Nordgren: Response to Physiological Stress Flashcards
How does intrathoracic pressure drive venous return?
Inspiration>
Increased negative intrathoracic pressure (-2 to -7)>
Lungs and cardiac chambers expand>
Decrease in RA pressure (central venous pressure)>
Decreased venous return
What is the respiratory pump?
Breathing in, expands the chest which in turn lowers the pressure in the thoracic cavity. The lower pressure causes air to fill the lungs, the same lower pressure cause the pressure in the right atria to be lower, allowing for more blood to flow in, increasing the venous input thus increasing the cardiac output of the heart.
How does inspiration affect SV and CO?
Inspiration>
increased right side filling>
Increase stroke volume (starlings)>
increased CO
How does a reduction in pulmonary vascular resistance affect SV?
It REDUES afterload and INCREASES stroke volume.
True or false…changes in the R heart induces the SAME changes in the L heart.
True.
What are direct effect and what do they do?
Direct effects lead to an INCREASE in arterial pressure and affect the ARTERIAL baroreceptors
What are the reflex effects of increased arterial baroreceptor firing?
The medullary cardiovascular center INCREASES parasympathetic activity and DECREASE SNS activity.
What are the effects of increased parasympathetic activity?
decreased: HR Contractility Venous constriction arteriolar constriction
What effect does exercise have on venous return?
Deep and rapid breathing associated with exercise INCREASES venous return and EXAGGERATES the respiratory pump.
What effect does coughing have on venous return?
Cough can increase intrathoracic pressure, compressing thoracic vessels and lead to REDUCED venous return.
What effect do positive pressure ventilators have on venous return?
INCREASE intrathoracic pressure leading to DECREASED venous return.
Compress the pulmonary microcirculation leading to INCREASED right ventricular afterload.
What does standing up do?
- increases blood volume in legs and feet> increased peripheral pressure > increased filtration (edema)
- Decreased SV > CO > MAP
- Sympathetic stimulation > vasoconstriction
- Skeletal muscle contracts
- Empty veins and lymphatics > lowered venous pressure
What is the net effect of standing?
higher HR and TPR
What are the immediate effects of long term bed rest?
shift of fluid from lower to upper portions of the body>
distension of veins, facial edema, decrease in calf girth/volume
What are the delayed effects long term bed rest?
Reduced renal sympathetic drive
- Promotes fluid loss > weight loss > hypovolemic
What is orthostatic (postural) hypertension and in what type of pt is it commonly seen in?
Often seen in hypovolemic pts or ones that have been on bed rest for a long time.
When this individual tries to stand, their normal response to gravity is ineffective because of a decrease in circulating blood volume. Standing causes blood to shift from the central to the peripheral pool, causing the SV to fall. The individual may become dizzy and faint because of a dramatic fall in bp.
What effect does standing have on the autonomic nervous system?
It triggers the SNS to reflexively increase BP.
Leading to increased: HR contractility venous/arteriolar constriction fluid retention
Why does HR, CO, MAP and PP increase with acute exercise?
Increased blood flow occurs in order to meet the increased metabolic demands of skeletal msucle.
What does physical conditioning do to your work capacity?
- Decreases HR
- increases SV
decreases arterial blood pressure - increases circulating blood volume (activation of SNS promotes fluid retention)
- ventricular chamber enlargement> improve pumping capabilities of the myocardium.
What affect does physical conditioning have on myocardial oxygen demand?
It DECREASES myocardial oxygen demand b/c of ability to achieve a given workload at a lower heart rate.
How does pregnancy affect blood flow?
Adding an organ in parallel REDUCES the overall systemic TPR by 40%, so you need an INCREASE in circulating blood volume to support cardiac filling in the presence of decreased TPR.
What would happen if there wasn’t a reflexive increase in blood volume during pregnancy?
You’d get a HUGE decrease in MAP.
Why does blood begin to flow in the fetal lungs after birth?
Lung ventilation DECREASES pulmonary vascular resistance >
pulmonary vasodiialtion >
blood begins to flow into the lungs
What is commonly seen in infants in terms of HR and BP?
HIGH HR
LOW BP
What happens to us as we age?
SLOWER, STIFFER, DRYER
Why is it awesome to have estrogen?
- it LOWERS cardiac afterload (d/t lower left ventricular mass to body ratio)
- it LOWERS arterial bp
- greater aortic compliance
- improved ability do induce vasodilatory mechanisms
What is the formula for MAP?
MAP = CO x TPR
What is the formula for CO?
CO = SV x HR
What is the formula for SV?
EDV-ESV
What is the formula for ejection fraction?
SV/EDV
What increases stroke volume?
Increased cardiac preload (via effect on EDV)
Increased cardiac contractility (via effect on ESV)
What decreases stroke volume?
Increased cardiac afterload (via effect on ESV)
What increases central venous pressure?
- Increased total blood volume
- increased peripheral venous tone
- increased skeletal muscle pump
- increased respiratory pump
What decreases central venous pressure?
- Standing
2. Increased CO
What increases venous tone?
Increased sympathetic activity via NE that acts on alpha-receptors of smooth muscle.
What increases contractility?
Increased sympathetic activity via NE on Beta recepors that acts on ventricular cells.
What increases HR?
Increased sympathetic activity>
NE>
Beta receptors>
increase SA node cell firing rate
What decreases HR?
Increased parasympathetic activity>
ACh>
decreases SA node cell firing rate
What increase TPR?
Increased sympathetic activity> NE> alpha receptors> smooth muscle of arterioles> increased arteriolar tone
What decreases TPR?
Increase in local metabolites>
arteriodilation
What decreases the elasticity of the carotid artery?
Age
