Effects of fasting and carbohydrate consumption on voluntary resting apnea duration

Breath holding is normally terminated due to the urge to breathe, mainly caused by the increasing carbon dioxide level. It was recently shown that a combination of 18 h of carbohydrate-free diet and prolonged exercise prior to breath holding lowered the respiratory exchange ratio (RER) and end-expiratory PO₂ at maximal breath-hold break-point (MBP). Current hypothesis: fasting will result in longer breath-hold duration than will fasting followed by carbohydrate intake. It was also hypothesized that breath-holds during carbohydrate supplementation would be ended at a higher alveolar PO₂. Ten male non-divers performed multiple breath-holds either to the first diaphragmatic contraction (PBP), or to MBP. The breath-holds were performed during normal diet (control; C), twice during fasting (F14 h, F18 h), followed by post fasting carbohydrate consumption (PFCC) and a repetition of the breath-hold testing 1–2 h after ingestion of carbohydrates. Duration, RER, end-tidal PO₂ and PCO₂, SaO₂ and blood glucose were determined. RER and blood glucose increased after PFCC compared with fasting and control conditions (P < 0.001). PBP breath-hold duration increased from 129 ± 34 s at C to 148 ± 33 s at F18 h, and was reduced during PFCC to 122 ± 30 s (P < 0.001). End-tidal PO₂ was higher at PFCC compared to F18 h (10.4 ± 1.2 vs. 9.5 ± 1.2 kPa at PBP, P < 0.05). Similar trends in breath-hold duration and physiology were seen in breath-holds that were terminated at MBP. Dietary restriction can affect breath-hold duration. The lower O₂ level at breakpoint during fasting suggests that breath holding may be less safe during fasting; the increased risk may be mitigated by ingestion of carbohydrates before breath holding.