Blood Flow Pulsatility Effects upon Oxygen Transfer in Artificial Lungs

  • Boschetti F
  • Cook K
  • Perlman C
 et al. 
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Abstract

This report discusses theoretical effects of blood flow pulsatility
upon the rate of oxygen transfer in artificial lungs, demonstrates
the effects with in vitro tests upon commercial oxygenators, and
applies the theory to these oxygenators and to a thoracic artificial
lung. Steady flow gas transfer theory is applied to pulsatile flow
by using the instantaneous value of flow rate at each instant of
time, that is, quasi-steady gas transfer. The theory suggests that
the local rate of oxygen transfer for a given device and blood composition
is proportional to the flow rate to a power less than unity and to
the hemoglobin saturation level. It predicts, for some cases, overall
reduced rates of gas transfer for pulsatile flow relative to those
at steady flow for the same mean blood flow rates. In vitro bovine
blood tests, using pediatric oxygenators, a pulsatile pump, and an
adjustable compliance chamber, indicate a significant average 10%
reduction of oxygen transfer for pulsatile flow relative to steady
flow. The application of the theory to the oxygenators predicts gas
transfer values that are in agreement with those measured during
the experiments. The results have implications in the design of implantable
thoracic artificial lungs, which should include a compliant section
to dampen the cardiac pulse. A relatively small compliance (0.2 ml/mm
Hg) at the thoracic artificial lung inlet is sufficient to obtain
approximately 95% of steady flow oxygen transfer.

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