Physical correlates of eardrum rupture.

Eardrum (tympanic membrane) rupture in humans and animals in relation to various blast pressure-time patterns was reviewed. There were few systematic studies on eardrum rupture as a consequence of blast overpressure. Most reports did not describe the area of the eardrum destroyed. The peak overpressures required to produce a 50% incidence of eardrum rupture (P50) were summarized. Most of the animal data pertained to dogs. The highest P50 for dogs, 296 kPa, was associated with smooth-rising overpressure. For complex wave patterns occurring inside open shelters subjected to nuclear blasts, the P50 was 205 kPa. For fast-rising blasts in a shock tube it was 78 kPa, and 105 kPa for statically applied pressures. The duration of the overpressure was not a factor unless it was very short. The influence of the orientation of the head to the oncoming blast was demonstrated. An ear facing the blast may receive reflected overpressures several times that for one side-on to the blast. An ear on the downstream side of the head was exposed to about the same overpressure as the side-on ear. A P50 for humans of 100 kPa and a threshold of 35 kPa has been used widely in blast criteria. A recent study suggests a threshold (P1) of about 20 kPa, and gives the overpressures required to produce minor, moderate, and major eardrum ruptures. These data were presented in the form of curves showing the overpressures as a function of duration required to inflict a P1 and a P50 of eardrum rupture of the three levels of severity.