Finger thermometry in the assessment of subjects with vibration-induced white finger.

BOVENZI M. Finger thermometry in the assessment of subjects with vibration-induced white finger. Scand J Work Environ Health 13 (1987) 348-351. The measurement of finger skin temperature (FST) is one of the most commonly used methods for evaluating the response of the digital vessels to cold stimulation. In well-controlled experiments a significant correlation has been observed between FST and digital blood flow over a wide range of water temperatures. On the contrary, FST in air is considered an inadequate index of digital skin circulation since, at a given ambient temperature, FST depends not only on the rate of blood flow through the digit but also on environmental conditions. Despite these limitations, FST recording after a cooling procedure has been used in surveys of vibratio n-induced white finger (VWF), and a delayed finger rewarming time has been proposed as an indicator of digital vasospasm in workers with VWF. Finger skin thermometry can differentiate between VWF groups and healthy groups, but it is unsuitable for diagnosing Raynaud's phenomenon on an individual basis. The thermometric method has good specificity but its sensitivity is lower than that of plethysmographic techniques. FST after cold provocation may be considered a useful screening test in field studies, while more sensitive methods should be employed to confirm VWF symptoms in individuals objectively, especially for insurance compensation purposes.

Man y objective tests have been developed to detect circulatory impairment in the fingers of vibration-exposed workers , but at present none of the proposed tests seems to be completely satisfactory. In vascular laboratories pleth ysmog raphic , Doppler ultrasound, and radioi sotope clearance method s are used for recording digital blood pressure and flow, while infrared thermography is employed to study in detail skin surface temperatu re distributions over the hand s and the fingers. These techniques have, however, the disadvantages of being expensive and time-con suming. Surveys of vibration-exposed workers are frequentl y carried out in the field , where detecting digital vasospastic disorders requires simple objective tests such as visual inspection of skin color and finger skin thermometry after cold pro vocation.

Skin temperature and blood flow in the human finger
Finger skin temperature (FST) is con sidered a useful physiological parameter for evaluating the response of the digital vessels to cold stimulation. Th e use of the thermometric method to assess periph eral vascular reactivity is based upon the assumption that FST depends 348 on the rat e of blood flow th rou gh the digit. Nevertheless there exists experimental evidence that this assumption is valid only under standardized laboratory conditions. Hsieh et al (5) observed a highly significant correlation between FST and blood flow in the fingertip s of nine volunteers whose fingers were immersed for 20 min in slowly stirred water at vario us temperatures (range 4.6°C -40°C), minimum blood flow through the fingertip occurring at about lQ0c. Mo ntgomery (7) reviewed 20 reports on quan titative determinat ions of human hand and finger blood flow as fun ctions of skin and room temperatures. At a skin temp erature of about 20°C, maximum vasoconstriction took place in the hand and digital vessels, and below 20°C cold vasodilatation could be observed. Above 20°C blood flow increased, and at progr essively higher temper atures the rat e of increase plott ed graphically displayed a rising slope tending to become vertical between 33 and 40°C. Skin temperature of the hand s plays a prominent role in the regulati on of heat exchange between the human bod y and its environment. At a given ambient tempe ratur e FST is determined by the complex interaction o f severa l physiological and physical variables so that its relation ship to blood flow differs from that observed in the afo rementioned experimental studie s. According to Greenfield (4) FST in air is an impe rfect index of digital blood flow because FST depends not only on the amount of bloo d passing through the digit but also on environmental param eters such as air temp erature, mean radi ant temperature, relat ive air velocity, and hum idity. Despite these limitations, the monitoring of FST aft er cold stress can be used in surveys of vibration-induced white finger (VWF), in studi es on human reaction to cold, and in the evaluation o f the effectiveness of medical treatment in patients with Raynaud ' s phenomenon .

Finger skin temperature and the cold provocation test in studies of vibration-induced white finger
Digital temperatures are usually measured by thermistors or thermocouples attached to the skin surface of the fingers. Montgomery & Williams (8) reported detailed thermal profiles of the forearms, hands, and fingers of seven restin g male subjec ts exposed to cold (9.8°C), neutral (23.4°C), and warm (46.8°C) ambient temperatu res. No differen ces between the right and left sides of the upp er extremit ies were observ ed at each ambient temperature. These results are consistent with other find ings in a field survey com prising 169 vibra tion-exposed shipya rd caul kers and 60 referents ( I). Within each gro up no asymmetry between the resting skin tempera tures of the right and left hand s and fingers was noticed, whereas significant differences were found between the two groups at every measurement location (figure I ). It is not eworthy that, in two investigation s, finger blood pressure and flow were found to be lower in a gro up of granite quarrymen ( 10) and in a group of chain sawyers (9) than in their corresponding reference group; the se findin gs indicate that , amon g vibration-exposed workers , digital blood perfusion may be reduced even at rest.
To pro voke digital vasospas tic attacks, several cooling procedures have been described for the hand s with different water temperatures and immersion times. It is believed that the pattern of FST followin g the cooling period reflects, to a large extent, the degree of cold-induced vasoconstriction in the digital vessels. As a result , the delayed recovery time of FST is considered a useful indicator o f persistent digital vasospasm. It should be remember ed, however, that , in addition to the environmental conditions previou sly mentioned , even ind ividual variables such as age, anthro pometric parameters, emotional state, and cigarette smoking (2, II , 13) have been found to influ ence finger rewarmin g time after cold pro vocat ion . It has been suggested that the rewarming time of fingertip s to ambient temper ature after combined ischemia and coo ling o f the hand s is a sensitive test to assess digital vasospasm (6). My co-workers and I have applied this test to a gro up of 76 vibration-exposed tra vertine quarr ymen and to a group of 56 unexposed subjects working at the same quarries. The mean rewarming time to room temperature (21°C) was more prolonged among the 27 tra vertine operators with VWF [7.5 (SD 7.9) min] than amo ng those without VWF Our data showed that th e rewarming time discrimi- nated between affected and nonaffected worker groups, but did not discriminate between indiv idual cases because of the negati ve test results ob served for some subjects with a positive histor y of VWF .
The recovery time of the baseline FST after cold exposure is another important par ameter for evalua ting indirectly the changes in skin blood flow resulting from the release of cold-induced digital vasospasm. The upper no rmal limit for the recovery time is diffi cult to def ine as it depends on the water temp erature and on the immersion time. Porter et al (12) found that , amo ng 30 norm al subjects , the recovery time a fter hand immersion in an ice-water mixtur e for 20 s averaged 10 (ran ge 5 -20) min . Cleophas et al (3) reported that healthy subjects recovered their FST within 12 min aft er finger cooling in water at 16°C for 5 min . Chucker et al (2) observed that 78.4 010 of 51 norm als showed thermogram s of complete recovery dur ing the first 20 min following the immersion of both hands in ice water for I min. In a recent laboratory investigatio n I have measured FST and digital blood pressure after combined bod y and local cooling in 84 vibration-exposed workers using chipp ing, riveting and grinding tools and in 26 comparable reference workers. The subjects equilibrated for 30 min at a room temperature of 22-24°C, and then baseline measurements were taken. After the cold pro vocation (immersion of one finger in ice water at 5°C for 5 min du ring ischemia) , finger systolic pressure (FSP) was recorded and the percentage of change in the resting digital blood pressure (FSP %) was calculated (10) . The FST was continuously monitored before , du ring , and after the cooling pro cedure by a the rmistor probe (figur e 2). The mean FST values from the 4th to the 30th minute after the remo val of the finger from the cold water were significantly lower for the   Speci· ficity (%j measurements of FSP immediately after cooling revealed that zero pressure in the provoked finger, meaning complete closure of the digital arteries, was found in none of the referents, in two of the 64 vibration workers without VWF, and in 14 of the 20 workers with VWF. The sensitivity of the method to dete ct Raynaud's phenomenon was therefore 0.70, and the specificity was 0.97 . Among the referents the lower normal limit for FSP% was 60. With an FSP % of < 60 as the indicator of abnormal cold reactivity in the digital arteries, the sensitivity of the test (hyperreactivity with VWF) increased to 1.00 and the specificity (normoreactivity without VWF) decreased to 0.89 . A good correlation was observed between FSP% and T%2omin (r = 0.42, P < 0.001).
Conclusions a Lower normal limits (mean -2 SO) from 26 referents. vibration-exposed workers with VWF (stages 1, 2, 3 and 4 of Taylor's classification) than in the referents and in the other vibration workers with no symptoms (stage 0) and with neurological disturbances (stages 0TN) ' Table 1 gives the sensitivity and the specificity of three diagnostic criteria to assess VWF by means of the cold provocation test used in this investigation. In the reference group the percentage of recovery of the base-line FST in the cooled finger (T%) averaged 100, ie, complete recovery, at about 20 min following the cold provocation. The lower limit for T% 2o min (mean -2SD) was found to be 86 % for the referents. Five of the 64 vibration workers without VWF (stages 0 and 0TN) had a T%20min below the lower normal limit (specificity 0.92), while 12 of the 20 VWF operators showed abnormal test results (sensitivity 0.60). The FST can provide useful information on digital vascular responsiveness to cold stress in normal subjects and in workers with different stages of VWF. Experimental studies, however, have demonstrated that FST is influenced not only by digital blood flow, but also by individual and environmental factors. Well-controlled test conditions are therefore needed to obtain reproducible results . It is also necessary to standardize the challenge procedure (water temperature, immersion time, body cooling or heating) in order to ·obtain comparable data from different studies. Skin thermometry after cold exposure can differentiate between VWF groups and healthy groups, but it is unsuitable for diagnosing Raynaud's phenomenon on an individual basis. The thermometric method has a good specificity but its sensitivity is lower than that of other laboratory techniques, as, for instance, digital blood pressure measurement. FST may be considered a useful screening test in field surveys, while more sensitive methods should be employed to confirm VWF symptoms objectively, especially for insurance compensation purposes.