Abstract
Apneas performed during hypoxia cause pronounced bradycardia and cardiac arrhythmias. What remains unclear is the intraindividual consistency of these responses. Therefore, we assessed the within-day and between-day repeatability of responses to hypoxic apneas, including the genesis of arrhythmias or electrocardiogram (ECG) changes. Sixteen participants (8F/8M, 25 ± 3 years, BMI 23.7 ± 3.4 kg/m(2), mean ± SD) completed four hypoxic apneas per day on consecutive days, time-matched to a maximal apnea on day 1 (39 ± 16 s). We quantified heart rate (HR) and mean arterial pressure (MAP) repeatability using within-subject standard deviations (WSSD), [95%CI]. We hypothesized that WSSDs would be <5 bpm and <4 mmHg for HR and MAP. We also assessed the repeatability of arrhythmias or ECG changes. Within-day, the HR WSSD was 4.4 bpm [3.7, 5.6], and the MAP WSSD was 4.1 mmHg [3.4, 5.1]. Between-day comparisons had somewhat higher WSSDs: HR was 5.7 bpm [5.0, 6.5] and MAP was 5.0 mmHg [4.4, 5.8]. Arrhythmias or ECG changes occurred during 45% of apneas. These data indicate poor repeatability of electrical conduction changes during apneas. Conversely, our WSSD data indicate good within-day and between-day repeatability, albeit somewhat higher than hypothesized. These data therefore indicate that hypoxic apneas are a repeatable laboratory stressor for HR and MAP, but that researchers should exercise caution in interpreting individual-level arrhythmia data.