Electrokymographic Studies of the Ventricular Isometric Relaxation Phase of the Cardiac Cycle in Man

Abstract

The duration of the isometric relaxation phase could be measured on 108 (95%) of 114 normal subjects, age 17 to 32 yrs. Approx. 20 cycles per subject were read; thus the over-all study consisted of some 2000 cycles. Only those cycles were measured and recorded in which the phase of isometric relaxation could be easily identified. The duration of the isometric relaxation phase in the normal group ranged from 0.06 to 0.16 sec., the mean value being 0.115 sec. The probable error was 0.013 sec. 71% of the cases were within the range of 0.115 [plus or minus] 0.013 sec. or 0.1 to 0.13 sec.. The duration of this phase was independent of age, sex, systolic, diastolic and pulse pressure and cycle length. The records of 79 subjects with hypertensive heart disease, myocardial infarction and bundle-branch block were studied in a manner similar to the normal. The range of duration was from 0.1 to 0.22 sec.; the mean value was 0.169 sec. The probable error was 0.017 sec. 70% of the cases were within the range of 0.169 + 0.017 sec. or 0.15 to 0.18 sec. The duration of the isometric relaxation phase was common to each of the types of heart disease included in the study. Neither the degree of increase nor the contour of the isometric relaxation complex appeared characteristic for any one of these types of heart disease. The difference between the mean of the normals (0.115 sec.) and the mean of the abnormals (0.169 sec.) was 0.054 sec. and by statistical study was found to be significant. The duration of this phase was 0.14 sec, or less in 98% of the normal readings and 0.15 sec. or more in 80% of the pathological readings.