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The developmental aspects of sleep and breathing are rarely treated as one subject. This report attempts to link the fields of sleep research and developmental pulmonology in a comprehensive description of development and control of sleep and breathing from gestation to adulthood. Unfortunately, much of the investigation in this area is basic physiology and was done some time ago. Although this subject matter need not be updated, some of these references are older; however, this may be new information for the pulmonologist. The second part of this report details the pathophysiologic mechanisms behind the development of sleep-disordered breathing in children and adults. In fact, developmental abnormalities that occur in childhood may recrudesce in adulthood. We conclude with a discussion of the familial and genetic aspects of sleep-disordered breathing and consider the place of sudden infant death syndrome in the spectrum of these disorders.

The terminal differentiation of myelinating glia involves complex interactions that culminate in the formation of myelin. The POU domain transcription factor Tst-1/Oct-6/SCIP is expressed transiently during myelination, and we report here that it has a critical role in this developmental process. Deletion of the Tst-1/Oct-6/SCIP gene produces a severe defect in peripheral myelination by arresting Schwann cell maturation before axonal wrapping. Unexpectedly, the activation of major myelin-specific genes appears to be unaffected by the Tst-1/Oct-6/SCIP mutation, demonstrating that multiple, independently regulated events are required for terminal differentiation of Schwann cells. In addition, aberrant differentiation and migration of specific neurons in Tst-1/Oct-6/SCIP mutant homozygotes is associated with a fatal breathing defect, providing a model for investigating the regulation of pulmonary homeostasis.

To better understand behavioural and genetic influences upon breathing, the breathing patterns of 8 pairs of monozygous (MZ) twins were measured under 4 behavioural conditions; relaxed without standardisation; eyes closed; eyes open; and reading. Breathing was quantified by inspiratory and expiratory durations (TI, TE), tidal volume (VT) and derived variables. Airflow shape was normalised and quantified using 8 dimensions. Reading caused breathing to increase by > 500 ml/min compared to the other four conditions. Differences in breathing between combinations of two conditions were compared by testing whether the differences within an individual were smaller than the differences between random pairs of individuals from the same 16 subjects. For almost all respiratory variables, and whatever the behavioural condition, there were highly significant similarities within an individual (p < 0.00025 on 32/80 comparisons). Under each condition, the differences within MZ twin-pairs were compared to the differences within random-pairs from the same subject population. There were highly significant similarities within twin-pairs for the airflow shape across all conditions. However, TI, TE and VT failed to consistently show significant similarities within twin pairs. Hence, an individual's airflow shape appears to be a fundamental characteristic which is conserved when behavioural condition and level of ventilation changes. Further, MZ twins have similar airflow shapes--whatever the behavioural situation. Hence, behavioural influences upon airflow shape act upon monozygous twin pairs in similar ways, or such influences were negligible under the conditions of the present study.

Familial aggregation of ventilatory function has been described in several populations, but the effects of age and cigarette smoking on the extent of aggregation have not been well characterized. We used data from a survey of a Hispanic population in New Mexico to obtain estimates of heritability for FVC and FEV1 as percentages of predicted value. Product-moment correlations for FVC of spouse pairs were 0.18 (n = 90 pairs) if neither smoked, 0.013 (n = 45 pairs) if only the wife smoked, 0.18 (n = 118 pairs) if only the husband smoked, and -0.04 (n = 83 pairs) if both smoked. Correlations for FEV1 of spouse pairs were similar. Because parent-child correlations did not vary with sex, we calculated product-moment correlations from the pooled data. The parent-child correlations for nonsmoking parents with nonsmoking children 6 to 17 yr of age and living in the same house were 0.16 (n = 335 pairs) and 0.17 for FVC and FEV1, respectively. For parents whose children were 25 yr of age or older, the parent-child correlations for those living in different houses were 0.37 (n = 63 pairs) for FVC and 0.40 for FEV1 if neither smoked, and 0.24 (n = 27 pairs) for FVC and 0.14 for FEV1 if both smoked. Heritability estimates, estimated by path analysis, were 0.43 for FVC and 0.42 for FEV1 if neither family member smoked and 0.65 for FVC and 0.44 for FEV1 if both family members smoked. We conclude that there is a moderate degree of heritability of FVC and FEV1 with no substantial change based on age or smoking status.

Burrowing mammals often demonstrate structural and functional characteristics which could be interpreted as aspects of adaptation to the low PO2 and high PCO2 of their environment. Whether these characteristics are acquired by each individual as the result of life in the burrow or are genetic traits established through evolution is not clear. To examine the latter possibility aspects of ventilatory control were studied in newborns and adults of two rodents, the surface dwelling white rat (Rattus norvegicus, R) and the semifossorial syrian hamster (Mesocricetus auratus, H), both born and raised in normoxia. Adult H, but not R, manifested the burrowing preference whenever offered the opportunity. Adult H presented numerous differences from the adult R, including a higher normoxic oxygen consumption (VO2, +44%), higher hematocrit and heavier right heart. Ventilation (VE) was similar between the two species both in air and hyperoxia, although H had a deeper and slower pattern. Hence, resting VE/VO2 in H was low, probably contributing to the hypoxemia reported in this species. The acute ventilatory response to hypoxia (10 min 10% FIO2), was less in H, because of no increase in tidal volume. Most of the morphological and functional differences between adult hamsters and rats were not apparent between the newborns of the corresponding species. It is concluded that some of the physiological characteristics reported in burrowing species are also observed in adult hamsters which never lived in burrows, but not in the newborns; hence, they could represent genetic traits which are expressed postnatally with no needs of the special environmental conditions of the burrow.

A coordinated field and chamber experiment assessed breed, sire, and cow differences in body temperatures and respiratory rates. During each of 4 yr, 10 lactating Ayrshire, Guernsey, Holstein, and Jersey cows, 40 animals per yr, were observed in the field on 10 d when the air temperature approached 32 degrees C. For the first 3 yr, each cow also was exposed in a controlled atmospheric chamber at 40 degrees C and 34 mm Hg vapor pressure. Significant breed differences were found for body temperature and respiratory rate. The order of tolerance to hot conditions was Jersey, Guernsey, Ayrshire, and Holstein both in the field and chamber. Significant sire differences, interpreted as genetic, were found for the field measures but not in the chamber. Repeatability of individual field observations for a cow on different days in a year ranged from .38 to .55. Correlations between the average of 10 observations for a cow in the field during a year and the chamber evaluation were positive but lower than the repeatability values. Correlations of ambient temperature with body temperatures and respiratory rates were highest; those for radiation were next, followed by vapor pressure and air movement.

The genetic-statistical analysis of 11 variables of the external respiration has been made in 90 twin pairs of the same sex divided into two age groups: 20-44 and 45-80 years. The following classification of indices of the lung ventilation function can be suggested: with high hereditary coefficients that remain unchanged with age, with low coefficients gamma 2 that are the same in both age groups, with increasing hereditary coefficients in aging, and with the high Ignatiev-Jensen criteria in the group of people aged 20-44 and declining ones in the group aged 45-80. The last group of ventilation variables is the largest. In the group aged 20-44 a test with oxygen inhalation increases the effect of environmental factors whereas in the group aged 45-80 it decreases this effect on the indices of the lung ventilation.

To test the hypothesis that there is genetic control of pulmonary function parameters independent of that influencing height, we evaluated 74 pairs of asymptomatic, nonsmoking twins. FVC, FEV1, FEF25-75%, TLCsb, RVsb, Dsb, and D/VA were measured. Pulmonary function indices were adjusted for height using simple linear regression. Mean intrapair differences (unadjusted and adjusted for height) were compared using t tests of independent samples. Within pair, Holzinger's, and Falconer's heritability estimates were calculated using height-adjusted residual values. When total variances of a function parameter were statistically different between monozygotes and dizygotes, the among component heritability estimate was calculated and used as the best indicator of heritability. Following adjustment for height, no measure of pulmonary function which satisfied the requirements of the analysis was found to be significantly heritable.