Which of the following factors can cause falsely low pulse oximetry measurements?

Falsely low pulse oximetry measurements can occur due to a variety of factors, and one notable cause is the vascular injection of indigo carmine. Indigo carmine is a dye that can interfere with the optical measurement of oxygen saturation by the pulse oximeter. This dye absorbs light in a manner similar to hemoglobin, which can skew the readings and lead to inaccurate assessments of a patient's oxygen saturation levels.

In contrast, the other options listed do not typically lead to falsely low pulse oximetry readings. Deep vein thrombosis primarily affects blood flow and does not directly impact the accuracy of pulse oximetry. Increased heart rate can influence circulation but does not interfere with the measurement tool itself. Elevated blood pressure also does not directly alter pulse oximeter readings, as this device primarily measures the absorption of light through oxygenated and deoxygenated hemoglobin in the blood rather than being affected by pressure variations.

Thus, understanding the properties of substances like indigo carmine and their interactions with light absorption in respiratory monitoring devices is critical for accurate interpretation of pulse oximetry results.