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Oxygen consumption (v@?O2) was measured during controlled and spontaneous ventilation with continuous positive airway pressure in newborn infants in whom chronic lung disease later developed. The oxygen cost of breathing (the difference in v@?O"2 between spontaneous and controlled ventilation) was significantly higher in infants with chronic lung disease than in control infants (20.1% +/- 7.5% and 4.8% +/- 4.9% of v@?O"2 during spontaneous ventilation [p < 0.05], respectively). (J PEDIATR 1995;127:984-7)

Acute intermittent repetitive hypoxia simulating sleep apnoea syndrome is responsible for acute rises in blood pressure (BP). In the rat, the BP rises are enhanced by added hypercapnia. To investigate the role of the autonomic nervous system (ANS) in acute hypertension during repetitive hypoxia alone, FiCO2 (inspiratory fractional concentration of oxygen) 2 to 5%, or combined with hypercapnia FiCO2 (inspiratory fractional concentration of carbon dioxide) 2 to 5%, we used autonomic blockade by atropine (1 mg kg1) + propranolol (1 mgkg1) + phentolamine (1 mgkg-1). Seven Wistar male rats were chronically instrumented with two aortic and venous catheters. Repetitive administration of N2 and N2 + C02 for 10s followed by 20 s compressed air was repeated for 4-5 min before (control) and after autonomic blockade. After autonomic blockade there was no significant difference in mean blood pressure (MBP) during severe hypoxia (SHO) (14.9 ± 0.5 mmHg) compared to control (10.5 ± 0.9 mmHg), while MBP was significantly decreased in severe hypoxia + hypercapnia (SHOHC) (14.1 ± 0.4 mmHg) compared to control (26.8 ± 0.3 mmHg) (p 0.001). We conclude that the acute BP rise observed during hypoxic breathing is not due to the activation of ANS, but when hypercapnia is added to the hypoxic stimulus about half of pressor response is caused by ANS.

Summary The time course of a and has been observed in two healthy subjects during moderate muscular exercise, and during inhalation of CO2 either at constant fraction or at constant flow rate. Six experiments of each type have been done on each subject.