A Non‐Invasive Method to Estimate Pulmonary Oxygen Transfer Rate

Abstract

ObjectiveIneffective transfer of oxygen from the atmospheric air to the circulation is associated with low cardiorespiratory fitness and increased disease risk. Unfortunately, measuring the efficiency of gas exchange requires invasive and expensive procedures. We first sought to develop a parameter (Do) that reflects the capacity to move oxygen from air to the arterial circulation using non‐invasive methods. We then tested the utility of Do to detect changes in pulmonary oxygen transfer rate under differing conditions of oxygen supply and demand. Last, we compared Do with the Oxygen Deficit (OD) method, a non‐invasive way to estimate gas‐exchange impairment.MethodsHeart rate (ECG), tidal volume (pneumotachometer), respiratory rate (pneumobelt), and oxygen saturation (finger pulse oximeter) were measured in 25 young healthy adult participants (13 males, 12 females; 25 ± 4 years of age). Participants completed 4 trials: 1) Resting normoxia, 2) Steady‐state hypoxia (80% SpO2, SSH), 3) Cold pressor test (CPT, to increase oxygen demand), and 4) SSH + CPT. Do was derived by engineering analysis considering the biophysics of the 3 major process essential for effective oxygen transfer (i.e., ventilation, alveolar gas exchange, hemoglobin binding). Do was estimated for each condition and results were compared with the OD method.ResultsDoincreased during SSH (5.13±1.07×10‐2L/min/kPa) and CPT (2.91±1.03 ×10‐2L/min/kPa) when compared to resting normoxia (2.24±0.66×10‐2 L/min/kPa, p<0.05). Dowas further increased during SSH+CPT (5.71±1.52×10‐2L/min/kPa) when compared to SSH alone (p<0.05). Applicability of the OD method was limited to SpO2<95%; thus OD could only be calculated in 40% of participants (n=10). OD was lower during SSH (2.18±0.63 kPa) and CPT (2.48±1.56 kPa) versus normoxia (3.15±1.3 kPa, p<0.05). In contrast, OD increased during SSH+CPT (2.42±0.59 kPa) when compared to SSH alone (p<0.05).ConclusionApplication of the novel parameter, Donot only showed the ability to respond to changes in supply and demand of oxygen but exhibited advantages over a conventional measure (OD). Specifically, Do showed consistent effect of CPT under normoxic and hypoxic conditions, whereas: 1) OD could only be determined in 40% of study participants, and 2) OD exhibited a paradoxical increase during SSH+CPT, despite a decrease during SSH and/or CPT alone. Future studies seek to test the utility of Do in cardiopulmonary patients.