Blunted hypoxic pulmonary vasoconstriction in apnoea divers.

Area of Science:

• Cardiovascular Physiology
• Environmental Physiology
• Pulmonary Medicine

Background:

• Competitive apnea divers face extreme hyperbaric, hypercapnic, acidotic, and hypoxic conditions.
• Repetitive exposure to these stresses may alter pulmonary vascular responses and right heart function.
• Previous hypotheses suggested divers would exhibit exaggerated hypoxic pulmonary vasoconstriction.

Purpose of the Study:

• To investigate the pulmonary vascular and right heart responses to hypoxic stress in apnea divers.
• To determine if repetitive diving leads to altered hypoxic pulmonary vasoconstriction.
• To assess the effect of sildenafil on pulmonary resistance in divers and controls under hypoxic conditions.

Main Methods:

• A double-blinded, placebo-controlled, cross-over study design was employed.
• 16 competitive apnea divers and 16 matched controls were recruited.
• Cardiopulmonary responses to isocapnic hypoxia (PaO2 = 50 mmHg) were measured with and without 50 mg sildenafil.

Main Results:

• Divers showed a significantly smaller increase in total pulmonary resistance during hypoxia compared to controls (p=0.0222).
• Sildenafil administration normalized the hypoxic pulmonary vasoconstriction response in both groups.
• Divers exhibited lower systemic vascular resistance after sildenafil in normoxia.

Conclusions:

• Repetitive apnea diving induces a blunted hypoxic pulmonary vasoconstriction.
• This adaptation may be beneficial, allowing for increased cardiac output with reduced right heart work.
• Blunted pulmonary vascular tone aids in oxygen utilization during hypoxemic conditions encountered in apnea diving.