Hypoxemia resulting among patients of obstructive sleep apnea syndrome (OSAS) increases purine catabolism and enhances anaerobic glycol sis, leading to elevated levels of uric acid and lactate. Studies assessing uric acid are available; however, serum levels of lactate had not been studied in patients of OSAS.
Twenty consecutive OSAS patients (OSAS group) who underwent night polysomnography (PSG) and 10 healthy controls (control group) in whom OSAS was ruled out participated in this study. Arterial blood samples were withdrawn for measuring serum uric acid (UA) and plasma lactate before and after PSG/sleep in respective groups.
Mean value of serum UA before and after sleep among OSAS group were 7.54 ± 1.63 and 7.66 ± 2.1 mg/dl respectively and among control group were 5.38 ± 1.12 and 5.30 ± 1.43 respectively. Both values in OSAS group were higher than standard laboratory reference and significantly higher than control group (p 0.001 and 0.002). However, there was no significant overnight change in OSAS group (p 0.8).Mean value of plasma lactate before and after sleep among OSAS group were 1.74 ± 0.6 and 2.28 ± 0.98 mmol/L respectively and among control group were 1.46 ± 0.62 and 1.53 ± 0.89 mmol/L respectively. Both values in OSAS group were higher than standard laboratory reference. When compared with control group only difference between after sleep samples came to be significant (p 0.03). Also, overnight change in OSAS group for lactate was significant with p 0.02. Both serum UA and lactate levels had a positive correlation with degree of hypoxia measured by sleep time spent below 95% and 90% SaO2 with p < 0.05.
UA and lactate both are positively correlated with degree of hypoxia in OSAS and are markers of hypoxic oxidative stress. Although UA elevated in OSAS, due to its slower metabolism, does not show overnight change in serum levels as seen with lactate.
Measurement of serum lactate level among patients of OSAS is a better marker of overnight tissue hypoxic oxidative stress than UA.
Harmanjit Hira, No Financial Disclosure Information; No Product/Research Disclosure Information