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Posts Tagged ‘squatting’

During  clinical examination of cyanotic congenital heart disease(CHD) ,  the major  task is to differentiate conditions with reduced  or increased pulmonary blood flow .

When a child with  CHD  is presented in clinical examinations , students are often asked to arrive at  the diagnosis  from history , physical examination before going in for ECG, X ray  or  echocardiography.

History,  surprisingly can  suggest  the  correct diagnosis in many (Most ?)

Reduced pulmonary blood flow is often associated with

  • Cyanosis   appearing with  /or worsening with   exertion*
  • Hypoxic spells.(Almost always occur in reduced pulmonary  blood flow )
  • History of squatting( Majority in reduced pulmonary flow)

Relief  of dyspnea   by assuming squatting position  convey   important hemodynamic information. It implies  there is significant reduction in pulmonary blood flow in standing posture , that  gets corrected  in the squat position.For squatting to improve pulmonary blood flow there must be a communication between right and left heart .This is most often due to a large VSD, rarely an  ASD .

Related article : How squatting relieves hypoxia in TOF ?

*Note :  Cyanosis  is  not  specific for reduced pulmonary  blood flow. In fact , simple reduction in pulmonary blood flow per se , cannot result in significant cyanosis .There need to be admixture /or right to left to shunt to produce cyanosis .Cyanosis in  pure admixutre states like TGV, Single ventricle , Common AV canal , Common atrium TAPVC,  are less Dependant on the reduction of  pulmonary  flow. In these situations RVOT obstruction if  present  will aggravate the baseline cyanosis.

Examination

Apart  from direct evidence for reduced pulmonary blood flow , lack of evidence for increased pulmonary  flow could  often mean ,  we are  actually  dealing  with  reduced pulmonary blood flow.

The following are the clinical clues to suspect  reduced pulmonary blood flow.

  • A quiet precardium*
  • A inconspicuous pulmonary component of S 2
  • Generally if  S 2 is well split  and both components are well heard it is highly likely the  pulmonary  blood flow is not reduced.
  • Lack of  pulmonary  arterial pulsations
  • Absence of mid diastolic  flow murmurs  in AV valves
  • Presence  of continuous murmur in a patient with cyanotic CHD almost always mean   reduced pulmonary flow and the lungs are perfused by alternate arterial collaterals (MAPCA)

* A silent  heart is the hall mark of Tetrology of Fallot which constitutes 80% of all CHD with reduced pulmonary blood flow.

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It is a well known fact squatting is a simple compensatory posture adapted by children with cyanotic heart disease during exertion to get relief from breathlessness. The children with tetrology of Fallot and related conditions have baseline hypoxia due to right to left shunting .This gets aggravated during exertion. Squatting promptly relieves this exercise-induced worsening of dyspnea. The oxygen saturation improves immediately after assumption of squatting posture. The exact mechanism by which squatting relives the dyspnea is not clear.

Apart from squat induced po2 raise there is a fall in the concentration of pco2 and raise in blood Ph that pacify the sensitive respiratory centers,thereby bringing down the tachypnea

Hemodynamics of squatting has two phases

  • Immediately ( First 15 seconds) after squatting there is a sudden drop in venous return.
  • Sustained squatting for 1-2 minutes result in steady increase in venous return, raised systemic vascular resistance.

Both these effects help the children with TOF. The initial trapping of highly desaturated blood in the lower extremity gives a quick relief as soon as the child assumes this posture. In the next 15 seconds or so the systemic vascular resistance increases and bring the aortic after load sufficiently high to divert the blood into the pulmonary artery.

The net effect of squatting is there is a transient or sustained (as long as child squats) increase in pulmonary blood flow and this is made possible by the relative reduction of right to left shunt as the aortic and systemic resistance is raised by this posture.

Other explanations

There is one more possible effect of squatting. By, compressing abdomen (Knee chest) cause a mechanical push on the splanchnic blood pool into the aorta which has high o2 saturation. This is thought to provide immediate relief to brain hypoxia and avoid the vicious respiratory/ hemodynamic cycle

What is the clinical inference from squatting in cyanotic heart disease?

Squatting implies there should be a large VSD, associated with a delicate right to left shunting very much dependent on the degree of pulmonary stenosis or ( any RVOT obstruction) and the systemic vascular resistance.

How common is squatting history in pulmonary atresia with VSD ?

It can occur with collaterals are sparse.The mechanism of relief is slightly different.

The likely mechanism of relief with squatting in Pulmonary Atresia, VSD is two fold.

1. The Initial relief is due to trapping of deoxygenated venous blood in squat posture, which is similar to TOF

2.The sustained benefit is due to raised systemic vascular resistance which favors more flow across MAPCAs from Aorta.

The second one has no authentic reference , but its a hemodynamic plausiblity as there is zero RVOT flow in PA with VSD.

What are the other cyanotic heart diseases in which squatting is reported ?

  • Tricuspid atresia
  • Double outlet right ventricle with pulmonary stenosis
  • Any combination of large VSD and RVOT obstruction
  • Rarely in Eisenmenger syndrome(10%)

Squat equivalents

Assuming a squat position has cultural issues. Grown-up children may avoid these public places. Standing with legs crosse is a common posture. In fact, the mother holding a crying baby in a chest with knees folded promptly prevents a spell . This can be called “squatting by proxy”

*Though squat equivalents do give relief from dyspnea they are given less significance in terms of diagnostic value of TOF

Reference

1.Paul R. Lurie ,Postural effects in tetralogy of Fallot The American Journal of Medicine Volume 15, Issue 3, September 1953, Pages 297-306

2. Warren G. Guntheroth. M.D.Beverly C. Mortan. m.Venous return with knee-chest position and squatting in tetralogy of Fallot American Heart Journal Volume Volume 75, Issue 3, March 1968, Pages 313-318

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