In this study, the level of methemoglobin (HbMet) will be increased in a controlled manner by administering sodium nitrite intravenously in healthy volunteers. The accuracy of the noninvasive HbMet measurement by a Pulse Oximeter Sensor will be assessed by comparison to blood measurements from a laboratory analyzer.

Inclusion Criteria:

1. The subject is male or female, aged ≥18 and <50.
2. The subject is in good general health with no evidence of any medical problems.
3. The subject is fluent in both written and spoken English.
4. The subject has provided informed consent and is willing to comply with the study procedures.

Exclusion Criteria:

1. The subject is obese (BMI>30).
2. The subject has a known history of heart disease, lung disease, kidney or liver disease.
3. Diagnosis of asthma, sleep apnea, or use of CPAP.
4. Subject has diabetes.
5. Subject has a clotting disorder.
6. The subject has a hemoglobinopathy or history of anemia, per subject report or the first blood sample, that in the opinion of the investigator, would make them unsuitable for study participation.
7. The subject has any other serious systemic illness.
8. The subject is a current smoker.
9. Any injury, deformity, or abnormality at the sensor sites that in the opinion of the investigators' would interfere with the sensors working correctly.
10. The subject has a history of fainting or vasovagal response.
11. The subject has a history of sensitivity to local anesthesia or allergy to the study drugs.
12. The subject has a diagnosis of Raynaud's disease.
13. The subject has unacceptable collateral circulation based on exam by the investigator (Allen's test).
14. The subject is pregnant, lactating or trying to get pregnant.
15. The subject has a history of migraine headaches.
16. Th subject is currently taking antidepressants.
17. The subject is unable or unwilling to provide informed consent, or is unable or unwilling to comply with study procedures.
18. The subject has any other condition, which in the opinion of the investigators' would make them unsuitable for the study.