Lesson 13

Lesson 13 Circulation O'Bryan 1. How do small arteries and arterioles regulate the flow to capillaries? a. Constricting -> Increasing resistance = Decreased flow; Dilating -> Decreasing resistance = Increased Flow b. Dilating -> Increasing resistance = Decreased flow; Constricting -> Decreasing resistance = Increased Flow c. Dilating -> Decreasing resistance = Decreased flow; Constricting -> Increasing resistance = Increased Flow d. Constricting -> Increasing resistance = Increased Flow; Dilating -> Decreasing resistance = Decreased flow 1. A: The very small arteries and arterioles have the function of regulating the flow to the capillaries. By constricting and increasing the resistance, they decrease flow; by dilating and decreasing the resistance they increase flow. BUT In some sites, e.g. skin, some blood may bypass the capillaries and flow directly from arterioles into venules through arterio-venous (A-V) anastomoses.

2. How do veins contain about 2/3 of the total circulating blood volume? a. Veins are thicker and 5-6x less distensible than arteries b. Veins have a relaxed volume (volume w/out changing pressure) that is 3-4x more than arteries’ c. Veins are thicker and 5-6x more distensible than arteries d. Veins have a relaxed volume (volume w/out changing pressure) that is 3-4x less than arteries’ 2. B: Veins are thinner and 5-6x more distensible than arteries. Veins have a relaxed volume (volume w/out changing pressure) that is 3-4x more than arteries’ relaxed volume. Because of this (Compliance (C) = ΔV (volume change) / ΔP (change in transmural pressure); veins are more compliant.

3. What is true about distensibility (specific compliance): a. Distensibility = change in Volume (Liters) / change in Pressure b. Compliance = Distensibility x Volume c. A vein with 3x Distensibility and 2x Volume has 9x Compliance d. Veins cannot act as volume stores in circulation due to their low compliance 3. B: Distensibility (specific compliance) = % change in Volume/ change in Pressure, Compliance = Distensibility (specific compliance) x Volume, A vein with 3x Distensibility and 2x Volume has 6x Compliance (2x3=6;DxV=C), Veins have high compliance and therefore act as volume stores 4. What does this curve indicate?

a. Compliance of veins is 2x lesser than arteries b. Compliance of veins is 20x lesser than arteries c. Compliance of veins after sympathetic stimulation is lesser than arteries in older patients d. Compliance of arteries in older patients is lesser that compliance of arteries 4. D: Since Compliance = V/P Compliance = Slope in this graph. A less steep slope means less compliance. The compliance of veins is 20x greater than arteries. The compliance of veins after sympathetic stimulation is (less steep slope) lesser than that of veins. The compliance of arteries in older patients (least steep slope) is lesser than the compliance of all other curves in the graph. *VOLUME(y)/TRANSMURAL PRESSURE(x) = JUST COMPLIANCE SLOPE (not distensibility/specific compliance).

5. What does this curve indicate (physiological pressure vein < 10mmHg, artery 75-150mmHg)?

A2

a. b. c. d.

At higher pressures, the compliance of the vein increases At higher pressures, the compliance of the arteries decreases.

At higher pressures, the distensibility of the arteries decreases.

At higher pressures, the distensibility of the arteries increases

5. C: At higher pressures, the distensibility of the arteries decreases. *VOLUME/VOLUME(y)/ PRESSURE(x) = DISTENSIBILITY/SPECIFIC COMPLIANCE SLOPE (not JUST compliance).

A/B are the high slope of the vein/artery which is high at lower pressures and low at higher pressures meaning the distensibility (which IS the slope) is high at lower pressures and low at higher pressures. A2 and C are the slopes which are at higher pressures and you can see that these slopes have decreased compared to A and B.

6. What is true about the characteristic of veins which causes the steep part of the distensibility curve? a. Biconcave->Elliptical->Circular change in shape of vein due to increase in volume (and distending pressure) b. Small circumference at relaxed volume, Large circumference at small increase in pressure c. Large area at relaxed volume, Small area at high volume d. High circumference with high increase in pressure (due to volume), increases distensibility of vein 6. A is true: Biconcave->Elliptical->Circular change in shape of vein due to increase in volume (and distending pressure), Circumference does not increase readily unless there is a significant increase in pressure/volume, there is a small area at relaxed volume and a large area at high volume, when the circumference finally does increase this increases pressure which leads to a DECREASE in slope/distensibility (refer to image above) .

From syllabus: â&#x20AC;?The steep part of the distensibility curve, at least for some veins, results from a change in shape of the cross-sectional profile of the vessel. At the relaxed volume (at zero distending pressure) the vein looks biconcave, like the cross-section of a red blood cell. As the volume increases and there are small increases in pressure the profile of the vein becomes elliptical and finally circular. These changes affect the cross-sectional area, but not the circumference of the vessel. When the circumference begins to increase with further volume increases, the distensibility of the vein (near the top of the curve) decreases.

7. The compliance (V/P) is linear over physiological pressure and therefor the pressure in an artery is determined by compliance and volume. Runoff is the blood volume in these resistance vessels. Because volume constantly changes in arteries, it is best predicted by equaling it to the volume that returns to the heart (which then goes back to aorta/arteries during ventricular ejection). Change in volume in the artery for a certain length of time is determined by the flow in and flow out (Arterial Volume/ Time = Qin - Qout). Which of the following is true regarding arterial flow. a. Stroke volume equals runoff volume when averaged over length of cardiac cycle b. Average volume and pressure of artery over length of cardiac cycle does not change in steady state c. Systole(ejection): Ejection causes large arteries to expand and act as high pressure (and volume) storage reservoir; Arterial volume is 50-70% of stroke volume at this specific time; flow in is higher than flow out of arteries due to ejection and expansion to hold more volume at high pressures d. Diastole(filling): Elastic wall recoil (does not use active energy) to push blood previously in expanded parts; volume/pressure to decrease; flow into artery is zero since no ejection occurring e. All of the above

7. E: All of the above are true, reread to review. “Role of the arteries as high pressure storage reservoirs. The flow of blood into the arteries from the heart during systole exceeds the flow out of the arteries through the arterioles and leads to an increase in arterial pressure and volume.

During diastole the elastic recoil of the arterial wall provides the driving force to propel blood out of the arteries.”

8. The arterial pressure wave is wider at the base than at the peak. Because of this MAP (mean arterial pressure, Part, Pa) is estimated as MAP = Pdiastolic + 1/3(Psystolic-Pdiastolic) or since Ps – Pd = Pulse pressure MAP = Pdiastolic + 1/3(Ppulse) Choose the right order of events using this aortic pressure curve.

I. Systole: Aortic pressure rises due to ejected volume II. Reaches peak pressure/aortic systolic pressure III. Diastole: Aortic wall recoil to push blood through body (pressure still falling) The lowest point of the wave is diastolic pressure ( Remember Ps – Pd = Pulse pressure) IV. Ventricular pressure falls below aortic pressure causing the aortic valve to close (dicrotic notch= end of systole) a. I, II, III, IV b. II, I, III, IV c. IV, I, II, III d. I, II, IV, III 8. D: Systole -> Peak pressure -> Aortic valve closes -> Diastole 9. Arterial blood pressure is affected by which two physical factors? a. Heart Rate; Stoke Volume b. Cardiac Output; Peripheral Resistance c. Arterial Blood Volume; Arterial Compliance d. Stoke Volume; Peripheral Resistance 9. C: The arterial blood pressure is determined directly by two major physical factors, the arterial blood volume and the arterial compliance.

10. Arterial Blood Volume is affected by which two physiological factors? a. Heart Rate; Stoke Volume b. Cardiac Output; Peripheral Resistance c. Arterial Blood Volume; Arterial Compliance d. Stoke Volume; Peripheral Resistance 10. B: Arterial blood volume is affected by cardiac output and peripheral resistance. Arterial blood volume and arterial compliance are physical factors that affect arterial blood pressure.

11. Cardiac output is affected by which two physiological factors? a. Heart Rate; Stoke Volume b. Cardiac Output; Peripheral Resistance c. Arterial Blood Volume; Arterial Compliance d. Stoke Volume; Peripheral Resistance 11. A: Cardiac output is affected by heart rate x stroke volume (CO = HR x SV). CO and PR both physiologically affect arterial blood volume. Arterial blood volume and arterial compliance physically affect arterial blood pressure.

12. What are factors that influence pulse pressure (Ps - Pd = Pulse Pressure) a. Stroke volume + Compliance of aorta b. The larger the stroke volume, the larger the pulse pressure c. Diastolic pressure d. All of the above 12. D: The pulse pressure is predominately determined by the stroke volume and the compliance of the aorta. The larger the stroke volume, the larger the pulse pressure. The actual systolic pressure that will be attained with a given pulse pressure will be dictated by the diastolic pressure. The SYSTOLIC PRESSURE following a stroke volume/ejection velocity depends on the diastolic pressure taken prior to the measured systolic ejection.

13. What factors influence JUST systolic pressure? a. Stroke Volume; Ejection velocity b. Stroke Volume; Ejection velocity; Aortic distensibility c. Heart Rate; Peripheral Resistance d. Heart Rate; Peripheral Resistance; Aortic distensibility 13. A: Stroke Volume & Ejection velocity are positivity correlated to systolic pressures. If at a given diastolic pressure the stroke volume is increases; the peak systolic pressure will also be increased. If just the time for ejection decreases (Ejection Velocity = Stroke Volume / Ejection Time) then the systolic pressure will also increase. This is because systole manages the inflow and outflow change. Thus when there is greater velocity of inflow or more volume of inflow, more volume will store in the aorta during ejection/systole.

14. What factors influence JUST diastolic pressure? a. Stroke Volume; Ejection velocity b. Stroke Volume; Ejection velocity; Aortic distensibility c. Heart Rate; Peripheral Resistance d. Heart Rate; Peripheral Resistance; Aortic distensibility 14: C: Heart Rate & Peripheral Resistance are positively correlated to diastolic pressure. High resistance = Slow rate of decline in arterial volume/pressure = More blood left over = Higher filling pressure (diastole). An increase in HR = decrease time for runoff = more filling time or less blood leaves = higher filling pressure (diastole).

15. What is the factor that influences BOTH systolic & diastolic pressure? a. Stroke Volume b. Ejection Velocity c. Heart Rate d. Aortic Distensibility 15. D: Aortic Distensibility is negatively correlated to both systolic & diastolic pressure. Decrease in aortic distensibility causes a greater change in pressure for any amount of volume change.

(IE veins can't store as much, aorta can't store as much).

16. What is true about the pressure pulse wave? a. Pressure pulse wave -> distal aorta and large arteries -> systolic pressure increase/diastolic pressure decreases -> heightening of the pulse pressure amplitude + steady decline of mean arterial pressure b. Peak pressure due to reflection of pulse waves in distal arteries does not exceed that in the aorta c. Pressure wave -> distal aorta and large arteries -> systolic pressure increase/diastolic pressure decreases -> heightening of the pulse pressure + steady increase of mean arterial pressure d. Peak pressure due to reflection of pulse waves in distal arteries will match pressure in the aorta because no energy is lost from friction 16. A: Pressure pulse wave -> distal aorta and large arteries -> systolic pressure increase/ diastolic pressure decreases -> heightening of the pulse pressure amplitude + steady decline of mean arterial pressure Peak pressure due to reflection of pulse waves in distal arteries CAN exceed that in the aorta 17. How does aortic pressure wave vary with age? a. Young: Elastic recoil allows low velocity reflected waves that return to aorta at start of diastole thus adding to the diastolic pressure to improve coronary flow. b. Old: Stiff elastic recoil allows fast velocity reflected waves that return to aorta during systole thus limiting coronary flow and increasing after load in heart. c. Old: Stiff elastic recoil allows slow velocity reflected waves that return to aorta at during systole thus limiting coronary flow and increasing after load in heart. d. Young: Elastic recoil allows fast velocity reflected waves that return to aorta at start of diastole thus adding to the diastolic pressure to improve coronary flow.

17. A: Young: Elastic recoil allows low velocity reflected waves that return to aorta at start of diastole/end of systole thus adding to the diastolic pressure to improve coronary flow. Old: Stiff elastic recoil allows fast velocity reflected waves that return to aorta during systole thus limiting coronary flow and increasing after load in heart.

18. Flow is determined by the pressure gradient between the aorta and right atrium over the the total peripheral resistance. Flow on the high pressure side is called cardiac output. (Remember that TPR and CO (HRxSV) also affect arterial blood volume). Flow on the low pressure side is called venous return. Venous return is equal to cardiac output.

What formula do we use to measure venous return at steady state? a. (Prightatrium- Paorta)/TPR = CO = VR b. (Paorta- Prightatrium)/TPR = CO = VR c. TPR /(Paorta- Prightatrium)= CO = VR d. TPR/(Prightatrium- Paorta)= CO = VR 18. B: Difference from aorta to right atrium over total peripheral resistance is equal to cardiac output and venous return at steady state. CO = VR = (Paorta- Prightatrium)/TPR 19. The pressure graduate which drives venous return as a specific point is the difference between peripheral venous pressure and (again) the pressure of the right atrium over the venous resistance. Which formula best describes the formula for the vis a tergo? a. Pvenous - Prightatrium = VR x Rvenous b. Pvenous/Prightatrium = VR x Rvenous c. Prightatrium - Pvenous = VR x Rvenous d. VR = Pvenous - Prightatrium/Rvenous 19. B is correct. Formula to memorize: VR = Pvenous - Prightatrium/Rvenous. D is incorrect because it is not directly solving for the pressure difference although it is the right formula.

20. What factors accurately describe how they influence venous return (VR)?

I. Skeletal muscle pumps: contraction of muscle compresses blood in veins can only move up due to valves II. Respiratory pump: negative intrapleural pressure during inhalation and lowering of diaphragm increased abdominal pressure to increase pressure gradient between veins and right atrium (higher Pvenous - same Prightatrium = higher Pgrad) III. Gravity: U-tube increases TFE so more likely to flow from bottom (lowered body parts) to top (right atrium) (TFE=lateral pressure + kinetic energy + gravitational potential energy; flow from high TFE to low TFE) IV. Valves; ensure blood can only flow towards heart and not fall back (large veins/head+neck veins lack valves)

V. Venomotor tone [Contraction of smooth muscle in walls: more venous tension (blood pushed to heart) vs more venous compliance (blood pools)] VI. Ventricular ejection (systole ejection pushes heart down which lowers right atrial pressure thus increases gradient difference) a. I, II, III b. I, II, III, IV c. I, II ,III, IV, V d. I, II, III, IV, V, VI

20. D: All are accurately described. Skeletal muscle pumps, respiratory pump, gravity, valves, venomotor tone, and ventricular ejection are secondary factors which influence venous return.

(Mnemonic if it helps: blood SuRGing up must go “VVV”room”).

21. For a given inflow pressure (Pi = 100) and outflow pressure (Po= 0), the pressure at the midpoint (Pm) depends on the orientation of the tube. What best explains the Pm for a flat horizontal tube? a. There is flow and no change in gravity. Pm = solely flow pressure (loss due to heat friction) (100-0)/2 = 50mmHg of solely flow pressure). b. There is no flow. Pm = solely hydrostatic pressure (pgh) = 80 mmHg (I think this number is assumed since height isn't given)

c. There is flow and change in gravity. Pm = Flow pressure and hydrostatic pressure.

50mmHg + 80mmHg = 130mmHg d. There is flow and negative change in gravity. Pm = Flow pressure and NEGATIVE hydrostatic pressure 50mmHg - 80mmHg = -30mmHg 21. A: There is flow and no change in gravity. Pm = solely flow pressure (loss due to heat friction) ((100-0)/2 = 50mmHg of solely flow pressure).

22. For a given inflow pressure (Pi = 0) and outflow pressure (Po= 0), the pressure at the midpoint (Pm) depends on the orientation of the U tube. What best explains the Pm for a Ushaped tube? a. There is flow and no change in gravity. Pm = solely flow pressure (loss due to heat friction) ((100-0)/2 = 50mmHg of solely flow pressure). b. There is no flow. Pm = solely hydrostatic pressure (pgh) = 80 mmHg. c. There is flow and change in gravity. Pm = Flow pressure and hydrostatic pressure.

50mmHg + 80mmHg = 130mmHg d. There is flow and negative change in gravity. Pm = Flow pressure and NEGATIVE hydrostatic pressure 50mmHg - 80mmHg = -30mmHg 22. B: There is no flow. Pm = solely hydrostatic pressure (pgh) = 80 mmHg. 23. For a given inflow pressure (Pi = 100) and outflow pressure (Po= 0), the pressure at the midpoint (Pm) depends on the orientation of the U tube What best explains the Pm for a Ushaped tube? a. There is flow and no change in gravity. Pm = solely flow pressure (loss due to heat friction) ((100-0)/2 = 50mmHg of solely flow pressure). b. There is no flow. Pm = solely hydrostatic pressure (pgh) = 80 mmHg. c. There is flow and change in gravity. Pm = Flow pressure and hydrostatic pressure.

50mmHg + 80mmHg = 130mmHg d. There is flow and negative change in gravity. Pm = Flow pressure and NEGATIVE hydrostatic pressure 50mmHg - 80mmHg = -30mmHg 23. C: There is flow and change in gravity. Pm = Flow pressure and hydrostatic pressure.

50mmHg + 80mmHg = 130mmHg

24. For a given inflow pressure (Pi = 100) and outflow pressure (Po= 0), the pressure at the midpoint (Pm) depends on the orientation of the U tube What best explains the Pm for a flipped U-tube? a. There is flow and no change in gravity. Pm = solely flow pressure (loss due to heat friction) ((100-0)/2 = 50mmHg of solely flow pressure). b. There is no flow. Pm = solely hydrostatic pressure (pgh) = 80 mmHg. c. There is flow and change in gravity. Pm = Flow pressure and hydrostatic pressure.

50mmHg + 80mmHg = 130mmHg d. There is flow and negative change in gravity. Pm = Flow pressure and NEGATIVE hydrostatic pressure 50mmHg - 80mmHg = -30mmHg 24. D. There is flow and negative change in gravity. Pm = Flow pressure and NEGATIVE hydrostatic pressure 50mmHg - 80mmHg = -30mmHg

Use as reference but try to visualize without referring to this diagram.

25. What happens to the driving pressure gradient between arterial and venous side (difference in lateral pressures) between laying down and standing up? a. Increases b. Decreases c. Does not change d. Not sure 25. C: It does not change because the change in lateral pressure is the same in arteries and veins = gradient is the same = driving pressure is the same. EXCEPT if measuring points at at TWO DIFFERENT HEIGHTS then must consider lateral pressure + kinetic energy + gravitational potential energy!

26. What does not describe the influence of factors on venous volume? a. Increased hydrostatic pressures = Decrease venous volume b. Above heart/below atmospheric pressure = Decrease venous volume c. Structures preventing collapse of veins = Increase venous volume d. Astronaut moving in space = No change in venous volume 26. A: Increasing hydrostatic pressure allows for blood to pool thus can lead to a increase in venous volume. Effect of body position on arterial (light gray) and venous (black) pressures. The numbers show the pressure in mmHg. Note that the venous pressure in the head of the recumbent subject (lower left) is 5 mmHg. Upon standing (right figure) the sum of the â&#x20AC;&#x153;flowâ&#x20AC;? pressure (5 mmHg) and the hydrostatic pressure in the head (-44 mmHg) result in a total lateral pressure of -39 mmHg. The pressure in the artery at the same level in the head in the recumbent subject is 95 mmHg. Upon standing that pressure also drops by -44 mmHg to 51 mmHg. Note also the 88 mmHg hydrostatic pressure increase in both veins and arteries in the feet of the upright subject.