High affinity hemoglobin and blood oxygen saturation in diving

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High affinity hemoglobin and blood oxygen saturation in diving Powered By Docstoc
					Jessica U. Meir and Paul J. Ponganis
   Made up of four heme groups (oxygen
   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
   P50 = concentration of oxygen in which Hb is
    50% saturated
   Vena Cava
    ◦ Made up of the superior and inferior vena cava
    ◦ Functions to return the deoxygenated blood from
      the body back to the heart
   Aorta
    ◦ Largest artery in the body
    ◦ Distributes oxygenated
      blood to all parts of the
   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?
   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.
   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     Mammals
        consumption (Powell et al., 2000)

        •P50 of most birds are much higher
        than those of mammals (Lutz,
        1980)                         P 50

   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

   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

   Non-breeding emperor penguins were
    captured near the McMurdo sound ice edge
    or at Terra Nova Bay
   Maintained at an isolated dive hole


   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

    warneronline.com                          Wikipedia.org
   Determined with the mixing technique of
    tonometered blood
    ◦ Analysis was completed within 6h of blood
    ◦ 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
   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

   Values obtained by applying PO2 profiles to a
    linear regression equation and solving for SO2
   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
    ◦ % 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
   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
   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
    ◦ 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
   Biochemical adaptation behind left-shifted
    O2-Hb dissociation curves = specific amino
    acids substitutions.
    ◦ Specific substitutions not altered in emperor
      Does show differences from human Hb
      Might be other structural features
   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
   Final Sa,O2 values remained high
    ◦ Minimize the risk of shallow water blackouts
   Because of pulmonary gas exchange with the
    blood, Sa,O2 remained close to 100% during
    ◦ Preserving a high O2 content in the arterial
      Brain
   Pre-dive and initial Sv,O2values = higher than
    Pv,O2 values of emperor penguins at rest.
    ◦ Arterialized venous values imply some degree of a-
      v 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
   Used values to calculate intrapulmonary
    shunting = 28% at rest
    ◦ Might be overestimated
      Capillary O2 content
   Using pre-dive values, intrapulmonary
    shunting = 14.3%
    ◦ Hyperventilation and tachycardia characteristic
      improves ventilation-perfusion matching prior to
      the dive
   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
     1.    A significant contribution from the exceptionally large muscle O2
           store to diving metabolic rate
     2.    The low field metabolic rate and the true bradycardia exhibited by
           emperor penguins
   Enhanced O2 affinity of emperor penguin Hb
    ◦ Similar to the high-altitude geese and other
      penguins species
   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
   Overall = Very well planed experiment
    ◦ Tedious work & detailed explanations for
   Surgery
    ◦ Invasive?
   Introduction – more background information
    on important topics (Shunting etc.)
   Use a lot of calculations in the discussion
   Second guessing them selves.