PHYSIOLOGICAL ASPECTS OK FLYING 201 



by way of the Eustachian tubes. For this reason the 

 Eustachian tubes of every aviator should be clear and 

 uncongested. This applies equally to both tubes, for, 

 if one be free and the other blocked, dangerous 

 symptoms due to changes of pressure may arise. It 

 is important, therefore, that every flying officer shall 

 be taught the correct procedure by which to equalize 

 the pressure on either side of the tympanic membrane 

 both during ascent and during descent. 



During ascent the pressure through the Eustachian 

 tubes may be diminished by forcibly swallowing, 

 when a clicking should be heard in both ears, or, 

 better still, by the first stages of a yawning move- 

 ment. 



During descent, particularly if very sudden, the 

 pressure within the Eustachian tubes may be increased 

 by holding the nose and gently insufflating by a 

 blowing-up movement, when a clicking should be 

 heard in both ears. 



A certain degree of discomfort may also arise as 

 a result of alterations in pressure upon the air con- 

 tained in cavities associated with the upper part of 

 the nose, such as the frontal sinuses. If the passages 

 connecting these with the nose be congested, pain 

 and discomfort may be experienced in the region of 

 the lower forehead. 



With these exceptions the effects of altitude are due 

 to diminished oxygen tension and not to pressure, 

 and it is obvious that the first thing required in any 

 flier is that he shall be able to withstand the strain 

 of frequently-repeated exposure to an atmosphere in 

 which the oxygen is progressively diminishing as the 

 height increases. Especial attention, therefore, is 

 devoted to this point in the selection of the flying 

 officer. By ordinary clinical examination it is deter- 

 mined that his lungs are sound and healthy, and an 



