A simplified holistic model of pulmonary oxygen transfer and its application in assessing exercise ability of pulmonary patients

Abstract

[EMBARGOED UNTIL 5/1/2024] Cardio-respiratory fitness is important in predicting health outcomes as it reflects one's capability to deliver and utilize oxygen. In this research, we first developed a simplified holistic model for oxygen transfer from supply air to blood. The model resulted in an overall oxygen transfer coefficient (Do), which can be computed from non-invasive measurements to reflect cardio-pulmonary responses to changes in oxygen supply and demand. We tested the utility of Do in detecting changes in environmental conditions. Next, we compared Do with oxygen uptake rate and the Oxygen Deficit (OD) method, a noninvasive estimate of gas-exchange impairment. Tidal volume, respiratory rate, and oxygen saturation (Spo2) were measured in 29 healthy adults (14M/15F; 29[plus or minus]4 yrs.) during resting normoxia, cold pressor test (CPT), steady-state hypoxia (80 percent SpO2, SSH), and SSH + CPT. Do increased during SSH (p[less than]0.01), which was not observable in oxygen uptake rate, and CPT (p[less than]0.05) compared to resting normoxia. Do increased during SSH+CPT compared to SSH alone (p[less than]0.05). The OD method was applicable to only 9 participants and did not show any difference among treatment conditions (p[greater than]0.05). Application of the novel parameter (Do) identified changes in oxygen supply and demand and exhibited advantages over a conventional measure. Specifically, Do showed consistent effect of CPT under normoxic and hypoxic conditions, whereas: 1) OD could only be determined in 31 percent of study participants, and 2) OD did not reflect differences between treatment conditions and oxygen uptake rate could not distinguish normoxia from hypoxia. We further tested the clinical utility of Do in predicting the exercise grouping and total exercise time in pulmonary patients. Breathing frequency, exercise power, minute ventilation, oxygen uptake rate, heart rate, carbon dioxide and production was measured in 26 deidentified pulmonary patients (20M/6F; 54[plus or minus]9 yrs.) during cardio-pulmonary exercise tests. The patients were assigned to 3 different exercise ramp protocols based on existing clinical evaluation procedures. Do was used to predict the protocol groupings (N=26) and exercise time within protocol group 2 (N=16) with one minute of data. Conventional measures such as oxygen uptake rate (Vo2) and blood oxygen saturation (Spo2) from such a short exercise were not useful in differentiating the protocol groupings and the exercise time within protocol group 2. The sensitivity of Do in predicting the protocol groups and exercise time hints at its potential ability to act as an early indicator of pulmonary health deterioration. Further research is warranted to confirm the utility of Do in clinical settings.