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 a noninvasive HbMet sensor will be assessed by comparison to blood measurements from a laboratory analyzer.

Inclusion Criteria

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

Exclusion Criteria:

• The subject is obese (BMI>30).
• The subject has a known history of heart disease, lung disease, kidney or liver disease.
• Diagnosis of asthma, sleep apnea, or use of CPAP.
• Subject has diabetes.
• Subject has a clotting disorder.
• 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.
• The subject has any other serious systemic illness.
• The subject is a current smoker.
• Any injury, deformity, or abnormality at the sensor sites that in the opinion of the investigators' would interfere with the sensors working correctly.
• The subject has a history of fainting or vasovagal response.
• The subject has a history of sensitivity to local anesthesia or allergy to the study drugs.
• The subject has a diagnosis of Raynaud's disease.
• The subject has unacceptable collateral circulation based on exam by the investigator (Allen's test).
• The subject is pregnant, lactating or trying to get pregnant.
• The subject has a history of migraine headaches.
• The subject is currently taking antidepressants.
• The subject is unable or unwilling to provide informed consent, or is unable or unwilling to comply with study procedures.
• The subject has any other condition, which in the opinion of the investigators' would make them unsuitable for the study.