The Research 

It appears the harp music is bringing this (blood pressure) back into balance, back into the normal range, which is ideal for healing               ”

—  Professor Anne Baldwin - Research Professor of Physiology  

For thousands of years, the harp has been used for therapeutic purposes and in recent times it has become increasingly common for the harp to be used in medical establishments across the globe. Here in the UK, in addition to many private hospices and care homes, the National Health Service is following suit with the Royal Brompton Hospital, in London, and Cardiff's Velindre Cancer Centre both employing harpists to play for patients. 

But why is this happening? It may be to do with growing scientific evidence - such as US research conducted by Dr Abraham Kocheril, the chief of cardiac electrophysiology at the Carle Heart Centre, in Illinois - showing that the harp really does have a positive effect not just on the mind and spirit but on the human body too. 

Kocheril said: "The harp seems to affect the part of the nervous system which regulates the heart. It relaxes the patient and the heart slows down." 

Also a recent study by the San Diego Hospice in California revealed that 63% patients reported a reduction in pain when harp music was present and that harp music helped: 

71% of patients to breathe more easily  
84% of patients to reduce their anxiety levels 

In another study at The University of Arizona Medical Centre the effects of live harp music on patients in the intensive care unit were measured and showed a remarkably positive effect on blood pressure levels.

Sources:
http://www.jpsmjournal.com/article/S0885-3924(14)00558-2/abstract
http://www.the-cma.org.uk/Articles/Study-Explores-Effects-of-Harp-Music-on-ICU-Patients-6119/
http://www.telegraph.co.uk/news/uknews/3334911/Harp-music-eases-pain-in-surgery.html