The effect of heart disease on pulmonary function

Abstract

SummaryIn pulmonary congestion dyspnoea is due not only to an increase in elastic but also in viscous work. Increased airway resistance can be reduced in most of these cases by inhalation of adrenergic or anticholinergic agents. Therefore, besides bronchial mucosal swelling induced by congestion in the bronchial vessels via bronchopulmonary anastomoses, bronchospasm can take place and lead to cardiac asthma. The possible genesis of this bronchoconstriction is discussed.THE close relationship between cardiac and respiratory function is apparent since cardiac and pulmonary disorders can lead to the same symptom, namely dyspnoea. Heart diseases with impaired blood drainage from the lung show effects similar to the bronchopneumopathies but the extent to which pulmonary congestion affects respiratory mechanics has not been determined.The cardiovascular system and the lung are one functional unit. The heart is an auxiliary organ for respiration in that it is the machine which renders the respiratory function of the lung effective in the peripheral areas of the body. The pulmonary circulation is perfused by the same blood flow volume as the systemic circulation; however, it differs in essential aspects from the latter.The mean pressure in the pulmonary artery is normally approximately one-sixth of the mean arterial pressure in the systemic circulation, and the resistance in the pulmonary circulation is approximately one-tenth of that in the systemic circulation. There are no valves in the pulmonary veins; this fact is of particular importance in connection with pulmonary hypertension in left venticular failure or mitral stenosis. If the blood from the lung is prevented from draining, the pulmonary arterial pressure is increased as a consequence of the increased pulmonary venous pressure. By contrast, in the systemic circulation a venous drainage block of the right atrium does not have any noteworthy effect on arterial blood pressure. Whereas the majority of arterial hypertensions are so-called essential hypertensions, pulmonary hypertension is almost exclusively secondary to a heart or lung disorder. Only the consequences of blood drainage impairments secondary to heart disease will be considered in this paper.Because of its low-pressure system the pulmonary circulation is more dependent upon external influences than the systemic circulation. Two factors are important for the distribution of blood in the lung.As early as 1934, Bjdrkman showed by means of bronchospirometry that when a person lies on his side there is a considerable increase in pulmonary blood flow in the lower side (Bjbrkman, 1934). In 1953, Martin, Cline and Marshall found by means of gas analyses from various bronchi a decrease in the ventilation-perfusion ratio from top to bottom when the body was in an upright position and hence a relatively increased blood flow in the base of the lung (Martin, Cline and Marshall, 1953). This was later confirmed by West and Dollery (1960) using a radioactive tracer. When pulmonary blood flow is increased, i.e. durin...