biqh altitude 



Fig. 18-10. There are several physical and chemical factors in the external environment that influence respiration. 

 Under normal atmospheric pressures (sea level) the gaseous exchange in the alveoli is adequate. At high alti- 

 tudes (beyond 14,000 feet) the air pressure is so reduced that an insufficient amount of oxygen passes into 

 the blood to maintain consciousness. In shock (a physiological response caused by serious lacerations or trauma) 

 the blood pressure drops so low in the alveoli that circulation is inadequate to pick up enough oxygen to main- 

 tain normal body activities, in the presence of carbon monoxide (CO) a stable compound (methemoglobin) is 

 formed in the blood, thus rendering hemoglobin incapable of carrying oxygen, if prolonged, breathing of CO 

 can be fatal. 



