Lower body negative pressure: a test of cardiovascular autonomic function

Lower body negative pressure (LBNP) may provide an alternative test of cardiovascular autonomic function for patients unable to perform the Valsalva maneuver (VM). LBNP at -40 mmHg for 30 s was compared to the VM at 40 mmHg for 15 s with heart rate and blood pressure measured continuously in three age groups: 10-25 years; 26-40 years; and 41-55 years. Heart rate and blood pressure responses were comparable, with moderately diminished changes in blood pressure and heart rate in the LBNP test. When heart response to LBNP was converted to a ratio similar to that calculated for the VM, a high degree of correlation was found (R(2) = 0.5711). The LBNP test shows promise as an alternative test of cardiovascular autonomic function based on studies in normal subjects. The less marked changes may relate to the more passive nature of the applied stress. Future work should improve the device's accessibility and establish values for patients with autonomic disorders.

Mutation frequency decline in a rel strain of E. coli coli B/r

Mutation frequency decline (MFD) occurs among certain suppressor mutations induced by UV irradiation of E. coli. When irradiated bacteria are incubated in conditions less than optimal for protein synthesis prior to plating, a large majority of the potential mutants are rapidly lost. For several years the belief has existed that MFD results because stringent control of transcription at tRNA genes may influence excision repair of premutational photoproducts at these sites. We have constructed a rel mutant of E. coli B/r strain WU3610, verified that it has a typical phenotype of a relaxed strain in terms of RNA and ppGpp synthesis, and measured MFD. The kinetics of MFD were the same in WU3610 and WU3610 rel. Thus stringent control is not essential to MFD and there is no reason to believe that moderation of transcription at tRNA genes is integral to the MFD mechanism.