Cardiac output & various conditions / factors

CARDIAC OUTPUT: Cardiac output is the volume of blood pumped per minute by each ventricle.

CARDIAC OUTPUT=Stroke volume x Heart rate

                                = (130-50) x72bm^-1

Stroke volume = Amount of blood eject from each ventricle in each heart beat ;80 ml

Stroke volume = End diastolic volume - End systolic volume

End diastolic volume =Amount of blood within the ventricle at the end of the ventricular diastole; about 130 ml

End systolic volume= Volume of blood remaining within the ventricle at the end of the ventricular systole; about 50ml

Effect of various conditions on cardiac output

No Effect:

·                   Sleep (it also may decrease cardiac output up to 25%)

·                    Moderate change in environmental temperature.

Increase:

·                    Anxiety and excitement (50-100%) :By ↑ adrenalin secretion

·                    

                         Eating (30%):↑ Metabolism → ↓ tissue Oxygen →Vasodilatation →↓peripheral resistance → ↑Cardiac output.

·                       

                Exercise (up to 700 %) :

*↑ Metabolism → ↓ tissue Oxygen →Vasodilatation →↓peripheral resistance → ↑Cardiac output.

*↑Skeletal muscle pump-↑ respiration-↑ venous return-↑cardiac output

*↑sympathetic discharge-↑Heart rate & myocardial contraction-↑↑stroke volume-↑cardiac output

·                       High environmental Temperature : ↑ body temperature-vasodilatation of skin→↓peripheral resistance

                → ↑ Cardiac output.

·                       

                             Pregnancy:

                                *↑ Plasma volume through Aldosteron -↑stroke volume-↑ Cardiac output

                                *During labour pain Cardiac output ↑ due to Catecholamine.

·                      

                   Anaemia: (↓Hb+↓viscosity of Blood+↓tissue O₂) →Vasodilatation →↓peripheral resistance → ↑Cardiac output.

·                     

                             Thyrotoxycosis :

*↑number of β adrenergic receptors

*↑response to circulatory catecholamine

↑p proportion of α myosin heavy chain( with high ATPase activity)

·                      Ionotropic Agent: Adrenaline,Isoprenaline,Dopamine

↑ Heart Rate

↑Cardiac index(The output per minute per square meter of body surface area; about 3.2L/min/m2 of body surface area)

↑Decrease peripheral resistance( Adrenaline,Isoprenaline)

↑myocardial Contractility(Dopamine)

Decrease

·                      Sitting or Standing from lying position : By Gravity & Baro receptor mechanism

·                    

                         Rapid Arrhythmia : ↓ Stroke volume - ↓ cardiac output

·                      

                          Heart Diseases : ↓ myocardial contractility- ↓ Stroke volume - ↓ cardiac output


  
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