Nasal and Parotid Blood Pool Activity Is Significantly Correlated with Metabolic Syndrome Components and Sleep Apnea

Background: Patients with metabolic syndrome components were frequently noted to have increased nasal and parotid activity on clinically referred scintigraphic whole-body blood pool scans. This increase in activity was not observed in patients without metabolic syndrome. Increased nasal blood pool activity in patients with elevated body mass indices (BMIs) has implications for (1) sleep apnea, (2) risk of nasal infection, and (3) possible impaired nasal lymphatic drainage of brain waste proteins. Methods: To follow-up this clinical observation, a retrospective study was performed on 200 patients having whole-body blood pool scans referred over a 3-year period. The whole-body blood pool scans were evaluated for an association between nose and parotid region of interest (ROI) to heart ROI maximum (max) pixel ratios as correlated with clinical conditions, including obesity, diabetes, hypertension, and sleep apnea. Continuous variables of BMI, hemoglobin A1c (HbA1c), blood glucose, and blood lipids were also correlated with these ratios. Results: A direct association of nose to heart max ratio (NHMR) with diabetes, sleep apnea, and hypertension was found with an increase in the ratio of +0.10 (P = 0.002), +0.13 (P = 0.0002), +0.08 (P = 0.0123), respectively. Correlation of NHMR with continuous variables had moderate correlation with BMI (r = 0.36, P < 0.0001), glucose (r = 0.27, P = 0.0001), HbA1c (r = 0.25, P = 0.0008) and less association with the number of diabetes medications (r = 0.22, P = 0.0021). Similar associations were found for parotid to heart max ratios but were weaker than the NHMR. Conclusions: Patients with metabolic syndrome components have significantly increased nasal and parotid activity on blood pool scans. These associations have implications for the treatment of sleep apnea, for nasal infections involving such agents as Covid-19, and for the risk of dementias related to decreased clearance of brain waste proteins through nasal turbinate lymphatics in patients with metabolic syndrome. If further studies support these findings, the nasal turbinates and the increased parasympathetic activity controlling their dilation could become a new therapeutic target.