restrictive physiology

Restrictive physiology describes lungs that cannot expand to their normal size, as if they were wrapped in a tight, stiff jacket. The problem is not getting air out, as in obstructive disease, but getting enough air in. Each breath is limited because the lung or chest wall resists stretching, so the total amount of air the lungs can hold is reduced.

On breathing tests this shows up as low lung volumes, particularly a reduced total lung capacity and vital capacity. Unlike obstruction, the FEV1/FVC ratio is usually normal or even high, because air flows out briskly from the smaller volume. The flow–volume loop looks tall and narrow, a miniature of the normal shape.

Two broad mechanisms produce restriction. The lung itself can be stiff and scarred, as in interstitial lung disease, which also lowers gas transfer. Alternatively the lung can be healthy but squeezed by problems outside it, such as obesity, chest-wall deformity, pleural disease, or weak respiratory muscles, in which case gas transfer is often preserved.

Recognizing a restrictive pattern is a starting point rather than a diagnosis, since the underlying cause must still be found. Pairing the lung volumes with the diffusing capacity helps separate intrinsic lung scarring from purely mechanical, extrapulmonary causes.