Cardiac problems - health & disease Flashcards
What is shock
Any situation in which a reduction of blood flow to the organs and tissues damages them
What is hypovolemic shock?
A decrease in blood volume secondary to hemorrhage or loss of fluid other than blood
What is low-resistance shock?
This is due to a decrease in total peripheral resistance secondary to excessive release of vasodilators, as in allergy or infection
Cardiogenic shock
This is due to an extreme decrease in cardiac output from any variety of factors (eg MI)
How can venous pooling leading to reduced BP
- Venous pooling due to gravity = increased hydrostatic pressure in legs when a person is standing pushes outward on highly distensible vein walls, causing distension. some blood from capillaries goes to the expanding veins rather than returning to the heart. (increased capillary pressure also causes increased filtration)
- this means there is a reduced venous return
- reduced end-diastolic pressure
- decreased stretch of ventricles
- reduction of SV, CO, BP
(reduced BP does then trigger baroreceptor reflex so the affect doesn’t last long)
gentle leg contractions produce intermittent, complete emptying of deep leg veins
What happens to blood flow during exercise and how?
Increased blood flow to -working skeletal muscles -heart -skin if heat needs to be dissipated Decreased flow to: -kidneys -abdominal organs
This is due to arteriolar vasodilation
- local metabolic factors mediate vasodilation in skeletal and smooth muscle
- in the skin vasodilation is achieved mainly by decreased sympathetic stimulation to the skin
- arterial vasoconstriction also occurs in the kidneys and abdominal organs due to increased symp stimulation
there is a net decrease in peripheral resistance this is due to the huge dilation of the muscle arterioles
What is the effects of mild upright exercise? eg jogging
- Increased skeletal muscle blood flow
- Increased meal arterial pressure
- Increased systolic pressure
- Constant diastolic pressure
- Reduced total peripheral resistance
- Increased CO (due to increased HR and SV)
- Increased HR (due to decrease parasymp to SA and increased symp)
- Increased SV (due to increased venticular contractibilty)
- Increased (small increase) end-diastolic ventricular volume (due to increased filling, starling mechanism=increased SV)
What factors promote venous return during exercise?
- Increased activity of skeletal muscle pump
- Increased depth and frequency of inspiration (resp pump)
- Symp mediated increase in venous tone
- Greater ease of blood flow from arteries to veins through the dilated skeletal muscle arterioles
How do control centres in the brain affect the body during exercise?
“Exercise centres” in the brain produce the primary outflow of symp and parasym outflow to the body
-descending pathways go to appropriate autonomic preganglionic neurons (symp to skeletal muscles, kidneys and abdominal organs) (parasym to skin increases dilation)
- Once exercise is underway or during intense exercise local chemical changes activate chemo receptors.
- Afferent input from these receptors goes to the medullary cardiovascular centre and facilitates the output reaching the autonomic neurons from higher brain centres
- This results in further increase in HR, myocardial contractility, and vascular resistance in nonactive organs
- Meachanoreceptors in active muscles are also activated and provide input to medullary cardiovascular centre.
- Baroreceptors react again causing a further increase in BP (they respond as though BP has decreased due to a ‘resetting’ as excecise begins’)
What differences occur during weight-lifting as opposed to jogging?
-high-force, slow-shortening velocity contractions
same -CO, BP increase and arterioles undergo vasodilation
differences - once contracting muscles exceed 10-15% of their maximal force the blood flow to the muscle is greatly reduced because the muscle are physically compressing the blood vessels that run through them. So cardiovascular changes are ineffective -contractions can only be maintained briefly before fatigue kicks in.
-total peripheral resistance is increased due to the compression, this leads to an increase in mean arterial pressure during contraction.
(frequent exposure can cause maladaptive changes to the left ventricle including wall hypertrophy and diminished chamber volume)
What is maximal oxygen consumption?
This is when oxygen consumption increases till it reaches a point where it fails to increase despite an increase in work load, after this point has been reached work can be increased and sustained only briefly by anaerobic metabolism.
What limits maximal oxygen consumption (or V0 max.)
1) Cardiac output
2) The respiratory systems ability to deliver oxygen to the blood
3) The exercising muscles’ ability to use oxygen
for most people (except highly trained atheletes) CO is the limiter (HR increases until it reaches a maximum)
- rapid heart rate which decreases diastolic filling time
- inability of the peripheral factors favouring venous return to increase filling further during short time avalible
What can change v0 max?
A person’s physical activity
- prolonged bed rest may decrease by 15-25%
- intense training may increase by 15-25%
Increased SV and decreased HR = same CO
1) increased ventricle size and hypertrophy
2) increased number of blood vessels in skeletal muscle which permits increased muscle blood flow and venous return
3) also increases concs of oxidative enzymes and mitochondria in the exercised muscles = this increases muscle endurance but does not affect V0max as it was not limiting it to start with
What is Ventricular hypertrophy?
Ventricular hypertrophy is the thickening of the ventricular walls (lower chambers) in the heart. Although left ventricular hypertrophy is more common, enlargement can also occur in the right ventricle, or both ventricles.
-Healthy cardiac hypertrophy (“athlete’s heart”) is the normal response to healthy exercise or pregnancy, which results in an increase in the heart’s muscle mass and pumping ability.
-Unhealthy cardiac hypertrophy (pathological hypertrophy) is the response to stress or disease such as hypertension, heart muscle injury (myocardial infarction), heart failure or neurohormones. Valvular heart disease is another cause of pathological hypertrophy.
pathological hypertrophy also leads to an increase in muscle mass, but the muscle does not increase its pumping ability, and instead accumulates myocardial scarring (collagen). In pathological hypertrophy, the heart can increase its mass by up to 150%.
What does ageing affect the heart’s performance?
- Decrease in max heart rate
- increased heart stiffness that decreases rapid filling during diastole
