Phrenic

Phrenic is an adjective used in anatomy and medicine to describe things related to the diaphragm or to the phrenic nerve. The term derives from the Greek phren, phrenos, historically associated with the mind but also used for the diaphragm in anatomical contexts.

Anatomy and function. The phrenic nerves, right and left, originate mainly from the cervical spinal cord segments C3 to C5. They travel through the neck and into the thorax, reaching the diaphragm. They provide motor innervation to the diaphragmatic muscle, enabling its contraction during inspiration. They also carry sensory fibers from the central portion of the diaphragmatic pleura, mediastinal pleura, and pericardium. Diaphragmatic contraction flattens the muscle, increasing thoracic volume and drawing air into the lungs.

Clinical significance. Phrenic nerve injury or palsy can cause diaphragmatic paralysis on the affected side, leading to dyspnea and reduced exercise tolerance, particularly when lying flat. Causes include trauma, cardiothoracic surgery, tumors, and inflammatory or ischemic processes. Diagnosis may involve ultrasound, fluoroscopy with a sniff test, nerve conduction studies, or chest imaging. Management ranges from observation in unilateral, asymptomatic cases to diaphragmatic pacing or surgical diaphragmatic plication in persistent bilateral dysfunction or severe symptoms.

Other uses. Historically, phrenic appears in phrenology, an outdated and unsupported theory linking skull features to mental faculties. In contemporary usage, phrenic primarily refers to the diaphragm and its nerve.