Cardio L15 Integrated Responses Flashcards
Central Venous Pressure (CVP):
.1. CVP is the pressure in the great veins at the point they join the heart.
a. SVC joins right atrium
2. CVP is described as the filling pressure of the right ventricle and is a key determinant of preload
CVP measurement
Central line into sub-clavian vein with tip near SVC entering the heart.
CVP Examination →
patient reclined at 45 degrees. Angle of Louis and he height of the internal jugular vein is filled with blood. RA is 5cm below angle of Louis estimated via JVP distance and the difference.
Determinants of central Venous Pressure:
Blood volume Peripheral venous tone Gravity Skeletal muscle pump Resp pump Cardiac output
Orthostatis: the challenge
- Gravity increases transmural pressure in lower limb veins →
- Blood pools in lower limbs
- Decreased blood volume in central veins ( ~500ml)
- Decreased CVP/preload
- Decreased stroke volume/cardiac output
- Decreased mean arterial pressure
- Impaired cerebral perfusion and dizziness
Orthostatis: The Result
If nothing corrected fainting
Orthostatis: The Actual response to avoid this
The Baroreceptor response
Orthostatis:The Response explained
- Fall in BP leads to reduced Baroreceptor firing
→Parasym and sympathetic input altered - Degree of venoconstriction
- R-A-A system activation
Aerobic Exercise: the challenge
Increased oxygen demand by skeletal muscle requires increased pulmonary blood flow, increased muscle blood flow and a reasonably stable blood pressure to maintain cerebral and coronary circulations
Aerobic Exercise: The Response
- Increased sympathetic tone and decreased vagal tone produces an increase in heart rate (positive chronotropic effect) and stroke volume (Positive ionotropic effect)
- The increased cardiac output (5-20 l/min) produces an increase in pulmonary blood flow and the increased stroke volume is partially responsible for an increase in systolic pressure.
- Increased blood flow to skeletal muscle occurs as the result of active hyperaemia. There may also be effects due to circulating adrenaline acting at beta2 adrenoceptors.
- The decrease in total peripheral resistance may produce a decrease in diastolic blood pressure.
Aerobic Exercise: The response → other systems that have reduced blood flow to compensate.
- In order to prevent a precipitous fall in blood pressure the sympathetic nervous system produces a “compensatory” vasoconstriction in the splanchnic and renal vascular beds
- Diverts some blood flow from the gut and kidney to exercising skeletal muscle.
Initiating of Responses: in aerobic excercise
- Central command theory → as the brain sends info to muscle some info goes to medulla to allow it make adjustments
- Baroreceptor reflex resetting → reset to a higher mean arterial pressure and to achieve increases BP
- Peripheral reflex hypothesis → metaboloreceptor sin muscles. Detected by sensory nerve fibres and causes adjustments in CNS.
Haemorrhage: the challenge
- Loss of blood volume
- Decreased blood volume in central veins
- Decreased CVP/preload
- Decreased stroke volume/cardiac output
- Decreased mean arterial pressure
Haemorrhage: response
Baroreceptor reflex
Detects low BP
Alters sympathetic tone and decreases parasympathetic tone.
Haemorrhage: long term response
Survival of Haemorrhage → need to replace therefore
- Thirst and increased fluid intake (days)
- Albumin synthesised by liver hepatocytes (1 week)
- Erythrocyte production by red bone marrow (several weeks)
