Comparative distribution of petechial haemorrhages as a function of aircraft cockpit geometry

One of the stresses to which aircrew are subjected in a modern highly manoeuvrable military aircraft is produced by high-speed turns; the resultant elevated G forces may cause petechial haemorrhages, particularly in the lower limbs. Since an aeroplane is an inconvenient laboratory, the mechanisms responsible for these haemorrhages are best investigated by elevated G forces produced in a human centrifuge on the ground, where a similar stress produces the same kind of haemorrhage. Such physical stimuli are in effect a modification of the normal terrestrial gravitational force (a force which under normal conditions is assumed to be +1 G) acting in a + Gz (head to foot) direction. The distribution of petechial haemorrhages is determined by a number of factors, including cockpit configuration. Differences in the distribution of petechial haemorrhages in the F-15 and F-16 aircraft (12 degrees tilt-back seat and 30 degrees tilt-back seat with elevation of the heel, respectively) lend an insight into those body areas where there is inadequate protection. The phenomenon usually begins to develop in healthy individuals at approximately +5 Gz (head to foot), with virtually everyone having petechial haemorrhages at +9 Gz. The kinetics of +Gz -induced petechiasis is interesting, because individuals develop an acclimatized resistance to these formations, whose exact aetiology is unknown; whether or not the petechiae are due to rupture of susceptible capillaries or to diapedesis is also unknown. Stasis and pooling of blood in the lower limbs play a specific role in the petechial formation; it is not only the +Gz stress, but also the protective equipment and techniques which determine the extent and magnitude of the petechiasis.(ABSTRACT TRUNCATED AT 250 WORDS)