factors influencing gas exchange

Question 1

what is V,Q and its relationship

Answer 1

• V Is ventilation
• Q is perfusion (blood flow)
• V/Q=1 suggest that flow of ventilation matches the blood flow
• humans have a v/q ratio of 0.8-1

Question 2

where is alveolar ventilation greatest- erect person

Answer 2

• alveolar ventilation is greatest at lower parts of the lungs
• intrapleural pressure is less negative in lower regions- due to gradient driven by gravity this gradient impacts compliance of alveoli ( compliance greater in lower regions)

Question 3

what is the distribution of blood flow in lungs - in erect person

Answer 3

• greater blood flow at lower regions of the lungs due to gravity
• intravascular pressure (pressure in blood vessels) greater in lower regions and therefore resistance is lower due to recruitment and distension

Question 4

how does v and q change down the lung and what happens to the v/q ratio down the lung

Answer 4

• both v and q increases down the lung
• however q increases more than v down the lung so ratio decreases down the lung

Question 5

what happens to the v and q in supine position

Answer 5

• in the supine position q is greater posterior, v is also greater in posterior compared to anterior however p is much greater so v/q is smaller in posterior in supine position and higher in anterior of the lung

Question 6

what are the 3 west zone sin erect person of lung and the differences in alveolar pressure, arteriolar and venous pressure

Answer 6

zone 1- apex (PA>Pa>PV)
zone 2- mid (Pa>PA>PV)
zone 3- base (Pa>Pv>PA)

Question 7

what is the v/q ratio in shunt and deadspace

Answer 7

• v/q ratio very low in shunt (less than 0.7)
• v/q ratio high greater than 1 in headspace
• so in shunt goo ventilation poor perfusion
• in deadspace poor ventilation and poor perfusion

Question 8

how does v/q ratio change up the lung

Answer 8

• ratio increase- shows an exponential increase in graph

Question 9

what is the flow and pressure like In pulmonary and systemic circulation

Answer 9

• flow is the same in both circulations
• pressure lower in pulmonary circulation compared to systemic so resistance is low in pulmonary circulation
• low resistance maintained by recruitment (opening of capillaries), distension (widening of vessels)

Question 10

what happens with exercise to pulmonary flow and cardiac output

Answer 10

• cardiac output increases 2-3 times
• inflow pressure to lungs only rises slightly

Question 11

capillary bed in lungs vs capillary network in tissues

Answer 11

systemic capillaries small diameter and represent a high resistance to blood flow
- pulmonary capillary bed are a sheet of blood that flows across the alveolar surface arrangement has less resistance to flow
- recruitment and distension of vessels allows flow to increase in the pulmonary vessels whilst resistance decreases

Question 12

what is the control of blood flow in pulmonary

Answer 12

• neurohumoral (sympathetic and parasympathetic cause vasoconstriction, vasodilation
• increased capillary blood flow (recruitment and distension)

Question 13

what happens to lungs during hypoxia (low oxygen levels)

Answer 13

• increased blood flow to ventilated alveolar
• decreases blood flow to hyperventilated alveolar via vasoconstriction of pulmonary arterioles

Question 14

what happens during hypercapnia

Answer 14

• bronchoconstriction of bronchioles
• diverts ventilation from poorly perufused alveoli towards ones that are better perfused

Question 15

what is ficks law and the factors affecting it

Answer 15

• factors that affect diffusion of gases across capillary to alveoli vice versa
• propertional include tissue area, difference in partial pressures, diffusion constance
• inversely proportional to tissue thickness
• ficks law consists of an equation proportional elements at the same and inversely proportional elements at the bottom of equation

Question 16

what is the surface area of lungs

Answer 16

• alveoli have a massive surface area
• surface area of tennis court (50 to 100 meters squared)

Question 17

what is the partial pressure difference of oxygen in the lungs

Answer 17

7kPa

Question 18

what is the partial pressure difference of carbon dioxide in lungs

Answer 18

0.7 kPa

Question 19

what effects does hyperventilation have on oxygen and carbon dioxide

Answer 19

• hyperventilation has a greater affect on carbon dioxide clearance than oxygen intake (600% difference in partial pressure of arterial and venous blood of carbon dioxide and 25% difference for oxygen)
• this is due to increased solubility of carbon dioxide compared to oxygen and also due to oxygen being mainly transported by hb so if hb is saturated increased ventilation would not gave any effects on oxygen uptake

Question 20

what factors make up the diffusion constant in ficks law

Answer 20

1. proportional to gas solubility
2. inversely proportional to square root of molecular weight

Question 21

what are the factors that impact oxygen delivery to tissues

Answer 21

-oxygen content of blood (hb levels, partial pressure of oxygen)
- cardiac output
- blood vessels

Question 22

what are the two forms of oxygen transport in blood

Answer 22

• binding to hb (one red blood cell has 250 million hb molecules), 99% transported by hb, pulse oximeter
• dissolved in blood (partial pressure of oxygen measured using arterial blood gas)

Question 23

what are the three ways carbon dioxide in transported

Answer 23

1. dissolved in plasma (7-10%)
2. as bicarbonate ions- carbon dioxide reacts with water in hb to form carbonic acid via enzyme carbonic anhydrase, acid dissociates into hydrogen ions and HCO3- ions, HCO3-ions diffuse out and chloride ion diffuses in (chloride shift)- 70-75%
3. bound to hb to form carbaminohaemoglobin (20-23%), bound to amino groups in global part

Question 24

what reduces affinity of hb to oxygen

Answer 24

• high temperuature
• increased carbon dioxide
• low partial pressure of oxygen
• increase DPG
• low ph

Question 25

what is hypoxia

Answer 25

• deficiency in the amount of oxygen reaching the tissues
• accounted for by the oxygen delivery equation

Question 26

what is hypoxaemic hypoxia

Answer 26

• insufficient oxygen reaching the blood which shows low saturation and partial pressure readings
• patient may look blue (central and peripheral cyanosis)

Question 27

what is stagnant hypoxia

Answer 27

-failure to transport sufficient oxygen due to poor flow (low cardiac output, local obstruction such as pe)

Question 28

what is anaemic hypoxia

Answer 28

reduced oxygen carrying capacity of the blood due to decreased hb levels or altered hb constituents
include all anaemia, co poisoning, methaemoglobinaemia

Question 29

what is histotoxic hypoxia

Answer 29

• impaired use of oxygen by tissues
• cyanide poisoning

Question 30

what are the four hypoxias

Answer 30

• hypoxemic hypoxia
• anemic hypoxia
• stagnant hypoxia
• histiotoxic hypoxia

Question 31

what is the causes/types of hypoxemic hypoxia

Answer 31

1. low inspired FiO2 (altitude, percentage of air in oxygen falling fires)
2. low ventilation (hypoventilation)
3. shunt
4. deadspace
5. impairment of diffusion e.g. alveolar thickness, diffusion gradient

Question 32

what is shunt and the two types

Answer 32

• v/q ratio is low
• blood from right side of heart makes it to left side without undergoing oxygenation
• cardiac shunt (hole in heart)
• intrapulmonary shunt due to filling of alveolar with blood, mucous, oedema or alveolar squishing such as pneumothorax, haemothorax

Question 33

what is dead space and the two types of deadspace

Answer 33

• v/q ratio is high
• air in the lungs that do not undergo ventilation
• always deadspace in lungs which doesn’t undergo ventilation which is normal this is the anatomical dead space which is found in trachea, bronchioles etc), physiological deadspace is made of anatomical dead space (normal) and alveolar dead space ( insignificant in healthy individuals however much larger in unhealthy individuals)
• mechanical deadspace - only in ventilated patients as a result of breathing apparatus

Question 34

how can we measure effectivnness of diffusion

Answer 34

• DLCO