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. Author manuscript; available in PMC: 2014 Apr 1.
Published in final edited form as: Arch Phys Med Rehabil. 2012 Nov 23;94(4):667–672. doi: 10.1016/j.apmr.2012.11.019

Effect of durations of wheelchair tilt-in-space and recline on skin perfusion over the ischial tuberosity in people with spinal cord injury

Yih-Kuen Jan 1, Fuyuan Liao 1, Maria A Jones 1, Laura A Rice 1, Teresa Tisdell 1
PMCID: PMC3608808  NIHMSID: NIHMS437596  PMID: 23178540

Abstract

Objective

To compare the efficacy of various durations of wheelchair tilt-in-space and recline on enhancing skin perfusion over the ischial tuberosity in people with spinal cord injury (SCI).

Design

Repeated measures, intervention and outcomes measure design.

Setting

University research laboratory.

Participants

Power wheelchair users with SCI (N=9).

Interventions

Three protocols of various durations (3 min, 1 min and zero) of wheelchair tilt-in-space and recline were randomly assigned to the participants. Each protocol consisted of a baseline 15 min sitting, a duration of zero to 3 min reclined and tilted, a second 15 min sitting, and a 5 min recovery. The position at the baseline and second sitting was no tilt/recline of the participant and at the reclined and tilted and recovery was at 35° tilt-in-space and 120° recline.

Main Outcome Measures

Skin perfusion response to tilt and recline was assessed by laser Doppler and was normalized to mean skin perfusion at the baseline sitting.

Results

The results showed that mean skin perfusion during recovery at the 3 min duration was significantly higher compared to the 1 min duration (P<.017), and mean skin perfusion was not significantly different between the 1 min and zero durations (N.S.). Skin perfusion during the second sitting was significantly higher at the 3 min duration compared to the 1 min and zero durations (P<.017).

Conclusions

Our findings suggest that performing the 3 min duration of wheelchair tilt-in-space and recline is more effective than the 1 min duration on enhancing skin perfusion of weight bearing soft tissues.

Keywords: Pressure ulcer, rehabilitation, skin blood flow, spinal cord injuries, wheelchairs

Pressure ulcers are among the most common secondary complications following spinal cord injury (SCI).1 Despite the establishment of clinical guidelines and the progress of support surface technology,2–4 the incidence of pressure ulcers in people with SCI remains high and relatively unchanged in the past 30 years (i.e. ranged 20%–35%).1, 5 The need to address this significant clinical problem has been pointed out by the Department of Veterans Affairs Quality Enhancement Research Initiative for Spinal Cord Injury (QUERI).6

Various interventions have been recommended for the prevention of sitting-induced pressure ulcers in people with SCI, including pressure redistribution cushions, pressure relieving activities (e.g. push-up and lean forward) and wheelchair tilt-in-space and recline.7 Wheelchair tilt-in-space and recline are especially suitable for people with tetraplegia who cannot perform pressure relieving activities by themselves.8 Both wheelchair tilt-in-space and recline provide relief of sitting-induced pressure while tilt-in-space works best for users with high muscle tone and orthopedic limitations and recline works best for users who require a full weight shift.9 Several studies have demonstrated the effect of tilt-in-space and recline angles on seating interface pressure and skin perfusion in wheelchair users.10–13 However, the current literature does not provide specific recommendations on the selection of wheelchair tilt-in-space and recline duration factor on reducing soft tissue ischemia.12, 14 The knowledge gap may limit the benefit associated with using wheelchair tilt-in-space and recline on reducing risk of pressure ulcers.

Clinically, bed-ridden patients are usually repositioned every two hours and wheelchair users are recommended to perform pressure reliving activities every 15–30 minutes for 30 sec.7, 15 However, assessing wheelchair push-ups and lean forwards on the recovery of skin perfusion showed that up to 42–300 sec were needed.16, 17 If a pressure relieving activity is not adequate to allow an increase of blood flow to ischemic tissues, the intervention may not benefit wheelchair users for preventing pressure ulcers.12 In the literature, there are several studies investigating the effect of wheelchair tilt-in-space and recline angles on seating interface pressure, but no research studies have been conducted to investigate the effect of the durations of tilt-in-space and recline on reducing soft tissue ischemia.8, 11, 12

Skin perfusion may be a good candidate to determine efficacy of various durations of tilt-in-space and recline on reducing soft tissue ischemia and risk of skin pressure ulcers.12 A major benefit associated with periodically performing pressure redistribution activities is to allow for a reactive hyperemic response to restore blood supply to the ischemic tissues.12, 18 Reactive hyperemia is a local blood flow regulatory mechanism and remains functioning even after SCI. Reactive hyperemia occurs after occlusion of blood vessels; for a total relief after the occlusion, blood flow may increase several folds as compared with the baseline level; and for a partial relief, blood flow may not increase beyond the baseline level.19, 20 When performing wheelchair push-ups for pressure relieving in paraplegics, a full reactive hyperemic response may occur due to fully unloaded weight-bearing soft tissues. When performing wheelchair tilt-in-space and recline for pressure redistribution in tetraplegics, a partial reactive hyperemic response may occur due to partially unloaded weight-bearing soft tissues. By examining reactive hyperemic response to various durations of wheelchair tilt-in-space and recline, a guideline of the duration factor of performing wheelchair tilt-in-space and recline may be determined.

Our long-term goal is to develop clinical guidelines of wheelchair tilt-in-space and recline for preventing sitting-induced pressure ulcers in people with SCI. We have designed a series of studies to investigate the effects of various settings of wheelchair tilt-in-space and recline on skin and muscle perfusion. In our previous study,12 we studied the effects of various angles of tilt-in-space and recline on skin perfusion and found that tilt-in-space should be at least 35° for enhancing skin perfusion over the ischial tuberosity when combined with 100° recline in people with SCI. In this study, we continue our effort to studying the influences of the duration of tilt-in-space and recline on skin perfusion in people with SCI. We hypothesized that: 1) Skin perfusion during recovery is higher when wheelchair users with SCI perform tilt-in-space and recline at the 3 min duration compared to the 1 min and zero durations, and skin perfusion does not show a significant difference between the 1 min and zero durations. 2) Skin perfusion during upright sitting after performing tilt-in-space and recline is higher at the 3 duration compared to the 1 min and zero durations.

METHODS

A repeated measures, intervention and outcomes measure research design was used in this study.

Participants

We recruited 9 wheelchair users with SCI into this study. The participants were recruited from a local rehabilitation hospital. The inclusion criteria included traumatic SCI at the level between C4 and T5, at least 6 months after spinal injury, use of a power wheelchair as a primary means of mobility, and wheelchair seat width of 0.43 m (17”) to 0.53 m (21”). The exclusion criteria included cardiorespiratory diseases or other diseases that may significantly affect cardiovascular function, diagnosed skeletal deformities (scoliosis, pelvic obliquity, or hip and knee contracture), body mass index over 30 kg/m2 or active pressure ulcers. All participants gave informed consent to this study approved by an institutional review board. The demographic data of participants were as follows (values are mean ± standard deviation): age 38.0±13.0 years; body mass index 24.5±2.3 kg/m2; 8 males and 1 female, and duration of injury 6.0±5.9 years. One participant had sensory complete injury (ASIA A), 1 participant had motor complete injury (ASIA B), and 7 participants had incomplete injury (ASIA C).

Apparatus

Laser Doppler flowmetry (LDF)a and probeb were used to measure skin perfusion over the right ischial tuberosity in response to changes of durations of wheelchair tilt-in-space and recline.12 LDF provides noninvasive, real-time measurement of skin perfusion at a depth of about 1 mm.3 Skin perfusion was sampled at 32Hz for additional off-line analysis. A power wheelchairc with tilt-in-space and recline functions was used in this study. Seat width of the wheelchair was 0.48 m (19”). A high density foam cushiond was used in this study. The wheelchair tilt-in-space was defined as a change of person’s orientation in space while maintaining the seat to back angle. The wheelchair recline was defined as a change of seat to back angle. The detailed configurations of wheelchair tilt-in-space and recline is provided in our previous study.12 Two angle gaugese were used to measure the angles of wheelchair tilt-in-space and recline.

Wheelchair Tilt-in-space and Recline Protocol

We selected commonly used time parameters by wheelchair users, including durations at 3 min, 1 min and zero min for a total of three protocols.15, 21–23 The duration of wheelchair tilt-in-space and recline was defined as the time spent on the tilted and reclined position. Each protocol consisted of a 15 min baseline sitting, a duration of zero to 3 min reclined and tilted, a 15 min second sitting and a 5 min recovery. The baseline and second sitting position was no tilt/recline of the participant and the reclined and tilted and recovery position was 35° tilt-in-space and 120° recline in this study. We chose the 15 min sitting and the 1 min duration because of clinically recommended settings of every 15 min for 30 sec.15, 21–23 We added 30 sec for a total of 1 min duration to count the time needed to adjust wheelchair tilt-in-space and recline angles.12 We chose the 3 min duration to examine whether a longer duration than clinically recommended 30–60 sec would be more effective on reducing skin ischemia of weight-bearing tissues. The zero duration (continuous sitting with tilt and recline) served as the control for comparing the efficacy of various durations of tilt-in-space and recline on reducing ischemia. The selection of 35° tilt-in-space and 120° recline was based on our previous study that such angles are effective more reducing skin ischemia.12 The detailed descriptions of three protocols are provided in Table 1. The order of the testing conditions was randomly assigned to the participants.24 A wash out period was 5 min at 35° tilt-in-space and 120° recline between two protocols.12 In this study, we did not have recline-only or tilt-in-space-only protocol because a combination of tilt-in-space and recline has shown to be superior to sole use of either wheelchair tilt-in-space or recline.25, 26

Table 1.

A repeated-measure design of the efficacy of durations of wheelchair tilt-in-space and recline on skin perfusion. Three protocols consist of 3 duration (3 min, 1 min and zero) of wheelchair tilt-in-space and recline randomly assigned to the participants. A 5 min wash out period was allowed between each protocol. Dependent variables are mean and peak skin perfusion over the ischial tuberosity.

Ischemia Period (baseline 15 min sitting) Tilted and Reclined Period Ischemia Period (second 15 min sitting) Recovery Period Total Time
3 min duration protocol 15 min sitting at no tilt/recline 3 min at 35° tilt & 120° recline 15 min sitting at no tilt/recline 5 min at 35° tilt & 120° recline 38 min
1 min duration protocol 15 min sitting at no tilt/recline 1 min at 35° tilt & 120° recline 15 min sitting at no tilt/recline 5 min at 35° tilt & 120° recline 36 min
Zero min duration protocol 15 min sitting at no tilt/recline Zero min 15 min sitting at no tilt/recline 5 min at 35° tilt & 120° recline 35 min
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Procedure

Room temperature was maintained at 23±2 °C. Participants were kept in the laboratory for at least 30 minutes to accommodate the room temperature. This step allowed us to minimize the influences of skin temperature on skin perfusion.27 During the acclimation period, participants with SCI were asked to empty their bladders. The participant was transferred to a mat table to tape the LDF probe onto the skin over the right ischial tuberosity. Then, he/she was transferred to the test power wheelchair. Regarding the procedure of applying a LDF probe, a participant was positioned in the side-lying posture with hips and knees flexed at 90°. The tester then palpated the right ischial tuberosity to place the probe. The purpose was to minimize the displacement of the probe when the participant was transferred back to the wheelchair. Then, a correct location of LDF probe on the skin over the ischial tuberosity was examined by palpation. Before the testing, the participants sat at 35° tilt-in-space and 120° recline for a duration of 5 min. Skin perfusion over the right ischial tuberosity was continuously measured throughout the study. The same person performed the adjustment of wheelchair tilt-in-space and recline settings (duration and angle of performing wheelchair tilt-in-space and recline) in all experiments in this study. The range of acceptable angles was plus minus 3° of the set angle. Each participant spent about 2 hours completing the experiment.

Statistical Analysis

The independent variables included three durations (3 min, 1 min, and zero min) of wheelchair tilt-in-space and recline. The dependent variables of this study were mean skin perfusion and peak perfusion of reactive hyperemia.28 Peak perfusion was defined as the maximal blood flow during a reactive hyperemic response. To minimize the influences of movement artifact on skin perfusion, we did not average the first 20 sec of each condition when tilt-in-space and recline was performing. The rationale for selecting 20 sec was based on our experiments because 20 sec was needed to complete the adjustment of wheelchair tilt-in-space and recline angles (35° tilt-in-space and 120° recline). We normalized individual’s skin perfusion response to his/her baseline sitting skin perfusion.29, 30 A one-way analysis of variances (ANOVA) with repeated measures design was used to examine the efficacy of various durations of wheelchair tilt-in-space and recline on enhancing mean and peak skin perfusion. Post-hoc analysis was implemented by paired t tests with Bonferroni corrections. All statistical tests were performed at an alpha level of 0.05. For repeated measures comparisons, the significance level was adjusted 0.017. All statistical analyses were analyzed by using SPSS 16f.

RESULTS

During the recovery period, mean skin perfusion of three protocols showed a significant increase compared to mean skin perfusion of the baseline sitting period (P<.05). Normalized mean skin perfusion was significantly higher at the 3 min duration (1.92±0.28) compared to the 1 min duration (1.35±0.05) (P<.017), but not the zero min duration (1.57±0.21) (N.S.) (fig 1). Normalized mean skin perfusion was not significantly different between the 1 min and zero min durations (N.S). (fig. 1)

Fig 1.

Fig 1

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Comparison of normalized mean skin perfusion over the ischial tuberosity during the recovery period in response to various durations of wheelchair tilt-in-space and recline. The results show that normalized mean skin perfusion at the 3 min duration significantly increases compared to the 1 min duration (P<.017); mean skin perfusion is not significantly different between the 1 min and zero durations (N.S.). Mean skin perfusion during the recovery period at 35° tilt-in-space and 120° recline was normalized to the baseline sitting period at no tilt-in-space and recline. Data shown as mean ± SE.

During the recovery period, normalized peak skin perfusion of the reactive hyperemic response of three protocols did not show a significant difference (N.S.), while normalized peak skin perfusion shows a higher value in the durations of 3 min (4.1±1.1) and zero min (3.7±1.5) compared to 1 min (2.15±0.15) (fig 2).

Fig. 2.

Fig. 2

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Comparison of peak skin perfusion over the ischial tuberosity during the recovery period in response to various durations of wheelchair tilt-in-space and recline. The results show there is no significant difference in normalized peak skin perfusion among three protocols. Peak skin perfusion during the recovery period at 35° tilt-in-space and 120° recline was normalized to the baseline sitting period at no tilt-in-space and recline. Data shown as mean ± SE.

During the sitting period, normalized skin perfusion of the second 15 min sitting was significantly higher at the 3 min duration (1.15±0.07) compared to the 1 min duration (0.96±0.06) (P<.017) and the zero min duration (0.98±0.03) (P<.017). Normalized skin perfusion was not significantly different between the 1 min and zero min durations (N.S.) (fig 3).

Fig 3.

Fig 3

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Comparison of normalized skin perfusion over the ischial tuberosity during the second 15 min sitting period at no tilt-in-space and recline after performing various durations of wheelchair tilt-in-space and recline at 35° tilt-in-space and 120° recline. The results show that normalized skin perfusion at the 3 min duration significantly increases compared to the 1 min and zero durations (P<.017); normalized skin perfusion is not significantly different between the 1 min and zero durations (N.S.). Skin perfusion during the second 15 min sitting period at no tilt-in-space and recline was normalized to the baseline 15 min sitting period at no tilt-in-space and recline. Data shown as mean ± SE.

DISCUSSION

Our study demonstrated that the duration factor of wheelchair tilt-in-space and recline affected skin perfusion over the ischial tuberosity in wheelchair users with SCI. Our results indicated that skin perfusion during the recovery period at the 3 min duration was significantly higher than at the 1 min duration and was not significantly different between the 1 min and zero min durations (fig. 1). Our study also showed that skin perfusion during the second sitting significantly increased after performing the duration of 3 min tilt-in-space and recline compared to the 1 min duration (fig 3). Along with our previous study,12 we demonstrated that various angles and durations of wheelchair tilt-in-space and recline significantly affect the efficacy on enhancing skin perfusion in wheelchair users with SCI. Our method can be used to determining the proper settings of wheelchair tilt-in-space and recline for enhancing skin perfusion of the weight bearing tissues.

We demonstrated that the 3 min duration of tilt-in-space and recline may be more beneficial for the weight bearing soft tissues compared to the l min duration during recovery. This finding indicates a significant issue that if the duration of tilt-in-space and recline is not adequate, ischemia caused by upright sitting may not be removed in wheelchair users with SCI.31, 32 This is consistent with previous research examining various pressure relieving activities.16, 17 Makhsous et al. demonstrated that wheelchair push-ups for 30 sec were not adequate for a full recovery of skin perfusion.17 Coggrave and Rose also showed a similar conclusion that about a 2 min of pressure relieving of the weight bearing soft tissues was needed to restore tissue oxygen to the unloaded level.16 Our finding does not support the current clinical practice that the Consortium for Spinal Cord Medicine7 published a clinical practice guideline recommending every 15–30 min for repositioning for 30 sec. Our results indicate that skin perfusion during recovery was not significantly different between the 1 min duration of tilt-in-space and recline and the continuous sitting condition (zero min duration). Based on our findings, we suggest wheelchair users to perform tilt-in-space and recline for a longer duration such as 3 min to minimize ischemia of weight bearing soft tissues. This statement warrants more research to validate its significance on reducing risk of pressure ulcers.

The position at 35° tilt-in-space and 120° recline was used to assess the efficacy of various durations on skin perfusion in this study. The decision was based on our previous study12 indicating that these angles can effectively increase skin perfusion during the recovery period. However, it needs to be aware that this finding can only be applied to angles of at least 35° tilt-in-space and 120° recline. Smaller angles of tilt-in-space and recline even with a duration of 3 min may not enhance skin perfusion. The clinicians should educate wheelchair users to perform large angles of tilt-in-space and recline (eg. greater than a combination of 35° tilt-in-space and 120° recline) to allow the development of reactive hyperemia to minimize ischemia of weight bearing soft tissues. Also, the duration of tilted and reclined position is preferred to be 3 min rather than clinically recommended 30 sec to 1 min based on our results. In real life, wheelchair users usually do not perform tilt-in-space and recline at these large angles and long duration.21, 22 This may partly contribute to a high incidence of pressure ulcers over the ischial tuberosity in people with SCI, especially tetraplegics.

Skin perfusion was used to evaluate the efficacy of various durations of wheelchair tilt-in-space and recline on reducing pressure ulcer risk in this study. We hypothesized that higher mean skin perfusion is beneficial for the weight bearing soft tissues in terms of pressure ulcer prevention.30, 33 This is based on the ischemia theory that an inadequate supply of blood and oxygen to local cells and tissues causes soft tissue ischemia, and beyond a threshold of ischemia, pressure ulcers will occur.18, 34, 35 Aligned with this principle, pressure relieving associated with performing wheelchair tilt-in-space and recline may reduce risk of pressure ulcers.36, 37 Although tissue ischemia may only be one of the contributing factors of pressure ulcers,12 we believe that soft tissue ischemia may be a better factor in assessing the efficacy of wheelchair tilt-in-space and recline on reducing risk of pressure ulcers. This is particularly important in people with SCI as they loss the sympathetic outflow to the skin (peripheral autonomic dysfunction, dependent on the injury level) and heart (central autonomic dysfunction, injury level above T4–T5) that causes microvascular dysfunction and higher risk of pressure ulcers.38, 39 According to the current result, we support the use of non-invasive laser Doppler flowmetry to determine proper settings of wheelchair tilt-in-space and recline.12

Reactive hyperemia is the underlying physiological mechanism that contributes to an increase in skin perfusion during tilted and reclined position.12, 30 Two theories have been proposed for the development of a reactive hyperemic response, including metabolic and myogenic theories.30 Both metabolic and myogenic controls are a local regulatory response of skin microcirculation and still function in people with SCI but with an attenuated response.12, 18, 40 Because metabolic and myogenic controls are mechanical stress dependent regulations, 12, 18, 30 skin perfusion response thus can be modulated by the patterns of mechanical stresses caused by wheelchair tilt-in-space and recline. Theoretically, a proper configuration of angles and durations of wheelchair tilt-in-space and recline may be developed to utilize these local blood flow regulatory controls for enhancing skin perfusion, thus reducing risk of pressure ulcers in people with SCI.

Study Limitations

We only assessed skin perfusion in such a short time rather than in real-life daily monitoring. Our findings may not be applied to determine the true efficacy of wheelchair tilt-in-space and recline on preventing pressure ulcers. Future studies may need to correlate the usage pattern of tilt-in-space and recline and the incidence of pressure ulcers to validate our finding. We only recruited 9 participants with SCI into this study. Concerning the variations of the level and severity of SCI, our results may not be extrapolated into all people with SCI. However, a homogenous group of power wheelchair users was recruited for this study and the repeated measures design was implemented in this study. Thus, the variations of spinal injury status may not confound our results.

CONCLUSIONS

Our study demonstrated that duration of performing wheelchair tilt-in-space and recline affected skin perfusion of weight bearing soft tissues over the ischial tuberosity. Based on our finding, we recommend wheelchair users with SCI to perform tilt-in-space and recline for around 3 min to minimize ischemia of weight bearing soft tissues and a duration of 1 min of wheelchair tilt-in-space and recline may not be effective on reducing ischemia.

ACKNOWLEDGMENT

We are grateful for the reviewers’ valuable comments on this manuscript. We appreciate the Permobil, Inc. for providing the power wheelchair for the experiments.

Supported by the National Institutes of Health (grant no. R03HD060751).

List of Abbreviations

ASIA

American Spinal Injury Association

LDF

laser Doppler flowmetry

SCI

spinal cord injury

Footnotes

Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.

Suppliers

a

Periflux system 5001 and LDF module 5010, Perimed, Sweden.

b

PR415 probe, Perimed, Sweden.

c

Power wheelchair C300 Corpus, Permobil, Inc., Lebanon, TN.

d

Corpus seating system, Permobil, Inc., Lebanon, TN.

e

Wixey digital angle gauge, Model WR300, WWW.WIXEY.COM online store.

f

SPSS, Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.

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