Aging, respiratory efforts during sleep, and pulsus paradoxus

Forty patients with either obstructive sleep apnea syndrome or a clinical complaint of daytime sleepiness with measured nocturnal increase in upper airway resistance and snoring were investigated during sleep for the presence of pulsus paradoxus, which is defined as a decrease in systolic blood pressure (SBP) of at least 10 mmHg during inspiration. Two thirds of the subjects presented pulsus paradoxus. Age, lowest oxygen saturation (SaO2), and negative inspiratory esophageal pressure nadir (an index of inspiratory effort) were the only studied variables which could statistically dissociate patients presenting pulsus paradoxus. We then divided the patient population into three different subgroups of equal number based upon the degree of decrease in SBP (i.e., > 20 mmHg, < 20 but > 10 mmHg, and < 10 mmHg). In this second analysis, age was the only significant variable that separated the three groups. Lowest SaO2 could not be used to statistically separate subjects with mild to moderate pulsus paradoxus from those without it; and negative inspiratory esophageal pressure measurements could only significantly identify subjects with severe pulsus paradoxus (i.e., > 20 mmHg) from those without any pulsus paradoxus. The variable which correlated best with age was negative inspiratory esophageal pressure nadir (R = 0.83). Our interpretation is that as age increased, negative inspiratory esophageal pressure became less negative, due to the known impact of aging on muscles, and pulsus paradoxus was no longer observed.