Date of Award

January 2025

Document Type

Thesis

Degree Name

Medical Doctor (MD)

Department

Medicine

First Advisor

Simon J. Mitchell

Second Advisor

Paul Heerdt

Abstract

Rebreather underwater breathing devices are commonly used for military, scientific and recreational diving. Malfunctions and human errors often manifest through hypoxia, hyperoxia, and/or hypercapnia. Very limited research exists on enhancing the ability of divers to recognize or directly monitor the physiological manifestations of hypoxia. We conducted a two-part study examining whether prior open-label hypoxia exposure enhances a diver’s ability to recognize hypoxia and initiate self-rescue.Forty participants were randomized to receive either an information leaflet or hypoxia prior to a blinded hypoxia testing event during a virtual reality dive. The primary outcome was the proportion of participants who initiated self-rescue before reaching a peripheral oxygen saturation of 70%. Inspired oxygen and time to bailout were recorded. Self-reported symptoms were recorded after each exposure. Ninety percent of divers performed a self-initiated bailout in the hypoxia exposure group, compared to 33% in the information leaflet group (P < .001). Divers in the information leaflet group had lower SpO2 values (73.4% vs 81.4%, mean difference 8% (95%CI = 2.5 to 13.5%, P = 0.005) and lower inhaled oxygen levels (7.6% vs 9.4%, mean difference 1.8% (95%CI = 0.6 to 3.1%, P = 0.005) at bail-out. The two most frequently and most severe reported symptoms were light-headedness and shortness of breath. Seventy percent had a consistent hypoxia symptom profile, which was not related to the ability to bail out. In a controlled laboratory environment self-rescue was three times more likely for divers who had experienced hypoxia compared to an information leaflet. Being immersed, exercising and gas narcosis could all negatively influence the ability to recognise and act on hypoxia symptoms.

Comments

This thesis is restricted to Yale network users only. It will be made publicly available on 05/14/2027

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