Use of novel intracoronary technology to investigate the effect of cold air inhalation during exercise on coronary microvascular resistance and blood flow in coronary artery disease: a cross-sectional study

Abstract Background Highest rates of exertion-related cardiac death occur during cold air inhalation (eg, shovelling snow), but the pathophysiological changes are unclear. Novel technology with intracoronary wires simultaneously and accurately measures coronary artery pressure and coronary blood flow, allowing physiological investigation of the effects of cold air during exercise. We explored the effects of exercise with and without cold air on coronary microvascular resistance and coronary blood flow in patients with coronary artery disease. Methods Patients with severe coronary artery stenoses undergoing coronary angiography were allocated to 5 min of cold air inhalation (–15°C), exercise (incremental supine ergometry), or exercise with cold air. We used two-way ANOVA to compare rest and peak measurements of coronary blood flow and microvascular resistance. We also used wave intensity analysis to identify waves that accelerate and decelerate coronary blood flow, and calculated the proportional contribution of accelerating waves as a coronary perfusion efficiency index. Findings We recruited 39 patients (mean 62 years [SD 9]), obtaining 51 datasets (14 cold air alone, 24 exercise, 13 exercise with cold air). 12 patients were in both the exercise and exercise with cold air groups, and for these patients the order was randomised. Microvascular resistance increased during cold air alone (558 mm Hg/cm per s [133] at rest vs 655 [221] at peak, p=0·04), and decreased during exercise (579 [192] vs 431 [166], p vs 495 [150]). The increase in coronary blood flow was similarly 34% less during exercise with cold air (19·3 cm/s [7·4] at rest vs 26·0 [10·7] at peak, p=0·04) than without (18·8 [7·3] vs 28·4 [11·3], p=0·04). An increase in coronary perfusion efficiency during exercise (69·8% [12·0] at rest vs 77·7 [9·2] at peak, p=0·05) was abolished with the addition of cold air during exercise (70·3 [10·7] vs 69·3 [10·0]). Interpretation We provide the first evidence, to our knowledge, that cold air substantially attenuates the reduction in microvascular resistance and the increase in coronary blood flow that normally occur during exercise. Moreover, although the heart has improved coronary perfusion efficiency during exercise, it can be reduced when combined with cold air. This finding suggests that cold air during exercise can impede coronary vasodilatation and ventricular relaxation, rendering the heart more susceptible to ischaemia. Funding British Heart Foundation, National Institute for Health Research.