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Thesis Format

Integrated Article


Master of Science




Keir, Daniel A.


We measured the peripheral chemoreflex sensitivity to hypoxia (PChS) at various isocapnic carbon dioxide tensions (PCO2) to determine the form of the relationship between PChS and central PCO2. Twenty participants completed three repetitions of modified rebreathing tests with end-tidal PO2 (PETO2) clamped at 150, 70, 60, and 45 mmHg. PChS was computed at 1-mmHg intervals of PETCO2 as follows: the differences in V̇E between the three hypoxic profiles and the hyperoxic profile (∆V̇E) were calculated; three ∆V̇E values were plotted against corresponding calculated oxyhemoglobin saturation (SCO2); and linear regression determined PChS (Lmin-1∙mmHg-1∙%SCO2-1). These processing steps were repeated at each PETCO2 to produce the PChS vs. isocapnic PCO2 relationship which was fitted with linear and polynomial functions. Chemoreflex sensitivity (V̇ES) rose (PCO2 fell progressively (pETCO2 and this relationship was best described by a liner model in 15 of the 20 individuals, indicative of an additive interaction.

Summary for Lay Audience

Breathing changes depending on our activity, behavior, and emotional state, yet the blood chemistry, oxygen supply, and the acidity of our tissues remain stable. In humans, this stability is controlled by two rapidly responding sensor organs located within 1) our blood vessels (oxygen sensors) and 2) our brain (carbon dioxide sensors). These sensors respond to increases in acidity in the blood and increase breathing as a response. Often, these oxygen and carbon dioxide sensors are working together, but how or whether they connect with each other in the control of breathing in humans remains under question. Therefore, the goal of this study was to assess the connection between the two sensors by exposing humans to progressively lower oxygen conditions and one level of high oxygen condition while progressively increasing the levels of carbon dioxide. The breathing responses in ten males and ten females was recorded while they completed three repetitions of breathing tests at progressively decreasing levels of oxygen (3 levels) and one level of high oxygen over four laboratory visits. We saw that the breathing response was significantly greater at the low oxygen conditions in comparison with the high oxygen level. We concluded that in 15 of the 20 participants the oxygen and carbon dioxide sensor worked together to control breathing. These findings are significant as they provide information to help the understanding of breathing in different environments, such as at high mountain levels and diseases such as COVID-19.