Am. J. Respir. Crit. Care Med.,
Volume 161, Number 5, May 2000, 1763-1763
HEART CATHETERIZATION IN ACUTE LUNG INJURY:AN OBSERVATIONAL STUDY
To the Editor :
In their retrospective analysis of right heart catherization in
acute lung injury (1), Marinelli and colleagues describe a
"moderately strong correlation" (r = 0.72) between right
atrial and pulmonary artery wedge pressures (Pra, Pw). It appears that most if not all of their patients received mechanical
ventilation with PEEP at the time of the measurements, unlike most of those in the prior studies cited. The correlation
may therefore have been forced, in part, by positive airway
pressure imposed on the pulmonary vasculature and the juxtacardiac space. Had estimates of transmural Pra and Pw been
available, the resulting correlation might have been weaker.
Also important to this question is the protocol used for the hemodynamic measurements (in particular, their timing within
the ventilatory cycle), which the authors do not describe.
The word parameter receives a broad interpretation in this
paper, as it does in many others appearing in the medical literature. Parameter has several well defined meanings pertinent
to scientific data and statistics (2). Its increasing use as an
omnibus term for whatever can be measured, described, or
otherwise commented upon hardly serves it well. Marinelli
and colleagues, for example, apply it to observations as disparate as blood gas data, sex, venipuncture site, and the indications for a procedure! The expanding, nontechnical uses of parameter are controversial. Some may be justified by analogy
with its accepted definitions or its root meaning, but others are
indiscriminate and pseudoerudite, leaving parameter diluted
and poorly understood by many. A word that one can apply to
almost anything signifies almost nothing.
A.
Ross Hill
Division of Pulmonary and Critical Care Medicine,SUNY Downstate Medical CenterBrooklyn, New York
1.
Marinelli, W. A.,
C. R. Weinert,
C. R. Gross,
J. P. Khoedler Jr.,
C. L. Burt,
J. R. Kangas, and
J. W. Leatherman.
1999.
Right heart catheterization in acute lung injury: an observational study.
Am. J. Respir. Crit.
Care Med
160:
69-76
[Abstract/Free Full Text].
2.
Webster's Third New International Dictionary of the English Language,
unabridged. 1986. Merriam-Webster, Springfield.
3.
The American Heritage Dictionary of the English Language, 3rd ed.
1992. Houghton Mifflin, Boston.
4.
Fisher, L., and G. Van Belle. 1993. Biostatistics: A Methodology for the
Health Sciences. J. Wiley, New York. 126.
From the Authors:
Dr. Hill's first question concerned the potential effect of positive airway pressure on the correlation between right atrial and pulmonary artery occusion pressure measurements. He
suggested the possibility of a weaker correlation between right
atrial and pulmonary artery occlusion pressure measurements
if estimates of transmural pressures were made. However, if
pleural pressure was measured and subtracted from both the
right atrial and pulmonary artery occlusion pressure measurements to calculate transmural pressure their correlation would
not be altered if measurements were made at the same time
during the respiratory cycle. In this regard, all intravascular
pressures were recorded at end-expiration in our study.
Dr. Hill's second concern focused on our frequent use of
the term parameter in our manuscript. We respect and appreciate his concern for the potential misuse of the word parameter in scientific writing. However, one recent source defines
parameter as a "measurable characteristic of a population," offering some defense for our use in this manuscript (1).
WILLIAM MARINELLI
Pulmonary and Critical Care Medicine
Hennepin County Medical Center
University of Minnesota Medical School
Minneapolis, Minnesota
1.
American Medical Association. 1998. American Medical Association
Manual of Style, 9th ed. Williams & Wilkins, Baltimore.
