(Chest. 1999;115:679-683.)
© 1999
American College of Chest Physicians
Partial Pressure of Oxygen Is Lower in the Left Upper Pulmonary Vein Than in the Right in Adults With Atrial Septal Defect*
Difference in PO2 Between the Right and Left Pulmonary Veins
Kanji Iga, MD;
Chisato Izumi, MD;
Masahiko Matsumura, MD;
Shouji Kitaguchi, MD;
Yoshihiro Himura, MD;
Hiromitsu Gen, MD and
Takashi Konishi, MD
*
From the Department of Cardiology (Drs. Iga, Izumi, Kitaguchi, Himura,
Gen, and Konishi), and the Department of Pediatrics (Dr. Matsumura), Tenri
Hospital, Tenri City, Japan.
 |
Abstract
|
|---|
Background: The right-to-left shunt at the atrial level
is responsible for arterial hypoxemia in patients with atrial septal
defect.
Objectives: This study investigated the
mechanism of arterial hypoxemia in patients with atrial septal defect
by measuring the PO2 in both the right and left
upper pulmonary veins.
Subjects and method: We
prospectively measured the PO2 in the femoral
artery and the right and left upper pulmonary veins during cardiac
catheterization in 13 adults (median age, 53 years) and 7 children
(median age, 7 years) with secundum atrial septal defect. The adults
and children were studied consecutively. Contrast
echocardiography was performed to evaluate right-to-left shunt in all
adults.
Results: Among the children, there were no
patients showing arterial hypoxemia, and there was no difference in the
PO2 (± SD) between the right and left
upper pulmonary veins (right, 100 ± 3.8 mm Hg vs left, 100 ± 7.8
mm Hg; p = 0.92). However, arterial hypoxemia was present in 11 of
the 13 adult patients, although contrast echocardiography showed more
than a moderate degree of right-to-left shunt in only four adults. The
PO2 was lower in the left upper pulmonary vein
than it was in the right upper pulmonary vein in all adult patients
(right, 91.6 ± 13.8 mm Hg vs left, 73.0 ± 11.5 mm Hg;
p < 0.0001).
Conclusion: The
PO2 was lower in the left upper pulmonary vein
than it was in the right upper pulmonary vein in adults with atrial
septal defect. Care must be taken in measuring pulmonary blood flow if
the PO2 in the left upper pulmonary vein is low
enough to influence oxygen content. The decreased
PO2 in the left upper pulmonary vein may
contribute to arterial hypoxemia in addition to right-to-left shunt at
the atrial level in adults with atrial septal
defect.
Key Words: atrial septal defect • intracardiac shunt • PO2 • pulmonary vein
|
Introduction
|
|---|
Right
-to-left shunt at the atrial level is responsible for decreased
saturation of arterial blood in patients with patent foramen ovale and
increased venous pressure1
,2
or in patients with large
atrial septal defect (ASD) and severe tricuspid
regurgitation.3
In either situation, there is an
assumption that saturation of the right and left pulmonary veins is
equally high if arterial hypoxemia is caused only by this reverse
shunt. To our knowledge, there has been no report of a comparison
between the right and left pulmonary veins regarding
PO2.
In the present study, we investigated whether
PO2 is equal in the right and left
upper pulmonary veins in both adults and children with ASD in order to
look for a cause of arterial hypoxemia that is other than the
right-to-left shunt.
|
Materials and Methods
|
|---|
Subjects consisted of 13 adults (median age, 53 years;
range, 40 to 78 years) and 7 children (median age, 7 years; range, 5 to
13 years) with secundum ASD. The adults and children were studied
consecutively. Using an NIH catheter, cardiac catheterization
was performed from the femoral approach in all patients. The catheters
were easily advanced into the right and left upper pulmonary veins
through the ASD. These upper pulmonary veins were identified as right
or left when the catheter was superior to the cardiac silhouette and
rightward and leftward, respectively. Blood was drawn from both
the right and left upper pulmonary veins as well as from other cardiac
chambers before the injection of contrast medium: 5 mL of blood in
adults and 2 mL in children. Because an NIH catheter has six side holes
about 2 cm proximal to the closed end, we were very careful about
keeping the sampling position in the pulmonary veins at a distance from
the cardiac silhouette such that it would not be contaminated by blood
from the left atrium. If the hemoglobin concentration of any blood
sample differed > 0.3 g/dL from other blood samples, it was discarded
as a sampling error. PO2 and
PCO2 were measured (Chiron 288 blood
gas system; Chiron Diagnostics Corp; Medfield, MA), and the oxygen
content was then calculated mathematically.
Using hand-agitated 5% dextrose in water from an antecubital vein,
contrast echocardiography was done during normal breathing in all
adults (Table 1
). We used the transesophageal technique in 11 adult patients to confirm
whether the right-to-left shunt was directed toward the left upper
pulmonary vein. The degree of right-to-left shunt on contrast
echocardiography was classified as follows: severe if the bubble was
seen entirely in the left atrium; mild if the bubble was slightly in
the left atrium; and moderate if in between. Ventilatory function tests
were done in all adult patients except for one, and pulmonary
ventilation by 133Xe gas and perfusion scan by
99mTc macroaggregated albumin were done in 10 adult
patients. Statistical analysis was done using Student's paired
t test. None of the patients had a history of thoracotomy.
|
Results
|
|---|
In the children, there was no arterial hypoxemia and no difference
in PO2 (± SD) between the right and
left upper pulmonary veins (right, 100 ± 3.8 mm Hg vs left,
100 ± 7.8 mm Hg; p = 0.92; Fig 1
). In the adults, arterial hypoxemia was present in 11 patients, if
arterial PO2 > 80 mm Hg is
considered normal, and PO2 (± SD)
was lower in the left upper pulmonary vein than in the right upper
pulmonary vein (right, 91.6 ± 13.8 mm Hg vs left, 73.0 ± 11.5 mm
Hg; p < 0.0001; Fig 2
). The PCO2 in the left upper
pulmonary vein was statistically greater than that of the right upper
pulmonary vein (right, 37.4 ± 5.4 mm Hg vs left, 39.4 ± 6.7 mm
Hg; p = 0.03; Fig 3
). The difference in oxygen content between the right and left upper
pulmonary veins ranged from 2 to 34 mL/L, with the difference being
> 5 mL/L in 11 adult patients (Fig 4
). The pulmonary blood flow in patient 1 was measured as 4.1 L/min when
only the oxygen content of the right pulmonary upper vein was used,
whereas it was measured as 8.3 L/min when the averages of both the
right and left upper pulmonary veins were used. Contrast
echocardiography showed that the right-to-left shunt was mild in eight
adult patients and that there was no shunt in one patient. During
contrast transesophageal echocardiography, no bubble was seen in the
left upper pulmonary veins of all 11 adult patients. In two adult
patients who had severe reverse right-to-left shunt, acquired cyanosis
was seen, and severe tricuspid regurgitation and atrial fibrillation
were observed to be present (patients 1 and 4). The mean cardiothoracic
ratio was 62%. Both the FEV1/FVC ratio and the
percent vital capacity (VC) were normal in five adult patients, and
either the FEV1/VC ratio or the percent VC was
abnormal in seven adult patients (Fig 5
). Five adult patients showed decreased perfusion in the left lung, and
one adult patient showed decreased perfusion in the right lung. A
ventilation/perfusion (
/
) mismatch was present in the
left lung in four adult patients (patients 1, 2, 4, and 12) and in the
right lung in one adult patient (patient 3). There was one adult
patient whose perfusion and ventilation were equally disturbed with no
/ mismatch (patient 9).
|
Discussion
|
|---|
Patients with ASD may become cyanotic with increasing age. This is
caused by a reverse shunt through the defect, which is caused by
progressive tricuspid regurgitation, which, in turn, is due to
pulmonary hypertension. A jet originating from tricuspid regurgitation
can cross the ASD, resulting in a right-to-left shunt.3
Performing contrast echocardiography by using hand-agitated 5%
dextrose in water from peripheral veins, is the most sensitive
method for looking for the reverse shunt. We performed contrast
echocardiography under normal breathing so as not to enlarge the
reverse shunt by straining. In the present study, although the
degree of right-to-left shunt was more than moderate in only 4 of the
13 adult patients, arterial hypoxemia was present in 11 adult patients,
if arterial PO2 of more than 80 mm Hg
is considered normal. Therefore, the degree of arterial hypoxemia seen
in the adult group cannot be completely explained by this reverse
shunt.
PO2 was lower in the left upper
pulmonary vein than in the right pulmonary vein in all of the adult
patients, but there was no difference between the right and left
pulmonary veins in the children. Therefore, this difference is not
congenital but acquired. It is not clear whether this is specific to
adult ASD patients, because drawing blood from both pulmonary veins is
possible only in the presence of ASD or patent foramen ovale. Hypoxemia
in the left upper pulmonary vein significantly contributed to arterial
hypoxemia in the adult group, because the difference in oxygen
saturation between the right and left upper pulmonary veins may derive
from the right-to-left shunt being directed to the left upper pulmonary
vein. However, because the transesophageal contrast echocardiography,
which can visualize the left upper pulmonary vein easily and was
performed in 11 of the 13 adult patients, did not show any bubble
toward the left upper pulmonary vein during right-to-left shunting in
any patient, this possibility is unlikely.
As patients with ASD age, the main pulmonary artery may enlarge and
compress the left bronchus, which is progressing pulmonary vascular
disease. Pulmonary vascular resistance was > 4 Wood units in 5
of the 13 adult patients. In addition, the increase in heart volume of
the left thoracic cavity may collapse that part of the lung, resulting
in / mismatch. / mismatch was present in 5
of the 10 adult patients undergoing the pulmonary / scan:
in the left lung in four patients, and in the right lung in one
patient.
The result of ventilatory function tests in the present study
showed that either FEV1/FVC or percentage of VC
was abnormal in seven patients, reflecting the above speculation.
Hypoxemia in the left upper pulmonary vein was present even in the
remaining five patients with normal pulmonary function tests whose
cardiothoracic ratio was rather small in comparison with that of
patients with abnormal pulmonary function tests. Accordingly, the
difference in PO2 between the right and left
pulmonary veins cannot be completely explained by this mismatch.
During cardiopulmonary bypass, some blood returns to the left atrium
while the aorta is cross-clamped.4
An abundant network of
collaterals has been observed between the bronchial vein and
the pulmonary vein in normal lungs obtained at
autopsy.5
In patients with inflammatory pleuritis,
neovascularization can develop from the internal thoracic artery and
intercostal arteries and drain into pulmonary veins.6
Pulmonary veins are also reported as a draining chamber for collaterals
derived from portal hypertension.7
,8
Most of the
collaterals reported so far were located in the left pulmonary
vein.9
In the present study, the pulmonary scintigram
showed hypoperfusion of the left lung in 5 of the 10 adult patients
undergoing pulmonary ventilation and the perfusion scan. This decreased
pulmonary blood flow in the left lung may change bronchial circulation
after an increase in pulmonary blood flow for a long period of time.
The deoxygenated blood, after passing through the capillary phase from
the bronchial artery or intercostal artery, might drain into the
left pulmonary vein more often than into the right vein.
The difference in PO2 between the right
and left upper pulmonary veins caused the difference in the calculation
of oxygen content to range from 3 to 34 mL. This difference in oxygen
content was sometimes severe enough to influence the measurement of
pulmonary blood flow but was often insignificant because the
relationship between PO2 and
saturation is not linear but sigmoid. When the shunt ratio is measured
using oximetry in patients with ASD, blood drawn from either pulmonary
vein is used as a reference.10
This is based on the
assumption that the oxygen contents in the right and left pulmonary
veins are equal. In the first patient who had severely disturbed
pulmonary function, presumably due to increased heart volume and
combined pulmonary vascular disease, the calculated pulmonary blood
flow was two times greater when the average of the right and left upper
pulmonary veins was used as a reference than when only the right upper
pulmonary vein was used. The use of average oxygen contents is
also based on the assumption that both the right and left pulmonary
flows are equal, which was not proved to be correct.
Care must be taken in measuring an intracardiac shunt in patients with
ASD if only the right upper pulmonary vein is used as a reference. In
addition to right-to-left shunt at the atrial level, decreased
PO2 in the left upper pulmonary vein
may contribute to decreased arterial
PO2.
Study Limitations
We did not offer a very clear explanation as to the cause of this
difference; we simply described the phenomenon. Even during thoracic
surgery, it is impossible to take blood samples from both pulmonary
veins simultaneously when the fraction of inspired oxygen is 20% of
the blood. Further study is necessary but can be done only in
the presence of an ASD or patent foramen ovale.
|
Acknowledgements
|
|---|
ACKNOWLEDGMENT: We acknowledge the helpful advice and comment of
Professor Peter Harris, formerly of the Royal Brompton and National
Heart Hospital, London, England.
|
Footnotes
|
|---|
Correspondence to: Takashi Konishi MD, Department of Cardiology,
Tenri Hospital, 200 Mishimacho, Tenri City, 632-8552 Japan; e-mail:
igakan@kcn.ne.jp
Abbreviations: ASD = atrial septal
defect; VC = vital capacity;
/ = ventilation/perfusion ratio
Received for publication June 6, 1998.
Accepted for publication October 13, 1998.
|
References
|
|---|
-
Remy-Jardin, M, Remy, J, Wallaert, B (1990) Right-to-left shunting through a patent foramen ovale without pulmonary hypertension. Chest 97,1250-1252[Abstract/Free Full Text]
-
Dear, WE, Chen, P, Barasch, E (1995) Sixty-eight-year-old woman with intermittent hypoxemia. Circulation 91,2284-2289[Free Full Text]
-
Kai, H, Koyanagi, S, Hirooka, Y, et al (1994) Right-to-left shunt across atrial septal defect related to tricuspid regurgitation: assessment by transesophageal Doppler echocardiography. Am Heart J 127,578-584[CrossRef][ISI][Medline]
-
Baile, EM, Ling, H, Heyworth, JR, et al (1985) Bronchopulmonary anastomotic and noncoronary collateral blood flow in humans during cardiopulmonary bypass. Chest 87,749-754[Abstract/Free Full Text]
-
Murata, K, Itoh, H, Todo, G, et al (1986) Bronchial venous plexus and its communication with pulmonary circulation. Invest Radiol 21,24-30[CrossRef][ISI][Medline]
-
Chino, M, Kawaguchi, T, Sakai, T, et al (1991) Intercostal-to-pulmonary arterial anastomosis, complicated by high-output heart failure: case report. Angiology 42,256-260
-
Sano, A, Kuroda, Y, Moriyasu, F, et al (1982) Porto-pulmonary venous anastomosis in portal hypertension demonstrated by percutaneous transhepatic cine-portography. Radiology 144,479-484[Abstract/Free Full Text]
-
Sano, A, Nishizawa, S, Sasai, K, et al (1984) Contrast echocardiography in detection of portopulmonary venous anastomosis. Am J Roentgenol 142,137-140[Abstract/Free Full Text]
-
Sano, A, Nishizawa, S, Sasai, K, et al (1983) Demonstration of porto-pulmonary venous anastomosis by cine-portography and contrast echocardiography [in Japanese]. Nihonrinshougazouigakuzasshi 2,402-412
-
Grossman, W, Baim, DS (1991) Cardiac catheterization, angiography, and intervention 4th ed. ,166 Lea & Febiger Philadelphia, PA.
TOP
Abstract
Introduction
