Forty patients with either obstructive sleep apnea syndrome or a clini
cal complaint of daytime sleepiness with measured nocturnal increase i
n upper airway resistance and snoring were investigated during sleep f
or 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 ox
ygen saturation (SaO2), and negative inspiratory esophageal pressure n
adir (an index of inspiratory effort) were the only studied variables
which could statistically dissociate patients presenting pulsus parado
xus. We then divided the patient population into three different subgr
oups 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. Lo
west SaO2 could not be used to statistically separate subjects with mi
ld to moderate pulsus paradoxus from those without it; and negative in
spiratory esophageal pressure measurements could only significantly id
entify subjects with severe pulsus paradoxus (i.e., >20 mmHg) from tho
se without any pulsus paradoxus. The variable which correlated best wi
th age was negative inspiratory esophageal pressure nadir (R = 0.83).
Our interpretation is that as age increased, negative inspiratory esop
hagel pressure became less negative, due to the known impact of aging
on muscles, and pulsus paradoxus was no longer observed.