Influence of G-suit abdominal bladder inflation on gas exchange during +GZ stress. 
Available data relating duration of +GZ stress to blood gas exchange status is limited.  Furthermore, studies focusing on pulmonary gas exchange during +GZ stress when abdominal restriction is imposed have yielded conflicting results.  To examine the time course of blood gas changes occurring during exposure to +GZ stress in dogs and the influence of G-suit abdominal bladder inflation on this time course, seven spontaneously breathing pentobarbital-anesthetized adult mongrel dogs were exposed to 60 s of up to +5 GZ stress with and without G-suit abdominal bladder inflation.  Arterial and mixed venous blood were sampled for blood gas analysis during the first and last 20 s of the exposure and at 3 min postexposure.  Little change in blood gas status was seen at +3 GZ regardless of G-suit status.  However, with G-suit inflation, arterial PO2 fell by a mean of 14.7 Torr during the first 20 s at +4 Gz (P less than 0.01, t test) and 20.6 Torr at +5 GZ (P less than 0.01).  It continued to fall an additional 10 Torr during the next 40 s at both +4 and +5 GZ.  Arterial PO2 was still 5-10 Torr below control values (P less than 0.05) 3 min postexposure.  A second series of experiments paralleling the first focused on blood gas status during repeated exposure to acceleration.  Blood gas status was assessed in five dogs during the late 20 s of two 60-s exposures separated by 3 min at 0 GZ.  No significant differences between the initial and repeated exposures were detected.  The data indicate that G-suit abdominal bladder inflation promotes increased venous admixture.