'n Nie-indringende benadering tot pulmonere hemodinamika
The original publication is available at http://www.samj.org.za
Currently available investigative methods employed in the evaluation of the pulmonary circulation involve cardiac catheterization and, in respect of exercise determinations, only supine data have been recorded. Consequent upon a 3-year study of pulmonary haemodynamics and gas exchange at rest and during exercise on the treadmill in patients with chronic hypoxaemic lung disease, correlations have been established which accurately characterize the venous admixture (Q(VA)/Q(t), the quantitative expression of hypoxaemia), cardiac output and pulmonary artery pressure (PA), permitting the prediction of these variables in the erect posture. The employment of fibre-optic oximetry obviates the need for arterial cannulation. The relevant regression formulae are as follows: Q(VA/Q(t) = 8,85 x In (Hb (100 - SaO2) x heart rate/VO2 - 3,66 (r = 0.97; SEE = 2,43) PA(m) (resting) = 0,4516 (Q(VA/Q(t)) + 8,2 (r = 0,90; SEE = 2,7) PA(m) (exercise) = 1,453 (Q(VA)/Q(t)) + 3,8 (r = 0,96; SEE = 4,0) Cardiac output may be derived directly from VO2 and the known components of Q(VA)/Q(t), and total pulmonary vascular resistance in turn from Qt and PAm. Direct comparison of the predicted values derived by this means with actual determinations yielded no systematic differences. The clinical application of these principles ensures reliable estimates of haemodynamic variables, without resort to invasive techniques, during free movement and graded exercise testing.