A physiologist in a hospital runs diagnostic tests that measure how well specific body systems are functioning. Rather than treating patients directly, physiologists operate specialized equipment, interpret test results, and provide data that doctors use to diagnose conditions and plan treatment. They work across nearly every major body system, from the heart and lungs to the brain, digestive tract, and urinary system.
Cardiac Physiology
Cardiac physiologists are among the most visible in hospital settings. They perform echocardiograms (ultrasound images of the heart), run stress tests, and record the heart’s electrical activity through EKGs. A large part of their work involves cardiac devices: programming and checking pacemakers, implantable defibrillators, and loop recorders that sit under the skin and continuously track heart rhythm. When a patient’s heart beats too slowly, too fast, or out of coordination, the cardiac physiologist is often the person running the test that identifies the problem.
They also assist during procedures like cardiac catheterization, monitoring heart function in real time and alerting the surgical team to changes. In patients with heart failure, cardiac physiologists may check whether a biventricular pacemaker is keeping both sides of the heart beating in sync, adjusting device settings to improve symptoms.
Respiratory and Sleep Physiology
Respiratory physiologists measure how well your lungs move air in and out, and how efficiently they deliver oxygen to your blood. The most common test is spirometry: you breathe into a mouthpiece connected to a measuring device while wearing soft nose clips, following instructions to inhale deeply and exhale as hard and fast as you can. The results show how much air your lungs hold, how quickly you can push it out, and whether your airways are obstructed.
A gas diffusion study takes this further by measuring how well gases cross from your lungs into your bloodstream. You breathe in a tiny, safe amount of carbon monoxide, and the machine calculates how much your lungs absorbed. This test is particularly useful for detecting conditions where the lung tissue itself is damaged, not just the airways. Respiratory physiologists also run sleep studies, monitoring patients overnight to diagnose disorders like obstructive sleep apnea.
Neurophysiology
Neurophysiologists focus on the electrical activity of the brain, spinal cord, and peripheral nerves. Their work splits into two main categories: diagnostic testing and surgical monitoring.
On the diagnostic side, they perform EEGs to record brain wave patterns in patients with suspected epilepsy, unexplained seizures, or altered consciousness. They also run nerve conduction studies and electromyography (EMG), tests that evaluate how well electrical signals travel through peripheral nerves and into muscles. These tests help diagnose conditions ranging from carpal tunnel syndrome to muscular dystrophy and ALS.
During surgery, neurophysiologists play a critical role that most patients never see. They continuously monitor the nervous system while surgeons operate near the brain, spinal cord, or major nerves. During spine surgery, for example, they use electrical stimulation to check that nerve pathways are still intact, alerting the surgeon immediately if a signal weakens. During brain tumor removal, they monitor brain wave activity to detect drops in blood flow that could cause a stroke. During operations on tumors near the hearing nerve, they track the brainstem’s response to clicking sounds delivered through earphones, helping surgeons preserve hearing. This real-time feedback helps avoid complications like paralysis, hearing loss, or stroke.
Gastrointestinal Physiology
GI physiologists investigate how well the digestive tract moves food and whether stomach acid is reaching places it shouldn’t. Their core test is esophageal manometry, considered the gold standard for evaluating how the muscles in the food pipe contract and relax. A thin, flexible catheter is passed through the nose into the esophagus, and sensors along its length measure pressure as you swallow. This reveals whether food is getting stuck because the muscles aren’t coordinating properly.
For reflux, GI physiologists use 24-hour pH monitoring. A small sensor, either on a catheter or a wireless capsule clipped to the esophageal wall, records acid levels over an entire day and night. This tells the clinical team exactly how often acid washes back up and whether it correlates with the patient’s symptoms. In some cases, a balloon-based catheter called EndoFLIP is used to measure how much the junction between the esophagus and stomach stretches open, which provides additional information when standard manometry can’t be completed or when surgeons need to gauge treatment success during a procedure.
Other Hospital Specializations
Beyond these core roles, physiologists work in several other areas. Vascular physiologists use ultrasound and other tools to assess blood flow through arteries and veins, helping detect blockages, clots, or aneurysms. Audiologists, a branch of physiological science, test hearing and balance. Ophthalmic physiologists assess visual function and investigate diseases of the eye and visual pathways. Urodynamic physiologists run tests that measure bladder pressure and urine flow to diagnose the cause of urinary difficulties. In critical care units, physiologists monitor the vital signs and organ function of the most seriously ill patients, often managing complex monitoring equipment at the bedside.
How Physiologists Fit Into the Care Team
Physiologists don’t work in isolation. A doctor orders a test, the physiologist performs it and provides a technical interpretation, and the results feed back to the medical team for diagnosis and treatment decisions. In surgical monitoring, the relationship is even more immediate: the neurophysiologist communicates directly with the surgeon in real time, sometimes changing the course of an operation within seconds.
Wearable monitoring technology is expanding what physiologists do beyond the walls of the testing lab. Devices that continuously track heart rhythm, oxygen levels, or sleep patterns generate streams of data that need expert interpretation. The challenge is filtering clinically meaningful signals from noise. AI algorithms are increasingly helping by analyzing trends and generating early warnings before a patient’s condition visibly deteriorates, but physiologists remain essential for validating those alerts and placing them in clinical context.
Education and Training
Becoming a clinical physiologist typically requires at least a bachelor’s degree in exercise science, exercise physiology, or a related field, combined with 1,200 hours of hands-on clinical experience. A master’s degree in clinical exercise physiology reduces the experience requirement to 600 hours. Basic life support certification is also required. In the UK, clinical physiologists register through the National School of Healthcare Science and follow a structured training pathway within the NHS. Subspecialties like neurophysiology or cardiac physiology involve additional focused training, and some neurophysiologists pursue fellowships in areas such as epilepsy or neuromuscular disease.