The Straight Dope - How do medical alert dogs know something is wrong?

Plus: How does an asphalt roller score on the Richter scale?

I play poker with this guy on a fairly regular basis at the casino. He’s got this medical alert dog he brings with him everywhere. Apparently, the dog will warn him 20 minutes prior to having a medical emergency that he needs to seek help. How does the dog know something is wrong with him?
— R.K.
Not that I would ever doubt what somebody told me in a casino, R.K. But how do you know the pooch’s alerts aren’t more along the lines of “This guy’s holding three of a kind”?
Fact is, there’s no such thing as a general-purpose medical alert dog. Closest I know of is a dog that recognizes seizures, due either to epilepsy or, in diabetics, low blood sugar (hypoglycemia). The experts distinguish two types of canine assistant. The first is a seizure response dog, trained to summon help or the like if its owner has an episode. Research suggests dogs do well at this task. The second is a seizure alert dog, which provides advance notice.
Here matters get murkier, as the notion that dogs can sense a looming medical crisis is controversial. One case written up recently involved a diabetic farmer. While driving back to his house for lunch, he’d often suffer hypoglycemia, which can lead to convulsions or unconsciousness. The farmer didn’t see the attacks coming but his dog, who liked to sleep on the seat next to him, apparently did: On numerous occasions over a 17-year period, the dog immediately awakened and barked until the farmer pulled over and ate some sugar.
Or so the farmer said. The problem with these accounts is you’re taking somebody’s word for it. In surveys of dog-owning epileptics, many report their pets can anticipate seizures and warn them in some way — barking, licking, etc. Perhaps so, but it’s not like dogs don’t do a lot of barking and licking at other times, too. In any case, the dogs hadn’t been trained to do whatever they did; they just picked it up on their own. Even if we accept claims of talented hounds at face value, how would you teach other animals to recognize signs with no clear notion of what the signs are? No one has attempted to do more than speculate on what the dog is sensing.
That is, if it’s sensing anything. Again, plenty of researchers are skeptical. One 2007 report tells of four individuals whose dogs allegedly could anticipate their seizures. On examination, the four were found to suffer not from epilepsy but from psychogenic nonepileptic seizures, or PNES. They didn’t have the chaotic brain activity of epileptics; to make a fine but crucial distinction, the problem was in their minds rather than their heads. One possibility raised: the dog’s behavior wasn’t a warning of a seizure but the trigger. Another research team reaching a similar conclusion observed: “Without objectively clarifying if patients have epilepsy or PNES, the current literature fails to support that canines can warn of impending seizures.” So I won’t say it never happens, but it may not happen much.
As I write, everything in my office is shaking. The culprit is the steamroller repaving a nearby road. My question: Does a steamroller, which I believe shakes rather than weights the road into place, register on the Richter scale? If so, how much?

— David, West Palm Beach, Fla.
First of all, David, it’s not called a steamroller, steam technology having been rare on construction sites since the days of Mike Mulligan. The diesel-powered machines you’re seeing are properly called asphalt rollers or just rollers.
While some rollers flatten by sheer weight, others are designed to vibrate, bouncing their heavy steel drums minutely for superior roadway compaction. The energy thereby transmitted can indeed be measured on the Richter scale. My assistant Una, a professional engineer, has proudly submitted a page of calculations demonstrating that, certain possibly risky assumptions having been made (among them that road crews put in a full eight-hour day), the total energy released by a jumbo asphalt roller would register a bit south of 2.5 on the Richter scale. That’s per day, not in one jolt, which you may say isn’t in keeping with the spirit of the thing. You should also know the Richter is a special logarithmic scale where every jump of two whole numbers represents a thousandfold increase in energy. In sum, 2.5 isn’t so much.
We can do better, though. We’re interested less in energy output at the source, as measured by Richter, than in how intense the shock feels to us. A better gauge is the Modified Mercalli Intensity scale, or MMI. Una judges the MMI rating of a roller to be 3 or 4. Using a table of equivalence prepared by the U.S. Geological Survey and waving our hands, we can then convert this back to Richter, enabling us to say the shaking you’re getting approximates what you’d experience near the epicenter of a quake measuring roughly 4.0 on the Richter scale — not San Andreas level, but in there with the New Madrid fault. Hope that’ll do.
Comments, questions? Take it up with Cecil on the Straight Dope Message Board,, or write him at the Chicago Reader, 11 E. Illinois, Chicago 60611.