“I can’t breathe”: The Challenge of Dyspnea Physiology and Pathophysiology Pawandeep Brar MD Palliative Care Physician Temmy Latner Centre for Palliative Care Mount Sinai Hospital

Objectives Review causes of dyspnea To review normal respiratory cycle Review pathophysiology of dyspnea

Causes of Dyspnea CAUSE EXAMPLE Directly related to Cancer Primary/metastatic lung involvement, pleural effusion, carcinomatosis lymphangitis, SVC syndrome, chest wall invasion, pathological rib fractures Indirectly Related to Cancer Pneumonia, cachexia, PE, anemia, metabolic abnormality, ascites Related to Cancer Therapy Surgery (lobectomy), radiation pneumonitis, chemotherapy induced fibrosis or cardiomyopathy Unrelated to Cancer COPD, CHF, asthma, anxiety, neuromuscular disorder, spiritual pain : we all know several different causes of dyspnea and this is what we are looking for when we exam a pt….odds are we will find more than one reason for a pt to be dyspneic. But what is the underlying pathophysiology that causes a person to feel sob?

Physiology of Respiration Respiratory Centre in the medulla and pons coordinates activity of: Diaphragm, Intercostal Muscle Accessory Muscles of Respiration : To understand how these clinical states may trigger dyspnoea, one must first understand how respiratory sensoryinformation is processed by the brain and leads trespiratory activity. The respiratory centre in the medulla andpons coordinates the activity of the diaphragm, theintercostal muscles, and the accessory muscles of respiration.

Physiology of Respiration Respiratory Centre receives sensory information from Central and Peripheral Chemoreceptors Peripheral Mechanoreceptors from muscles Pulmonary Vagal Afferents

Physiology of Respiration Respiratory system designed to maintain homeostasis with respect to gas exchange (adequate oxygenation) & the acid-base status of the organism (adjust PaCO2 to maintain normal pH) Derangements in oxygenation as well as acidemia lead to breathing discomfort

Pathophysiology of Dyspnea Pathophysiology of dyspnea is complex & multiple Can break it down into 3 components Work of Breathing: increase effort of breathing against increased resistance of breathing with weakened muscles (sensed through mechanoreceptors) Chemoreceptors: sense hypercapnea and hypercarbia Neuromechanical Dissociation: when there is a mismatch between what the brain desires for respiration and the sensory feedback it receives

Take Home Points Respiratory system is a complex feedback loop designed to maintain homeostasis Hypoxia is not the only factor in dyspnea There is still much to be learned about the pathophysiology of dyspnea!

Thank you!