Heart rate response to breath-holding during supramaximal exercise

Summary

The cardiovascular responses to breath-holding (BH) during short-lasting supramaximal exercise (415 W) on a cycle ergometer were investigated in 15 healthy male subjects. The arterial oxygen saturation, heart rate (HR), endtidal PO₂ and PCO₂ were continuously monitored. Firstly, 15 subjects performed exercise during BH, preceded by air breathing (air-BH test), and secondly, exercise without BH. Then 9 of the subjects performed the same procedure as in the air-BH test, except that all subjects breathed 100% O₂ for 1 min before apnoea (O₂-BH test). In 2 of these subjects, the systemic arterial blood pressure was continuously measured via a catheter in the radial artery and plasma catecholamine concentration [CA] was also measured both during the air-BH and the O₂-BH tests. In the later period of the air-BH test, the high HR level became progressively depressed. This response, however, was absent in the O₂-BH test. There was a late increase in the arterial blood pressure in both tests, and both tests produced hypercapnia. Only the air-BH test resulted in hypoxia, substantial hypertension and HR-depression. The increase in plasma CA was similar in both tests. The marked HR-depression demonstrated here is ascribed mainly to activation of the peripheral arterial chemoreceptors by asphyxia, and partially to baroreceptor activity due to elevated blood pressure.