A 4-year-old child with tetralogy of Fallot instinctively squats during cyanotic spells. The benefit of squatting is explained by:

• A Stimulation of the dive reflex, causing bradycardia and reduced oxygen consumption
• B Venous pooling in the legs decreasing pulmonary blood flow demand
• C Kinking of the overriding aorta and improving coronary perfusion
• D Compression of femoral arteries raising systemic vascular resistance, reducing right-to-left shunting across the VSD ✓

Explanation

Squatting kinks the femoral arteries, acutely raising systemic vascular resistance. In tetralogy of Fallot, flow across the ventricular septal defect depends on the relative resistance of the systemic and right ventricular outflow circuits; higher systemic resistance diverts more venous blood into the pulmonary circulation, improving oxygenation. Venous return transiently rises with squatting, not falls, and the improvement relates to shunt dynamics rather than coronary anatomy or any diving reflex.

Reference: Nelson Textbook of Pediatrics, 22nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.