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Letters to the Editor |
Department of Radiology, Bristol Royal Infirmary, Upper Marlborough Street, Bristol, Avon BS2 8BW, England. e-mail: drsanjuuk@yahoo.co.uk
Editor:
I read with great interest the article by Dr Schillinger and colleagues in the June 2004 issue of Radiology (1). I would like to make a few observations that could affect the results in this and other studies involving smokers.
The first issue is the chemical content of different brands of cigarettes, which may have a significant effect on the pharmacodynamics in these patients. Tar, nicotine, and carbon monoxide content of cigarettes varies markedly. For example, carbon monoxide content in cigarettes can vary from less than 0.05 to 3.0 mg per cigarette (2). This difference would affect the intravascular levels of carbon monoxide and carboxyhemoglobin (which were not measured in the study) and would therefore affect the degree of any presumed pathophysiologic effect on the arterial walls. I admit that this effect is difficult to quantify, since tar, carbon monoxide, and nicotine levels determined by the U.S. Federal Trade Commission method for individual brands are misleading because smokers can increase the amount of smoke that they take in depending on how they smoke their cigarettes. The amount of tar and nicotine a smoker actually gets can also increase if the smoker blocks tiny ventilation holes in cigarette filters that are designed to dilute smoke with air. In addition, many smokers of "low tar" or "light" cigarettes compensate by taking deeper, longer, or more frequent puffs from their cigarettes (2).
Second, the demographics data in this study do not include elaboration on the ethnic distribution of the study population. It has been well documented that clearance of cotinine is slower and intake of nicotine per cigarette is higher in black smokers than in white smokers (3).
Finally, although the authors admit in their discussion that bias could have been introduced by means of underreporting of daily cigarette consumption, they do not indicate the degree of this underreporting. In almost every study of smoking habits, measurement of biochemical markers of smoking is applied, in addition to self-reporting. When information is totally reliant on self-reported smoking habit, there is good evidence that smokers, when questioned about a smoking-related illness, frequently underreport their cigarette consumption. To overcome this bias, biochemical verification of smoking by means of measurement of nicotine metabolites has become almost obligatory (4).
In spite of these limitations, I believe that the interesting results in this study are worth investigating further with modifications to minimize bias, as outlined earlier.
REFERENCES
Department of Internal Medicine II, Division of Angiology, University of Vienna Medical School, Währinger Gürtel 18–20, Vienna A-1090, Austria. e-mail: martin.schillinger@meduniwien.ac.at
We read with interest the letter of Dr Prabhu concerning our article, "Effect of Smoking on Restenosis during the 1st Year after Lower-Limb Endovascular Interventions" (1). We appreciate the critical comments and agree on most of the mentioned study limitations.
First, the chemical content of different brands of cigarettes may indeed have a potentially relevant influence on the findings. Some of these effects could be measured by means of determination of CO and carboxyhemoglobin levels. Other effects, such as differences in tar levels, potential impact of filtered versus nonfiltered cigarettes, and "technique" of smoking, can hardly be quantified sufficiently. Nevertheless, even adjustment for all these factors would leave considerable statistical uncertainty, and only a randomized trial involving the use of standardized smoking conditions could exclude a relevant bias. Such a trial should certainly never be initiated, however, given the overall deleterious effects of smoking.
The second point should indeed be further specified: All study participants were white. A relevant bias with respect to ethnicity can therefore be excluded.
We totally agree with the third point, which remains a limitation of the present study. We tried to account for this problem by means of segregation into only two major categories: non- or light smokers versus habitual or heavy smokers. In any future study, however, we would certainly include objective measurements of cigarette consumption.
REFERENCES
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