The interrelationship between alveolar ventilation and PaC02 is as follows: which means

living in the planes but blood pH is normal (iv) they show less response to hypoxia. However, sometimes these compensatory mechanisms may break down in isolated individuals and give rise to serious symptoms (Monge's disease ) Some glaring examples of acclimatization Acclimatized persons and persons who are born and have grown up on high mountain peaks, carry on their daily activities and engage in spoils and other strenuous work like their counterparts at sea level. Some examples are given: (1) Permanent residents at very high altitude, like the residents of Peruvian altitudes (15,000 ft) participate regularly in tough sports like football. At this altitude PI02 is about 90 mm Hg only. (2) In 1962 an armed clash developed between India and China over the Himalayan mountains Indian soldiers failed very badly and suffered seriously from high altitude sickness; after this Indian Military Administration took up the problem of high altitude sickness, imparted rigorous training to acclimatize India's mountain divisions. Subsequently in 1965 an Western journalist was so fascinated with the ease with which the Indian soldiers were in very high peaks, that he likened them with mountain goats. In 1984, the Indian mountain soldiers, stationed atSiachen of Ladakh (altitude 19000 ft = about 5.7 km) had to repulse the enemy (Pakistan soldiers) repeatedly and gave a very good account of themselves. This, therefore, shows that even at that altitude, not only survival but also fighting is possible by an acclimatized person. 'Adult (respiratory distress syndrome'ARDS ) is a condition characterized by low Pa02 and low PaC02 (cf. high altitude sickness). A very large number of diseases and environmental hazards can ultimately lead to ARDS. The mortality of ARDS, if not treated properly is very high; diseases which can lead to ARDS, include, (i) inhalation of injurious gases/smokes (ii) overdose of heroin/morphine (iii) several viral diseases of the lung (iv) aspiration of gastric content into the lung and so on The cause of tram of symptoms (and signs) of ARDS is 'a form of pulmonary edema'. As a result of challenge by one of the causes mentioned above, neutrophils appear in heavy number in the lung alveoli. These neutrophils release various substances like prostaglandms (AAM, see chap 4 sec II), thrombaxane and so on. Recall (chap 4 sec II, 'functions of the neutrophils' and 'inflammation' ) these are the materials which produce inflammation in any part of the body. As a result of these merchants of inflammation, the endothehal walls of the pulmonary capillary develop increased permeability fluid escapes into the alveoli. This is what is meant by a form of pulmonary edema. [Note that in left ventricular failure, 'If, also, pulmonary edema develops. But in 'If, there is increased hydrostatic pressure within the pulmonary capillaries (due to the accumulation of blood in the left heart) and this causes pulmonary edema - and this is the classical form of pulmonary edema]. Presence of pulmonary edema causes two important changes, viz, (i) it hampers the it opposes theactiongaseous exchange and introduces alveolocapillary block and (ii) it opposes the action of surfactant (recall surfactant reduces the surface tension within the alveoli). The increased surface tension and the pulmonary edematous fluid, both, reduce the compliance of the lung. Reduction of the compliance and the alveolocapillary block together result in lowered Pa02 (= arterial hypoxia = hypoxic hypoxia). C02 diffusivity is not hampered and because of the increased respiratory drive due to hypoxia (hyperventilation), the PaC02 falls. [Note, that in 'hyaline membrane disease (chap 2 sec IV), which is also called respiratory distress syndrome (RDS) of the new bprn,'the primary fault is a deficiency of surfactant which in turn causes (i) collapse of the alveoli and (ii) pulmonary edema. In ARDS, there is loss of surfactant no doubt, but this loss (of'surfactant) is secondary]. HYPERCAPNIA This means excessive C02 concentration in blood. The term "C02 retention" may be used alternatively. Ultimately this leads to "C02 narcosis'". A common cause is hypoventilation. The sequence of events is as follows: Hypoventilation [which may be due to such causes like poisoning by drugs (morphine /barbiturates) or lesions in the brain (hemorrhage)] fall of alveolar ventilation C02 retention. The interrelationship between alveolar ventilation and PaC02 is as follows: which means, where the alveolar ventilation is reduced, the PaC02 rises. As PaC02 is practically equal to the PaC02, reduction of alveolar ventilation causes elevation of PaC02. Hypoventilation therefore causes elevation of PaC02 . Officially speaking reduction of alveolar ventilation should concomitantly produce reduction of Pa02; however mspite of the fall of Pa02, it usually remains sufficiently high so that cyanosis does not appea and clinically therefore, overt symptoms of hypoventilation are primarily due to C02 retention. Pickwickian syndrome" is another condition characterized by C02 retention due to alveolar hypoventilation. Its victims are usually young males who are very fat ['fat boy of (Charles) Dickens', the English Novelist of 19th century, who created such a character in his "Pickwick Papers", wherefrom the name has come] and show a high PaC02 level although the cause of hypoventilation is not known; there are however, some evidences of pituitary hypofunctioning in most of these cases. Therapeutically progesterone administration improves these patients. Even in normal sleep there is some hypoventilation