Repeated normoxic hyperbaric exposures induce haemodynamic and myocardial changes in rats

Area of Science:

• Physiology
• Cardiovascular Research
• Hyperbaric Medicine

Background:

• Understanding the physiological effects of hyperbaric environments is crucial for human safety in diving and space exploration.
• Previous research has explored short-term effects of pressure, but long-term adaptations of cardiac function require further investigation.

Purpose of the Study:

• To assess the impact of repeated exposure to high ambient pressures, specifically helium-nitrogen-oxygen atmospheres, on rat cardiac function and morphology.
• To investigate potential cardiac adaptations and adverse effects following prolonged hyperbaric exposure.

Main Methods:

• Conscious rats were subjected to daily 5 bar (500 kPa) chamber dives for 40 days, with controlled oxygen and nitrogen partial pressures.
• Cardiac output (Qc) and myocardial blood flow (Qmyocardial) were measured using the microsphere method.
• Cardiac morphology was assessed, and hemodynamic parameters were evaluated at normobaric pressure post-exposure.

Main Results:

• Test rats exposed to high pressure showed a significant increase in heart mass (12% greater ventricular mass to body mass ratio) compared to controls.
• Despite increased heart mass, left ventricular pressure and contractility significantly increased (25%-96%) in test rats.
• Microscopic analysis revealed focal necroses in the left ventricle of test rats, indicating minor tissue damage.

Conclusions:

• Repeated hyperbaric helium exposure induces cardiac hypertrophy and enhances left ventricular function in rats.
• While cardiac function improves, localized myocardial damage suggests a need for careful consideration of long-term hyperbaric exposure limits.