Cross-correlation of voice and heart rate as stress measures

Heart rate and O₂ uptake, etc. have been widely used to assess the physical fitness of human subjects. Recently developed Hayre voice-based parameters for physical stress or fatigue are validated by the results of this work. These parameters are not only non-obtrusive means of real time observation of clinical, educational and physical training of subjects but also provide a unique comparative means of monitoring physical fatigue among various professionals such as athletes, truck drivers, pilots and doctors of medicine, etc. Subjects of various ages running on a treadmill were instrumented for recording heart rate, EKG, treadmill speed and slope. The treadmill was run at 3·3 mph (90 m/min) and the grade was increased by one per cent a minute up to a maximum of 25 per cent and then the speed was increased by 0·2 mph until exhaustion. Each subject was asked to count from one to ten and utter two other preselected words separated by silence gaps in between for ease of analysis. An analysis of these utterances indicates that a monotonic increase in heart rate is highly correlated with Hayre parameters $\text{G}{}_{\mathrm{<mtext>1</mtext>}}$ and $\text{F}{}_{\mathrm{<mtext>1</mtext>}}$ mentioned above, up to the time of maximum stress and the associated peak heart rate of 175. After stopping the treadmill run and letting the subject sit down, the heart rate starts dropping rapidly whereas the Hayre stress parameter $\text{G}{}_{\mathrm{<mtext>1</mtext>}}$ tends to increase to a saturation level, thus verifying that the continued physically stressed state of the subject has not significantly lessened as one would perceive from the above mentioned drop in heart rate.