ANSC 306 (Exam 3): Lecture (1) -Cardiovascular & Respiratory Systems in the Equine Athlete

What percentage of equine athletic performance is attributed to heritability?

11-35%

What percentage of equine athletic performance is attributed to environment (training and management)?

65-89%

What are the three general steps in a horse's ability to use oxygen for work?

• Moving air into/out of lungs

• Moving oxygen from airways into blood

• Moving oxygen into working muscles and mitochondria.

What is the primary function of the equine cardiovascular system regarding gas exchange?

To deliver oxygen from the lungs to individual tissues and carbon dioxide out of the body.

Name two additional functions of the cardiovascular system beyond gas transport.

Delivering nutrients from the digestive tract and transporting hormones to target tissues.

How does the cardiovascular system help regulate body temperature?

By diverting blood toward the periphery (skin surface) to cool the animal.

What are the three main components of the cardiovascular system?

The heart (pump), vasculature (pipes), and blood (liquid).

What is the approximate total blood volume of a 1,000 lb horse?

Approximately 50 liters (about 13 gallons).

What is the function of erythrocytes (RBCs)?

To transport oxygen.

What is the typical resting heart rate (HR) for a horse?

28-40 bpm.

What is the maximal heart rate (HRmax) range for a horse?

210-240 bpm.

Define Stroke Volume (SV).

The volume of blood pumped out of the left ventricle during each contraction.

What is the typical stroke volume of a horse at rest?

1-1.5 liters.

What is the typical stroke volume of a horse during maximal exercise?

Approximately 1.7 liters.

Define Cardiac Output (CO or Q).

The amount of blood pumped in one minute.

What is the formula for calculating Cardiac Output?

Heart Rate (HR) multiplied by Stroke Volume (SV).

What is the maximal cardiac output of a horse during exercise?

Approximately 282 liters per minute (75 gallons per minute).

What is the primary role of the equine spleen during exercise?

It acts as a reservoir for red blood cells, releasing them into circulation to increase oxygen-carrying capacity.

Define respiration.

The process of inspiration (breathing in) and expiration (breathing out).

What does the term 'anaerobic threshold' refer to in equine exercise?

The point during exercise where the horse's energy demand exceeds the oxygen supply, leading to reliance on anaerobic metabolism.

What is 'respiratory-locomotor coupling'?

The phenomenon where a horse's breathing rhythm is synchronized with its stride, often described by the piston pendulum theory.

What is the 'work of breathing' (WOB)?

The energy required to move air into and out of the lungs, which increases significantly during exercise.

Which equine breed is known for sprinting 440 yards in 20 seconds?

Quarter Horse.

Which equine breed is typically used for 50-100 mile endurance races?

Arabian.

How does conditioning/training generally affect a horse's cardiovascular capacity?

It improves efficiency, increases maximal stroke volume, and optimizes the heart's ability to handle high workloads.

How does the body provide extra blood to exercising muscles?

By redistributing blood away from less active tissues and increasing cardiac output.

What is the relationship between exercise intensity and heart rate in horses?

Heart rate and cardiac output generally increase in proportion to exercise intensity.

What happens to a horse's heart rate once it reaches HRmax?

Further increases in exercise intensity will not cause a further increase in heart rate.

Which organ contracts during exercise to release additional oxygen-carrying red blood cells?

The spleen.

What fraction of a horse's total red blood cells can be stored in the spleen?

Up to 1/2.

List three physiological increases resulting from cardiovascular conditioning.

Increased heart size, increased blood plasma volume, and increased number of capillaries.

What is the overall effect of cardiovascular conditioning on performance?

More efficient transport of O2 and CO2, which increases performance and delays fatigue.

What is the benefit of cardiovascular conditioning regarding heart rate during submaximal work?

It allows the horse to perform at a lower heart rate.

Define aerobic capacity.

The ability to predominately supply energy needed for exercise through oxygen-dependent pathways.

What is the anaerobic threshold?

The highest sustained intensity of exercise performed under aerobic conditions.

What is the typical heart rate range at the anaerobic threshold?

120 to 180 bpm, with 150 bpm being a common reference point.

What are the primary examples of highly aerobic horse activities?

Walking, trotting, Western pleasure, horsemanship, and equitation.

What are the primary examples of highly anaerobic horse activities?

Jumping a fence, pulling heavy objects, Quarter horse sprinting, and Thoroughbred racing.

What are the primary examples of mixed aerobic/anaerobic horse activities?

Reining, stadium jumping, and cutting.

What are the two main components of gas exchange?

Inspiration (uptake of air) and expiration (removal of CO2 as waste).

What structures comprise the upper airway in horses?

Nose, pharynx (throat), larynx, and trachea (windpipe).

What structures comprise the lower airway in horses?

Bronchi and lungs.

What is the resting respiratory frequency (RR) of a horse?

8 to 16 breaths per minute.

What is tidal volume (VT)?

The amount of air inhaled and exhaled with every breath (approximately 6 L at rest).

How is minute volume (VE) calculated?

VE = VT x RR.

How does respiration change during the canter and gallop?

It couples with stride frequency in a fixed 1:1 ratio.

What is the 'visceral piston effect'?

The movement of abdominal viscera acting as a piston to assist in respiration during locomotion.

What is the 'pendulum theory' in equine respiration?

The concept that the shoulder acts as a pendulum to assist in respiratory movement.

What is the primary benefit of delaying the anaerobic threshold?

It delays fatigue and reduces recovery time.

What are the two primary ways a horse increases air intake during exercise?

By breathing faster or deeper (or both).

What is the typical range for a horse's respiratory rate (RR) during exercise?

8-16 bpm at rest up to 120-148 bpm during exercise.

What is the maximum fold-increase for tidal volume (VT) in a horse?

Approximately 3-fold.

At what level does minute ventilation (VE) plateau during strenuous exercise?

Approximately 2,000 L/min.

What term describes the peak rate at which a horse can consume oxygen during exercise?

VO2 max.

How does a horse primarily increase minute ventilation (VE) at a walk and trot?

By increasing respiratory rate (RR).

What is the relationship between stride and breathing in a canter or gallop?

They are linked in a 1:1 ratio.

What is the primary factor that creates speed increases in a horse's gallop?

Stride length, rather than stride frequency.

Why do longer strides benefit a horse's breathing?

They provide more time to fill the lungs.

What three physiological changes occur to increase tidal volume (VT) during exercise?

• Larynx fully opens

• Increased bronchodilation

• External nares dilate considerably.

How much does the work of breathing (WOB) per minute increase from rest to maximal exercise?

Almost 100-fold.

What are the three physical forces the horse must overcome during the work of breathing?

Frictional resistance of airways, inertial forces of airflow, and elastic forces of the lung and chest wall.

What happens to the oxygen cost of breathing as a horse gallops?

It increases dramatically.

What is the relationship between ventilation units and the oxygen cost of breathing?

The oxygen cost for any added units of air ventilated becomes greater with any increase of ventilation.

What can happen to a horse's airways during exercise due to high pressure?

They may become compressed and partially obstructed.

How can the extension of the trachea affect breathing?

It may reduce turbulence and stiffen the trachea, making it less vulnerable to dynamic compression.

What type of breathers are horses?

Obligate nasal breathers.

Besides anaerobic work, what else is a horse's 'blowing' after exercise related to?

Body temperature.

Do horse lungs respond to training?

No, they do not.

What is the most common reason for horses to perform below expectations after lameness?

Respiratory problems.

What is the long-term effect of keeping a horse in a dusty environment or feeding moldy hay?

Respiratory damage that cannot be overcome by training.

What is the typical stride duration for a racing Thoroughbred?

300 milliseconds.

What is the stride frequency of a racing Quarter Horse?

2.88 strides per second.

What is the stride frequency of a racing Thoroughbred?

2.34 strides per second.

What does the acronym VE stand for in equine respiratory physiology?

Minute volume (or Minute ventilation).

What percentage of athletic performance is attributed to genetics versus environment?

11-35% genetic and 65-89% environmental.

What are the three sequential steps of oxygen use in the body?

Ventilation, gas exchange, and cellular respiration.

What is the primary function of the cardiovascular system?

To deliver oxygen to tissues and remove carbon dioxide.

How does the spleen contribute to exercise performance?

It contracts during exercise to release up to 50% of stored red blood cells, increasing oxygen-carrying capacity.

What is the formula for calculating Cardiac Output (CO)?

CO = Heart Rate (HR) × Stroke Volume (SV).

What is the typical resting heart rate of a horse?

24-40 beats per minute.

What is the anaerobic threshold in terms of heart rate?

Approximately 150 beats per minute.

What physiological cardiovascular adaptations occur due to conditioning?

Increased heart mass, plasma volume, red blood cell count, capillary density, and vessel integrity.

How does conditioning affect heart rate at submaximal work?

It decreases the heart rate and allows for faster recovery.

What are the components of the upper airway?

The nose, pharynx, trachea (windpipe) and larynx.

What is the formula for Minute Volume (VE)?

VE = Respiratory Rate (RR) × Tidal Volume (VT).

What is the stride-to-breath ratio during a canter or gallop?

1:1.

What does the piston-pendulum theory explain?

How abdominal organs (piston) and shoulders (pendulum) assist in breathing to save energy during locomotion.

By how much does the work of breathing (WOB) increase from rest to maximal exercise?

It increases 500-fold.

How does neck extension affect the airway during exercise?

It reduces airway collapse.

Do the lungs adapt to physical training?

No, the lungs do not adapt to training.

What is the second leading cause of poor performance in horses?

Respiratory disease.

What is the effect of dusty environments on the equine respiratory system?

It causes irreversible airway damage.

What is the maximum heart rate (HRmax) of a horse?

210-240 beats per minute.

What type of exercise is considered highly anaerobic?

Quarter Horse sprinting and jumping.

What is the primary purpose of nasal strips in equine athletes?

To reduce inspiratory resistance and airway collapse.