Carl-Johan Göthe

Carpal tunnel syndrome (CTS) and exposure to vibration, repetitive wrist movements, and heavy manual work: a case-referent study.

Possible connections between carpal tunnel syndrome (CTS) and exposure to vibrating handheld tools, repetitive wrist movements, and heavy manual work were examined in a case-referent study. The cases were 38 men operated on for CTS between 1974 and 1980. For each case, two referents were drawn from among other surgical cases (hospital referents) and two further referents from the population register and telephone directory, respectively (population referents). Thirty four of 38 cases (89%) and 143 of 152 referents (94%) were interviewed by telephone. An increased prevalence of obesity, rheumatoid disease, diabetes, or thyroid disease was observed among the cases but most did not suffer from any of these disorders. CTS was significantly correlated with exposure to vibration from handheld tools and to repetitive wrist movements but showed a weaker correlation with work producing a heavy load on the wrist. A cause-effect relation between CTS and exposures to handheld vibrating tools and to work causing repetitive movements of the wrist seems probable. Some differences between hospital and population referents indicate that a case-referent study of this type could be biased by inappropriate selection of referents.

A Simple Method of Estimating Air Recirculation in Ventilation Systems

A method for quantitative measurement of the overall air recirculation in ventilation systems is presented. The air recirculation is calculated from the concentrations of a tracer at three well-defined points, viz., the background concentration in outside air (C1), the tracer concentration in the recirculated air (C2), and the tracer concentration in the inlet air after the recirculation system (C3). The recirculation quotient is calculated according to the following formula: Q2/Q3 = (C3−C1)/(C2−C1). Q2 = recirculated airflow; Q3 = total inlet airflow including recirculated airflow. Thus, a quotient between flows is identical with a quotient between tracer concentrations. The method allows the usage of both natural tracers (e.g., contaminants, such as CO2, occuring in the examined building) and artificial tracers (e.g., fluorocarbon 12 or sulfur-hexafluoride). The method has been tested with good results. At these tests, the tracer was CO2 emitted from exhaled air and indoor activities in the buildings.

Evaluation of CO2 detector tubes for measuring air recirculation

There are both technical and medical hygienic needs for accurate and useful methods to measure air recirculation in ventilation systems. This is possible by analysis of the CO{sub 2}-concentrations in outdoor air (C{sub 1}) and at two well-defined points before (C{sub 2}) and after (C{sub 3}) the mixing point for recirculated fresh air. The percentage of recirculated air in the mixed inlet air is represented by the quotient 100 (C{sub 3}-C{sub 1})/(C{sub 2}-C{sub 1}). The accuracy of the method is excellent when the Co{sub 2} concentrations are determined with a sensitive instrument, such as an IR spectrophotometer. However, detector tubes for CO{sub 2}-analysis obtainable on the market today are not usable in this situation. Air recirculation in peopled spaces could result in CO{sub 2}-concentrations in the inlet air which are considerably higher than 500{mu}L/L.

Local exhaust ventilation and exposure to nitrous oxide in ambulances

SummaryUnder extreme conditions, ambulance attendants and drivers could be exposed to nitrous oxide administered to transported patients in concentrations causing acute effects. Special arrangements are necessary to prevent such exposure, which is influenced by travelling speed, local exhaust ventilation and the use of an excess gas transfer tube evacuating expired air and overflow gas from the face mask to the outside. The separate eliminative effects of travelling speed and local exhaust varied considerably with the experimental conditions. The excess gas transfer tube reduced the levels of nitrous oxide in the air by 86 to 97% inside the ambulance at different experimental conditions. The combination of excess gas transfer tube and local exhaust resulted in a relatively constant reduction of the airborne nitrous oxide levels by about 98% when the ambulance was at a standstill and 99% when it was running.

Emission of ink aerosol from ink-jet recorders.

As a follow-up of two patients found to be allergic to EKG*ink, a study was made, using spectrophotometric and light microscopic methods, of the factors influencing the emission of ink aerosol from ink-jet recorders used in electrocardiographs. Ink aerosol concentrations were only detectable by spectrophotometry under extreme conditions. However, the light microscopic method was sufficiently sensitive. At the slow paper speeds normally used (10-25 mm/sec) and under normal working conditions, the concentration of ink aerosol near the recorder was less than 0.1 microgram/m3; but aerosol emission increased exponentially with increasing ink pressure, i.e. increasing paper speed. At the highest paper speed studied (200 mm/sec), the aerosol concentration 36 cm from the ink nozzles was about 65 micrograms/m3. An increase in the distance from the ink nozzles to the chart paper resulted in a decrease in ink aerosol emissions. Aerosol dissipation was decreased by local exhaust ventilation of the ink-jet recorder. However, a protective shield designed to catch emitted ink aerosol only reduced the aerosol concentration at the measuring point at slow paper speeds. At higher paper speeds, the concentration increased. The average ink aerosol concentration near modern electrocardiographs is low, but some EKG operations may result in high peak concentrations. The formation of ink aerosol could be considerably reduced by changing the rheologic properties of the ink.