Lecture 11: Blood pressure Flashcards
What two factors does hypertension lead to?
- Increased afterload
- Arterial damage (shear damage)
What can cause increased afterload? And what is the impact of increased afterload on the heart on a pathological level?
Hypertension -> Inc. afterload
- Systolic dysfunction
- LVH —–> diastolic dysfunction
- Increased myocardial oxygen demand (MI risk)
= Heart failure
Hypertension causes arterial damage, what are the consequences of this?
Hypertension -> arterial damage
- Accelerated atherosclerosis (coronary (Dec. O2 supply), cerebral (ischeamic stroke), aorta(aneurysms and dissection))
- Weakened vessel walls, Cerebral (stroke risk), Renal vessels (Renal failure->viscous cycle), opthalmic vessels (retinopathy)
Describe the pathophysiological impact of hypertension on vessel walls:
Hypertension
->
Increased wall tension
->
ANG2, VGF, Endothelin, oxidative stress etc (factors released)
->
Remodelling: Thicker, stiffer wall, smaller lumen (hypertrophy)
How is MAP calculated? Using blood pressure cuff measures
MAP = P(D) + 1/3 (P(S)-P(D))
1/3 contraction
2/3 Relaxation
What happens to blood pressure with age?
Systolic, Diastolic and mean increase with age.
What are the determinants of MAP?
MAP = CO x TPR
What are the cardiac and non-cardiac influences of cardiac output
Cardiac:
- Heart rate
- Inotropic state
- Neural
- Hormonal
Renal fluid, volume control:
- Renin-Angiotensin
- Pressure natriuresis
- Aldosterone
- Atrial Natriuretic factor
What influences peripheral resistance?
Hint (SLH)
SNS
- Vasoconstrictor (alpha)
- Vasodilator (beta)
Local Autoregulation
Humoral
- Vasodilator
- Vasoconstrictor
- Prostaglandin
- Angiotensin
- Kinins
- Catecholamines
How is pulse pressure calculated?
Pulse pressure = Systolic pressure - diastolic pressure
What influences systolic pressure?
Systolic pressure:
- Aortic compliance
- Stroke volume (and ejection rate)
Compliance changes pulse pressure doesnt change MAPB
What influences diastolic pressure?
Diastolic pressure
- Aortic compliance
- Diastolic run off:
- HR
- TPR
How does compliance change pressures?
Diastolic and systolic pressure change with aortic compliance
MABP - Depends on downstream
What is the equation for compliance?
Change volume / Change pressure = Compliance
For a given stroke volume into the aorta (V), the aortic pulse pressure is increased when the compliance is reduced.
Describe what aortic pulse pressure is;
During systole the aorta stretches to absorb the blood
- Flow continues during diastole due to compliant nature of blood vessels
- The more compliant the large blood vessels the smaller the pulse pressure i.e pulse becomes non-pulsitile by the time it reaches the small arterioles
What happens to compliance with age?
Compliance of blood vessels decreases with age
i.e pulse pressure decreases
What does compliance ensure?
Continuous capillary flow throughout the cardiac cycle
What is a consequence of decreased compliance with age?
- Systolic pressure increases
- Diastolic pressure may decrease
What happens with aortic pulse pressure and age?
Compliance of the aorta tends to decrease with age and results in a larger pulse pressure.
How does stroke volume influence pulse pressure?
Larger SV increases arterial pulse pressure (Inc. SV = Inc. systolic pressure)
Systolic pressure can increase in exc. b/c of this
What influences SV?
Preload
Afterload
Chronotropy
Inotropy
What determines diastolic pressure and what influences these?
Diastolic run off determines diastolic pressure i.e the ability of blood to flow forward which is dep. on;
- TPR (Inc TPR = Inc DP)
- HR
When taking someones pulse what are you feeling?
The pulse wave i.e you feel the pulse that has travelled through the blood from the heart not the flow of blood which travels much slower.
On a standard pulse waveform from the proximal aorta, what is the incisura?
Semilunar valve closure
What is the palpation method of pressure measurement?
Attains systolic pressure only as can feel when the pulse returns following occlusion i.e what the systolic pressure would be
How does asculatory method of BP measurement work?
As the pressure of the cuff is reduced it will reach the point of the systolic pressure where turbulent flow will resume until the diastolic pressure is reached and the vessel is sufficiently uncompressed for smooth flow to occur i.e at diastolic pressure
Whats the impact of gravity on blood pressure?
Hydrostatic pressure is influenced by gravity i.e P = (Density x 9.81 x Height)
Thus when standing pressure in a specific vessel can equal (Hydrostatic + Pressure created by heart)
Describe the regulation effects on blood pressure over time;
Short term: Neural
Minutes-Hours: Hormonal and fluid shifts
Long term: Blood volume regulation
