Search

Tracheal suctioning of a patient on a ventilator may induce hypoxemia. Bennett 7200 microprocessor ventilator has an "100% O2 suction" key which is claimed to provide 100% oxygen for two minutes and switch back automatically when this function is set. Four 7200 ventilators were tested to verify this function. We found that the mean lag time varied from 20.1 seconds to 103.3 seconds and the mean recovery time varied from 33.0 seconds to 134.6 seconds according to the difference of initial tidal volume, ventilator rate and fractional inspired oxygen setting. When the ventilator was on "100% O2 suction", the delivered tidal volume was less than the preset tidal volume. In order to hyper-oxygenate and hyper-inflate the patient to prevent suction-induced hypoxemia, those finding should be taken into consideration when the clinicians apply this function in clinical situation.

We have examined the binding of Mnt repressor to operator DNA in vitro and have determined how this binding affects the level of transcription from two nearby promoters, Pant and Pmnt. Mnt binds to a region of DNA that overlaps the startpoint of transcription of Pant and the -35 region of Pmnt. Mnt represses transcription in vitro from Pant and enhances transcription from Pmnt. Protection and interference experiments show that Mnt binds to a single, 17 base-pair operator site. The operator sequence and the protein-DNA contacts are symmetric. Mnt makes major groove contacts on both faces of the operator DNA. At pH 7.5, 200 mM-KCl, 22 degrees C, the Mnt tetramer binds operator with high affinity (Kd = 2.2 X 10(-11M) and the protein-DNA complex is quite stable (t1/2 = 48 min). Operator binding shows large dependencies on pH, salt concentration, and temperature.

Are repressor binds to a single, partially symmetric, 21 base-pair operator site that is centered between the -10 and -35 regions of the Pant promoter. Protection and interference experiments show that Arc makes contacts with the operator on one side of the DNA helix. Although Arc is a small protein (53 residues/subunit), it makes contacts that are farther from the center of the operator than those made by many larger repressors. These extended contacts include the phosphate groups at the ends of the 21 base-pair site. Under standard conditions (pH 7.5, 100 mM-KCl, 3 mM-MgCl2, 22 degrees C) half-maximal operator binding is observed at an Arc concentration of 2.5 X 10(-9) M and the protein-DNA complex is very stable (t1/2 approximately equal to 80 min).