Determinants of Respiratory Function in Boy and Girl Twins

The functional dimensions of the lung, including the ventilatory capacity, the lung volume, the gas transfer factor and its subdivisions, are positively correlated with stature and other indices of body size. In adults the function declines with age from about 25 years; before this, after allowing for stature, age does not contribute significantly to the overall variability. For a given stature the vital capacity is less in females than in males, and compared with people of European descent is less in most other ethnic groups. The evidence is reviewed elsewhere ( Cotes, 1975 ). It demonstrates unequivocally that lung function is largely genetically determined. In addition, for ventilatory capacity Higgins and Keller (1975 ) have shown a family resemblance between fathers and sons, and between mothers and daughters; however, little is known of the mechanisms, including the possible role of factors which are correlated with the cardiac frequency response to exercise. This is of practical importance since the frequency response also reflects the state of training of the cardiorespiratory apparatus and, in some studies is negatively correlated with the functional dimensions of the lung (e.g. Cotes, 1976 ; Miller, Gilson and Saunders, 1976). The conclusion from the latter studies that a high level of habitual activity during adolescence has a beneficial effect upon the lung might be in error if there are other genetic effects which have not been taken into account. To illuminate this problem, measurements of lung function and the cardiac frequency response to exercise have been made on boy and girl twins.