The measurement of vascular and neurological function in workers exposed to hand-transmitted vibration
Four methods for measuring disorders of vascular function and neurological function associated with occupational exposure to hand-transmitted vibration have been defined by reference to the available literature. For measuring vascular function the methods are: i) measures of the finger systolic blood pressure (FSBP) response to local cooling and ii) measures of the finger skin temperature (FST) response to local cooling. For measuring neurological function the methods are: i) measures of vibrotactile thresholds at the fingertips and ii) measures of thermal thresholds at the fingertips. Measures of the FSBP and the FST response to cold provocation were appraised in 109 dockyard workers. The FST test did not differentiate between 82 healthy subjects and 27 subjects with vibration-induced white finger (VWF) whilst the FSBP test was found to be sensitive, specific and responsive to VWF. Vibrotactile and thermal thresholds were found to be sensitive, specific and responsive to symptoms of numbness in another study of 104 dockyard workers, of whom 67 reported neurological disorders. It was concluded that whilst the above tests could be useful for monitoring the vascular and neurological disorders, a number of improvements to the measurement methods could be worthwhile. Further experiments were carried out to investigate these improvements. The simultaneous measurement of FSBPs on multiple test fingers was developed to improve the practicality of this test when measuring FSBPs on more than one test finger. Increased central sympathetic activity was hypothesised to result from increasing the stimulus by cooling more fingers. In two experiments on 12 healthy subjects, it was found that FSBPs measured simultaneously on four test fingers gave similar results to FSBP measurements on one test finger. Simultaneous FSBP measurements on four test fingers had comparable repeatability to measurements on one test finger. It was concluded that measuring FSBPs on multiple test fingers is a useful improvement to this test. When measuring FSBPs, changing the order of presentation and the period of recovery between thermal stimuli was hypothesised to influence the results by altering central sympathetic activity. In 12 healthy subjects it was found that the order of presentation of thermal stimuli was not important but that inter-subject variability increased when recovery was allowed between thermal stimuli. It was concluded that minimising the time interval between successive applications of thermal provocation reduces undesirable inter-subject variability. Another study on 12 healthy subjects showed that different reference measurement locations give different results. It was concluded that the thumb is suitable location for making reference measurements. The FSBP test and the FST test both involve application of cold provocation. The two tests are sometimes performed in succession but multiple thermal provocations may have cumulative effects on central sympathetic activity. When the two vascular tests were performed in succession on 36 subjects, including 12 subjects with VWF, any effects of the order of test presentation were small although a test performed first tended to be more repeatable. It was concluded that if both tests are performed consecutively, greater emphasis should be placed on the test performed first. The data for the FST test were reanalysed and showed that the sensitivity and specificity to VWF of this test is improved by changing the method of interpreting the results. Three methods of interpreting the FST response to cold provocation that represent an improvement to the test are suggested. The two vascular tests have been shown in the literature to be repeatable for healthy subjects but not for subjects with VWF. The repeatability of the vascular tests was assessed in 36 subjects (12 manual workers, 12 office workers and 12 subjects with VWF). The repeatability of both tests was found to be low amongst workers with VWF; some of these subjects showed a negative test result on one occasion and a positive test result on another occasion. It was concluded that a repeat test may be required when a false negative result is obtained. For the vibrotactile threshold test, the skin-stimulus contact force is usually controlled. Controlling the skin indentation would simplify measurement equipment. An experiment on ten healthy subjects investigated the relationship between skin-stimulus contact force, skin indentation and vibrotactile thresholds. It was concluded that the vibrotactile threshold test could be improved by implementing control of skin-indentation. Skin indentations giving comparable vibrotactile thresholds to those obtained using controlled contact forces were identified. It is concluded that a test battery comprising the four test methods identified from the literature and subsequently developed during the course of this research can be used to monitor disorders of both vascular and neurological function associated with occupational exposure to hand-transmitted vibration. A number of recommendations are made for further improvements that might be achievable as a result of further work.