Cardiovascular/Hematopoeitic Systems Flashcards
What are the majority of exercise intolerance issues due to?
Musculoskeletal problems, respiratory issues, cardiovascular issues
(in that order)
What does splenic contraction do for the horse?
Increases circulating blood volume which increases oxygen carrying capacity of the blood
What how much does hematocrit increase doe splenic contraction result in?
from 40% (resting) to 60-70%
What can be an issue with increased PCV?
Also increases the viscosity of the blood which can decrease the perfusion
More reasons why blood doping is dumb
What is the issue with exogenous EPO administration in order to boost blood production?
Immune mediated reaction that results in bone marrow suppression and lifelong/fatal anemia
What is cardiac output a product of?
Heart rate and stroke volume
How much does cardiac output increase from rest to exercise?
25L/min to 300L/min
What is the typical exercise HR of a horse?
200-250BPM
What factors contribute to increased stroke volume?
- Myocardial contractility
- Venous return
- Blood volume
- Filling time
What is venous return enhanced by?
Vasoconstriction, muscular contraction, air pressure changes in the thorax
Air pressure likely the most important component
How much volume can splenic contraction contribute?
12L
~25% of normal circulating BV
What cardiac event dysfunction is most likely to contribute to exercise intolerance and poor performance?
Atrial contraction dysfunction
How much does SV increase with submaximal exercise?
20-50%
T/F: Increased heart rate will always have a positive effect on stroke volume.
False- if heart rate is high enough to decrease diastolic filling time it will negatively impact it
What system is believed to be the primary limiting factor to maximal exercise?
Respiratory system
What pathology supports the thought that the respiratory system is the limiting factor for maximal exercise?
Exercise induced pulmonary hemorrhage
What is the difference in respiratory volume between rest and exercise?
80L/min vs 1800L/min
How is tidal volume increased?
- Increasing diaphragm contraction
- Increasing pleural pressure changes
- Increasing flow
- Limiting muscular activity
Why does limiting muscular activity help increase tidal volume?
The energy needed to increase ventilation uses more oxygen than it delivers.
At what speeds does the horses respiratory rate match the stride frequency?
Gallop and canter
Feet cannot go faster than the breathing
What is the respiratory rate limited to at a gallop and canter?
~130 breaths/min
What acts as a pump to assist breathing at a gallop and canter?
Visceral contents
As the front feet hit the ground the contents hit the diaphragm which causes the horse to exhale and visa versa
What A-V O2 gradient favors diffusion of gases?
High gradient- improves O2 extraction
What what kind of shit of the O2 dissociation curve favors offloading?
Right shift due to hypercarbia, high temps, or tissue acidosis
T/F: The horse has more muscle mass than the cardiovasular and respiratory systems can reasonably maintain during maximal exercise
True- reasons why horses have been selectively breed for bigger hearts
At what percentage of VO2 max does hypoxemia ensue?
65%- passage of the RBCs in pulmonary capillaries is too fast for them to get adequate oxygenation
What two things will have a negative impact on performance in the cardiovascular system?
Limited SV increase and extreme HR increase
What is the most significant limitation to respiratory function?
Resistance to flow in the upper airways
What are the limitations of the respiratory system?
Limit to increase in rate
Limit to ventilation
Resistance to upper airway flow
What muscle fibers fatigue fastest in endurance horses?
Type I and then type 2 aerobic metabolism
What muscle fibers fatigue fastest in race horses?
Type 2 anaerobic metabolism
What does training and conditioning improve oxygen delivery by?
- Increase in heart mass
- Increase in SV
- Increase in PCV
- Increase in total RBC volume
- Increase capillary supply to muscles
- Redistribution of blood
- Increased capillary surface area
- Increase delivery to working muscles
Training a horse increases which metabolic pathway?
Aerobic- more 2A fibers, increased mitochondria and glycogen stores
When is exercise evaluation performed?
Poor performance- sudden onset or never reached potential
Exercise intolerance- suboptimal performance of a usually good perfoming horse
Fitness assessment- to assess general fitness and potential
T/F: Horses with exercise intolerance do not appear sick under normal condition or at rest.
True
