Transcript High affinity hemoglobin and blood oxygen saturation in diving

Jessica U. Meir and Paul J. Ponganis
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Made up of four heme groups (oxygen
binding)
Reversibly binds O2 with a cooperative
binding behavior.
Low partial pressure of oxygen (PO2) = Low
binding affinity of oxygen
As PO2 increases, so does the affinity of
oxygen
P50 = concentration of oxygen in which Hb is
50% saturated
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Vena Cava
◦ Made up of the superior and inferior vena cava
◦ Functions to return the deoxygenated blood from
the body back to the heart
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Aorta
◦ Largest artery in the body
◦ Distributes oxygenated
blood to all parts of the
body
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Tallest and heaviest of all living penguins
Endemic to Antarctica
Flightless
◦ Streamlined body
◦ Wings stiffened and flattened into flippers
Diet consists of fish, crustaceans,
and cephalopods
During hunting can dive to depths of
535m and remain submerged for
over 23 mins (Wienecke et al,2007).
How are they doing this?
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Exceptional low tolerance to O2
◦ Biochemical and molecular adaptations
 A shift in the O2- hemoglobin (Hb) dissociation?
 O2-Hb dissociation curve of whole blood of emperor
penguins have yet to be defined.
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Generally, Hb of birds has a lower O2 affinity
than that of mammals
◦ May reflect a shift toward favoring O2 unloading at
the tissues
•Avian respiratory system is
inherently more efficient at oxygen
consumption (Powell et al., 2000)
Mammals
•P50 of most birds are much higher
than those of mammals (Lutz,
1980)
P
50
Birds
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Certain penguins and the bar-headed goose
have P50 values in the mammalian range.
◦ Favoring O2 uptake from the lungs when PO2 is low.
◦ Determination of the P50 and dissociation curve in
whole blood still remains necessary
www.tropicalbirding.com/tripReports/TR_NorthI
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The researchers characterized the O2-Hb
dissociation curves of the emperor penguin in
whole blood
◦ Investigate the adaptation of Hb in this species
◦ Address blood O2 depletion during diving, by
applying the dissociation curves to previously
collected PO2 profiles to estimate in vivo Hb
saturation.
www.polarconservation.org/education/antarctic
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Non-breeding emperor penguins were
captured near the McMurdo sound ice edge
or at Terra Nova Bay
Maintained at an isolated dive hole
upload.wikimedia.org/wikipedia/commons/d/d8/D
www.phys.unsw.edu.au/nature/antarctica_map2.gif
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PO2 electrodes and thermistors inserted
percutaneously into the aorta or vena cava
connected to a PO2 / temperature recorder
Mk9 time-depth recorder (TDR)
Penguins allowed to dive 1-2 day before
removal of equipment
PO2 electrode
Time-depth recorder
Thermistor
warneronline.com
Wikipedia.org
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Determined with the mixing technique of
tonometered blood
◦ Analysis was completed within 6h of blood
collection
◦ Mixed 0% oxygen and 100% oxygen to achieve
desired hemoglobin saturation at various points
along the curve with subsequent measurements of
the PO2
◦ i-STAT analyzer – pH and PCO2
◦ Tucker chamber analyses – O2 content
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CO2 Bohr effect – changing CO2 concentration
Dissociation curves – pH values of 7.5, 7.4,
7.3, and 7.2.
All data from all penguins were combined
Lactic Acid effect- added lactic acid to sample
Validate equipment and methods, S02 was
determined for chicken and pinniped species
with previously published data
Tonometer
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Values obtained by applying PO2 profiles to a
linear regression equation and solving for SO2
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Cyanomethemoglobin technique
Hb concentration – oxygen content for initial
and final dive time points calculated from the
corresponding SO2
◦ Hb concentration of 18.3g dl-1
◦ Initial SO2 was estimated at 7.5 and the final SO2 at
7.4
◦ % O2 content depletion = (initial O2 content-final O2
content)/initial O2 content x 100
◦ Rate of O2 content depletion = (initial O2 content –
final O2 content)/dive duration
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ANOVA – differences between arterial and
venous results
Spearman rank order correlation tests –
correlation between dive duration and final
SO2, pre-dive S02, percentage O2 content
depleted and depletion rate
Max SO2, initial SO2, final SO2, Δ SO2 were all significantly different between arterial
and venous compartments.
Blood O2 store depletions rates between the two compartments were not significant
P50 = 28±1 mmHg at pH 7.5
Fixed Bohr effect was not significantly
Different that of CO2
[Hemoglobin] = 18.3±1.1 gdl-1
Sa,O2 remained near 100% for much of the dive
Pre-dive and initial Sv,O2 = higher than emperor
penguins at rest
Sv,O2 quite variable among dives with marked
fluctuations, transient increases during the dive,
and a large range of final values.
Significant amount of overlap between
arterial and venous values
With only one exception, Sv,O2
decreased below 20% only in dives that
Were longer than measured ADL
Final Sa,O2 and Sv,O2 demonstrated a strong and
significant neg correlation to dive time
% O2 content depleted showed a strong
positive correlation with dive durations
Blood O2 store depletion rate had a significant positive
relationship to dive duration
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Because of its potential to contribute to
tolerance to low O2 in this species, the O2-Hb
dissociation curve of the emperor penguin is
left-shifted relative to most birds.
◦ Similar to other penguin species and bar-headed
goose.
◦ Left-Shifted curve = more O2 is available at any PO2
 Prevent such events as shallow water blackouts
◦ Increase O2-Hb affinity allows for more complete
depletion of respiratory O2 store
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Biochemical adaptation behind left-shifted
O2-Hb dissociation curves = specific amino
acids substitutions.
◦ Specific substitutions not altered in emperor
penguins
 Does show differences from human Hb
 Might be other structural features
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Final Sv,O2 values reached very low levels in
dives that were longer than the ADL
◦ Wide range of final Sv,O2, and venous PO2 for dives of
similar durations.
 Reflect differences in the peripheral vascular response
 Regulation of blood flow to muscle and other organs
 Arterio-venous (A-V) shunts
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Final Sa,O2 values remained high
◦ Minimize the risk of shallow water blackouts
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Because of pulmonary gas exchange with the
blood, Sa,O2 remained close to 100% during
dive
◦ Preserving a high O2 content in the arterial
compartment
 Brain
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Pre-dive and initial Sv,O2values = higher than
Pv,O2 values of emperor penguins at rest.
◦ Arterialized venous values imply some degree of av shunting (or lack of tissue uptake)
 To convert (venous blood) into bright red arterial blood
by absorption of oxygen in the lungs.
◦ Lack of lactate build up, muscle temperature
profiles, dramatic bradycardia and lack of
association between heart rate and stroke
frequency also support Shunting
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Used values to calculate intrapulmonary
shunting = 28% at rest
◦ Might be overestimated
 Capillary O2 content
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Using pre-dive values, intrapulmonary
shunting = 14.3%
◦ Hyperventilation and tachycardia characteristic
improves ventilation-perfusion matching prior to
the dive
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Calculation of the blood O2 store to overall metabolic
rate was made
◦ Included dives in which SO2 increased during the
dive and then exclude them
 Respiratory depletion was 2.3 and 5.3 times that in the
venous and arterial blood compartments
 Simultaneous air sac and blood PO2 data would allow
calculation of the net contribution of these O2 store to
diving metabolic rate
 Not currently feasible
◦ Consistent with
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A significant contribution from the exceptionally large muscle O2
store to diving metabolic rate
The low field metabolic rate and the true bradycardia exhibited by
emperor penguins
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Enhanced O2 affinity of emperor penguin Hb
◦ Similar to the high-altitude geese and other
penguins species
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SO2 profiles during diving demonstrated
◦ The maintenance of Sa,O2 levels near 100% throughout
most of the dive
◦ A wide range of final Sv,O2 values and optimization of the
venous blood O2 store resulting from arterialization and
near depletion of venous blood O2 during longer dives
◦ Estimated contribution of the blood O2 store to diving
metabolic rate was low and highly variable
 Influx of O2 from the lungs into the blood during diving
and variable rates of tissue O2 uptake
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Overall = Very well planed experiment
◦ Tedious work & detailed explanations for
everything
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Surgery
◦ Invasive?
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Introduction – more background information
on important topics (Shunting etc.)
Use a lot of calculations in the discussion
Second guessing them selves.