Respiratory Challenges

which factors affect haemoglobin affinity in different partial pressure environments

• pH

• temperature

• CO2 partial pressure

shifting of haemoglobin curve

• shift right = haemo dissociates O2 more regularly

• shift left = haemo hangs onto O2 more tightly

pH on haemoglobin affinity

• more acidic = lower pH = lower affinity = haemo more generous

• more basic = higher pH = higher affinity = haemo holds more tightly

temperature on haemoglobin affinity

• higher = decrease affinity = haemo more generous

• lower = increase affinity = haemo holds tighter

CO2 partial pressure on haemoglobin affinity

• higher than 40 mm Hg = decrease affinity = haemo more generous

• lower than 40 mm Hg = increase affinity = haemo holds tighter

where/when would haemoglobin curve shift right

exercising muscles and increased metabolism esp anaerobic bc

• anaerobic lowers pH

• increased temp

• increased PCO2 bc CO2 as byproduct

where would oxygen-haemoglobin curve shift when at lungs

Normal curve bc pH, temperature and PCO2 in lungs should be at standard conditions

2,3-DPG.2,3-BPG

compound made as byproduct during glycolysis pathway (anaerobic metabolism). It attaches itself to red blood cells

effect of 2,3-DPG on haemoglobin affinity

2,3-DPG increases due to low O2 = affinity decreases = haemo more generous

how does 2,3-DPG differ from pH, temp and PCO2 in terms of haemoglobin dissociation curve?

With 2,3-DPG curve doesn’t go back to normal when in lungs bc 2,3-DPG is attached to red blood cells = not local conditions like pH, temp and CO2 that change tissue to tissue

• shift in curve due to 2,3-DPG persists in lungs

the effect of 2,3-DPG on hameoglobin when in lungs with normal PO2 (100 mm Hg)

2,3-DPG hameoglobin has same saturation as normal haemoglobin (98%)

effect of 2,3-DPG when lungs PO2 is lower than normal (<100 mm Hg)

2,3-DPG decreases haemoglobin affinity = lower saturation than normal 98%

hypoxaemia

abnormally low level of oxygen in the arterial blood

hypoxia

low oxygen levels in tissue

anemia

blood lacks enough healthy red blood cells or haemoglobin to carry adeqaute oxygen to tissue

5 causes of hypoxaemia

1. low fraction of inspired air

2. poor ventilation

3. diffusion limitation

4. poor V/Q matching

5. respiratory shunt

low fraction inspired oxygen

the percentage of oxygen in the air being breathed is lower than the normal 21%

e.g. when at high altitude

how does poor ventilation cause hypoxaemia

reduces amount of air entering alveoli due to causes

• fast and shallow breathing - more air in dead space

• increased airway resistance

• decreased lung compliance

how does diffusion limitation cause hypoxaemia

harder for O2 in alveoli to enter blood bc of

• reduced surface area

• increased distance by thickened membrane or amonut of interstitial fluid

how does poor V/Q matching cause hypoxaemia

too much blood is sent to poorly ventilated alveoli = blood with lower oxygen enters body system

respiratory shunt

airflow to area of lung is completely blocked but blood still flows through region = blood doesn’t get oxygenated

• perfusion but no ventilation (V/Q = 0)

carbon dioxide transport in blood from cell tissue

1. dissolved into blood (7%)

2. CO2 binds to haemoglobin (25%)

3. in red blood cell CO2 combines with water = carbonic hydrase splits into bicarbonate and hydrogen ions. Hydrogen binds to haemoglobin

how does hydrogen ions bound to haemoglobin enter lungs as CO2

Haeomoglobin releases H+ so can pick up oxygen = carbonic hydrase recombines H+ and bicarbonate to make CO2 and water = CO2 diffuses into alveoli

what happens to plasma pH when PCO2 increases in plasma

decreases = more acidic bc CO2+ water releases hydrogen ions

• more H+ = more acidic

Under normal resting conditions at sea level, which of the following would control ventilation?

1. Plasma Oxygen levels

2. Plasma Carbon dioxide levels

3. Both Oxygen & Carbon dioxide levels in plasma

2 bc ventilation is monitored using changes in pH

why does CO2 control ventilation

primary regulation done by central chemoreceptors which detect pH changes (H+ ions)

• CO2 releases H+ when in water = focus on CO2 levels

central chemoreceptors

medulla oblongata - monitor CO2 and H+ in cerebrospinal fluid

• CO2 passes blood-brain barrier = dissociates into H+ and bicarbonate

peripheral chemoreceptors

in carotid and aortic arteries - activated when O2 is below 60 mm Hg

• detects PO2, PCO2 and pH but less sensitive than central

High altitude

atmo pressure decreases = partial pressure is lower = decreases partial pressure in lungs as outside air mixes with air in lungs

• plasma PO2 decreases

• plasma PCO2 decreases

• ventilation increases

why does high altitude cause deacrease in plasma PCO2

high altitude lowers PO2 = activates peripheral chemoreceptors = increased ventilation = more PCO2 exhaled

what happens to plasma pH at high altitude

increases bc PCO2 decreases = Respiratory Alkalosis (more basic)

how to acclimatise to high altitudes

• increased red blood cell production =oxygen-carrying capacity increases

• increase no of capillaries in tissue = reduce distance and increase blood flow

• nitric oxide increases = doubles blood flow

oxygen consumption beginning, during and after exercise

• B = anaerobic for energy until oxygen consumption increases to match energy needed

• D = oxygen and energy match = plateu

• A = O2 consumption stays high as replenish what was used to meet metabolic demand

VO2

max oxygen consumption during hard exercise

pulmonary oedama

Accumulation of fluid in the alveoli = impaired gas exchange and hypoxaemia

heart and pulmonary oedema

left-side heart failure can cause pulmonary oedema

• failure = increased arterial pressure = blood flows back into pulmonary veins = increased hydrostatic capillary pressure = pushes blood into interstitial fluid of alveoli = accumulation = oedema

indications of pulmonary oedema

oedema reduces the rate at which gasses may pass between the alveoli and the blood = plasma P_O2 will be reduced

• lung volumes and airflow not affected

chronic obstructive pulmonary disease (COPD)

causes airway inflamation, narrowed passage ways and damaged air sacs = harder to breath e.g. emphysema

causes of COPD

long-term exposure to irritating substanes that damage the lungs and airways

how to tell if its COPD

• dramatic decrease in FEV1/FVC bc impairment to airflow

• increase in residual volume

• total lung capacity relatively stable

= impairment to ventilation causes decrease in circulating O2