PROOf Purpose of the study Heart rate(HR) and Heart rate variability(HRV) are two of the most widely known physiological measures for assessing mental workload. In this study the effect of a simple arithmetic mental task on HR and HRV in a group of ten young volunteers was investigated. Material and Methods One hundred and fifty numbers (range 0-29) were pre- sented visually on a 14"CRT computer screen one at a time for 2 secs. One third of the numbers were asterix (*) marked.Subjects added these numbers mentally and told the sum at the end of experiment which con- tinued for 5min. HR was recorded during 5min rest before the test and while performing the mental task. Time and frequency domain analysis were carried out. Results & Conclusions Results showed that HR increased significantly while performing mental task with decrease in both low fre- quency (LF) and high frequency (HF) components. No significant changes in LF/HF ratio and time domain component were observed. The decrement in LF com- ponent during mental task may be explained as the influence of parasympathetic efferent nerves. Keywords: Heart rate, workload, mental processes, heart physiology INTRODUCTION M ental workload is an invasive topic in recent times and it represents a subject of increasing interest. As modern technology imposes more cognitive demand upon us than physical demands in many work environments, the understanding how mental workload affects the performance is critical.A number of measurement techniques for mental workload are available. Among those the main categories of workload measures are: primary task performance; secondary task performance; physiological measures; and subjective rating. Physiological measures are many and varied. The physiological method generally involves the measure- ment and data processing of one or more variables related to human physiological processes. For instance, various researchers have used respiration 1, 2 heart rate and heart rate variability 3, 4, 5 brain-evoked potentials6, electro dermal response, 1 eye movements and pupillary responses 7 as indices of mental effort. These measures offer advantages such as continuous monitoring of data; greater sensitivity and that they do not interfere with primary task performance. Among these parameters, heart rate (HR) and heart rate vari- ability (HRV) have been considered as most common, sensitive and authentic measures. 3,4 In addition, unlike other parameters HR and HRV can be easily used in field condition and do not require any sophisticated instrument or technology. Heart rate has been implicated in the measurement of workload 8 and its relation to mental effort is ambiguous. 9 In general, increases in heart rate are found with increased mental demands of the task. Tonic heart rate is activated by the sympathetic branch of the autonomic nervous system and responds to a wide range of influences. In one of the study Zwaga 10 found that HR decreased with anticipation stress. In case of HRV, studies performed so far show diverse and in many cases opposite findings. Jex and Allen (1970), 11 Kalsbeek (1973) 12 found that HRV decreased as mental load increased. It was hypothe- sized that "concentration of attention" causes reduc- tion in HRV. Spyker et al (1971) 1 found correlations of the R-T interval with workload. Stackhouse (1973) 13 found that HR and HRV measures were correlated with performance in precision hover experiments. There is evidence that variations in workload may pro- duce change in the midfrequency (mainly 0.10 Hz) res- piratory band component, which has been more con- sistently found to be sensitive to demands for increased mental effort. 3 In contrast, Mobbs et al (1971) 14 and Sherman (1973) 15 in their studies found no systematic relation- ship between mean heart rate and task difficulty. Similarly, they found no relationships between HRV and task difficulty. Luczak and Laurig (1973) 16 demon- strated that only certain measures of HRV would pro- duce statistically significant changes as a function of operator loading. Sayers (1973) 17 found that HR and HRV were unreliable measures of taskload, but the so called interval spectrum did provide consistent changes. Hicks and Wierwille (1979), 18 in a comparison of five methods of assessing workload, found that The INTERNATIONAL JOURNAL of MEDICINE 30 Effect of Arithmetic Mental Task on Short Term Measurement of Heart Rate and Heart Rate Variability Jayeeta Banerjee, Sougata Karmakar, Madhu Sudan Pal, Deepti Majumdar, Dhurjati Majumdar Defence Institute of Physiology and Allied Sciences Defense Research & Development Organisation, Ministry of Defense, Delhi, India ABSTRACT Address correspondence to: Dhurjati Majumda, Ph.D, Scientist ‘E’, Defense Institute of Physiology and Allied Sciences, Defence Research & Development Organisation, Ministry of Defence, Goverment of India, Lucknow Road, Delhi - 110054, India, Phone: 91-11-23935745 Fax: 91-11-23914790, E-mail: majum55@yahoo.com TIJM Volume I; Issue 1 January 2008 ORIGINAL ARTICLE