Impedance cardiography for non‐invasive assessment of systolic time intervals during exercise

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Abstract
Phono‐mechano‐cardiography (PMC) methodology for measuring such systolic time intervals (STI) as the pre‐ejection period (PEP), ventricular ejection time (VET) and the ratio (PEP/VET) is not an adequate method when STI are evaluated in an exercising subject (e.g. stress testing, functional capacity etc.). This is due to the complexity of positioning and keeping PMC transducers at the recording site secure while the body is moving. In this report a novel technique, impedance cardiography (IC), which does not require mechanical transducers being positioned over the body has been used to evaluate STI parameters in 6 subjects performing a cycle ergometer incremental exercise (10 W/min) up to 175 ± 12.5 W in order to compare IC traces with PMC traces obtained in the same session. The comparison of 460 recorded beats provided by both IC and PMC methods with proper statistic tests (correlation and linear regression, two‐way ANOVA, Fisher exact test) did not show any significant difference between the STI value obtained from IC and PMC methods respectively: PEPpmc = 0.13 ms + 0.99 ms PEPIC, p ≤0 0.0001, r = 0.92; VETpmc = 13.5ms + 0.95ms VETrc, p ≤ 0.0001, r = 0.98; PEP/VETpmc = 0.0036 + 0.85 PEP/VETic, p ≤ 0.0001, r = 0.84. Bland and Altman's (1986) analysis also showed a close agreement between the PEP, VET, PEP/VET ratio measured by PMC and IC instruments (mean differences were ‐ 0.89 ± 6.53 ms, 1.41 ± 6.67 ms, ‐0.0069 ± 0.33 respectively for PEP, VET and PEP/VET). It may be concluded that the IC system can be used in place of PMC to assess STI during exercise.