The therapist is treating a 12-year-old boy who is experiencing an asthmatic attack. The therapist notices that the child's systolic pressure decreases about 15 mm Hg, and the pulse weakens during inspiration. Which of the following cardiovascular effects would the therapist expect to see after the patient is given heliox to breath via a non-rebreather mask?

A. No change would be expected.
B. The systolic pressure should decrease no more than 10 mm Hg, and the pulse should become stronger and increase during each inspiration.
C. The systolic pressure should decrease to more than 20 mm Hg, and the pulse should decrease during each inspiration.
D. The systolic pressure and the pulse should fluctuate during each inspiration.

ANS: B
A. Incorrect response: See explanation B.
B. Correct response: Normally during inspiration, systolic arterial blood pressure can decrease up to 10 mm Hg, and pulse increases to compensate. A greater decrease in systolic blood pressure or weakening of the pulse during inspiration is considered pulsus paradoxus. It occurs commonly in cardiac tamponade and severe asthma. Systolic pressure decreases during inspiration with severe asthma particularly because negative intrathoracic pressure increases venous return. A number of studies have shown that the administration of heliox to patients experiencing an asthma attack results in decreased work of breathing, decreased dyspnea, and significantly lower pulsus paradoxus.
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B.