Circulatory and Respiratory Systems - Anatomy

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.

"Sawtooth" P waves are characteristic of atrial flutter.

A prolonged P-R interval, that does not get progressively longer is typical of a type I A-V block.

A premature junctional/nodal beat would be represented on an ECG as an inverted or absent P wave. In a premature junctional/nodal beat, the atrioventricular (AV) node is firing before the sinoatrial (SA) node. Since the AV node is at the bottom of the right atrium, the net vector of atrial depolarization is occurring in a more upward direction, causing the P wave to be absent or inverted. Note that there would be a compensatory pause after the premature beat.The answer could not be a premature atrial contraction because the P wave is absent or inverted (P wave would be normal in a premature atrial contraction (PAC)).

Ventricular fibrillation is a very serious issue that requires immediate defibrillation. Ventricular fibrillation is the result of ventricular beats originating from many different automaticity foci, so the QRS looks squiggly, very fast, and incoherent. There are no P waves since the beats are originating in the ventricles.

In First Degree AV Block, there is a longer than normal PR interval (>.20s) due to slowed AV node conduction. Second degree, Mobitz Type 1 (Wenckebach) is progressive lengthening of the PR interval followed by a dropped QRS. Second Degree, Mobitz Type 2 is sudden dropping of the QRS (no lengthening of PR interval). Third Degree AV Block is when there is no relationship between the P and the QRS.

A bundle branch block is a block in one of the bundle branches, causing a long QRS (>.10 seconds). It is different than a PVC in that a bundle branch block will show a P wave since the beats are still originating in the atria. Bundle Branch Blocks also tend to show a notched QRS.

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.

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.

This man is deteriorating from cardiac tamponade, a condition in which blood is pooling around the heart and hindering its ability to fill during diastole (relaxation).

Doctors should suspect cardiac tamponade when a patient has hypotension, muffled heart sounds, and jugular venous distention (Beck's triad). Ultrasound will show a fluid collection in the pericardial sac surrounding the heart. Treatment is with immediate pericardiocentesis and fluid resuscitation.

Tension pneumothorax occurs when damage to the lung results in leakage of air into the pleural space. This causes equilibration of pressures between the lung and pleural space, leading to difficulty during inhalation. Positive pressure ventilation can help alleviate this condition. A splenic laceration will result in internal bleeding in the upper left quadrant of the abdomen. Pelvic fractures generally result from trauma during a fall or lateral impact and may cause damage to pelvic organs, but would not likely be linked to cardiac abnormalities. Acute myocardial infarction, or heart attack, occurs from blockage of or damage to the coronary arteries, resulting in a loss of blood flow to the tissues of the heart.

Aortic regurgitation is the term for leaky, insufficient valves. Aortic regurgitation can be repaired via a valve replacement procedure. Aortic stenosis is hardening of the arteries. Pulmonary embolisms is a blockage in one of the pulmonary arteries. Hypertension is also known as high blood pressure.

If the sinoatrial node becomes damaged and is unable to drive the rate of spontaneous depolarization in the heart (at its normal rate of 60-100 beats per minute), other cardiac pacemaker cells exist to ensure that the heart continues beating. The atrioventricular node is also known as the secondary pacemaker because these cells spontaneously discharge at a rate of 40-60 beats per minute. It is worth noting that if both the sinoatrial and atrioventricular nodes are damaged, the bundle branches, and Purkinje fibers are also capable of producing a spontaneous action potential at a rate of 30-40 beats per minute.

Myocardial ischemia occurs when the heart demands more oxygen than the coronary arteries can supply. Ischemia means lack of blood. The ability for the coronary circulation to deliver oxygen may be reduced due to the formation of a blood clot, embolism, or atherosclerosis. Premature ventricular contraction and atrial fibrillation are irregular heart beats that can result in arrhythmias and, in some cases more serious complications. Coronary artery disease involves damage (usually via plaque deposition) to the arteries that supply the heart muscle. Congestive heart failure involves any one or more issues with the strength of the heart muscle.

Troponin is a complex of proteins that play an important role in skeletal and cardiac muscle contraction. Troponin is released into the bloodstream when there is damage to the heart. This is a common diagnostic laboratory test for patients with heart problems or chest pain.