In 19 pentobarbital sodium-anesthetized kittens aged 5-34 days, inspired O2 was reduced from 21 to 6-12%. Respiratory frequency (f) and tidal volume (VT) increased within 30 s. Over 5 min f fell to about 60% below control; VT usually fell but remained above control. Arterial pressure fell in 80% of trials, sometimes before f fell. Arterial CO2 was below control, but raising inspired CO2 to keep expired CO2 at control did not prevent the fall in f and VT. The relation between VT and esophageal pressure or diaphragm electromyogram (EMG) did not change consistently, nor was the ratio of high to low frequencies in the diaphragm EMG altered. Carotid chemoreceptor discharge increased within 15 s, and at 5 min it was much above control. We conclude that the change in the breathing pattern in hypoxia is probably due to the activation of a central mechanism.

The effects of fetal tracheostomy on lung development in lambs have been investigated. Seven ewes, all with twin fetuses, were given a general anesthetic. One fetus in each set of twins was tracheostomized and the other fetus was sham operated (117-122 days gestation). The fetuses were delivered by cesarean section between 137 and 140 days gestation. Fetal tracheostomy decreased lung weight and volume, altered DNA concentration and the structural development of the acinus, and decreased lung distensibility. However, tissue and airway saturated phosphatidylcholine and lung stability during deflation were not significantly affected by fetal tracheostomy. It seems that tracheostomy in fetal lambs alters lung growth but does not affect the formation or release of surfactant. These data support the hypothesis that lung volume is actively maintained and lung growth promoted by the secretion of lung fluid against the resistance of the upper airway in fetal lambs.

SUMMARYThis study examines the effect of hand-rearing developing lambs in a warm (WR; 25°C) or cool (CR; 10-15°C) ambient temperature on the control of thermoregulation and breathing patterns, when maintained at a fixed level of nutrition over the first month of postnatal life. Measurements were made during non-rapid eye movement sleep whilst lambs were maintained for at least 1 h at warm (28-19°C) and cold (14-5°C) ambient temperatures at 1, 7, 14 and 30 days of age. All lambs were able to maintain normal body temperature, but oxygen consumption was higher in CR lambs at 14 and 30 days of age. At 1 day of age shivering was rarely observed in any lambs, but at 7 and 14 days of age more WR than CR lambs responded to cold exposure via shivering. Plasma concentrations of triiodothyronine were higher at 7 and 14 days of age in CR lambs. Breathing frequencies were similar in WR and CR lambs, and from 7 days of age the incidence of expiratory laryngeal braking was higher in warm compared with cold study temperatures. By 30 days of age the recruitment of this mechanism was greater in CR lambs. Mean growth rate was slower over the first week of postnatal life in CR compared with WR lambs. This difference decreased over the first month of life, as growth rate increased from 83 to 130 g day-' in the CR group but remained constant at approximately 150 g day-' in the WR lambs. Total weight of the lungs and heart, but not the liver, were lower at 1 month but not at 1 week of postnatal life in CR lambs. It is concluded that a modest decrease in the ambient temperature in which postnatal lambs are reared, when on a fixed feed intake, alters lung size, the recruitment of laryngeal braking and the control of body temperature.

We studied respiratory patterns and transcutaneous gas pressures in two infants with Arnold-Chiari type II malformation referred to us due to repeated episodes of stridor and cyanosis. During both active and quiet sleep, respiration was irregular and absent or inverse thoracic breathing movements and frequent decreases in oxygen saturation to below 80% were observed. When breathing air with 2% CO2 or when given acetazolamide 10 mg/kg, chest wall movements normalized and oxygenation increased to near normal levels. After three months of treatment with acetazolamide 20 mg/kg/24 h no further episodes of hypoventilation or hypoxemia were observed and further treatment could be discontinued. We conclude that stimulation of respiration by CO2 or by acetazolamide appears to recruit chest wall muscles and promote upper airway patency in Arnold-Chiari malformation. A treatment trial with acetazolamide seems justifiable in these infants when respiratory problems are present.

A case of accidental paracetamol overdose in a patient suffering from pericoronitis is described. Self-medication with paracetamol was exacerbated by the prescription of a compound analgesic containing paracetamol by the patient's dental practitioner. The consequent overdose of paracetamol resulted in liver toxicity and acute liver failure. The hazards of accidental paracetamol overdose are discussed and analgesic preparations containing paracetamol described.