Respiration under hypo- & hyperbaric conditions Flashcards
Physiological stresses with immersion act primarily on the
respiratory,
cardiovascular, and renal systems.
with immersion The body experiences:
• Increased pressure, or hyperbarism 1 atm (760 mm Hg) for every 10 m depth. Effects air-filled cavities of the body. (Boyle's Law) • Reduced gravitational effects Central shift in blood volume: diuresis, Na+ & K+ excretion. • Reduced ambient temperature Hypothermia.
Immersion up to the Neck: Respiratory factors results in
Positive pressure exerted by surrounding water on
the chest wall >10 cm H2O:
• Decrease in FRC, ERV
• Slight decrease in VC, RV
• IRV increases
• Pressure gradient from top to lung base (25 mm Hg)
Immersion up to the Neck:
Cardiovascular &
• Increased venous return, RA pressure, SV & CO.
• Increased abdominal pressure.
• Decreased peripheral pooling of blood due to
decreased gravitational effects.
• Vasconstriction due to reduced temperature.
• Increased intra-thoracic blood volume.
Breath-hold diving (voluntary) • Limited by? • Changes associated with the? • Changes in \_\_\_\_ \_\_\_\_\_ \_\_\_\_during the decent, and ascent phases of a dive.
oxygen stores.
‘dive reflex’.
alveolar gas exchange
For every 10 m below the surface ambient pressure
is increased by
~ 1 atm.
10 x 100 cm H2O, equivalent to 98kPa, 735 mm Hg,
Breath-hold can be prolonged by prior ________,
but this is dangerous!
hyperventilation
• Hypoxia alone does not trigger ?
ventilation
• Most people can breath-hold?
~1 min with practice.
Full inspiration yields ~ 1L O2 in lungs (i.e. VC ~ 5L).
\ 600 - 700 mL O2 available for consumption before
PaCO2 rises to ~ 50 mmHg, at this point….?
the urge to breathe
takes over.
High PaCO2 (and low pH) causes the subject to
breathe sooner.
• Breathing is also stimulated by low
PaO2 (“hypoxic drive”), but only
under extreme conditions.
• During descent to 10m there will be
incr. compression of
the abdomen. PAO2 maintained, although VO2
continues & quantity O2 decr..
Transfer of CO2 from the blood into the alveoli is
compromised during descent, resulting in
significant
retention of CO2 in the blood (respiratory acidosis).
• During ascent there will be expansion of the
_______& reversal of _________. The transfer of O2 from the alveoli to the blood will then be compromised as PAO2 _________.
abdomen
pressure
decreased
Adaptations with Free diving training:
• Bradycardia. • Vasoconstriction of peripheral vessels. • Splenic contraction, RBCs. • Plasma accumulates in pulmonary circulation, reducing VR, & preventing collapse of lungs at depth >30m.
Free-divers reduce ___to a
minimum: restrict effort &
wear wet suit for warmth.
VO2
Shallow water blackout (SWB):
Latent Hypoxia
loss of
consciousness at shallow depths.
Shallow water blackout (SWB): • Most commonly occurs
within 5m of the surface,
where expanding lungs literally suck oxygen
from the divers blood reducing PaO2.
Blackout occurs quickly, insidiously and without
warning. Victims die without any idea of their
impending death.
• Pre-dive ________increases risk of SWB
by ¯PaCO2 level at the start of the dive
hyperventilation
At sea level the FIO2 is 0.21. What is it
at the top of Mt Everest (8848 m)?
the same
• As altitude increases, ___________
decreases.
• Consequently, fewer molecules of?
• A fall in PAO2 is predicted by the?
barometric pressure (PB) O2 per unit volume of inspired air.
alveolar gas
equation.
Moderate or Intermediate Altitude: 1,500 - 2,440 m High Altitude: 2,440 - 4,270 m Mt Ruapehu (2,797 m); Mt Cook (3754 m) Very High Altitude: 4,270 - 5,490 m Extreme Altitude: 5,490 - 8,848 m
Significant altitude illness rare.
Very accessible, & therefore where most problems occur.
Typical for base camps.
Gradual acclimatization needed.
Short time only possible.
Slow ascent & light workloads only.
hypoxemia gives rise to
compensatory responses at High Altitude
• If PACO2 were to remain at the normal resting value of 40mm Hg, then PAO2 would be ~ (PIO2 - PACO2) = 54 mm Hg.
• But, ventilation is stimulated by _______ -_____________
in the carotid bodies sensitive to PO2. VA = fR(VT - VD).
• Result of VA is to ¯PACO2, allowing an _________in PAO2.
• However, the decline in PaCO2 ______stimulation of central chemoreceptors, counteracting the initial hypoxic response.
peripheral chemoreceptors
increase
reduces
At high altitude ∆PO2 between alveolar and mixed venous is less, therefore reducing
the pressure gradient for diffusion.
Altitude Hypoxia typically has 3 Forms:
• Sudden (acute) exposure e.g. Aircraft decompression • Exposure over several weeks e.g. Low-lander acclimatization • Lifelong exposure e.g. Permanent residents at high altitude
Acute Exposure to Very High Altitude
Physiological responses:
• Hyperventilation, and consequent lowering of
PaCO2 (hypocapnia & respiratory alkalosis).
• Increased heart rate (abolished by b-adrenergic
blockcade).
• Increased plasma and urinary catecholamines.
• Increased cardiac output.
• Effects on cerebral function (loss of consciousness
with severe hypoxia).
• Alterations to regional blood flow in lungs due to
selective hypoxic vasoconstriction.
Time course of altitude effects:
• Initial
Initial hyperventilation & hypocapnia followed by reflex inhibition of ventilation.
• adaptations of altitude effects:
achieved through renal
reduced HCO3- reabsorption & conserving H+.
high cap and mito density
Acclimatization is the process by
which tolerance
and performance are improved over a period of
hours to months at altitude.
Adaptation refers to
physiological and genetic
changes that occurs over a period of years to
generations who live permanently at high altitude.
• Overall increase in work of breathing ~___
Immersion up to the Neck:
60%
Immersion up to the Neck:
Renal results in
- ADH suppression (diuresis).
* Increased ANP release (diuresis & NaCl excretion).
two types of acute mountain sickness
benign acute- 6-12 hours in 40% of people in high altitude
malignant- odema rare life threatening
the acclimatised person has
high haem count
incr. O2 transport
large blood volume
may grow RV from hypoxic pulmonary vasoconstrict.
