INSTANTANEOUS HEART-RATES AND OTHER TECHNIQUES INTRODUCING ERRORS IN THE CALCULATION OF HEART-RATE

Data on heart rate can be analyzed in terms of beats per unit of time (heart rate) or its reciprocal, time per beat (interbeat interval). We show that counting beats (including fractions), averaging interbeat intervals, and measuring the time for a fixed number of beats are correct techniques to measure heart activity within observation periods. QRS counts are less precise, but not systematically biased. Conversely, averaging instantaneous heart rates always overestimates true heart rate. Arithmetic means across trials of equal duration are correct only when heart activity for each trial is expressed as mean heart rate. For observation periods with equal numbers of beats, heart activity for each trial must be expressed as mean interbeat interval. A literature survey showed that biased techniques were frequently used to calculate heart rate, and that about half of the studies did not provide sufficient information on the methods used.