Exercise Physiology - Unit 1 Exam

Chapters 15, 16, & 17

What does Cardiac output (Q) express?

Amount of blood pumped by the heart during a 1-min period

What does maximal values for cardiac output reflect?

the functional capacity of the cardiovascular system

• Cardiac output (Q, ml·min^-1 or liters·min^-1) =Heart rate (HR, beats·min^-1)·Stroke volume (SV, ml·beat^-1)

What is cardiac index?

a body surface area (BSA) normalized clinical expression of Q, calculated as Q·m^-2 BSA where BSA is determined by the DuBois-Meeh formula:

• BSA m²=0.007184·Mass^0.425·Stature^0.725

What are methods to assess cardiac output?

• Direct Fick

• indicator dilution

• CO₂ rebreathing

What does direct fick determine?

Determines Q based on the relationships between Q (ml·min^-1), VO₂ (ml·min^-1) and a-vO₂diff (ml O₂·100 ml blood^-1) to determine Q.

What does Direct Fick require?

Measurement of HR as well as simultaneous measurement of the following using complex invasive methodology:

• VO₂ (l·min^-1) using indirect open circuit calorimetry

• The average difference between O₂ content of arterial (C_aO₂) and mixed-venous (C_vO₂) blood. a-vO₂diff=C_aO₂- C_vO₂       

What does C_aO₂ measurement require?

Arterial catheterization and sampling of high-pressure arterial blood in a sterile field

What does well-mixed C_vO₂ measurement require?

Venous catheterization and sampling from the right heart or preferably the pulmonary arteries in a sterile field.

What is catheterization?

An invasive procedure that is performed by a trained medical professional (e.g., cardiothoracic surgeon) in a clinical setting and not in an applied human performance laboratory setting. 

Direct Fick is known as what type of method?

Gold standard

When can’t a person use direct fick?

During intense (non-steady state, e.g., VO_2max) exercise.

What is the Indicator Dilution Method?

A rearrangement of Archimedes’ Principle:

• Density=Concentration=  Mass/Volume; Volume=  Mass/Concentration

• A known quantity( mass, the numerator) of an appropriate tracer is injected into the vascular compartment

What is thermal dilution?

The use of a cold or warm indicator to measure serial change in temperature downstream

The Indicator Dilution Method know as?

A quantity (mass, the numerator) of an appropriate tracer is injected into the vascular compartment.

What does the CO₂ rebreathing method use?

A variant of the direct Fick method does not require medical supervision

What type of circuit is used during CO2 rebreathing?

Open-circuit calorimetry using a rapid-response infrared CO₂ analyzer determines breath-by-breath VCO₂.

True or false: Valid estimates of mixed-venous and arterial CO₂ levels can be made based on reasonable assumptions about gas exchange.

True

What does CO₂ rebreathing not require?

Blood sampling or medical supervision

True or false:CO₂ rebreathing is a common technique in many applied physiology research laboratories.

True

When can a person only use CO2 rebreathing?

During steady-rate conditions.  The method cannot be used for non-steady-state or maximal measurement of Q.

What variables affect (cardiac output ) Q ?

Stress, body size and body surface area and can vary considerably during rest.

SV and Q values for females are-

20-25% below male values due to smaller body mass.

Trained state results in decreased resting HR and increased SV due to following factors-

• Increased vagal influence on SA node and decreased sympathetic drive, both of which decrease HR

• Increased blood volume, myocardial contractility, and compliance of left ventricle all of which increase SV

  • Q_rest consistent, but values that make up Q change drastically

What does systemic blood flow increases directly with?

Intensity of physical activity

True or false: Cardiac output increases rapidly during the transition from rest to steady-rate exercise and then rises gradually until it plateaus when blood flow meets the exercise metabolic requirements

True

What does an endurance athlete achieve?

Large maximal cardiac output solely through a large SV and not through any increase in HR.

Effects of training on HR at rest and during exercise-

• Little effect of training on HR_MAX 

• Lower HR response to a standard submaximal work rate

• Lower resting HR with training 

Effects of training on SV at rest and during exercise

• Much greater exercise SV with training

• Plateau in SV during exercise

• Greater resting SV with training

Effects of training on Q at rest and during exercise-

• Resting Q similar between trained states

• Sub-maximal exercise Q similar between trained states

• Lower post-trained Q_submax reflects greater O₂ extraction and greater efficiency of resource utilization

Max values for Q, HR, and SV for men with very low, normal, and high VO_2MAX values- Mitral stenosis (decreased LV end-diastolic volume, decreased SV and Q) vs sedentary (normal)

• VO_2MAX: -50%

• SV_MAX: -50%

• Q_MAX: -53%

Max values for Q, HR, and SV for men with very low, normal, and high VO_2MAX values- Mitral stenosis vs athlete (trained)

• VO_2MAX: -69%

• SV_MAX: -69%

• Q_MAX: -69%

Max values for Q, HR, and SV for men with very low, normal, and high VO_2MAX values-Athlete vs sedentary

• VO_2MAX: +62%

• SV_MAX: +60

• Q_MAX: +52%

What does mitral stenosis decrease?

Stroke volume and Q due to reduced left ventricular end-diastolic volume

What is the difference in VO_2MAX between the groups is largely explained by?

Difference in SV_MAX and Q_MAX

Mechanism that could increase SV:

• Enhanced cardiac filling in diastole

• Normal ventricular filling with subsequent more forceful ejection and emptying during systole

• Training adaptation that increase cardiac output and reduce resistance to blood flow in peripheral tissues

What is Ejection Fraction?

Stroke volume (SV) expressed as a percentage of left ventricular end-diastolic volume (LVEDV).  EF=SV÷LVEDV·100

What is Frank-Starling law of the heart?

Within physiological limits, the force of contraction of cardiac muscle remains proportional to the initial length of the cardiac muscle fiber.

What does enhanced venous return increase?

Left ventricular end-diastolic volume. The stretched (lengthened) cardiac fibers result in a more forceful systole (i.e., a greater inotropic response).

What can enhance venous return and result in a greater SV through a Frank-Starling-mediated inotropic response.

Body position (supine vs. standing: swimming vs. upright exercise)

What is Ischemic heart disease known for-

Decrease ventricular wall compliance which increases left-ventricular diastolic pressure, impairs left ventricular end-diastolic volume, and decreases SV

True or False: It is unclear if endurance training increases left ventricular compliance to accept a greater blood volume during exercise.

True

What position has greatest effect on SV?

Supine

• increased preload; increased venous return, increased fiber stretch; more forceful Frank-Starling mediated systole

True or false: Incremental exercise elicits relatively small increased in SV and Q over supine rest

True

What impairs venous return during upright exercise (decreased preload) with smaller SV?

Gravity

• Decrease preload

True or false: Greater increase in SV from rest in upright moderate and strenuous vs supine moderate and strenuous exercise

True

What also occurs during exercise?

Enhanced systolic ejection of blood

True or False: Arterial resistance to blood flow increases which is reflected by increased systolic and mean arterial blood pressure

True

Arterial resistance to blood flow is known as-

Afterload and explained by increased Q despite decrease downstream total peripheral resistance

• increased vasodilation and conductance of blood flow to active muscle

When does greater systolic emptying (contributes to greater Q) occur?

During exercise despite increased afterload

Why does enhanced systolic ejection occur?

ventricles always contain a functional residual blood volume

What are Catecholamines?

Released during exercise exert an inotropic response (increased force of contraction) on the heart by stimulating ß₁ (primarily) and ß₂-adrenergic receptors to enhance myocardial contractile force and facilitate systolic emptying.

What is Afterload (arterial pressure)?

Arterial resistance against which the heart ejects blood

• Related to increased aortic pressure due to increased Q

Increased after-load decreases stroke volume by-

• Increasing LV end-diastolic pressure

• Decreasing myocyte shortening velocity (decreased inotropic response0

• Decreasing LV ejection velocity 

• Increasing LV end diastolic pressure

An increase in LV end diastolic pressure also increases-

Preload

What is Cardiovascular drift?

A gradual time-dependent downward “drift” in cardiovascular responses, most notably stroke volume (SV) with a compensatory increase in HR, during prolonged steady-state exercise

When is Cardiovascular Drift most notable

During hyperthermic exercise with decreased SV secondary to thermoregulatory mechanisms: increased cutaneous blood flow and plasma volume loss through sweating.

True or false: Cardiovascular drift increases cutaneous flow and fluid loss from sweating decreases central venous volume which decreases venous return and left ventricular diastolic filling pressure.

True

True or false: Under hyperthermic conditions, exercise is performed at a lower intensity than if cardiovascular drift did not occur

True

What are consequences of cardiovascular drift?

Decreased VO₂ with decreased performance

• Submaximal exercise for >15 minutes decreases plasma volume, thus decreasing SV

True or false: The increased HR response is a compensatory response to reduced SV to maintain Q (and oxygen transport [T_aO₂]) during exercise

True

True or false: During hyperthermic exercise, decreased SV is the “cause” and increased HR is the compensatory response for cardiovascular drift.

True

Progressively larger percentages of total Q are diverted to active muscles from-

Rest to maximal exercise

What is The physiological conductance of blood?

Through the sketetal muscle vascular beds increases from 4-7 ml·100 g muscle^-1· min^-1 at rest to 50 to 75 ml·100 g muscle^-1·min^-1 at maximal exercise some skeletal muscles (e.g., diaphragm) may have conductances as high as 300-400 ml·100 g muscle^-1·min^-1

Some skeletal muscles (e.g., diaphragm) may have conductances as high as-

300-400 ml·100 g muscle^-1·min^-1

For trained individuals, anticipatory blood redistribution begins just prior to-

Exercise (feed-forward control and override of C-R center).

Hormonal vascular regulation and local metabolic conditions divert blood flow to-

Active muscles from areas that tolerate compromised blood flow (e.g., renal and splanchnic vascular beds).

Blood redistribution among specific tissues occurs primarily during

Intense exercise

True or False: Most of this increased conductance diverts to muscle fibers with high oxidative capacity (e.g.,Type I, Type IIa) at the expense of muscle fibers with high glycolytic capacity (e.g., Type IIx/IIb).

True

Exercise diverts blood flow to and away from-

Active muscle and away from splanchnic and renal vasculature with high α-adrenergic receptor density.

Environmental stress and fatigue also affects-

Q distribution during exercise

True or False:Endurance training attenuates sympathetic-mediated adrenergic vasoconstriction to splanchnic vasculature which in theory contributes to enhanced performance (enhanced lactate clearance; increased plasma [glucose] from hepatic glycolysis and gluconeogenesis)

True

The heart and brain cannot tolerate-

compromised blood supply

At rest, the myocardium uses how much O2 in blood?

75% of O₂ in blood flowing through the coronary circulation

True or False: In contrast to skeletal muscle, a widening of myocardial a-vO_2diff is not a significant compensatory mechanism for increased myocardial oxygen consumption during exercise.

True

During exercise, the coronary circulation has a-

Four- to five-fold increase in blood flow (e.g., from ~200 to ~1000 ml·min^-1).

How much does cerebral blood flow increases during exercise?

~25-30% compared with the resting flow

True or false:Bone blood flow volume remains fairly constant from rest to maximal exercise with progressively decreasing proportions of total Q from rest to maximal exercise.

True

Utilization of oxygen- Greater O₂ diffusion equals

less C_vO₂.a-vO_2diff=C_aO₂-C_vO₂ =  widening of the a-vO_2dif

True or false: Utilization of oxygen increased [mitochondria], mitochondrial

size, and oxidative capacity=greater O₂ bioenergetics to active tissue=

greater O₂ diffusion

True

What does an increase in Q_Max produces proportionate increases in the

Capacity to circulate O₂ and increases VO_2max

What is the Q_Max:VO_2max ratio is

~5.5:1.0 and ~6.0:1.0 for sedentary and endurance athletes, respectively, regardless of exercise mode.

When are Q and VO₂ linearly related?

During graded exercise for males and females of all ages.

What does a low VO_2max corresponds with?

low Q_max

OxyHb bound =

15 g Hb·100 ml^-1·1.34 ml O₂·g Hb^-1· 0.98  = 19.7 ml O₂·100 ml blood^-1

Dissolved O₂ =

0.3 ml O₂·100 ml blood^-1 (determines P_aO₂ of  ~100 mm Hg)

Total C_aO_{2 =}

20.0 ml O₂·100 ml blood^-1

Arterial blood carries

~200 ml O₂·liter arterial blood^-1. 200 ml O₂·liter arterial blood^-1=20.0 ml O₂·100 ml blood^-1 · 1000 ml·l^-1 (20·1000÷100=200)

What does proportionate increases in Q_Max accompanies increase in?

VO_2max with endurance training

High VO_2max and Q_max are distinguishing characteristics for-

Preadolescent and adult endurance athletes.

Teenage and adult women exercise at submaximal VO₂ with-

5 to 10% larger Q than their male counterparts as a compensatory response to ~10% lower [Hb] (slightly lower C_aO₂ and T_aO₂ in females than males).

True or false:Higher submaximal exercise HR (HR_submax) response in children do not compensate for smaller SV (SV_submax).

True

True or false: •As a result, submaxmal Q (Q_submax) is smaller in children than in adults.

True

Oxygen requirements to exercising muscles are met by a widening of?

a-vO₂ difference

What is the Fick Equation?

VO₂, cardiac output, and a-vO₂diff relationship expressed

What does a-vO₂diff = C_aO₂ – C_vO₂ =

Oxygen extracted from arterial blood by the tissues, i.e., oxygen diffusion from capillaries to the mitochondria

At rest, a-vO₂diff = 20 ml O₂·100 ml blood^-1 - 15 ml O₂·100 ml blood^-1 =

5 ml O₂·100 ml blood^-1 perfusing the whole-body tissue–capillary bed.

True or false: 15 ml O₂·100 ml blood^-1 (75% of blood’s original O₂ content) still remains bound to hemoglobin.

True

Arterial blood O₂ content (C_aO₂) varies little from-

rest throughout the exercise intensity range

Mixed-venous O₂ content (C_vO₂) varies between

12 to 15 ml O₂·100 ml blood^-1 during rest to 2 to 4 ml O₂·100 ml blood^-1 during maximal exercise.

True or false:Progressive expansion (widening) of a-vO₂diff results from an increased cellular O₂ extraction leading to a reduced venous O₂ content.

True