How to assess skin temperature with hand

Skin Temperature–Assisted Relaxation

Skin temperature–assisted relaxation was discovered unexpectedly. During a standard evaluation at the Menninger Clinic, an individual's migraine attack abruptly subsided with a flushing in the hands and a rapid increase in hand temperature.58 Consequently, the clinicians who observed this event tested hand-warming treatment in migraineurs. Increasing hand temperature became a method of regulating stress and headache activity. Skin temperature is believed to provide an indirect measure of activity in the sympathetic nervous system. A reduction in arousal, or sympathetic outflow, leads to an increase in vasodilation and blood flow to the peripheral areas of the body, which is indicated by an increase in skin temperature. Conversely, an increase in arousal and sympathetic outflow constricts peripheral blood flow and results in a lower skin temperature.

Thermistors containing semiconductors and, occasionally, thermocouples are used to monitor temperature change in the skin. These temperature-sensitive sensors are placed on the fingers. Thermal-assisted biofeedback generally involves aspects of autogenic training59 in an effort to achieve an increase in peripheral skin temperature. The procedure has been named “autogenic feedback.” While recording an individual's skin temperature activity, the practitioner needs to keep in mind that measurements may be influenced by clinic, laboratory, and outdoor temperature and humidity. Heat build-up on the conductive leads and sensors can also affect the accuracy of the measurements.

The primary procedures in the general biofeedback approach are EMG-, skin conductance–, and skin temperature–assisted relaxation, also known as the “workhorses.” These therapies promote a decrease in sympathetic arousal and an overall state of relaxation. A common feature of relaxation is distraction, which has been illustrated by functional MRI research to activate areas within the periaqueductal gray region.60 This brain region has been associated with higher cortical control of pain. General relaxation-assisted biofeedback may be influencing these central mechanisms of pain.51 For a more detailed description of relaxation therapies, including autogenic training, see Chapter 123. In some instances, a brief psychophysiologic assessment, or psychophysiologic stress profile, is used for biofeedback-assisted relaxation. A more thorough psychophysiologic assessment is used in the specific biofeedback approach, which is described in the ensuing portion of this chapter. (For more information on biofeedback instrumentation, see Peek54).

Mean skin temperature

Mean skin temperature values are often reported in studies of thermoregulation as the skin represents the interface between the body and the environment. Similarly to estimates of core temperature, there are a number of methods for obtaining estimates of mean skin temperature.

Although mean skin temperature formulae are widely employed in interpreting the results obtained during thermoregulatory studies, they may not be applicable for examining the thermoregulatory responses of spinal cord-injured participants (Ready, 1984). The loss of sensory information below the level of spinal cord lesion (Rawson and Hardy, 1967) would result in the calculation of mean skin temperature values which do not accurately represent the extent of peripheral influences on the thermoregulatory system. Furthermore, a single mean skin temperature value would likely not be able to differentiate between differences in upper- and lower-body thermal state such as those observed for persons with SCI during heat exposure at rest (Guttman et al., 1958) and during exercise (Gass et al., 1988; Hopman et al., 1993a; Dawson et al., 1994; Price and Campbell, 1997). Furthermore, due to the variation in thermoregulatory responses between persons with different levels and types of SCI, particularly below the 10th thoracic vertebra (T10) (Normell, 1974; Burkett et al., 1988; Gass et al., 1988; Ishii et al., 1995), the assessment of individual skin temperature sites may be more appropriate for this population.

There are a number of factors, such as regional differences in heat production and dissipation, which mean that in general skin temperature responses are far more variable than those of core temperature. Differing ambient temperatures for baseline measurement of skin temperature between studies may add to this variability. However, a number of key differences between skin temperatures of the able-bodied and those with SCI are apparent. For example, mean skin temperature (calculated using the formula of Ramanathan (1964)) at rest in neutral ambient temperatures (20°C) for able-bodied and SCI groups have been reported to be similar (i.e., 31.7°C and 31.4°C, respectively; Price and Campbell, 1997) as those for persons with paraplegia and tetraplegia (29.5°C and 30.6°C, respectively; Griggs et al., 2015b). However, the thigh and calf skin temperatures of those with paraplegia were reported to be much lower (30.3°C and 29.0°C, respectively; Price and Campbell, 1997) than for able-bodied individuals, whose data were similar to the mean weighted value (31.6°C and 31.7°C, respectively).

Figure 50.1 demonstrates the difference between skin temperatures for a range of sites for persons with SCI and the able-bodied. The consistently warmer upper-body skin temperature sites for persons with paraplegia may reflect the habitual mode of locomotion, i.e., the upper arms and chest. However, most apparent are the cooler skin temperatures for the thigh and calf sites across studies, particularly the calf site. The greater difference for the calf site observed by Price and Goosey-Tolfrey (2008) may be a result of seasonal differences (i.e., data recorded in the colder winter months), suggesting peripheral regions are more susceptible to environmental conditions.

Using digital infrared thermography rather than skin thermistors Song et al. (2015) observed similar anterior thigh and calf skin temperatures for able-bodied persons and those with low-level SCI (below the seventh thoracic vertebra), whereas in those persons with lesions above the sixth thoracic vertebra these temperatures were cooler (Fig. 50.2). Thus, mean skin temperature values mask regional differences in skin temperature (Price, 2006), a factor which should be considered in the analysis of skin temperature data.

Limb ischemia

Skin color and temperature can provide information about severity of limb arterial perfusion. The feet, hands, fingers and toes should be examined for temperature and skin color, and the nails for evidence of fragility and pitting. Limb temperature can best be appreciated using the back of the examiner's hand. Temperature changes of adjacent segments on the ipsilateral limb and comparisons with the contralateral limb can be made. Presence of foot pallor while the leg is horizontal is indicative of poor perfusion and may be a sign of ischemia. Foot pallor may be precipitated in patients with PAD (who do not have CLI) by elevating the patient's leg to 60 degrees for 1 minute. Repetitive dorsiflexion and plantar flexion of the foot may also precipitate pallor on the sole of the foot when PAD is present. To qualitatively assess collateral blood flow, the leg is then lowered as the patient moves to the seated position. This is done to elicit rubor, indicative of reactive hyperemia, and determine pedal vein refill time. The time to development of dependent rubor is indicative of the severity of PAD. Severe PAD and poor collateral blood flow may prolong reactive hyperemia by more than 30 seconds. Normally, pedal venous refill occurs in less than 15 seconds. Moderate PAD subserved by collateral vessels is suspected if venous refill is 30 to 45 seconds; severe disease with poor collateral development is likely when venous filling time is longer than 1 minute.

Objective examination