Impact of Habitual Cocaine Smoking on the Physiologic Response to Maximum Exercise

¹ From the Department of Medicine, UCLA School of Medicine, Los Angeles
² From the Departments of Medicine and Physiology, UCLA School of Medicine, Los Angeles
³ From the West Los Angeles Veterans Affairs Medical Center, Los Angeles

Background: Habitual smoking of alkaloidal cocaine (crack) has been reported to be associated with a number of cardiopulmonary complications that may not be clinically obvious but could potentially interfere with normal physiologic responses to exercise and thus impair maximum exercise performance.

Study objective: To evaluate the impact of regular use of cocaine on maximum exercise.

Design: Observational study in crack users and age- and gender-matched control subjects.

Subjects: Thirty-five habitual cocaine smokers (21 male and 14 female) and 29 age-matched sedentary control nonsmokers of cocaine (15 male and 14 female), all of whom were in good general health.

Methods: In these subjects, we compared physiologic responses to symptom-limited, incremental maximal exercise performed on a cycle ergometer using a ramp protocol. Comparisons were made for men and women separately.

Results: For both men and women, long-term cocaine smokers had a reduced aerobic capacity (maximum oxygen consumption) compared with control nonsmokers but did not show evidence of ventilatory limitation, reduced gas exchange threshold, increased physiologic dead space, or gas exchange abnormality at maximum exercise compared with the healthy control subjects. Although cocaine smokers had reduced maximum heart rates compared with control subjects, the relationship between submaximal heart rate and oxygen uptake was normal, indicating a normal cardiovascular response pattern. However, effort perception was similar between the two groups despite the difference in heart rate at maximum exercise, suggesting the possibility of perceptual dysfunction for effort. Differences in aerobic capacity between the crack users and nonusers could not be explained by differences in physical fitness or altered perception of dyspnea.

Conclusion: In the subjects we studied, long-term cocaine smoking was associated with reduced maximum exercise performance, probably due to poor motivation or altered effort perception. No other identifiable physiologic abnormality appeared to limit exercise in the habitual crack users.

Key Words: cardiovascular response • cocaine smoking • crack • gas exchange • maximum exercise • ventilatory response

Submitted on January 13, 1997
Accepted on March 17, 2007