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A decreased inspiratory capacity (IC)/total lung capacity (TLC) ratio is associated with dynamic hyperinflation and decreased exercise capacity. The present authors hypothesised that static (low IC/TLC) and dynamic hyperinflation impair cardiac function as assessed by oxygen pulse at rest and during cardiopulmonary exercise testing (CPET). Lung function, body mass index, hand grip strength and CPET parameters were measured (oxygen uptake (mL x kg(-1) x min(-1)) and oxygen pulse (mL x beat(-1))) in 87 chronic obstructive pulmonary disease (COPD) patients (American Thoracic Society/European Respiratory Society/Global Initiative for Chronic Obstructive Lung Disease stage 3-4) and 46 controls. The patients were divided into those with IC/TLC > 25% or < or = 25%. The IC/TLC ratio at rest and at peak exercise was associated significantly with oxygen pulse. Patients with IC/TLC < or = 25% (n = 45) had significantly lower exercise capacity, peak oxygen pulse, peak minus baseline oxygen pulse, peak IC, peak IC/TLC ratio and % change from baseline to peak IC/TLC ratio compared with patients with IC/TLC > 25% and controls. During CPET, the oxygen pulse was lower at iso-work in patients with IC/TLC < or = 25% than in those with IC/TLC > 25%. Resting hyperinflation (inspiratory capacity/total lung capacity) is associated with lower oxygen pulse, peak exercise inspiratory capacity/total lung capacity and exercise capacity in patients with severe chronic obstructive pulmonary disease. The present results support an interaction between hyperinflation and decreased cardiac function that may contribute to exercise limitation in these patients.

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Plasma renin activity has been measured by radioimmunoassay at frequent intervals after passive upright tilting and correlated with pulse and blood pressure in normotensive man. In the normal response to upright posture, renin activity in both peripheral and renal veins increases consistently within a few minutes. The renin rise lags behind the increase in pulse rate and diastolic blood pressure. Renin activity falls to base-line level soon after return to the horizontal position. In the 25% of normal subjects who develop vasovagal syncope after upright tilting, the increase in renin activity is smaller in magnitude and duration than in the normal response. Renin levels fall just before syncope appears and rise sharply after return to the horizontal position. Anephric patients are able to effect adequate postural adjustments even in the absence of renin activity. This study indicates that the renin angiotensin system participates in the acute response to postural change in normal man and that it functions abnormally in vasovagal syncope.