Abstract
Total respiratory system compliance (C) is derived from resonant frequency (fr) and inertance (I) according to C=(4π2·I–fr2) by analogy with electrical circuit theory. It was hypothetized that I of a narrow endotracheal tube (ETT, I calculable from length and diameter) far supersedes that of the bronchial tree (unknown). For measurement of fr a resonant oscillation was induced by overcompensating the ETT's and airways' resistances using a negative ventilator resistance. Our new method (Cr) was validated against the “constant flew inflation method compliance” (Ci).
In each of 10 tracheotomized rabbits (4.4±.5 kg) Ci and Cr values (mL/kPa) were obtained in 3 experimental situations(TAB.). Linear regression equation of the paired values was Cr=1.1Ci-.74 (r=.97; p<.0001). In 18 critically ill infants (body weight 880-6520g) the regression equation for the paired Ci (range 3-42) and Cr (1.8-43) values was Cr=.97Ci + .13 (r=.98) p<.0001). Median difference between individual paired data was .14mL/kPa (range - 4.2 to 3.8). CONCLUSION: Cr proved accurate. This method also works with the respiratory muscles in function.
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Schulze, A., Schaller, P., Dinger, J. et al. 173 DETERMINATION OF TOTAL. RESPIRATORY SYSTEM COMPLIANCE FROM RESONANT FREQUENCY IN INTUBATED SLBJECTS. Pediatr Res 28, 306 (1990). https://doi.org/10.1203/00006450-199009000-00197
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DOI: https://doi.org/10.1203/00006450-199009000-00197