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Since the early 15th century, several methods have been used to induce respiration-like activity in the body (artificial respiration or insufflation) in order to treat persons who are unable to sustain respiratory effort on their own such as victims of drowning, choking, suffocation, hypothermia, etc. Among these methods, manually or mechanically blowing air into the patient's lungs has been found to be most effective. This may be done by:
Mouth-to-Mouth : The rescuer makes a seal between their mouth and the patient's mouth and blows air into the patient's mouth. This is the most common method.
Figure 1.1 : Mouth-to-Mouth Method
Mouth-to-Nose : The rescuer forms a seal between their mouth and the patient's nose in order to blow air into it. This method is generally used when the patient has maxillofacial injuries, has vomit or other contaminants in the mouth or when the procedure is done in water.
Figure 1.2 : Mouth-to-Nose Method
Mouth-to-Mouth and Nose : The rescuer forms a seal with their mouth, covering both the mouth and the nose of the patient. This method is generally used for infants and is the most effective.
Figure 1.3 : Mouth-toMouth and Nose Method
Mouth-to-Mask : A filter or barrier is placed between the rescuer and patient in order to prevent air-borne foreign particles or microorganisms from being transferred from one to another.
Figure 1.4 : Mouth-to-Mask Method
Bag Valve Mask : A flexible bag is connected to the mouth or nose of the patient through a tube. The rescuer squeezes the bag in order to push the air from it into the patient's airway.
Figure 1.5 : Bag Valve Mask Method
Mechanical Ventilator : This is an electrical unit which is designed to force air into the patient's airway. It is used mainly in hospital settings and not in public places. Thus this is a post-emergency care equipment and is not meant for out-of-hospital emergency situations.
Figure 1.6 : Mechanical Ventilator
These methods, however, are only effective in cases of respiratory arrest and do not offer any benefits when the patient is suffering from circulatory cardiac arrest.
1.1.2. External Chest Compressions:
Sudden Cardiac Arrest(SCA) refers to the complete, unpredictable and sudden cessation of cardiac fuction. It can occur even in those who have previous history or indications of cardiovascular disease and occurs almost immediately after the onset of symptoms. During the 19th century, attempts were made to perform artificial respiration by applying pressure on the victim's chest, abdomen or diaphragm. Further studies proved that compression of the chest have a three-fold effect :
The thorax is alternately compressed and relaxed which mimics the motion of the chest during natural respiration, thus allowing air to be forced into and out of the airway.
Compression of the thorax pushes blood from the chest and abdomen to vital organs such as the cardiac muscles and brain which are more in need of oxygen.
The heart muscles are physically pushed during every compression which could lead to return of spontaneous circulation of blood.
Figure 1.7 : External Chest Compressions
For external chest compressions to be effective, the blood has to be pushed with enough force and often enough for it to reach both the brain as well as cardiac muscles, thus producing an effect of artificial circulation. This requires the rescuer to apply pressure on the patient's sternum, using the heel of both hands, placed one on top of the other, at a very high rate. Also this has to be done immediately after the collapse of the patient in order to prevent irreversible damage to vital tissues such as cardiac muscles and brain neurons.
External cardiac compressions provide arterial pressure and cardiac output which are much lower than the normal values, but can still sustain life for several hours. However, the neurons in the brain tend to begin dying a maximum of half an hour after cardiac arrest, even if chest compressions are applied. Hence it is important that the paramedics respond as soon as possible, even if lay persons are applying chest compressions.
Durind external chest compressions, the blood is forced through the ventricles of the heart into the systemic and pulmonary circulations. During the relaxation phase between two subsequent compressions, the chest wall recoils to its original position due to its inherent elastic nature. This produces a relative negative pressure in the thoracic cage and accelerated the flow of venous blood back to the atria and ventricles. When this is repeated 80 to 100 times per minute, circulation adequate to sustain the vital organs of the body is produced, for as long as the blood is sufficiently oxygenated.
1.1.3. CardioPulmonary Resuscitation (CPR):
Cardiopulmonary resuscitation is an emergency procedure which is recommended for persons in cardiac arrest or respiratory arrest when defibrillation or other suitable medical procedures are not possible immediately. This method combines external chest compressions with artificial respiration, thus assisting both respiration as well as circulation. The rescuer ventilates the patient's lungs quickly within 5 seconds and then applies chest compressions for 15 seconds, applying approximately 20 compressions. The process is then repeated until additional help arrives.
The American Heart Association has defined the procedures and protocols to perform CPR for both lay rescuers as well as medical professionals in 2005.
Lay rescuers should perform chest compressions and ventilations after administering two rescue breaths to the victim. Checking for pulse or other signs of circulation is not required to be done by lay rescuers.
Healthcare providers should assess the most likely cause of collapse of the victim and treat them accordingly. In cases of sudden collapse, defibrillation using an Automatic External Defibrillator is the most preferred option. CPR should be administered before and after defibrillation. In the case of victims of respiratory arrest, such as drowning, choking etc., the healthcare provider should deliver two rescue breaths and then check for a pulse or palpations. If a pulse is present, the provider should apply rescue breaths only, without any chest compressions. In case pulse is absent, standard CPR should be performed.
Figure 1.8 : CardioPulmonary Resuscitation
After cardiac arrest, the amount of time before serious brain damage occurs is variable and depends on several factors. The main affecting factor however is whether the cardiac arrest was caused by respiratory arrest or circulatory arrest. In the case of circulatory arrest, such as due to fibrillation or arrhythmia, the pulse stops immediately and breathing after a maximum of a few minutes. In such cases, the pupils dilate within 30-40 seconds and serious brain damage can occur within 2-4 minutes. After 4 minutes, neurologically intact survival is very rare. If the underlying cause was respiratory arrest such as drowning, choking, drug overdose, suffocation etc., the heart continues to function for a short duration after the respiration stops. Hence the blood is still circulated, even if the oxygen content in it continues to decrease. Therefore, neurological damage occurs only after 4-6 minutes or even longer. Pupil dilation occurs only after a few minutes in these cases.
When a patient is suffering from circulatory arrest, their body goes through three phases - an electrical phase, a haemodynamic phase and finally a metabolic phase. During the electrical phase, which lasts for approximately 5 minutes, the most preferred mode of treatment if defibrillation. If defibrillation is not performed in this time, the body enters the second phase or haemodynamic phase, during which, circulation must be artificially induced, especially to the brain and cardiac muscles, before defibrillation is performed. Defibrillation before artificial circulation during this phase, is found to decrease survival rates. The final metabolic phase requires more study.
Figure 1.9 : Plot of Survival rates against quality of CPR
Admnistration of CPR immediately and correctly, before performing defibrillation can increase the duration of neurologically intact survival to 15 minutes or even longer, which allows more time for defibrillation to be performed or a mechanical ventilator to be connected to the patient.
1.1.4. CardioCerebral Resuscitation (CCR):
In the conference held by the American Heart Association in 2010 on Resuscitation, it was found that the existing procedures of CPR were far from optimal and new methods had to be introduced in order to improve survival rates as well as quality of life of survivors.
During the haemodynamic phase, the most important factor affecting cerebral perfusion is found to be the arterial pressure generated during external chest compressions.[11-15] Production of adequate myocardial and coronary perfusion pressure and keeping coronary arteries open can help maintain the fibrillilating ventricle for prolonged durations. As shown in Figure 1, once chest compressions are begun, it takes time to develop cerebral and coronary perfusion pressures. However, every time chest compressions are halted to perform artificial respiration, the cerebral perfusion decreases abruptly and has to be brought up again. Coronary perfusion also decreases significantly.
Figure 1.10 : Aortic and Right Atrial Pressures during first 15 compressions
Figure 1.11 : Variation of Return of Spontaneous Circulation with Coronary Perfusion Pressure
Other studies found that administration of bystander CPR increased survival to hospital discharge by three times or more  and that bystander initiated CPR was strongly correlated with increase in survival rates and improved quality of life  . However several bystanders exhibit reluctance to perform CPR, or in particular, mouth-to-mouth artificial respiration. Fewer than 50% of persons in cardiac arrest receive bystander CPR, one reason for which is the difficulty faced in opening the airway and delivering rescue breaths. Starting with chest compressions might ensure that more victims receive CPR and that rescuers who are unable or unwilling to provide ventilations will at least perform chest compressions.
Also the vast majority of cardiac arrests occur in adults. In these patients the critical initial elements of CPR are chest compressions and early defibrillation . Artificial respiration is required only after several minutes of chest compressions as till then, the blood already contains sufficient oxygen. However in cases where cardiac arrest is unlikely or ruled out, artificial respiration is still recommended.
These factors led to doubts about the existing methodologies and the AHA conducted studies on swine to test the effectiveness of chest-compression - only CPR. It was found that both the group that received ideal standard CPR and the group that received chest-compression - only CPR exhibited similar rates of successful resuscitation and neurologically intact survival. However, in the group that received no compressions for 12.5 minutes, to imitate absence of bystander CPR and late arrival of medical personnel, only 2 out of 8 animals survived, out of which one was in coma.
Further research studied the achieved haemodynamic response of the subject during CPR and compared it to the haemodynamic which should be produced when ideal CPR is given. Ideal CPR was considered to be 4 seconds of ventilation interspersed between two 15 second intervals during which chest compressions are applied. It was found that ventilation took greater than half a minute in most cases, thus largely decreasing the time spent performing chest compressions.
Figure 1.12 : Simultaneous recording of aortic and right atrial pressures during CPR in which 2 ventilations are delivered within 4-second time period.
Figure 1.13 : Simultaneous recording of aortic and right atrial pressures during CPR administered by a lay rescuer.
These factors caused the AHA to modify the guidelines regarding resuscitation in 2010, especially those for layperson rescuers. For this, CPR was renamed into Continuous Chest Compression CPR (CCC CPR) or CardioCerebral Resuscitation (CCR). According to the new guidelines put forward:
Laypersons are not instructed to check for pulse or pupil dilation for adult victims, but are to assume cardiac arrest has occurred and begin resuscitation if the victim is not breathing or is breathing abnormally.
Hands-only or compression-only CPR is encouraged for untrained laypersons, as it is easier to perform and instruct.
Chest compressions should be given before administering rescue breaths as positioning the head, forming the seal with the mouth and assembling the mask take up more time. This allows compressions to be started sooner, improving survival.
Quality of the compressions, both rate and depth are highly emphasised, as is allowing the chest to recoil completely after each compression. For adults, compression depth recommended is atleast 2 inches and rate is 80-100 compressions per minute. Focus on minimizing pauses in compressions and avoiding over-ventilation is increased, as pauses decrease effectiveness of resuscitation.
Healthcare providers are advised to work as a team and perform several resuscitation tasks at once, such as rhythm detection, airway management, rescue breathing, chest compressions, defibrillation and drug administration if required.
While instructions are being given to laypersons or during training, the irregular presentations of cardiac arrest must be made known to the rescuer in order to avoid confusion and panic.
Figure 1.14 : Aortic and Right Atrial Pressures during CCR
The project involves design of a device which can perform the following functions:
Check whether the subject has a normal heart beat.
If no heart beat is present, the device should request for input from the user about the age group of the subject - Infant, Adult or Elderly.
Retrieve the depth of compression required for the subject based on their chest diameter and age group.
Applies chest compressions to the subject by tightening a belt around their chest.
Continues to apply chest compressions to the subject for 15 minutes (maximum time for which the blood contains sufficient oxygen) or until the device is stopped.
For design purposes, the device may be considered to consist of 4 blocks :
Signal Processing to
Determine presence of
interface with the user
and control rate and
depth of compressions
consisting of a pair of
DC Motors and a belt
Figure 1.15 : Block Diagram