Analysis of biomechanical and ergonomic aspects of the cervical spine in F-16 flight situations.

With the help of a biomechanical neck model, several normal postures of an F-16 pilot were analysed. Measurements of accelerations and head positions were obtained during four flights, including simulated air combat. With the help of a model, muscle forces and joint reaction forces in the neck were estimated. Although at the present stage of research results of calculations must be interpreted carefully, conclusions can be drawn with respect to sitting posture, head position and helmet devices. The backward inclined back rest of the F-16 chair decrease the lordosis of the cervical spine, resulting in reduced calculated forces in the lower cervical spine. In high load situations, calculated maximal forces are of the same order of magnitude as failure loads of vertebrae and estimations of maximum muscle forces. The calculated neck load is increased substantially by the helmet and helmet-mounted devices. This load can be reduced by lightening the helmet or shifting the centre of mass of the helmet backwards.

Prevalence of achlorhydria in a normal population and its relation to serum gastrin.

In a middle-aged group of normal subjects achlorhydria after maximal stimulation with pentagastrin was found in 12 out of 366 males (3%) and 2 out of 198 females (1%); 13 of these 14 (93%) had an elevated serum gastrin, of which nine were more than two times normal. In another 11 persons a moderately elevated serum gastrin - less than two times normal - was found in absence of achlorhydria. At least seven of them had hypochlorhydria. Of 540 persons with a normal serum gastrin one had achlorhydria. Determination of the serum gastrin appeared to be fairly reliable as a method of detecting achlorhydria.

Parietal cell antibodies in relation to basal serum gastrin in a normal population.

Parietal cell antibodies, basal gastric pH and serum gastrin were determined in 544 normal non-achlorhydric subjects. Serum gastrin was significantly higher in subjects with parietal cell antibodies, both in the group with a weakly positive and in that with a strongly positive fluorescence score. The elevated serum gastrin level in subjects with circulating parietal cell antibodies was independent of gastric pH. It is suggested that parietal cell antibodies may interfere with gastrin receptors on the membrane of the parietal cell, thus influencing the feedback mechanism between the secretion of acid and gastrin, and resulting in an increase of the basal serum gastrin level at an unchanged basal gastric pH.

Is discrimination between type A and B atrophic gastritis clinically useful in achlorhydria?

We tested the validity of the concept that chronic atrophic gastritis can be subdivided into type A and B in hospital patients and normal subjects with proven pentagastrin-refractory achlorhydria. Classification was based on the determination of the basal serum gastrin and parietal cell antibodies. Of 59 hospital patients with achlorhydria, 71% could be classified as belonging to either type A or B; for 29% the criteria for neither type were fulfilled. Of 14 asymptomatic persons with achlorhydria found in 564 normal persons, five could be classified as having type A gastritis, and one as type B gastritis. In eight (53%) persons, an elevated serum gastrin was found in the absence of parietal cell antibodies, representing an intermediate type of atrophic gastritis. Because one-third of the hospital patients and more than half the persons with achlorhydria in a normal population had to be classified as belonging to an intermediate type, the discrimination between type A and B atrophic gastritis in achlorhydria seems to be of limited practical value.