Respiratory: USMLE Step 1 video lessons
Lung mechanics, gas exchange, ventilation-perfusion matching and respiratory disease.
How the lungs move and exchange air: lung volumes and spirometry, obstructive versus restrictive disease, compliance and surfactant, V/Q mismatch, the A-a gradient, the oxygen-haemoglobin curve, CO2 transport, the control of breathing, hypoxic pulmonary vasoconstriction, and the tissue-hypoxia poisons carbon monoxide, cyanide and methaemoglobin.
5:26Lung volumes and capacities, explained
Every lung volume and capacity on a spirogram, and why residual volume, FRC and total lung capacity need more than spirometry.
5:23Obstructive vs restrictive lung disease: FEV1/FVC and loops
How the FEV1/FVC ratio, total lung capacity and the shape of the flow-volume loop separate obstructive from restrictive lung disease in a patient who is short of breath.
5:23Lung compliance, Laplace and surfactant: why alveoli stay open
A film of water lines every alveolus and pulls inward on it. Lung compliance, the law of Laplace and surfactant explain why the lungs do not collapse at the end of each breath.
5:18V/Q mismatch: shunt, dead space and the oxygen test
Shunt, dead space and low V/Q all mismatch ventilation and perfusion, yet only shunt barely responds to oxygen. The oxygen test sorts the three.
5:39A-a gradient: the alveolar gas equation and the causes of hypoxaemia
A low arterial PO₂ does not say whether the lung is failing or the patient is under-breathing. The A-a gradient, calculated with the alveolar gas equation, does.
5:19Oxygen-hemoglobin dissociation curve: P50, shifts and content
The oxygen-hemoglobin dissociation curve plots saturation against oxygen pressure. Learn to read it, predict its shifts, and see why a normal saturation can hide a low oxygen content.
5:29CO₂ transport: bicarbonate, the chloride shift, Bohr vs Haldane
Blood carries carbon dioxide in three forms, mostly as bicarbonate made inside the red cell. One rule then separates the Bohr effect from the Haldane effect.
5:27Central vs peripheral chemoreceptors and oxygen-induced hypercapnia
What the central and peripheral chemoreceptors sense, why the classic hypoxic-drive story is incomplete, and how to think about oxygen in COPD.
5:41Hypoxic pulmonary vasoconstriction and cor pulmonale
Low oxygen constricts the small pulmonary arteries. In one poorly ventilated patch this protects gas exchange; across the whole lung, it strains the right ventricle.
5:34CO, cyanide and methaemoglobin: why SpO₂ and PaO₂ fool you
CO, cyanide and methaemoglobin can all starve tissue of oxygen while the pulse oximeter or the arterial PaO₂ looks reassuring. Each poison leaves a different fingerprint.