Physiology of Pulse and Heart Function

Pulse

• Pulse is the wave of blood forced through arteries by the left ventricle's contraction.
• Pulse is also created by alternating expansion and recoil of arteries during the cardiac cycle.
• The sinoatrial (SA) node initiates the electrical impulse in the heart, typically 60-100 times per minute in adults.
• The electrical impulse travels through the conduction system to the rest of the heart, causing the heart muscle fibers to contract synchronously.
• The blood circulates continuously throughout the body. The cardiac centers in the medulla of the brainstem control the heart rate via sympathetic and parasympathetic innervation.
• Stroke volume (SV) is the amount of blood ejected per beat (approximately 70 mL).
• Cardiac output (CO) is the amount of blood pushed by the ventricles per minute (CO = SV x HR).
• Normal heart function maintains a relatively constant circulation of blood (approximately 70-72 mL per contraction).

Pulse Characteristics

• Pulse characteristics include rate, rhythm, and volume.
• Rate is the number of pulsations felt over an artery per minute.
• Rhythm refers to the time intervals between each pulse beat.

Factors Affecting Pulse Rate

• Age: Pulse rate is slightly higher in females than males until menopause.
• Sex: Females experience greater nervous activity than males until menopause.
• Exercise and Muscular Activity: Exercise increases pulse rate, while rest and sleep decrease it.
• Temperature: Pulse rate increases by about 10 beats per minute per degree of temperature elevation.
• Stress and Emotions: Stress and emotions can increase sympathetic stimulation, leading to a higher heart rate.
• Medications:
  • Positive chronotropic drugs (e.g., atropine) increase pulse rate.
  • Negative chronotropic drugs (e.g., digitalis) decrease pulse rate.
• Hemorrhage: Loss of blood increases sympathetic stimulation and pulse rate.
• Position Changes: Pulse rate is higher in standing or sitting than lying down.
• Pulmonary Conditions: Diseases causing poor oxygenation tend to increase pulse rate.
• Disease Conditions: Infections, thyrotoxicosis, pulmonary embolism, and anemia increase pulse rate; heart block decreases it.

Pulse Rhythm

• Normal pulse rhythm is regular, with equal intervals between beats.
• Irregular intervals between beats indicate an abnormal rhythm (arrhythmia or dysrhythmia), possibly due to early, late, or missed beats.

Pulse Deficit

• A pulse deficit occurs when the heart's contraction fails to transmit a pulse wave to the periphery.
• To assess, compare radial and apical pulse rates.
• The difference between the apical and radial pulse rates represents the pulse deficit.

Pulse Volume (Strength)

• Pulse strength reflects the blood ejected against the arterial walls and the arterial systems' condition.
• Normally, pulse strength remains consistent with each heart beat.
• Pulse strength grades: normal, thready, weak, or bounding.

Pulse Types

• Weak Pulse: Difficult to palpate and easily lost during palpation.
• Normal Pulse: Full, easily palpable, and not easily obliterated by the examiner's fingers.
• Strong/Bounding Pulse: Easily palpable and difficult to obliterate.

Pulse Assessment Methods

• Palpation: Palpate with the middle three fingers on the artery of interest.
• Auscultation: Using a stethoscope to listen to the apical (heart) pulse is useful when peripheral pulses are difficult to palpate or when the rhythm is irregular.

Stethoscope

• Major parts: earpieces, binaural tubing, and chest piece (with bell and diaphragm)

Pulse Sites

• Diagram of common pulse locations on the body. (External Maxillary, Superficial Temporal, Carotid, Brachial, Posterior Tibial, Ulnar, Radial, Femoral, Popliteal, Dorsalis Pedis)

Pulse Abnormalities

• Tachycardia: Abnormally elevated pulse rate (above 100 beats per minute in adults).
• Bradycardia: Abnormally slow pulse rate (below 60 beats per minute in adults).
• Bigeminy: Premature beat (weak) alternates with a normal sinus beat (strong).
• Trigeminy: Premature beat alternates with two normal sinus beats.
• Ventricular Tachycardia: Weak pulse (150-250 beats per minute) due to hyper-excitable ventricles. Palpitations often occur.
• Atrial Fibrillation: Irregular and weak pulse, often diagnosed via pulse deficit assessment. The heart's atria contract irregularly preventing coordinated impulses from being conducted effectively to the ventricles (resulting from high rate of atrial excitation).