Vital Signs: Pulse & Heart Rate

Vital Signs: Pulse & Heart Rate

• The heart is a hollow, cone-shaped organ located in the mediastinum, between the pleural cavities, and within the pericardial cavity.
• The pericardium anchors and protects the heart.
• The esophagus and trachea lie posterior to the heart.

The Heart's Internal Structure

• The heart has four compartments (chambers): two atria (superior) and two ventricles (inferior).
• Ventricular walls are thicker than atrial walls to pump blood to the systemic and pulmonary circulation.
• The interatrial and interventricular septa prevent blood mixing between the chambers.
• The right atrium receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus.
• The right ventricle pumps deoxygenated blood into the pulmonary trunk.
• The left atrium receives oxygenated blood from the pulmonary veins; the left ventricle pumps oxygenated blood into the aorta.

The Cardiac Cycle

• The cardiac cycle involves alternating atrial and ventricular contraction and relaxation.
• Atrial contraction pushes blood into the ventricles.
• Ventricular contraction forces blood into the pulmonary trunk or aorta.
• Heart valves (atrioventricular and semilunar) ensure one-way blood flow.
• Electrical activity from the SA node initiates the cycle.
• The electrical impulses cause the heart muscles to contract, creating heart sounds (S1 and S2).

Heart Sounds and Assessment

• Heart sounds (S1 and S2) are related to valve closure-- S1 is usually heard first followed by S2.
• Auscultation enables assessing heart sounds and heart rate.
• Physicians listen for heart sounds in multiple locations and associate them with specific valves.
• Heart rate is measured at the point of maximal impulse.
• Identifying irregular heart sounds may indicate a problem.

Cardiac Output

• Cardiac output (CO) is the volume of blood ejected by the heart per minute. It is calculated as heart rate (HR) multiplied by stroke volume (SV).
• Stroke volume (SV) is the volume of blood ejected per heartbeat and is calculated as end diastolic volume (EDV) minus end systolic volume (ESV).
• Physiological factors influence cardiac output.
• The autonomic nervous system regulates cardiac output by influencing heart rate and stroke volume.
• Sympathetic activity increases HR & SV; parasympathetic activity decreases HR.

Heart Rate

• Heart rate refers to the number of contractions per minute.
• HR is measured by palpating or auscultating.
• The pulse can be felt in various locations depending on the artery.