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EFFECTS OF CHANGING HAEMATOCRIT, VENTRICULAR RATE AND MYOCARDIAL INOTROPY ON THE ACCURACY OF IMPEDANCE CARDIOGRAPHY
Author(s) -
Quail A. W.,
Traugott F. M.
Publication year - 1981
Publication title -
clinical and experimental pharmacology and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 103
eISSN - 1440-1681
pISSN - 0305-1870
DOI - 10.1111/j.1440-1681.1981.tb00737.x
Subject(s) - impedance cardiography , inotrope , cardiology , medicine , heart rate , stroke volume , blood pressure
SUMMARY 1. The accuracy and limitations of the non‐invasive impedance cardiograph technique were examined in dogs with electromagnetic flow‐transducers mounted on the aortic root over a wide range of physiological conditions of anaemia, heart rate, stroke volume and myocardial inotropy. 2. The in vivo blood resistivity (ρ)‐haematocrit relationship is linear and slightly inverse, and is thus opposite to the curvilinear, direct relationship of the bench‐derived p‐haematocrit relationship. At haematocrit 41%, in vivo ρ is 135 ohm. cm (s.e.m. = 1.0, n ‐ 134) and rises only to 143 ohm. cm (s.e.m. = 1.6, n = 134) as haematocrit falls to 26%. 3. When in vivo ρ is used in the Kubicek formula for stroke volume (SV) calculation, the instrument is linear and accurate for heart rates over 38–156 min ‐1 . Thus 82% of all points fall within ±20% of the line of equal value over stroke volumes ranging from 8–46 ml (N = 3, n = 105). The standard error of the estimate for pooled data is ±2% of the mean impedance stroke volume value of 22.2 ml. The instrument tends to overread at heart rates lower than 60 min ‐1 .