title: Effects of hypoglycaemia on ventilation and arousal responses to hypoxia, and newborn calves during active and quiet sleep.
abstract: Ventilatory and arousal responses to progressive, isocapnic hypoxia were assessed in five full-term calves, aged 1-8 d, during normo-glycaemia and insulin-induced hypoglycaemia; replicate tests were made during both quiet and active sleep. Hypoxia was produced by rebreathing 8-10% (W/V) oxygen; end-tidal PO2 and PCO2 confirmed the mask-seal, and the constancy of PCO2 achieved by a soda-lime CO2-absorber. Oxygen saturation was recorded continuously by aspirating aortic blood through a cuvette-oximeter. Airflow through a tightly fitting face-mask was digitized at 50 ms intervals to calculate breath-by-breath ventilation and rate. Sleep-state and arousal were characterized by EEG, electro-oculogram, nuchal electromyogram and behaviour. An intravenous dose of 2.5 units/kg of soluble insulin produced hypoglycaemia within 60 min (blood glucose less than 1 mmol/l). In the normoglycaemic control state, ventilation during quiet sleep increased linearly; typically the ventilation ratio to pre-hypoxic control was 1.5 at an arterial O2-saturation of 85-90%. In contrast, during active sleep, hypoxaemia progressed without any ventilatory response to a very low arterial O2-saturation of less than 70%. Severe hypoglycaemia did not alter these ventilatory responses during either quiet or active sleep. Thus, the relationship between ventilation ratio and arterial O2-saturation at a saturation of 75% did not differ significantly from control. In quiet sleep the mean ventilation ratio values at an arterial O2-saturation of 75% were 1.92 +/- 0.07 (SEM) and 1.62 +/- 0.07 (P greater than 0.05) for normoglycaemia and hypoglycaemia respectively; in active sleep these were 1.08 +/- 0.09 (SEM) and 1.06 +/- 0.04 (P greater than 0.20). The arterial O2-saturation at which reflex arousal occurred differed between sleep-states but was not altered by hypoglycaemia. In quiet sleep, values were 85.0 +/- 1.4 (SEM) and 84.4 +/- 2.5; in active sleep, 57.8 +/- 3.9 (SEM) and 60.4 +/- 1.4, for normoglycaemia and hypoglycaemia respectively.
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001143:Arousal / Q000502:physiology*; D002417:Cattle; D007003:Hypoglycemia / Q000139:chemically induced / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D007328:Insulin / Q000494:pharmacology; D008168:Lung / Q000503:physiopathology; D010100:Oxygen / Q000097:blood; D012119:Respiration; D012890:Sleep / Q000502:physiology*
chemical_list: D007328:Insulin; D010100:Oxygen