Cardiovascular Physiology Overview

Pulse

• The stimulus for heart conduction starts as an electrical impulse in the sinoatrial (SA) node of the right atrium.
• In adults, the SA node initiates the impulse 60-100 times per minute.
• The impulse quickly spreads through the conduction system to the rest of the heart, causing synchronous muscle fiber contractions.
• Pulse is the wave of blood forced through arteries by left ventricle contraction.
• Pulse is created by alternating expansion and recoil of arteries during each cardiac cycle.

Physiology and Regulation

• Blood flows continuously through the body.
• Cardiac centers (medulla of the brain stem) control the heart through sympathetic and parasympathetic pathways.
• Cardiac centers adjust heart rate based on sensory input, such as aortic arch stretch (blood volume).
• Increased blood volume leads to a reflex decrease in heart rate (parasympathetic).

Cardiac Output (CO) and Stroke Volume (SV)

• Cardiac output (CO) is the amount of blood pumped by the ventricles per minute.
• Stroke volume (SV) is the amount of blood ejected per heartbeat (typically 70 mL).
• CO = SV x Heart Rate (HR)
• Blood volume increase increases heart rate.
• Blood volume decrease decreases heart rate.
• The heart maintains a relatively constant circulatory blood flow (approximately 70-72 mL of blood entering the aorta per ventricular contraction).
• Pulse wave travels rapidly through the arteries, palpable at peripheral arteries.

Characteristics of Pulse

• Pulse characteristics include rate, rhythm, and volume/strength.
• Rate: Number of pulsations per minute.
• Factors influencing pulse rate include:
  • Age
  • Sex (slightly higher in females until menopause)
  • Exercise/muscular activity (increases rate), rest/sleep (decreases rate)
  • Temperature (increases with elevation)
• Rhythm: Time intervals between pulses; normally regular. Irregularity (arrhythmia) can indicate problems.
  • Arrhythmias: Result from early, late or missed beats
  • Pulse deficit is the difference between apical and radial pulse rates, indicating an inefficient contraction of the heart.

Factors Affecting Pulse Rate

• Stress and emotions increase sympathetic stimulation, increasing heart rate.
• Medications:
  • Positive chronotropics (e.g., atropine) elevate pulse rate.
  • Negative chronotropics (e.g., digitalis) decrease pulse rate.
• Hemorrhage leads to increased sympathetic stimulation and pulse rate.
• Position changes (standing/sitting) result in higher pulse rates.
• Pulmonary conditions (poor oxygenation) increase pulse rate.
• Various diseases (e.g., infection, thyrotoxicosis, anemia) can impact pulse rate.

Pulse Volume/Strength

• Pulse strength reflects blood volume against arterial walls and vascular system condition.
• Normally, pulse strength remains consistent with each beat.
• Strength graded as: normal, thready, weak, or bounding.
• A weak pulse is difficult to palpate and lose during palpation.
• A normal pulse is easily palpable and not easily obliterated.
• A strong/bounding pulse is easily palpated and difficult to obliterate.

Methods for Pulse Assessment

• Palpation: Use fingertips to locate strongest pulse, count rate, evaluate rhythm, and assess volume.
• Auscultation: Use a stethoscope to assess apical pulse (more accurate for irregular rhythms or difficult peripheral palpation).

Stethoscope Parts

• The stethoscope has earpieces, a binaural spring, tubing, a stem, and a chest piece (with bell and diaphragm).

Pulse Sites

• Illustration/diagram shows various pulse points, such as carotid, brachial, radial, femoral, popliteal, dorsalis pedis, etc.

Abnormalities of Pulse

• Tachycardia: Abnormally high pulse rate (>100 bpm in adults).
• Bradycardia: Abnormally low pulse rate (<60 bpm in adults).
• Pulsus bigeminus (bigeminy): Premature beat (weak) alternates with normal sinus beat (strong).
• Pulsus trigeminus (trigeminy): Premature beat alternates with two normal sinus beats.
• Ventricular Tachycardia: Weak pulse with rate of 150-250 bpm; caused by impulses originating from an area of the ventricles, not the SA node.
• Atrial Fibrillation: Irregular, weak pulse with pulse deficit. Impulses are discharged irregularly from different areas of the atria that don't coordinate with the AV node and bundle of His; cannot transmit high atrial excitation rate.