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The effect of peripheral vasodilators on the human diving response
1Pediatric Ophthalmology and Adult Strabismus, Anchorage, Alaska 99501.
Alaska Medicine
|July 1, 1993
Summary
The human diving response involves a temperature-dependent bradycardia (slowed heart rate) and reduced blood flow. Peripheral vasoconstriction is crucial for this response, as shown by vasodilator drug effects.
Area of Science:
- Cardiovascular physiology
- Human diving response
- Thermoregulation
Background:
- The human diving response is a complex physiological reaction to cold water immersion.
- Understanding the mechanisms, particularly the role of bradycardia and vasoconstriction, is important for physiological research.
Purpose of the Study:
- To investigate the effects of vasodilators on the human diving response.
- To determine the role of peripheral vasoconstriction in the bradycardia observed during cold-water facial immersion.
Main Methods:
- Five healthy subjects underwent facial immersion in cold water (1°C, 10°C, 25°C) with a breath hold.
- Physiological responses were measured under control conditions and after administration of vasodilators (Nitropaste, Hydralazine, Prazosin).
Main Results:
- A temperature-dependent bradycardia and decreased forearm blood flow were observed during control dives.
- Nitropaste had minimal effect; Hydralazine only reduced bradycardia at 1°C.
- Prazosin consistently reduced temperature-dependent bradycardia, while forearm blood flow remained unaffected by vasodilators.
Conclusions:
- Acute peripheral vasoconstriction plays a significant role in mediating the bradycardia of the human diving response.
- Vasodilators, particularly Prazosin, can modulate the diving bradycardia, highlighting the involvement of vascular tone.