Chest
Volume 84, Issue 4, October 1983, Pages 370-375
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clinical investigations
Cardiac Augmentation By Phasic High Intrathoracic Pressure Support In Man

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Left ventricular performance can be significantly influenced by changes in intrathoracic pressure. In man, sustained increases in intrathoracic pressure unload the left ventricle, but since venous return decreases, increased intrathoracic pressure is associated with a decreased cardiac output. In a canine model of acute ventricular failure, it has been shown that phasic increases in intrathoracic pressure, which do not decrease venous return, improve steady-state cardiac output. We thus studied the cardiovascular effects of phasic high intrathoracic pressure support (PHIPS) in seven patients with shock in our intensive care unit whose condition was not responsive to conventional types of therapy. The PHIPS was generated by abdominal and chest wall binding during positive-pressure ventilation. As compared to the state before PHIPS, the PHIPS was associated with an increase in esophageal pressure (6.6 ± 1.1 mm Hg; p<0.01) and in mean arterial pressure (43.0 ± 6.1 to 51.0 ± 7.7 mm Hg; p<0.01) while not changing arterial pressure relative to esophageal pressure. Cardiac output also increased from 3.6 ± 0.5 to 4.2 ± 0.6 L/min (p<0.05), while left ventricular filling pressures remained constant. In one subject a gated cardiac blood pool scan demonstrated a PHIPS-associated increase in ejection fraction and decreased end-diastolic volume. These results are consistent with the hypothesis that PHIPS, by increasing intrathoracic pressure, augments left ventricular performance by reducing left ventricular afterload. This appears to be a promising area for future research.

Section snippets

MATERIALS AND METHODS

Seven patients in the medical intensive care unit of Johns Hopkins University Hospital, Baltimore, served as our subjects for this study. All subjects were gravely ill with severe shock either due to sepsis (four) or myocardial infarction (three). All were being treated aggressively with conventional fluid resuscitation and vasoactive drugs. Profiles of the patients are shown in Table 1. Criteria for entrance into this study included the following: (1) severe hypotension secondary to depressed

RESULTS

The hemodynamic data for all seven subjects are summarized in Table 2. The PHIPS was associated with an increase in mean Pes of 6.6 ± 1.1 mm Hg (mean±SE) over the control states (p<0.001). There was no significant difference between the two control states in any of the hemodynamic variables, although the trend over time was to a lower cardiac output, mean arterial pressure, and Pes. This is consistent with the progressive hemodynamic deterioration that the subjects demonstrated both before and

DISCUSSION

Left ventricular function can be described by the relationship between cardiac output and left ventricular filling pressure.9 Our study demonstrates that in the setting of severe left ventricular dysfunction (ie, with an expanded intravascular blood volume), increasing intrathoracic pressure improves left ventricular performance. These results are in agreement with recent reports.4,10,11 Buda and co-workers4 found that with sustained increases in intrathoracic pressure, left ventricular

ACKNOWLEDGMENTS

We thank Ms. Nancy Gordon for secretarial assistance in preparing this manuscript.

REFERENCES (16)

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Supported by National Research Service Award IF32HL-06238-01.

Manuscript received November 20; revision accepted April 28.

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