In these versions, {TAIL ~ the required stiffness} of {HEAD ~ the leaflets} is achieved by a mechanism activated hydraulically, electrically or with other similar means 
In these versions , { TAIL ~ the required stiffness } of { HEAD ~ the leaflets } is achieved by a mechanism activated hydraulically , electrically or with other similar means
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH