioral problem in Alzheimer's disease. Apathy has profound consequences, such as functional impairment, higher service utilization, higher caregiver burden, and increased mortality. The authors' objective was to study the effects of methylphenidate on apathy in Alzheimer's disease. METHOD: A 12-week, prospective, double-blind, randomized, placebo-controlled trial (methylphenidate versus placebo) was conducted in community-dwelling veterans (N=60) with mild Alzheimer's disease. The primary outcome for apathy (Apathy Evaluation Scale-Clinician) and secondary outcomes for cognition (Mini-Mental State Examination, Modified Mini-Mental State Examination), functional status (activities of daily living, instrumental activities of daily living), improvement and severity (Clinical Global Impressions Scale [CGI]), caregiver burden (Zarit Burden Scale), and depression (Cornell Scale for Depression in Dementia) were measured at baseline and at 4, 8, and 12 weeks. RESULTS: Participants were all men (77 years old, SD=8). After adjusting for baseline, the methylphenidate group had significantly greater improvement in apathy than the placebo group at 4 weeks, 8 weeks, and 12 weeks. At 12 weeks, there was also greater improvement in cognition, functional status, caregiver burden, CGI scores, and depression in the methylphenidate group compared with the placebo group. CONCLUSIONS: Methylphenidate improved apathy in a group of community-dwelling veterans with mild Alzheimer's disease. Methylphenidate also improved cognition, functional status, caregiver burden, CGI scores, and depression.

Tutorial for using SliceOmatic to calculate thigh area and composition from computed tomography images from older adults.

OBJECTIVE: Area of muscle, fat, and bone is often measured in thigh CT scans when tissue composition is a key outcome. SliceOmatic software is commonly referenced for such analysis but published methods may be insufficient for new users. Thus, a quick start guide to calculating thigh composition using SliceOmatic has been developed. METHODS: CT images of the thigh were collected from older (69 ± 4 yrs, N = 24) adults before and after 12-weeks of resistance training. SliceOmatic was used to segment images into seven density regions encompassing fat, muscle, and bone from -190 to +2000 Hounsfield Units [HU]. The relative contributions to thigh area and the effects of tissue density overlap for skin and marrow with muscle and fat were determined. RESULTS: The largest contributors to the thigh were normal fat (-190 to -30 HU, 29.1 ± 7.4%) and muscle (35 to 100 HU, 48.9 ± 8.2%) while the smallest were high density (101 to 150 HU, 0.79 ± 0.50%) and very high density muscle (151 to 200 HU, 0.07 ± 0.02%). Training significantly (P<0.05) increased area for muscle in the very low (-29 to -1 HU, 5.5 ± 7.9%), low (0 to 34 HU, 9.6 ± 16.8%), normal (35 to 100 HU, 4.2 ± 7.9%), and high (100 to 150 HU, 70.9 ± 80.6%) density ranges for muscle. Normal fat, very high density muscle and bone did not change (P>0.05). Contributions to area were altered by ~1% or less and the results of training were not affected by accounting for skin and marrow. CONCLUSIONS: When using SliceOmatic to calculate thigh composition, accounting for skin and marrow may not be necessary. We recommend defining muscle as -29 to +200 HU but that smaller ranges (e.g. low density muscle, 0 to 34 HU) can easily be examined for relationships with the health condition and intervention of interest. TRIAL REGISTRATION: Clinicaltrials.gov NCT02261961.

Repetitive transcranial magnetic stimulation for apathy in mild cognitive impairment: A double-blind, randomized, sham-controlled, cross-over pilot study.

Apathy is a common and disabling behavioral concomitant of many neurodegenerative conditions. The presence of apathy with Mild Cognitive Impairment (MCI) is linked with heightened rates of conversion to Alzheimer's disease. Improving apathy may slow the neurodegenerative process. The objective was to establish the efficacy of repetitive transcranial magnetic stimulation (rTMS) in improving apathy in older adults with MCI. An 8-week, double-blind, randomized, sham-controlled cross-over study was conducted in nine subjects (66 ± 9 years) with apathy and MCI. Subjects were randomized to rTMS or sham treatment (5 days/week) for 2 weeks following which they underwent a 4-week treatment-free period. Subjects then crossed-over to receive the other treatment for 2 weeks. The primary (apathy (AES-C)) and secondary (cognition (3MS & MMSE), executive function (TMT-A & TMT-B), and clinical global impression (CGI)) outcomes were assessed at baseline, 2, 6, and 8 weeks. After adjusting for baseline, there was a significantly greater improvement in the AES-C with rTMS compared to sham treatment at 2 weeks. There was significantly greater improvement in 3MS, MMSE, TMT-A, and CGI-I with rTMS compared to the sham treatment. This study establishes that rTMS is efficacious in improving apathy in subjects with MCI.

Effects of muscle strength training and megestrol acetate on strength, muscle mass, and function in frail older people.

OBJECTIVES: To determine the independent and combined effects of progressive resistance muscle strength training (PRMST) and megestrol acetate (MA) on strength, muscle mass, and function in older recuperative care patients. DESIGN: Double-blind, randomized, controlled intervention using a two-by-two factorial design and conducted between 1999 and 2001. SETTING: University-affiliated Department of Veterans Affairs hospital. PARTICIPANTS: Twenty-nine patients (mean age 79.4 +/- 7.4, 90% white) aged 65 and older and had recent functional decline. INTERVENTIONS: After randomization to one of four treatment groups (low-resistance exercises plus 800 mg per day of MA or a placebo or high-intensity PRMST plus 800 mg/d of MA or placebo), subjects received training and the drug or placebo for 12 weeks. MEASUREMENTS: Change in muscle strength, mid-thigh muscle area, and aggregate functional performance score as assessed using analysis of covariance. RESULTS: Five subjects withdrew from the study before its completion. Based on intent-to-treat analyses, subjects who received high-intensity PRMST and placebo experienced the greatest strength gains. The addition of MA was associated with worse outcomes than with high-intensity exercise training alone, especially with regard to the leg exercises. Post hoc analysis demonstrated that subjects who received high-intensity PRMST and placebo experienced significantly greater percentage increases in leg strength than subjects in either of the MA treatment groups (P<.05 for each comparison). There was also a significant negative effect of MA on physical function. In general, subjects who received MA experienced a deterioration in aggregate physical function scores, whereas the remaining subjects improved (-0.80+/-0.40 vs 0.48+/-0.41, P=.04). There was not a significant interaction between exercise and MA for any outcome. CONCLUSION: High-intensity PRMST is a safe and well-tolerated exercise regimen for frail elderly patients. The addition of MA appears to blunt the beneficial effects of PRMST, resulting in less muscle strength and functional performance gains.

Fat distribution and glucose metabolism in older, obese men and women.

BACKGROUND: Previous studies have identified relationships between subcutaneous abdominal fat (SAF), visceral fat (VF), and insulin resistance. In addition, lower muscle attenuation and decreased adiponectin have also been associated with insulin resistance. METHODS: In order to define these relationships within a group of older, obese adults, we studied 48 individuals (20 men; 71+/-1 years and 28 women; 65+/-1 years) who underwent a single, hyperinsulinemic, euglycemic clamp procedure, computed tomography scan at the L4-L5 level, and whole-body plethysmography or dual energy x-ray absorptiometry. Endogenous glucose production (basal glucose R(a)) was also measured at baseline and during the clamp procedure using an infusion of [6,6(2)H(2)] glucose. RESULTS: Mean body mass index (BMI; 31+/-1 kg/m(2)) and glycosylated hemoglobin A1c (HbA1c; 5.7+/-0.1%) levels were not significantly different between men and women. In men, there was an inverse relationship between SAF and insulin-stimulated glucose disposal (ISGD) (r= -.60, p=.01). In addition, there was a trend between thigh muscle attenuation and ISGD in men (r=.41, p=.07). Adiponectin was associated with ISGD in men (r=.46, p=.04) and women (r=.48, p =.01). There were no significant relationships between body fat distribution and basal glucose R(a) in men or women, and no relationships between triglycerides and glucose metabolism. CONCLUSIONS: Our results indicate that (i) SAF was negatively associated with ISGD in men, (ii) thigh muscle attenuation demonstrated a trend toward ISGD in men, and (iii) adiponectin was associated with ISGD in men and women.

Concurrent exercise and muscle protein synthesis: implications for exercise countermeasures in space.

INTRODUCTION: Exercise countermeasures for long duration space crews incorporate aerobic and resistance exercise (i.e., concurrent training). Microgravity simulation studies show that resistance exercise alone can be completely effective at preventing muscle loss, yet crews return from missions with reduced muscle mass and function. Some Earth-based studies show human skeletal muscle size and strength increases typically noted with resistance training are blunted when aerobic and resistance training are performed concurrently. The purpose of this study was to determine if the addition of aerobic exercise prior to performing resistance exercise blunts the acute anabolic response to resistance exercise. METHODS: Myofibrillar protein synthesis rates were determined in 12 individuals (6 men, 6 women, 26 +/- 2 yr) by measuring the incorporation of [2H5]phenylalanine into vastus lateralis muscle protein following resistance exercise (4 sets of 10 repetitions of both leg press and leg extension) and following resistance exercise that had been preceded by 90 min of strenuous aerobic cycling exercise. RESULTS: Myofibrillar protein synthesis following resistance exercise (0.092 +/- 0.006% x h(-1)) was not suppressed (p > 0.05) compared with following concurrent exercise (0.100 +/- 0.007% x h(-1)). DISCUSSION: It appears the anabolic response to resistance exercise cannot explain the attenuated muscle mass and strength gains imposed by chronic concurrent aerobic and resistance training, nor the response of space crews to in-flight concurrent countermeasures. These findings have important implications for future optimization of the concurrent aerobic and resistance exercise countermeasures for long duration space crews.