DYNAMICS OF PULMONARY CIRCULATION 



[72 1 



values at rest but that the increment in pulmonary 

 arterial pressure during exercise was still excessive for 

 the increment in blood flow. 



Penaloza et al. also found that young children (1-5 

 years of age), born and raised at altitude, had more 

 marked pulmonary hypertension (of the order of 

 58/32, 45 mm Hg) than older children (of the order 

 of 41/18, 28 mm Hg) and adults; in this respect, 

 the youngsters at altitude differed strikingly from 

 their counterparts at sea level who achieved normal 

 pulmonary arterial pressures during the third to sixth 

 month of life. 



Pulmonary hypertension and right ventricular en- 

 largement are characteristic not only of acclimatized 

 man but also of acclimatized cattle (199). Malaccli- 

 matization to altitude results in "mountain sickness," 

 both in man and in animals. Although mountain 

 sickness is not a distinct clinical entity, at least two 

 different types have been identified, i.e., "brisket 

 disease" in cattle and "seroche" in man (table 4); 

 both seem to originate in alveolar hypoventilation. 

 Seroche is manifested by polycythemia, easy fatiga- 

 bility, and respiratory distress during exertion; its 

 physiological hallmarks are severe hypoxemia, hyper- 

 capnia, polycythemia, and pulmonary hypertension 

 (9, 362). Removal of the native suffering from seroche 

 to sea level results in a prompt clinical improvement 

 and, within 2 months at sea level, in return of blood 

 gases, circulation, and respiration at rest to virtually 

 normal values except for a slight residual pulmonary 

 hypertension (Penaloza et al.). On the other hand, 

 the clinical picture of brisket disease is dominated by 

 the consequences of severe pulmonary hypertension 

 and cor pulmonale, i.e., by severe right ventricular 

 failure, functional tricuspid insufficiency, and de- 

 pendent edema of the brisket. Although the clinical 

 pictures of seroche and brisket disease overlap some- 



table 4. Chronic Mountain Sickness in Cattle and in Man* 



Cattle Man 



SYNONYM BRISKET DISEASE SEROCHE 



Altitude 8,000 to 1,200 ft. > 12,000 ft. 



Prepotent Pulmonary vaso- Severe hypoxemia 



mechanism constriction and hypercapnia 



Major conse- Severe pulmonary Polycythemia; mod- 



quences hypertension; erate pulmonary 



cor pulmonale hypertension 



Clinical Congestive heart CNS disturbances; 



disability failure lassitude, fatigue, 



dyspnea 



* Based on observations of Hecht et al. (199). 



what, hypoxemia and polycythemia are far less 

 striking in the animals than in man (table 4). 



At least part of the severe pulmonary hypertension 

 of brisket disease is attributable to the sphincteric 

 construction of the small precapillary pulmonary 

 vessels in cattle; presumably this anatomical arrange- 

 ment not only affords unusual intrinsic resistance to 

 blood flow but also effects an intense pulmonary 

 precapillary vasoconstriction in response to mild 

 hypoxia (199). It is not yet settled if postcapillary 

 events (left heart failure, constriction of the pulmonary 

 veins, or "throttles") are also involved in severe 

 brisket disease. 



Thick pulmonary precapillary vessels are also found 

 in native residents at high altitudes. Thus, the small 

 precapillary vessels are thicker than their counter- 

 parts at sea level and smooth muscle extends further 

 down the pulmonary vascular tree at altitude than at 

 sea level. This medial hypertrophy of the pulmonary 

 precapillary vessels suggests that the pulmonary 

 hypertension of man at altitude originates in morpho- 

 logic changes as well as in vasomotor activity (Arias- 

 Stella and Saldana, unpublished observations). 



Acute Hvperoxia 



Enrichment of the inspired air with oxygen, or the 

 substitution of 100 per cent oxygen for air, is without 

 appreciable effect on the normal pulmonary circula- 

 tion (132). This lack of effect is consistent with the 

 notion that the resistance vessels of the normal pulmo- 

 nary circulation — despite the normal unsaturation of 

 mixed venous blood — ordinarily have little "tone." 

 On the other hand, oxygen-rich mixtures have been 

 shown to partially relieve pulmonary hypertension of 

 chronically hypoxic and hypoxemic animals and man 

 (132, 164, 389). The effectiveness of oxygen-rich mix- 

 tures as pulmonary vasodilators in hypoxemic states 

 has led to the use of oxygen-rich mixtures to relax 

 hypertonic pulmonary vascular smooth muscle in 

 nonhypoxemic states. However, there is no apparent 

 reason to suspect that hvperoxia will dilate pulmo- 

 nary vessels which are not hypoxemic. 



Acute Hypercapnia 



At first encounter, the published accounts of the 

 effects of breathing 5 to 10 per cent C0 2 in air on the 

 pulmonary circulation are utterly confusing. Un- 

 doubtedly, part of the confusion arises from the failure 

 to take into account the peculiarities of the different 

 preparations and experimental conditions. The situa- 

 tion is improved by sorting the results according to 



