Friday, December 08, 2006

Conflating Coronary Blood Flow and Coronary Flow Velocity Reserve: The Basis for Anti-Smoking Groups' Misleading Health Claims

I thought it might be worthwhile to devote one post to explain the basis for much of the deception of the public that is going on regarding the acute cardiovascular effects of brief secondhand smoke exposure, including the deception by ClearWay Minnesota which I highlighted yesterday, the deception of ANR which I highlighted back in March, and the deception of the American Cancer Society and Campaign for Tobacco-Free Kids which I highlighted in May.

You may recall that one of the deceptive claims being made by ClearWay is that secondhand smoke exposure decreases coronary artery blood flow in healthy young adults.

First, it is important to recognize the significance of this claim. A reduction in coronary artery blood flow implies that there is a serious risk that not enough blood flow which reach the heart muscle. And if that occurs, the person will suffer a heart attack. Such a heart attack can be fatal. Therefore, what ClearWay and other anti-smoking groups which have made similar statements are implying is that a healthy young adult exposed to secondhand smoke is at risk of death due to that exposure.

That bears repeating. What anti-smoking groups are implying is that a healthy young person exposed to secondhand smoke is at risk of death due to that exposure.

If this claim were accurate, then I think it would provide strong justification for banning smoking altogether. After all, how can we take the risk that healthy young people who are simply walking down the street and happen to be exposed to secondhand smoke might suffer a decrease in coronary artery blood flow and drop dead from a heart attack?

Not only is Clear Way Minnesota making this claim, but they are encouraging local anti-smoking groups to make the same claim. The claim appears in a smoking ban manual whose purpose is to provide direction and advice to anti-smoking groups advocating for smoking bans. ClearWay is essentially telling these groups that an appropriate tactic for promoting smoking bans is to publicly state that exposure to secondhand smoke can kill healthy young adults by decreasing the blood flow in their coronary arteries.

Note that whether ClearWay intends to imply this or not isn't important. What's important is that their statement inherently implies the risk of heart attack and death. So if this implication is false, then the statement is what I would consider to be wildly deceptive.

A similar claim is being made by Americans for Nonsmokers' Rights (ANR), which claims that: "Even a half hour of secondhand smoke exposure causes heart damage similar to that of habitual smokers. Nonsmokers' heart arteries showed a reduced ability to dilate, diminishing the ability of the heart to get life-giving blood."

Clearly, this statement is implying that a half hour of secondhand smoke exposure impairs the body's ability to get life-giving blood to the heart, putting even a healthy young individual at risk of a heart attack and therefore of death.

If this statement is false, then ANR's statement is wildly deceptive. After all, would it not be deceptive to imply that secondhand smoke impairs the body's ability to provide adequate blood to the heart and therefore puts a person at risk of a heart attack and death if that is untrue?

At an even higher level, a similar claim is being made by the American Cancer Society and the Campaign for Tobacco-Free Kids in a strategy document intended to guide anti-smoking groups nationwide in communication tactics to promote smoking bans.

One strategy put forward to help advocates overcome barriers to the adoption of smoking bans is to convey to the public that some of the effects of secondhand smoke are "virtually instant" because "these messages convey the issue's urgency." Specifically, the strategy urges advocates to emphasize the following messages:

1. "Immediate effects of secondhand smoke include cardiovascular problems such as damage to cell walls in the circulatory system, thickening of the blood and arteries, and arteriosclerosis (hardening of the arteries) or heart disease, increasing the chance of heart attack or stroke."

2. "Short-term exposure to tobacco smoke has a measurable effect on the heart in nonsmokers. Just 30 minutes of exposure is enough to reduce blood flow to the heart."

Here, not only are anti-smoking groups instructed to tell the public that 30 minutes of secondhand smoke reduces blood flow to the heart, but they are told to explicitly state (rather than merely imply) that this 30 minute exposure causes atherosclerosis, heart disease, heart attacks, and stroke.

What the American Cancer Society and Campaign for Tobacco-Free Kids are stating, then, is that just 30 minutes of secondhand smoke exposure reduces blood flow to the heart and causes hardening of the arteries, heart disease, heart attack, and stroke. This particular communication leaves little to the imagination.

The Rest of the Story

So here's the truth: The truth is that what acute secondhand smoke exposure does is to reduce not coronary artery blood flow, but coronary flow velocity reserve. There's a huge difference between these two, and they should not be conflated.

Coronary flow velocity reserve is a measure of the ability of the coronary arteries to dilate in order to increase blood flow under experimental conditions. What a decline in coronary flow velocity reserve indicates is something called endothelial dysfunction - an impairment of the ability of the coronary arteries to dilate in response to a variety of stimuli. This ability to dilate is mediated by the endothelial cells -- the cells which line the blood vessel.

The endothelial cells respond to certain stimuli by producing nitric oxide and other chemicals which diffuse into the smooth muscle in the artery wall, sending a chemical message that causes the muscle to relax and therefore causing the artery to dilate. There are a number of exposures that impair the ability of the endothelium to accomplish this function; among them are active smoking, secondhand smoke, high cholesterol, consumption of trans-fats, and consumption of a high-fat meal.

When endothelial dysfunction is triggered repeatedly over a long period of time, it has been shown to result, ultimately, in atherosclerosis (narrowing of the coronary arteries). When this occurs, coronary blood flow is reduced.

It is important to note that a reduction in coronary blood flow is not observed acutely when the endothelial dysfunction is being measured from a single experimental exposure (such as in the Otsuka et al. study). The reduction in coronary blood flow does not occur until the process has been sustained long enough that atherosclerosis has progressed and the coronary artery has actually narrowed. It is the narrowing of the artery that causes reduced coronary blood flow.

A single high-fat meal has been documented to cause endothelial dysfunction. If you were to go to Burger King for a Whopper, fries and a milk shake and then go to a laboratory to have your coronary flow reserve velocity tested, you would find that it is reduced. In fact, it will probably be reduced to the same level as in an active smoker.

Would it therefore be accurate for an anti-obesity group to claim that eating a hamburger reduces coronary artery blood flow in healthy young adults?

I would argue that it would not. In fact, I think such a statement would be very misleading and deceptive to the public.

Instead, what the science shows is that eating a hamburger or any high-fat food causes endothelial dysfunction. Therefore, if you chronically eat lots of fatty foods over a long period of time (many years), the evidence indicates that this could cause atherosclerosis and heart disease. If you do develop heart disease, then your coronary blood flow will be decreased and you will be in danger of possibly suffering a heart attack. But there is no danger of death or a heart attack after simply eating one Whopper.

By conflating coronary blood flow with coronary flow velocity reserve, anti-smoking groups have, I think, been able to deceive people into thinking that the effects of acute secondhand smoke exposure are much more severe than they actually are.

This is a clever tactic, I believe, because it sensationalizes the acute health effects of secondhand smoke, implies to the lay public that a brief exposure can be fatal for even a healthy, young person, and I think it would scare people sufficiently that it would increase support for smoking bans - which is the ultimate goal (and a goal I support [at least workplace smoking bans]).

But in order to achieve the "benefit" of a much more shocking and emotional public communication, have we not distorted the science and ended up misleading and deceiving the public?

I think the answer is a definite "yes." I see no compelling way to argue that by using the term "coronary blood flow" rather than "coronary flow velocity reserve," we have not ended up deceiving anyone. In fact, I think the difference is enormous and the difference in the implications are even more enormous.

I don't think it's fair to do this to the lay public, because they are simply not in a position to be able to understand and interpret these communications in a critical and informed manner. When they are told that coronary blood flow is reduced, they are naturally going to assume (at least many of them will) that this is reducing blood flow to the heart, which even the lay public understands is what causes a heart attack.

There is no question in my mind that the implication of these public statements to a large segment of the lay public is that acute and brief secondhand smoke exposure can cause death by heart attack among healthy young adults. Such an implication, it is important to point out, is completely false.

I think the conclusion is therefore inescapable that these anti-smoking groups - such as ClearWay - which have stated that brief exposure to secondhand smoke reduces coronary blood flow in healthy young adults, are deceiving the public.

Since we criticize the tobacco companies all the time for deceiving the public in their public communications, especially regarding the effects of tobacco smoke, what possible justification can we provide for deceiving the public ourselves in our own public communications?

I don't think there is one. I think this deception is unjustified and wrong. It is unethical, and I think it needs to stop. I also think we need to retract or correct our statements and apologize for having deceived the public, whether that deception was intentional or not.

UPDATE (December 8, 2006; 12:30 pm): ClearWay Minnesota's smoking ban manual, which contained the statement referred to in this post, has been removed, at least temporarily, from its website (it is unaccessible). It will be interesting to see whether the deceptive claims are being retracted or corrected, but at any rate, this appears, possibly, to be an encouraging sign.

No comments: