Test 2 long concepts Flashcards
Why are we interested in alveolar gas composition
Inspired air contains virtually no CO2. Therefore, the CO2 contained in the alveoli must come from metabolism
However, VCO2 depends not only on how fast O2 is utilized, but also on the kind of fuel metabolised.
Physiological stresses with immersion of water
Body experiences:
increased pressure or hyperbarism, pressure increases 1 atm for every 10m depth
Effects air-filled cavities of the body (Boyle’s Law)
Reduced gravitational effects. Central shift in blood volume. Increased diuresis, Na+ and K+ excretion
Reduced ambient temperature - hypothermia
Immersion up to the neck (Respiratory)
Positive pressured by surrounding water on the chest wall
Decrease in FRV
Decrease ERV
Slight decrease in VC
IRV increases
Small decrease in RV
Pressure gradient from top to lung base
Increase in work of breathing (60%)
Immersion up to Neck: Cardiovascular & Renal
Increased venous return, RA pressure, SV & CO
- Increased abdominal pressure
- Decreased peripheral pooling of blood due to decrease gravitational effects
- Vasoconstriction due to reduced temperature
Increased intra-thoracic blood volume
- ADH suppression
- Increased ANP release
Breath-hold diving (voluntary)
Limited by oxygen stores
Full inspiration yields - 1L O2 in lungs
Hypoxia alone does not trigger ventilation
Changes associated with the “dive reflex”
Changes in alveolar gas exchange during ascent and descent
Breath-hold diving up to 10m (descent and Ascent)
During descent - compression of abdomen. PAO2 maintained, although VO2 decreases
Transfer of CO2 from the blood into the alveoli is compromised during descent, resulting in significant retention of CO2 in the blood
During ascent, theres expansion of abdomen & reversal of pressure. The transfer of O2 from the alveoli to the blood will then be compromised as PAO2 decreased.
Free diving adaptations with training
Bradycardia
Vasoconstriction of peripheral vessels
Splenic contraction ^ RBC
Plasma accumulates in pulmonary circulation, reducing VR & preventing collapse of lungs at > 30m
Shallow water blackout (Latent hypoxia)
Loss of consciousness at shallow depth
Occurs within 5m of surface where expanding lungs literally suck oxygen from the divers blood
Blackout occurs quickly, victims die without any idea of their impending death
Compensatory responses to altitude hypoxia by chemoreceptors
Ventilation is stimulated by peripheral chemoreceptors sensitive to PaO2
Result of increased volume of alveolar gas is to decrease PACO2, allowing an increase in PAO2
However, the decline in PaCO2 reduces stimulation of central chemoreceptors, counteracting the initial hypoxic response
Acute response to very high altitude
Physiological responses
Hyperventilation and consequent lowering of PaCO2
Increased heart rate
Increased plasma 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.
High altitude adaptation/acclimatisation changes process
Primary disturbance
Decrease PaO2
Environmental hypoxia
Leads to increased pulmonary ventilation
Leads in increased PaO2 and decreased PaCO2
Causes secondary disturbance increasing blood pH
Increased renal excretion of bicarbonate lowering blood pH
Hypoxia leads to… (physiological changes)
Increased pulmonary ventilation leading to increased PaO2, increasing organ oxygen delivery
Increased CO - increased blood flow increasing organ oxygen delivery
Increased blood vessel density - increased blood flow increasing organ oxygen delivery
Increased renal sodium and water excretion - increased RBC increasing organ oxygen delivery
What helps improve arterial blood O2, oxygen delivery, aerobic exercise performance?
Increasing:
Erythropoiesis
Muscle capillary density
Haemoglobin
Haemoconcentration
High altitude adaptations of blood, muscles and respiratory system
Blood: Increased haemoglobin-oxygen affinity and plasma volume
Muscles: Decreased mitochondrial volume density and muscle cross sectional area. Increased muscle capillary density and increase myoglobin concentration and decreased oxygen consumption during exercise
Respiratory : Increased ventilation efficiency and lung size
Acute mountain sickness
Depends on:
Speed of ascent
Altitude reached
Physical exertion
Individual factors
Can develop into life-threatening high altitude cerebral edema and high altitude pulmonary edema
