Mechanisms of cold intolerance in patients with angina.

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 ischemic response to exercise at cold temperatures and to assess the role of catecholamines 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 degrees C with 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 response 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 angina (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 pressure 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 baroreceptor function is abnormal, heart rate may not decrease in response to a cold-induced increase in blood pressure. This mechanism may account for some of the variability in tolerance to cold exposure that affects patients with exertional angina.