The mild cold challenge test is frequently used to assess the hands of patients with Raynaud's phenomenon. Great emphasis is placed on the degree of mild cold challenge, temperature measurement technique, follow-up period, and subsequent analysis. However, protocols involving subject preparation, the key starting point to the measurement process, are also very important. Subjects need to achieve cardiovascular and thermal acclimatization prior to the cold challenge. Typically, 20 minutes is often used for microvascular measurements, irrespective of external ambient temperatures, dress, or subject preparation. The aims of this study were to (a) investigate an appropriate pre-test subject preparation protocol for mild cold challenge testing and, (b) assess an appropriate time for thermal acclimatisation in normal healthy subjects.
The pre-test preparation protocol was compiled from information obtained from five European microvascular measurement centres who undertake mild cold challenge testing of the hands. The protocol asked subjects to follow guidance on diet and medication, dress, relaxation, and hand preparation within specified times prior to the study. Initially, subjects completed a health questionnaire to exclude cardiovascular disease, persistently cold hands or Raynaud's phenomenon. The minimum time for thermal acclimatization was then estimated from hand temperature measurements from 16 normal subjects (8 male and 8 female) of age 33 ±12 years (mean ± standard deviation). All subjects gave their written informed consent. Each subject followed the pre-test preparation protocol before sitting in a cool temperature-controlled room for 20 minutes (local study temperature 17 ±1 ºC). This was sufficient to result in peripheral vasoconstriction but without inducing shivering or significant discomfort. Each subject then sat quietly in a medical infrared imaging facility (ambient temperature 24 ±1 ºC) for 40 minutes whilst their hand skin temperatures were measured at 1 minute intervals (FLIR SC300 thermal imaging system). The operator and subject were blinded from the measurements during this follow-up. The temperature data were processed using dedicated FLIR ThermaCam Researcher image processing software, with skin emissivity assumed to be 0.97. Each sequence of images was studied twice and averaged to give an estimate of the time taken for the hands to reach a plateau with warm and evenly distributed temperatures.
The median (2.5-97.5 percentile) time for the 13 subjects (6 male and 7 female) whose hands re-warmed within the follow-up period was 14 (9-31) minutes. The recovery generally showed bilateral similarity between the right and left hands and there was no significant difference between males and females (Mann-Whitney test). When all subjects were considered, including the 3 that did not adequately re-warrn, the median time increased to 18 minutes, with no significant difference between the sexes. Four of the 16 normal subjects (25%) had not recovered within 30 minutes.
The pre-test protocol was acceptable for the subjects. We have shown that 30 minutes is not always long enough for acclimatization, even in normal subjects. These preliminary findings have implications for cold challenge testing of the hands using dynamic thermal imaging.
Allen J., Young AL, Griffiths B, Kumar N, Murray A. Subject preparation and thermal acclimatization prior to mild cold challenge testing using dynamic thermal imaging. Ninth European Congress of Medical Thermology, Krakow, Poland, May 2003. Abstract published in: Thermology International, 2003; 13(2):63-64.
Dr. John Allen, Freeman Unit, Newcastle upon Tyne. Tel: +44 (0)191-223-6161.