Analysis of obstructive sleep apnea patients with "sawtooth sign" on the flow-volume curve

The aims of the present study are to determine whether there is an obstructive sleep apnea (OSA) subgroup presenting with sawtooth sign on the spirometric flow-volume curve, and to identify the clinical importance of the sawtooth sign in these patients.

The study subjects consisted of 134 OSA patients (≥18 years) whose spirometric tests were made on the same day with the polysomnography. Patients without sawtooth sign were taken as the control group. Patients with sawtooth sign and control subjects were retrospectively analyzed in terms of distinctive demographic, anthropometric, polysomnographic, and spirometric characteristics.

OSA patients with sawtooth sign (n = 36) had greater neck circumference and body weight, and were taller than control subjects (n = 98). Patients with sawtooth sign were mainly males (p < 0.01). Female/male ratios were similar in control subjects. The presence of coronary artery disease was higher (p = 0.024), and current smokers were more (p = 0.014) among the patients with sawtooth sign than control subjects. In logistic regression analysis, the presence of sawtooth sign and age were the only statistically significant parameters (p = 0.028 and p = 0.002, respectively) that affect the likelihood of coronary artery diseases. There were no differences among the groups with regard to age, BMI, wrist circumference, and other comorbid conditions. The duration time of oxygen desaturation (<90%), avarage, and longest duration of total apnea were longer (p = 0.050, p = 0.034 and p = 0.014, respectively) and the obstructive apnea index was more (p = 0.035) in OSA patients with sawtooth sign when compared to control subjects. There were no differences with regard to other polysomnographic parameters, sleep architecture, Epworth sleepiness score, and spirometric parameters.

As an OSA subgroup, the OSA patients with sawtooth sign may have more frequent and longer duration of obstructive apneas, longer duration time of oxygen desaturation, and greater risk for the coronary artery disease.