1. Special Circulations Mark T Ziolo, PhD, FAHA Associate Professor, Physiology & Cell Biology 019 Hamilton Hall 614-688-7905 ziolo.1@osu.edu

2. Learning Objectives Describe the regulation of coronary, cerebral, and skeletal muscle blood flow Differentiate flow regulation in cutaneous, splanchnic, renal and pulmonary circuits

3. Detailed Objectives  Understand how coronary blood flow is regulated  Know why coronary blood flow must be increased and the primary factor responsible for coronary blood flow  Understand extravascular compression in the heart  Understand how cerebral blood flow is regulated  Know why cerebral blood flow is always maintained  Know what is the purpose of Cushing’s Phenomenon  Know how skeletal muscle blood flow is regulated  Understand why skeletal muscle blood flow switches from neuronal to local (metabolic) regulation  Know the role of the “muscle-pump mechanism”  Know the purpose of blood flow to the following organs: cutaneous, splanchnic, renal, and pulmonary  Understand the major mechanisms of blood flow regulation in the following organs: cutaneous, splanchnic, renal, and pulmonary

4. Mohrman DE, Heller LJ. Cardiovascular Physiology 8th Edition. Lange Medical Books/McGraw-Hill Publishers, 2014. Berne RM, Levy MN. Cardiovascular Physiology Sixth Edition. Mosby-Year Book, Inc., 2010. MediaPhys 3.0. An Introduction to Human Physiology. The McGraw-Hill Publishers, 2010. References

5. Coronary Blood Flow  Myocardium extracts ~75% of the oxygen  Increase in myocardial O 2 consumption must be accompanied by an increase in blood flow  1° factor responsible for perfusion is the aortic pressure  Local control (metabolic)

6. Flow directly related to O 2 consumption

7. Extravascular Compression

8. Myocardial O 2 demand : Myocardial O 2 supply Myocardial Metabolic rate Vasodilator metabolites Coronary blood flow Arterial O 2 content Coronary Blood Flow, cont

9. Local Control  Vasodilator metabolites  Adenosine Activates adenosine receptor  O 2, CO 2, H +, K +  Neuronal Control  Sympathetic activation Vasodilation (increase myocardial contractility)

10. Lack of Blood Flow  Myocardial Ischemia  Arrhythmias  Endocardial layer of left ventricle

11. Cerebral Blood Flow  In ALL situations, blood flow to the brain is preserved (55 ml/min/100g)  Whole brain has a nearly constant metabolic rate  Blood flow to discrete regions is not constant  Regulated almost entirely by local mechanisms O 2, H + (PCO 2 ), K +, adenosine  Excellent autoregulation  Some sympathetic vasoconstriction

12. Hand Reasoning Problem Solving Cerebral Blood Flow, cont

13.  No reserves- very intolerant to ischemia  5 sec: fainting  Minutes: death

14. Cushing’s Phenomenon Tumor Intracranial pressure CBF Metabolic vasodilation Ischemic stimulation of vasomotor regions in medulla systemic blood pressure Maintain CBF

15. Skeletal Muscle  Rate of blood flow directly related to contractile state of muscle  At rest, large percentage of capillary bed is not perfused  Regulation of flow  Neuronal and local influences  Physical factor- squeezing effect of contracting muscle

16. Skeletal Muscle, cont  Neuronal Influence  High basal tone  Sympathetic fibers elicits vasoconstriction Predominates in resting muscle

17. Skeletal Muscle, cont  Local Influence  Very strong in working muscle Muscle O 2 consumption, adenosine, H +, K +, lactic acid  Neuronal and local influences oppose each other, in working muscle the local (metabolic) influence predominates

18. Skeletal Muscle, cont  “muscle-pump mechanism”  Contracting muscles push blood in veins towards thorax

19. Cutaneous  Very low O 2 and nutrient requirements  Maintain constant body temperature  Arterioles and arteriovenous anastomoses  AV anastomoses shunt blood from arterioles to venules  Governed by nervous system in response to temperature receptors  NE and E elicit vasoconstriction  Chiefly influenced by environmental temperature

20. Splanchnic  GI tract, spleen, pancreas, and liver  ~25% of resting cardiac output  Neuronal and local influences  Sympathetic causes vasoconstriction Shifts blood to central venous pool (liver important blood reserve)  Gastrointestinal hormones- functional hyperemia  Autoregulation not well developed

21. Renal Blood Flow  0.5% TBW but 20% of cardiac output  Strong autoregulation  Regulate GFR  Myogenic mechanism (stretch)  Tubuloglomerular feedback Tubular flow sensed by macula densa sends signal via juxtaglomerular apparatus to afferent arterioles JGA also releases renin (angiotensin II)  Neuronal Influence Sympathetic decreases RBF, but GFR only slightly

22. Pulmonary Blood Flow  Vascular system is low-resistance and highly distensible  Capillaries aligned in thin sheets between adjacent alveoli  Gravitational effects (regional distribution)  Hypoxia most important influence on tone  Low alveolar PO 2 leads to shunting of blood from poorly ventilated regions to better ventilated regions

23. Summary  Coronary blood flow is regulated by metabolic influences and the primary factor responsible is arterial pressure  With increased oxygen demand, coronary blood flow must be increased because of the bulk flow principle  Extravascular compression occurs in the heart due to high systolic forces  Cerebral blood flow in mostly under metabolic influence  Cerebral blood flow is always maintained since it is the least tolerant organ to ischemia and there are no reserves  Cushing’s Phenomenon is elevation of intracranial pressure results in an increase in systemic blood pressure to maintain cerebral blood flow  Skeletal muscle blood flow is regulated by the neuronal influence at rest, and by the metabolic influence in working muscle  The muscle pump mechanism pushes blood back towards the heart

24. Summary, cont  Purpose of cutaneous blood flow is temperature regulation and is under neuronal control  Purpose of splanchnic blood flow is nutrient reabsorption and is under neuronal control and functional hyperemia  Purpose of renal blood flow is filtration and has strong autoregulation and is under neuronal control  Purpose of pulmonary blood flow is gas exchange and has hypoxic vasoconstriction

26. Thank you for completing this module Questions- mark.ziolo@osumc.edu

27. Survey We would appreciate your feedback on this module. Click on the button below to complete a brief survey. Your responses and comments will be shared with the module’s author, the LSI EdTech team, and LSI curriculum leaders. We will use your feedback to improve future versions of the module. The survey is both optional and anonymous and should take less than 5 minutes to complete. Survey