diving physiology I

physiological response to diving (immediate responses)

• Vasoconstriction

• Bradycardia → abnormally slow resting heart rate

afferent vs efferent activation of diving reflex

• Afferent activation is through cold receptors on the skin + chemoreceptors + baroreceptors

• Efferent activation includes both sympathetic and parasympathetic nervous activation

Ambient or atmospheric pressure arises due to air molecules which is greatest at sea level and is reduced with increasing (?)

altitude → reduction in air molecules

pressure calculation for within a body of water

density (p) x gravity (g) x depth (d)

what is 1 atm in pascals?

101.325 × 10³ pascals

density of sea water vs fresh water

1025 kg/m³ vs 1000kg/m³

calculate the pressure underwater (at 40.3m depth, given that the density of sea water is 1025kg/m³) → then calculate atmospheres

atmospheres absolute

• atm (water) + atm (surface)

• surface atmospheric pressure plus the additional pressure exerted by water is equal to atmospheres absolute pressure

change in blood pressure (upright on land vs upright in water)

1. Upright on land

• High peripheral blood pressure

• Pressure in our feet is high due to weight of blood

• Pressure in our capillaries is high and exceeds the oncotic pressure that allows for reabsorption of fluid -> lose plasma volume

• Pressure causes veins to expand -> more blood stored in peripheral veins

• Decrease blood in central veins -> decrease in venous return

• Reduces cardiac output

• Reduces blood pressure

 

2. Upright in water

• Low peripheral blood pressure

• Pressure inside blood vessels increasing at same rate as pressure outside our blood vessels due to the aqueous environment

• Low pressure -> veins do not expand

• Increased venous return

• Increase in cardiac output

• Increases blood pressure

why urination increases in the pool

1. Blood pressure increases (due to decreased peripheral blood pressure → reduces expansion of veins and reduces loss of fluid from capillaries)

2. Glomerular capillary blood pressure increases → increases glomerular filtration

3. Atrial stretch increases from increased blood pressure → increases atrial natriuretic peptide (ANP)

4. ANP increases water and salt excretion into our urine → water follows via osmosis

5. Full bladder → urination

a maximal breath to total lung capacity and subsequent free dive with no equipment will cause (?) of the air in your lungs

compression

boyle’s law (explain and calculation)

• At a constant temperature, the volume of gas is inversely proportional to pressure

• P1 x V1 = P2 x V2

if the lung contains 5L after maximal inspiration, what will be the volume after a dive to 40.3m in sea water? (given 4 atm at 40.3m depth)

• previously calculated → pressure at 40.3m depth is 5 ATA

• P1 = 1 ATA (sea level)

• V1 = 5L (maximal inspiration)

• P2 = 5 ATA

• V2 = P1 X V1 / P2 = 1L

• the lung is compressed to 1/5th its volume

residual volume

total amount of air remaining in your lungs after maximal expiration

lung squeeze

• When lung volume compression falls below residual volume

• Crushing pressure causes blood vessels to leak fluid and blood into the lungs

• Causes haemoptysis (coughing up blood) and pulmonary oedema (fluid in lungs)

calculate the depth at which a female diver’s lung would compress from TLC (at the surface) to RV in sea water?

mechanisms preventing lung squeeze

1. Lungs contain collagen and elastin fibres

• Provides rigidity to the lung (elastic matrix) and resists compression

 

2. Redistribution of blood from the periphery to the thorax

• Increases the volume of an incompressible material into the lung

 

• Both reduce the magnitude of lung squeeze

ear barotrauma

• External auditory canal is exposed to depth-induced hydrostatic pressure

• Liquid filled vestibulocochlear apparatus under same hydrostatic pressure

• Eustachian tube is connected to the back of the throat and allows for ear pressure equalisation

• However if the eustachian tube is closed

• Pressure in the middle ear is not equalised

• Air is not compressible in the ear like in the lung

• Tympanic membrane (ear drum) is displaced inwards and ruptures

• Can cause permanent hearing loss

frog breathing (glossopharyngeal insufflation)

• Humans draw air into the lung by creating negative pressure

• Frogs push positive pressure into the lungs

1. Nostrils open and buccal cavity expands

2. Nostrils close and glottis opens

3. Buccal cavity contracts pushing air into lungs

4. Lungs expand as result of positive pressure

total lung capacity is the sum of residual volume and:

vital capacity

glossopharyngeal insufflation can increase:

total lung capacity → allows for greater diving depth

shallow water blackout

• Loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive in shallow water

• Diver has reached targeted depth -> shallow water blackout can occur on the way back up

dalton’s law

sum of the partial pressure of each gas is equal to the total pressure exerted by the mixture

what is the partial pressure of atmospheric O₂

760 x 0.21 = 160mmHg

760mmHg → atmospheric pressure

0.21 -> 21% -> fraction of oxygen in the air

central vs peripheral chemoreceptors

Central

• Responds to changes in H+ (caused by increase in CO2 diffusion across BBB-> bicarbonate) in the CSF

• Contributes to 80% of the response to an increase in arterial CO2

 

Peripheral

• Responds to CO2 and H+

• Contributes to 20% of the response to an increase in arterial CO2

• Activated when arterial O2 falls below 60mmHg -> coma

which chemoreceptor is responsible for our inability to hold our breath

central chemoreceptor

explain what occurs at each depth

 

1. Surface

• Alveolar oxygen -> 100mmHg

• Alveolar carbon dioxide --> 40mmHg

 

2. Hyperventilation

• Alveolar oxygen -> increaase

• Alveolar carbon dioxide -> 20mmHg -> decrease

• Hyperventilation removes carbon dioxide at the same rate as it is being produced

• Thus CO2 levels in blood/alveoli will decrease

 

3. 10m after diving

• Alveolar oxygen -> 150mmHg -> increase

• Alveolar carbon dioxide -> increase

• Increase in alveolar oxygen and carbon dioxide due to hydrostatic pressure compressing lung

 

4. 10m before resurfacing

• Alveolar oxygen -> 80mmHg

• Alveolar carbon dioxide -> more than 40mmHg -> activate chemoreceptors

• Drop in alveolar oxygen as it is used up by cells

• Diver is alerted to return to surface

5. Surface

• Pressure acting on the body is drastically reduced upon return to surface

• Partial pressure of oxygen also reduced

shallow water blackout explained

1. Levels of alveolar O2 and CO2 normal at surface

2. Diver hyperventilates which expels CO2 and resists urge to breathe

3. At 10m hydrostatic pressure increases which increases partial pressure of O2

4. O2 is used up by working muscles → CO₂ production

5. Eventually, CO2 levels will increase beyond threshold -> chemoreceptors

6. As diver returns to surface the hydrostatic pressure decreases -> decreases partial pressure of alveolar O2

7. Partial pressure gradient now favours the movement of O2 from the blood into the alveoli -> leads to cerebral hypoxia if severe

summary