COVID-19 Smell Impairment and Crosstalk with Hypoxia Physiology

Since its apomorphic appearance in 2019, severe acute respiratory syndrome Coronavirus type 2 (SARS-CoV-2) nowadays circulates as a plesiomorphic human virus in several synapomorphic variants. The respiratory tract is the most important site of infection, the viral effects in the lungs are well described, and more than half of the patients could develop shortness of breath and dyspnea and require ventilatory support. The physiological sign of this condition is the decrease in the partial pressure of oxygen in the blood, leading to acute hypoxia, which could be a factor in the disease. In severe patients, we recorded several physiological parameters: breath frequency (BF), partial pressure of oxygen in the blood (pO₂), partial pressure of carbon dioxide in the blood (pCO₂), hemoglobin (Hb), heart rate (HR), and blood pressure in correlation with the olfactory threshold. We found significant correlations between reduced olfactory threshold with pO₂ and hemoglobin levels, changes in heart rate, and increased HR and pCO₂. These results suggest that COVID-19 causes an impaired sense of smell that decreases in threshold corresponding to the disease severity.