Clinical study
Mechanisms of cold intolerances in patients with angina

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Abstract

Objectives. Patients with angina often report that symptoms are worse in cold weather, This study was designed to determine differences between cold-tolerant and cold-intolerant patients in the hemodynamic and ichemic response to exercise at cold temperature and to assess the role of catechlomines and baroreceptor function.

Background. Studies have suggested that the heart rate response may differ at cold temperatures, but the mechanism and role of this variation have not been examined.

Methods. Seven cold-intolerant and seven cold-tolerant patients with angina underwent exercise treadmill testing at 6 and 25 °C wtth measurement of catecholamines. Baroreceptor function was assessed by the decrease in systolic blood pressure after patients stood up from the supine position.

Results. Norepinephrine levels increased by 139% in the cold environment, but there were no differences between cold-intolerant and cold-tolerant patients. Consequently, blood pressure was higher in the cold environment in all patients, but the heart rate was similar. However, cold-intolerant patients had a steeper heart rate response in the cold and developed ischemia (mean [±SEM] 201 ± 58 vs. 242 ± 50 s, p = 0.05) and (348 ± 87 vs. 449 ± 60 s, p = 0.04) earlier in the cold environment, a difference not seen in the cold-tolerant patients Baroreceptor function was impaired in cold-intolerant patients. (decrease in systolic blood presure after patients stood up from the supine position 19 ± 7 vs. 0 ± 4 mm Hg, p = 0.04).

Conclusions. Exposure to cold causes an increase in blood pressure with an associated increase in myocardial oxygen demand in all patients. In cold-tolerant patients, this increase may be offset by a reduction in heart rate if baroreceptor function is normal. If baroceptor function is abnormal, heart rate may not decrease in response to a cold-induced increased in pressure. This mechanisms may account for some of the variability in tolerance to cold exposure that affects patients with exertional angina.

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Dr. Marchant is funded by the British Heart Foundation. Marquette Electronics supplied the treadmill testing equipment.