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Download High affinity hemoglobin and blood oxygen saturation in diving
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Jessica U. Meir and Paul J. Ponganis 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 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 body 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 consumption (Powell et al., 2000) Mammals •P50 of most birds are much higher than those of mammals (Lutz, 1980) P 50 Birds 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 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 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 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 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 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 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 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 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 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 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 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 dive ◦ Preserving a high O2 content in the arterial compartment Brain 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 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. 2. 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 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 everything Surgery ◦ Invasive? Introduction – more background information on important topics (Shunting etc.) Use a lot of calculations in the discussion Second guessing them selves.
