COR PULMONALE

Heart failure secondary to respiratory disease deserves special consideration, since it differs from heart failure of conventional pattern not only in the under¬lying physiological derangements but in its treatment. In this country cor pulmonale is in the vast majority of instances secondary to chronic bronchitis and emphysema . The very high prevalence of chronic bronchitis in these islands has led to its being named as " the English disease ", and it has largely displaced rickets from this soubriquet in the literature of our continental colleagues. In a comparatively small proportion of cases cor pulmonale develops as a sequel to other diseases of the lungs such as pulmonary fibrosis and pneu-moconiosis, and lesions with infiltration or destruction of the lungs, for example by lymph-spread carcinomatosis, sarcoidosis or infiltration by Hodgkin tissue.
In countries where schistosomiasis is endemic a form of cor pulmonale secondary to infection of the lungs by that worm is prevalent.
While chronic bronchitis and emphysema lead over the course of years to progressive limitation of effort, congestive heart failure is a late event in their course, occurring after many years of winter cough as episodes of cardiac failure precipitated by acute respiratory infections. Contrary to traditional teaching, the progressive destruction of the pulmonary vascular bed in emphy¬sema produces little continuing burden on the right heart, and in fact no appreciable rise in the resting pulmonary arterial pressure occurs in the uncom¬plicated case. This is related to the enormous capacity of the normal pulmonary vascular bed and the great reserve area of respiratory epithelium available in health. However, when such a predisposed person develops an acute infection particularly capillary bronchitis or bronchopneumonia with patchy atelectasis, the resultant anoxia leads to a steep rise in the pulmonary arterial pressure which in turn places a considerable load on the right ventricle. Bronchospasm and " air-trapping " add to the anoxia. Then cardiac failure tends to develop rapidly, and such patients are commonly in desperate straits, with gross oedema, venous engorgement in the neck and enlargement of the liver ; owing to their anoxia they are cyanosed, and the cyanosis may be intensified by the polycy-thasmia which commonly accompanies emphysema. The clinical picture differs from that of heart failure resulting from valvular or ischasmic heart disease in that warm flushed hands and extremities are characteristic, the pulse is bounding and of full volume and a regular heart action is the rule, atrial fibrillation being uncommon. This clinical picture of a hyperkinetic circulation is related to the raised cardiac output which has been demonstrated in such patients. The cardiac output, despite the presence of congestive failure, may in fact be two or three times that of the average normal patient at rest, so that the condition falls into the group of " high-output failure ". In some patients, however, far advanced in the course of their illness, the cardiac output falls and the peripheral coldness and small pulse of conventional cardiac failure may develop with the low-output state. Superimposed on the cardiovascular symptoms are those of hypercapnia affecting the central nervous system.
In patients with a " high-output failure " digitalis is in general disappointing, and lacks much of the efficiency which it displays in conventional cardiac failure. Some years ago its use was considered to be contraindicated on theoretical grounds, since the high venous pressure in such cases is necessary for the maintenance of the high output which is in its turn necessitated by the anoxia. It is, however, clear that digitalis has a place in the treatment of failure due to cor pulmonale, though its use must be tempered with caution.
Since the failure is usually precipitated by anoxia, infection and broncho-spasm, the prime need is treatment for those factors. The administration of suitable antibiotics is the first step and such treatment should be vigorous.
The oxygen saturation of the arterial blood in patients in this state can fall to levels as low as 65 or 70 per cent., comparable to those in the mixed venous blood of a normal person, and clearly the relief of anoxia is of paramount importance. The administration of oxygen, however, has to be cautious, since precipitate exposure of the patient to high oxygen concentrations may lead to serious consequences. Every doctor and every nurse in charge of patients should be aware of this curious therapeutic paradox, whereby a blue conscious dyspneic patient when placed in an oxygen tent may rapidly become pink and comatose. If oxygen administration is continued in such a case the patient will die. The explanation is that patients in this state are not only anoxic, but have hypercapnia, the partial pressure of carbon dioxide in the blood rising to a high level. At such levels of COa the respiratory centre becomes insensitive to its normal stimulus, and the patient's respiration is controlled by oxygen-lack. When this is relieved by giving oxygen the breathing becomes shallow, hyper¬capnia increases and the blood carbon dioxide rapidly mounts to a level which produces unconsciousness and, if unchecked leads to coma and death. The danger attendant on the administration of oxygen to such patients has led many to avoid giving it to them. This is clearly against their best interests, since such patients require oxygen desperately, and it is the duty of the doctor to administer it in such a manner that distress and anoxia are relieved without the hazards of hypercapnia. This can be done by giving the patient oxygen at a relatively low concentration (2 or 3 litres per minute) so that the anoxia is to some extent mitigated but the risk attendant on its complete relief avoided. In this event the patient must be kept under close observation by a skilled nurse so that with the development of drowsiness or even natural sleep the oxygen may be discontinued and the patient allowed to become anoxic and awake. One type of mask utilizes the Venturi principle to supply oxygen in a safe and effective range of concentration. The practice is all too widespread today of denying oxygen to such desperately anoxic patients on the basis of the dangers attendant on its use.
Many patients respond rapidly to the control of infection and of anoxia. The relief of bronchospasm and clearing of airways are highly important. Digitalization, if adopted, should be done gradually, the effect on the individual patient being closely watched. Diuretics are also of value and it is in this condition that acetazolamide can on occasion play a useful role, since under the existing condition of hypercapnia the substrate on which the carbonic anhydrase inhibitor acts is abundantly present.
The after-care of patients who have recovered from cardiac failure secondary to respiratory infection should be directed to the prevention of recurrences (p. 677). It is unhappily true, however, that the occurrence of heart failure of this type is commonly a sub-terminal event; few patients so affected survive more than two years after their first attack.