Microcirculation, BP, Cardiorespiratory mechanisms and ventillation Flashcards
Function of microcirculation?
Metabolic exchange at tissue site.
How do you calculate flow rate?
Pressure gradient / resistance.
What are the 3 factors that affect resistance in a vessel?
Vessel length, Vessel radius and blood viscosity.
What does an increase in vessel length do to resistance?
Increases resistance.
What does an increase in vessel radius do to resistance?
Decreases resistance.
What does an increase in blood viscosity do to resistance?
Increases resistance.
Why does an increase is blood pressure increase flow rate?
Increase in pressure gradient.
Why does arterial vasoconstriction decrease blood flow?
Decrease in radius of vessel increases resistance to blood flow.
Arterioles main function?
Major resistance vessel. Regulate blood flow by altering resistance by altering radius of blood vessel.
How are arterioles adapted?
Extensive smooth muscle in their walls and display a partial state of contraction at rest allowing them to vasoconstrict and vasodilate (vascular tone).
Arterioles detect an increase in O2 usage and vasodilate. What is this an example of?
Active hyperaemia.
What can result in active hyperaemia?
Local metabolites sensed by arterioles. Increase in O2 usage.
During exercise your small intestine arterioles experience unnecessary stretch. What occurs next and what is this called?
Myogenic vasoconctriction. Myogenic autoregulation.
What can cause myogenic autoregulation?
Change in blood temperature and stretch due to an increase in blood pressure.
What helps regulated systemic arterial blood pressure?
Cardiovascular control centre in medulla via sympathetic nervous system and endocrine hormones.
What is the blood pressure equation?
Blood pressure = cardiac output x total peripheral resistance
Using the blood pressure equation explain how the cardiovascular control centre can restore low blood pressure?
Increase total peripheral resistance by increasing vasoconstriction in certain areas such as the gut.
Vasoconstriction hormones?
AVP, Angiotensin II and adrenaline/NA.
In relation to capillaries what do more metabolically active tissues have?
Denser capillary networks.
Types of capillary structures?
Continuous, fenestrated and discontinuous.
What can diffuse out of continuous capillary gap junctions?
Small molecules like oxygen and water.
What is the difference between the different types of capillary structures?
Size of gap junctions. Size of gap junctions increases from continuous to fenestrated to discontinuous.
What is bulk flow?
A volume of protein-free plasma filters out of the capillary, mixes with the surrounding interstitial fluid (IF) and is reabsorbed.
Term used to describe movement of fluid from capillary into interstitial fluid is known as?
Ultrafiltration.
Term used to describe movement of fluid from interstitial fluid into capillary?
Reabsorption.
How does the lymphatic system prevent the blood pressure from dropping due to hydrostatic force being greater than colloidal osmotic pressure?
Reabsorption of fluid into blood.
Where does reabsorption of fluid into blood occur?
Thoracic duct into left subclavian veins
What moves lymph around the body?
Skeletal muscles and respiratory movement.
Lymph vessel structure
Blind-ended, single-layered and contain large permeable water-filled one-way channels.
What are the pulsatile circulatory sounds heard upon auscultation of the brachial artery?
Korotkoff sounds.
The first soft tapping sound when doing an auscultation of the brachial artery represents what?
Systolic blood pressure
The last soft tapping sound when doing an auscultation of the brachial artery represent what?
Diastolic blood pressure.
What do the terms Hyperpnoea / Hypopnoea mean?
Increased depth of breathing / Decreased depth of breathing.
What does the term apnoea mean?
Cessation of breathing (no air movement)
What does the term orthopnoea mean?
Positional difficulty in breathing (when lying down)
What is tidal volume?
Volume of air exchanged during each normal breath.
What is inspiratory reserve volume?
Maximal volume of air that can be forcibly inspired after tidal inspiration.
How to calculate inspiratory capacity?
Inspiratory reserve volume + Tidal volume.
What is residual volume?
Volume of air the remains in lungs after forced expiration.
How to calculate total lung capcity?
Residual volume + expiratory reserve volume + tidal volume + inspiratory reserve volume
How to calculate vital capacity?
Total lung capacity - residual volume
What is functional residual volume?
Total amount of air present in lungs after tidal expiration.
How to calculate functional residual volume?
Expiratory reserve volume + residual volume
What is minute ventilation?
Amount of air moving in and out of lungs per minute.
How do you calculate alveolar ventilation?
[Tidal volume - dead space] x breathing frequency
What is dead space?
Part of lungs where there is no gas exchange.
What affects total lung capacity?
Height, sex, pulmonary disease.
What is conducting zone in the lungs?
Provides passageways for air to travel into and out of lungs.
Why is conducting zone regarded as anatomical dead space?
No gas exchange takes place in the conducting zone.
What is the respiratory zone in the lungs?
Areas with alveoli that have a blood supply.
Which area of the lungs is equivalent to alveolar ventilation?
Respiratory zone.
Why is non-perfused parenchyma regarded as alveolar dead space?
Non perfused parenchyma contain alveoli with no blood supply and so no gas exchange can take place here.
How is physiological dead space calculated?
Anatomical dead space (conducting zone) + alveolar dead space (non perfused parenchyma)
At functional residual capacity what are the lungs forces like?
The lung-chest forces are in equilibrium. Chest recoil = lung recoil.
What membrane surround the lungs?
Visceral pleural membrane.
What membrane covers the inner surface of the chest wall?
Parietal pleural membrane.
What is the function of the pleural fluid in the pleural cavity?
Reduces friction between the membranes when you breath.
Why is normal breathing regarded as negative pressure breathing?
Pressure of alveolar reduced bellow pressure of atmosphere.
What is positive pressure breathing?
Pressure of atmosphere increased above alveolar pressure.
Examples of positive pressure breathing?
Mechanical ventilation, CPR, High pressure chamber.
What occurs in inspiration?
Diaphragm moves down and intercostal muscles move rib cage up and out.
What is dalton’s law?
Pressure of gas mixture is equal to sum of partial pressure of gases in the mixture.
What is fick’s law?
Diffusion is directly proportional to concentration gradient, exchange surface area and diffusion capacity of gas and inversely proportional to thickness of exchange surface.
What is henry’s law?
Solubility of gas is directly proportional to partial pressure of that gas in equilibrium with that liquid.
What is boyle’s law?
At constant temperature, volume of gas is inversely proportional to pressure of that gas.
What is charles law?
At constant pressure, volume of gas is proportional to temperature of that gas.
Modification of inspired air in airways?
Air is warmed, humidified, slowed (air lower in lungs is barely moving) and mixed.
Why is haemoglobin essential to life?
Dissolved oxygen is not enough to sustain life.
Why does HbO2 saturation need to be interpreted with haemoglobin?
Someone who has lost lots of blood can still have a HbO2 of 100%.
What are factors that increase Hb oxygen affinity?
A decrease in temperature, alkalosis, hypocapnia (low blood C02 levels) and low 2,3-DPG levels in blood.
What does 2,3 DPG do? What kind of protein does this make haemoglobin?
Release oxygen from haemoglobin. Haemoglobin is an allosteric protein.
What are the factors that decrease Hb oxygen affinity?
An increase in temperature, acidosis, hypercapnia (high blood C02 levels) and high 2,3-DPG levels in blood.
How does haemoglobin and haemoglobin oxygen saturation change in a normal person, anaemic patient and a patient with polycthaemia?
Haemoglobin oxygen saturation will be the same but haemoglobin would be different. Low Hb in anaemic and high Hb in polycthaemia patient.
What does carbon monoxide do to blood O2 and HbO2 saturation?
Low blood O2 as its harder to release oxygen from carbon monoxide bound haemoglobin. Reduced HbO2 saturation as haemoglobin binds to carbon monoxide instead of oxygen.
What protein has a greater affinity to oxygen than HbA or HbA2?
Fetal haemoglobin.
Purpose of fetal haemoglobin having a greater affinity to oxygen that HbA?
To extract oxygen from mothers blood in placenta.
What protein has a greater affinity to oxygen than fetal haemoglobin?
Myoglobin.
Purpose of myoglobin having a greater affinity for oxygen that HbA?
To extract oxygen from circulating blood and store it.
What is the HbO2 of blood arriving to alveoli like?
Still fairly high at around 75%.
Why may the blood leaving the lungs not have 100% HbO2?
Due to bronchial circulation drainage of deoxygenated blood into pulmonary vein
What are the 3 ways in which CO2 is transported in the blood?
CO2 in blood. CO2 that reacts with water to produce carbonic acid in the blood. Carbonic acid in haemoglobin.
What happens to carbonic acid in haemoglobin?
H+ ions bind to haemoglobin chain. Bicarbonate leaves red blood cell in exchange of a chloride ion via the AE1 transporter.
Why is the AE1 transporter on red cells important?
Allows negative chloride ions to enter the RBC to maintain resting membrane potential.
How does pressure of alveoli and volume of lungs change during inspiration?
Pressure of alveoli decreases. Volume of lungs increases.
How does the pressure of pleural cavity change during inspiration?
Decreases.
How does the pressure of pleural cavity change during expiration?
Increases.
Why isn’t total resistance to air flow and airway generation a linear relationship?
Increase in number of airways at a certain airway generation offsets decrease in radius of airways.
Why does resistance to airflow decrease later in inspiration?
Greater lung volume and more dilated airways results in lower resistance.
What blood vessels hold most of the blood volume?
Veins and venules.
Why is the mean arterial pressure equation an approximation?
Assumes steady flow (which does not occur due to the intermittent pumping of the heart). Rigid vessels
Right atrial pressure is negligible.
Types of blood flow?
Laminar flow and turbulent flow.
What is laminar blood flow?
Velocity of fluid is constant at any one point and flow in layers. Blood flows fastest closest to the centre of lumen; blood cells closest to the wall experience more friction.
What is turbulent blood flow?
Blood flows in irregular manner and is prone to pooling.
What can turbulent blood flow damage?
Endothelium of blood vessels.
How do you calculate pulse pressure?
Systolic blood pressure - diastolic blood pressure.
How to calculate MAP using pulse pressure?
Diastolic blood pressure + 1/3 (pulse pressure).
Why is there negative pressure in pleural cavity at rest?
Lungs trying to contract inwards and chest wall trying to contract outwards.
Why can small to medium airways collapse but large airways can’t?
Large airways contain cartilage rings that prevent airway collapse.
What is compliance and how is it calculated?
Tendency to distort under pressure. Change in volume / change in pressure.
What is elastance and how is it calculated?
Tendency to recoil to its original volume. Change in pressure / change in volume.
What can result in decreased arterial compliance?
Increase in stiffness of arteries as we age.
What does an increase in arterial stiffness result in?
Increase in systolic blood pressure. Lower diastolic pressure as less diastolic flow.
What induces diastolic blood flow after systole?
Recoil of elastic arteries.
Why does pressure fall slowly in aorta after aortic valve closes?
Diastolic flow in the downstream circulation.
What facilitates venous return?
Contraction of skeletal muscle around veins. Movement of diaphragm and chest.
What can incompetent valves in veins cause? Where does this usually happen?
Varicose veins. Happens usually in the legs.
Prolonged elevation of venous pressure can cause what?
Oedema.
How does an aneurysm happen?
Weak muscle fibres in artery wall. Inward force produced by artery wall doesn’t match the blood pressure and so blood vessel expands until it ruptures.
Why is it important that veins are more compliant than arteries?
Veins store most of the body’s blood. A small increase in pressure expands the volume of veins a lot.
When are veins the most compliant?
At low pressures.
When standing upright, why does the bottom of the lung have greater ventilation?
Smaller and more compliant alveoli at the bottom of the lungs and effects of gravity.
When standing upright, why does the bottom of the lung have greater perfusion?
Due to gravity which results in higher flow rate.
Why does perfusion vary more than ventilation when comparing base and apex of lungs?
Blood is more dense than air. Blood experiences effects of gravity more.
During exercise what shift is seen in an oxygen dissociation curve?
Rightwards shift.
A person with polycthaemia what shift would we see in the oxygen dissociation curve compared to a normal person?
Shift upwards.
A person with anaemia what shift would we see in the oxygen dissociation curve compared to a normal person?
Downwards shift.
A person with carbon monoxide poisoning what shift would we see in the oxygen dissociation curve compared to a normal person and why?
Downwards and left shift.
Decreased capacity so can’t carry as much oxygen. Increased affinity to oxygen, can’t lose oxygen as easily from haemoglobin.
How may type 1 diabetes shift the oxygen dissociation curve?
Shift to the right due to development of diabetic ketoacidosis.
What increases the concentration of dissolved oxygen in the blood?
Increase in tidal volume.
Why can tachycardia cause myocardial ischaemia?
Reduced diastolic filling time of coronary arteries.
