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.

Let me give you an 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.
The answer to this example can be: Ventricular Fibrillation
Here is why: 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.

OK. solve this:
Abstract: Release of prostaglandin E (PGE) was examined in leukocyte cultures from patients with definite MS who had had at least one recent exacerbation, others with chronic progressive or stable MS, and healthy controls. MS patients had higher baseline levels of PGE than did controls. Patients with active symptoms exhibited a sharp increase in PGE release early in or just before the onset of clinical symptoms. Levels dropped early in exacerbation immediately after the burst in PGE synthesis activity. Values gradually increased to control levels and then to preexacerbation levels. Similar rises and falls were not seen in stable MS. MS patients may have a circulating population of activated leukocytes that produce PGE.
Answer:
Acute Disease