Mechanical reaction of the frontal abdominal wall to the impact load during gravidity.

THE AIM OF THE STUDY: Selected parameters of mechanical characteristics of the gravid abdomen under impact load.

TYPE OF THE STUDY: Experimental biomechanical study carried out in a human in vivo.

METHOD: Damped vibration of the gravid abdomen was detected after a defined impact load using speed cinematographic recording of 103 pictures/sec. A women in 32nd week of gestation, performing toe stand and fall down to the heel, the drop was 0.08 m. The recording was digitalized and the values mathematically analysed. The method used was PAM (polynomial approximation method) of approximation of discrete coordinates. The umbilikus' trajectory in reaction to the impact load was described analytically and interpreted graphically. Parameters of abdomen vibration were detected in horizontal profile by tensometric belt. Impact in interaction of soles with the underlay was detected with the help of tensometric platform Kistler. Ultimate strength point of myometrium was set by tearing experiment in 12 samples.

RESULTS: Calculation of characteristics of damped, aperiodic vibration of hydro-viscous elastic system as the outside behaviour of the gravid abdomen. Parameters in vertical direction of umbilicus: impulse in abdominal area - 2,72 Ns, T-period - 0.1299 s, amplitude - 0,009 m, frequency - 7,7 Hz, functional damping - from -6 to +12 Nsm-1. In horizontal direction: frequency 5,4 Hz, damping 123 Nsm-1. Impact in soles' sphere 40 Ns with maximum value 1511 N, which represents level 2,2 G. Ultimate strength point of myometrium is 0,1 - 1,1 MPa.

CONCLUSION: The results show one of the possible critical, risky frequencies of the gravid abdomen, that is, in this concrete case, the frequency of the vibrating system of cca 7,7 Hz in vertical direction and cca 5,4 Hz horizontally. This implies that e.g. this frequency is dangerous (possible abruptio placentae) and is necessary to be avoided e.g. when travelling by means of public transportation. The applied analytic methods and presented parameters will be used for e.g. modelling the examined gravid system under impact load of a general character--locomotion, work-load, car accidents, etc.