Changes in left ventricular function and cerebral blood flow during apnea in exercising humans

Abstract

In exercising humans, large cardiovascular changes occur during apnea. Such cardiovascular changes have been proposed to maintain the oxygen supply to vital organs. However during apnea the responses in cerebral blood flow and left ventricular (LV) volume and function are unknown. The purpose of this study, therefore, was to examine the changes in cerebral blood flow and LV volume and function during apnea in exercising humans. In 14 healthy subjects (10 males) who performed a two-legged dynamic knee extension exercise, we measured changes in heart rate (HR), mean arterial pressure (MAP), arterial oxygen saturation (SaO2), LV end diastolic and end systolic volumes (LVEDV and LVESV, respectively: echocardiography), cardiac output [CO; stroke volume (LVEDV - LVESV) · HR], common carotid artery blood flow (CBF), and middle cerebral artery mean blood flow velocity (McaVm) (by the ultrasound Doppler method) during apnea. During apnea, significant decrease (P < 0.05) in SaO2 (97 ± 0.7 vs. 81 ± 2.8 %, before apnea vs. peak response during apnea, the same applies below), HR (96 ± 1.9 vs. 47 ± 2.9 beats min-1), CO (9.6 ± 0.7 vs. 5.4 ± 0.4 l min-1), and significant increase in MAP (90 ± 4.2 vs. 147 ± 6.1 mmHg), CBF (568 ± 36.5 vs. 723 ± 52.2 ml min-1), and McaVm (64 ± 4.4 vs. 81 ± 6.9 cm s-1) were observed. LVEDV (133 ± 6.3 vs. 135 ± 5.7 ml), LVESV (34 ± 3.2 vs. 33 ± 3.5 ml), and ejection fraction (SV / LVEDV · 100; 74.3 ± 2.0 vs. 75.5 ± 1.9 %) were not significantly changed (P > 0.05) during apnea. These results suggest that during apnea, cerebral blood flow increases in spite of a large decrease in CO and that the LV volume and functions are maintained despite marked bradycardia and a large increase in ventricular afterload. This study was supported by grants from COE projects and the Ministry of Education, Science, and Culture of Japan.