Can you come back to life after being dead? Well, that depends on how dead you are. Imagined being mowed down by a tractor and turned into an egg splat; well, it will really be hard to come back to life after that, except some supernatural and mystical power come into play or some sort of miracle (or magic) happens.
Understanding the processes governing death is helping experts try to halt and reverse it. It’s also challenging our ideas about the nature of death itself.
You might be thinking why we are writing an article on this topic; ‘Can you come back to life after being dead?’ But it may surprise you that this is a common question many troubled people, especially devastated mothers, wives, fathers, husbands, and distressed girlfriends/boyfriends ask doctors and paramedics when their wards or partners have been declared dead in the hospital. The answer to this question just might surprise you. Yes.
However, there is a catch. The patient can't be too dead. This is a question of survival, not about zombies or chanting at the full moon.
It begins with whether we're discussing clinical death or biological death. Both mean the patient is technically dead, but each term refers to a different level of permanency. One is fixable; the other is not.
And also, there is a clinical term known as the ‘Lazarus syndrome’ that many people associate with the aspect of coming back to life after death.
In this article, we aim to look at these, and how they come into play to answer this question; “Can you come back to life after being dead?”.
Can you come back to life after being dead? Read on to find more on the answer to this and to fully understand all there’s to know about it.
Can You Come Back to Life After Being Dead?
Understanding the processes governing death is helping experts try to halt and reverse it. It’s also challenging our ideas about the nature of death itself.
Read the following true life story from BBC:
Zach Conrad died on a lovely Sunday afternoon in Philadelphia. It was 3 June 2012, and the 36-year-old financial analyst had decided to take a solo bike ride, as he often did on weekends. As the ride progressed, however, Conrad sensed that something was wrong. He pulled over to the side of the road, took off his helmet, and slumped to the ground. His heart stopped beating and he stopped breathing. He was having a sudden cardiac arrest.
The odds weren’t on Conrad’s side that day. Each year, around 300,000 people in the US suffer a cardiac arrest. Most victims die: of those who make it to the hospital, 85-90% leave in a box or a bag.
But instead of adding to that sorry figure, Conrad was about to join a group of people who are challenging our notions of mortality. In some communities, up to 30-40% of arrest victims leave the hospital alive. One likely difference is that these lucky few wound up at a hospital that implements the latest practices in resuscitation science.
Conrad made it to one such resuscitation facility, at the University of Pennsylvania, but his route to get there was circuitous. The emergency crew first rushed him to a local hospital, but the staff there were unsure of what was wrong with Conrad – he was hardly the typical heart attack victim – and did not know what course of action would best aid his survival and recovery. Conrad’s wife, a doctor, had by then arrived. She recalled hearing about resuscitation research taking place at the nearby university, and insisted Conrad be transferred.
By that evening, he was admitted to the University of Pennsylvania’s hospital, where Benjamin Abella, a physician and the clinical research director at the Center for Resuscitation Science, ordered that Conrad should undergo a 24-hour cooling treatment to reduce inflammation, and slow metabolism – two components that seem to be key for helping the body recover from resuscitation injury. Following that treatment, Conrad lay in a medically induced coma for several days, during which time he received post-arrest care, including blood pressure support, cardiac catheterization, and mechanical ventilation. On Friday, he regained consciousness.
“It is conceivable that, had I stayed at the local hospital, I’d have been just fine and would have recovered – that I don’t know,” Conrad says. “But I’m happy I wasn’t the control.”
Cases like Conrad's are far from unheard of. And they are helping physicians and scientists who specialize in resuscitation tease out the mechanisms governing the death process. Their ultimate goal is to halt and reverse that process.
“When you’re freshly dead, your brain isn’t necessarily irreversibly, irrefutably damaged yet,” explains Sam Parnia, a critical care physician and director of resuscitation research at Stony Brook University School of Medicine in New York. “You have to both die and have brain death to really be dead.”
In fact, as new technology and knowledge of the body enhance our proficiency at resuscitation, it is transforming our ideas about the nature of death itself. Researchers are coming to understand that death occurs more on a sliding scale than at a single moment.
In other words, we often do not die all at once. Even if the heart has stopped, the body can remain alive for hours – some parts even days. “At this point, we’ve got two domains: the slightly dead and the very dead, for lack of better terms,” says Abella. “Or the not-quite-dead-yet. It’s definitely getting blurry.”
There are Two Types of Death
First comes clinical death, which is when breathing and blood flow stop. Clinical death is the same as cardiac arrest; the heart has stopped beating and blood has stopped flowing.
Technically, clinical death requires both the heart and the breathing to stop, but that's just semantics. Breathing and consciousness will cease within a few seconds of the heart stopping.
Clinical death is reversible. Researchers believe there's a window of about four minutes from the moment of cardiac arrest to the development of serious brain damage. (as you can probably imagine, that's a pretty hard statistic to validate through a random control trial).
If blood flow can be restored—either by cardiopulmonary resuscitation (CPR) or by getting the heart pumping again—the patient could come back from clinical death. It's not a sure thing; success rates for CPR are pretty dismal.
Before we get too morbid here, it's important to note that the application of CPR and of an automated external defibrillator (AED) increased the chances of survival significantly. All is not lost with clinical death, but you must act quickly.
Clinical death is also associated with the Lazarus syndrome which we will talk about later in this article.
Biological death, on the other hand, is brain death, and there's no turning back from brain death. That is irreversible death.
Just to make things a bit more complicated, however, it is possible to keep the body alive while the brain is dead. The heart is more of a subcontractor than an employee of the body; it keeps its own hours and works without direct supervision by the brain.
Since the heart works without brain input, it's possible to keep it going for a long time after the brain is dead. Indeed, that's one way that organ donation happens.
There are physical signs of irreversible death that emergency medical responders use to decide whether to attempt CPR on a cardiac arrest victim. The hard truth is: Some people are just plain dead by the time they're found.
The Passing Time
Death is a necessary caveat for every living thing and – as the sole species (we think) capable of conceiving of its own demise – it’s constantly on our minds. Yet the more we learn, the more we realize how crude our understanding of death actually is.1 https://www.verywellhealth.com/can-people-come-back-from-the-dead-1298424
Most people consider death as a single moment – a person is present, and then he or she is not. It is the turning off of life’s switch, typically registered as the moment that person’s heart stops beating.
Today, around 95% of death certificates use this event to note the time of passing, and for the vast majority of human history, this thinking reflected reality. If a person’s heart stops beating, he or she has been issued a death sentence. There was no bringing them back.
In the early 1960s, however, researchers began to challenge that assumption. Closed chest compressions combined with mouth-to-mouth breathing could alter a person’s fate by restarting their heart.
Even then, doctors presumed that within moments after blood ceases to flow the victim’s brain begins to break down, soon rendering them into a vegetative state – even if their heart was restarted.
“We were all taught that we have five minutes after the heart stops,” Parnia says. “Now we realize that’s outdated, that in fact brain cells don’t die immediately.”
Researchers now understand that cells and organs undergo their own deaths, a process that can take hours or even days depending upon circumstances. In an extreme example, muscle stem cells can remain viable in human cadavers for up to 17 days, a 2012 study found, so long as they are not contaminated by oxygen.
A person who does not respond after 20 to 30 minutes of resuscitation efforts will probably not make a meaningful recovery, but that time limit is not set.
Science is far from establishing when a body’s capacity for consciousness actually leaves it. “We don’t know how long it takes after death for the cells to decay to such a point that no matter what you do, you can never get them back again,” Parnia says.
Which means that humans may take hours to fully die. In a remarkable 2011 case, a woman in Japan, intent on committing suicide, wandered into a forest and overdosed on pills. The next morning, a passerby found her. When emergency personnel arrived, her body temperature was 20C. She had no pulse and was not breathing. Efforts to shock her heart into action failed, but rather than send her to the morgue, doctors connected her to an extracorporeal membrane oxygenation (ECMO) machine – a device that acts as an artificial lung and heart, and is a standard of care in Japan – and left her to circulate.
Several hours into the procedure, her heart fluttered back to life. The woods’ cool temperature, it turned out, had prevented the woman’s cells from breaking down as quickly as they would have in a warmer environment, allowing her to lay dead in the forest for around four hours, plus survive an additional six hours between the time the passerby called the ambulance and the time her heart began beating again.
Three weeks later, she left the hospital, and today she is happily married and recently delivered a baby. “If one of our [emergency medical service] crews found that young girl, she would have just been declared dead,” Parnia says.
What About the Issue of the Walking Dead?
Conquering death, like any disease, requires knowing the enemy and devising ways to combat it, Parnia explains in his book,Erasing Death. The first step is simply getting the patient’s heart to restart. Special defibrillators can boost the odds of success by monitoring CPR on the spot.
They provide audio and visual coaching to optimize a doctor’s performance, such as instructing him to push harder or to allow more time between compressions. The devices also store data for later review.
Most doctors, however, do not bother with these machines, though data indicate that they should. In one study, initial CPR success rates averaged at 45%, but making doctors use the feedback-providing defibrillator pushed up success rates to 60%.
To buy time, ECMO devices like the one used in the Japanese woman’s case can keep the body functioning until doctors can get the heart restarted. These machines remove the patient’s blood and then circulate it back into the body full of oxygen.
In South Korea and Japan, doctors have reported up to 90% success rates in restarting the heart using ECMO devices. In the US and Europe (where doctors typically report a 50% success rate in restarting the heart), however, no standardized procedures exist for implementing ECMO machines. Even if a doctor successfully restarts a patient’s heart, it is often a short-lived victory.
As scientists tease out the mechanisms of death at the biological level, they are beginning to learn that some standard critical-care practices – flooding a cardiac arrest victim’s system with oxygen and increasing their blood pressure immediately following the heart attack – are not the best way to ward off an ensuing cascade of cellular suicide.
Cooling down the body is probably the most important breakthrough in increasing the chances that those cells stop their death rampage. Since 2003, some hospitals have been championing this mild form of hypothermia – the same procedure that Conrad underwent after his heart attack.
Doctors lower the patient’s temperature by around four degrees, to 33C, using either liquid-filled pads or catheters that cool him or her from the inside. This sends the body into a hibernation-like state, allowing it time to recover from the injury and trauma of cardiac arrest.
It lessens swelling and pressure on the brain and reduces cellular activity, including cells’ instructions to commit suicide. One study found that for every six patients who undergo this treatment, one benefited.
Combining all of these methods – from the time a person first suffers a heart attack to the critical period after – increased patient survival from 26 to 56%, according to a 2007 study conducted in Norway. Of those survivors, 90% did not suffer any long-term neurological or physical repercussions.
All of which suggests that the accumulating information and techniques are beginning to slide the scale in our favor. “In biology, if you can do it once, it’s very likely you can do it a second time,” says Lance Becker, director of Penn’s Center for Resuscitation Science. “And if you work it out, you can do it every time.”
Resuscitation is still a very young field, however, and experts say there are several major areas to tackle. For instance, there are no scientifically validated guidelines about when to stop a resuscitation effort for a particular patient.
Current efforts are “frighteningly variable”, Becker said in a recent panel discussion at the New York Academy of Sciences. A 2012 study examining current practices across 435 US hospitals demonstrated this. In an analysis of more than 64,000 events, the authors found that the majority of doctors stop their efforts at 20 minutes if the patient did not respond.
However, hospitals with the shortest resuscitation attempts for non-survivors – 16 minutes – saved significantly fewer cardiac arrest patients than those that put in 25 minutes – just 10 extra minutes of effort. “If a doctor just stops in an arbitrary fashion, for the patient that’s a permanent death sentence,” Parnia says.
Research is underway on the technology and methods that will shape new guidelines. Abella suspects that traditional CPR, for example, might need a makeover. CPR currently helps millions of people, but it uses a uniform approach of about 100 compressions per minute regardless of the patient.
Abella and his colleagues’ research suggest that this life-saving practice may be more effective if it is dosed differently depending on the patient, much like medication.
Parnia’s group and others are developing what he calls a “GPS system that navigates the quality of care that patients are receiving.” The method, formally referred to as cerebral oximetry, uses near-infrared spectroscopy that penetrates the skull and monitors how much oxygen reaches the brain during each beat of the heart or CPR chest compression.
By knowing exactly how much oxygen is reaching the brain, doctors can adjust their CPR regime accordingly to minimize brain damage. “I see this becoming the standard of care, as opposed to doing CPR blindly as we have for decades,” Parnia says.
He and his colleagues are already using cerebral oximetry in patients, and they will present some of their results at an upcoming American Heart Association meeting next month.
Smoothing out the recovery process is another priority. Currently, doctors induce mild hypothermia, as with Conrad’s case, for 24 hours. Whether that is the optimal time, however, is an open question.
In addition to using hypothermia, researchers are also figuring out ways to directly prevent cell death at the biological level. “There’s going to be all sorts of important discoveries in the coming years about tissue interaction and communication at the border of life and death,” Abella predicts.
One way to manipulate that process is to inject drugs that inhibit apoptosis, or programmed cell death. Some researchers are working on preventing damage by designing drugs that target the cells’ energy source, the mitochondria.
Other groups are developing ways to block enzymes called calpains that induce cell death by acting like scissors and shredding proteins. In one laboratory experiment, rats that were asphyxiated for 10 minutes and given a calpain blocker had significantly less brain damage than those that received a placebo.
Despite the advances, there’s still much to learn. “We know quite a bit about how cells die,” Parnia says. “Where we’re lacking is how to switch off that process.” If that process becomes more clear, he imagines creating drugs that target those pathways and could be administered on the spot by emergency personnel to keep someone in a viable state, even in death, until they can reach a hospital.
“I could inject you with a drug that prevents those pathways from causing your brain cells to become irreversibly damaged,” he says. “Then I hibernate you, transfer you to a hospital, and hours later still have a chance of getting a whole person back.”
For patients that do survive, like Conrad, physical and neurological rehabilitation – methods that are still being worked out – may be necessary.
Memory loss plagues some survivors, including Conrad. When he came back to life, he thought it was the year 2010. He got married two months before his accident, and although he remembered who his wife was, he had no recollection of their marriage.
As days passed, however, his memory slowly returned. Now, he has a two-week memory blank starting at about noon on the day of the accident, but he’s grateful to have reclaimed full access to memories from before and after that event. Abella notes that these new rehabilitation problems are ones he’s happy to take on, however. People who today struggle with post-resuscitation issues would have just died ten years ago.
Those who are lucky enough to receive treatment, that is. Despite existing advances, today only an estimated 10% of patients in the US who are eligible for undergoing resuscitation techniques receive them. As Conrad noted, it was only “happenstance” that he received those potentially life-saving treatments, thanks to his wife’s – not his local hospital’s – insistence.
The American Heart Association, the European Resuscitation Council and the equivalent entities in Canada, Australia, and New Zealand published joint guidelines outlining state-of-the-art resuscitation procedures in 2008 and 2010, but many hospitals, for whatever reasons, still do not implement these methods.
It’s not that hospitals don’t have the capability to induce hypothermia or monitor CPR efforts, Parnia says, but rather that they simply do not implement them. “That’s the biggest ethical dilemma – things are not being done that are currently available,” he says. “Most places are doing 20th Century – not 21st Century – resuscitation.”
It’s difficult, if not impossible, to predict how significantly survival could be boosted if promising technologies come to pass and hospitals implement them on a standardized, best-practice basis. Parnia ventures, however, that the survival figure could reach up to 50% in the next ten years.
Avoiding a Monster Problem
No matter how advanced and standardized resuscitation science becomes, however, it almost certainly will never enable a Frankenstein-like situation. In the case of cadaver stem cells being rescued after 17 days, for example, those special cells alone survived the ravages of death.
“The muscle itself is completely destroyed,” says Fabrice Chretien, a professor of histology at the Paris Descartes University and senior author of the stem cell work. “You cannot resuscitate the patient, and you cannot use his tissue for organ grafting,” he emphasizes. “I’m only talking about one very special cell type.”
Likewise, after remaining dead for long enough, the basic structures that permit consciousness probably decay far beyond repair, Abella explains.
“We’re very interested in trying to resuscitate those who have suddenly lost their life in very recent minutes and hours,” Abella says. “I’m less interested in the business of bringing someone back from longer than that, and my suspicion is that it’s probably not possible.”
Immortality is not an option, either, at least not in the near term. Cardiac arrest is usually triggered by some underlying condition, such as coronary heart disease or diabetes; there is little meaning in bringing a terminal cancer patient back from the dead, only to make them suffer another agonizing death hours or days later.
Without finding a permanent fix for every disease, injury, and condition that cause death, resuscitation only postpones the inevitable. Even if a healthy person, like Conrad, is brought back from the brink of death, eventually mortality will catch up. “Clearly there is a point at which it will be futile,” Parnia says.
For now, however, Conrad is rejoicing in his restored life and health. Abella and the other physicians were never able to determine what caused Conrad’s heart attack, but as a precaution, they implanted a tiny defibrillator in his chest. So far, he has not had cause to use it.
He is enjoying married life and is back to working and biking again. “I still wake up pretty much every day and smile for a second,” he says. “If I’m stuck in traffic, I think to myself, ‘This is no big deal, it’s better to be breathing here than not at all.’”
While Conrad did not see a light at the end of the tunnel or gaze down at his body from above, he did wonder at the many small but significant coincidences that likely added up to save his life. He had randomly opted for a slightly different bike route that day, for example, which took him down a more populated path rather than his usual secluded one.
He was lucky enough to be spotted by people with the compassion to stop and help a stranger in distress – one of which was an ER nurse who gave him CPR while waiting for the paramedics – and on top of that, he managed to find his way to Abella. “I’ve been incredibly lucky,” he says. “By all accounts, very few people survive this.”
In an effort to “pay it forward”, Conrad attended a scientific conference on hypothermia treatment and gave a talk to the doctors in attendance about his experiences. “There are champions like Dr. Abella in various hospitals and communities all over the country, pushing the envelope on this,” he says. “I’m trying to cheer them on and tell them to keep going, because it can have an impact.”
The Lazarus Syndrome - What Exactly is It?
Lazarus syndrome refers to your blood circulation returning spontaneously after your heart stops beating, and fails to restart despite cardiopulmonary resuscitation (CPR). In short, it’s returning to life after it appears that you’ve died.2https://www.healthline.com/health/lazarus-syndrome
Lazarus is a character in the Bible who emerged from his tomb alive and well 4 days after his death. The syndrome was named after him because when your circulation spontaneously restarts, it looks like you’ve come back from the dead.
It’s also known by several other names, such as:
- Lazarus phenomenon
- Lazarus heart
- Autoresuscitation after failed CPR
- Delayed return of spontaneous circulation after failed CPR
Cases like Conrad's which have been outlined in this article are far from unheard of. And they are helping physicians and scientists who specialize in resuscitation tease out the mechanisms governing the death process.
Their ultimate goal is to halt and reverse that process. “When you’re freshly dead, your brain isn’t necessarily irreversibly, irrefutably damaged yet,” explains Sam Parnia, a critical care physician and director of resuscitation research at Stony Brook University School of Medicine in New York. “You have to both die and have brain death to really be dead.”
In this article you’ll discover that, although it looks like you’ve returned from the dead, in Lazarus syndrome you never really die at all.
Your heart is a pump that pushes blood through your blood vessels to all your organs and tissues in your body. When it stops beating, circulation stops, and your organs begin to fail because they’re no longer getting oxygen.
Usually, the reason your heart stops can’t be corrected or reversed, and death soon follows despite CPR. Sometimes, CPR is successful and restarts your heart, especially if the cause is a reversible problem.
Very rarely, a problem develops during CPR that prevents your heart from restarting. Lazarus syndrome happens when that problem resolves itself shortly after CPR stops, and your heart starts beating again.
Lazarus syndrome is very rare. One 2015 case report found that only 32 cases were reported between 1982 and 2008.
How Soon After Death Does Lazarus Syndrome Happen?
According to the Bible, Lazarus was dead for 4 days before Jesus brought him back to life. In Lazarus syndrome, “death” doesn’t last nearly as long.3https://www.bbc.com/future/article/20131031-will-we-ever-bring-the-dead-back
According to a 2020 research review, in most documented cases of Lazarus syndrome, circulation typically returned within 10 minutes of stopping CPR. Many people think that death occurs as soon as the heart stops beating and breathing ceases.
But in fact, death is a process in which all your organs necessary for life progressively fail. You aren’t actually considered dead until the function of all your organs, including your brain, irreversibly stops.
Declaring someone dead immediately after CPR stops leaves the door open for Lazarus syndrome to occur. Doctors can avoid this by:
- Waiting at least 10 minutes after CPR stops before declaring someone dead
- Keeping a heart monitor attached to the person to confirm loss of a heart rhythm for 10 minutes or more
- Disconnecting the device used for ventilation for 10 seconds to relieve air trapping when it’s suspected
Most importantly, medical personnel needs to confirm the loss of function of multiple organs before declaring death. This includes:
- Lack of audible heart sounds
- Absence of a palpable pulse
- Fixed and dilated pupils that don’t respond to light
- Lack of response to pain
What Causes This Lazarus Syndrome?
It’s not known why Lazarus syndrome happens, but there are several theories that may explain it. Let’s look at some possibilities.
- Air trapping
Air trapping is the most common explanation for Lazarus syndrome. It’s more likely to happen if you have chronic obstructive lung disease (COPD). When air is pushed into your lungs too rapidly during CPR (hyperventilation), there’s no time to exhale it, so it builds up. This is called air trapping.
As the air builds up, the pressure inside your chest increases. Eventually, it gets so high that your blood has trouble moving through your chest veins to your heart, and your heart has trouble pumping blood out to your body. This can:
- Stop your circulation
- Cause cardiac arrest
- Prevent your heart from restarting during CPR
When CPR stops, the trapped air starts leaving your lungs, which reduces the pressure in your chest.
Eventually, blood from your body can flow to your heart and be pumped to the rest of your body. Circulation can return, and it can look like your heart has restarted itself.
- Delayed medication delivery and action
Medications given during CPR need to reach your heart to work. When air trapping stops blood from returning to your heart, anything in your blood, including medication given through intravenous (IV) injection in your arms or legs, can’t get there.
Once air trapping resolves and the pressure in your chest is low enough, blood will flow to your heart, carrying the medication with it. If the medications are effective, your circulation will spontaneously return.
- Temporary cardiac arrest after defibrillation
During CPR, a defibrillator may be used to send an electrical shock to your heart to try to restart it or to reset an irregular heart rhythm known as arrhythmia. Sometimes there’s a delay between the shock and its effect. If it’s long enough, it appears that your circulation returns spontaneously rather than because of the shock.
Other Reversible Causes
Some conditions such as a high level of potassium or too much acid in your blood can cause your heart to stop beating. These conditions are usually treated during CPR, but they can take some time to resolve. If they don’t improve until CPR stops, it may look like your circulation returns spontaneously.
What Are the News Saying About Lazarus Syndrome?
Only about 63 cases of Lazarus syndrome have been documented in medical journals. Some of these cases have made it into the news headlines, such as:
- A 20-year-old woman in Detroit was declared dead after 30 minutes of CPR. She was taken to the funeral home where staff discovered she was breathing. She was treated in the hospital, but died 2 months later.
- A 23-year-old British man was pronounced dead after failed CPR. About 30 minutes later, a priest gave him last rites and noticed he was breathing. He died in the hospital 2 days later.
- In Ohio, a 37-year-old man collapsed at home. In the hospital, his heart stopped, and he was pronounced dead despite 45 minutes of CPR. Several minutes later, his family noticed his monitor showed a heart rhythm. A week later, he was well enough to go home.
Watch the video to see more about the Lazarus syndrome:
The Bottom Line
Although it may seem like some people come back to life after dying, someone with Lazarus syndrome experiences their circulation returning spontaneously after their heart stops beating.
The syndrome is very rare and only happens after CPR is performed. Many doctors think air trapping due to hyperventilation during CPR is the most likely cause of this syndrome.
Doctors can avoid declaring someone’s death by observing the person for at least 10 minutes after CPR stops.
You can check the FAQs section below to know more on the issue of 'Can You Come Back to Life After Being Dead', and if you have any comments, drop them in our comment section below.
Bone, tendon, and skin can survive as long as 8 to 12 hours. The brain, however, appears to accumulate ischemic injury faster than any other organ. Without special treatment, after circulation is restarted, full recovery of the brain after more than 3 minutes of clinical death at normal body temperature is rare. The longest time someone has been cardiac arrest and successfully revived and fully recovered is 17 hours. The record is held by Velma Thomas from West Virginia US.
Frequently Asked Questions Associated with the Question of Coming Back From the Dead
Bone, tendon, and skin can survive as long as 8 to 12 hours. The brain, however, appears to accumulate ischemic injury faster than any other organ. Without special treatment, after circulation is restarted, full recovery of the brain after more than 3 minutes of clinical death at normal body temperature is rare.
The longest time someone has been cardiac arrest and successfully revived and fully recovered is 17 hours. The record is held by Velma Thomas from West Virginia US.
Additional resources and citations