SESSION TITLE: Physiology/PFTs/Rehabilitation Posters
SESSION TYPE: Original Investigation Poster
PRESENTED ON: Wednesday, October 30, 2013 at 01:30 PM - 02:30 PM
PURPOSE: In 1972, Pontoppidan et al published a computer-generated plot of arterial oxygen tension (paO2) versus percentage shunt (N Engl J Med 1972; 287: 743-752) for multiple values of alveolar oxygen tension (pAO2). In their graphic, the “shunt” figure represents the level of shunting that would exist if Ventilation/Perfusion (V/Q) mismatching were completely absent. It is widely recognized that patients suffering from Chronic Obstructive Pulmonary Disease (COPD) typically exhibit significant hypoxemia during air breathing. In addition, V/Q mismatching, as opposed to shunting, is generally acknowledged to be the principal cause of hypoxemia for COPD patients in the face of air breathing.
METHODS: After the manner of Pontoppidan and co-workers, we chose to depict the typical response of COPD patients to an increase in FIO2 diagrammatically. In lieu of the family of (twelve) pAO2 isopleths which were incorporated in the Figure of Pontoppidan and colleagues, we chose to incorporate only two computer-generated isopleths in the diagram (below), referable to the administration of air and of 100% oxygen. The paO2 values (50 torr and 540 torr) depicted in the Figure correspond to those observed in an actual COPD patient breathing air and pure oxygen, respectively.
RESULTS: Inspection of the Figure reveals that a reduction in Equivalent Shunt from 32% to 6% would be compatible with the parameters listed under the heading of “Assumptions”. The dramatic decrease in the Equivalent Shunt values, to a level which is virtually normal, in the wake of oxygen administration, constitutes a veritable signature for the presence of COPD and V/Q mismatching for patients who exhibit profound desaturation during air breathing.
CONCLUSIONS: Hence, oxygen administration proves to be, at one and the same time, an ideal strategy to both diagnose and treat V/Q mismatching.
CLINICAL IMPLICATIONS: Profound desaturation during air breathing is a sensitive indicator for lung pathology, but is, regrettably, non-specific, and could be compatible with COPD, Acute Lung Injury (ALI) or Congestive Heart Failure (CHF). The subsequent delivery of oxygen confers the specificity needed to discriminate between these etiologies.
DISCLOSURE: The following authors have nothing to disclose: Robert Demers, Wayne Wallace
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