Special Articles
Comparison of Published Pressure Gradient Symbols
and Equations in Mechanics of Breathing
David F Wolfe MSEd RRT RPSGT AE-C and Joseph G Sorbello MSEd RRT
In the literature of pulmonary medicine we found dismaying diversity of and inconsistency in terms
used to describe physiologic pressure gradients. Standardized terms, definitions, symbols, and
equations published by the American Physiological Society, the American College of Chest Physi-
cians, the American Thoracic Society, and the American Association for Respiratory Care have not
been consistently used. Rather, researchers have often used their own definitions for transpulmo-
nary pressure, transairway pressure, transthoracic pressure, transrespiratory pressure, and trans-
diaphragmatic pressure. We describe the variety of definitions and equations we found for those
terms. We contend that it would benefit researchers, students, clinicians, and educators to define
these terms precisely and use them consistently. Key words: transpulmonary pressure, transairway
pressure, transthoracic pressure, transrespiratory pressure, transdiaphragmatic pressure, terminology,
respiratory mechanics/physiology. [Respir Care 2006;51(12):1450 –1457. © 2006 Daedalus Enterprises]
Introduction
A clear understanding of respiratory physiology is crit-
ical to the provision of competent respiratory care as well
as the scientific advancement of the field. Comprehension
of the pressure gradients involved in the mechanics of
breathing is an important part of this understanding. There
are, however, differences among the definitions, symbols,
and equations used to convey this information in the med-
ical literature, including respiratory care texts.
Although a standardized set of definitions, symbols and
equations has been published by those who establish such
standard terms, various medical authors, including those in
respiratory care, have chosen to express these definitions,
symbols, and equations differently from that standard. Ad-
ditionally, the authors differ among themselves in express-
ing those terms. The differences among various authors
have created confusion for many, particularly students,
who depend on published standards to guide them in es-
tablishing a solid foundation. This foundation helps to
achieve understanding of physiology and pathophysiol-
ogy, from which flows critical components of their pro-
fessional knowledge and skills.
The purpose of this article is to articulate these dif-
ferences, as presented in the literature. Armed with this
information, the respiratory care community will per-
haps come to some consensus on the terminology of
breathing mechanics and begin to use this terminology
consistently.
The first attempt to document standard respiratory phys-
iologic definitions and symbols was in 1950.
1
In 1964,
1965, and 1986, the American Physiological Society pub-
lished similar documents.
2,3
In 1975 and 1997 the Amer-
ican College of Chest Physicians and the American Tho-
racic Society,
4
and American Association for Respiratory
Care
5
also published similar documents. Despite these pub-
lications, there is still no agreement concerning definitions
and symbols used in respiratory physiology, particularly
those used to describe mechanics of breathing, among the
many authors who publish in the medical literature.
David F Wolfe MSEd RRT RPSGT AE-C and Joseph G Sorbello MSEd
RRT are affiliated with the Department of Respiratory Therapy Educa-
tion, College of Health Professions, State University of New York, Up-
state Medical University, Syracuse, New York.
The authors report no conflicts of interest related to the content of this
paper.
David F Wolfe MSEd RRT RPSGT AE-C presented a version of this
paper at the 19th Annual State University of New York Upstate Medical
University Charles R Ross Research Poster Session, held November 30,
2005, at the Institute for Human Performance, Syracuse, New York.
Correspondence: David F Wolfe MSEd RRT RPSGT AE-C, Department
of Respiratory Therapy Education, College of Health Professions, State
University of New York, Upstate Medical University, 750 E Adams
Street, Syracuse NY 13210-2375. E-mail: [email protected].
1450 RESPIRATORY CARE • DECEMBER 2006 VOL 51 NO 12
Review of Literature
Symbols
Symbols used in respiratory physiology to identify spe-
cific points of reference relating to pressure gradients and
the understanding of breathing mechanics are also critical
to ensure no impedance to rigorous scientific communica-
tion. We offer Table 1 to illustrate the variety of symbols
discovered in our literature search. It’s our belief that even
though it may be acceptable to use different symbols, it’s
still confusing, especially to students, for whom the con-
cepts of pressure gradients are not fully developed. Our
contention is that although different symbols are used and
commonly accepted, standardized symbols used by all au-
thors would be beneficial to the field.
Pressure Gradients
A comprehensive review of major textbooks (Table 2)
was performed.
6-28
A brief synopsis is also provided be-
low, organized by pressure gradient. One inconsistency we
found was that some sources did not define or give equa-
tions for many pressure gradients critical in the illustration
of respiratory mechanics. One example was the text by
Slonim and Hamilton entitled Respiratory Physiology,
which defined only transpulmonary pressure.
15
Transpulmonary. Several pressure gradients are en-
countered in the respiratory system. Transpulmonary pres-
sure (Table 3) is commonly defined as the pressure gra-
dient from the alveolar to the pleural spaces (P
alv
–P
pl
).
Although most agree on the spaces between which this
gradient is defined, the text edited by Kacmarek et al
7
reverses the symbols and, therefore, the direction of this
gradient (P
pl
–P
alv
).
Expanding the review to include original peer-reviewed
research articles revealed even greater confusion.
29-40
For
instance, Davis defined transpulmonary pressure as the
difference between airway opening pressure and pleural
pressure (as measured via esophageal balloon), rather than
the difference between alveolar pressure and pleural pres-
sure.
29
Airway opening and alveolar pressure are equal
under static conditions, as may be the case with specific
research protocols (under controlled conditions). This is a
special scenario, and casual extrapolation of this estima-
tion may confound the reader. Davis’s review
29
defined
transpulmonary pressure within the context of the mea-
surement of dynamic airway resistance, in which both pres-
sure and flow were dynamic rather than static.
Transairway. Transairway pressure (Table 4) is de-
scribed alternately as the pressure gradient between the
alveolar space and either the mouth or the airway opening
(P
m
–P
alv
,orP
ao
–P
alv
).
41,42
The direction of the gradient
was reversed in the text for our own course in cardiopul-
monary physiology: Respiratory Care Anatomy and Phys-
iology by Beachey.
6
Munakata et al describe transairway
pressure as the difference between “airway opening and
alveolar pressure,” without regard to direction.
41
Hicks
states that transairway and transrespiratory pressure are
synonymous and expressed as P
rs
⫽ P
A
–P
B
.
28
Transthoracic. Perhaps the greatest confusion regard-
ing respiratory pressure gradients surrounds transthoracic
pressure (Table 5).
32,43-47
The equation for and definition
of the transthoracic pressure gradient is inconsistent, even
within the same textbook. For example, the equation P
pl
–
P
bs
appears in Chapter 9 of both the 7th and 8th editions of
Egan’s Fundamentals of Respiratory Care.
12,13
However,
Chapter 40 of the 8th edition states that transthoracic pres-
Table 1. Symbols Used in the Medical Literature to Represent
Pressures and Pressure Gradients in Mechanics of
Breathing
Pressure at a Location
P
aw
,P
ao
,P
awo
,P
airway
airway pressure, airway opening pressure
P
AW
flow-resistive pressure in airway
P
pa
proximal airway pressure
P
m
mouth pressure
P
alv
,P
A
alveolar pressure
P
pl
pleural pressure
P
ab
abdominal pressure
P
bs
,P
BS
body surface pressure
P
b
,P
B
,P
ATM
atmospheric pressure
P
es
esophageal pressure
P
gas
,P
GA
gastric pressure
P
tr
tracheal pressure
P
E
total pressure in the external ambient
P
in
pressure inside a vessel or airway
P
out
pressure outside a vessel or airway
Pressure Gradients
and Differences
P
TA
,P
aw
,P
ta
,P
transairway
transairway pressure, flow-resistive
pressure in the airways
P
TR
,P
RS
,P
rs
,P
tr
,P
tres
transrespiratory pressure
P
trs
,P
transrespiratory
transrespiratory system pressure
P
TP
,P
L
,P
tp
,P
transpulmonary
transpulmonary pressure
P
transalveolar
transalveolar pressure
P
TT
,P
W
,P
tt
,P
transthoracic
transthoracic pressure
P
Di
,P
TD
,P
di
transdiaphragmatic pressure
P
RC
pressure across the rib cage
P
cw
across the chest wall
P
abW
transabdominal wall pressure
P
Eq
pressure across the equipment
P
el(L)
elastic recoil pressure of the lung
(pressure across lung tissue)
P
tm
,P
TM
,P
transmural
transmural pressure
PRESSURE GRADIENT SYMBOLS AND EQUATIONS IN MECHANICS OF BREATHING
RESPIRATORY CARE • DECEMBER 2006 VOL 51 NO 12 1451
Table 2. Comparison of Pressure Gradient Terms and Equations Used in Respiratory Care Texts
First Author
Pressure Gradients
Transairway Transrespiratory Transpulmonary Transthoracic Transdiaphragmatic
Beachey
6
“pressure gradient
across the airways
...⫽ P
A
⫺ P
ao
”
P
rs
⫽ P
A
⫺ P
bs
P
L
⫽ P
A
⫺ P
pl
P
W
⫽ P
pl
⫺ P
bs
No equation,
definition, or symbol
Kacmarek
7
“alveolar minus body
surface pressure”
“pressure difference
across the lung-
thorax system . . .
alveolar-body
surface pressure”
“TPP: the pressure
difference across the
lung (pleural minus
alveolar pressure)”
“pressure difference
across the thorax,
including chest and
diaphragm (pleural-
body surface
pressure)”
“pressure difference
across the
diaphragm
(abdominal-pleural
pressure)”
Martin
8
“Transairway
(pressure) ⫽ Pm ⫺
Palv ⫽ pressure
driving air into or
out of the lungs”
No equation,
definition, or
symbol
“Transpulmonary ⫽
Palv ⫺ Ppl ⫽
pressure tending to
inflate or deflate the
lungs”
“Transthoracic ⫽ Palv
⫺ Pbs ⫽ pressure
tending to inflate or
deflate the lungs and
chest wall together”
No equation,
definition, or symbol
Des Jardins
9
P
ta
⫽ P
m
⫺ P
alv
P
m
⫽ P
ao
No equation,
definition, or
symbol
P
tp
⫽ P
alv
⫺ P
pl
P
tt
⫽ P
alv
⫺ P
bs
No equation,
definition, or symbol
Cottrell
10
P
ta
⫽ P
m
⫺ P
a
No equation,
definition, or
symbol
P
tp
⫽ P
alv
⫺ P
pl
Ptt ⫽ Ppl ⫺ Pbs
Pbs ⫽ Patm
No equation,
definition, or symbol
Pilbeam
11
P
TA
⫽ P
aw
⫺ P
A
P
TR
⫽ P
awo
⫺ P
bs
P
L
⫽ P
A
⫺ P
pl
P
W
⫽ P
A
⫺ P
bs
No equation,
definition, or symbol
Ruppel
12
No equation,
definition, or
symbol
P
rs
⫽ P
alv
⫺ P
bs
P
rs
⫽ P
alv
⫺ P
ao
in
spontaneous
breathing
P
L
⫽ P
alv
⫺ P
pl
P
W
⫽ P
pl
⫺ P
bs
No equation,
definition, or symbol
Ruppel
13
No equation,
definition, or
symbol
P
rs
⫽ P
alv
⫺ P
bs
P
rs
⫽ P
alv
⫺ P
ao
in
spontaneous
breathing
P
L
⫽ P
alv
⫺ P
pl
P
W
⫽ P
pl
⫺ P
bs
No equation,
definition, or symbol
Op’t Holt
14
P
ta
⫽ P
aw
⫺ P
alv
P
tr
⫽ P
ao
⫺ P
bs
P
L
⫽ P
alv
⫺ P
pl
P
w
or P
tt
⫽ P
bs
⫺ P
alv
No equation,
definition, or symbol
Slonim
15
No equation,
definition, or
symbol
No equation,
definition, or
symbol
“pressure difference
between alveolar
pressure and
intrapleural
pressure”
No equation,
definition, or symbol
No equation,
definition, or symbol
Op’t Holt
16
No equation,
definition, or
symbol
“pressure difference
between the alveoli
and the mouth”
No equation,
definition, or
symbol
No equation,
definition, or symbol
No equation,
definition, or symbol
Grippi
17
No equation,
definition, or
symbol
No equation,
definition, or
symbol
Pl ⫽ Palv ⫺ Ppl Prs ⫽ Palv ⫺ Pbs Pdi ⫽ Pab ⫺ Ppl
Loring
18
Not defined as
“transairway
pressure”; however,
“P
aw
⫽ flow
resistive pressure in
the airways; P
aw
⫽
P
ao
⫺ P
alv
”
P
RS
⫽ P
ao
⫺ P
bs
P
TP
or P
L
⫽ P
ao
⫺ P
pl
Not defined as such;
however, P
CW
is the
pressure difference
“across the chest
wall”; P
CW
⫽ P
pl
⫺
P
bs
P
Di
⫽ P
pl
⫺ P
ab
Chatburn
19
“P
transairway
. . . airway
opening pressure
minus lung
pressure.”
P
transrespiratory
⫽
P
transairway
⫹
P
transthoracic
“pressure at the
airway opening
minus the pressure
at the body surface”
P
transpulmonary
⫽
P
transairway
⫹
P
transalveolar
“airway
opening pressure
minus pleural
pressure”
(derived) P
transthoracic
⫽
P
transrespiratory
⫺
P
transairway
“lung
pressure minus body
surface pressure”
No equation,
definition, or symbol
(Continued)
PRESSURE GRADIENT SYMBOLS AND EQUATIONS IN MECHANICS OF BREATHING
1452 RESPIRATORY CARE • DECEMBER 2006 VOL 51 NO 12
sure is P
bs
–P
alv
.
14
Other authors add to the confusion by
variously defining this gradient as P
alv
–P
bs
,
9
P
A
–P
bs
,
11
and “difference between gastric pressure. . . and the pleu-
ral pressure...attheendofexpiration.”
44
The equation that uses alveolar pressure minus body
surface pressure, in its various forms, is the same as that
used by other authors to define transrespiratory pres-
sure.
6,7,12,13
As a summary, we found the following various equa-
tions or relationships from the various authors for trans-
thoracic pressure: P
pl
–P
bs
,
6,10,12,13,18
P
alv
–P
bs
,
8,9,17
P
bs
–
P
alv
,
14
P
transrespiratory
–P
transairway
,
20
esophageal pressure
Table 2. Continued
First Author
Pressure Gradients
Transairway Transrespiratory Transpulmonary Transthoracic Transdiaphragmatic
MacIntyre
20
Illustrated as
transrespiratory
pressure minus
transthoracic
pressure
“airway pressure minus
body surface
pressure.” Illustrated
as transairway
pressure plus
transthoracic
pressure
No equation,
definition, or
symbol
Illustrated as
transrespiratory
pressure minus
transairway pressure
No equation,
definition, or symbol
Matthews
21
No equation,
definition, or
symbol
No equation,
definition, or symbol
“Transpulmonary
pressure ⫽ P
alveolar
⫺ P
pleural
”
No equation,
definition, or symbol
No equation,
definition, or symbol
Leff
22
No equation,
definition, or
symbol
No equation,
definition, or symbol
P
tp
⫽ P
alv
⫺ P
pl
Not defined as
“transthoracic
pressure”; however,
P
trans-chest wall
⫽ P
pl
⫺
P
atmospheric
No equation,
definition, or symbol
Chatburn
23
Illustrated as
transrespiratory
pressure minus
transthoracic
pressure
Illustrated as
transairway pressure
plus transthoracic
pressure
No equation,
definition, or
symbol
Illustrated as
transrespiratory
pressure minus
transairway pressure
No equation,
definition, or symbol
Culver
24
No equation,
definition, or
symbol
Not defined as
“transrespiratory
pressure”; however
transmural pressure
of the respiratory
system equals “(P
A
⫺ P
PL
) ⫹ (P
PL
⫺
P
ATM
) ⫽ P
A
⫺
P
ATM
”
Not defined as
“transpulmonary
pressure”; however,
transmural pressure
of the lungs equals
“Alveolar pressure
(P
A
) ⫺ pleural
pressure (P
PL
)”
Not defined as
“transthoracic
pressure”; however,
transmural pressure
of the chest wall
equals “P
PL
⫺
atmospheric pressure
(P
ATM
), or simply
P
PL
”
No equation,
definition, or symbol
West
25
No equation,
definition, or
symbol
“difference between
the inside and
outside of the lung”
No equation,
definition, or
symbol
No equation,
definition, or symbol
No equation,
definition, or symbol
Levitsky
26
No equation,
definition, or
symbol
No equation,
definition, or symbol
“equal to the pressure
in the trachea minus
the intrapleural
pressure. Thus, it is
the pressure
difference across the
whole lung.”
No equation,
definition, or symbol
No equation,
definition, or symbol
Drumheller
27
“(Pta) is the pressure
difference between
the mouth (Pm), or
airway pressure, and
the alveolar pressure
(Palv)”
No equation, definition
or symbol
“(Ptp), or alveolar
distending pressure,
is the difference
between Palv and
pleural pressure
(Ppl)”
“(Ptt) is the difference
between Palv and
body surface
pressure (Pbs)”
No equation,
definition, or symbol
Hicks
28
P
rs
⫽ P
A
⫺ P
B
Stated to be the same
as transairway
pressure
P
L
⫽ P
A
⫺ P
pl
P
W
⫽ P
pl
⫺P
B
P
di
⫽ P
pl
⫺ P
abd
PRESSURE GRADIENT SYMBOLS AND EQUATIONS IN MECHANICS OF BREATHING
RESPIRATORY CARE • DECEMBER 2006 VOL 51 NO 12 1453
minus atmospheric pressure,
45
and mouth pressure minus
body surface pressure.
43
Transrespiratory. In the 7th edition of Egan’s Funda-
mentals of Respiratory Care, transrespiratory pressure (dur-
ing spontaneous breathing) was similarly defined in Chap-
ters 9 and 39 as the difference between pressure in the
alveoli and the mouth (airway opening or body surface).
12,16
In comparison, the 8th edition had a completely different
equation for transrespiratory (and transthoracic) pressure.
14
Chapter 9 of both editions defines transrespiratory pres-
sure as P
alv
–P
bs
or as P
alv
–P
ao
(for spontaneous breath
-
ing),
12,13
and Chapter 40 of the 8th edition defines it as
P
ao
–P
bs
.
14
Chapter 9 of both editions defines transtho-
racic pressure as P
pl
–P
bs
12,13
and Chapter 40 of the 8th
edition defines it as P
bs
–P
alv
.
14
Additionally, other au-
thors state that transrespiratory pressure equals transair-
way pressure (Table 6).
6,28
Table 3. Comparison of Transpulmonary Pressure Gradient Symbols, Definitions, and Equations in Published Articles
First Author Symbol, Definition, and/or Equation (only if included in article)
Davis
29
“Transpulmonary pressure is defined as the difference between the pressure measured at the airway opening and the
pressure measured at the esophagus.”
Mundie
30
Easa
31
Ptp ⫽ difference between airway opening pressure (Pao) and esophageal pressure (Pes)
Chaunchaiyakul
32
Transpulmonary pressure: alveolar minus pleural pressure
Permutt
33
Transpulmonary pressure ⫽ “airway pressure relative to pleural pressure”
Murali
34
“The resistance of the pulmonary circulation is represented by the gradient across the pulmonary vascular bed or the
transpulmonary pressure gradient (pulmonary artery mean pressure minus mean pulmonary wedge pressure).”
Sanchez
35
“Transpulmonary pressure was defined as the difference between the intrapleural and atmospheric pressures.”
Schulze
36
; Coates
37
Ptp
Hobbhahn
38
“The transpulmonary pressure gradient (TPP) was calculated from MPAP and PCWP.”
Gamillscheg
39
“transpulmonary pressure gradient (CVP ⫺ LAP)”
Pelosi
40
Transpulmonary pressure (PL) is “the difference between Paw and Ppl”
Ptp ⫽ transpulmonary pressure
MPAP ⫽ mean pulmonary artery pressure
PCWP ⫽ pulmonary capillary wedge pressure
CVP ⫽ central venous pressure
LAP ⫽ left atrial pressure
Paw ⫽ airway pressure
Ppl ⫽ pleural pressure
Table 4. Comparison of Transairway Pressure Gradient Symbols, Definitions, and Equations in Published Articles
First Author Definitions, Equations, Symbols (only if included in the article)
Munakata
41
Transairway pressure (Pta) ⫽ “difference between airway opening and alveolar pressure”
Liu
42
“transairway pressure gradient (PE ⫺ PA)”
PE ⫽ total pressure in the external ambient
PA ⫽ total pressure in the alveolar zone
Table 5. Comparison of Transthoracic Pressure Gradient Symbols, Definitions, and Equations in Published Articles
First Author Definitions, Equations, Symbols (only if included in the article)
Chaunchaiyakul
32
Transthoracic pressure: pleural minus body surface pressure
Suratt
43
“Transthoracic pressure is taken as the difference between mouth pressure measured at the proximal pneumotachometer
port and body surface (atmospheric) pressure.”
Lazenby
44
“Transthoracic pressure was defined as the pressure difference between the gastric pressure (abdomen) and the pleural
pressure (mid-esophagus) at the end of expiration.”
Barnas
45
“Transthoracic pressure (esophageal pressure minus atmospheric pressure)”
Saunders
46
Pes (esophageal pressure) equivalent to PTT (transthoracic pressure)
Eyal
47
No definition, equation, or symbol
PRESSURE GRADIENT SYMBOLS AND EQUATIONS IN MECHANICS OF BREATHING
1454 RESPIRATORY CARE • DECEMBER 2006 VOL 51 NO 12
As we understand these concepts, they may be equiva-
lent in some cases, because pressure at the body surface
(P
bs
) and pressure at the “airway opening” (or “mouth” or
“airway”) is equivalent in spontaneous breathing. How-
ever, this would not be true if, for example, an endotra-
cheal tube was in place. In such a case, it would be incor-
rect to say that the pressure at “the mouth” of this patient
is equivalent to “airway” or “airway opening.” The pres-
sure in the mouth of this patient would be barometric
pressure (P
B
) or body surface pressure (P
bs
). Depending on
the text, transairway pressure may qualitatively equal trans-
thoracic pressure
9
or transairway pressure may equal trans-
respiratory pressure.
6,28
Transdiaphragmatic. One essential gradient, especially
in spontaneous breathing mechanics, has rarely been de-
scribed in textbooks. This is transdiaphragmatic pressure
(Table 7), which has been described in only 4 text-
books.
7,17,18,28
Transdiaphragmatic pressure is defined by
Kacmarek et al as “the pressure difference across the di-
aphragm (abdominal – pleural pressure).”
7
Grippi defined
transdiaphragmatic pressure as “the pressure generated
across the diaphragm during inspiration. It is calculated as
the difference between intraabdominal pressure (P
ab
) and
pleural pressure (P
pl
).”
17
Consideration of this pressure
gradient is not only beneficial but essential in the descrip-
tion and understanding of breathing mechanics.
Summary
Our review of the literature exposed great variability in
the definition and symbolic representation of pressure gra-
dients among experts and researchers involved in respira-
tory medicine. The extent of this variability is made evi-
dent by conflicting descriptions found in the medical
literature and even in chapters of the same textbook. Al-
though the ultimate impact of these discrepancies is not
profound, it is our contention that this wide variability is
confusing and unnecessary. Agreement among authors and
consistent use of these terms will advance the understand-
ing of pressure gradients, improve clarity, and allow for
reliable scientific communication among students, clini-
cians, researchers, and educators.
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1. Pappenheimer JR, Comroe JH, Cournand A, Ferguson JK, Filley GF,
Fowler WS, et al. Standardization of definitions and symbols in
respiratory physiology. Fed Proc 1950;9(3):602–605.
2. Fishman AP, Macklem PT, Mead J, Geiger SR, editors. Handbook of
physiology, Section 3: the respiratory system, Volume III, Part 1.
Baltimore: Waverly Press; 1986.
3. Fishman AP, Macklem PT, Mead J, Geiger SR, editors. Handbook of
physiology, Section 3: the respiratory system, Volume III, Part 2.
Baltimore: Waverly Press; 1986.
4. American College of Chest Physicians-American Thoracic Society.
Pulmonary terms and symbols: a report of the ACCP-ATS Joint
Committee on Pulmonary Nomenclature. Chest 1975;67(5):583–593.
Table 6. Comparison of Transrespiratory Pressure Gradient
Symbols, Definitions, and Equations in Published Articles
First Author
Definitions, Equations, Symbols (only if
included in the article)
Mundie
30
Ptr ⫽ “difference between Paw and body
surface pressure at end-inspiration”
Easa
31
Transrespiratory system pressure (Ptrs) ⫽
“difference between Pao and body surface
pressure”
Chaunchaiyakul
32
“Transrespiratory pressure: alveolar minus body
surface pressure”
Loring
48
; Zhang
49
;
Suen
50
No definition, equation, or symbol
Hantos
51
Prs ⫽ airway opening pressure
Hall
52
Ptr
Taylor
53
“Transrespiratory pressure (Ptres ⫽ alveolar
pressure minus body surface pressure)”
Sly
54
Transrespiratory pressure ⫽ airway opening
pressure (Pao)
Blease
55
“Transrespiratory pressure equals change in
tracheal pressure minus change in mouse
chamber pressure”
Petak
56
Ptr ⫽ tracheal pressure, Pes ⫽ esophageal
pressure
Table 7. Comparison of Transdiaphragmatic Pressure Gradient
Symbols, Definitions, and Equations in Published Articles
First Author
Symbol, Definition, Equation (only if
included in article)
Permutt
33
Transdiaphragmatic pressure ⫽ “a function of
the difference between pleural and abdominal
pressure”
Saunders
46
“Transdiaphragmatic pressure (P
di
) was taken as
the difference between P
es
and P
ab
”
Pinet
57
No symbol, definition, or equation
Wanke
58
;
El-Kabir
59
P
di
de Torres
60
P
di
⫽ P
ga
⫺ P
pl
Riou
61
Pdi ⫽ gastric pressure (Pgas) ⫺ esophageal
pressure (Pes)
P
es
⫽ esophageal pressure
P
ab
⫽ abdominal pressure
P
ga
⫽ gastric pressure
P
pl
⫽ not defined, but assumed to be pleural pressure
PRESSURE GRADIENT SYMBOLS AND EQUATIONS IN MECHANICS OF BREATHING
RESPIRATORY CARE • DECEMBER 2006 VOL 51 NO 12 1455
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