Blood Pressure: Variation and Homeostasis
Blood Pressure
MAP: mean arterial pressure = diastolic pressure + 1/3 pulse pressure
pulse pressure = SP - DP
Blood Flow
blood flows from higher to lower pressure
Q = P/R
Excessive Blood flow --> rupture blood vessels --> hemorrhage
stroke, blindless, heartfailure, kidney disease, heart attack
increase in age --> increase risk of ruptured blood vessels bc blood vessels become stiff/hardened
Systolic Pressure
Major factors affecting: stroke volume and arterial compliance
Minor factors affecting: heart rate
Diastolic Pressure
Major factors affecting: TPR
Minor factors affecting: stroke volume, heart rate
Changes Blood Pressure
Obesity increases BP: overstimulation of SNS, and RAAS, insulin resistance
Sleep lowers BP
Emotional stress increase BP
it peaks during middle of afternoon
Gender differences
before menopause, male has higher BP than female
after menopause, female has higher BP than male
Increases with Age
more production of ADH and less control on RAAS
replacement of elastic fiber of tunica media with inelastic fibers
increase sympathetic tone and decrease vascular compliance
estrogen hormone: vasodilator and ACE downregulator
Sympathetic tone increases after menopause
Vascular Compliance
degree of ability for blood vessel to hold blood without changing their pressure
veins has a larger vascular compliance than arteries
Gravity
vessels above the heart has lower pressures than below the heart
risk if air embolism occur during brain surgery
bc brain vessel pressure are negative, slight changes in pressure can lead to rupture --> stroke
Regulation
Short term
Long term
Hormonal
Neural
Baroreceptor reflex
Chemoreceptor
RAAS
control of respiration
sensitive to (-) O2, (-) pH, (+) CO2 in cerebrospinal fluid (CSF)
stimulates ventilation and SNS
stimulated by brain hypoxia
increase ICP
brain ischemia
stimulate chemoreceptor
stimulate SNS
increase CO, TPR, MAP
decrease heartrate
(-) MAP --> (-) RBF --> (-) GFR --> (+) RAAS
(+) BP
increase urine volume --> increase MAP
Postural Hypotension
Veins has the lowest pressure specifically venae cavae
pulse pressure measures compliance