pressure ulcers are a common problem seen in patients who are immobile and/or elderly , and 
 a serious national health concern impacting cost of care , reimbursement , and quality of 
 life1,2,3 . for instance , physical inactivity after 
 stroke may contribute to immobile everyday lives of stroke survivors4 . it is estimated that 2.5 
 million pressure ulcers are treated each year in us acute care facilities . the pressure 
 ulcer incidence rate has been reported to be 0.4% to 38.0% in acute care , 2.2% to 23.9% in 
 long - term care , and 0% to 17% in home care . the estimated cost of managing a single , 
 full - thickness pressure ulcer can be as high as $ 70,000 . furthermore , the estimated cost of 
 treating pressure ulcers has been estimated to be $ 11 billion per year in the usa6 . effective repositioning methods for 
 pressure ulcer prevention are crucial , because manual repositioning by caregivers is 
 expensive and can result in loss of productive time . manual repositioning is one of the most 
 expensive interventions , accounting for 75% of the total cost of pressure ulcer 
 prevention7 and 40% of all nursing time 
 on day shifts8 . in addition , traditional 
 repositioning is one of the highest occupational risks experienced by caregivers9 . manual lateral turning by caregivers has been a standard method of pressure ulcer 
 prevention . some clinical practice guidelines recommend repositioning at least every two 
 hours for immobile patients and elderly people , but these guidelines are based on a small 
 number of epidemiological studies , with inconsistent findings . manual repositioning every two hours and other additional pressure ulcer prevention 
 strategies , such as lateral turning , are used extensively for pressure ulcer prevention . , 
 pressure ulcers occur due to pressure distributed through soft tissue located under bony 
 prominences . thus , common pressure ulcer sites include the occiput , scapula , sacrum , greater 
 trochanter , and heel . the major factors of pressure ulcer development are duration and 
 magnitude of pressure , because a single pressure level is not enough to represent the 
 threshold of pressure ulcer development10 , 11 . continuous lateral turning has been used in the care of critically ill patients receiving 
 mechanical ventilation in order to prevent and treat respiratory complications12 , but few studies have examined the effect 
 of pressure relief in continuous lateral turning . the design of our continuous lateral 
 turning device was motivated by the need for adequate pressure - relieving devices or beds for 
 immobile and/or elderly people . the typical steps involved in the manual repositioning of 
 patients , specifically turning the patients and translating them to the center of the bed , 
 were embodied in our continuous lateral turning device . after initial development , this 
 device was tested to evaluate the pressure - relieving effect of continuous lateral turning on 
 common pressure ulcer sites . in this study , the pressure - relieving effect of the continuous lateral turning device on 
 common pressure ulcer sites was investigated , and the pressure relief effect was quantified 
 using peak pressure , mean pressure , and pressure time integration . the effects of pressure 
 relief and comfort grades at different turning angles of continuous lateral turning were 
 also investigated and compared . twenty - four healthy adults ( 12 men and 12 women ) were recruited for this study . the mean 
 ( sd ) age , weight , height , and body mass index of the participants were 28.2 ( 4.3 ) years , 
 63.6 ( 16.7 )  kg , 1.7 ( 0.1 ) m , and 22.2 ( 4.2 )  kg / m , respectively ( table 1table 1.demographic characteristics of the study participantscharacteristicall participants ( n = 24)n ( % ) gendermale12 ( 50)female12 ( 50)asian ethnicity24 ( 100)mean ( standard deviation)age ( years)28.2 ( 4.3)weight ( kg)63.6 ( 16.7)height ( m)1.7 ( 0.1)bmi ( weight[kg]/height[m])22.2 ( 4.2)bmi : body mass index ) . all the participants were free of neck and back pain for a minimum of two 
 years before this study , as well as skin disorders such as chronic pressure ulcers . the study protocol followed 
 the principles of the declaration of helsinki and was approved by the institutional review 
 board of yonsei university . written informed consent we did not try to include or exclude any participants based on gender or 
 ethnicity . confirmation of eligibility was obtained by face - to - face interviews with 
 potential participants . participation in the study was voluntary , and the participants were 
 free to withdraw at any time . this study used a one - group , repeated - measures design . before the experiments , the head , 
 shoulders , hips , upper extremities , and lower extremities of all the participants were 
 positioned supine on the bed , and the positions of the eight common pressure ulcer sites , 
 the occiput , both scapulas , sacrum , both greater trochanters , and both heels on the bed , 
 were respectively identified and specified with 68.0  mm  68.0  mm sensing areas . the 
 interface pressure sensors were attached to the surface of the bed and calibrated . after 
 that , the bed turned each participant to the right from 0 to 0 , 15 , 30 , or 45 for 15 
 minutes , and returned the participant to the supine position in the following 15 minutes at 
 a constant angular speed . the experiment was simplified by assuming a nearly symmetric 
 pressure distribution between a right and left turn , e.g. pressure distribution for the left 
 scapula when a right turn was applied was similar to the pressure distribution for the right 
 scapula when a left turn was applied . each participant s comfort grade on the bed at each angle of continuous lateral 
 turning was also evaluated . participants were instructed to maintain their posture during 
 the measurement period and allowed to rest for five minutes between tests . the newly developed continuous lateral turning device consists of a sliding part able to 
 translate in the x - axis ( left shoulder to right shoulder axis ) , two lateral tilting parts 
 able to rotate around each axis parallel to the y - axis ( head to feet axis ) , and back panels , 
 seat panels , thigh panels , and calf panels . the mattress referred to as the standard mattress was made of 80-mm - thick polyurethane with 
 60  kg / m density and a polyurethane - ethylene cover . our continuous lateral turning device was developed for repositioning patients who are 
 immobile and/or elderly . the person s location , including position in the x - axis and 
 orientation in the xz - plane was controlled under no - slip conditions . the typical steps 
 involved in the manual repositioning of patients , specifically turning the patients and 
 translating them to the center of the bed , were embodied in our continuous lateral turning 
 device . the specially designed device was used to induce a change of orientation of the 
 person by continuously turning the person around the axis parallel to the y - axis at a 
 constant angular speed . the device is capable of accurate continuous lateral turning with a 
 range of from 0 to 45 within a set time period at a constant turning speed . the interface pressure and time values were measured using the body pressure measurement 
 system ( tekscan , south boston , ma , usa ) . the number of sensing 
 elements per sensor is 1768 (= 34 by 52 ) . the element size of each sensing element is 
 17.0  mm  17.0  mm . the thinness and flexibility of the sensors allow precise measurement of 
 the pressure at the bed - skin interface . the sensors were calibrated to measure pressures 
 ranging from 0 to 200 mmhg . the sampling rate for data acquisition natick , ma , usa ) was used to sort pressure and time value data at 
 common pressure ulcer sites from the whole data set . to describe the effect of pressure 
 relief , pressure and time at eight common pressure ulcer sites the peak 
 pressure and mean pressure ( mmhg ) at the bed - skin interface during turning were obtained . 
 inspired by studies in which tissue injury is closely related to not only pressure but also 
 exposure time10 , pressure time 
 integration ( mmhg  sec ) was calculated . pressure  time can be used as a tissue tolerance 
 guideline for allowable pressure versus exposure time11 . the pressure - time threshold for 2-hour repositioning in this study was defined as 460,800 mmhg  sec on the basis of the results of linder - ganz et al.13 . for comparisons of pressure time integration values and the pressure - time threshold , we repeated each 30-minute measurement 
 session four times . each participant s comfort grade on the bed at each angle of continuous lateral turning was 
 evaluated using a subscale of the comfort and quality of sleep questionnaire developed by 
 yinnon et al.14 which encompasses 
 duration of sleep , number of wakenings , and quality of sleep . this subscale was adapted 
 primarily to include a question relating to the comfort of the mattresses as follows : 1 
 ( extremely comfortable ) , 2 ( very comfortable ) , 3 ( comfortable ) , 4 ( fairly comfortable ) , 5 
 ( uncomfortable ) , 6 ( very uncomfortable ) , and 7 ( extremely uncomfortable)14 . the statistical package for the social sciences ( spss ; ibm , armonk , ny ) version 18.0 was 
 used to analyze the data . the overall analysis design was a one - way repeated measures 
 analysis of variance ( anova ) with one factor , turning angle , followed by bonferroni s 
 significance level adjustment for multiple comparisons . the characteristics of the participants are expressed as 
 counts , proportions , or means with standard deviations . the pressure and time parameters are 
 expressed as means with standard deviations ( i.e. , mean ( standard deviation ) ) . the peak pressures of almost all sites were significantly reduced at turning angles of 15 , 
 30 , and 45 compared to 0 , except the right scapula at 15. the peak pressure of the right 
 greater trochanter was significantly increased at 30 and 45 compared with 0 ( p < 0.05 ) 
 ( table 2table 2.peak pressure at common pressure ulcer sitespeak pressure ( mmhg)0153045mean ( standard deviation)occiput58.8 ( 10.0)43.0 ( 15.2)*26.3 ( 15.3)*24.3 ( 11.6)*left scapula37.4 ( 4.7)32.0 ( 5.1)*29.2 ( 4.2)*25.2 ( 8.0)*right scapula36.8 ( 6.7)33.6 ( 10.1)24.4 ( 12.3)*16.8 ( 13.1)*sacrum70.5 ( 24.9)47.9 ( 10.1)*38.0 ( 7.9)*27.1 ( 8.5)*left greater trochanter0.0 ( 0.0)0.0 ( 0.0)0.0 ( 0.0)0.0 ( 0.0)right greater trochanter0.0 ( 0.0)0.5 ( 1.4)8.3 ( 12.4)*35.5 ( 17.8)*right heel77.3 ( 26.3)54.7 ( 24.6)*32.9 ( 21.6)*27.3 ( 20.3)*left heel86.6 ( 24.3)70.3 ( 27.0)*57.3 ( 38.7)*46.9 ( 40.5)**p < 0.05 compared with 0. p < 0.05 compared with peak pressures at an angle that is 15 lower ) . * p < 0.05 compared with 0. p < 0.05 compared with peak pressures at an angle that is 15 lower the peak pressures at 15 , 30 , and 45 were compared to those at 0 , 15 , and 30 , 
 respectively . the peak pressures of the occiput and right heel significantly decreased at 
 15and 30 ( p < 0.05 ) , but not at 45. the peak pressures of the left scapula and left 
 heel showed significant decreases only at 15 ( p < 0.05 ) . the peak pressure of the right 
 scapula significantly decreased at 30 and 45 ( p < 0.05 ) , but not at 15. the peak 
 pressure of the sacrum significantly decreased at all the angles ( p < 0.05 ) . the peak 
 pressure of the right greater trochanter significantly increased at 30 and 45 ( p < 
 0.05 ) , but not at 15 ( table 2 ) . the mean pressures of almost all sites were significantly reduced at turning angles of 15 , 
 30 , and 45 compared to 0 , except for the right heel at 15. the mean pressures of the 
 right greater trochanter were significantly increased at 30 and 45 compared to 0 ( p < 
 0.05 ) ( table 3table 3.mean pressure at common pressure ulcer sitesmean pressure ( mmhg)0153045mean ( standard deviation)occiput34.9 ( 5.8)23.0 ( 8.6)*14.3 ( 7.3)*12.1 ( 4.6)*left scapula25.9 ( 3.3)20.4 ( 4.1)*18.2 ( 2.4)*15.7 ( 3.2)*right scapula24.8 ( 3.2)19.2 ( 4.5)*12.9 ( 5.9)*8.9 ( 5.3)*sacrum43.7 ( 7.8)32.7 ( 5.1)*25.5 ( 4.9)*16.2 ( 5.2)*left greater trochanter0.0 ( 0.0)0.0 ( 0.0)0.0 ( 0.0)0.0 ( 0.0)right greater trochanter0.0 ( 0.0)0.5 ( 1.3)5.4 ( 7.8)*20.7 ( 10.9)*right heel27.8 ( 6.9)23.1 ( 10.8)14.8 ( 8.2)*13.8 ( 8.5)*left heel31.6 ( 6.3)26.0 ( 7.6)*21.2 ( 11.0)*17.1 ( 12.7)**p < 0.05 compared with 0. p < 0.05 compared with mean pressures at an angle that is 15 lower ) . * p < 0.05 compared with 0. p < 0.05 compared with mean pressures at an angle that is 15 lower the mean pressures at 15 , 30 , and 45 were compared to those at 0 , 15 , and 30 , 
 respectively . < 0.05 ) , but not at 45. the mean pressure of the left scapula significantly decreased at 
 15 and 45 ( p < 0.05 ) , but not at 30. the mean pressures of the right scapula and 
 sacrum significantly decreased at all the angles ( p < 0.05 ) . the mean pressure of the 
 right heel significantly decreased only at 30 ( p < 0.05 ) . the mean pressure of the left 
 heel showed a significant decrease only at 15 ( p < 0.05 ) . the mean pressure of the right 
 greater trochanter significantly increased at 30 and 45 ( p < 0.05 ) , but not at 15 
 ( table 3 ) . the values of pressure time integration of almost all sites were significantly reduced at 
 turning angles of 15 , 30 , and 45 compared to 0 except for the right scapula at 15 and 
 30 , but the pressure time integration of the right greater trochanter was significantly 
 increased at 45 compared to 0 ( p < 0.05 ) ( table 
 4table 4.pressure time integration at common pressure ulcer sitespressure time integration ( mmhg  
 sec)0153045mean ( standard deviation)occiput471,318 ( 45,935)334,074 * ( 58,340)260,866 * ( 86,104)227,919 * ( 78,836)left scapula266,277 ( 32,635)231,091 * ( 28,370)218,148 * ( 32,480)199,957 * ( 41,047)right scapula259,803 ( 36,376)249,667 ( 55,267)225,394 ( 68,862)194,361 * ( 65,994)sacrum504,298 ( 170,112)386,950 * ( 89,928)366,383 * ( 106,445)295,585 * ( 68,478)left greater trochanter0 ( 0)0 ( 0)0 ( 0)0 ( 0)right greater trochanter292 ( 1,429)978 ( 2,678)10,327 ( 17,545)45,857 * ( 38,050)right heel549,528 ( 191,596)442,565 * ( 172,656)378,888 * ( 137,788)347,725 * ( 127,868)left heel609,617 ( 171,748)451,360 * ( 119,789)352,407 * ( 158,300)293,906 * ( 131,612)*p < 0.05 compared with 0. p < 0.05 compared with pressure time integration values at an angle 
 that is 15 lower . values below the pressure - time threshold 460,800 mmhg  sec ) . * p < 0.05 compared with 0. p < 0.05 compared with pressure time integration values at an angle 
 that is 15 lower .  values below the pressure - time threshold 460,800 mmhg  sec the values of pressure time integration at 15 , 30 , and 45 were compared to those at 0 , 
 15 , and 30 , respectively . the values of pressure time integration of the occiput and left 
 heel significantly decreased at 15 and 30 ( p < 0.05 ) , but not at 45. the values of 
 pressure time integration of the left scapula and right heel significantly decreased only at 
 15 ( p < 0.05 ) . the pressure time integration of the sacrum significantly decreased at 
 15 and 45 ( p < 0.05 ) , but not at 30. the pressure time integration of the right 
 scapula significantly decreased only at 45 ( p < 0.05 ) . the pressure time integration of 
 the right greater trochanter significantly increased only at 45 ( p < 0.05 ) ( table 4 ) . the mean comfort grades at the different turning angles were 2.1 at 0 , 2.9 at 15 , 4.0 at 
 30 , and 5.2 at 45. the degree of discomfort increased with the elevation of the angle of 
 continuous lateral turning . the comfort grades were significantly higher at 15 , 30 , and 
 45 than at 0 ( p < 0.05 ) , and also significantly higher at 15 , 30 , and 45 than at 0 , 
 15 , and 30 , respectively ( p < 0.05 ) ( table 
 5table 5.comfort grade with angle of continuous lateral turninganglecomfort grademean ( standard deviation)02.1 ( 1.1)*152.9 ( 1.1)*304.0 ( 1.2)*455.2 ( 1.2)**p < 0.05 compared with 0. p < 0.05 compared with comfort grade at an angle that is 15 lower ) , indicating greater discomfort with increasing angle . * p < 0.05 compared with 0. p < 0.05 compared with comfort grade at an angle that is 15 lower in this study , we verified and quantified the pressure relief effect of our continuous 
 lateral turning device . our participants showed pressure time integration values below the 
 pressure - time threshold at 15 , 30 , and 45 at all the common pressure ulcer sites due to 
 pressure relief induced by the continuous lateral turning device . our observations about the 
 different effects of pressure relief according to various angles of continuous lateral 
 turning at common pressure ulcer sites have implications for the repositioning of patients 
 and pressure relief using continuous lateral turning . in particular , we tried to examine 
 which angles of continuous lateral turning were the most effective for pressure relief at 
 each targeted site . the pressure time integration values at almost all sites , with the 
 exception of the right scapula and right greater trochanter , were significantly lower at 
 15 , 30 , and 45 than at 0 , indicating a decreased risk of developing pressure ulcers . with respect to common pressure ulcer sites , we conclude that the most effective angles of 
 continuous lateral turning satisfy several conditions . first , the most effective angles have 
 significantly lower pressure time integration values than that of 0. second , the most 
 effective angles have significantly lower pressure time integration values than the pressure 
 time integration values at angles that are 15 lower . third , among the angles satisfying the 
 two previous conditions , the one with the lowest pressure time integration value is the most 
 effective angle . overall , the most effective angles of continuous lateral turning were 15 
 for the left scapula and right heel , 30 for the occiput and left heel , and 45 for the 
 right scapula and sacrum . however , at 45 continuous lateral turning , increasing pressure 
 was applied to the right greater trochanter as a side - effect . table 6table 6.comparison of maximum interface pressure ( mmhg ) from four studiesstudyparticipants positionsupinelaterally turned position ( turning angle)present study ( sacrum)70.547.9 ( 15 ) , 38.0 ( 30 ) , 27.1 ( 45)peterson et al . sacrum)174648.0 ( 14 ) compares the tested maximum interface pressure of our continuous lateral 
 turning device with the results of previous studies that measured pressure - relief . various attempts have been made to develop effective methods for preventing pressure ulcers 
 and relieving pressure , but none have reported uniformly successful results . in one study , no significant differences in interface pressure were observed when comparing turning 
 intervals of 60  min , 90  min , and 120  min18 . the incidence of pressure ulcers decreased when repositioning 
 alternated between 2 hr in the lateral position and 4 hr in a supine position compared to 
 repositioning every 4 hr , but no significant difference was found between the two 
 protocols19 . one investigation found 
 that rotating beds resulted in nearly the same incidence of pressure ulcers as common 
 hospital beds20 . these studies suggest 
 that 30 lateral turning induces a lower interface pressure than 90 lateral turning and 
 might be sufficient to prevent pressure ulcers21 , 
 22 . however , another study found that 
 the incidence of pressure ulcers between a 30 tilt position and 90 lateral position was 
 not significantly different23 . overall , 
 while limited interventions are important components of methods for pressure ulcer 
 prevention and pressure relief , there has been little significant improvement in the 
 effectiveness of methods for pressure ulcer prevention and pressure relief6 . one of the limitations of this study was the small number of study participants . generally , healthy adults are likely to have 
 muscle characteristics different from those of immobile patients or the elderly . different 
 muscle characteristics would cause different pressure distributions . additional 
 considerations and clinical studies may be needed to investigate whether the same 
 pressure - relieving effect is found for patients or the elderly , as well as the impact of 
 covariates such as age and gender . further studies are needed to investigate the 
 pressure - relieving effect of our continuous lateral turning device , considering interface 
 pressure and shear force together24 . in conclusion , continuous lateral turning with our specially designed device effectively 
 relieved the pressure at targeted sites , potentially reducing the risk of developing 
 pressure ulcers . moreover , the optimal angles of continuous lateral turning vary by site , 
 and should be applied in a targeted way . the continuous lateral turning device can be 
 employed for pressure ulcer prevention and care with the goal of assisting caregivers 
 providing bedside care and improving pressure ulcer prevention and quality of care .
[ purpose ] the purpose of this study was to examine the pressure - relieving effects of a 
 continuous lateral turning device on common pressure ulcer sites . 
 [ subjects ] twenty - four 
 healthy adults participated . [ methods ] 
 the design of our continuous lateral turning device 
 was motivated by the need for an adequate pressure - relieving device for immobile and/or 
 elderly people . 
 the procedure of manual repositioning is embodied in our continuous 
 lateral turning device . 
 the interface pressure and time were measured , and comfort grade 
 was evaluated during sessions of continuous lateral turning at 0 , 15 , 30 , and 45. we 
 quantified the pressure - relieving effect using peak pressure , mean pressure , and pressure 
 time integration . 
 [ results ] participants demonstrated pressure time integration values 
 below the pressure - time threshold at 15 , 30 , and 45 at all the common pressure ulcer 
 sites . moreover , the most effective angles for pressure relief at the common pressure 
 ulcer sites were 30 at the occiput , 15 at the left scapula , 45 at the right scapula , 
 45 at the sacrum , 15 at the right heel , and 30 at the left heel . 
 however , angles 
 greater than 30 induced discomfort . 
 [ conclusion ] continuous lateral turning with our 
 specially designed device effectively relieved the pressure of targeted sites . 
 moreover , 
 the suggested angles of continuous lateral turning can be used to relieve pressure at 
 targeted sites .