The remarkable cardiovascular system of giraffes Christian Aalkjr - PowerPoint PPT Presentation

The remarkable cardiovascular system of giraffes Christian Aalkjær Aarhus University

Why giraffes?

Danish Giraffe Research Expedition 2010

Wildlife Assignments International Hammanskraal, South Africa

”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 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 tibial artery of giraffes narrows immediately below the knee 1 cm

Giraffes have a unique narrowing of the tibial artery distal to the knee! 1 c m

Femoral artery from Structural changes in a newborn giraffe? a newborn giraffe 2 cm between each slice For the giraffe the ”hen and egg” question is pretty easy to answer! 2 c m

The narrowing seen with ultrasound - functional importance

There is a significant hydrodynamic resistance in the conduit arteries 100 µ g noradrenaline 10 µ g mmHg proximal distal

There is a significant hydrodynamic resistance in the conduit arteries

Why giraffes do not get dependent edema! Resistance artery structure

The pressure that the arteries can constrict against Equivalent pressure Ca. 500 mmHg Ca. 400 mmHg

Interstitial pressure and tissue compliance 40 200 Interstitial fluid pressure (mmHg) Interstitial fluid pressure (mmHg) 30 150 20 100 10 50 0 Near ground Upper neck -10 0 46 48 50 52 54 2 min 1 2 3 4 5 6 Position along the giraffe 175 ∆ interstital fluid pressure (mmHg) 150 125 100 75 N = 6 giraffes 50 25 Near ground Upper neck 0 1 2 3 4 5 6 Position along the giraffe

”The big four” 1. How are leg edema prevented? 2. How can the heart produce 1.Sphincter 200 mmHg? 2.Resistance in conduit arteries 3. How is the kidney protected 3.Thick media in small arteries against the 200+ mmHg? 4.High interstitial pressure (strong fascia) 4. How are cerebral catastrophes avoided?

”The big four” 1. How are leg edema prevented? The giraffe's heart is an enormous two feet long 2. How can the heart produce and twenty-five pounds 200 mmHg? huntingsociety.org 3. How is the kidney protected against the 200+ mmHg? Heartweight 1.9 ± 0.40 kg or ~0.5 % of bodyweight (n=6) 4. How are cerebral Brøndum et al., Am J Physiol 2011 catastrophes avoided? The human heart is 0.54 % of the bodyweight (de la Grandmaison GL, 2001)

Comparison of stroke volume/body mass for different mammals and giraffes Based on Seymour and Blaylock, Phyiol Biochem Zool 2000;73:389-405

”The big four” 1. How are leg edema prevented? 2. How can the heart produce 200 mmHg? 3. How is the kidney protected 1.By compromizing on the stroke volume, against the 200+ mmHg? which is small. This presumably means 4. How are cerebral that giraffes are “unfit” catastrophes avoided?

”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?

Giraffes have high capsular hydrostatic pressure Interstitial pressure: 47 ± 3 mmHg (n=4) Where the pressure catheter was placed

”The big four” 1. How are leg edema 1.A high capsular hydrostatic pressure prevented? 2.Presumably a high afferent arteriolar 2. How can the heart produce resistance. 200 mmHg? 3. How is the kidney protected against the 200+ mmHg? 4. How are cerebral catastrophes avoided?

”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?

110/70 mmHg 220/180 mmHg 330/? mmHg

Anaesthetized giraffe

Mean arterial pressures in ”drinking” anaesthetized giraffes 200 (n=5) 150 mmHg 100 Upright Head down 50 0

Flow profile of jugular vein giraffe neck Venous return stops! Is there an accumulation of blood in the neck??? 14 venous return at the base of the neck 12 Venous return at the base of neck 10 l min-1 (l/min) 8 Flow 6 Estimated accumulation ~2 L 4 2 0 63 64 65 66 Time (min) time (min)

Starling! Tobias Wang

Blood pressure changes buffer arterial pressure excursions near the head 200 Head pressure 150 mmHg 100 5 min 50 200 Central 150 pressure mmHg 100 G7 50

Drinking may cause headache 225 225 No water in the pond! Now with water Central 175 175 pressure mmHg 125 125 25 sec 75 75 30 30 Central 20 20 jugular 10 10 pressure 0 mmHg 0 -10 -10 -20 -20 -30 -30 80 80 Heart 60 rate 60 40 40 20 G5 20

Starling! Tobias Wang - modified

The giraffe gets to its feet after anaesthesia - or the giraffe has no problem with a high distal carotid pressure 450 450 350 350 Central pressure mmHg 250 250 150 150 50 50 1 min 200 450 150 350 100 Head Beats per min 250 pressure mmHg 50 150 0 50 G7

So how are the capillaries in the head protected?

Cerebral small artery under pressure 260 mmHg 160 mmHg 80 mmHg 80 mmHg 500 10 µM noradrenaline Artery diameter µ m 400 3 min 50 µ m

Cerebral small artery under pressure 260 mmHg 160 mmHg 80 mmHg 80 mmHg 500 10 µM noradrenaline Artery diameter µ m 400 3 min Tongue small artery under pressure 260 mmHg 160 mmHg 80 mmHg 80 mmHg 350 Artery diameter µ m 2 min 300

Myogenic tone in different small arteries at the giraffe head Muscle 50 40 30 muscle Myogenic tone 20 % 10 0 50 100 150 200 250 0 50 100 150 200 250 Transmural pressure, mmHg

Myogenic tone in different small arteries at the giraffe head 50 tongue 40 30 muscle Myogenic tone 20 % 10 0 50 100 150 200 250 0 50 100 150 200 250 Transmural pressure, mmHg

Myogenic tone in different small arteries at the giraffe head CSF pressure 80 70 50 tongue 40 60 head down mmHg cerebral 30 muscle Myogenic 50 head up tone 20 % 40 10 30 0 30 min 50 100 150 200 250 0 50 100 150 200 250 Transmural pressure, mmHg 20

Hydrodynamic resistance when drinking? Pressure Flow Up Drinking Up Velocity Drinking Pressure Flowvelocity prox carotis (cm/sec) (Flow) 30 Mean pressure prox carotis 350 25 300 20 250 Resistance = Perfusion pressure / Flow 15 200 10 150 Resistance 2.0 Relative resistance 1.5 1.0

”The big four” 1.Removing blood from the circulation (in 1. How are leg edema the neck veins) prevented? 2.Precapillary vasoconstriction (myogenic and possibly nervous) 2. How can the heart produce 200 mmHg? 3.High CSF pressure 4.Valves in the jugular veins 3. How is the kidney protected against the 200+ mmHg? 4. How are cerebral catastrophes avoided?

Thank you very much