Ronita L. Cromwell

Horizontal plane head stabilization during locomotor tasks.

Abstract Frequency characteristics of head stabilization were examined during locomotor tasks in healthy young adults (N = 8) who performed normal walking and 3 walking tasks designed to produce perturbations primarily in the horizontal plane. In the 3 walking tasks, the arms moved in phase with leg movement, with abnormally large amplitude, and at twice the frequency of leg movement. Head-in-space angular velocity was examined at the predominant frequencies of trunk motion. Head movements in space occurred at low frequencies (< 4.0 Hz) in all conditions and at higher frequencies (> 4.0 Hz) when the arms moved at twice the frequency of the legs. Head stabilization strategies were determined from head-on-trunk with respect to trunk frequency profiles derived from angular velocity data. During natural walking at low frequencies (< 3.0 Hz), head-on-trunk movement was less than trunk movement. At frequencies 3.0 Hz or greater, equal and opposite compensatory movement ensured head stability. When arm swing was altered, compensatory movement guaranteed head stability at all frequencies. Head stabilization was successful for frequencies up to 10.0 Hz during locomotor tasks Maintaining head stability at high frequencies during voluntary tasks suggests that participants used feedforward mechanisms to coordinate head and trunk movements. Maintenance of head stability during dynamic tasks allows optimal conditions for vestibulo-ocular reflex function.

The Effect of Microgravity on Ocular Structures and Visual Function: A Review

Ocular structural and functional changes, including optic disk edema and reduction of near visual acuity, have been recently described in some astronauts returning from long-duration space travels. It is hypothesized that ocular changes related to spaceflight may occur, in predisposed individuals, as a result of cephalad shift of body fluids, possibly leading to elevated intracranial pressure (ICP). Results from head-down bed-rest studies (used to simulate the effects of microgravity) and from parabolic flight experiments (used to produce transient periods of microgravity) indicate that ocular blood flow and intraocular pressure (IOP) may undergo changes in a low-gravity environment. Recent studies suggest that changes in translaminar pressure (i.e., IOP minus ICP) may be implicated in the pathophysiology of optic disk neuropathies. Because postural changes exert an effect on both IOP and ICP, the head-down bed-rest analog may also be used as a platform to characterize the relationship between IOP and ICP, and their reciprocal influence in the pathophysiology of conditions such as optic disk edema or glaucoma.

ASSOCIATION OF BALANCE MEASURES AND PERCEPTION OF FALL RISK ON GAIT SPEED: A MULTIPLE REGRESSION ANALYSIS

ABSTRACT Gait speed, commonly modified to adapt to the balance and stability challenges of aging, is related to measures of balance and mobility. This study investigated associations between age, Berg Balance Scale, Activities-Specific Balance Confidence (ABC) Scale, One Question Fear of Falling (1QFOF), and gait speed in adults using regression analysis. Results suggested an interaction between 1QFOF and ABC scores. An expanded five-variable model explained 49% of gait speed variance. Age, ABC, and 1QFOF-ABC interactions were significantly associated with gait speed. Regression analysis is useful in investigating associations between performance variables and function. Continued research needs to identify optimal variable combinations and improve prediction of function.

Movement strategies for head stabilization during incline walking.

Changes in body orientation with respect to space during incline walking can alter vestibular information requiring a different solution to the problem of head stabilization. Eleven young adults walked along a level walkway, and ascended and descended an inclined surface. Head, neck and trunk angular positions in space were collected. Changes in the gravitoinertial vector imposed by the inclined surface, produced concomitant changes in body segment orientation that decreased head stability during the inclined walking tasks. Head, neck and trunk segments were least stable while ascending the incline creating the greatest challenge to head stability during this task. Movement strategies reflected adjustments of head-neck and neck-trunk patterns to accommodate changes in the gravitoinertial vector and insure balance of the head over the trunk.

Effects of 30-Day Head-Down Bed Rest on Ocular Structures and Visual Function in a Healthy Subject

INTRODUCTION We report ocular changes occurring in a healthy human subject enrolled in a bed rest (BR) study designed to replicate the effects of a low-gravity environment. CASE REPORT A 25-yr-old Caucasian man spent 30 consecutive days in a 6 degrees head-down tilt (HDT) position at the NASA Flight Analogs Research Unit. Comprehensive ophthalmologic exams, optic disc stereo-photography, standard automated perimetry (SAP), and optic disc Spectralis OCT scans were performed at baseline, immediately post-BR (BR+0), and 6 mo post-BR. MAIN OUTCOME MEASURES changes in best-corrected visual acuity, intraocular pressure (IOP), cycloplegic refraction, SAP, and Spectralis OCT measures. At BR+0 KIOP was 11 and 10 mmHg in the right (OD) and left eye (OS), respectively (a bilateral 4-mmHg decrease compared to baseline); SAP documented a possible bilateral symmetrical inferior scotoma; Spectralis OCT showed an average 19.4 microm (+5.2%) increase in peripapillary retinal thickness, and an average 0.03 mm3 (+5.0%) increase in peripapillary retinal volume bilaterally. However, there were no clinically detectable signs of optic disc edema. At 6 mo post-BR, IOP was 13 and 14 mmHg in OD and OS, respectively, and the scotoma had resolved. Spectralis OCT measurements matched the ones recorded at baseline. DISCUSSION In this subject, a reduction in IOP associated with subtle structural and functional changes compared to baseline were documented after prolonged head-down BR. These changes may be related to cephalad fluid shifts in response to tilt. Further studies should clarify whether decreased translaminar pressure (i.e., the difference between IOP and intracranial pressure) may be responsible for these findings.

Ocular outcomes evaluation in a 14-day head-down bed rest study.

INTRODUCTION We evaluated ocular outcomes in a 14-d head-down tilt (HDT) bed rest (BR) study designed to simulate the effects of microgravity on the human body. METHODS Healthy subjects were selected using NASA standard screening procedures. Standardized NASA BR conditions were implemented (e.g., strict sleep-wake cycle, standardized diet, 24-hour-a-day BR, continuous video monitoring). Subjects maintained a 6° HDT position for 14 consecutive days. Weekly ophthalmological examinations were performed in the sitting (pre/post-BR) and HDT (in-bed phase) positions. Equivalency tests with optimal-alpha techniques evaluated pre/post-BR differences in best-corrected visual acuity (BCVA), spherical equivalent, intraocular pressure (IOP), Spectral-domain OCT retinal nerve fiber layer thickness (RNFLT), optic disc and macular parameters. RESULTS 16 subjects (12 men and 4 women) were enrolled. Nearly all ocular outcomes were within our predefined clinically relevant thresholds following HDTBR, except near BCVA (pre/post-BR mean difference: -0.06 logMAR), spherical equivalent (-0.30 D), Tonopen XL IOP (+3.03 mmHg) and Spectralis OCT average (+1.14 μm), temporal-inferior (+1.58 μm) and nasal-inferior RNFLT (+3.48 μm). Modified Amsler grid, red dot test, confrontational visual field, and color vision were within normal limits throughout. No changes were detected on stereoscopic color fundus photography. DISCUSSION A few functional and structural changes were detected after 14-d HDTBR, notably an improved BCVA possibly due to learning effect and RNFL thickening without signs of optic disc edema. In general, 6° HDTBR determined a small nonprogressive IOP elevation, which returned to baseline levels post-BR. Further studies with different BR duration and/or tilt angle are warranted to investigate microgravity-induced ophthalmological changes.

Ocular Outcomes Comparison Between 14- and 70-day Head-down Tilt Bed Rest

Purpose To compare ocular outcomes in healthy subjects undergoing 14- and/or 70-day head-down-tilt (HDT) bed rest (BR). Methods Participants were selected by using NASA standard screening procedures. Standardized NASA BR conditions were implemented. Subjects maintained a 6° HDT position for 14 and/or 70 consecutive days. Weekly ophthalmologic examinations were performed in the sitting (pre/post-BR only) and HDT positions. Mixed-effects linear models compared pre- and post-HDT BR observations between 14- and 70-day HDT BR in best-corrected visual acuity, spherical equivalent, intraocular pressure (IOP), Spectralis OCT retinal nerve fiber layer thickness, peripapillary and macular retinal thicknesses. Results Sixteen and six subjects completed the 14- and 70-day HDT BR studies, respectively. The magnitude of HDT BR–induced changes was not significantly different between the two studies for all outcomes, except the superior (mean pre/post difference of 14- vs. 70-day HDT BR: +4.69 μm versus +11.50 μm), nasal (+4.63 μm versus +11.46 μm), and inferior (+4.34 μm versus +10.08 μm) peripapillary retinal thickness. A +1.42 mm Hg and a +1.79 mm Hg iCare IOP increase from baseline occurred during 14- and 70-day HDT BR, respectively. Modified Amsler grid, red dot test, confrontational visual field, color vision, and stereoscopic fundus photography were unremarkable. Conclusions Seventy-day HDT BR induced greater peripapillary retinal thickening than 14-day HDT BR, suggesting that time may affect the amount of optic disc swelling. Spectralis OCT detected retinal nerve fiber layer thickening post BR, without clinical signs of optic disc edema. A small IOP increase during BR subsided post HDT BR. Such changes may have resulted from BR-induced cephalad fluids shift. The HDT BR duration may be critical for replicating microgravity-related ophthalmologic changes observed in astronauts on ≥6-month spaceflights.

Balance Abilities of Homebound Older Adults Classified as Fallers and Nonfallers

Purpose: Balance instability and falling are not well documented in homebound older adults.This study examined balance, falls, and related variables in older adults primarily confined to their homes. Subjects: Thirty older adults between the ages of 66 and 99 years participated. Fifteen were classified as fallers and 15 classified as nonfallers. Methods: Subjects were assessed on the Berg Balance Test (BBT) and measures of fear of falling and activity levels. The number of environmental hazards in their homes that could contribute to falls was recorded. Results: Mean scores for the fallers and nonfallers were similar on the BBT (36.5 vs 35.7), Falls Efficacy Scale (16.8 vs 14.7), and Tinetti Activity Index (4.5 vs 4.9). A cut‐off score on the BBT of ≤ 45 yielded a sensitivity of 60%, a specificity of 40%, and a predictive value of 50% for determining fall risk. Conclusion: On the basis of BBT scores, homebound older adults receiving therapy services should be considered at risk of falling regardless of 6‐month fall history. These homebound individuals may be at higher risk of falling because their current health and medical condition precipitated the need for home care physical therapy.The BBT and screening for environmental hazards should be a standard part of all assessments for older adults using home care services.

The Relationship Between Physical Performance and Obesity in Elderly African-American Women

ABSTRACT Objective. To examine the relationship between physical performance and obesity in older African-American women. Methods. Obese (n = 45) and nonobese (n = 88) women were assessed using instrumental activities of daily living, physical function subscale of the Medical Outcomes Short Form-36, and the physical activity scale for the elderly. Physical performance was assessed by Berg Balance Scale, Tandem Stance and Single Test Stance Tests, Multidirectional Reach Test, Timed Up and Go Limb, Six-Minute Walk Test, gait stability ratio, and self-report of daily walking. Results. The obese group had significantly lower self-reported daily activities and poorer scores on several physical performance measures than nonobese older African-American women. Conclusions. Our findings substantiate a relationship between obesity and physical performance in African-American women. Although urban obese women have poorer physical performance, their impairments may be counterbalanced by their daily walking. Clinicians should consider this finding when developing rehabilitative and preventive strategies for older obese African-American women.

Ophthalmological Evaluation of Integrated Resistance and Aerobic Training During 70-Day Bed Rest

INTRODUCTION We evaluated ophthalmic changes in healthy individuals who underwent integrated resistance and aerobic training (iRAT) during 70-d 6° head-down tilt (HDT) bed rest (BR). METHODS Participants were selected using NASA standard screening procedures. Standardized NASA BR conditions were implemented. Subjects were randomly assigned to the iRAT protocol or no exercise during HDTBR. Weekly ophthalmic examinations were performed in the sitting (pre/post-BR only) and HDT (BR only) positions. Mixed-effects linear models compared pre- and post-HDTBR intraocular pressure (IOP), Spectralis OCT circumpapillary retinal nerve fiber layer (cpRNFL) thickness, and peripapillary retinal thickness observations between groups. RESULTS Six controls and nine exercisers completed the study. There was an overall effect of BR on our outcomes. Except Goldmann IOP (mean pre/post difference in controls and exercisers: -0.47 mmHg vs. +1.14 mmHg), the magnitude of changes from baseline was not significantly different between groups. There was a +1.38 mmHg and a +1.63 mmHg iCare IOP increase during BR in controls and exercisers, respectively. Spectralis OCT detected a +1.33 μm average cpRNFL thickness increase in both groups, and a +9.77 μm and a +6.65 μm peripapillary retinal thickening post-BR in controls and exercisers, respectively. Modified Amsler grid, red dot test, confrontational visual field, color vision, and stereoscopic fundus photography were unremarkable. CONCLUSIONS HDTBR for 70 d induced peripapillary retinal thickening and cpRNFL thickening without visible signs of optic disc edema. The magnitude of such changes was not different between controls and exercisers. A slight IOP increase during BR subsided post-BR. Further study should evaluate whether different physical exercise paradigms may prevent/mitigate the risk of space-related visual impairment.Taibbi G, Cromwell RL, Zanello SB, Yarbough PO, Ploutz-Snyder RJ, Godley BF, Vizzeri G. Ophthalmological evaluation of integrated resistance and aerobic training during 70-day bed rest. Aerosp Med Hum Perform. 2017; 88(7):633-640.