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Gender and Prognosis of Chronic Obstructive Pulmonary Disease

I read with interest the article by Dr. Han and colleagues (1) about the complex relationship between gender and chronic obstructive pulmonary disease (COPD). They found that women with COPD appear to have a survival advantage, confirming findings of a meta-analysis (2) and a Japanese study (3). However, they stated that "Machado and coworkers [4] reported in patients with COPD receiving [long-term home oxygen therapy] LTOT that survival was significantly worse in females, those with lower body mass index, and lower Pa_O2. The study did not stratify the analyses by sex, thus, it is not clear if the mentioned risk factors were determined by male or female sex."

We would like to point out that our study (4) did indeed stratify the analysis by sex. As stated in our article, "None of the baseline patient characteristics significantly modified the association between sex and survival in the multivariate model (test for interaction with age [P = 0.28], pack-years smoked [P = 0.25], Pa_O2 [P = 0.74], FEV₁ [P = 0.22], BMI categories [P = 0.64] and Charlson comorbidity index [P = 0.29])." Therefore, our conclusion that survival was significantly worse in females and those with lower BMI and lower Pa_O2 was based on appropriate statistics that controlled for risk factors for gender.

We also would like to point out that Han and coworkers failed to mention other studies (5, 6) whose findings are similar to ours, showing worse survival in women with COPD. We agree that the issue of gender effect on COPD prognosis is fraught with complexities and still open to controversy. In this case, however, we believe Han and coworkers misinterpreted our main study results.

Maria-Christina L. Machado

Federal University of São Paulo
and
State Public Hospital of São Paulo
São Paulo, Brazil

FOOTNOTES

Conflict of Interest Statement: M.-C.L.M. has no financial relationship with a commercial entity that has an interest in the subject of this manuscript.

REFERENCES

1. Han MK, Postma D, Mannino DM, Giardino ND, Buist S, Curtis JL, Martinez FJ. Gender and chronic obstructive pulmonary disease: why it matters. Am J Respir Crit Care Med 2007;176:1179–1184.[Abstract/Free Full Text]
2. Crockett AJ, Cranston JM, Moss JR, Alpers JH. Survival on long-term oxygen therapy in chronic airflow limitation: from evidence to outcomes in the routine clinical settings. Intern Med J 2001;31:448–454.[CrossRef][Medline]
3. Miyamoto K, Aida A, Nishimura M, Aiba M, Kira S, Kawakami Y; Respiratory Failure Research Group in Japan. Gender effect on prognosis of patients receiving long-term home oxygen therapy. Am J Respir Crit Care Med 1995;152:972–976.[Abstract]
4. Machado MCL, Krishnan JA, Buist SA, Bilderback AL, Fazolo GP, Santarosa MG, Queiroga F Jr, Vollmer WM. Sex differences in survival of oxygen-dependent patients with chronic obstructive pulmonary disease. Am J Respir Crit Care Med 2006;174:524–529.[Abstract/Free Full Text]
5. Ström K, Boe J; Swedish Society of Chest Medicine. Quality assessment and predictors of survival in long-term domiciliary oxygen therapy. Eur Respir J 1991;4:50–58.[Abstract]
6. Ström K. Survival of patients with chronic obstructive pulmonary disease receiving long-term domiciliary oxygen therapy. Am Rev Respir Dis 1993;147:585–591.[Medline]

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