Transthoracic Impedance: V. Effects of Early and Late Clamping of the Umbilical Cord with Special Reference to the Ratio Air‐to‐Blood during Respiration

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Abstract
Summary: Transthoracic impedance TTI in combination with recordings of air volume change and oesophageal pressure has been used to analyze time dependent variations in the ratio airlfluid during the first day of life, as well as the dynamic interrelationship between air and fluid in the lungs during respiration.Two groups of infants, seven with early and seven with late clamping of the umbilical cord, were studied a t 2, 6, 12 and 24 hours of age. These groups are known to have a dif‐ference in total blood volume, decreasing during the time of study.Especially in late‐clamped infants charac‐teristic changes in impedance variables are noted. Basic transthoracic impedance lZo(, reflecting the static ratio air/fluid, is initially low and increases till 12 hours of age, a net result of a decrease in pulmonary blood volume, interstitial fluid and possibly some contribu‐tion from an increase in pulmonary air volume.A tendency towards a fall in IZ, I from 12 to 24 hours coincides with an enlargement of the total blood volume.Variations between early and late‐clamped infants are larger for the dynamic impedance variables than for IZoI. The ratio IZ, I/V, of impedance variation per unit air volume change during respiration is higher for late‐clamped infants during the whole study, though decreasing with time. This implies that these infants have a larger amount of fluid in the lungs as compared with early‐clamped infants, also decreasing with time. n accordance with the presented physical model for volume relations in the lungs the amount of blood that needs to be moved into the lungs with inspiration is relatively smaller when the pulmonary blood volume is higher.A looped relation between air volume change and impedance change during a breath lZdl, is most pronounced in late‐clamped infants a t the commencement of the study, significantly decreasing with time. The existence of a IZ, I means that a larger blood volume than necessary for the geometrical requirements has entered the lungs during inspiration, a volume that is allowed to leave in early expiration. The prerequisite of a high IZ, I is a large pulmonary blood volume. For infants with early clamping of the umbilical cord no significant variations are noted in the impedance variables.It is concluded that late‐clamped infants, compared to early‐clamped infants, in addition to their larger total blood volume also have larger pulmonary fluid volume, the increment, mainly consisting of blood. A correlation found between change in lung compliance and the impedance variables, especially con‐cerning the late‐clamped group, and a suggestion is made that lung compliance varies inversely with the pulmonary fluid volume.