Heart Sounds
Auscultation : the act of listening to sounds within the body.
The sound of a heartbeat comes primarily from blood turbulence caused by closing of heart valves . During each cardiac cycle, there are 4 heart sounds but generally only the first two is able to be heard (S1 and S2) S1 – the first sound is described as a “Lubb” and is louder/stronger than the S2 sound. It is associated with closure of the AV valves soon after ventricular systole. S2 – the second sound is shorter than and not as loud as S1. It is described as a “Dubb”. It is associated closure of the SL valves at the beginning of ventricular diastole.
S3 – not normally heard is associated with ventricular filling.
S4 – not normally heard is associated with atrial systole.
Cardiac Output
Cardiac Output is the volume of blood ejected from the left ventricle (or the right ventricle) into the aorta (or pulmonary trunk) each minute.
Some terms:
Cardiac output (CO – mL/min)
Stroke volume (SV – mL/beat)
Heart rate (HR – beat/minute)
Therefore: CO = SV x HR
Example 1
resting horse:
SV = 800 mL/beat
HR = 30 beats/min
Example 2
Maximal exercising horse:
SV = 1500 mL/beat
HR = 240 beats/min
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