Relative effects of submersion and increased pressure on respiratory mechanics, work, and energy cost of breathing

• Published in: Journal of applied physiology (1985) Vol. 114; no. 5; pp. 578 - 591
• Main Authors: Held, Heather E., Pendergast, David R.
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.03.2013
• Subjects: Adult; Airway Resistance - physiology; Diving; Diving - physiology; Exercise; Exercise - physiology; Exhalation - physiology; Humans; Immersion - physiopathology; Inhalation - physiology; Male; Nitric oxide; Nitric Oxide - metabolism; Oxygen; Oxygen - metabolism; Oxygen Consumption - physiology; Oxygen uptake; Pressure; Respiration; Respiratory Mechanics - physiology; Respiratory system; Rest - physiology; Ventilation
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00584.2012

Submersion and increased pressure (depth) characterize the diving environment and may independently increase demand on the respiratory system. To quantify changes in respiratory mechanics, this study employed a unique protocol and techniques to measure, in a hyperbaric chamber, inspiratory and expiratory alveolar pressures (interrupter technique), inspiratory and expiratory resistance in the airways (Raw I and Raw E , esophageal balloon technique), nitric oxide elimination (thought to correlate with Raw), inspiratory and expiratory mechanical power of breathing, and the total energy cost of ventilation. Eight healthy adult men underwent experiments at 1, 2.7, and 4.6 atmospheres absolute (ATA) in dry and fully submersed conditions. Subjects rested, cycled on an ergometer at 100 W, and rested while voluntarily matching their ventilation to their own exercise hyperpnea (isocapnic simulated exercise ventilation). During isocapnic simulated exercise ventilation, increased O 2 uptake (above rest values) resulted from increased expired ventilation. Raw I decreased with submersion (mean 43% during rest and 20% during exercise) but increased from 1 to 4.6 ATA (19% during rest and 75% during exercise), as did Raw E (53% decrease with submersion during rest and 10% during exercise; 9% increase from 1 to 4.6 ATA during rest and 66% during exercise). Nitric oxide elimination did not correlate with Raw. Depth increased inspiratory mechanical power of breathing during rest (40%) and exercise (20%). Expiratory mechanical power of breathing was largely unchanged. These results suggest that the diving environment affects ventilatory mechanics primarily by increasing Raw, secondary to increased gas density. This necessitates increased alveolar pressure and increases the work and energy cost of breathing as the diver descends. These findings can inform physician assessment of diver fitness and the pulmonary risks of hyperbaric O 2 therapy.