Which factor does not affect pulse oximetry readings?

Pulse oximetry is a non-invasive method used to measure the oxygen saturation of hemoglobin in the blood. Accuracy in these readings can be influenced by various factors.

Chronic exposure to nicotine primarily affects the blood's hemoglobin, potentially leading to higher carboxyhemoglobin levels, which could alter oxygen saturation measurements. However, it does not have a direct and uniform impact on pulse oximetry readings compared to the other factors listed. Patient movement can compromise accuracy due to motion artifacts, while fingernail polish, particularly darker colors, can obstruct the light sensor, leading to erroneous readings. Asthma medications may cause changes in respiratory function but do not inherently interfere with the technology used in measuring oxygen saturation through pulse oximetry.

In this context, the correct answer is that asthma medications do not directly affect pulse oximetry readings in the way that the other factors do, which leads to variability in the measurements.