Seven x-ray table mattress each of 2.5 cm thickness but with different ages from diffrent manfacturers that were in current use in clinical practise were examined. A novel validated three-dimensional (3D) printed phantom of length 175cm, representing skin ulceration jepordy areas (head, heels and sacrum), was used to simulate an adult standard size human (Figure 1). Peak pressure value was measured from the head, pelvis and heels using Xsensor pressure mapping equipment (an industry standard method for assessing pressure distribution,) (Figure 2 and 3) [3] in two diffrent conditions – a) with and b) without the use of the x-ray table mattress. Xsensor was placed between the 3D phantom and mattress; a control condition was also created in which the Xsensor was placed between phantom and X-ray table without a mattress. Five different weights of sand were used to simulate adult head, pelvis and heels for five body sizes (Figure 4).
Xsensor, pressure mapping system was used because it is more accurate than other options [4]. It has a sensing area of 61cm x 183cm, 12.7mm resolution with 6,912 sensing points; this includes 5-50 mmHg & 10-200mmHg pressure ranges with a rate of accuracy of ±10 percent for the calibrated values [5].
During the pressure measurements, the 3D phantom was placed on the mattress for 3 minutes while the mattress is stabilised. Data collection then occurred over a 15 minute period for each of the five weights. To reduce random error, for each weight, this procedure was repeated three times and pressure measurements were taken, from which averages, means and confidence intervals were calculated.
.
Interface Pressure Ratio
Using phantom data, a novel Interface Pressure Ratio (IPR) has been developed to indicate mattress interface pressure redistribution efficiency. IPR serves as a simple indicator to compare between mattresses and for the same mattress over time. IPR uses phantom PPVs from head, sacrum and heels when a ‘mattress is used’ (experimental condition) against ‘no mattress’ (control condition). IPR formula is indicated below
PPV when Mattress is used / PPV for no mattress
IPR varies between 0 and 1. ‘1’ implies the mattress has the same interface pressure distribution properties as a hard surface (e.g. X-ray table surface). As the ratio approaches ‘0’, the interface pressure redistribution properties of the mattress improve. To illustrate its use, Table 1 shows IPRs from a 15-year-old X-ray table mattress that is in current clinical use. For the 5 weight categories, the IPR indicates the mattress interface pressure redistribution properties are similar to the X-ray table itself (i.e. approaching ‘1’, which is very poor).
Table 1
|
|
Peak Pressure Index mmHg
|
Pressure Ratio
Head Sacrum Heels
|
Value
|
Head
|
Sacrum
|
Heels
|
Maximum
|
88.5
|
110.7
|
97.3
|
0.93
|
0.85
|
0.95
|
Third quartile
|
68.9
|
93.4
|
78.1
|
0.92
|
0.78
|
0.90
|
Mean
|
60.6
|
79.2
|
70.2
|
0.85
|
0.78
|
0.86
|
First quartile
|
55.4
|
62.5
|
53.9
|
0.84
|
0.70
|
0.94
|
Minimum
|
50.1
|
47.5
|
35.1
|
0.83
|
0.93
|
0.92
|
Statistical Analysis
The peak pressure data were analysed using SPSS version 22.0 (IBM Inc, Armonk, New York, US). Shapiro-Wilk test was used to investigate the normality of the data prior for using any statistical test to select the valid test. The data were found to be normally distributed (p > 0.05) and then Paired T-Test was used to compare peak pressure with and without a mattress.