Final answer:
The pressure below the vocal folds or larynx is referred to as subglottic pressure, which can be either positive or negative relative to atmospheric pressure. This pressure fluctuates with breathing phases but is usually monitored in clinical settings.
Step-by-step explanation:
The pressure that can be measured immediately beneath the level of the vocal folds or larynx is known as subglottic pressure. This type of pressure can be categorized as positive pressure or negative pressure relative to the atmospheric pressure.
Negative pressure is pressure lower than the atmospheric pressure, while positive pressure is higher than the atmospheric pressure. In respiration, the intra-alveolar pressure (intrapulmonary pressure) within the alveoli equates to the atmospheric pressure, as the alveoli are connected to the atmosphere via the airways.
Different phases of breathing will see changes in intra-alveolar pressure. However, pressures like subglottic pressure are typically monitored in settings such as surgery or intensive care using invasive measures, such as catheters.