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Cardiovascular System and Exercise

Cardiovascular System

Functions during physical activity includes: Oxygen delivery Blood aeration Thermoregulation Nutrient delivery Hormone Transportation

Components of the Cardiovascular System

Heart

Arteries

Capillaries

Veins

Cardiovascular Dynamics During Exercise

Parameters Heart Rate Stroke Volume Cardiac Output Blood Pressure Blood Flow Blood

Heart Rate

Defined as the number of beat per unit of time, usually expressed in beats per minute.

Ones heart rate can be determined through: Palpation Auscultation Heart Rate Monitor ECG Recorder

Heart Rate

Resting Heart Rate Values Averages 60 – 80 beats/min Averages 28 – 40 beats / min - highly conditioned, endurance trained

athletes Secondary to increase in vagal tone Affected by environmental factors, it increases with extremes in

temperature and altitude Best taken when totally relaxed, such as early mornings.

Heart Rate During Exercise HR increases directly in proportion to the increase in exercise intensity

Heart Rate

Moving towards maximal intensity, the HR starts to plateau even with further increase in exercise intensity.

This indicates that HR is reaching a maximum value.

Maximum heart rate (HRmax) is the highest HR value achieved in an all out effort to the point of exhaustion.

Heart Rate

HR max can be estimated based on age because of a slight but steady decrease of about one beat per year beginning at age 10 – 15 years

Equations: HRmax = 220 – age HRmax = 208 – (0.7 X age)

Heart Rate

If intensity is held at a submaximal intensity, HR increases fairly rapidly until it reaches a plateau.

This plateau is the steady state HR. This is an optimal HR for meeting the circulatory

demands at that specific rate of work.

Valid predictor of cardiorespiratory fitness

A lower steady state HR reflects a greater cardiorespiratory fitness.

Stroke Volume

Defined as the volume of blood pumped from one ventricle of the heart with each beat.

Determinants of SV: Preload

Ventricular Distensibility

Ventricular Contractibility

Afterload

Stroke Volume

SV increases above resting values during exercise.

Untrained: 60 – 70 ml/ beat @ rest to 110 – 130 ml/beat during maximal exercise.

Highly trained endurance athletes: 80 – 100ml/beat @ rest to 160 – 200 ml/ beat during maximal exercise.

Percentage increase can be determined by body position.

Stroke Volume

Contributing Factors for increase: Frank Starling mechanism

States that the stroke volume of the heart increases in response to an increase in the volume of blood filling the heart. The increased volume of blood stretches the ventricular wall, causing cardiac muscle to contract more forcefully.

Increased contractility Increased neural stimulation Increased release of circulatory catecholamines

Decreased afterload

Cardiac Output

Defined as the volume of blood pumped by the heart per minute (L/min).

CO is the product of HR and SV CO = HR x SV

Resting CO is approx. 5 L/min

Maximal CO varies between 20 (sedentary person) and 40 (elite endurance athlete) L/min

Cardiac Output

One of the major purpose for the increase in CO is to meet the muscles’ demand for oxygen.

Ensuring that adequate supply of oxygen and nutrients reach the exercising muscles, and waste products of muscle metabolism are removed quickly.

Blood Pressure

Pressure exerted by circulating blood against the wall of the blood vessels.

Blood Pressure

During dynamic exercise mean arterial blood pressure (MAP – average pressure exerted by the blood as it travels through the arteries) increases substantially.

Rhythmic whole body endurance exercise increases systolic blood pressure in direct proportion to the increase exercise intensity.

Diastolic pressure does not change significantly, and may even decrease.

Blood Pressure

Blood pressure responses to resistance exercise is exaggerative.

High intensity resistance training, blood pressure can reach 480/350 mmHg.

Because of the sustained muscular force which compresses the peripheral arterioles, considerably increasing resistance to blood flow.

Blood Pressure

Blood pressure increases more in rhythmic arm compared with rhythmic leg exercise.

The smaller arm muscle mass and vasculature offers greater resistance to blood flow than the larger and more vascularized lower – body region.

The difference between the systolic blood pressure during upper and lower body exercise has important implications for the heart.

Myocardial oxygen uptake and myocardial blood flow are directly related to the product of HR and systolic blood pressure [rate pressure product/ double product (DP = HR X SBP)]

Blood Pressure

In Recovery After a bout of sustained light to moderate intensity

exercise, systolic blood pressure temporarily decreases below pre exercise levels for up to 12 hours in normal and hypertensive individuals.

Blood Flow

Exercise Effects

Acute changes in CO and BP during exercise allows for an increase in total blood flow to the body.

This facilitates getting blood flow to the exercising muscle.

Additionally, sympathetic control of the cardiovascular system can redistribute blood to areas of greatest metabolic need.

Blood Flow

Blood Flow Regulation

Pressure differentials and resistances determine fluid movement through the vessel.

Resistance varies directly with the length of the vessel and inversely with its diameter.

Flow = Pressure ÷ Resistance

Blood Flow

Three factors determine resistance to blood flow: Viscosity or Blood thickness Length of conducting tube Radius of blood vessel

Poiseuille’s Law expresses the general relationship between pressure differential (gradient), resistance, and flow in a cylindrical vessel: Flow = Pressure gradient × Vessel radius4 ÷ Vessel

length × Fluid viscosity

Blood Flow

Blood viscosity and transport vessel length remains relatively constant in the body.

Blood vessel radius represents the most important factor affecting blood flow.

Resistance to blood flow changes with vessel radius raised to the fourth power (reducing a vessel’s radius by one half decreases flow by a factor of 16, conversely doubling the radius increases volume 16 fold).

This means that a relatively small degree of vasoconstriction or vasodilation can dramatically alter regional blood flow.

Blood

Blood is the fluid of life, growth and health.

As metabolism increases during exercise, the function of the blood becomes more critical for optimal performance.

At rest the blood’s oxygen content varies from 20 ml of oxygen per 100 ml of arterial blood to 14 ml of oxygen per 100 ml of venous blood.

Blood

The difference between these two values is referred to as the a-v O2 difference.

With increasing exercise intensity, the a-v O2 difference increases progressively and can increase approximately threefold from rest to maximal exercise intensities.

Blood

With the onset of exercise there is almost an immediate loss of plasma from the blood to the interstitial space.

Approx. 10 – 15% reduction in plasma volume can occur in prolonged exercise and with brief bouts of exhaustive exercise.

Blood

If exercise intensity or environmental conditions cause sweating, additional plasma volume is lost.

For prolonged duration activities in which dehydration occurs and heat loss is a problem, a reduction in plasma volume will impair performance.

When plasma volume is reduced, hemoconcentration occurs. Increases red blood cell concentration substantially (20% – 25%) Hematocrit increases from about 40% - 50%. Total volume and number of red blood cells do not change substantially. Increases the blood’s oxygen carrying capacity during exercise.

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Respiratory System and Exercise

Pulmonary Structure and Function

Lung Volumes and Capacities

Static Lung Volumes Evaluates the dimensional component for air

movement within the pulmonary tract and impose no time limitation on the individual.

Dynamic Lung Volumes Evaluates the power component of pulmonary

performances during different phases of the ventilatory excursion.

Static Lung Volumes

Lung Volume/ Capacity

Definition Average Values (mL)Male Female

Tidal Volume (TV) Volume inspired or expired per breath. 600 500

Inspiratory Reserve Volume (IRV)

Maximum inspiration at end of tidal inspiration.

3000 1900

Expiratory Reserve Volume (ERV)

Maximum expiration at end of tidal expiration.

1200 800

Inspiratory Capacity (IC)

Maximum volume inspired after tidal expiration.

3600 2400

Functional Residual Capacity (FRC)

Volume in lungs after tidal expiration 2400 1800

Forced Vital Capacity (FVC)

Maximum volume expired after maximum inspiration

4800 3200

Residual Lung Volume (RLV)

Volume in lungs after maximum expiration.

1200 1000

Total Lung Capacity (TLC)

Volume in lungs after maximum inspiration

6000 4200

Dynamic Lung Volumes

Normal values for vital capacity can exist in severe lung disease if no time limit is present to expel air.

Hence, why a dynamic lung function measure such as percentage of the FVC expelled in 1 second (FEV1.0) serves as a more useful diagnostic purpose than static measures.

Forced Expiratory Volume to Forced Vital Capacity Ratio (FEV1.0 / FVC) Reflects the expiratory power and overall resistance to air

movement in the lungs. Normally this averages 85% of the vital capacity.

Dynamic Lung Volume

Maximum Voluntary Ventilation This dynamic assessment of ventilatory capacity

requires rapid, deep breathing for 15 seconds. This 15 second volume is then extrapolated to the

volume breathed for 1 minute. Healthy young men: 140 – 280 L/min Healthy young women: 80 – 120 L/min

Pulmonary Ventilation

Pulmonary Ventilation – Describes how ambient air moves into and exchanges with air in the lungs.

Minute ventilation – Volume of air breathed per minute. Minute ventilation = Breathing rate × Tidal Volume

Alveolar ventilation – Refers to the portion of the minute ventilation that mixes with the air in the alveolar chamber. Anatomic dead space – Portion of the air that does not enter the alveoli

and engage in gaseous exchange with the blood. 150 – 200 mL or ~30 % of the resting TV.

Physiologic dead space – Portion of the alveolar volume with poor tissue regional perfusion or inadequate ventilation. This can increase to 50% of the resting TV.

Relationship amongst Tidal Volume, Breathing Rate, and Minute and Alveolar Minute Ventilation

Breathing Condition

Tidal Volume (mL)

×

Breathing Rate (breaths/min)

=

Minute Ventilation (mL/min)

-

Dead Space Ventilation (mL/min)

=

Alveolar Ventilation (mL/min)

Shallow 150 40 6000 150 × 40 0

Normal 500 12 6000 150 × 12 4200

Deep 1000 6 6000 150 × 6 5100

Partial Pressure of Gases

Partial Pressure – Individual pressures from each gas in a mixture. The air breathed is a mixture of gases; and each exerts a

pressure in proportion to its concentration in the gas mixture.

Dalton’s Law – the total pressure of a mixture of gases equals the sum of the partial pressures of the individual gases in that mixture.

Partial pressure = Percentage concentration × Total pressure of gas mixture (standard atmospheric pressure)

Movement of Gas

According to Henry’s Law Gases dissolves in liquids in proportion to their

partial pressures, depending also on their solubilities in specific fluids and on the temperature.

The amount of gas dissolved in a fluid depends on two factors Pressure differential between the gas above the fluid

and dissolved in it Solubility of the gas in the fluid.

Gas Exchange

Oxygen Exchange PO2 = 159 mmHg of ambient air PO2 = 105 mmHg when inhaled and enters the alveoli. Due to the

increased water vapor pressure and increased partial pressure of carbon dioxide in the alveoli.

PO2 = approx. 40 mmHg in the pulmonary capillaries Fick’s Law

States that the rate of diffusion through a tissue such as the respiratory membrane is proportional to the surface area and the difference in the partial pressure of gas between the two sides of the tissue. The rate of diffusion is also inversely proportional to the thickness of the tissue in which the gas must diffuse.

Gas Exchange

Carbon Dioxide Exchange Moves along a pressure gradient PCO2 = 40 mmHg in the alveoli PCO2 = 46 mmHg in the venous blood

Partial Pressure of Respiratory Gases at Sea

LevelPartial Pressure (mmHg)

Gas % in dry air

Dry air Alveolar air

Arterial Blood

Venous Blood

Diffusion Gradient

Water 0.00 0.0 47 47 47 0

Oxygen 20.93 159.1 105 100 40 60

Carbon Dioxide

0.03 0.2 40 40 46 6

Nitrogen 79.04 600.7 568 573 573 0

Total 100.00 760 760 760 706 0

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Transport of Oxygen and Carbon Dioxide

in the Blood

Oxygen Transport

By two means:

Combined with hemoglobin

Dissolved in blood plasma 3 ml dissolved in every L of plasma If total blood plasma is 3 – 5 L only 9 – 15 ml can be

carried in the dissolved state.

Hemoglobin Saturation

Each molecule of hemoglobin can carry 4 molecules of oxygen. The combine molecule is termed oxyhemoglobin.

Binding depends on: Partial pressure of oxygen in the blood Bonding strength, affinity between haemoglobin and

oxygen.

Oxygen Dissociation Curve

Blood Oxygen Carrying Capacity

The oxygen carrying capacity of blood is the maximal amount of oxygen the blood can transport.

Dependent on: The blood hemoglobin content 100 ml of blood – 14 to 18 g of Hb (men), 12 – 16 g of

Hb (women). Each gram of Hb can combine with about 1.34 ml of

oxygen, hence the oxygen carrying capacity of blood is approx. 16 – 24 ml per 100 ml of blood

At rest: Blood is in contact with the alveolar air for approximately 0.75 secs.

With exercise: the contact time is greatly reduced…

Carbon Dioxide Transport

Carbon dioxide is carried in the blood in three forms: As a bicarbonate Dissolved in plasma Bound to hemoglobin (carbaminohemoglobin)

Bicarbonate Ion

Majority carried in this form, accounting for the transport of 60% to 70% of the carbon dioxide in the blood.

Carbon dioxide and water combines to give carbonic acid; catalyzed by the enzyme carbonic anhydrase.

Carbonic acid is unstable and quickly dissociates, freeing the hydrogen ion and forming a bicarbonate ion.

The free hydrogen can bind to hemoglobin triggering off the Bohr effect.

Bicarbonate diffuses into the plasma.

When blood enters the lungs where the partial pressure of oxygen is lower, the reverse holds true.

Dissolved Carbon Dioxide

Only approximately 7% to 10% of the carbon dioxide released from the tissues dissolves in plasma.

The dissolved form comes out of solution when its partial pressure is low as in the lungs.

Here it diffuses from the pulmonary capillaries into the alveoli to be exhaled.

Carbaminohemoglobin

Binding of the gas to hemoglobin will give carbaminohemoglobin.

So named because it binds to the amino acids in the globin part of the Hb molecule.

No competition with oxygen when binding, however binding varies with the oxygenation of the Hb and the partial pressure of carbon dioxide.

Gas Exchange in Muscle

Arterial venous oxygen difference.

Oxygen transport in muscle. Myoglobin

Factors Influencing Oxygen Delivery and Uptake

Oxygen Content in blood

Blood Flow

Local Conditions

Pulmonary Ventilation During Dynamic Exercise

Onset of exercise is accompanied by an immediate increase in ventilation, followed by a more gradual increase, then a slow rate steady decrease to resting values.

Respiratory recovery takes several minutes suggesting that: The rate of breathing does not perfectly match the

metabolic demands of the tissue. Post exercise is regulated primarily by acid base

balance, partial pressure of dissolved carbon dioxide, and blood temperature.

Ventilatory Response to Exercise

Breathing Irregularities During Exercise

Dyspnea Common among individuals in poor physical

condition. Increased levels of carbon dioxide and hydrogen ions

concentration triggers the inspiratory center to increase the rate and depth of breathing.

Although sensed as an inability to breathe the underlying cause is the inability to adjust breathing to blood carbon dioxide and hydrogen ion concentration.

Hyperventilation Increase in ventilation in excess of that needed for

exercise metabolism. Decreases normal partial pressure of carbon dioxide

from 40 mmHg to about 15 mmHg. Decrease in arterial carbon dioxide concentration,

increases blood pH. Resulting in a reduced ventilatory drive

Valsalva Maneuver Closure of glottis increase intra abdominal

pressure increase intrathoracic pressure. As a result air is trapped and pressurized in the

lungs. Restricted venous return, reducing volume of blood

returning to the heart, decreasing cardiac output, and altering arterial blood pressure.

Ventilation and Energy Metabolism

Ventilatory equivalent for oxygen (VE/ VO2) The ratio between the volume of air expired or ventilated and

the amount of oxygen consumed by the tissues in a given amount of time.

Measured in liters of air breathed per liter of oxygen consumed per minute.

At rest: 23 to 28 L of air per liter of oxygen Mild exercise: Varies little Moderate – Near maximal levels: can be > 30 L of air per liter of

oxygen consumed. Generally speaking it remains relatively constant over a wide

range of exercise intensities, indicating the control of breathing is properly matched to the body’s demand for oxygen.

Ventilatory Threshold Point at which ventilation increases

disproportionately to oxygen consumption. Reflects the respiratory response to increased

carbon dioxide levels. Ventilation increases dramatically beyond this point.

Respiratory Regulation of Acid - Base Balance

The metabolism of carbohydrate, fats, or protein produces inorganic acids that dissociate, increasing the hydrogen ion concentration in the body fluid lowering the pH.

To minimize this effect the blood and muscles contains base substances that combines with and hence buffer or neutralize the ion.

At rest the body fluids have more bases than acids, resulting in a slightly alkaline tissue (7.1 in muscle to 7.4 in arterial blood).

Acidosis – occurs with increased levels of H ions.

Alkalosis – occurs with decreased level of H ions.

The pH of intra and extra cellular fluid is kept within a relatively narrow range by: Chemical Buffers Pulmonary Ventilation Kidney Function

Chemical Buffers

Major chemical buffers: Bicarbonate Inorganic phosphates Protein

Bicarbonate combines with H ion to give carbonic acid, which dissociates to give carbon dioxide and water in the lungs.

In the muscle fibers and kidney tubules H ion is primarily buffered by phosphates.

Blood and chemical buffers are required only to transport metabolic acids from their sites of production to the lungs or kidneys for removal.

Once the H ion is transported and removed the buffer molecule can be re used.

Pulmonary Ventilation

Increased levels of free H ions in the blood stimulates the respiratory center to increase ventilation.

Both the chemical buffers and respiratory system provides short term means of neutralizing the acute effects of exercise acidosis.

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