The heart is a hollow muscular organ which lies in the chest cavity slightly left of the midline. By constant rhythmic contraction and dilation blood is kept circulating through the body. Heart function may fail due to a number of factors including coronary artery occlusion, commonly called heart attack, electric shock, drowning or asphyxia. In such situations external cardiac massage (ECM) is used to provide artificial blood circulation.
In ECM firm pressure is exerted on the lower half of the sternum, in order to compress the heart and major vessels between the sternum and the spine, resulting in cardiac output. The pressure needed vary from about 36 kgs to 55 kgs and the sternum should be depressed about 3.5 to 5 cm, varying from patient to patient. The cycle is repeated uniformly and smoothly at about 40-100 strokes per minute, allowing approximately equal time for depression and relaxation of the sternum.
The problems associated with manual ECM include fatigue to the operator, variation in the rate, force and duration of compressions, and limited facility for transportation and movement of the patient while ECM is being carried out. Further, inexperienced operators often cause injuries to the patient such as fractures to the ribs and sternum, lung damage, laceration to the liver or costochondral separation.
A number of mechanical devices have been developed with a view to overcoming the problems of manual external cardiac massage. However, these devices display a number of deficiencies.
There is a tendency for the sternum depressor to shift position on the sternum which leads to greater instances of rib and sternal fractures, liver laceration, lung damage and costochondral separation.
The complexity of prior art machinery or operating instructions leads to improper use or fitting of the device and thus to inadequate compression.
The ECM devices are often very heavy and cumbersome and require a relatively long time to set up, some as long as 4 minutes or more. Such a delay is excessive in emergency situations.
The prior art units are not entirely portable and tend to shift position from the sternum if the patient is transported up or down a stairway.
Many ECM devices use compressed gas cylinders as a power source, such a power source being heavy and cumbersome.
The pressure applied to the sternum during operation varies abruptly, alternating between mere contact with the patient to maximum compression, resulting in bruising and other injuries as described above.