It's one of the heart-wrenching images now etched into our minds: A Boston Marathon runner blown off his feet by a bomb blast -- one of two explosions on Monday that killed three people and injured more than 170 others.
"Shock waves just hit my whole body and my legs just started jittering around. I knew I was going down," 78-year-old Bill Iffrig of Lake Stevens, Wash., told CNN on Monday.
Iffrig walked away on his own. He later told reporters that he felt fine, with the exception of a scraped knee and ringing in his ears.
For runners and bystanders near the bombings, however, an absence of obvious physical injury may not guarantee an escape from bodily harm. Recent research on Gulf War veterans and NFL football players highlights the dangers posed by even mild brain trauma. Exposure to shock waves from the powerful explosions near the marathon finish line, experts warned, may result in initially silent yet potentially serious long-term effects on the brain.
A bomb blast's short-lived supersonic wave "packs a wallop," said Dr. Lee Goldstein, a biomedical engineer at Boston University. "It can knock you off your feet." He added that it's the second component of a blast that raises the biggest concern for the brain.
"Right behind that is this blast wind that goes back-and-forth, causing the head to swing back-and-forth on the neck, like a bobblehead, very quickly," Goldstein explained.
While health experts have long believed that one explosion exposure is unlikely to cause long-term damage, Goldstein pointed to emerging evidence that suggests otherwise. In a study published in May, Goldstein and his colleagues found that soldiers exposed to a single roadside bomb blast had brain trauma similar to football players who had suffered multiple concussions.
"One blast is really like getting multiple head injuries over a compressed period of time," Goldstein said, comparing each slug of alternating air to a hard-hitting tackle from a 300-pound linebacker.
Autopsies of both military veterans and former athletes showed signs of chronic traumatic encephalopathy, or CTE. Over time, the degenerative disease can resemble Alzheimer's, with symptoms that include irritability, memory and attention-span problems, dementia and suicidal thoughts. In the same study, Goldstein's team also found that animals developed evidence of the disease just two weeks after exposure to a single simulated blast.
Goldstein emphasized that much remains to be learned about CTE, and that we can't say whether anyone at the bomb site will actually develop the disease. The bombs used in Boston appear to have been made with relatively low-grade explosives. Still, he said, the possibility "certainly raises concern."
Dr. Linda C. Degutis, director of the Centers for Disease Control and Prevention Injury Center, also expressed concern.
"We know based on a lot of research done that with any explosive device there is a possibility of having some traumatic brain injury even if you're not actually hit with pieces of the bomb itself," said Degutis. Brain injuries frequently go undiagnosed after blasts, she said.
The CDC and the National Institute of Neurological Disorders and Stroke list potential early symptoms of a moderate or severe traumatic brain injury: repeated vomiting or nausea, convulsions or seizures, an inability to awaken from sleep, dilation of one or both pupils, slurred speech, weakness or numbness in the extremities, loss of coordination and increased confusion, restlessness, or other abnormal behavior.
The difficulty in recognizing milder injuries, generally accompanied by subtle symptoms such as headaches or a ringing in the ears, worry Degutis. Such minor damage can still lead to major problems in the future, particularly if the victim goes undiagnosed and untreated.
"Just like other injuries you might have, such as a sprained ankle, resting the brain is important," Degutis said, noting that a secondary injury while the brain is recovering may be more likely to cause devastation.
Dr. Jeff Bazarian, a brain injury expert at the University of Rochester Medical Center, referred to lessons from 9/11.
"People went to hospitals with fractures and internal organ injuries," Bazarian said. "But long after those bones healed and internal organs were fixed, it was the overlooked concussions that ultimately interrupted their ability to go back to what they were doing before.
"Concussions often get missed because other injuries are more life-threatening," added Bazarian, who, has studied impacts of head injuries on athletes and soldiers. Some people never go to the hospital, he said. They may feel fine at the time.
So just how many of these people, which Bazarian refers to as the "walking wounded," might there from the Boston bombings? That, of course, depends on how far the damaging waves travelled from the blast. And that, too, depends.
The U.S. military uses a bomb blast threshold of 50 meters as a rough radius within which it will classify someone as brain-injured. The military requires these soldiers to rest for 24 hours, regardless of symptoms.
While 50 meters is a good "rule of thumb," according to Bazarian, the strength and location of the blast is also key. A blast on the side of an urban street, where tall buildings can concentrate and reflect shock waves, would look very different than one detonated in the desert.
In fact, depending on the geometry of building walls and streets, it's possible that someone 10 feet from the blast may have greater injury than someone standing just three feet away, noted Goldstein.
Vulnerability to the blast also depends on the person. Young children, whose brains have not fully developed, and the elderly tend to be at greatest risk.
Bazarian noted that a pair of promising blood tests could one day help first responders identify people who have sustained brain injuries. The tests are not yet approved by the Food and Drug Administration.
For now, experts agreed that health professionals and victims should watch carefully for brain injury symptoms.
Of course, some of the symptoms can overlap with those of post-traumatic stress disorder, another serious concern after an emotionally-charged event like the Boston bombings.
"That's another reason for folks to see their doctor," said Bazarian. "If not recognized and treated early, PTSD can also become more of a long-term problem."
ALSO ON HUFFPOST:
04/19/2013 2:30 AM EDT
GLOBE: Bombing Suspect In Custody, Another Remains On The Loose
One marathon suspect has been captured, according to an official with knowledge of the investigation.
Another remains on the loose in Watertown after a firefight with police. Authorities have established a 20-block perimeter as they search for him.
Read more here.
04/19/2013 12:44 AM EDT
Unconfirmed Photo Of Suspect 2 In Boston Marathon Bombing Emerges On Facebook
Just hours after the FBI released the first photos of suspects in the Boston Marathon bombing, a new photo of Suspect 2 may have emerged.
David Green, 49, of Jacksonville, Fla., had just completed his first Boston Marathon, when he snapped a picture with his iPhone 4S, taken at 2:50, just after the two blasts ripped through the finish line area, killing three people and injuring more than 180 others.
The FBI has not publicly confirmed this photo as Suspect 2, but Green told the Huffington Post that an agent told him, "this is probably the best we have right now."
The man who appears to be Suspect 2 is wearing a white hat with a "3" on the side as seen in the publicly-released photos.
Read more here.
04/18/2013 10:19 PM EDT
Boston Bombing Victim in Iconic Photo Helped Identify Attackers: Bloomberg
Minutes before the bombs blew up in Boston, Jeff Bauman looked into the eyes of the man who tried to kill him.
Just before 3 p.m. on April 15, Bauman was waiting among the crowd for his girlfriend to cross the finish line at the Boston Marathon. A man wearing a cap, sunglasses and a black jacket over a hooded sweatshirt looked at Jeff, 27, and dropped a bag at his feet, his brother, Chris Bauman, said in an interview.
Read more here.
04/18/2013 9:04 PM EDT
Federal Law Enforcement Says Suspects Stayed To Watch Carnage: CNN Reports
04/18/2013 7:26 PM EDT
Right Wing Journalist Goes Ballistic During Press Conference
BOSTON -- Moments after the FBI revealed images of two baseball cap-wearing men wanted for questioning about the Boston bombings, the press conference descended into a sideshow.
A journalist from a far-right wing website called Info Wars shouted out a question accusing the government of carrying out the attack that killed three, and maimed or injured 170 others.
FBI Special Agent in Charge Richard Deslauriers ignored the allegation of a government conspiracy from reporter Daniel Bidondi, but the Alex Jones protege did not stop hollering.
"The FBI lies," Bidondi said. "We've got the proof," he said accusing the government of a "false flag" attack in which it staged the blasts and made them appear like the work of terrorists.
Bidondi found himself at the center of an media scrum with cameras and microphones pointed at his face after law enforcement officials left the podium in the Sheraton hotel.
Another reporter ridiculed Bidondi from across the room, telling him to shut up and calling him an asshole.
The excitement quickly dissipated as reporters returned to delivering the news about the official images of the suspects.
Bidondi has been a presence at other press conferences this week related to the bombing investigation.
--Michael McLaughlin / HuffPost Crime
CORRECTION: An earlier version of this story misspelled Bidondi's last name. We regret the error.
04/18/2013 7:00 PM EDT
Is The Suspect's Hat A Clue?
04/18/2013 6:46 PM EDT
Facial Recognition Expert Reacts To FBI Photos
Dr. Ralph Gross, a facial recognition expert at Carnegie Mellon University, said the FBI photos of two suspects in the Boston Marathon bombing are likely too grainy to be matched against a driver's license database or Facebook. But he thinks they may be just good enough for someone who knows the individuals to identify them.
"The resolution isn't particularly good. The one that's kind of best is unfortunately a side view -- and in general the face recognition software works best with frontal view," he said.
Research has consistently found, however, that people can spot people they know even in grainy, off-center photographs.
"Humans are actually very good at recognizing people that they are familiar with," Gross said. "Somebody that might know these guys, or might know the way they dress, might certainly be able to recognize them."
The FBI said the men should be considered armed and dangerous, and urged tipsters to call 1-800-CALL-FBI if they believe they have information that could lead to an arrest.
04/18/2013 6:21 PM EDT
Daily News Doctored Photo
The New York Daily News reportedly doctored its front page photograph of the Boston bombings (see update below).
WARNING: LINK GOES TO GRAPHIC PHOTO
04/18/2013 5:37 PM EDT
Hi-Res Image Of People Of Interest
04/18/2013 5:30 PM EDT
FBI Website Down
CNN reports that, because of a flood of traffic, the FBI's site is temporarily down.