Naming difficulties may be rank ordered along a continuum. Items are rank ordered in terms of their ability to be named, which is correlated with their frequency. This type of picture-naming test is also useful in the examination of children with learning disabilities and the evaluation of brain-injured adults.
The Jarvik-7 heart was developed by American scientist Robert Jarvik and his mentor, Willem Kolff. In 1982, Seattle dentist Dr. Barney Clark was the first person implanted with the Jarvik-7, the first artificial heart intended to last a lifetime.
The first recorded surgical operation on a heart valve took place in 1913. Replacement of diseased valves did not take place until 1962, when the first successful biological valves were invented using human tissue from a donor. Ball valves were the first type of mechanical valves and were developed around the same time. Miles Edwards, an electrical engineer who founded a medical device company called American Edwards Laboratories in the 1950s, is credited with co-inventing the first commercially available artificial heart valve.