Carbon monoxide disposition and permeability-surface area product in the foetal circulation of the perfused term human placenta

In order to estimate the placental barrier to gas transfer, a novel carbon monoxide (CO) wash-in method was used to estimate the permeability-surface area (PS) product for the transfer of gas across the foetal circulation in the perfused human term placenta. The PS product for CO was 0.0096 ± 0.006 ml/s/g or 0.012 ± 0.007 ml/s/g using compartmental or Crone-Renkin analysis, respectively. Using this result and a published estimate of the placental capillary surface area, the permeability coefficient to CO across the foetal circulation was found to be approximately 4 × 10^-5 cm/s. This result is compatible with the hypothesis that the foetal circulation of the human placenta imposes a potentially significant barrier to gas transfer.