Ch 13/14 Cardiovascular Physiology (Day 6) Flashcards
Blood Pressure
Affected by blood volume, stroke volume, total peripheral resistance, and HR
- Increase in any of these will increase blood pressure.
- Vasoconstriction of arterioles raises blood pressure upstream in the arteries.
BP(arterial) = CO X TPR CO = SV x HR TPR = vasoconstriction
The blood pressure of blood vessels is related to the total cross- sectional area
- Capillary blood pressure is low because of large total cross-sectional area.
- Artery blood pressure is high because of small total cross-sectional area
Blood Pressure Regulation
- Kidneys can control blood volume and thus stroke volume.
- Sympathoadrenal system stimulates vasoconstriction of arterioles (raising TPR) and increased CO.
Baroreceptor Reflex
- Activated by changes in blood pressure detected by baroreceptors (stretch receptors) in the aortic arch and carotid sinuses
- Increased blood pressure stretches these receptors, increasing action potentials to the vasomotor and cardiac control centers in the medulla.
- Most sensitive to drops in blood pressure
- The vasomotor center controls vasodilation and constriction.
- The cardiac center controls heart rate.
- Fall in blood pressure = Increased sympathetic and decreased parasympathetic activity, resulting in increased heart rate and total peripheral resistance
- Rise in BP has the opposite effects.
- Good for quick beat-by-beat regulation— (e.g. going from lying down to standing)
Structures of the Baroreceptor Reflex
- Baroreceptors (sensors)
- Vasomotor & cardiac control centers in medulla (integrating centers)
- Symp/parasymp axons to heart & blood vessels (effectors)
Atrial Stretch Reflexes
Activated by increased venous return to:
- Stimulate reflex tachycardia (sympathetic)—physiologic significance unknown
- Inhibit ADH release; results in excretion of more urine
- Stimulate secretion of atrial natriuretic peptide; results in excretion of more salts and water in urine
BP Measurement
- Measured in mmHg using sphygmomanometer.
- Blood pressure cuff produces turbulent flow of blood in the brachial artery—detected as Korotkoff sounds via stethoscope.
1) Cuff inflated to beyond systolic blood pressure to occlude artery;
2) Pressure gradually released, the first (tapping) sound is heard at systole; 3) second “sound” is the last “tap” before sounds disappear—when pressure in cuff = diastolic pressure. - Average BP is 120/80 (systolic/diastolic).
Pulse Pressure
“Taking the pulse” is a measure of heart rate.
Each “pulse” = increased blood pressure in that artery at systole.
- -> P(systolic) – P(diastolic) = pulse pressure.
- -> e.g. if BP = 120/80, pulse pressure = 120 – 80 = 40 mmHg.
Pulse pressure is a reflection of stroke volume
How is pulse pressure a reflection of stroke volume?
Mean Arterial Pressure
MAP = average pressure in the arteries in one cardiac cycle.
Significance: MAP – venous pressure = driving force for blood flow into capillaries.
Not a simple arithmetic average, since diastole is longer than systole.
Approximated as: diastolic pressure + 1/3 pulse pressure
–> e.g. for BP = 120/80, pulse pressure = 40, and MAP = 80 + 1/3* 40 = 93 mm Hg.
Hypertension
High Blood Pressure
- Incidence increases with age
- Increases risk of cardiac diseases, kidney diseases, and stroke.
- Classified as “essential” or “secondary.”
- Essential or primary hypertension—Most people fall in this category. Causes not clearly defined in all cases; may include:
a) ↑salt intake coupled with decreased kidney filtering ability
b) ↑ sympathetic nerve activity ↑’s HR
c) altered responses to paracrine regulators from the endothelium
d) ↑ TPR
Secondary hypertension is a symptom of another disease, such as kidney disease.
Dangers of Hypertension
- Vascular damage within organs, especially dangerous in the cerebral vessels and leading to stroke
- Ventricular overload to eject blood due to abnormal hypertrophy, leading to arrhythmias and cardiac arrest
- Contributes to the development of atherosclerosis
Treatments for Hypertension
- Lifestyle modification: ↓ salt intake; ↓ smoking and drinking; ↓ weight; ↑ exercise
- K+ (and possibly calcium) supplements
- Diuretics to increase urine formation
- Beta blockers to decrease cardiac rate
- ACE inhibitors to block angiotensin II production
What is circulatory shock?
Inadequate blood flow to match oxygen usage in tissues
What is hypovolemic shock?
- Due to low blood volume from an injury, dehydration, or burns
- ↓ CO and BP
- Blood is diverted to the heart and brain at the expense of other organs.
- Compensation includes baroreceptor reflex, which in response to lower pressure, raises heart rate, raises peripheral resistance, and produces cold, clammy skin and low urine output.
What is septic shock?
- Dangerously low blood pressure (hypotension) due to an infection (sepsis)
- Bacterial toxins (endotoxins) induce NO production, causing widespread vasodilation.
- Mortality rate is high (50−70%).
What are other causes of circulatory shock?
- Severe allergic reactions –> anaphylactic shock due to production of histamine and resulting vasodilation.
- Spinal cord injury or anesthesia –> neurogenic shock due to loss of sympathetic stimulation.
- Cardiac failure –> cardiogenic shock due to significant loss of myocardial function.
