Arterial System Physiology

Arterial Blood Pressure - Pressure Points

Arterial Blood Pressure (BP): Lateral pressure by blood on vessel walls.

• Systolic BP (SBP): Peak pressure during ventricular systole.
• Diastolic BP (DBP): Minimum pressure during ventricular diastole. Formula: $BP = CO \times TPR$ (Cardiac Output $\times$ Total Peripheral Resistance/Systemic Vascular Resistance). Normal: <120/80 mmHg. Hypertension (ACC/AHA simplified):
  • Elevated: 120-129 SBP & <80 DBP
  • Stage 1: 130-139 SBP or 80-89 DBP
  • Stage 2: ≥140 SBP or ≥90 DBP

Factors influencing BP:

• Age (↑)
• Gender
• Diurnal variation
• Exercise (↑ SBP)
• Emotion (↑)
• Posture

⭐ Korotkoff sounds: Phase I (tapping) indicates SBP; Phase V (silence) indicates DBP in adults.

MAP & Pulse Pressure - Meaningful Measures

• Mean Arterial Pressure (MAP): Average pressure driving blood to tissues; crucial for organ perfusion.
  • Formula: $MAP \approx DBP + \frac{1}{3}(SBP - DBP)$ (DBP: Diastolic, SBP: Systolic)
  • Normal Range: 70-100 mmHg.

⭐ Mean Arterial Pressure (MAP) is considered a better indicator of vital organ perfusion than systolic blood pressure.

• Pulse Pressure (PP): The difference between SBP and DBP; reflects arterial wall stress.

  • Formula: $PP = SBP - DBP$
  • Determinants: ↑ with ↑ Stroke Volume (SV); ↑ with ↓ Arterial Compliance (stiffer arteries).

• Clinical Significance of PP:

  Finding	PP	Common Causes
  Wide PP	↑	Aortic Regurgitation, Hyperthyroidism, Atherosclerosis, Anemia, AV fistula
  Narrow PP	↓	Aortic Stenosis, Cardiac Tamponade, Hypovolemia, Severe Congestive Heart Failure

BP Regulation - Control Central

Short-Term Regulation:

• Baroreceptor Reflex: Stretch receptors.
  • Locations: Carotid Sinus (CN IX), Aortic Arch (CN X). 📌 "Sinus by IX, Aorta by X."
  • Mechanism: ↑BP → ↑firing → ↓SNS, ↑PNS → ↓BP. Adapts (resets).
• Chemoreceptor Reflex:
  • Locations: Carotid & Aortic bodies.
  • Stimuli: ↓PaO₂, ↑PaCO₂, ↓pH (acidosis). Result: ↑SNS → ↑BP, ↑Respiration.
• CNS Ischemic Response: Severe cerebral ischemia.
  • Cushing Reflex: Hypertension, Bradycardia, Irregular Respiration. Triggered by ↑ICP.

Long-Term Regulation:

• Renin-Angiotensin-Aldosterone System (RAAS): Activated by ↓renal perfusion. Ang II effects: Vasoconstriction, Aldosterone/ADH release, thirst.

• Vasopressin (ADH): From Post. Pituitary. Stimuli: ↑Plasma osmolality, ↓blood volume. Actions: ↑H₂O reabsorption (collecting ducts), vasoconstriction (high levels).
• Atrial Natriuretic Peptide (ANP): From Atria. Stimulus: Atrial stretch. Actions: Vasodilation, natriuresis, ↓renin & aldosterone → ↓BP.

⭐ Baroreceptors adapt (reset) to sustained changes in blood pressure (e.g., in chronic hypertension), making them less effective for long-term BP control.

Arterial Pulse & Waves - Rhythmic Reads

• Arterial Pulse: Palpable rhythmic expansion of an artery due to left ventricular ejection.
  • Normal: Rate 60-100/min, regular rhythm, normal volume & character, soft vessel wall.
• Pulse Waveform:
  • Anacrotic limb (systolic upstroke)
  • Systolic peak
  • Catacrotic limb (diastolic downstroke)
  • Dicrotic notch (aortic valve closure)
  • Dicrotic wave
• Pulse Wave Velocity (PWV): Speed of pulse wave. ↑ with age, ↑ BP, ↑ arterial stiffness.

⭐ The dicrotic notch on an arterial pulse wave tracing is primarily caused by the closure of the aortic valve.

• Clinically Important Abnormal Pulses:

  Pulse Type	Description	Key Cause(s)
  Water hammer (Corrigan's)	Rapid upstroke & collapse (collapsing pulse)	Aortic regurgitation
  Pulsus parvus et tardus	Weak (parvus) & delayed (tardus) pulse	Severe Aortic Stenosis
  Pulsus alternans	Alternating strong & weak beats	Left Ventricular Failure
  Pulsus bisferiens	Two systolic peaks	Aortic Stenosis + Regurgitation, HOCM
  Pulsus paradoxus	SBP ↓ >10 mmHg during inspiration	Cardiac tamponade, constrictive pericarditis

High‑Yield Points - ⚡ Biggest Takeaways

• Mean Arterial Pressure (MAP) ≈ Diastolic Pressure + 1/3 Pulse Pressure; primarily determined by Cardiac Output (CO) & Total Peripheral Resistance (TPR).
• Pulse Pressure (PP) directly reflects Stroke Volume (SV); inversely related to arterial compliance.
• The Windkessel effect of large elastic arteries converts intermittent ejection into continuous flow.
• Arterioles are the primary sites of Total Peripheral Resistance (TPR), regulating blood flow distribution.
• Poiseuille's Law states flow resistance is inversely proportional to the radius to the fourth power (r⁴).
• Endothelium-derived Nitric Oxide (NO) is a major vasodilator; Endothelin-1 is a potent vasoconstrictor.