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1 Department of Medicine,
To simulate the
immediate hemodynamic effect of negative intrathoracic pressure during
obstructive apneas in congestive heart failure (CHF), without inducing
confounding factors such as hypoxia and arousals from sleep, eight
awake patients performed, at random, 15-s Mueller maneuvers (MM) at
target intrathoracic pressures of
20 (MM
20) and
40 cmH2O (MM
40),
confirmed by esophageal pressure, and 15-s breath holds, as apneic time
controls. Compared with quiet breathing, at baseline, before these
interventions, the immediate effects [first 5 cardiac cycles
(SD), P values refer to MM
40
compared with breath holds] of apnea, MM
20, and MM
40 were, for left ventricular (LV) systolic transmural pressure (Ptm), 1.0 ± 1.9, 7.2 ± 3.5, and 11.3 ± 6.8 mmHg
(P < 0.01); for systolic blood
pressure (SBP), 2.9 ± 2.6,
5.5 ± 3.4, and
12.1 ± 6.8 mmHg (P < 0.01); and for
stroke volume (SV) index, 0.4 ± 2.8,
4.1 ± 2.8, and
6.9 ± 2.3 ml/m2
(P < 0.001), respectively.
Corresponding values over the last five cardiac cycles were for LVPtm
6.4 ± 4.4, 5.4 ± 6.6, and
4.5 ± 9.1 mmHg (P < 0.01); for SBP
6.9 ± 4.2,
8.2 ± 7.7, and
24.2 ± 6.9 mmHg (P < 0.01); and for SV
index
0.4 ± 2.1,
5.2 ± 2.8, and
9.2 ± 4.8 ml/m2
(P < 0.001), respectively.
Thus, in CHF patients, the initial hemodynamic response to the
generation of negative intrathoracic pressure includes an immediate
increase in LV afterload and an abrupt fall in SV. The magnitude of
response is proportional to the intensity of the MM stimulus. By the
end of a 15-s MM
40, LVPtm falls below baseline values, yet SV
and SBP do not recover. Thus, when
40
cmH2O intrathoracic pressure is
sustained, additional mechanisms, such as a drop in LV preload due to
ventricular interaction, are engaged, further reducing SV. The net
effect of MM
40 was a 33% reduction in SV index (from 27 to 18 ml/min2), and a 21% reduction
in SBP (from 121 to 96 mmHg). Obstructive apneas can have adverse
effects on systemic and, possibly, coronary perfusion in CHF through
dynamic mechanisms that are both stimulus and time
dependent.
breath holds; obstructive apnea; cardiopulmonary interactions
Deceased.
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