1. We have examined the effects of (a) reducing the density of the inspired gas and of (b) increasing inspired oxygen concentration on the exercise performance of eight men with chronic obstructive bronchitis (COB).2. Each subject performed two types of exercise test breathing three different gas mixtures: air, 35% oxygen in nitrogen and 21% oxygen in helium. The exercise capacity, ventilation and heart rate were recorded. Indices of pulmonary mechanics were measured to determine where and how any change in ventilatory capacity might have been achieved.3. (a) Effort tolerance at a constant load (70% capacity breathing air) was greater when the inspired gas mixture was 35% oxygen in nitrogen than when air or 21 % oxygen in helium was breathed.(b) Peak expiratory flow (PEF) was greater when the helium mixture was breathed, but the forced expiratory volume in 1 s (FEV,) and maximum expiratory flow at 50% vital capacity (MEFSOX) were the same as when breathing air. Effort tolerance was the same breathing the helium mixture and air in both the progressive and constant load tests.(c) PEF, FEV and MEF5O% were greater immediately after than before exercise on all gas mixtures. 4. It is concluded that a reduction in the density of the inspired gas does not improve effort tolerance in patients with COB. Possible reasons for this lack of benefit are discussed.In normal subjects it has been shown that a reduction in the density of the inspired gas results in an increased ventilatory capacity (Miles, 1957;Maio & Farhi, 1967), and a reduction in oxygen consumption at a given level of exercise (Murphy, Clark, Buckingham & Young, 1969).
. (1974). Thorax, 29,[394][395][396][397][398][399][400]. Bronchial and extrabronchial factors in chronic airflow obstruction. Chronic airflow obstruction may be due either to disease of the airway wall and lumen or to loss of airway-distending forces acting on the outer wall of the bronchus. In 17 patients with chronic airflow obstruction the relative importance of bronchial and extrabronchial factors was assessed by analysing the relation between airways conductance and static transpulmonary pressure over a range oflung volumes. Using previously established clinical, radiological, and functional criteria (which did not include measurements of the mechanical properties of the lungs), six of these patients had evidence of widespread emphysema and six patients had predominant 'bronchial' disease. In four of the six 'emphysematous' patients there was no functional evidence of disease of the bronchial wall or lumen during quiet breathing, and airway narrowing could be explained by loss of airway-distending forces. The six patients with characteristic 'bronchial' features showed functional evidence of disease of the bronchial wall or lumen.In 1955 Domhorst described two contrasting types of patient with chronic irreversible airways obstruction-the first characterized by disabling breathlessness without cyanosis or tendency to heart failure ('pink and puffing') and the second in whom the clinical picture was dominated by cyanosis and recurrent right heart failure ('blue and bloated'). Subsequently numerous clinical and physiological studies have confirmed this broad distinction
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