The normal PR interval length is .12 - .20 seconds. The PR interval represents the time lag from the onset of atrial depolarization to the onset of ventricular depolarization. Most of the time lag occurs in the AV node, and it allows atrial systole to occur. This allows the ventricles to have time to fill before ventricular systole.

Tachycardia is an abnormally rapid heart rate of rate >100 beats per minute.

Bradycardia is defined as heart rate <60 bpm. In an endurance athlete, there tends to be higher stroke volume/higher vagal tone, so it is typical for an endurance athlete to have a resting heart rate below 60 and still meet normal cardiac output. It a non-endurance athlete, a resting heart rate of 45 bpm may warrant some investigation.

Ejection fraction is a measurement of how much blood blood the ventricles pump out with each contraction as a fraction of the end-diastolic volume. Mathematically, this is (stroke volume) divided by (end-diastolic volume). In congestive heart failure, the heart is weakened and quivers, and it has a hard time pumping blood out. An ejection fraction (EF) < 40% may be evidence of congestive heart failure.

Arterial blood gas (ABG) is a test that measures various capacities of gases to enter or exit the bloodstream, the saturation of oxygen in the blood, and materials involved in maintaining the pH level of blood. It is widely considered one of the most useful diagnostic tools for a host of circulatory conditions, and is a standard procedure for many hospital stays.

Hematocrit cannot be measured by an arterial blood gas test.

Blood is around 55% plasma, 45% erythrocytes (red blood cells), and less than 1% of leukocytes and platelets.

Pulmonary function tests or spirometric tests are tests designed to measure a host of breathing functions. Since values vary depending on body position, time of day, and other factors, most metrics have a high tolerance for variance and typically require a person to score below 80% or above 120% of their expected values before a result is considered "abnormal". These tests are most often employed diagnostically, but may also be used to check up on the progress of a treatment program.

A laryngoscope is used to view the larynx and epiglottis, but does not provide quantitative functional data.

Spirometric tests typically measure between 10-20 metrics of respiratory health, including airflow, intake/outtake, and total volume. Oxygen saturation is a measure of the blood's ability to bond oxygen to hemoglobin, and is typically measured during one or more blood tests.

The carina seems to be consistently located between the T4/T5 intervertebral disk level in most people. These vertebral levels are used as landmarks to identify the carina and, consequently, the trachea above it and the left and right primary bronchi below it.

Hormone imbalances can result in numerous diseases and disorders.

Excess adrenocorticotropic hormone can result in Cushing's disease, characterized by excess weight, fatigue, and redness and roundness in the facial features.

A deficiency in adrenocorticotropic hormone can result in Addison's disease, characterized by low blood pressure and hyperpigmentation.

Excess growth hormone can have different results, depending on the age at which the imbalance occurs. Gigantism results when there is an excess of GH during childhoos, while acromegaly results during adulthood.

Excess thyroid-stimulating hormone can result in Grave's disease, which has many symptoms similar to hyperthyroidism. Such symptoms include weight loss and hyperactivity. Grave's disease can also produce goiters.

A deficiency in thyroid-stimulating hormone can have different results, depending on the age at which the imbalance occurs. Cretinism, myxedema, and Hashimoto's disease are all caused by TSH dificiency.