Effects of Exercise and Nutrition on the Coagulation System During Bedrest Immobilization

Retinal venular vessel diameters are smaller during ten days of bed rest

Older individuals experience cardiovascular dysfunction during extended bedridden hospital or care home stays. Bed rest is also used as a model to simulate accelerated vascular deconditioning occurring during spaceflight. This study investigates changes in retinal microcirculation during a ten-day bed rest protocol. Ten healthy young males (22.9 ± 4.7 years; body mass index: 23.6 ± 2.5 kg·m-2) participated in a strictly controlled repeated-measures bed rest study lasting ten days. High-resolution images were obtained using a hand-held fundus camera at baseline, daily during the 10 days of bed rest, and 1 day after re-ambulation. Retinal vessel analysis was performed using a semi-automated software system to obtain metrics for retinal arteriolar and venular diameters, central retinal artery equivalent and central retinal vein equivalent, respectively. Data analysis employed a mixed linear model. At the end of the bed rest period, a significant decrease in retinal venular diameter was observed, indicated by a significantly lower central retinal vein equivalent (from 226.1 µm, CI 8.90, to 211.4 µm, CI 8.28, p = .026), while no significant changes in central retinal artery equivalent were noted. Prolonged bed rest confinement resulted in a significant (up to 6.5%) reduction in retinal venular diameter. These findings suggest that the changes in retinal venular diameter during bedrest may be attributed to plasma volume losses and reflect overall (cardio)-vascular deconditioning.

Hospital-associated deconditioning: Not only physical, but also cognitive

INTRODUCTION

Hospital-associated deconditioning (HAD) or post-hospital syndrome is well recognized as reduced functional performance after an acute hospitalization. Recommendations for the management of HAD are still lacking, partly due to a poor understanding of the underlying processes. We aimed to review existing data on risk factors, pathophysiology, measurement tools, and potential interventions.

MATERIALS AND METHODS

We conducted a systematic review from bibliographical databases in English, Spanish and French with keywords such as 'post-hospitalization syndrome' or 'deconditioning'. We selected studies that included people aged 60 years or older. Three researchers independently selected articles and assessed their quality.

RESULTS

From 4421 articles initially retrieved, we included 94 studies. Most were related to risk factors, trajectories and measures, and focused on the physical aspects of deconditioning. Risk factors for HAD included age, nutritional status, mobility, and pre-admission functional status, but also cognitive impairment and depression. Regarding interventions, almost all studies were devoted to physical rehabilitation and environmental modifications. Only one study focused on cognitive stimulation.

DISCUSSION

In the last decade, studies on HAD have mostly focused on the physical domain. However, neurological changes may also play a role in the pathophysiology of HAD. Beyond physical interventions, cognitive rehabilitation and neurological interventions should also be evaluated to improve deconditioning prevention and treatment in the hospital setting.

The Association Between Early Versus Late Physical Therapy Initiation and Outcomes of Trauma Patients With and Without Traumatic Brain Injuries

BACKGROUND

There is a lack of literature regarding the most effective timing to initiate physical therapy (PT) among traumatically injured patients. We aim to evaluate the association between early PT/mobilization versus delayed or late PT/mobilization and clinical outcomes of trauma patients.

METHODS

A retrospective cohort analysis of an urban level-I trauma center from 2014 to 2019 was performed. Univariate analyses and multivariable logistic regression were performed with significance defined as P < 0.05.

RESULTS

A total of 11,937 patients were analyzed. Among patients without a traumatic brain injury (TBI), late PT initiation times were associated with 60% lower odds of being discharged home without services (P < 0.05), significantly increased hospital and ICU length of stay (H-LOS, ICU-LOS) (P < 0.05), and significantly higher odds of complications (VTE, pneumonia, pressure ulcers, ARDS) (P < 0.001). Among patients with a TBI, late PT initiation time had 76% lower odds of being discharged home without services (P < 0.05) and significantly longer H-LOS and ICU-LOS (P < 0.05) however did not experience significantly higher odds of complications (P > 0.05).

CONCLUSIONS

Among traumatically injured patients, early PT is associated with decreased odds of complications, shorter H-LOS and ICU-LOS, and a favorable discharge disposition to home without services. Adoption of early PT initiation/mobilization protocols and establishment of prophylactic measures against complications associated with delayed PT is critical to maximize quality of care and trauma patient outcomes. Multi-center prospective studies are needed to ascertain the impact of PT initiation times in greater detail and to minimize trauma patient morbidity.

Effect of Vibrotherapy on Body Fatness, Blood Parameters and Fibrinogen Concentration in Elderly Men

Elderly people need activities that will positively contribute to a satisfactory process of getting older. Vibration training uses mechanical stimulus of a vibrational character that, similarly to other forms of physical activity, affects metabolic processes and conditions of health. The aim of this work was to assess the influence of thirty vibration treatments on body fatness, hematologic and rheologic indexes of blood, and proteinogram and fibrinogen concentration in elderly men’s blood. The study included twenty-one males, aged 60–70 years (mean age 65.3 ± 2.7), who were randomly assigned into a vibrotherapy group (VG) and took part in interventions on mattresses generating oscillatory-cycloid vibrations, and a control group (CG), without interventions. In all patients the following assessments were performed twice: an assessment of body fatness using the bioimpedance method, a complete blood count with a hematology analyzer, and erythrocyte aggregation by a laser-optical rotational cell analyzer; whereas, total plasma protein and fibrinogen values were established, respectively, by biuret and spectrophotometric methods. In order to compare the impact of vibrotherapy on changes in the analyzed variables, analysis of variance (ANOVA) or the Wilcoxon test were used. After applying thirty vibration treatments in the VG, a significant decrease in body fatness parameters was confirmed: BM (∆BM: −2.7 ± 2.0; p = 0.002), BMI (∆BMI: −0.9 ± 0.7; p = 0.002), BF (∆BF: −2.5 ± 2.5; p = 0.013), and %BF (∆%BF: −2.0 ± 2.7; p = 0.041), as well as in RBC (∆RBC: −0.1 ± 0.1; p = 0.035). However, changes in erythrocyte aggregation and proteinogram were not confirmed. It was found that after thirty treatments with VG, a significant decrease of fibrinogen level took place (∆ = −0.3 ± 0.3, p = 0.005). Application of thirty vibrotherapy treatments positively affected body fatness parameters and fibrinogen concentrations in the examined. However, further research should include a greater number of participants.

The thrombotic risk of spaceflight: has a serious problem been overlooked for more than half of a century?

The first ever venous thrombotic condition associated with spaceflight, an internal jugular vein thrombus requiring anticoagulation, has recently been reported. Systematic investigation of space travel-associated thrombotic risk has not been conducted. Cellular, animal, and human studies performed in ground-based models and in actual weightlessness revealed influences of weightlessness and gravity on the blood coagulation system. However, human study populations were small and limited to highly selected participants. Evidence in individuals with medical conditions and older persons is lacking. Evidence for thrombotic risk in spaceflight is unsatisfactory. This issue deserves further study in heterogeneous, high risk populations to find prevention strategies and to enable safe governmental and touristic human spaceflight.

Fluid Shifts Induced by Physical Therapy in Lower Limb Lymphedema Patients

Complete decongestive therapy (CDT), a physical therapy including manual lymphatic drainage (MLD) and compression bandaging, is aimed at mobilizing fluid and reducing limb volume in lymphedema patients. Details of fluid shifts occurring in response to CDT are currently not well studied. Therefore, we investigated fluid shifts before, during and after CDT. Thirteen patients (3 males and 10 females, aged 57 ± 8.0 years, 167.2 ± 8.3 cm height, 91.0 ± 23.4 kg weight) diagnosed with stage II leg lymphedema participated. Leg volume, limb and whole-body fluid composition (total body water (limbTBW/%TBW), extracellular (limbECF/%ECF) and intracellular (limbICF/%ICF fluid), as well as ECF/ICF and limbECF/limbICF ratios were determined using perometry and bioelectrical impedance spectroscopy. Plasma volume, proteins, osmolality, oncotic pressure and electrolytes were assessed. Leg volume (p < 0.001), limbECF (p = 0.041), limbICF (p = 0.005) and limbECF/limbICF decreased over CDT. Total leg volume and limbTBW were correlated (r = 0.635). %TBW (p = 0.001) and %ECF (p = 0.007) decreased over time. The maximum effects were seen within one week of CDT. LimbICF (p = 0.017), %TBW (p = 0.009) and %ICF (p = 0.003) increased post-MLD, whereas ECF/ICF decreased due to MLD. Plasma volume increased by 1.5% post-MLD, as well as albumin and the albumin-to-globulin ratio (p = 0.005 and p = 0.049, respectively). Our results indicate that physical therapy leads to fluid shifts in lymphedema patients, with the greatest effects occurring within one week of therapy. Fluid shifts due to physical therapy were also reflected in increased plasma volume and plasma protein concentrations. Perometry, in contrast to bioelectrical impedance analysis, does not seem to be sensitive enough to detect small fluid changes caused by manual lymphatic drainage.

Coagulation Changes during Central Hypovolemia across Seasons

Lower body negative pressure (LBNP) application simulates hemorrhage. We investigated how seasons affect coagulation values at rest and during LBNP. Healthy participants were tested in cold (November–April) and warm (May–October) months. Following a 30-min supine period, LBNP was started at −10 mmHg and increased by −10 mmHg every five minutes until a maximum of −40 mmHg. Recovery was for 10 min. Blood was collected at baseline, end of LBNP, and end of recovery. Hemostatic profiling included standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and thrombin formation markers. Seven men (25.0 ± 3.6 years, 79.7 ± 7.8 kg weight, 182.4 ± 3.3 cm height, and 23.8 ± 2.3 kg/m² BMI) and six women (25.0 ± 2.4 years, 61.0 ± 8.4 kg weight, 167 ± 4.7 cm height, and 21.8 ± 2.4 kg/m² BMI) participated. Baseline levels of prothrombin (FII), tissue factor (TF) and markers for thrombin generation F1+2 and the thrombin/antithrombin complex (TAT) were higher during summer. Factor VIII, prothrombin fragment 1+2 (F1+2), TAT and the coagulation time showed significant increases during LBNP in both seasons. Some calibrated automated thrombography variables (Calibrated automated thrombography (CAT): lag, time to peak (ttPeak), peak) shifted in a procoagulant direction during LBNP in summer. Red blood cell counts (RBC), hemoglobin and white blood cell counts (WBC) decreased during LBNP. LBNP application reduced prothrombin time in winter and activated partial thromboplastin time in summer. Greater levels of FII, TF, F1+2, and TAT—a more pronounced LBNP-induced procoagulative effect, especially in CAT parameters (lag time (LT), Peak, ttPeak, Velindex)—were seen in summer. These results could have substantial medical implications.

Menstrual Phase Affects Coagulation and Hematological Parameters during Central Hypovolemia

Background: It has been reported that women have a higher number of heart attacks in the “follicular phase” of the menstrual cycle. We, therefore, tested the hypothesis that women in the follicular phase exhibit higher coagulability. As lower body negative pressure (LBNP) has been used previously to assess coagulation changes in whole blood (WB) samples in men and women, effects of menstrual phase on coagulation was assessed during LBNP. Methods: Seven women, all healthy young participants, with no histories of thrombotic disorders and not on medications, were tested in two phases of the menstrual cycle (early follicular (EF) and mid-luteal (ML)). LBNP was commenced at −10 mmHg and increased by −10 mmHg every 5 min until a maximum of −40 mmHg. Recovery up to 10 min was also monitored. Blood samples were collected at baseline, at end of LBNP, and at end of recovery. Hemostatic profiling included comparing the effects of LBNP on coagulation values in both phases of the menstrual cycle using standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and markers of thrombin formation. Results: LBNP led to coagulation activation determined in both plasma and WB samples. During both phases, coagulation was affected during LBNP, as reflected in their decreased partial thromboplastin time (PTT) and elevated coagulation factor VIII FVIII, F1 + 2, and thrombin-antithrombin (TAT) levels. Additionally, during the ML phase, greater PT [%] and shorter time to peak (ttPeak) values (implying faster maximum thrombin formation) suggest that women in the ML phase are relatively hypercoagulable compared to the early follicular phase. Conclusions: These results suggest that thrombosis occurs more during the midluteal phase, a finding with substantial medical implications.

Prolonged bedrest reduces plasma high-density lipoprotein levels linked to markedly suppressed cholesterol efflux capacity

Recent observations strongly connect high-density lipoproteins (HDL) function and levels with coronary heart disease outcomes and risk for infections and sepsis. To date, our knowledge of factors determining this connection is still very limited. The immobility associated with prolonged bedrest is detrimental to health, affecting several systems, including the cardiovascular, pulmonary, gastrointestinal, musculoskeletal and urinary. Effects of prolonged bedrest on the composition and functional properties of HDL remain elusive. We evaluated metrics of HDL composition and function in healthy male volunteers participating in a randomized, crossover head-down bedrest study. We observed that HDL cholesterol efflux capacity was profoundly decreased during bedrest, mediated by a bedrest associated reduction in plasma levels of HDL-cholesterol and major apolipoproteins (apo) apoA-I and apoA-II. Paraoxonase activity, plasma anti-oxidative capacity and the activities of lecithin-cholesterol acyltransferase and cholesteryl ester transfer protein were not affected. No change was observed in the content of HDL-associated serum amyloid A, a sensitive marker of inflammation. Resistive vibration exercise countermeasure during bedrest did not correct impaired cholesterol efflux capacity and only tended to increase arylesterase activity of HDL-associated paraoxonase. In conclusion, prolonged bedrest reduces plasma HDL levels linked to markedly suppressed HDL cholesterol efflux capacity. Resistive vibration exercise during bedrest did not correct HDL levels and impaired cholesterol efflux capacity.

Cardio-postural interactions and muscle-pump baroreflex are severely impacted by 60-day bedrest immobilization

To understand fundamental mechanisms associated with post-flight orthostatic intolerance we investigated the interaction between the cardiovascular and postural functions before and after 60 days of head down bedrest (HDBR). Twenty healthy young males (35.0 ± 1.7 years) were subjected to 60-day HDBR at 6˚ to simulate spaceflight-induced fluid shifts. A supine-to-stand (STS) test was conducted to evaluate cardio-postural control before and after (R) HDBR while an assessment of cardiovascular function was performed during HDBR. Beat-to-beat heart period, systolic blood pressure, and electromyography impulses were derived for wavelet transform coherence and causality analyses of the cardio-postural control and used to assess changes in the muscle-pump baroreflex. During quiet stand of the STS test, compared to baseline, heart rate was 50% higher on the day of exit from bedrest (R0) and 20% higher eight days later (R8). There was a 50% increase in deoxygenated hemoglobin on R0 and R8. Leg muscle activity reduced, and postural sway increased after HDBR. Causality of the muscle-pump baroreflex was reduced on R0 (0.73 ± 0.2) compared to baseline (0.87 ± 0.2) with complete recovery by R8. The muscle-pump baroreflex also had decreased gain and fraction time active following HDBR. Overall, our data show a significantly impaired muscle-pump baroreflex following bedrest.

MNX (Medium Duration Nutrition and Resistance-Vibration Exercise) Bed-Rest: Effect of Resistance Vibration Exercise Alone or Combined With Whey Protein Supplementation on Cardiovascular System in 21-Day Head-Down Bed Rest

Current inflight countermeasures do not completely prevent bone and cardiovascular changes induced by microgravity. High load Resistance Exercise combined with whole body Vibration (RVE) demonstrated benefits on bone and cardiovascular system during previous Head-Down Bed Rest (HDBR) studies. We examined the effectiveness of RVE alone or combined with a nutritional supplementation of Whey protein (NeX) on cardiovascular deconditioning. Eight male subjects (age 34 ± 8 years) in a crossover design completed three 21-day HDBR campaigns (Control-CON, RVE, and NeX). Pre and post HDBR Orthostatic Tolerance (OT) was evaluated by a 15-min head-up tilt test followed by increasing levels of Lower Body Negative Pressure (LBNP). Heart rate (HR), blood pressure (BP), and Sympathetic Index (ΣI) through spectral analysis were measured during OT test. Plasma Volume (PV), and Maximal Oxygen Uptake (VO2max) were measured before and after each campaign. Left ventricular mass, left ventricular end diastolic (LVEDV), end systolic (LVESV), stroke (SV) volumes, and circumferential deformation at rest and during an orthostatic stress simulated by a 30 mmHg LBNP were measured by cardiac MRI. RVE failed to prevent any change in these variables and NeX did not have any additional effect over exercise alone. In the 3 groups, (1) OT time dropped similarly (bed rest p < 0.001), (2) HR and ΣI were increased at rest at the end of HDBR and HR increased markedly during LBNP-tilt test, with inability to increase further the ΣI, (3) PV dropped (bed rest p < 0.001), along with LVEDV, LVESV and SV (p = 0.08, p < 0.001, and p = 0.045, respectively), (4) Left ventricle mass did not change significantly, (5) Deformation of the heart assessed by global circumferential strain was preserved and early diastolic circumferential strain rate was increased during orthostatic stress at the end of HDBR, illustrating preserved systolic and diastolic function respectively, without any difference between groups. Despite the drop in PV and LV volumes, RVE and NeX tended to alleviate the decrease in VO2max. In conclusion, RVE and NeX failed to prevent the cardiovascular deconditioning induced by a 21 day-HDBR.

Coagulation changes induced by lower-body negative pressure in men and women

We investigated whether lower-body negative pressure (LBNP) application leads to coagulation activation in whole blood (WB) samples in healthy men and women. Twenty-four women and 21 men, all healthy young participants, with no histories of thrombotic disorders and not on medications, were included. LBNP was commenced at −10 mmHg and increased by −10 mmHg every 5 min until a maximum of −40 mmHg. Recovery up to 10 min was also monitored. Blood samples were collected at baseline, at end of LBNP, and end of recovery. Hemostatic profiling included comparing the effects of LBNP on coagulation values in both men and women using standard coagulation tests, calibrated automated thrombogram, thrombelastometry, impedance aggregometry, and markers of thrombin formation. LBNP led to coagulation activation determined in both plasma and WB samples. At baseline, women were hypercoagulable compared with men, as evidenced by their shorter “lag times” and higher thrombin peaks and by shorter “coagulation times” and “clot formation times.” Moreover, men were more susceptible to LBNP, as reflected in their elevated factor VIII levels and decreased lag times following LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. Women appear to be relatively hypercoagulable compared with men, but men are more susceptible to coagulation changes during LBNP. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.

NEW & NOTEWORTHY LBNP led to coagulation activation determined in both plasma and whole blood samples. At baseline, women were hypercoagulable compared with men. Men were, however, more susceptible to coagulation changes during LBNP. LBNP-induced coagulation activation was not accompanied by endothelial activation. The application of LBNP might be a useful future tool to identify individuals with an elevated risk for thrombosis, in subjects with or without history of thrombosis.

The Role of Enhanced Cognition to Counteract Detrimental Effects of Prolonged Bed Rest: Current Evidence and Perspectives

Prolonged periods of physical inactivity or bed rest can lead to a significant decline of functional and cognitive functions. Different kinds of countermeasures (e.g., centrifugation, nutritional, and aerobic interventions) have been developed to attempt to mitigate negative effects related to bed rest confinement. The aim of this report is to provide an overview of the current evidence related to the effectiveness of computerized cognitive training (CCT) intervention during a period of complete physical inactivity in older adults. CCT, using a virtual maze navigation task, appears to be effective and has long-lasting benefits (up to 1.5 years after the study). Moreover, enhanced cognition (executive control) reduces decline in the ability to perform complex motor-cognitive dual-tasks after prolonged period of bed rest. It has been demonstrated that CCT administration in older adults also prevents bed rest stress-related physiological changes [these groups showed minimal changes in vascular function and an unchanged level of brain-derived neurotrophic factor (BDNF)] while control subjects showed decreased peripheral vascularization and increased plasma level of the neurotrophin BDNF during a 14-day bed rest. In addition, the effects of CCT are evident also from the brain electrocortical findings: CCT group revealed a decreased power in lower delta and theta bands while significant increases in the same EEG spectral bands power were found in control subjects. If we consider an increase of power in delta band as a marker of cortical aging, then the lack of shift of EEG power to lower band indicates a preventive role of CCT on the cortical level during physiological deconditioning induced by 2-week bed rest immobilization. However, replication on a larger sample is required to confirm the observed findings. Applications derived from these findings could be appropriate for implementation of hospital treatment for bed ridden patients as well as for fall prevention programs.

Artificial Gravity as a Countermeasure to the Cardiovascular Deconditioning of Spaceflight: Gender Perspectives

Space flight-induced physiological deconditioning resulting from decreased gravitational input, decreased plasma volume, and disruption of regulatory mechanisms is a significant problem in returning astronauts as well as in normal aging. Here we review effects of a promising countermeasure on cardiovascular systems of healthy men and women undergoing Earth-based models of space-flight. This countermeasure is produced by a centrifuge and called artificial gravity (AG). Numerous studies have determined that AG improves orthostatic tolerance (as assessed by various protocols) of healthy ambulatory men, of men deconditioned by bed rest or by immersion (both wet and dry) and, in one case, following spaceflight. Although a few studies of healthy, ambulatory women and one study of women deconditioned by furosemide, have reported improvement of orthostatic tolerance following exposure to AG, studies of bed-rested women exposed to AG have not been conducted. However, in ambulatory, normovolemic subjects, AG training was more effective in men than women and more effective in subjects who exercised during AG than in those who passively rode the centrifuge. Acute exposure to an AG protocol, individualized to provide a common stimulus to each person, also improved orthostatic tolerance of normovolemic men and women and of furosemide-deconditioned men and women. Again, men's tolerance was more improved than women's. In both men and women, exposure to AG increased stroke volume, so greater improvement in men vs. women was due in part to their different vascular responses to AG. Following AG exposure, resting blood pressure (via decreased vascular resistance) decreased in men but not women, indicating an increase in men's vascular reserve. Finally, in addition to counteracting space flight deconditioning, improved orthostatic tolerance through AG-induced improvement of stroke volume could benefit aging men and women on Earth.

Falls and Fall-Prevention in Older Persons: Geriatrics Meets Spaceflight!

This paper provides a general overview of key physiological consequences of microgravity experienced during spaceflight and of important parallels and connections to the physiology of aging. Microgravity during spaceflight influences cardiovascular function, cerebral autoregulation, musculoskeletal, and sensorimotor system performance. A great deal of research has been carried out to understand these influences and to provide countermeasures to reduce the observed negative consequences of microgravity on physiological function. Such research can inform and be informed by research related to physiological changes and the deterioration of physiological function due to aging. For example, head-down bedrest is used as a model to study effects of spaceflight deconditioning due to reduced gravity. As hospitalized older persons spend up to 80% of their time in bed, the deconditioning effects of bedrest confinement on physiological functions and parallels with spaceflight deconditioning can be exploited to understand and combat both variations of deconditioning. Deconditioning due to bed confinement in older persons can contribute to a downward spiral of increasing frailty, orthostatic intolerance, falls, and fall-related injury. As astronauts in space spend substantial amounts of time carrying out exercise training to counteract the microgravity-induced deconditioning and to counteract orthostatic intolerance on return to Earth, it is logical to suggest some of these interventions for bed-confined older persons. Synthesizing knowledge regarding deconditioning due to reduced gravitational stress in space and deconditioning during bed confinement allows for a more comprehensive approach that can incorporate aspects such as (mal-) nutrition, muscle strength and function, cardiovascular (de-) conditioning, and cardio-postural interactions. The impact of such integration can provide new insights and lead to methods of value for both space medicine and geriatrics (Geriatrics meets spaceflight!). In particular, such integration can lead to procedures that address the morbidity and the mortality associated with bedrest immobilization and in the rising health care costs associated with an aging population demographic.

Variation in Definitions of Immobility in Pharmacological Thromboprophylaxis Clinical Trials in Medical Inpatients: A Systematic Review

BACKGROUND

Although immobility is a common risk factor for venous thromboembolism (VTE) in medical inpatients, lack of a consistent definition of this term may limit accurate assessment of VTE risk for thromboprophylaxis.

OBJECTIVE

To examine various definitions of immobility used in recent pharmacological thromboprophylaxis clinical trials.

DATA SOURCES

PubMed and relevant references from articles/reviews from 2008 to 2016 were searched. Randomized controlled trials (RCTs) and other clinical studies involving adult hospitalized medical patients in acute care hospital settings that used the term immobility were selected. Two investigators independently abstracted data in duplicate, and accuracy was checked by a third investigator.

RESULTS

Twenty-one clinical studies were included. There was heterogeneity among individual VTE risk factors, with respect to the definition of immobility in medical inpatients in these trials. Thirteen studies utilized objective criteria to define "immobility" including duration (12 studies) and distance or time walked (6 studies). In contrast, 7 studies focused principally on subjective definitions (ie, describing the nature of immobility rather than specifying its quantitative measurement). Three RCTs vaguely defined the level of patient's immobility after hospitalization.

CONCLUSION

Despite the well-known effectiveness of pharmacological thromboprophylaxis for the prevention of VTE in acutely ill medical patients, there is no current consensus on how to define immobility. The heterogeneous nature of definitions of immobility has led to uncertainty about the importance of immobility in VTE risk assessment models. Although clinical studies have incorporated varying definitions of immobility into their inclusion criteria, immobility as a specific VTE risk factor has not been clearly defined.