Andrew I. Heusch

The vagaries of ear temperature assessment

There have been a growing number of reports suggesting that ear temperature measurement is unreliable and by implication so is the device. Examination of the measurement site, the tympanic membrane (eardrum) and the walls of the external auditory meatus (ear canal) reveals that at least some of the unreliability might derive from poor aiming of the infrared thermometer: the ear canal walls have a lower temperature than the eardrum. Additionally, anatomical properties of the ear canal may increase the difficulty of aiming the thermometer at the eardrum. Furthermore, the rich vascularization, innervation and variations in skin properties (thickness, oil secretion and hair) along the length of the ear canal affect the black body-like nature of the structure. It is concluded that such factors are more likely underlying reasons for the difficulties in reliably reproducing temperatures from this site. We conclude that concerns should extend beyond the reliability of the device and there should be greater study of the measurement site. The argument extends to all sites chosen for clinical assessment of the patient, as previous studies of the alternative temperature measurement sites are also unfortunately few and tend to be lacking in scientific rigour.

Studying thermal characteristics of seating materials by recording temperature from 3 positions at the seat-subject interface

AIM OF THE STUDY To determine whether 3 fixed positions of seat-subject interface temperature measurement offer more information than a single point of measurement. MATERIALS AND METHODS Temperature data was simultaneously acquired (sampling frequency 1 Hz/sensor) from each of three sensor positions (right & left mid-thigh and coccyx), from the subject-seat interface. The data was acquired whilst subjects (6 males, 5 females: 21-40 yrs: BMI 19.3-26.4) sat for 20 min on each of three types of seat material (foam, gel mould and solid wood). Data collection was performed at the same time of day for each subject: ambient temperature between 21.1 and 21.2 °C, ambient relative humidity 50.9%. RESULTS Analysis of data from the sensors, post mathematical smoothing, for each subject (n = 11; ANOVA, followed by post-hoc t-tests) revealed each of the measurement positions to have a significantly different recorded temperature (p < 0.01). However, profile of temperature change at the same measurement position using the same seating material during the 20 min sitting period, was highly correlated (r > 0.99) between subjects, a consistent finding across all 11 subjects regardless of seat material selected. CONCLUSION Use of 3 positions of measurement (3 sensors) appears necessary when performing detailed studies of temperature change at the seat-subject interface. The high level of comparability of results between subjects supports potential of this method to resolve quantitative components of qualitative measurements, e.g., thermal comfort.

Assessment of humidity and temperature sensors and their application to seating

Humidity and temperature are considered to be important factors in designing comfortable seat surfaces. A small number of studies have attempted to address this; however the methods used were limited regarding the placement of their sensors. This study aimed to design a sensor array system to investigate changes in humidity and temperature for eventual use in the study of factors affecting sitting comfort and incontinence detection. The system was subjected to three types of experiments: sensor response verification, thermal radiation testing and in situ trials. The variance in output within each type of sensor was small (±3.5% and ±0.3°C) and there was no apparent change to the variance in output of the sensors, when used in air or on a foam cushion loaded with a 50 kg sandbag (p > 0.1). In the human sitting experiments, although the profile from sensors under the thighs and ischial tuberosities were similar, the magnitude of change could be affected by position and body mass of the subject. This was especially noticeable with the sensors under the coccyx. These results support the use of multiple sites for sensor placement over the use of a single site when studying these parameters at the interface between subject and seating material at the seat base.

A methodology using in-chair movements as an objective measure of discomfort for the purpose of statistically distinguishing between similar seat surfaces

This study presents a method for objectively measuring in-chair movement (ICM) that shows correlation with subjective ratings of comfort and discomfort. Employing a cross-over controlled, single blind design, healthy young subjects (n = 21) sat for 18 min on each of the following surfaces: contoured foam, straight foam and wood. Force sensitive resistors attached to the sitting interface measured the relative movements of the subjects during sitting. The purpose of this study was to determine whether ICM could statistically distinguish between each seat material, including two with subtle design differences. In addition, this study investigated methodological considerations, in particular appropriate threshold selection and sitting duration, when analysing objective movement data. ICM appears to be able to statistically distinguish between similar foam surfaces, as long as appropriate ICM thresholds and sufficient sitting durations are present. A relationship between greater ICM and increased discomfort, and lesser ICM and increased comfort was also found.

Performance Assessment of a Humidity Measurement System and Its Use to Evaluate Moisture Characteristics of Wheelchair Cushions at the User–Seat Interface

Little is known about the changes in moisture that occur at the body–seat interface during sitting. However, as increased moisture can add to the risk of skin damage, we have developed an array of MEMS (Micro-Electro-Mechanical System) humidity sensors to measure at this interface. Sensors were first evaluated against traceable standards, followed by use in a cross-over field test (n = 11; 20 min duration) using different wheelchair cushions (foam and gel). Relative humidity (RH) was measured at the left mid-thigh, right mid-thigh and coccyx. Sensors were shown to be unaffected by loading and showed highly reliable responses to measured changes in humidity, varying little from the traceable standard (<5%). Field-test data, smoothed through a moving average filter, revealed significant differences between the three chosen locations and between the gel and foam cushions. Maximum RH was attained in less than five minutes regardless of cushion material (foam or gel). Importantly, RH does not appear to distribute uniformly over the body–seat interface; suggesting multiple sensor positions would appear essential for effectively monitoring moisture in this interface. Material properties of the cushions appear to have a significant effect on RH characteristics (profile) at the body–seat interface, but not necessarily the time to peak moisture.