CVR Response to Exercise

The Circulatory, Vascular & Respiratory Systems are responsible for the delivery of oxygen and nutrients to the working muscles and the removal of waste products. Homeostatic adjustments are made to CVR systems in response to different levels of exercise stimulus, which are demonstrated at rest, sub-maximal and maximal exercise intensities. The CVR systems also adjust to different environmental conditions, and are best developed using continuous, Fartlek and interval training methods.

CVR Response and Regulation to Exercise

Cardiac Cycle

Exercise increase blood flow through the heart so that the cardiac cycle accelerates to accommodate the increase demand for oxygen. Atrial and ventricular contractions become faster and more powerful, as stimulated by the cardiac centre in the medulla oblongata.

Heart rate also increases with exercise due to:

·         Increased frequency of impulses from the sympathetic nerves

·         Stimulation of the SA node by the release or noradrenaline

There is greater filling and more efficient emptying of the ventricles. Negative feedback works via the parasympathetic system to slow the heart rate down upon detection of a dramatic rise in blood pressure as detected by receptors in the aorta and carotid arteries.

Cardiac Output

CO = SV x HR ie the volume of blood pumped per minute

Blood Pressure

A rise in blood pressure it caused by the resistance of blood vessels to blood flow. It is expressed as systolic over diastolic. It can be defined in three ways:

·         Peripheral resistance x blood flow

·         Pressure of blood exerted on the vessel walls

·         Force per unit area exerted on the wall of a blood vessel

In endurance activities systolic pressure increases in direct proportion to the increasing intensity of exercise. Diastolic pressure changes little.

Blood Vessels

The vasomotor centre brings about vasoconstriction to the non-essential areas and vasodilation to the muscles. This is controlled by the sympathetic nervous system, which control the contraction of smooth muscle in the tunica media (middle layer of a blood vessel).

Oxygen Transport

The transport of oxygen into the muscle cell takes place as myoglobin receives oxygen from haemoglobin. Myoglobin has a higher affinity for oxygen that haemoglobin and therefore will transport oxygen to the mitochondria, which is the site of aerobic respiration. During exercise, venous return increases as assisted by:

·         Skeletal pump

·         Venous valves to prevent back flow

·         Thoracic pressure decreases, caused by the increase in thoracic volume during exercise, causing the surrounding veins to expand and ‘suck’ blood upwards

·         Cardiac contraction ‘sucks’ blood upwards

·         Hydrostatic pressure – the attraction between fluid molecules moving in a particular direction

Ventilation

Ventilator control is governed by the respiratory centre in the medulla oblongata, which stimulates a combination of chemical, nervous and hormonal changes that stimulate breathing:

·         Proprioceptors that detect movement

·         Chemoreceptors

·         Excessive levels of CO₂

·         Insufficient O₂

·         Stretch receptors in the lungs

·         Respond to excessive inflation as a preventative measure

·         Initiates inhibitory responses that stimulates expiration until the lungs recoil to a safe size

·         Irritant receptors

·         When stimulated, promotes reflexes to keep the airway clear by means of coughing

Respiratory volumes:

·         Tidal volume = the volume inspired or expired per breath

·         Inspiratory reserve volume = the maximal volume inspired from end-inspiration

·         Expiratory reserve volume = the maximal volume expired from end expiration

·         Residual volume = the volume remaining at the end of maximal expiration

·         This remains the same throughout exercise to prevent lung collapse

Gaseous Exchange

-          External respiration is the process of gas exchange at the lungs. Oxygen passes through the pulmonary capillaries and carbon dioxide leaves the blood and enters the lung alveoli.

-          Internal respiration is the process of gas exchange between the systemic capillaries and the tissues. Carbon dioxide enters the blood and oxygen leaves the blood and enters the tissues.

Haemoglobin saturation (formation of oxyhaemoglobin in red blood cells) is almost 100% in the lungs however, as the acidity in the blood increases towards the tissues, caused by increased levels of CO₂ or lactic acid, the partial pressure of oxygen decreases. This causes oxygen to be disassociated (released) from the haemoglobin to the tissue. This is known as oxygen disassociation.

The Bohr Effect dictates that as levels of carbon dioxide increase, pH lowers even more, thus allowing the oxygen to unload even quicker. Only during very heavy exercise do blood carbon dioxide, oxygen and pH values change much from their normal values.

The effect of asthma on athletic performance is to restrict the passage of air through the bronchiole pathways and this can therefore inhibit performance. Use of the steroid-based inhalers can relieve the restriction.

It is thought that after a period of training the brain ‘learns’ to match the rate of respiration with the intensity of the exercise. Well trained individuals will therefore match their respiratory rates subconsciously to their physical exertions more efficiently than untrained individuals.

Exercise & Training

Homeostasis is ‘the body’s ability to maintain stable internal conditions during heavy or prolonged activity’ (Galligan et al, 2000). During exercise, these stable internal conditions are disturbed and a dynamic state of equilibrium is put in place. At the end of exercise, the exercise stimulus is removed triggering the recovery process.

Warm Up

The warm up consists of a pulse raiser, stretching and skills practice. It should be gradual in intensity, progressing towards the intensity of the activity. The pulse raiser increases temperature allowing bodily systems to occur at their optimum, showing a 10% increase of chemical reactions in comparison to rest. Temperature is controlled by the hypothalamus within the following narrow ranges:

·         At rest > 36.9 degrees

·         Moderate > 37.7 degrees

·         Severe exercise > 41.1 degrees (although this may lead to the suppression of nervous system function)

Immediate Effects of Exercise

·         Increase in heart rate

·         Increase in CO

·         Increase in the depth and rate of ventilation

·         Increased heat generation

·         Increased nervous stimulation of the muscles

Circulatory, vascular and respiratory (CVR) rate rises occur as a result of the engagement of the nervous system. It is a balance between the sympathetic and parasympathetic nervous system activity that dictates any adjustment of the CVR systems needed to meet these changing physiological demands. These two systems originate in the cardiac centre in the medulla oblongata of the brain.

                                                Sympathetic --> increased heart rate
                                                Parasympathetic --> decreased heart rate

Aerobic Exercise

This occurs when the body is able to meet the physiological requirements to maintain activity continuously. As well as the immediate effects of exercise:

·         Certain blood vessels constrict to re-direct blood away from non-essential areas such as the gut to the muscles that requires oxygen

·         Blood vessels in the active muscles dilate to increase blood flow

·         The increase in ventilation rate and activity indicates the active use of a greater range of respiratory muscles

Cool Down

This should consist of active recovery exercises of decreasing intensity to allow a gradual readjustment to a normal resting state. It allows a slow decrease of the CV rates and RR and a slow decrease of metabolism. It helps to dissipate waste products such as lactic acid and lessens the potential of DOMS. It encourages venous return, therefore reducing the chances of dizziness and encourages the lowering of blood levels of adrenaline, as high levels put excess stress on the heart.

Any cool down should last for at least 5 minutes in order to achieve a recovery HR of at least 120bpm 3 minutes after cessation. After 5 minutes you should be aiming for around 100bpm, however this depends on levels of fitness.

Long-term Adaptation of the CVR Systems

The benefits of long-term structural and functional adaptations to the CVR systems are as follows:

• Cardiac hypertrophy
• Endurance athletes develop larger chambers
• Power athletes increase the thickness of the left ventricular wall
• Stroke volume increases
• Improved extensibility and contractability
• At rest, CO remains constant therefore bradycardia ensues
• Increase blood volume
• Training stimulates increased plasma and red blood cell volumes
• Oxygen delivery and waste removal effectiveness increases
• Endurance activities increase blood plasma volume, making the blood more dilute
• Slight increases in all lung volumes as respiratory muscles become stronger and enhance an individual’s pulmonary diffusion capacity
• Improves lung function
• Assists in diffusion of blood via the pulmonary artery
• Increased capillarisation at the muscles
• Oxygen consumption (VO₂) decreases due to increased physiological and bio-mechanical efficiency
• Blood flow to muscles decreases as muscles extract more O₂ increasingly effectively from the blood, leads to increased VO₂ max.
• Recovery rates improve
• Blood flow to the skin improves, enhancing sweat production and the cooling of the body