Olli Korhonen

Hand-arm vibration in the aetiology of hearing loss in lumberjacks.

A longitudinal study of hearing loss was conducted among a group of lumberjacks in the years 1972 and 1974--8. The number of subjects increased from 72 in 1972 to 203 in 1978. They were classified according to (1) a history of vibration-induced white finger (VWF), (2) age, (3) duration of exposure, an (4) duration of ear muff usage. The hearing level at 4000 Hz was used to indicate the noise-induced permanent threshold shift (NIPTS). The lumberjacks were exposed, at their present pace of work, to noise, Leq values 96-103 dB(A), and to the vibration of a chain saw (linear acceleration 30-70 ms-2). The chain saws of the early 1960s were more hazardous, with the average noise level of 111 dB(A) and a variation acceleration of 60-180 ms-2. When classified on the basis of age, the lumberjacks with VWF had about a 10 dB greater NIPTS than subjects without VWF. NIPTS increased with the duration of exposure to chain saw noise, but with equal noise exposure the NIPTS was about 10 dB greater in lumberjacks with VWF than without VWF. With the same duration of ear protection the lumberjacks with VWF consistently had about a 10 dB greater NIPTS than those without VWF. The differences in NIPTS were statistically significant. The possible reason for more advanced NIPTS in subjects with VWF is that vibration might operate in both of these disorders through a common mechanism--that is, producing a vasoconstriction in both cochlear and digital blood vessels as a result of sympathetic nervous system activity.

PHYSIOLOGICAL RESPONSES OF FIREFIGHTING STUDENTS DURING SIMULATED SMOKE-DIVING IN THE HEAT

While wearing a self-contained breathing apparatus and fire-protective clothing, 35 healthy firefighting students aged 19-27 years performed smoke-diving (entry into a smoke-filled room) during a simulated shipboard fire. The mean (+/- SD) ambient temperature inside the simulator was 119 +/- 12 degrees C, and the task lasted 17 +/- 4 min. All subjects were fit according to their maximal oxygen consumption, which was 52.4 +/- 5.2 mL/min/kg (4.08 +/- 0.45 l/min). During the smoke-diving the average heart rate was 150 +/- 13 beats/min (79 +/- 6% of maximal heart rate attained in a cycle-ergometer test), and the peak heart rate was 180 +/- 13 beats/min (95 +/- 6% of maximal heart rate). The estimated oxygen consumption was 2.4 +/- 0.5 L/min (60 +/- 12% of maximal oxygen consumption). Neither ability to tolerate stress (as determined by the instructors) nor previous experience in smoke-diving tasks seemed to influence the heart rate or estimated oxygen consumption during experiment. Smoke-diving was physically very demanding even for the young and fit subjects, showing the importance of regular evaluation of the health and physical fitness of every firefighter who has to carry out smoke-diving tasks.

Hand-grip force in lumberjacks: two-year follow-up.

SummaryHand-grip force was measured in 63 professional lumberjacks in 1978 and again in 1980. Lumberjacks with vibration-induced white fingers (VWF) had lost 21% of their muscle force during the two years. Lumberjacks with no hand-arm symptoms had lost 5% of their muscle force in the same time period. Lumberjacks with subjectively diminished hand muscle force had a slight increase in muscle force during the follow-up time. These results suggest that long-term exposure to vibration causes a decrease in muscle force.

Forestry workers exposed to vibration: a neurological study

Neurological findings were examined in 186 forestry workers with a mean exposure to chain saw vibration of 16.6 hours. The prevalence of active vibration induced white fingers was 5%, parethaesias of the hands 53%, and muscle weakness 13%. Clinical polyneuropathy was observed in 16 forestry workers in the hands (7.5%) which did not correlate with alcohol consumption. Seventy nine forestry workers of the total population were selected for electromyographic examination. Generalised EMG based polyneuropathy in the hands was observed in only two of the 79 forestry workers (2.5%). The carpal tunnel syndrome was found in 20 of the 79 forestry workers (26%). Headache and vertigo were not linked with exposure to vibration in forestry and a significant part of the numbness reported may be due to the carpal tunnel syndrome. Sensorimotor polyneuropathy is rare among forestry workers. The rise in the vibration detection thresholds was linked to the carpal tunnel syndrome.

Vibration-induced decrease in the muscle force in lumberjacks.

SummaryIsometric maximal hand grip force was measured with a strain gauge dynamometer in 91 lumberjacks and 31 controls during a 2-min compression-relaxation task. Measurements were carried out on both hands with and without simultaneous vibration exposure. The muscle forces of older subjects were smaller than those of younger men, independent of occupational vibration exposure. The fatigue curves of lumberjacks and control subjects had the same shape. During vibration exposure in the test, the forces diminished in the left hand significantly in the lumberjacks but not in the control subjects. The force level of fatigue curves of the lumberjacks with a history of diminished grip force was lower and decreased more during vibration exposure than in the lumberjacks with a history of normal grip force. The reduction in the hand grip force during vibration exposure in the lumberjacks seemed to be linked to lesions in the peripheral nerves and to activation of a tonic vibration reflex, but probably not to circulation disturbances. The fatigue mechanism seemed to be the same in lumberjacks and control subjects.

Vibration syndrome and vibration in pedestal grinding.

At one Finnish foundry all the workers had typical symptoms of vibration induced white finger (VWF) after they began using a new type of pedestal grinding machine. The objectives of this study were to establish the severity of the symptoms and the difference in vibration exposure between the new and the old machines. Vibration detection thresholds and grip forces were measured, as well as the vibration in the casting and in the wrist simultaneously. The mean latency for VWF among the grinders was 10.3 months after the change of pedestal grinding machines. All the grinders had numbness in their hands. The vibration detection threshold was significantly higher for the grinders than for their referents. At the same circle speed, the new wheels caused vibration levels up to 12 dB more than the old wheels. The circle speed had a slight influence on the vibration. The vibration levels of light (0.5 kg) casting were up to 25 dB higher than the heavy (5 kg) casting. The use of a pneumatic pressing device decreased the vibration levels in the wrist by 5-10 dB. The increase in vibration, which occurred when the new wheels were taken into use, was too small to explain such a dramatic outbreak of VWF. This led to the conclusion that some other feature such as the impulse character of the vibration also contributed to the effects of vibration.

Hand grip forces during chain saw operation and vibration white finger in lumberjacks.

The hand grip forces at the front and rear handles of a chain saw were measured during work, in 89 professional lumberjacks. The symptoms caused by vibration to the upper limbs were compared with the hand grip force (HGF) during work. To allow better comparison between subjects we used the ratio of hand grip force (HGF) to the maximal voluntary compression force (MVC), HGF/MVC expressed as a percentage. The mean HGF during sawing varied from 5 to 12 N in all subjects. The variation in HGF was greater at the front handle than at the rear handle, during sawing. The lumberjacks who had vibration-induced white fingers (VWF), had a higher HGF/MVC in both hands than the lumberjacks without VWF. Those lumberjacks affected by VWF used over 12% of their MVC at work. Subjects without HGF/MVC ratio. The lumberjacks with and without numbness in their hands had equal HGF/MVC ratios.

Responses of young and older men during prolonged exercise in dry and humid heat

SummaryEight young, sedentary men (aged 34 years, SD 3) and six older moderately active, unacclimated men (aged 57 years, SD 2) walked on a treadmill at 30% of their maximum oxygen consumption up to 3.5 h in a thermoneutral [dry bulb temperature (Tdb) 21°C, relative humidity (r.h.) 43%)], a warm humid (Tdb 30°C, r.h. 80%) and a hot dry (Tdb 40°C, r.h. 20%) environment while wearing ordinary working clothes (0.7 c/o). Their oxgen consumption, heart rate (fc), rectal (Tre) and mean skin temperature (Tsk), sweat rate (SR), and evaporative rate (ER) were measured during the tests. The ratings of thermal sensation (TS) and perceived exertion (RPE) were assessed using standard scales. In the heat stress tests, the number of experiments discontinued did not significantly differ between the two groups. The mean levels and end-exercise values of Tre, Tsk, fc, TS and RPE were not significantly different between the young and older subjects in any of the environments. In the warm humid environment, however, the Tre and RPE of the older subjects increased continuously (P<0.05) during the test compared to the young subjects. No significant difference between the groups was observed in SR or in ER. In the hot dry environment, however, the ER of older men increased more slowly compared to the young men. In spite of some time-related differences observed in Tre, RPE, and ER, the older subjects did not exhibit higher fc during exercise in the heat, they were not more hyperthermic and their performance times were similar to the young subjects. Therefore, it was concluded that older calendar age is not necessarily associated with a reduced ability to exercise in a hot environment and other factors, such as physical activity habits and aerobic capacity, may be equally important in determining heat tolerance in the elderly.

Skin blood flow during incremental exercise in a thermoneutral and a hot dry environment

SummaryEight physically fit men performed two incremental bicycle ergometer tests, one in an ambient temperature of 25° C and the other at 40° C. Oesophageal temperature (Tes) increased continuously throughout the tests up to 38.0 and 38.3° C, respectively. In both enviroments, forearm blood flow (plethysmography) was linearly related to Tes above the Tes threshold for vasodilation, but at the heaviest work loads this relationship was clearly attenuated and therefore indicated skin vasoconstriction, which tended to be more pronounced at 25° C. During recovery at 25° C, in some subjects the forearm blood flow increased above the levels observed at the end of the graded exercise in spite of a decreasing Tes. Skin blood flow, measured by laser Doppler flow meter at the shoulder, was quantitatively different but, on average, seemed to reveal the same response pattern as the forearm blood flow. In spite of the higher level of skin blood flow in the heat, blood lactate accumulation did not differ between the two environments. The present results suggest that there is competition between skin vasoconstriction and vasodilation at heavy work rates, the former having precedence in a thermoneutral environment to increase muscle perfusion. During short-term graded exercise in a hot environment, skin vasoconstriction with other circulatory adjustments seems to be able to maintain adequate muscle perfusion at heavy work levels, but probably not during maximum exercise.

Blood pressure, flow, and peripheral resistance of digital arteries in vibration syndrome.

The peripheral circulation was studied in 19 lumberjacks and in 12 control subjects. Twelve of the lumberjacks were free from vascular symptoms and seven had vibration induced white finger (VWF). Using the strain-gauge plethysmographic technique, the digital circulation was examined at rest, during cooling of the upper body, and during heating of the upper body. At rest and during vasodilatation no significant differences were found between the lumberjacks and the controls. During reflexive vasoconstriction, digital blood flow in the upper body was more reduced in lumberjacks with VWF than in control subjects. Furthermore, digital blood pressure of the lumberjacks with VWF fell more than in the control group. The peripheral resistance also increased more, but this difference was not statistically significant. There was no evidence that the exaggerated vasoconstriction of VWF resulted from a narrowing of the lumen of arterioles due to hypertrophy of the vessel wall. The present findings suggest that VWF is produced by the highly sensitive responsiveness of the affected vessel to normal vasoconstrictor stimuli.