Effects of Fasting and Carbohydrate Replenishment on Voluntary Apnea Duration in Resting Humans

Abstract

PURPOSE: Voluntary breath-hol ding is normally ended by the urge to breathe, which is caused by the rising carbon dioxide in arterial blood. For a given energy output lipid metabolism causes less carbon dioxide to be produced than during carbohydrate metabolism. It has recently been shown that a combination of 18 h of carbohydrate free diet and prolonged exercise prior to breath-holding lowered Respiratory Exchange Ratio (RER) and PO2 at Maximal Breath-hold Break-Point (MBP). We hypothesized that fasting alone would result in longer breath-hold duration due to a delay in the Physiological Break-Point (PBP) and MBP. We also hypothesized that if subjects' diet were supplemented with carbohydrates the breath-hold durations would be shorter, and blood glucose and end-tidal PO higher, i.e. safer. METHODS: Ten male non-divers performed multiple resting breath-holds either to the first diaphragmal contraction (PBP), or alternating, to MBP. The breath-holds were performed during Control (uncontrolled diet, C), after 14 hours (F14h) and 18 hours of fasting (F1 8h) and followed immediately by Carbohydrate Supplementation (CS). Duration, RER, end-tidal PO and PCO, SaO and blood glucose were determined. RESULTS: RER and blood glucose increased after CS as compared with fasting and control conditions (p <0.001). Maximal breath-hold duration increased from C: 155±30 s to F18h: 177±31 s, and was reduced during CS to 144±27 s (p <0.001). End-tidal PO2 was higher at CS compared to F1 8h (8.5±1.5 vs. 7.4±1.7 kPa at MBP, p <0.05). Corresponding values for SaO2 at MBP, CS: were 88±5% vs F18h: 85±6%, p <0.05. Similar changes were seen in the breath-holds that were terminated at PBP. CONCLUSIONS: Dietary restriction alone can cause a change in energy metabolism and respiratory physiology during breath-holding. The lower oxygen level at breakpoint (fasting) suggests that breath-holding may be less safe during fasting and that this increased risk may be mitigated by ingestion of carbohydrates before breath-holding.