Understanding cardiac physiology – the SARCOMERE

[ CAR SHOCK ABSORBER ANALOGY – to sarcomere ]

The SARCOMERE, the basic functional unit (contractile unit) of muscle, in this case cardiac muscle,

can be thought of as a shock absorber.

shckabsbr001

the shock absorber (a common day item in our lives)  at its extremes can represent

the sarcomere at its extremes.

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SEVERE DEHYDRATION

the above pair of shock absorbers would represent severe dehydration.

(piston pair pictured above – entitle “severe dehydration”).

There is practically no more room for the pistons to be pushed together.

CONGESTIVE HEART FAILURE

(piston pair picture below that – entitled “congestive heart failure”).

There is practically no more room to pull the pistons apart.

 

[ HAND GRASP ANALOGY – to sarcomere ]

shckabsbr003

pictured above :

baby grasping hand – analogous to congestive heart failure.

barely any grip left.

hand shake – analogous to good grasp (Goldilocks zone).

good grasp.  Good allowance for give or take of the grip.

rescuer’s grip – analogous to severe dehydration.

not very good at contracting anymore.  However, plenty of room for give.

starling curve 004

Such is the sarcomere :

A grip between actin and myosin filaments.

For purposes of our discussion, the sarcomere should be in the Goldilocks zone

allowing for enough give or take – to handle the “fluid bumps in our lives as we

indulge in liquid intake or neglect”.

Pharmacology – Milrinone – Primacor

 

Milrinone – for pulmonary vasodilation.

useful in this scenario :

your patient’s pulmonary vascular resistance (PVR) is high

and your patient’s systemic blood pressure is high (ex 220 / 140 mmHg).

 

If your patients PVR is high and the (systemic) blood pressure is normal (120 / 80),

after MIRINONE is done coursing thru the patient’s blood vessels, this vasodilator

(global vasodilator – it will dilate everything in the body) will be 50 / 20.

 

((MORE TO COME)) !!!

Understanding cardiac physiology – putting it all together

 

 

pvroute005

It becomes glaring obvious what needs to be done.

The RV needs to be decongested.

The LV needs to be refilled.

We can do this many ways :

> give a pulmonary vasodilator –

via inhalational route : nitric oxide, Iloprost.

via intravenous route : milrinone (we’ll discuss later).

> oxygenate the pulmonary interstitum properly (increase FiO2).

> oxygenate the pulmonary interstitium and reverse HPV via alveolar recruitment maneuver (ARM).

 

 

 

 

Understanding cardiac physiology – the LV – the thick ventricle

 

starling curve 003

The cardiac chambers are marked in this CAT-scan image :

RA = right atrium … notice that the RA is engorged with blood (moreso than the RV or the LV).

RV = right ventricle … notice that the RV is thin wall of muscle and is overfilled.

LV = left ventricle … notice that the cross section of the LV is a thick wall of muscle.

The normal capacity of the LV or RV should be 100mls.

The LV is thick because it has to generate high pressures : 120 / 80 mmHg.

The RV is thin walled because it only has to generate a pressure of : 25 / 15 mmHg.

starling curve 002

TEE (TransEsophageal Echocardiography) is the test of choice for a fast evaluation of cardiac chamber

volumes and efficacy of functionality.

CAT scans are great by are time-intensive, labor intensive and costly and with moderate risk.

TEE is fast becoming the tool of choice at bedside in the CTICUs and the ORs.

Understanding cardiac physiology – the Starling curve.

starling curve 001

pictured above – the inset boxes in the bottom portion of cardiovascular decompensation and

cardiac dysmorphia are representations of the RV and LV startling curves.

The green dots on these starling curves represent the “Goldilcoks” zones.

The red dots represent their location in their current state of cardiac dysmorphia.

starling curve 005

We will get to the point in our discussion where we will understand how CPR may actually

get us back in the “Goldilocks” zone.

starling curve 007

This Starling curve is where we all currently exist.

If you gave 1L (one liter) of NSS fluid challenge, the cardiac output would increase by a given amount.

starling curve 009

If you were on a “booze cruise” in the sunny isles, between alcohol exerting its diuretic effects and

dehydration in the hot, hazy atmosphere, your status on the Starling curve would shift rightward.

In this case, a 1L NSS intravenous fluid (IVF) challenge,  your cardiac output would increase by a

significant amount.

This is because the sarcomeres were understretched and after 1L of extra IVF in your vascular

system, the cardiac output generated by a then underfilled LV and now properly filled (and in the

Goldilocks zone) will give you great “bang for the buck” (great cardiac output).

starling curve 008

In the case of heart being overfilled and being challenged by 1L of IVF, the heart will

further exacerbate itself and result in further deterioration of cardiac function.

In this case the sarcomeres would go from overstretched to severely overstretched

and essentially become useless with cardiac failure not far in its future.

starling curve 010

The Starling curve is represented with the aforementioned three scenarios of

(from left to right on the curve) understretched, to “just right” to overstretched

sarcomeres (as represented on the bottom of each graph).

Just imagine a shock absorber in its place.

Understanding cardiac physiology 101 – the sarcomere

starling curve 001

This is the complex physiology of HPV (hypoxic pulmonary vasoconstriction)

as explained earlier.

starling curve 004

It is important to understand the basic structure of the cardiac muscle and

its functioning in the heart.

This is the SARCOMERE.

The sarcomere is the basic functional unit of any muscle unit (fascicle).

It is the basic contractile unit in any muscle.

Think of a sarcomere analogous to a shock absorber of a car.

It is important to realize that it, like Goldilocks, may find that it can be

OVERSTRETCHED, UNDERSTRETCHED, or “JUST RIGHT”.

The sarcomere is overstretched in the case of CHF.

The sarcomere is understretched in the case of dehydration / “alcohol poisoning”.

The sarcomere is “just right” most of our lives.

 

 

 

 

Understanding cardiac physiology 007 – the dysmophia of the heart.

 

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pictured above : the normal hearts shape.

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with pulmonary vasoconstriction, the RV overdistends and the LV gets underfilled.

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when the RV overdistends, the heart muscle is overstretched and

the intercardiac septum shifts leftward.

This leftward shift of the intercardiac septum compromises some

of the left ventricles volume.

cor012LVnlvsunderfilled

The compromisation of the LV exacerbates the underfilling of the LV.