Obstructive lung disease (especially status asthmaticus) can indeed cause pulsus paradoxus. The mechanism is probably lung hyperinflation, causing excessive inspiratory pooling of blood, and thus a greater drop in
systolic blood pressure. Since this form of pulsus paradoxus depends on respiratory rate and effort, it is
not a very sensitive indicator of severe bronchospasm (in fact, only half of status asthmaticus patients have a pulsus >10). It is, however, quite specific, with values >20 usually indicating FEV1 <0.5–0.7 L. Hence, it can serve as a “poor man’s” spirometer (or peak flow meter) for situations in which these devices are not
readily available