Cardiovascular and Respiratory Systems: Getting Oxygen From Air to Muscle

Integration of Ventilation, Heart, and Circulation

Cardiorespiratory System

 

Functions of cardiorespiratory system:

 transportation of O 2 and CO 2  transportation of nutrients/waste products  distribution of hormones thermoregulation maintenance of blood pressure

Ability of cardiorespiratory system to maintain high arterial oxygen levels (PaO 2 ) during graded exercise to exhaustion

Critical elements of O 2 Transport Pathway

   Ventilation – Moving air in/out of lungs  External respiration – Gas exchange between alveoli and blood Heart and circulation O 2 diffusion into mitochondria

Role of the Heart

Moving O 2 from lungs to muscle

Oxygen Delivery Determines VO

2

(Fick Principle)

VO 2 VO 2 VO = [ = [ 2 HR BP = Q    (Ca O 2 SV ]  – Cv (Ca O 2 O 2 ) – Cv O 2 ) TPR ]  (Ca O 2 – Cv O 2 )

Cardiac Cycle

 

systole



diastole cardiac output

(Q) =

stroke volume

(SV) 

heart rate

(HR) examples – – rest: SV = 75 ml; HR = 60 bpm; Q = 4.5 L  min -1 exercise: SV = 130 ml; HR = 180 bpm; Q = 23.4 L  min -1

Cardiac output affected by

:

1. preload

– end diastolic pressure (amount of myocardial stretch)

2. afterload

– resistance blood encounters as it leaves ventricles

3. contractility

– strength of cardiac contraction

4. heart rate

Muscle pump and one-way valves assist venous return

Cardiac Output Regulation

Extrinsic control

 autonomic nervous system – sympathetic NS (1  control at HR >100 bpm) • NE released as neural transmitter – parasympathetic NS (1  control at HR <100 bpm) • ACh released as neural transmitter  hormonal – EPI, NE

Ventilation and External Respiration

Getting O 2 from air into blood

A.

Major pulmonary structures

B.

General view showing alveoli and blood vessels

C.

Section of lung showing individual alveoli

D.

Pulmonary capillaries surrounding alveolar walls

RBC Single alveoli at rest showing individual RBCs Single alveoli under high flow showing increased RBCs

Lungs and Pulmonary Circulation

   alveolar membrane thickness is ~ 0.1 total alveolar surface area is ~75 m 2 µm 80-90% of alveoli are covered by capillaries  pulmonary circulation varies with cardiac output and matched to ventilation rate

Gases Move Down Pressure Gradients

O 2 and CO 2 transit time in lungs (left) and tissue (right) at rest

Notice rapid saturation with O 2 traveled ⅓ around alveolus by the time RBCs have

PO 2 in blood returning to the lungs is ____ PO 2 in the alveoli.

A. greater than B. less than C. similar to

PO 2 in arterial blood is ____ PO 2 mitochondria.

in the

A. greater than B. less than C. similar to

PCO 2 in venous blood is ____ PCO 2 the alveoli.

in

A. greater than B. less than C. similar to

What would be the effect on the saturation of arterial blood with O 2 (SaO 2 ) when pulmonary blood flow is faster than the diffusion rate of O 2 ?

A. SaO 2 would remain unchanged B. SaO 2 would be decreased C. SaO 2 would be increased

Rate of gas diffusion is dependent upon pressure (concentration) gradient.

Erythrocyte (RBC)

 ~98% of O 2 is bound up with hemoglobin (Hb)  Hb consists of four O 2 -binding heme (iron containing) molecules  combines reversibly w/ O 2 (forms oxy-hemoglobin)  1-2% of O 2 is dissolved in plasma

Transport of CO

2

in blood

~75% ~5% ~20% CO 2 + H 2 O  H 2 CO 3  H + + HCO 3 -

Oxygen is transported from lungs to muscle primarily A. dissolved in blood.

B. bound to hemoglobin.

C. as a bicarbonate ion.

Carbon dioxide is transported from muscle to the lungs A. dissolved in blood.

B. bound to hemoglobin.

C. as a bicarbonate ion.

D. all of the above are transport mechanisms for CO 2

Ventilatory Response to Exercise and Control of Blood pH

Minute ventilation (VE) response to different exercise intensities

Ventilatory Control Mechanisms

Current thought is that primary control of ventilation is:

•

from muscle afferents sensory inputs

•

to control arterial PCO 2 ,(peripheral PCO 2 chemoreceptors)

•

to minimize

 in

blood pH (peripheral pH chemoreceptors)

Ventilatory responses to incremental exercise

VCO2 vs VO2 VE vs VO2

5 4.5

4 3.5

3 2.5

2 1.5

1 0.5

0 0 1 5 6 200 180 160 140 120 100 80 60 40 20 0 0 1 2 3 4

VO2 (L/min)

5 6 2 3

VO2 (L/min)

4 Why are there a breakpoints in the linearity of VE and VCO 2 ?

7

Ventilatory Regulation of Acid-Base Balance

CO 2 + H 2 O  H 2 CO 3  H + + HCO 3     at low-intensity exercise, source of CO 2 substrate metabolism is entirely from bicarbonate (HCO 3 ) buffers H + intensity exercise produced during high at high-intensity exercise, bicarbonate ions also contribute to CO 2 production – source of CO 2 is from substrates and bicarbonate ions (HCO 3 )  blood [H + ] stimulates VE to rid excess CO 2 (and H + )

Can RER ever exceed 1.0? When? Explain

Blood Lactate

12 10 8 6 4 2 0 50 100 150 200 250

Treadmill Speed (m/min)

300 350

Blood pH

7.45

7.40

7.35

7.30

7.25

7.20

7.15

7.10

7.05

4 5 6 7 8 9 10 11 12

Treadmill Speed (mph)

13 14 15

Respiratory Exchange Ratio

1.3

1.2

1.1

1.0

0.9

RER = VCO 2 VO 2 0.8

4 5 6 7 8 9 10 11 12

Treadmill Speed (mph)

13 14 15

CO2 Production

90 80 70 60 50 40 30 20 10 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Treadmill Speed (mph)

Minute Ventilation

200 180 160 140 120 100 80 60 40 20 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Treadmill Speed (mph)

5 4.5

4 3.5

3 2.5

2 1.5

1 0.5

0 0

VCO2 vs VO2

200 180 160 140 120 100 80 60 40 20 0 0

VE vs VO2

6 7

Ventilation Questions

1. Describe how ventilation regulates blood pH.

2. Explain why the ventilatory threshold is related to the lactate threshold 3. Can RER ever exceed 1.0? Under what circumstances? Explain.

Young cowboys in the old west

Matching O

2

to muscle O

2

delivery needs

Regulation of cardiorespiratory system

Vascular system

aorta  arteries  capillaries arterioles   venules  veins  vena cava

Vascular smooth muscle allows vessels to constrict in response to SNS stimulation or local factors

Arterioles and Capillaries

   arterioles  terminal arterioles (TA)  collecting venules (CV)  capillaries  arterioles regulate circulation into tissues – under sympathetic and local control precapillary sphincters fine tune circulation within tissue – under local control

Blood vessels are surrounded by sympathetic nerves.

A feed artery was stained to reveal catecholamine-containing nerve fibers in vascular smooth muscle cell layer. This rich network extends throughout arterioles but not into capillaries or venules.

• • • • • •

Local factors that control arterioles

PO 2 PCO 2 pH adenosine K + Nitric oxide

(  1 -adrenergic receptor blocker) 30 s

Rapid adaptation of blood flow

Onset of exercise

Precapillary sphincters fine-tune local blood flow

Local control factors

• PO 2 • PCO 2 • pH • adenosine • K + • temperature

Blood Distribution During Rest

Blood Flow Redistribution During Exercise

At rest, most blood is found in the ______ while at exercise most blood is in _____.

A. venous system; active muscle B. pulmonary circulation; heart C. arterioles; capillaries D. heart; heart E. liver; active muscle

What is the primary mechanism to increase blood flow to working muscle?

A. baroreceptors B. sympathetic innervation C. local factors D. epinephrine E. central command

What effect would these local conditions (from resting values) have on arteriole blood flow?

 PO 2 ,  PCO 2 ,  pH,  temperature A. increase flow B. decrease flow C. no effect on flow D. cannot be determined

O

2

Extraction

Moving O 2 from blood into muscle

Factors affecting Oxygen Extraction

VO 2 Fick equation = Q   (aO 2 – vO 2 )

O

2

extraction response to exercise

Represents mixed venous blood returning to right heart

a-v O

2

difference

   Bohr Effect : effect of local environment on oxy-hemoglobin binding strength amount of O 2 released to muscle depends on local environment – PO 2 , pH, PCO 2 , temperature, 2,3 DPG 2,3 diphosphoglycerate (DPG) – produced in RBC during prolonged, heavy exercise – binds loosely with Hb to reduce its affinity for O 2 which increases O 2 release

Bohr effect on oxyhemoglobin dissociation Oxyhemoglobin binding strength affected by:

PO 2 PCO 2 H + temperature 2,3 DPG

O 2 unloading in muscle O 2 loading in lungs

A change in the local metabolic environment has occurred: pH and PO 2 and PCO 2 have have  .

 ; temperature

What effect will these changes have on the amount of O 2 released to the muscle?

A. increase O 2 release B. decrease O 2 release C. no change in O 2 release D. cannot be determined

A change in the local metabolic environment has occurred: pH and PO 2 and PCO 2 have have  .

 ; temperature

What do these changes in local environmental suggest has occurred?

A. the muscles changed from an exercise to a resting state B. the muscles began to exercise C. no change D. cannot be determined

During graded exercise,

A. VCO 2 increases linearly B. A breakpoint occurs in VCO 2 that coincides with lactate threshold C. A breakpoint occurs in VE that is caused by increased VO2 D. A breakpoint occurs in VCO 2 that results from increased epinephrine release

Which of the following would NOT cause local vasodilation?

A.

B.

C.

D.

E.

     PCO 2 PO 2 temperature pH nitric oxide production

Which of the following would NOT cause greater O 2 unloading from hemoglobin?

A.

B.

C.

D.

E.

     PCO 2 PO 2 temperature pH nitric oxide production

Which of the following adaptations likely had the LEAST influence for explaining why VO 2max increased 12% after completing a cross country

A.

B.

C.

D.

E.

cardiac output

season?

   blood volume mitochondrial volume   capillary density number of RBC

Which of the following does NOT occur during exercise?

A. Vasodilation occurs throughout body.

B. Blood is redirected towards exercising muscle.

C. Local factors loosen binding of O 2 hemoglobin.

to D. Increased venous return causes increased stroke volume.

E. There is increased afterload to heart.

Which of the following does NOT occur during moderate-intensity running exercise?

A. Sympathetic stimulation increases blood B.

flow to working muscles.

 PCO 2 causes greater unloading of O 2 working muscles from hemoglobin.

to C. Sensory inputs from muscle afferent nerves stimulate ventilation and heart rate.

D. PO 2 in alveoli drops to less than the PO 2 blood returning to the lungs.

in E. There is little change to diastolic BP.

Control of cardiac function and ventilation

Parallel activations

What would be the effect of local arteriole dilation on BP?

A. Decrease BP B. Increase BP C. No effect on BP

During running exercise, total peripheral resistance ____ because of _____.

A. increases; sympathetic stimulation B. increases; local control factors C. decreases; vasoconstriction D. decreases; local control factors

Reflex control of cardiac output

Primary regulators  Central command control center (medulla) – Input from motor cortex • parasympathetic inhibition predominates at HR <~100 bpm • sympathetic stimulation predominates at HR >~100 bpm – Sensory input from skeletal muscle afferent • sense mechanical and metabolic environment Secondary regulator  arterial baroreceptors – Provide input to central command – located in carotid bodies and aortic arch – respond to arterial pressure • Reset during exercise

Maintaining Blood Pressure

Pressure is Necessary for Blood Flow

Pressure is necessary for blood to flow. Notice that blood flow decreases with BP

Regulation of Blood Flow and Pressure

Blood flow and pressure determined by

:

A. Vessel resistance (e.g. diameter) to blood flow A B. Pressure difference between two ends cardiac output A arterioles B B

BP = Q  TPR

Regulation of Blood Flow and Pressure

120 Pressure (mm Hg) 80 Time

BP = Q  TPR

At what level is peripheral resistance greatest?

Effects of Exercise on Cardiac Output

Effects of Exercise Intensity on TPR

25 20 15 10 5 0 0 50 100 150 200 250 300

Treadmill speed (m/min)

350 400

Effects of Incremental Exercise on BP

250 225 200 175 150 125 100 75 50 25 0 0 50 100 150 200 Workload (W)

Systolic BP Diastolic BP

250 300

Cardiovascular Response to Exercise

Fick equation VO 2 VO 2 VO = [ = [ 2 = Q HR BP     (aO 2 SV ] – vO 2 )   (aO 2 – vO 2 ) TPR ]   (aO 2 – vO 2 )

Exercise effects on heart

    – – – HR caused by    sympathetic innervation parasympathetic innervation release of catecholamines  SV, caused by –  –   sympathetic innervation venous return cardiac output

Cardiorespiratory adaptations to endurance training

How does endurance training affect VO 2max ?

Maximal oxygen consumption (VO 2max )

VO 2max – highest VO 2 attainable – maximal rate at which aerobic system utilizes O 2 and synthesizes ATP – single best assessment of CV fitness VO 2

VO 2max

intensity

 VO 2max affected by: – genetics (responders vs. nonresponders) – age – gender – specificity of training

Cardiorespiratory training adaptations

VO 2max



~15% with training

   ventilation? – training has no effect on ventilation capacity O 2 delivery?

– CO (  ~15%) – –   plasma volume SV O 2 utilization?

– mitochondrial volume  >100%

1995 marathon training data (women)

VO 2 5 mph

6 mph

RER 5 mph 6 mph HR 5 mph 6 mph VO 2max HR max Pre-training

30.7 35.5 0.92 0.95 168 182 54.4 206

Post-training

29.8 34.6 0.88

* 0.92

* 151 * 167 * 58.5

* 198 * *P < 0.05

Heart adaptations to training

 sympathetic sensitivity  heart size, blood volume

Heart adaptations to training

Left ventricular adaptations depend on training type

 LV-EDV Endurance trained  preload (volume overload) Sedentary  myocardial thickness Resistance  trained afterload (pressure overload)

Normalized data for VO

2max (ml



kg -1



min -1 )

Category Excellent %ile

>80

Age 20-29

>44

Age 40-49

>39

Age 60+

>33

Women

Average

40-60 36-39 31-35 25-28

Poor

<20 <31 <28 <22

Excellent

>80 >52 >49

Average

40-60 43-47 39-44 >41 33-36

Poor

<20 <31 <28 <22 Aerobic Center Longitudinal Study, 1970-2002

Men

Which of the following would likely result in an increase of VO 2max ?

A. breathing faster and deeper during maximal exercise B. faster HR at maximal exercise C. ability to deliver more O2 to muscles during maximal exercise D. more mitochondria

Which of the following does NOT occur following endurance training?

A.

B.

C.

D.

E.

F.

      blood volume HR max SV max CO max mitochondrial volume maximal ventilatory capacity

How would you evaluate a VO 2max of 28.9 mL/kg/min for a 22-year-old man?

A. excellent B. above average C. average D. very low E. dead

Which of the following exercises would likely decrease TPR the LEAST?

A. jogging B. fast walking C. shoveling snow D. cycling E. the above would decrease TPR similarly

What is the mechanism for the sudden increase in VE when the lactate threshold is reached during an incremental exercise test?

A. greater muscle afferent input B. greater stimulation of peripheral baroreceptors C. greater stimulation of peripheral PCO 2 chemoreceptors D. greater stimulation of peripheral PO 2 chemoreceptors E. greater stimulation from motor cortex