Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.
Example: Abstract: Some patients converted from ventricular fibrillation to organized rhythms by defibrillation - trained ambulance technicians(EMT - Ds) will refibrillate before hospital arrival.The authors analyzed 271 cases of ventricular fibrillation managed by EMT - Ds working without paramedic back - up.Of 111 patients initially converted to organized rhythms, 19(17 % ) refibrillated, 11(58 % ) of whom were reconverted to perfusing rhythms, including nine of 11(82 % ) who had spontaneous pulses prior to refibrillation.Among patients initially converted to organized rhythms, hospital admission rates were lower for patients who refibrillated than for patients who did not(53 % versus 76 % , P = NS), although discharge rates were virtually identical(37 % and 35 % , respectively).Scene - to - hospital transport times were not predictively associated with either the frequency of refibrillation or patient outcome.Defibrillation - trained EMTs can effectively manage refibrillation with additional shocks and are not at a significant disadvantage when paramedic back - up is not available.
Example solution: Ventricular Fibrillation
Example explanation: This term is directly present in the abstract and it is one of the main topic in it. So can be chosen as the medical subject heading.

Problem: Abstract: A mathematical model was constructed to predict motor performance in rats for 8 weeks after spinal cord injury. The model is based on experimental data generated from an investigation of the static-load technique of inducing cord injury and was derived using multiple linear regression. The regression coefficients for weight of the injury-producing load were statistically significant (P less than 0.001), and it was found that the weight of the load contributes over 95% of the posttrauma motor deficit, whereas the time duration of the load resting on the cord contributes less than 5% to the deficit. Sex, pretrauma motor performance, and pretrauma body weight are insignificant covariates. The model may be used to establish expected motor deficits and to derive dose-response curves.

Solution: Animal