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Archive for the ‘cardiac physiology’ Category

We know pleural effusion (hydrothorax) is disproportionately more common on right side in cardiac failure.Though its a well observed phenomenon, the mechanism of which  has not been clear to us. It could be due to multiple  anatomical , physiological factors.

 

*The are  right and left lymphatic (Thoracic) ducts that drain the corresponding lungs and pleural space . There can be overlap and contribute to the differential occurrence of pleural effusion

 

Reference 

A meticulous paper written some 75 years ago (1946) from Harvard medical school teach us some important points in this phenomenon.

There is still lot, to be understood about pleural effusion in cardiac failure. We need to know why some pleural effusions tend to occur independent of hydrostatic forces.  It is also noted long-standing transudative effusions can become true exudates. Role of local pleural capillary hypoxia resulting increasing permeability is underestimated.Hepatic congestion and trans-abdominal seepage of fluid is a distinct possibility.

One more area we are not clear is  the relationship  between the  genesis of  pericardial effusion in cardiac failure and concomitant pleural effusion. Post operatively , after univentricular repair (as in Fontan ), pleural effusions can be much problematic with high venous pressure interfering with  pleural drainage.

Impact on symptoms

Finally, even mild pleural effusion can increase the work of breathing and result in dyspnea which is out of proportion to cardiac dysfunction.While we expect the diurteics to clear the effusion of cardiac failure, it doesn’t happen always arguing for a non transudative mechanism in at least some of them.

Further reading

Discerned readers are advised to study the pleural space dynamics in detail.

Link to the original Article of Edgar Mcpeak and Levine 1946

 

 

 

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The right ventricle  is considered as a docile cardiac chamber with passive filling and  emptying  properties .

This belief  was reinforced when Fontan  in early 1970s suggested a principle in the management of  cyanotic heart disease  when  the right side of the heart is underdeveloped. He  proved  RV can be by-passed safely , with  great veins  (IVC/SVC)  by  themselves  take care of filling the pulmonary circulation  without the need of RV pumping function.

While it is true for few complex cyanotic heart disease, largely this a misleading  concept. In clinical cardiology practice  ,sudden or non sudden  RV deaths happen every day in the form of . . .

  • RV Infarction
  • Acute RV dysfunction in massive pulmonary embolism
  • COPD with RV dysfunction
  • Most cases dilated cardiomypathy  the terminal event is due to RV  failure.

So , RV function can never be dispensable in day to day cardiac hemodynamics.

RV has some unique properties in terms of shape , size and  hemodynamics . We are getting more insights from  modern blood pool imaging by MRI , about  how the RV handles the blood volume .

We know RV has a unique shape  triangular ( partially  pyramidal ) . It can be inferred the RV cavity is formed by fusion of  many  eccentric spacial planes. We have always believed  RV handles the blood it receives from right atrium in a unique way .Now we are beginning to understand it .It is now documented the RV segregates the blood it receives into 4 components.

 

right ventricle physiology anatomy hemodynamics

It is curious  to know  RV inflow is connected to the outflow by an invisible   physiologic Bridge . About 44% of  blood traverse the RV in this fashion.

 

RVOT blood flow right ventricle

Note : RV blood flow preferentially enters the RVOT with out transiting RV body and apex.Image courtesy http://ajpheart.physiology.org/

 

Which is the most important part in RV ? (Among Inflow, Body, Apex, Out flow)

After reading this article it seems to me , the mechanical  function of RVOT could be most  vital. If it fails to handle the first increment  which  comes directly from  RV inflow, stasis  is likely in RV body and apex , elevating RVEDP and later promoting stasis leading to clinical events.

Clinical implication of this study

  • Differential dilatation RV chambers to pressure or volume  overload is observed .
  • We need to analyse why RV dilates in some   but   goes for hypertrophy in others when confronted with pressure overload (VPS vs PAH)
  • RV apical clot in restrictive cardiomyopathy  is a direct consequence of stasis  of blood  in RV apical zone .
  • RVOT pacing  may have a hemodynamic advantage  over RV apical pacing  . However , for anatomical reasons RV apical pacing  is  far safer than RVOT pacing where the lead  is subjected to constant life long strain due to this busy RV inflow to outflow express  high way !

Final message

Traditionally we have labeled  RV  as a  passive venous chamber .It is clearly a misnomer.It  has to handle both the venous and pumping function beat to beat with precision  without  back log .Obviously ,  RV has to think and work  more than it’s  big brother !

Reference

I wonder , if  there is  any other site other than APS . . . to  find crucial  answers in cardiac physiology  !

 

Right ventricle physiology blood flow  3d 4d analysisAfter thought

  • There is huge gap between physiologists  who work in research labs and the physicians at bed side .
  • I appeal all young cardiologists  to visit  APS  once in a while ,between your busy cath lab schedule and help narrow this gap.
  • Without understanding the physiology properly how are we going to intervene the pathology ?

 

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I used to tell my students ,the relationship between the heart and kidney  is so close , it is never justified for  the  two departments of Nephrology and Cardiology  are  physically away by two blocks in our institute .

Kidneys are vital to maintain the volume and pressure of body fluids and heart is responsible for keeping this fluid circulating.

In clinical setting  it is a well known secret ,most deaths in patients who are on dialysis is cardiac while  most  deaths in patients  with CHF are renal.

It remains a mystery  why kidneys were   ever considered as a circulatory organ  , when  our medical pundits de-compartmentalised  human organ systems !

CKD is pre-cardiac failure and CHF is pre-renal failure

The Heart /Kidney affair is so intimate in many  pathological situations both either succeed or fail  simultaneous or sequentially.

While CKD  results in and pressure and volume overload of heart , cardiac failure cause pressure and volume under load (pre-renal  factor) which worsen the renal function and aggravate cardiac function alter.

In essence,  it is vicious cycle of two  serial organs  performing  the vital circulatory function with body fluids playing a  role of diligent mediator.Whenever the kidney  fails heart  is stretched and stressed  to its Frank starling limits by the volume  as well as the accompanying HT load.

While text books link these two organ as simple cardio-renal syndrome it is not happening at the level of patient’s bed side.

Cardiologists and  Nephrologists must realise they need do work in tandem like  their  respective  departmental  organs  which accomplish this task easily !

To tackle this much  maligned  cardio-renal conundrum

Consider CKD as CHF equivalent  and CHF as CKD’s

I would recommend this concept to be infused  right in the third year medical school and  try de- compartmentelise  clinical  medicine.

Need of the hour : How to Moderate ACEI dosing in CKD

ACEI has been a major pharmacological   revolution in controlling and reversing the adverse events of cardiac failure . Some where along ,  a significant fear complex arose regarding the damage it could cause to kidneys.

Recently , we know the role of  ACEI in CKD made U turn(Like what  Beta  blockers did to CHF) .Now, it is presumed ACEI are indeed  safe in most CKD and may  even regress  CKD. Still this concept  has not been fully disseminated  into general physician domain.

Let cardiologist and Nephrologist sit together and sort out this issue.

I guess ,  ACEI controversy is  a sort of  ongoing ego clash  between Nephrologist and Cardiologist . Both like it , both make fuss about it ! In my observation , if  a cardiologist titrate it upwards  Nephrologist would  lower it  and reverse happens if cardiologist express caution about it ! Do you agree ?

Final message

Mankind has  accrued  great benefits  from stunning break throughs in modern medical science . . . but it has come  only at a huge  cost ! Medical knowledge has completely fragmented the physician mind-set .Every good therapeutic concept is  hanging aloof .It requires periodic de-fragmentation (As we do it to our PCs by anti-viral soft ware !)

To begin with , let us  consider   CKD and CHF as single sequential circulatory  entity !

Let us vouch to  create new generation medical professional  devoid of skewed  medical vision !

Reference

Guidelines for ACEI in CKD

NKF national kidnye foundation

https://www.kidney.org/professionals/kdoqi/guidelines_bp/guide_11.htm

acc aha  accf guidelines chf 2013

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Note :This is a copy of  my earlier blog on coronary micro-circulation  published few years ago.Recently this got numerous hits .Hence I have just reposted it with slight modification.

Human coronary circulation stands unique among  others as it is a  life-sustaining circulation.It is indeed a great medical achievement  to visualise  the right and left coronary artery  system by coronary angiogram.  Actually,  what we see is  only a fraction  of  the surface area of coronary circulation .The surface area of  epicardial coronary arteries   constitutes  less than 5 % of entire coronary vascular tree .

And  . . .

An in vitro heart with special catheters showing the true extent of coronary circulation: Courtesy http://eurheartj.oxfordjournals.org/content/28/3/278.full.pdf+html

This  is the reason  normal coronary angiogram can never mean normal  coronary circulation !

This huge gap in our perception is the single important factor  that  explains the vagaries  of modern coronary care .

This also make any clinical coronary  scenario  a  reality .

“A patient with normal coronary angiogram getting a myocardial infarction , the next day and a severe triple vessel disease living comfortably  for  decades with medical management”

So , it is essentially a  false  sense of  scientific accomplishment  by the cardiac scientists  at  least in the  of coronary circulatory physiology.

What determines the extent of these invisible coronary micro circulation ?

There are innumerable channels of micro vessels traversing across the heart, sharing , bridging , branching, penetrating  and  perfusing the muscle mass.They can be anatomically patent , physiologically non patent .They can be recruited by hemodynamic stress .These are never visualized by current imaging modalities..It is also influenzed by  favorable growth milieu and hormonal and neural stimuli.

Ignorance based cardiology

What is the mechanism  of primary VF following acute STEMI ?

The quantum of  coronary micro circulation is like the vast  cerebral neuronal net work .We have every reasons to believe they are have unique genetic imprint.How else you can explain a man with full blown STEMI come 24 hours later comfortably to the OPD while another loses his life with a stormy primary VF before even boarding the ambulance !

Why many cardiologists   do not give due credit  the   coronary collateral  circulation  ?

Right from the days  of  Levine in 1970s( Who made a seminal contribution  about coronary collateral)  the  utility value of  coronary  collateral  circulation  was never able to convince the cardiology professionals .

It has been our traditional  teaching ( without much evidence of course  !) coronary collateral circulation  is not effective to support blood flow during exercise . This fact has been  disproved  many times . Coronary collateral circulation was indeed useful in limiting damage in ACS and  relieve symptoms in stable angina.It helps  in reverse remodeling and provided electrical stabilty as well in post MI population.

Still , the concept  was  alienated  and   made   totally irrelevant  in the interventional  era  . Many   cardiologists  found well-developed collateral’s as an interference to their expertise and ego since it has a potential to alter the indication of PCI.They  continue to have  strong  scientific conviction (Pseudo ?)   that man made collaterals must always been superior to God made collaterals !

Whenever  some credible  reports emerge about  collateral circulation   being   equivalent to  revascularisation procedure , these concepts were  prematurely buried for some reason.

In the last decade there was a concern  about  performing  PCI in patients with well-developed collaterals  .The argument was , they tend to develop early stent occlusion and restenosis . It  was a genuine  query  raised by few thought leaders in the field as  collateralised vessels  suffer from  low flow   after PCI ,   if the pre -existing collateral continue to function.

But  then , few  studies countered this , and PCI was shown to be safe and  in fact may  fare well   in  patients  with  extensive collaterals .

In these  studies  interventionist’s  argument looked  amusing !  as they  seem to  define a  successful  PCI  as  not only to open the occluded vessel  but also  make sure to close  all functioning  collaterals  .(What a  a pity for our natural biological  angiogenic forces which had  worked  and  grown meticulously for months!)

Cardiac science in the current format,  makes   the future look  bleak for coronary a collateral circulation .With  early PCI  becoming a norm we will never ever allow the natural collaterals to  grow  ,  and even the  established collaterals  will have to face a stiff   fight  for survival  with  sophisticated coronary interventions .

Competing interest in the filed of  coronary collateral   research

While the basic scientists want  to  grow collaterals with angiogenesis ,  stem cells etc  interventionists   continue to  indulge in rampant angioplasties which  will suppress  collateral growth.

This implies we will struggle to  establish  the true  importance of  coronary collateral circulation .

Final message

Can it be an  effective form of revascularisation  ? 

My personal  inference  is   coronary collateral  circulation  “would and should”  have  a definite role  in at- least  some of the subsets  with chronic coronary  syndromes. If we think otherwise . . .    it’s against the principle of  natural biological science .

A good  collateral   system with optimal medical management  can save not only our  patient’s  lives but also  their hard earned currencies !

Reference

Here is a rare article in European heart   journal that discuses coronary collateral circulation  . Let us welcome such wonderful  reviews which keep the interest alive on the filed.

http://eurheartj.oxfordjournals.org/content/28/3/278.full.pdf+html

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electrical CONDUCTION OF HEART

Image source and courtesy http://www.heart-consult.com

Answer

I am afraid the 4th response is closer to truth .Readers may share their thoughts. If there are three distinct pathways   spreading widely connecting the two spacious chambers and   converging again with  precision at the compact  AV node , it  is a  marvel .

Further , If these pathways are real ,  we must  experience different types of  inter nodal re-entrant  tachycardias.Of-course ,we do come across few macro re-entrant tachycardia in the form of atypical atrial flutters  They need a close  watch .Tracking these arrhythmia may throw light on existence of these pathways.

However, the presence of nodal approaches  with preferential inputs to AV node from different parts of atria would indeed  suggest existence of such pathways !

Further study

What does  sophisticated carto and other electro anatomic mapping say about these inter nodal pathways ?

Reference
An excellent article from imperial college London
Atrial anatomy and inter nodal pathway thorel bachman wenkeback

Heterogeneous three-dimensional anatomical and electrophysiological model of human atria . Seemann G, Höper C, Sachse FB, et al. Institute of Biomedical Engineering, University Karlsruhe (TH), Kaiserstrasse 12, 76128 Karlsruhe, Germany. Transact A Math Phys Eng Sci 2006 Jun 15; 364(1843) :1465-81.

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Normal  left atrial  (LA) volume is about  22ml/sq.meter body surfacearea  at all ages.Maximum LA volume in physiology is  about 46ml in  females and 56 ml  in males( Average 35 ml)

LV stroke  volume  for each beat is  about  70  ml . . . so where does  the remaining 35ml come from ?

Answer .

  • Pulmonary veins ?
  • Residual LV end systolic volume ?
  • Mix of the two ?

It is logical to assume about 35 ml of fresh  blood  from 4 pulmonary vein*  rushes into LV with every diastolic cycle  .It  never stays in LA  .It just uses LA as a transit  route ,

*In diastole the four PVs,LA  and LV all act like one single chamber .

 

Is this reasoning correct ?.

If we believe the continuity equation this explanation is correct . However still what  we need to know the fate of residual  LV volume (End systolic LV  volume which is also  about 35 ml that would be  in queue for ejection into Aorta  for the next beat !)

Further , we know the LV end systolic volume is not constant .During exertion it  can reach  negligible levels (<10 ml) .At times of vigorous contractions  it can touch near zero as well . Then , It become vital for the  pulmonary venous reservoir  to be act as a  major donor for  LV blood volume for  every ensuing beat.

If the hemodynamics of pulmonary vein LA interface is tricky even in physiology ,  one can imagine the complexities  if the LV diastolic function and left atrial compliance  is affected

Debit and credits of  LV end -diastolic volume .

Let us assume LVEDV is about  1o5  ml .LA blood volume is  roughly one third of LV volume .For every beat equal amounts of fresh blood  from pulmonary vein . These two (LA+PV)  adds to the  residual  blood in LV  to make LVEDV 105   ml . From this 70 ml is ejected as stroke volume leaving behind 35 ml.


lvedv lvesv stroke volume wiggers cycle left atrial volume pressure volume loop residual diastasis

Image template from http://www.cvphysiology.com

 Further questions

LA Chamber volume and blood volume need not be same .What  I struggle to understand is , total anatomical  LA volume  measures  35ml , while the amount of blood it is supposed to hold is also about the same .Does  it mean the LA is completely filled with blood . . . air tight !

Will the LA compliance make it accommodate twice or thrice the blood volume during exercise ?

What is quantum of residual end diastolic  LA volume ?

 

Reference.(Normal LV and LA volumes )

echopedia

 

 

 

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Obesity is a major cardio vascular risk factor.We earnestly  believe  this  by  evidence from Framingham and other studies.However , epidemiological  truths   can be dissociated from individuals .

We now understand  some  of the obese  patients fare better in CHF outcomes  apparently because of the obesity ! Even patients who undergo PCI show some benefits.This concept  is being proved in large data base of  > 200,00 patients.

Possible mechanisms

The lay man’s logic may apply (Science hidden somewhere !) Obese persons  have basically a  large heart with better cardiac reserve and  muscle mass .These hearts are  pre-conditioned to extra burden of MVO2  in it’s life time . So it  is able to tackle  hypoxia better, takes more time  to get fully exhausted .After all heart can consume fatty acids for it’s energy requirement.

Adipose tissue may also  secrete favorable anti-inflammatory  chemicals , though majority of adipocytokines are detrimental  except adiponectin .Paradoxically  the tumor necrosis factor TNF  (Same as cachectin or Interleukin 6)  is less  in obese patients .

 

Reference

obesity paradox

obesity paradox 3

obesity paradox 4

obesity paradox 3 jama archives of internal medicine

Reference

The landmark Lancet article that first raised the question of obesity paradox

http://www.ncbi.nlm.nih.gov/pubmed/16920472

http://care.diabetesjournals.org/content/36/Supplement_2/S282.full.pdf+html

Counter to the  concept

obesity pardox does it exist

http://science.howstuffworks.com/life/human-biology/obesity-paradox.htm/printable

Obesity   paradox applies in stroke too ! This study (TEMPIS) from Berlin  Germany  suggest controversially though

 

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