Mechanical Aspects of the First Breath

¹ From the Istituto di Fisiologia Umana, Università di Milano, Milano, Italy

The mechanical features of the first breath have been studied on mature fetuses of the guinea pig, cat and goat. The first inspiration encounters a marked resistance due a) to the high viscosity of the liquid present in the airways, b) to the surface tension of the air-liquid interphase and c) to the fact that the expansion of the thorax is accomplished only by the inspiratory muscles and is not appreciably facilitated, as in the adult, by the tendency of the thorax to expand due to elastic forces. Because of these factors the first inspiration may not fulfill its practical purpose and many breaths are necessary before all the liquid is removed and the lung completely aerated. The mechanical features of the lung at birth are similar to those of the adult with regard both to the pressure-volume curves and to hysteresis.

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				G. Polgar Basic Science Review : The First Breath: A Turbulent Period of Physiologic Adjustment Clinical Pediatrics, October 1, 1963; 2(10): 562 - 571. [PDF]