Product limit estimation for capturing of pressure distribution dynamics.

Measurement of contact pressures at the wheelchair-seating interface is a critically important approach for laboratory research and clinical application in monitoring risk for pressure ulceration. As yet, measures obtained from pressure mapping are static in nature: there is no accounting for changes in pressure distribution over time, despite the well-known interaction between time and pressure in risk estimation. Here, we introduce the first dynamic analysis for distribution of pressure data, based on the Kaplan-Meier (KM) Product Limit Estimator (PLE) a ubiquitous tool encountered in clinical trials and survival analysis. In this approach, the pressure array-over-time data set is sub-sampled two frames at a time (random pairing), and their similarity of pressure distribution is quantified via a correlation coefficient. A large number (here: 100) of these frame pairs is then sorted into descending order of correlation value, and visualized as a KM curve; we build confidence limits via a bootstrap computed over 1000 replications. PLEs and the KM have robust statistical support and extensive development: the opportunities for extended application are substantial. We propose that the KM-PLE in particular, and dynamic analysis in general, may provide key leverage on future development of seating technology, and valuable new insight into extant datasets.

Proxy study on minimizing risk of sacral pressure ulcers while complying with ventilator-associated pneumonia risk reduction guidelines.

Bed positioning poses a subtle, yet important, tradeoff in the competing needs of hospitalized patients, particularly those susceptible to lower respiratory tract infections and/or pressure ulcers. Although it is widely held that a minimum 30° incline is necessary to mitigate risk of ventilator-acquired pneumonia, it is unclear what effect semirecumbent positioning has on the risk of pressure ulcerations. The authors test several hypotheses with the objective of elucidating the relationship between bed incline, posture, and incline, pursuant to a more evidence-based recommendation for practice in clinical care. To this end, interfacial pressures from 40 healthy subjects were analyzed following observation in both supine and sidelying positions, at shallow (30°) and moderate (45°) bed-angle incline. Summarily, the authors report that supine postures reduce pressure signatures associated with pressure ulceration versus sidelying position: 15% increase area of contact (P = 1.3×10), and 17% decrease in ratio of peak to average pressure (P = 3.1×10). Within supine posture, the authors found significant increases in 4 measures of local pressure, including average pressure (10.4% decrease, P = .005) and coefficient of pressure variation (22.1%, P = 2.2×10) at moderate incline. The authors conclude that supine bed positionings at moderate incline appear to reduce predictors of pressure ulceration.

Prevalence of Sensor Saturation in Wheelchair Seat Interface Pressure Mapping.

Pressure mapping is a frequently used tool with great power to provide information about the forces between a patient and a wheelchair seat. One widely recognized limitation to this paradigm is the possibility of data loss due to sensor saturation. In this study, we seek to quantify and describe the saturation observed in the measurement of interface pressures of wheelchair users. We recorded approximately two minutes of interface pressure data from 22 elderly wheelchair users (11M/11F, 80 ± 10 years) and found that 4.7% of data frames had 1 saturated sensor, and 9.0% had more than one saturated sensor, for a total of 13.7% of all frames of data. Data from three of the 22 subjects (13.6%) were substantially affected by the persistent presence of saturated sensors. We conclude that for this population of elderly wheelchair users, sensor saturation may be a concern and should be factored properly into study design a priori.

Effect of tilt and recline on ischial and coccygeal interface pressures in people with spinal cord injury.

OBJECTIVE: Clinicians commonly recommend that power wheelchair users with spinal cord injury perform wheelchair tilt and recline maneuvers to redistribute seating loads away from the ischial tuberosities. However, ischial pressure reduction may be accompanied by coccygeal pressure increases. Although the coccyx is among the most common sites of pressure ulcers, few studies have reported coccygeal interface pressure. The purpose of this study was to investigate both ischial and coccygeal interface pressures in response to changes in wheelchair tilt and recline angles. DESIGN: Thirteen power wheelchair users were recruited into this study. Six combinations of wheelchair tilt (15, 25, and 35 degrees) and recline (10 and 30 degrees, corresponding to traditional recline conventions of 100 and 120 degrees, respectively) angles were tested in random order. Each combination was tested with 5 mins of upright sitting, 5 mins of tilt and recline, as well as 5 mins of maximal pressure relief recovery. Peak pressure indices were calculated at the ischial and coccygeal sites. RESULTS: Ischial pressures monotonically decreased in response to increasing combinations of tilt and recline. Increments of 15 degrees of tilt did not produce significant differences under either recline angle, whereas increments of 25 degrees of tilt produced significant differences under both recline angles. Coccygeal pressures increased in response to the four smallest (of six) combinations of tilt and recline, whereas they decreased in response to the largest two combinations. CONCLUSIONS: Ischial pressures seemed to be redistributed to the coccyx in response to the four smallest angle combinations and redistributed to the back support in response to the two largest angle combinations. Future work should confirm this pressure redistribution to the back support and determine the back support locations of redistribution.

Investigation of peak pressure index parameters for people with spinal cord injury using wheelchair tilt-in-space and recline: methodology and preliminary report.

The purpose of this study was to determine the effect of the sensel window's location and size when calculating the peak pressure index (PPI) of pressure mapping with varying degrees of wheelchair tilt-in-space (tilt) and recline in people with spinal cord injury (SCI). Thirteen power wheelchair users were recruited into this study. Six combinations of wheelchair tilt (15°, 25°, and 35°) and recline (10° and 30°) were used by the participants in random order. Displacements of peak pressure and center of pressure were extracted from the left side of the mapping system. Normalized PPI was computed for three sensel window dimensions (3 sensels × 3 sensels, 5 × 5, and 7 × 7). At least 3.33 cm of Euclidean displacement of peak pressures was observed in the tilt and recline. For every tilt angle, peak pressure displacement was not significantly different between 10° and 30° recline, while center of pressure displacement was significantly different (P < .05). For each recline angle, peak pressure displacement was not significantly different between pairs of 15°, 25°, and 35° tilt, while center of pressure displacement was significantly different between 15° versus 35° and 25° versus 35°. Our study showed that peak pressure displacement occurs in response to wheelchair tilt and recline, suggesting that the selected sensel window locations used to calculate PPI should be adjusted during changes in wheelchair configuration.

Comparison of muscle and skin perfusion over the ischial tuberosities in response to wheelchair tilt-in-space and recline angles in people with spinal cord injury.

OBJECTIVE: To compare the efficacy of wheelchair tilt-in-space and recline on enhancing muscle and skin perfusion over the ischial tuberosities in people with spinal cord injury (SCI). DESIGN: Repeated-measures and before-after trial design. SETTING: University research laboratory. PARTICIPANTS: Power wheelchair users with SCI (N=20). INTERVENTIONS: Six combinations of wheelchair tilt-in-space and recline angles were presented to participants in a random order. The testing protocol consisted of a baseline 5 minutes sitting with no tilt/recline and 5 minutes positioned in a tilted and reclined position at each of 6 conditions, including: (1) 15° tilt-in-space and 100° recline, (2) 25° tilt-in-space and 100° recline, (3) 35° tilt-in-space and 100° recline, (4) 15° tilt-in-space and 120° recline, (5) 25° tilt-in-space and 120° recline, and (6) 35° tilt-in-space and 120° recline. MAIN OUTCOME MEASURES: Muscle and skin perfusion were assessed by near-infrared spectroscopy and laser Doppler flowmetry, respectively. RESULTS: Muscle perfusion was significantly increased at 25° and 35° tilt-in-space when combined with 120° recline, and skin perfusion was significantly increased at 3 tilt-in-space angles (15°, 25°, 35°) when combined with 120° recline and at 35° tilt-in-space when combined with 100° recline (P<.05). Even in the positions of increased muscle perfusion and skin perfusion (25° and 35° of tilt-in-space combined with 120° of recline), the amount of muscle perfusion change was significantly lower than the amount of skin perfusion change (P<.05). CONCLUSIONS: Our results indicate that a larger angle of tilt-in-space and recline is needed to improve muscle perfusion compared with skin perfusion. A position of 25° tilt-in-space combined with 120° recline is effective in enhancing muscle and skin perfusion of weight-bearing soft tissues at the ischial tuberosities.

Wheelchair tilt-in-space and recline does not reduce sacral skin perfusion as changing from the upright to the tilted and reclined position in people with spinal cord injury.

OBJECTIVE: To investigate the effect of various wheelchair tilt-in-space and recline angles on sacral skin perfusion in wheelchair users with spinal cord injury. DESIGN: Repeated-measures, intervention and outcomes measure design. SETTING: University research laboratory. PARTICIPANTS: Power wheelchair users with spinal cord injury (N=11). INTERVENTIONS: Six protocols of various wheelchair tilt-in-space and recline angles were randomly assigned to the participants: (1) 15° tilt-in-space and 100° recline, (2) 25° tilt-in-space and 100° recline, (3) 35° tilt-in-space and 100° recline, (4) 15° tilt-in-space and 120° recline, (5) 25° tilt-in-space and 120° recline, and (6) 35° tilt-in-space and 120° recline. Each protocol consisted of a 5-minute upright sitting and a 5-minute tilted and reclined period. MAIN OUTCOME MEASURES: Skin perfusion over the sacrum (midpoint between the right posterior superior iliac spine and the adjacent spinous process) and right ischial tuberosity was measured using laser Doppler flowmetry. RESULTS: Sacral skin perfusion did not show a significant difference in all 6 protocols of various tilt-in-space and recline angles when changing from an upright to a tilted and reclined position (not significant). However, as previously reported, skin perfusion over the ischial tuberosity showed a significant increase at 15°, 25°, and 35° tilt-in-space when combined with 120° recline and at 35° tilt-in-space when combined with 100° recline (P<.008). CONCLUSIONS: Our results indicate that wheelchair tilt-in-space and recline enhances skin perfusion over the ischial tuberosities without reducing sacral skin perfusion when changing from an upright to a tilted and reclined position.

Intrarater and interrater reliability of 22 clinical measures associated with lower quarter malalignment.

OBJECTIVE: The purpose of this study was to assess the intrarater and interrater reliability of a broad range of techniques commonly used to assess the lower quarter. METHODS: A test-retest single group design was used to investigate the intrarater and interrater reliability of 22 lower quarter evaluation measures. Two raters conducted each measure twice on a total of 18 unimpaired subjects with an average age of 23.7 years. This study was conducted in the Human Performance Research laboratory in a university setting. Intraclass correlation coefficients were used to assess reliability of continuous variables, and weighted kappa was used to assess nominal or ordinal results. RESULTS: Side differences were not found (P > .05); thus, data for right and left legs were pooled (n = 36) where applicable. Intraclass correlation coefficient and weighted kappa results ranged from a low of 0.06 to a high of 0.99. Intrarater reliability results were generally higher than interrater reliability results. CONCLUSION: Many of the clinical measures demonstrated good overall reliability. For those tests where acceptable intrarater and interrater reliability cannot be demonstrated, additional training of raters, modification of the technique, or elimination of the technique's use should be considered.

In patients with heart failure elevated soluble TNF-receptor 1 is associated with higher risk of depression.

BACKGROUND: Pro-inflammatory cytokines may contribute to the development and progression of heart failure (HF) and are also implicated in depressive disorders. In this cross-sectional study, we investigated whether systemic inflammation, as assessed by circulating levels of inflammatory cytokines, was associated with comorbid depression in patients with heart failure. METHODS AND RESULTS: Baseline clinical variables, depression status, and inflammatory marker levels were measured in 129 ambulatory HF patients. We hypothesized that pro-inflammatory cytokines, specifically tumor necrosis factor (TNF)-alpha, interleukin (IL)-1, and IL-6, would be elevated in HF patients with comorbid depression. In unadjusted analyses, levels of soluble TNF-alpha receptor1 (sTNFr1) were significantly higher among depressed (1.6 ng/mL), compared with nondepressed (1.1 ng/mL), HF patients (P = .01). After multivariate adjustment, compared with patients in the lowest quartile of sTNFr1 levels, those in the highest quartile had an adjusted near 5-fold higher risk of depression (OR 4.6, 95% CI 1.2-17.3; P for trend .008). The subgroup of patients on antidepressants but not currently depressed had a trend toward higher levels of sTNFr1, suggesting that antidepressants may not lower cytokine levels even when adequately treating depressive symptoms. IL-1beta and IL-6 levels were not significantly different among depressed versus nondepressed HF patients. CONCLUSIONS: In this cross-sectional analysis, HF patients with comorbid depression, compared with nondepressed HF patients, had higher levels of sTNFr1 and trend toward higher levels of sTNFr1 even when adequately treated for depression.

A dynamic seating intervention for wheelchair seating discomfort.

OBJECTIVE: The objective of this study was to examine the effectiveness of a new user-adjustable wheelchair seating system designed to relieve discomfort for long-duration wheelchair users. DESIGN: This objective was carried out using the newly developed Tool for Assessing Wheelchair disComfort (TAWC) as the primary outcome measure. Two wheelchair users each tested two different designs and feedback from the wheelchair users regarding the first design was used to guide development of the second design. A single-subject research methodology was used, allowing long-duration (up to 2 wks per test) evaluation of the wheelchair seating systems and comparison of subject discomfort levels with those experienced during a baseline period using their own wheelchairs. The experimental wheelchair seating systems employed existing automotive seating with embedded pneumatic bladders that allowed adjustment of the seat and back-support characteristics. The test wheelchair also had tilt, recline, and elevating leg rests. RESULTS: The two subjects completed limited periods of testing with the first design, both finding poor results with either stable or increased levels of discomfort. Subject feedback was used to redesign the wheelchair seat. After redesign, both subjects tested the second design and found it substantially more comfortable. CONCLUSIONS: The selected research methodology was a very positive method for a progressive wheelchair seating design and the second design provided improved comfort for both users when compared with that experienced using their own wheelchairs and the first test wheelchair. Future research of this type of user-controlled technology is recommended.

Responsiveness of the TAWC tool for assessing wheelchair discomfort.

PURPOSE: The purpose of this research was to determine the clinical usefulness of the Tool for Assessing Wheelchair disComfort (TAWC) by examining floor and ceiling effects and responsiveness when used with two groups of wheelchair users--one known to have experienced real changes in discomfort levels and the other with unchanged levels. METHOD: In a retrospective analysis of data from two previous studies, change scores were compared across two groups of subjects--one stable group (NON-CHANGERS) and one experiencing a seating intervention (CHANGERS) intended to decreased seating discomfort. RESULTS: No significant floor or ceiling effects were found. The average General Discomfort Score (GDS) change among the NON-CHANGERS was 2.0 (with a possible score range of 13-91) and average Discomfort Intensity Score (DIS) change was 1.8 (with a possible score range of 8-99) for the same group. Conversely, average GDS change among the CHANGERS was 8.7 and the average DIS change was 7.7. Additionally, both scores demonstrated a moderate effect size (d) for two tested treatments (GDS = 0.53 and 0.50, DIS = 0.31 and 0.33) and the standardized response means were 0.78 and 0.77 for the GDS and 0.80 and 1.2 for the DIS. CONCLUSIONS: All analyses indicate good responsiveness of the TAWC, supporting its use clinically and in future research.

Usefulness of relative lymphocyte count as an independent predictor of death/urgent transplant in heart failure.

The usefulness of low relative lymphocyte count as an independent predictor of death/urgent transplant in patients with heart failure (HF) and the association between low relative lymphocyte count and neurohormone and cytokine activation were investigated. Relative lymphocyte count, clinical variables, neurohormones, and cytokines were measured in 129 outpatients with HF. Follow-up extended to a mean of 3.0 +/- 1.2 years for death/urgent transplant. Low relative lymphocyte count was independently associated with a 3.4-fold increased risk of death/urgent transplant. Relative lymphocyte count was positively associated with hemoglobin and inversely associated with age, jugular venous pressure, creatinine, leukocyte count, and soluble tumor necrosis factor receptor-1. There was only a borderline inverse association with cortisol levels during evening hours.

Test-retest reliability, internal item consistency, and concurrent validity of the wheelchair seating discomfort assessment tool.

Discomfort is a common problem for wheelchair users. Few researchers have investigated discomfort among wheelchair users or potential solutions for this problem. One of the impediments to quantitative research on wheelchair seating discomfort has been the lack of a reliable method for quantifying seat discomfort. The purpose of this study was to establish the test-retest reliability, internal item consistency, and concurrent validity of a newly developed Wheelchair Seating Discomfort Assessment Tool (WcS-DAT). Thirty full-time, active wheelchair users with intact sensation were asked to use this and other tools in order to rate their levels of discomfort in a test-retest reliability study format. Data from these measures were analyzed in SPSS using an intraclass correlation coefficient (ICC) model (2,k) to measure the test-retest reliability. Cronbach's alpha was used to examine the internal consistency of the items within the WcS-DAT. Concurrent validity with similar measures was analyzed using Pearson product-moment correlations. ICC scores for all analyses were above the established lower bound of .80, indicating a highly stable and reliable tool. In addition, alpha scores indicated good consistency of all items without redundancy. Finally, correlations with similar tools, such as the Chair Evaluation Checklist and the Short Form of the McGill Pain Questionnaire, were significant at the .05 level, and many were significant at the .001 level. These results support the use of the WcS-DAT as a reliable and stable tool for quantifying wheelchair seating discomfort. Its application will enhance the ability to assess and to research this important problem and will provide a means to validate the outcomes of specialized seating interventions for the study population of wheelchairs users.

Usefulness of depression to predict time to combined end point of transplant or death for outpatients with advanced heart failure.

In a prospective cohort study of 142 outpatients with advanced heart failure followed for a mean of 3 years, 29% of subjects with a depression diagnosis at baseline were significantly more likely to experience the combined end point of death or transplantation (hazard ratio 2.54, 95% confidence interval 1.16 to 5.55). After adjustment for a range of sociodemographic and clinical characteristics, patients with depressive disorders were still significantly more likely to reach the combined end point (hazard ratio 2.41, 95% confidence interval 1.24 to 4.68). Depressed patients also had more heart failure related hospitalizations (1.5 +/- 1.8 vs 0.6 +/- 1.4, p = 0.04) and clinic visits (2.4 +/- 1.7 vs 1.7 +/- 1.8, p = 0.04) over the first year of follow-up.

Development of a consumer-driven Wheelchair Seating Discomfort Assessment Tool (WcS-DAT).

This study examined the concept of seating discomfort in a population of full-time wheelchair users with intact sensation. The goal was to construct a tool that would quantify seating discomfort experienced by wheelchair users. Ten participants were interviewed using ethnographic interview techniques. Data were analyzed using a cross-classifying matrix to examine commonalities among the 10 participants' responses. There were 16 discomfort and 13 comfort descriptors used by the participants. Of these, eight discomfort and five comfort descriptors were selected to include in the Wheelchair Seating Discomfort Assessment Tool (WcS-DAT). The discomfort descriptors selected were: aches and pains, need to move, pressure points, feeling poorly positioned, unable to concentrate, instability, not comfortable, and feeling too hot, cold or damp. The comfort descriptors selected were: absence of discomfort, feeling good, having no pain, able to concentrate, and feeling stable. The WcS-DAT also includes general information, such as the amount of time spent sitting and whether the individual was transferred into the chair properly--factors thought to affect discomfort--and ratings of discomfort intensity--in general and differentiated by body area. The WcS-DAT is a comprehensive tool for quantification of wheelchair seat discomfort for this population.