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To evaluate the role of genetic and environmental factors in the genesis of large lungs in high-altitude natives, we measured forced vital capacity (FVC), static lung pressure-volume characteristics and maximum expiratory flow-volume loops in 17- to 20-yr-old Peruvian natives to 3,850 m (highlanders) and 800 m (lowlanders). Forced vital capacity was 5.11 +/- 0.64 liters in highlanders, 116 +/- 11% of predicted; and 3.73 +/- 0.32 liters in lowlanders, 84 +/- 7% of predicted. Lung elastic recoil at functional residual capacity and at total lung capacity, and size-corrected pressure volume curves were similar in the two groups. Despite the larger volumes in highlanders, density-corrected maximum flow rates were similar in highlanders and lowlanders, and flow expressed in FVC'S-S-1 was less in highlanders. Upstream conductance at 50% FVC expressed in fvc's-s-1-cmH2O was 0.094 +/- 0.023 in highlanders vs. 0.147 +/- 0.050 in lowlanders. Flow rates did not change in sojourners to altitude, suggesting that the lower values of highlanders were due to anatomic factors. These findings suggest that airways, which form in fetal life, do not participate in adaptation to altitude, and that the large lungs of highlanders result from postnatal environmental hypoxic stimulation of lung growth. Our results illustrate the importance of "dysynaptic" lung growth in determining patterns of adult lung function.

Four infants with Down syndrome developed cor pulmonale and heart failure in association with chronic upper airway obstruction. Features of the sleep apnea syndrome were conspicuous; namely, noisy breathing with retraction, cyanosis and frequent apnea during sleep, and daytime lethargy and somnolence. The clinical picture masqueraded as cyanotic congenital heart disease. Arterial blood gas analyses revealed alveolar hypoventilation, especially during sleep. The nature of the obstructive element was variable. Adenoidectomy provided partial relief in one patient, and tonsillectomy and adenoidectomy resulted in temporary improvement in two others. Three patients were markedly benefitted by tracheostomy. Functional inspiratory pharyngeal closure was demonstrated fluorographically in one patient. Infants with Down syndrome may be predisposed to upper airway obstruction by virtue of hypoplasia of facial and oropharyngeal structures and generalized hypotonia. Additional obstructive elements may be contributed by hypertrophied lymphoid tissue, excessive secretions, and glossoptosis. Removal of the obstructive element is helpful, but functional obstruction may only be relieved by tracheostomy.

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Periodic apnea and exercise hypoventilation were observed in a 14-year-old boy. Hyperphagia, obesity, serum hyperosmolality without diabetes insipidus or appropriate thirst, and retardation of growth and sexual development indicated a hypothalamic disorder. Neurologic evaluation was normal except for electroencephalographic changes induced by apnea. Pulmonary function tests, resting arterial blood gases in the wakeful state, and ventilatory response to inhaled CO2 were also normal. Acute hypoxemia and respiratory acidosis occurred with apnea during sleep and with insufficient ventilation during exercise. The central origin of sleep apneas was shown by esophageal pressure monitoring. The hypothalamic dysfunction and exercise hypoventilation distinguish this patient from others with obesity and periodic apnea.