DETERMINATIONS OF PHYSIOLOGICAL DEAD-SPACE AND ALVEOLO-ARTERIAL OXYGEN GRADIENTS BY THE INDIRECT METHODS OF RILEY AND ENGHOFF II. STUDIES IN PATIENTS WITH CLINICAL RADIOLOGICAL AND SPIROMETRIC EVIDENCE OF PULMONARY EMPHYSEMA AND FIBROSIS.

Journal/Book: Reprint from The Scandinavian Journal of Clinical & Laboratory Investigation. 1962. Vol. 14 No. 5.. 1962;

Abstract: From the Department of Chest Diseases Rikshospitalet Oslo Norway Received for publication March 20 1962. CONCLUSION AND SUMMARY (A-a)O2i gradients and physiological deadspace determined by the indirect methods of Riley and Enghoff bear a close enough relation to mean (A-a)O2i gradients and true physiological dead space i. e. Anatomical + alveolar dead space to be substituted for these concepts in the clinical evaluation of patients with pulmonary disease. Such determinations are of value in analysing the character of the pulmonary failure in the inhomogeneous group of cases diagnosed as pumonary fibrosis by clinical-radiological-spirometric criteria. A normal (A-a)O2i gradient is found in many cases diagnosed as pulmonary fibrosis by these criteria thus indicating that a measurable alveolar-capillary block is not always present in these cases. On the other hand determinations of (A-a)O2i gradients may provide evidence of alveolar-capillary block in cases where clinical radiological and spirometric evidence of fibrosis are absent. The subjective complaint of dyspne does not in cases of fibrosis always correlate well with the magnitude of the (A-a)O2i gradients. Since uneven distribution of ventilation-perfusion in some cases may enlarge the (A-a)O2i gradient without demonstrable effect an the VDiX100/VT ratio such determinations do not always differentiate between fibrosis and emphysema even if an enlargement of the VDiX100/VT ratio probably indicates that emphysema is present. For clinical purposes determinations of (A-a)O2i gradients and VDiX100 VT ratios provide a fairly good estimate of the impairment of the respiratory function caused by uneven distribution of ventilation-perfusion in cases of pulmonary emphysema. It should however be stressed that both (A-a)O2i and VDiX100/VT must measured to obtain an assay of uneven distribution of ventilation perfusion and that other methods will have to be developed for an exact quantitative assay of the variance of the ventilation-perfusion ratios. ___MH

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