Helium is an inert, noble gas most commonly recognized for filling party balloons, but its unique physical characteristics make it useful in specialized medical applications. The gas is colorless, odorless, and non-toxic. Its extremely low density sets it apart from other atmospheric gases like nitrogen and oxygen. These properties allow helium to be safely inhaled and utilized in two distinct ways: to ease the physical effort of breathing and to provide detailed diagnostic images of the lungs.
Using Heliox to Aid Breathing
One of the most frequent medical applications of helium is in Heliox, which combines helium with oxygen, typically 70-80% helium to 20-30% oxygen. This mixture is employed as a temporary therapeutic measure for patients experiencing severe respiratory distress due to narrowed airways. The low density of helium significantly reduces the resistance to gas flow within the respiratory tract compared to breathing air or pure oxygen. Airflow in the bronchial tubes can be laminar or turbulent, with turbulent flow requiring more effort. Helium’s low density promotes a more laminar flow even through constricted passages. This reduces airway resistance, meaning the patient exerts less energy to move air. Heliox therapy is utilized for conditions involving upper airway obstruction or acute lower airway narrowing, such as severe asthma attacks, croup, or post-extubation stridor. By decreasing the work of breathing, Heliox provides a necessary bridge, allowing time for definitive medical treatments like bronchodilators or steroids to take effect.
Advanced Lung Imaging with Hyperpolarized Helium
Helium-3 (\(^3\)He) is used in diagnostic imaging of the lungs. Standard Magnetic Resonance Imaging (MRI) relies on the magnetic signal from protons in water molecules, but the lungs’ air-filled spaces lack sufficient water for a clear image. To overcome this, \(^3\)He gas is prepared using hyperpolarization, which aligns the nuclear spins of the helium atoms. This alignment creates a detectable magnetic signal when the gas is inhaled, turning the invisible gas into an MRI contrast agent. Once inhaled, the hyperpolarized helium fills the air sacs, allowing visualization of the entire ventilation process. The resulting images provide a detailed map of how air is distributed throughout the lungs, which is useful for detecting and quantifying ventilation defects. This technique is significantly more sensitive than conventional imaging for diagnosing diseases that cause structural damage to the air spaces. For example, it assesses the extent of emphysema or Chronic Obstructive Pulmonary Disease (COPD) by highlighting poorly ventilated regions that do not receive the helium gas.
Safety and Clinical Administration
The administration of medical helium requires specialized equipment and careful oversight. Since helium is inert, it carries no inherent toxicity; however, the primary risk is asphyxiation if the gas is not properly mixed with adequate oxygen. Heliox mixtures must always contain a minimum of 20% oxygen to maintain safe breathing levels. The physical properties of helium necessitate the use of specialized, helium-compatible flowmeters for delivery. Standard flowmeters calibrated for air or oxygen provide inaccurate readings due to helium’s lower density, potentially leading to under-delivery. Heliox is typically administered through a tight-fitting mask or specialized ventilator to prevent the entrainment of room air, which would dilute the mixture. Furthermore, the hyperpolarized \(^3\)He used for imaging presents logistical challenges. The hyperpolarization state is temporary and costly to achieve, and the polarized gas must be produced immediately before the procedure. It has a short lifespan before the magnetic signal fades, contributing to its limited availability and high expense.