Sir.—In addition to measuring oxygen saturation noninvasively, the Nellcor N-100 pulse oximeter (Nellcor Inc, Hayward, Calif) also gives a qualitative display of the pulse amplitude of the vascular bed underlying the probe. This is displayed on the front of the monitor as a vertical 16-segment light-emitting diode (LED) post. This feature of the pulse oximeter may be useful in detecting and monitoring pulsus paradoxus, an exaggeration of the normal reduction in pulse pressure on inspiration, which is an important index of small airway obstruction during an acute asthmatic attack.
Patient Report.—While using the Nellcor N-100 pulse oximeter in a 12-year-old boy in severe status asthmaticus, alternating decreases and increases in the LED pulse post of the pulse oximeter were observed in association with inspiration and expiration, respectively. The LED postexcursion decreased to one to two segments on inspiration but rose to ten segments on expiration. The pulse