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Cardiovascular Physiology Lecture 8 (Objective 2: Learn how blood pressure…
Cardiovascular Physiology Lecture 8
Objective 1: Understand the adjustments made by the CV system to provide sufficient oxygen to
exercising
skeletal muscles.
CV Response to Exercise:
Combination of faster HR and greater SV increases cardiac output during exercise
Redistribution of blood flow shifts toward muscle, away from digestive tract and kidneys
During strenuous exercise, CO rises dramatically
-CO= heart rate x stroke volume
-CO= (SA node rate + autonomic nervous system input) x (venous return + force of contraction)
BP rises only slightly during exercise because of skeletal muscle vasodilation (decreased peripheral resistance to offset increased CO)
CO at rest= 5.8 L/min
CO during exercise= 25.6 L/min (more to skeletal m. and less to brain)
but 13% of 5.8 L/min ~ 3% of 25.6 L/min
Skeletal Muscle and Respiratory Pumps Increase Venous Return During Exercise
Respiratory pump
Inhalation:
Increases blood flow into thoracic veins
Decreased intrathoracic pressure
Diaphragm contracts
Blood moves superiorly
Increased intra-abdominal pressure
Exhalation:
Increases blood flow into heart and abdominal veins
Increased intrathoracic pressure
Diaphragm relaxes
Decreased intra-abdominal pressure
Autonomic Nervous System Pathways
SNS: NE alpha receptors: vasoconstriction of GI, kidneys, non-active muscle. Beta receptors: positive iontropy and increased HR
Epi from adrenal medulla: Beta 1: positive inotropy and increased HR. Beta 2: vasodilation of active muscle, heart
PNS at SA node (HR) -> ACh bind to nicotinic receptor, ACh then released and binds to muscarinic receptors on Autonomic effectors
Overall drop in TPR due to vasodilation in exercising muscle, but minimized by vasoconstriction elsewhere
What about the Baroreceptoor Reflex?
-Exercise is normally associated with a rise in both arterial pressure and HR
-If arterial baroreceptor function were not modified:
->increased arterial pressure would trigger reflex bradycardia
Instead, the CNS modifies the baroreceptor reflex (resets to a higher control point)
Objective 2: Learn how blood pressure is affected by changes in
body position
and how the cardiovascular system responds to these changes.
Physical Conditioning
-Lower HR, higher SV at rest = greater capacity to increase both during exercise
-Lower HR at given workload
Environmental Conditions:
-Altitude: decrease arterial O2 = decrease O2 delivery -> decrease cardiac function
-Heat: increase blood flow diverted to skin - less available for exercising muscle
Body Posture
-Supine/prone= increase venous return -> increase SV at rest (with decreased HR)
-Limited ability to increase SV via Frank-Starling mechanism
-Increased contribution of HR and positive inotropy to increased CO
Age:
-decrease max HR; decrease Frank-Starling due to decrease ventricular compliance = decrease CO
Types of Exercise
"Dynamic" (running, biking) vs. "static" (isometric)
Objective 3: Understand the causes, consequences, and treatment of: Anemia and Hypotension
Anemia: inadequate # of RBCS
-Compromises oxygen delivery to tissues
-leads to fatigue, weakness
Can be caused by accelerated RBC loss or decreased RBC production
Treatment: depends on cause
-Correct iron/vitamin deficiency
-Blood transfusions
-Synthetic erythropoietin (EPO) to stimulalate RBC production
Hypotension
Vascular (Peripheral Resistance)
Cardiac (low output)
CV Response:
-Decrease Arterial pressure
-Decrease Baroreceptor firing
-Increase Sympathetic
-Decrease Vagal (parasympathetic activity)
-Increase CO and TPR
Rapid (short term):
-Baroreceptor Reflex Activation
Increased SNS outflow to increase CO and TPR ->increase Bp
Chronic (long term):
-Activation of Hormone Systems
-Angiotensin II: vasoconstriction, increased thirst, fluid retention (via aldosterone release) -> increase BP
-Vasopressin (aka Anti-Diuretic hormone): Increase fluid retention, vasoconstriction -> increase BP
Orthostatic Hypotension: standing up too quick, feel faint
Drop in BP due to change in position
Baroreceptor reflex
Hypotension from Blood loss (Hemorrhage)
Decrease Venous Pressue
Decrease Stroke Volume
Blood Loss
Decrease CO
Decrease Arterial pressure
Decrease Baroreceptor firing
Increase Sympathetic
Increase HR and Contractility
Increase Systemic Vascular Resistance
Increase Venous tone
Decrease Parasympathetic
Increase HR and Contractility