Validity of heart rate as an indicator of cardiac strain

¹ Haskell Laboratory for Toxicology and Industrial Medicine, E. I. du Pont de Nemours and Co., Wilmington, Delaware

Total cardiac cost is a measurement of the area under the curve obtained by plotting the heart rate for each minute during work and recovery. In a constant environment it varies with the work accomplished in a given time and, for a constant work performance, it varies with the severity of the conditions. The work accomplished per beat has a reciprocal relation to total cardiac cost when work and recovery times are constant. Recovery cost and the average of three early recovery heart rates, P₁, P₂, and P₃, vary linearly with total cardiac cost when work or environmental stress increases. In these experiments P₁, P₂, and P₃ are the heart rates per minute recorded during the last 30 sec of the 1st, 2nd, and 3rd min, respectively, of the recovery period. These recovery pulse rates provide a simple measurement of the degree of cardiac strain induced by work in any environment.

Submitted on July 13, 1961