The evaluation of medical devices with healthy people?
Much of the research of thermal and physical comfort is completed with healthy participants in regular life scenarios. The translation of these findings into clinical settings for people with disease, deficiency or restrictions adds a level of complexity. As an example this study evaluated the effectiveness of a patient warming mattress device on body temperature and ratings of thermal comfort/sensation. Hypothermia has been linked to higher mortality rates in trauma patients admitted to hospital. Patient warming devices have been developed to assist the temperature of the patient and studies on these report varied effects. Laboratory trials with shivering inhibition (Goheen et al, 1997, Greif et al, 2000) found improvements from forced air and resistive blankets but without shivering inhibition (Williams et al, 2005) showed no benefit in warming from 35°C. A physical evaluation of the warming mattress device with a thermal manikin reported an energy contribution to the user (~70W). To support the physical evaluation a user trial was conducted. Nine healthy volunteer participants (27.78+4.99 Years) were exposed to three conditions using a repeated measures counterbalanced design. The participants were cooled in an environment with an air temperature of 0°C (60 minutes) then exposed to 30 minutes of a warming intervention. 1.Hot mattress HM. Mattress preheated to 18°C, under standard blankets 2.Warmed mattress WM. Mattress turned on at start of warming period, under standard blankets 3.Cold mattress CM. Control condition, no power to mattress, under standard blankets. During the cooling phase, aural and mean skin temperature (Tsk) significantly decreased for all conditions (p<0.01). Tsk increased following each warming intervention but aural temperature continued to decline. Significant increase in overall mean thermal comfort was seen during the first ten minutes of the warming phase for HM in comparison to CM and WM (p<0.05) but not at 20 and 30 minutes. This was mirrored by the overall mean thermal sensation rating across the same timeframe. HM increased thermal sensation from very cold to cool with CM and WM showing and increase from very cold to cold. This study revealed the effect of the device (HM) gave short term comfort and sensation gains at the start of the warming phase but the passive insulation provided (CM) also allowed re-warming to occur. This was the expected thermoregulatory response for a group of healthy participants. This group does not necessarily represent the hospital population with pathology that inhibits their normal responses to cold, e.g. circulatory shut-down, shock or trauma. For accurate application, the trial data needs to be closely matched with the limitations of the health condition in the target population. The challenge is now to explore the relationship between data from healthy cohorts and how that can be used for groups of patients with known physical and physiological conditions and limitations. The validity of a patient’s subjective assessment of their condition lying in a hospital bed is currently unclear. Evidence needs to show whether a patient in a hospital bed can accurately report joint position, thermal comfort, skin wettedness, pressure points etc to assist in the management of their condition.
The research work reported here was made possible by equipment donated by Frontier Medical and Research Contract LUEL 6964.