Ejection Time by Ear Densitogram and Its Derivative

Ear densitographic ejection times (EDET) and first derivative ear densitogram ejection times (dEDET) were studied to determine whether their reliability and validity justify their substitution for ejection times derived from the far less stable carotid pulse tracing. Inter- and intra-subject comparisons were made on thirty individuals under a wide variety of disease and challenge states. Statistical analysis of the data-which had been obtained through a blinded procedure-showed an overall correlation (r) of .98 for carotid vs EDET and .99 for carotid vs dEDET. The t-test demonstrated no significant differences among ejection times derived from the three methods. Moreover, the close tracking at rest and during challenges of ejection times derived from these curves with those from the carotid indicate that either method may be substituted for standard carotid curves without sacrificing reliability or validity of the measure. Both ear curves offer distinct advantages over carotid pulse curves because their sensor is self-retaining and they remain stable during exercise and other body and respiratory movements. The additional feature of simplicity in reading the first derivative of the ear densitogram over its undifferentiated curve makes dEDET the preferred method.