السبت 22 يونيو 2024

The Equine Heart

موقع أيام نيوز

When you first start examining patients as a veterinary student youre very keen to gently poke and prod every animal you come across. Realizing you can assess cardiovascular function by palpating peripheral pulses is very empowering! 
Once you find a pulse in a healthy cow you simply hang on and count as the pulse waves come to you in a more or less steady stream 60 to 80 times a minute. You can confidently anticipate when the next one is going to arrive. Then you examine a horse perhaps a mare in her late teens quiet cooperative and relaxed and all of your confidence disappears. One minute you have the pulse the next you dont. One minute the pulse is strong then it disappears and youre sure you didnt move your fingers. The book says the rate should be 28 to 40 beats per minute but in this horse sometimes its 40 and sometimes its 12.

Generations of veterinary students have gone through this examining supposedly healthy horses whose hearts do not beat regularly horses whose hearts take frequent breaks beat much more slowly and sometimes much more rapidly than they are supposed to. The horse has a huge range of normal resting heart rates and a huge range of different normal rhythms and in a healthy horse none of them are really regular. This is your introduction to equine cardiology all over the map! 
Cardiovascular Reserve and the Microcirculation
The cardiovascular system of the horse consists of a heart the arteries that convey cardiac output blood to functioning tissues the microcirculation inside those tissues that moderates local distribution of blood flow and the venous system that collects blood from tissues and returns it to the heart. If I were to ask you which part of this system is most important which part is in charge you would probably say the heart but thats not true. Its actually the microcirculation. 
The cardiovascular system exists for no reason other than to meet the needs of tissues muscle for example and in this regard the heart is an essential but slavish bag of muscle a pump. It goes like this blood flows from areas of high pressure to areas of low pressure. The highest pressure is at the left ventricle of the heart during systole or contraction where the pressure is generated and its lowest in the right ventricle in diastole or relaxation when