01-07-2007 | Original Article
Effects of fasting and carbohydrate consumption on voluntary resting apnea duration
Published in: European Journal of Applied Physiology | Issue 4/2007
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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.