BP Control Flashcards
Pulse Pressure
Systolic BP - Diastolic BP
How to calculate mean arterial pressure
Diastolic BP + (Pulse Pressure)/3
heart spends more time in systole than diastole which is why pp is divided by 3
Factors affecting Systolic BP
Stroke Volume - Increased SV, increased SBP
Aortic Elasticity - Decreased elasticity, increased SBP
Factors affecting diastolic BP
Peripheral resistance - Increase PR, increase DBP
Aortic elasticity - Decrease elasticity, decrease DBP
Heart Rate - Decrease HR, decrease DBP
How does aging of the aorta cause hypertension in the elderly
Normally, the elastic aorta takes up kinetic energy from blood during systole & dampens rise in BP
During aging though, the aorta loses elasticity, causing systolic hypertension
Formula for Mean Arterial BP (MAP)
Cardiac Output x Total Peripheral Resistance
Typical MAP, Cardiac Output and Total Peripheral Resistance in Systemic Circulation
MAP - 100mmHg
Cardiac Output - 5 L/min
TPR - 20 Units (mmHg/L/min)
Typical MAP, Cardiac Output and Total Peripheral Resistance in Pulmonary Circulation
MAP - 10mmHg
Cardiac Output - 5 L/min
TPR - 2 Units (mmHg/L/min)
Mechanisms that support control of arterial BP
Pressure Sensors (in circulation) - Afferent Input
Integration centres (in CNS)
Effector Mechanisms (via ANS) - Efferent Output
Arterial Baroreceptors - What are they, Where, What do they do/how
High Pressure BP Sensors
In walls of carotid arteries & aortic arch
They detect an increase in stretch of vessels, increasing afferent nerve discharge via IX and X (vagus) cranial nerves
Effector Mechanisms to Control BP via ANS in heart
Parasympathetic - ACh, Muscarinic Receptors; decrease HR
Sympathetic - NA, B1 Adrenoceptors; Increase HR & StV
Effect of SNS on arteries
Sympathetic nervous system activates a2 adrenoceptors causing vasoconstriction, increasing resistance and thus BP
Low Pressure Baroreceptors - Where, What do they do/how
Located in pulmonary vasculature, Atrial-vena caval junctions, ventricular walls
‘volume receptors’ of the heart
Increase in transmural pressure increases afferent nerve discharge - vagus
What are the groups of neurons in the medulla that play a role in BP control
The caudal depressors only a role in highly elevated BP
**FOCUS ON MIDDLE ROW
How do the following values changes when going from a supine to standing position to maintain BP: HR Stroke Volume Cardiac Output Total Peripheral Resistance