Combined effect of noise and workload on heart rate changes in thermal comfort condition: A laboratory- controlled study

Noise is one of the annoying agents in the environment and it is harmful agent in workplaces that its occurrence with work load, there are in many workstations. The aim of this study was to determine the combined effects of exposure to noise and work load on heart rate changes. This cross-sectional study performed on 14 male students into climatic chamber in 2011.The mean ± SD of age 23±1.5 years, height 175±2.5 cm, weight 67±7.5 kg and body mass index 21.9± 1.7 kg/m2. Heart rate was measured under climatic conditions controlled (Wet bulb globe temperature= 22.1±0.9) in four levels of work load including resting state (15 minute), sitting state (50 minutes), light work load (50 minutes), moderate work load (50 minutes) and heavy work load (50 minutes) and five level of noise exposure (No exposure, 65 dBA.75 dBA, 85 dBA and 95 dBA). Data were analyzed with Repeated Measures test. The mean (SD) of heart rate was 60.1± 7.5 beats per minute (bpm) at rest. Heart rate was increased significantly (2.4 bpm) when the noise exposure level was 95 dB (P=0.032) compared with no exposure to noise in sitting state.In light work load, heart rate increased in noise exposure levels of 65 dB, 75 dB and 95 dB compared with no exposure to noise were 2.1 bpm, 1.4 bpm and 2.8 bpm respectively (P>0.01). In moderate work load, the average of heart rate increased in noise exposure levels of 65 dB, 75 dB, 85 dB and 95 dB compared with no exposure to noise were 2.9 bpm, 3.8 bpm. 4.9 bpm and 5.7 bpm respectively (P>0.001). In heavy work load, the average of heart rate increased in noise exposure levels of 65 dB, 75 dB, 85 dB and 95 dB compared with no exposure to noise were 5.5 bpm, 8.4 bpm. 10.8 bpm and 12.5 bpm respectively (P> 0.001). The results showed that the combined effects of exposure to noise and work load at thermal comfort conditions was enhanced heart rate so that increase trend of heart rate in moderate and heavy work load was higher during exposure to noise more than 85 dB.