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The remarkable cardiovascular system of giraffes
Christian Aalkjær
Aarhus University
The remarkable cardiovascular system of giraffes Christian Aalkjr - - PowerPoint PPT Presentation
The remarkable cardiovascular system of giraffes Christian Aalkjr - - PowerPoint PPT Presentation
The remarkable cardiovascular system of giraffes Christian Aalkjr Aarhus University Why giraffes? Danish Giraffe Research Expedition 2010 Wildlife Assignments International Hammanskraal, South Africa The big four 1. How are leg
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Danish Giraffe Research Expedition 2010
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Wildlife Assignments International Hammanskraal, South Africa
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided?
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided?
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1 cm
The tibial artery of giraffes narrows immediately below the knee
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1 c m
Giraffes have a unique narrowing of the tibial artery distal to the knee!
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Structural changes in a newborn giraffe? 2 c m Femoral artery from a newborn giraffe
2 cm between each slice
For the giraffe the ”hen and egg” question is pretty easy to answer!
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The narrowing seen with ultrasound
- functional importance
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10 µg 100 µg noradrenaline
proximal
mmHg
There is a significant hydrodynamic resistance in the conduit arteries
distal
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There is a significant hydrodynamic resistance in the conduit arteries
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Why giraffes do not get dependent edema!
Resistance artery structure
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- Ca. 500 mmHg
The pressure that the arteries can constrict against
- Ca. 400 mmHg
Equivalent pressure
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- 10
10 20 30 40 1 2 3 4 5 6
Interstitial fluid pressure (mmHg)
Position along the giraffe
Near ground Upper neck 25 50 75 100 125 150 175 1 2 3 4 5 6
∆interstital fluid pressure (mmHg)
Position along the giraffe
Near ground Upper neck
46 48 50 52 54
50 100 150 200
2 min Interstitial fluid pressure (mmHg)
Interstitial pressure and tissue compliance
N = 6 giraffes
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided? 1.Sphincter 2.Resistance in conduit arteries 3.Thick media in small arteries 4.High interstitial pressure (strong fascia)
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided?
The human heart is 0.54 % of the bodyweight
(de la Grandmaison GL, 2001)
The giraffe's heart is an enormous two feet long and twenty-five pounds huntingsociety.org Heartweight 1.9 ± 0.40 kg or ~0.5 % of bodyweight (n=6)
Brøndum et al., Am J Physiol 2011
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Based on Seymour and Blaylock, Phyiol Biochem Zool 2000;73:389-405
Comparison of stroke volume/body mass for different mammals and giraffes
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided? 1.By compromizing on the stroke volume, which is small. This presumably means that giraffes are “unfit”
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided?
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Giraffes have high capsular hydrostatic pressure
Interstitial pressure: 47 ± 3 mmHg (n=4)
Where the pressure catheter was placed
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided? 1.A high capsular hydrostatic pressure 2.Presumably a high afferent arteriolar resistance.
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided?
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330/? mmHg 110/70 mmHg 220/180 mmHg
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Anaesthetized giraffe
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(n=5)
50 100 150 200
mmHg
Mean arterial pressures in ”drinking” anaesthetized giraffes
Upright Head down
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Venous return stops!
Flow profile of jugular vein giraffe neck
time (min)
63 64 65 66
l min-1
2 4 6 8 10 12 14
venous return at the base of the neck
Time (min) Flow (l/min) Venous return at the base of neck Is there an accumulation of blood in the neck??? Estimated accumulation ~2 L
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Starling!
Tobias Wang
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Blood pressure changes buffer arterial pressure excursions near the head
Head pressure mmHg Central pressure mmHg
50 100 150 200
5 min
G7
50 100 150 200
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75 125 175 225
Central pressure mmHg
No water in the pond!
75 125 175 225
Drinking may cause headache
- 30
- 20
- 10
10 20 30
- 30
- 20
- 10
10 20 30
Central jugular pressure mmHg
20 40 60 80 20 40 60 80
Heart rate
G5
25 sec
Now with water
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Starling!
Tobias Wang - modified
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50 150 250 350 450
Head pressure mmHg
50 100 150 200
The giraffe gets to its feet after anaesthesia
- or the giraffe has no problem with a high distal carotid pressure
G7
50 150 250 350 450 1 min
Central pressure mmHg
50 150 250 350 450
Beats per min
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So how are the capillaries in the head protected?
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80 mmHg 160 mmHg 260 mmHg 80 mmHg 10 µM noradrenaline
400 500 Artery diameter µm
Cerebral small artery under pressure
3 min
50 µm
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260 mmHg 80 mmHg 80 mmHg 160 mmHg
300 350
80 mmHg 160 mmHg 260 mmHg 80 mmHg 10 µM noradrenaline
400 500 Artery diameter µm Artery diameter µm
Cerebral small artery under pressure Tongue small artery under pressure
3 min 2 min
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Myogenic tone %
Myogenic tone in different small arteries at the giraffe head
50 100 150 200 250
Muscle
200 250 50 40 30 20 10 150 50 100
Transmural pressure, mmHg
muscle
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Myogenic tone %
Myogenic tone in different small arteries at the giraffe head
50 100 150 200 250
200 250 50 40 30 20 10 150 50 100
Transmural pressure, mmHg
muscle tongue
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Myogenic tone %
Myogenic tone in different small arteries at the giraffe head
50 100 150 200 250
200 250 50 40 30 20 10 150 50 100
Transmural pressure, mmHg
cerebral muscle tongue
20 30 40 50 60 70 80
30 min
mmHg
CSF pressure
head down head up
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Hydrodynamic resistance when drinking?
Pressure
150 200 250 300 350
Mean pressure prox carotis
Resistance
1.0 1.5 2.0
Relative resistance
Velocity
10 15 20 25 30
Flowvelocity prox carotis (cm/sec)
(Flow)
Resistance = Perfusion pressure / Flow
Up Drinking Pressure Up Drinking Flow
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”The big four”
- 1. How are leg edema
prevented?
- 2. How can the heart produce
200 mmHg?
- 3. How is the kidney protected
against the 200+ mmHg?
- 4. How are cerebral
catastrophes avoided? 1.Removing blood from the circulation (in the neck veins) 2.Precapillary vasoconstriction (myogenic and possibly nervous) 3.High CSF pressure 4.Valves in the jugular veins
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