Breathing is controlled by neurons located in the pons and the medulla.
They are located in
Respiratory and Cardio vascular systems
Muscles and tendons
Viscera and brain
Sensors in the respiratory system.
Pulmonary stretch receptors
Pulmonary irritant receptors
3 Control of Breathing
1. Pulmonary stretch receptors
Inflation of lung stimulates
Located in the tracheal and bronchial smooth muscle
Response results in decrease of Rf and bronchodilation
2. Irritant Receptors
Located in the epithelium of the larynx and URT.
Chemical or mechanical irritation of airways can stimulate
4 Control of Breathing
3. Type-J Receptors are thought to be responsible for the hypernea that accompanies pulmonary embolism or pulmonary vascular congestion.
It is thought that these receptors are located in the walls of the pulmonary capillaries.
5 Control of Breathing
Are sensors that detect changes in arterial blood gases or chemical composition.
Peripheral located in the carotid bodies of the bifurcation of the common carotid arties and aortic body.
They are sensitive to changes in arterial O2 PP.
Central located near the ventral aspect of the medulla.
Responds to changes in the interstitial tissue fluid pH.
6 Lung Volumes and Ventilation 7 Respiratory System
Ultimate importance of the pulmonary ventilatory system is to continually renew the air in the gas exchange areas of the lungs
where the air is in the proximity to the pulmonary blood.
These areas include
alveoli alveolar sacs alveolar ducts and respiratory bronchioles.
8 Respiratory System
Main respiratory processes involved in gas exchange are
Ventilation movement of gas(es) into and out of the lungs
Perfusion flow of blood per unit volume of tissue
Ventilation/perfusion ratio (V/Q) how matching of air and blood in the lung influences gas exchange.
9 Respiratory System
Diffusion how gas gets across the air- blood barrier.
Gas transport how gases are moved from lungs to the tissues.
Mechanics of breathing how the lungs are moved.
Control of breathing how the supply of gas exchange is adjusted to the demand.
How much air goes in and out
The volume of air inhaled or exhaled during a normal breath is termed tidal volume (VT).
Also known as the depth of a breath
In a healthy resting athletic horse its about 12 ml/kg of body weight (5-6 liters).
Respiratory frequencies (Rf) the number of complete breaths taken per minute
Expired minute volume (VE)
tidal volume x respiratory frequency
Exercise imposes a potent stress on the ventilatory pump
Minute ventilation (MV) increases almost linearly.
Which is the volume of gas that enters or leaves the airways in any minute.
The expired minute ventilation (VE) which averages 80 l/min at rest may reach values in the vicinity of 1800 l/min during heavy exercise.
To accommodate the change in minute ventilation a horse can alter its
tidal volume (VT)
respiratory frequency (Rf)
In Trotter horses increase in MV is achieved by both (VT and Rf) at low exercise and increase respiratory frequency at high exercise intensities.
Values as high as 133 breaths/ min have been reported on treadmills.
In galloping horses respiratory and the locomotion are coupled.
Step and respiratory frequencies average 110 to 130 per minute with max. values of 148 per minute.
Therefore increase ventilation with increasing speeds is due mainly to the increase in tidal volume (12 - 15 liters).
VO2max 15 Ventilation liters VT 16 Ventilation
Alveolar and Dead Space Ventilation
Only a part of the inspired volume reaches the area of the lung where gas exchange takes place Alveolar ventilation (VA).
The remaining part of the minute ventilation is wasted in the regions of lung where no gas exchange occurs Physiologic dead space ventilation (VD).
Which includes the conducting airways and alveoli that ventilated but do not perfuse
17 Alveolar Ventilation
Rate of Alveolar Ventilation
Alveolar ventilation per minute is the total volume of new air entering the alveoli each minute.
Its equal to the respiratory rate (Rf) times the amount of new air that enters the alveoli with each breath.
On expiration the air in the dead space is expired first before any of the air from the alveoli reaches the atmosphere.
The dead space is equally disadvantageous for removal of the expiratory gases from the lungs.
19 Ventilation liters Value 20 Ventilation
Exercise-induced changes in VA and VD to VT ratio in horses depend on the type of exercise.
During mild to moderate exercise
The dead space volume does not change significantly
If exercise is prolonged at a constant rate
The dead space ventilation will increase by a simultaneous increase in Rf and in VD to VT ratio
During intense efforts
There is a decrease in the same ratio from 60 to 20
In absolute terms the physiologic dead space is reduced from 3.5 liters at rest to 2.5 liters during heavy exercise.
The dead space to tidal volume ratio averages 50 to 60 in the resting horse.
Studies have shown evidence that adequate gas exchange is maintained with very low tidal volume and very high respiratory frequency.
For a given minute ventilation the lower the physiologic dead space ventilation
The higher the alveolar ventilation and the better the gas exchange.
24 Respiratory System
From a functional standpoint the respiratory system can be divided into two major components
Upper or extrathoracic respiratory tract
Lower or intrathoracic respiratory tract
25 Respiratory System
Distinction can be made by the neg. and pos. pressure experienced by the airways during breathing.
Exercise magnifies these pressures and
Enhances detrimental effects when disease and malfunction is present
26 Respiratory System
Elastic properties of the lung.
The normal lung is a network of elastin and collagen fibers.
27 Elastic properties of the lung
Measure of the distensibility of the lung.
A measure of the ease w/ which a hollow viscus may be distended.
Can be illustrated in the
slope of either the inflation
or deflation curve of the
28 Elastic properties of the lung
Is responsible for helping to determine the elasticity and thus the compliance of the lung.
If to high atelectasis may occur.
Absence of gas from a part or the whole of the lungs
Due to failure of expansion or resorption of gas from the alveoli
29 Elastic properties of the lung
Is the phenomenon whereby alveoli are held open from support offered by neighboring lung units.
Helps prevent atelectasis
Also may play a role in exercise-induced pulmonary hemorrhage.
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