A 5-year-old boy with tetralogy of Fallot presents to the emergency department with acute dyspnea and presyncope during soccer practice. His parents note he frequently assumes a squatting position when fatigued during play. On examination, the child is cyanotic with oxygen saturation of 78% on room air. Cardiac auscultation reveals a single loud S2 and a systolic ejection murmur. Chest X-ray demonstrates a boot-shaped cardiac silhouette with decreased pulmonary vascular markings. Which of the following physiologic mechanisms explains the symptomatic benefit of the squatting posture in this patient?
- A)Decreased pulmonary vascular resistance that facilitates left-to-right shunting across the VSD
- B)Increased left ventricular preload that augments systemic cardiac output
- C)Increased systemic vascular resistance that reduces the right-to-left shunt fractionGABARITO
- D)Decreased intrathoracic pressure that improves coronary perfusion pressure
- E)Lower extremity venous compression that increases pulmonary blood flow
Explicação
In tetralogy of Fallot, the squatting position increases systemic vascular resistance (SVR) through lower extremity muscle contraction and postural changes. Increased SVR reduces the pressure gradient favoring right-to-left shunting across the ventricular sept... Ver explicação completa e trilha adaptativa →