Heart Rate and the Concept of Circulatory Load∗

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Abstract
The functional demands of different types of work-load (dynamic and static muscular work, exposure to extreme hot or cold climates and the mental load caused by emotional stress and by the processing of information) are discussed in this paper. The need for absolute and comparative or relative measurement or estimation of these functional physiological demands in different work situations are considered. The validity of oxygen consumption of the body and of heartrate as an integral ergonomics measure are critically discussed. It is pointed out that these measures have only a high validity when (heavy) dynamic muscular work is considered. However, in muscular work of a static type and in the other type3 of work-load mentioned (climatic and mental conditions) there are many restrictions on their validity Moreover, from the point of view of occupational medicine and ergonomics there is a need for specific knowledge about the load of different organic (functional) systems. Therefore, the concept of circulatory load is put forward and its value as an ergonomics measure is advocated The use of heart rate alone as a measure of circulatory load has a rather restricted value. It is shown that the intrinsic value of each heartbeat as a measure of circulatory load differs greatly in different types of work-load, since apart from heart rate stroke-volume and mean blood pressure show various patterns of reaction in those conditions The possibilities of exact measurement of these data in the practical work situation, however, are still rather limited. Nevertheless, when using heartrate as an ergonomics measure, those additional quantitative data determining the circulatory load and their reactions on different types of work-load should be carefully estimated and taken into account as much as possible