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.
One 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.
Solution is here: Ventricular Fibrillation
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.

Now, solve this: Abstract: The effects of electrical stimulation of the vagi on gas transport mediated by high-frequency, low tidal volume ventilation (HFV) was examined in 10 anesthetized, paralyzed, propranolol-treated dogs. Gas transport efficiency was estimated by measuring the rate of CO2 removed from the lungs (Vco2) achieved during 45-s bursts of HFV applied before (control 1), during, and after (control 2) electrical stimulation of the transected vagi. During vagal stimulation the heart rate was maintained by electrical pacing. During the 15-s phase of vagal stimulation pulmonary impedance increased from 3.6 +/- 0.7 to 6.2 +/- 2.2 cmH2O X l-1 X s, and Vco2 increased. When the electrical stimulation of the vagi was stopped, impedance and Vco2 returned to prestimulation values. Vco2 was always higher during electrical stimulation of the vagi when HFV of a fixed volume was applied over a range of frequencies or when a fixed oscillation frequency was used over a range of tidal volumes. The effects of vagal stimulation on HFV-mediated gas transport were quite similar to the effects of moving the locations of the bias flow inlet and outlet into the lung such that tracheal volume was decreased by 20 ml, an amount equivalent to estimated change in control airway volume thought to occur during vagal stimulation. We simulated the effects of vagal stimulation and decreased tracheal volume on Vco2 by using a previously described model of HFV-mediated gas transport.(ABSTRACT TRUNCATED AT 250 WORDS)
Solution:
Animal