shows an extreme example of probable contamination of the sensor by condensation, mucus deposition, or fingers partially obstructing the sensor. The FVC in curve 8 is 2.29 L larger than the FVC in curve 7, suggesting that the sensor was grossly contaminated by condensation or mucus deposition after the seventh maneuver. (The lead author has produced similar patterns experimentally, by slightly dampening the resistance element with water drops.) When the resistance element is partially blocked, the pressure drops measured across the resistance element throughout the expiration are greatly increased. These large pressure drops correspond to high flows, which when integrated, yield the large volumes seen in Figure 3. The peak expiratory flow (PEF) is 15.9 L/s, which exceeds the ATS instrumentation limit of 14 L/s for accurate flow measurement.4 This very large PEF causes the flow-volume curve to exceed the scale, a characteristic that is not uncommon with moisture and sensor-blockage problems. However, a smaller person could have an inflated PEF that would not exceed the scale, making the problem more difficult to recognize. Finally, the PEF, FVC, and FEV1 are all 130 to 170% of predicted, which is the range that we have seen for many blocked-sensor problems.