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A valve assembly for studying pulmonary function in trauma patients
A valve assembly for studying pulmonary function in trauma patients Kenneth W. Spitzer, Alan H. Morris, and Hartmut Arnhold, Fort Sam Houston, Texas
During the course of studying lung function in acutely burned patients, we have developed an apparatus which has greatly facilitated the performance of our pulmonary measurements. The central element is a rotating valve assembly, similar to that described by Svanberg,' which accepts several interchangeable attachments. The patient is brought into the laboratory in either a bed or wheelchair and is positioned at the desired angle. No further patient manipulation is required. The valve attachments are simply interchanged for the performance of different tests of lung function. The valve (Figs. 1 and 2) consists of two sliding acrylic plastic plates, ~~ ti inch thick, which can be adjusted to connect the patient, at port AI, to either port A2 or port A3. The plates rotate about a central axis at C and are held together by a compression spring at C and a spring assembly at B. The plates are moved by grasping the stainless steel handles (}) t; inch diameter). The clamp provides attachment for a % inch diameter If-shaped steel support rod. In order to prevent leaks and reduce friction, From the Metabolic Branch (Pulmonary Section) and the Bioengineering Branch, United States Army Institute of Surgical Research. Brooke Army Medical Center, Fort Sam Houston, Texas 78234. Received for publication June 25, 1973. Address for reprints: Alan H. Morris, M.D., Pulmonary Section, L.D.S. Hospital, 325 8th Ave., Salt Lake City, Utah 84103.
a liberal supply of stopcock grease is applied to the interface between the two plates. The support rod and valve are suspended by an adjustable length of cotton cord (Fig. 3). The angle of the apparatus with respect to horizontal is controlled by moving sliders SI or S2 along the support rod. S2 is used with patients in the supine position and SI with patients in the semisupine or upright positions. The adjustable suspension cord and sliders enable the apparatus to be quickly positioned, regardless of patient position. Tests Valve attachments permit the following tests or groups of tests to be performed: ( 1) Douglas bag collections for ventilation and open-circuit oxygen consumption studies, (2) pulmonary mechanics, (3) nitrogen washout, and (4) rebreathing diffusing capacity for carbon monoxide (OLeo). Douglas bag collection. The patient is connected at port A 1 and breathes room air through a modified Otis-McKerrow nonrebreathing valve (Warren E. Collins, Inc., Braintree, Mass.) attached at port A3 (Fig. 1), as shown in Fig. 3. Different size reduction fittings make it possible to attach a variety of mouthpieces and cuffed tracheostomy tubes to the valve. The reduction fitting for the large rubber mouth-
607
The Journal of
608
Spitzer, Morris, Arnhold
Thoracic and Card iovascular Surgery
Fig . 1. Rot ating valve . A 1, Patient port. A 2 and A3, Ports for attachments. B. Spring assembly which helps hold sliding plates together. C, Cen tral axis with compression spring . Clamp is used to connect va lve to support rod.
piece (Warren E. Collins, Inc . ) is an aluminum tube (1 .312 inches outer diameter [0. D.], 1.19 inches inner diameter [I. D.], and 2.88 inches long) (Fig. 3). We have, with this apparatus, made 158 measurements of oxygen consumption, carbon dioxide production, and minute ventilation in 31 burned patients. Pulmonary mechanics. A shutter and pneumotachygraph are employed with the valve for lung mechanics studies. The shutter is similar to the one described by Mead" and is used to occlude the airway for 1 to 3 seconds in order to make static pressure-volume measurements of the lung. It is made of two plates of 0 .5 inch thick acrylic plastic held together by several bolts. The stainless steel shutter blade (0 .0 1 inch thick) is attached to a rotary solenoid (Model H2383-032, Ledex, Inc ., Dayton, Ohio), which is remotely activ ated by a foot switch . Transpulmonary pressure is measured with a differential pressure transducer (PM 131 TC ± 2.5 , Statham Instru-
ments, Inc. , Oxnard, Calif.) mounted on top of the shutter. One chamber of the transducer measures lateral airway pressure on the patient side of the shutter blade and the other is connected to an esophageal balloon similar to that described by MilicEmili .3 A volume signal is obtained by electronic integration of the flow signal from a Fleisch No . 4 pneumotachygraph (Instrumentation Associates, Inc ., New York, N. Y.) and a differential pressure transducer (Model DP45, Validyne Engineering Corp., Northridge, Calif.) (Fig. 4). The Model DP45 is a variable-reluctance differential pressure transducer with chambers of equal volume ( 10-2 cubic inches) and a pressure range of ± 1 inch of water. It is very insensit ive to mechanical movement and gravitational effects and can be attached directly to the pneumotachygraph, eliminating the need to isolate it from the patient. This eliminates the need for long connecting tubes between the pressure transducer and pneurnotachygraph and avoids the associated adverse effect upon frequency response. Other transducers of comparable sensitivity which we examined (Statham PM 15 ± 0.04 and Statham PM 5 ± 0.2) required isolation from the patient. Another transducer used with pneumotachygraphs, the Hewlett Packard Model 270 (Sanborn Co., Waltham, Mass.), also required isolation. Acrylic plastic plates, :yg inch thick , are bolted to each side of the pressure transducer and glued to a thick acrylic plastic support arm (Fig. 4) . A concave depression (0.27 inch deep) in each plate is located directly over each transducer port, and an airtight connection is maintained with a rubber O-ring (1/2 inch O.D. and :yg inch J.D .) . Stainless steel tubes (0.202 inch O.D., 0 .169 inch J.D., and 0.625 inch long), connected to the depressions, extend 0.25 inch beyond the acrylic plates. These tubes are connected to the flowmeter (pneumotachygraph) pre ssure ports with polyvinyl chloride tubing (0 .238 inch O.D., 0.188 inch J.D ., and 1.5 inches long) . The acrylic plastic support arm, holding the
Volume 66 Number 4
Valve assembly for studying pulmonary function
609
October, 1973
------r----
---/06· 4/·
4/·
Handle
Fig. 2. Top view (top) and end view (bottom) of valve, AI, Patient port. A2 and A3, Ports for attachments. B, Spring assembly which helps hold sliding plates together. C, Central axis with compression spring. Clamp is used to connect valve to support rod.
transducer, is bolted to the flowmeter (pneumotachygraph). The flowmeter/transducer unit is attached to the rotating valve at port A2 with a conical acrylic. plastic fitting. Air flow, transpulmonary pressure, and tidal volume are simultaneously recorded on a Model DR12 recorder (Electronics for Medicine, Inc., White Plains, N. Y.). The output of the shutter and flowmeter/ transducer assembly (Fig. 5) is a linear function of flow up to the maximum flow tested (5 L. per second). The response of the flowmeter/transducer system was tested
by step function analysis' (damped natural frequency = 160 Hz; damping ratio = 0.15). The frequency response of the system was also tested with a constant sinusoidal volume signal of varying frequency. * A mechanical piston pump (stroke volume = 20 ml.) was used as the volume generator. The output (RMS voltage) of the Model DP45 transducer was proportional to frequency at all volume generator frequencies ·Courtesy of Dr. Edward Michaelson, Biodynamics Branch, U. S. Air Force School of Aerospace Medicine, Brooks Air Force Base, San Antonio, Texas.
The Journal 0/
6 10
Spitzer, Morris, Arnhold
Thoracic and Cardiovascular Surgery
Fig. 3. Valve with Otis-McKerrow valve attached for collection of expired air. Sliders (51 and 52) are used to adjust the angle of the apparatus. as required by the patient's position . SUPPORT ARM
TRANSDUCER
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I
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,
,
:"~
ATTACHMENT I\ \. POINT FOR ARM '\, ,, ~ . ~
/
TRANSDUCER
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I
-: :;_= '- - ~=-":'"'- : "~ " /" , Ii
0 \
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~,
RUBBER O-RING
r:
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ACRYLIC PLASTIC. \; thick
,
~
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/ FLOWMETER PORT FLOWMETER
:
I- "L~I
.~od.
\ 'id
CONCAVE DEPRESSION.O.27"deep METAL TUBE. O.202'oo.O.169"id.O.625"long
, I O.238"od.O.l89"id,1.50"long 'l .
POLYVINVLCHLORIDE TUBING.
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FLOWMETER
Fig. 4. Front view (left) and side view (right) of the flowmeter (pneumotachygraph) and transducer showing assembly details and dimensions of the transducer to flowmeter connectors.
up to 14 Hz, the highest frequency tested. The apparatus (shutter and flowmeter/ transducer assembly) can therefore accurately record, without amplitude distortion, respiratory events with frequency contents up to at least 14 Hz and probably up to 25 or 30 Hz. The esophageal balloon signal and the flow signal were found to be in phase at all respiratory rates up to 120 breaths per minute, the highest respiratory frequency with which we tested the apparatus. Using this apparatus, we have recorded approximately 200 individual static lung deflation pressure-volume curves in 11 normal and 15 burned pati ents. We have also performed, in the same number
of subjects , approximately 200 measurements of dynamic lung compliance (breathing spontaneously and at about 60 breaths per minute), inspiratory pulmonary pressure-volume work of breathing (at two respiratory frequencies) , and total pulmonary resistance. Nitrogen washout. In this arrangement (Fig. 6) , the breathe-through sample head of a nitrogen meter (Model 700, Ohio Medical Products, Madison, Wis.) is attached to the patient port Al of the valve and the Otis-McKerrow valve to port A3 (Fig. 1) . The flowmeter is attached to port A2 . The subjects breathe humidified 99.5 to 100 per cent oxygen through the Otis-
Volume 66 Number 4 October, 1973
Valve assembly for studying pulmonary function
Fig. S. Valve with shutter, flowmeter, and transducer connected, as used for pulmonary mechanics studies.
611
Fig. 6. Valve with nitrogen meter sample head, flowmeter, and Otis-McKerrow valve attached, as used for nitrogen washout studies.
Fig. 7. Valve with rebreathing bag and flowmeter in place, as used far carbon monoxide diffusing capacity studies.
McKerrow valve, and the expired gas is collected in a Douglas bag for the calculation of functional residual capacity or residual volume. Tidal volume and end-tidal nitrogen are recorded (Electronics for
Medicine, Model DR 12 recorder). An arterial blood sample drawn for POz analysis at the end of the washout permits an estimation of right-to-left shunting. Rebreathing DLco. The use of the valve
The Journal 0/
6 I 2
Spitzer, Morris, Arnhold
Thoracic and Cardiovascular Surgery
for measurement of OLeo by the rebreathing technique" is illustrated in Fig. 7. The contents of the 6 L. rubber rebreathing bag are continuously circulated through an infrared carbon monoxide analyzer (Model 215A, Beckman Instruments, Inc., Fullerton, Calif.), through inlet and outlet tubes. The bag is attached to the valve with an acrylic plastic cylinder (1.375 inches 0.0., 1.125 inches 1.0., and 2.50 inches long). The patient breathes room air through the flowmeter at port A2. After exhaling to residual volume, the subject is quickly switched to the rebreathing bag. We have made 83 measurements of OLc(I on 14 burned patients and 7 normal subjects with this apparatus. A proposed additional test. The rebreathing carbon dioxide response test described by Read" could be carried out with this valve assembly without the need for a bagbox system. Attachment of the rebreathing bag to the end of the flowmeter would allow measurement of the minute ventilation. The applications of this system are not limited to the tests described above. Modifications of this apparatus should prove useful in the study of lung function in severely ill patients.
tient manipulation. The apparatus has been used to perform numerous measurements of pulmonary mechanics, ventilation, oxygen consumption, carbon monoxide diffusing capacity, and nitrogen washouts in severely burned patients.
Summary
5
A valve assembly which facilitates pulmonary function testing in trauma patients is described. By providing the support and central location for a number of interchangeable parts, it eliminates excessive pa-
We thank Julius V. George, Specialist Sixth Class, for his valuable technical assistance in constructing this apparatus, Drs. B. A. Pruitt, Jr., A. D. Mason, Jr., W. McManus, F. D. Foley, and D. W. Wilmore for reviewing the manuscript, Miss C. Chalkley for the drawn illustrations, and J. A. Kafka and F. T. Rodriguez for the photographs.
REFERENCES
2
3
4
6
Svanberg, L.: Influence of Posture on the Lung Volumes, Ventilation and Circulation in Normals: A Spirometric-Bronchospirometric Investigation, Scand. J. Clin. Lab. Invest. 9: I, 1957 (Suppl. 25). Mead, J., and Whittenberger, J.: Evaluation of Airway Interruption Technique as a Method for Measuring Pulmonary Air-Flow Resistance. J. Appl, Physiol. 6: 408, 1954. Milic-Emili, 1., Mead, J., Turner, J. M., and Glauser. E. M.: Improved Technique for Estimating Pleural Pressure From Esophageal Balloons, J. Appl. PhysioI. 19: 207. 1964. Fry, D. F.: Physiologic Recording by Modern Instruments With Particular Reference to Pressure Recording, Physiol. Rev. 40: 753, 1960. Lewis, B. M., Lin, T. H., Noe, F. E., and Hayford-Welsing, E. J.: The Measurement of Pulmonary Diffusing Capacity for Carbon Monoxide by a Rebreathing Method, J. Clin. Invest. 38: 2073, 1959. Read, D. J. C.: A Clinical Method for Assessing the Ventilatory Response to Carbon Dioxide, Aust. Ann. Med. 16: 20, 1967.
Introductory abstracts Beginning in January, 1974, it is requested that each article begin with a brief abstract. Authors submitting articles on or after September I, 1973, should supply an abstract of ISO words or less.
During the course of studying lung function in acutely burned patients, we have developed an apparatus which has greatly facilitated the performance of our pulmonary measurements. The central element is a rotating valve assembly, similar to that described by Svanberg,' which accepts several interchangeable attachments. The patient is brought into the laboratory in either a bed or wheelchair and is positioned at the desired angle. No further patient manipulation is required. The valve attachments are simply interchanged for the performance of different tests of lung function. The valve (Figs. 1 and 2) consists of two sliding acrylic plastic plates, ~~ ti inch thick, which can be adjusted to connect the patient, at port AI, to either port A2 or port A3. The plates rotate about a central axis at C and are held together by a compression spring at C and a spring assembly at B. The plates are moved by grasping the stainless steel handles (}) t; inch diameter). The clamp provides attachment for a % inch diameter If-shaped steel support rod. In order to prevent leaks and reduce friction, From the Metabolic Branch (Pulmonary Section) and the Bioengineering Branch, United States Army Institute of Surgical Research. Brooke Army Medical Center, Fort Sam Houston, Texas 78234. Received for publication June 25, 1973. Address for reprints: Alan H. Morris, M.D., Pulmonary Section, L.D.S. Hospital, 325 8th Ave., Salt Lake City, Utah 84103.
a liberal supply of stopcock grease is applied to the interface between the two plates. The support rod and valve are suspended by an adjustable length of cotton cord (Fig. 3). The angle of the apparatus with respect to horizontal is controlled by moving sliders SI or S2 along the support rod. S2 is used with patients in the supine position and SI with patients in the semisupine or upright positions. The adjustable suspension cord and sliders enable the apparatus to be quickly positioned, regardless of patient position. Tests Valve attachments permit the following tests or groups of tests to be performed: ( 1) Douglas bag collections for ventilation and open-circuit oxygen consumption studies, (2) pulmonary mechanics, (3) nitrogen washout, and (4) rebreathing diffusing capacity for carbon monoxide (OLeo). Douglas bag collection. The patient is connected at port A 1 and breathes room air through a modified Otis-McKerrow nonrebreathing valve (Warren E. Collins, Inc., Braintree, Mass.) attached at port A3 (Fig. 1), as shown in Fig. 3. Different size reduction fittings make it possible to attach a variety of mouthpieces and cuffed tracheostomy tubes to the valve. The reduction fitting for the large rubber mouth-
607
The Journal of
608
Spitzer, Morris, Arnhold
Thoracic and Card iovascular Surgery
Fig . 1. Rot ating valve . A 1, Patient port. A 2 and A3, Ports for attachments. B. Spring assembly which helps hold sliding plates together. C, Cen tral axis with compression spring . Clamp is used to connect va lve to support rod.
piece (Warren E. Collins, Inc . ) is an aluminum tube (1 .312 inches outer diameter [0. D.], 1.19 inches inner diameter [I. D.], and 2.88 inches long) (Fig. 3). We have, with this apparatus, made 158 measurements of oxygen consumption, carbon dioxide production, and minute ventilation in 31 burned patients. Pulmonary mechanics. A shutter and pneumotachygraph are employed with the valve for lung mechanics studies. The shutter is similar to the one described by Mead" and is used to occlude the airway for 1 to 3 seconds in order to make static pressure-volume measurements of the lung. It is made of two plates of 0 .5 inch thick acrylic plastic held together by several bolts. The stainless steel shutter blade (0 .0 1 inch thick) is attached to a rotary solenoid (Model H2383-032, Ledex, Inc ., Dayton, Ohio), which is remotely activ ated by a foot switch . Transpulmonary pressure is measured with a differential pressure transducer (PM 131 TC ± 2.5 , Statham Instru-
ments, Inc. , Oxnard, Calif.) mounted on top of the shutter. One chamber of the transducer measures lateral airway pressure on the patient side of the shutter blade and the other is connected to an esophageal balloon similar to that described by MilicEmili .3 A volume signal is obtained by electronic integration of the flow signal from a Fleisch No . 4 pneumotachygraph (Instrumentation Associates, Inc ., New York, N. Y.) and a differential pressure transducer (Model DP45, Validyne Engineering Corp., Northridge, Calif.) (Fig. 4). The Model DP45 is a variable-reluctance differential pressure transducer with chambers of equal volume ( 10-2 cubic inches) and a pressure range of ± 1 inch of water. It is very insensit ive to mechanical movement and gravitational effects and can be attached directly to the pneumotachygraph, eliminating the need to isolate it from the patient. This eliminates the need for long connecting tubes between the pressure transducer and pneurnotachygraph and avoids the associated adverse effect upon frequency response. Other transducers of comparable sensitivity which we examined (Statham PM 15 ± 0.04 and Statham PM 5 ± 0.2) required isolation from the patient. Another transducer used with pneumotachygraphs, the Hewlett Packard Model 270 (Sanborn Co., Waltham, Mass.), also required isolation. Acrylic plastic plates, :yg inch thick , are bolted to each side of the pressure transducer and glued to a thick acrylic plastic support arm (Fig. 4) . A concave depression (0.27 inch deep) in each plate is located directly over each transducer port, and an airtight connection is maintained with a rubber O-ring (1/2 inch O.D. and :yg inch J.D .) . Stainless steel tubes (0.202 inch O.D., 0 .169 inch J.D., and 0.625 inch long), connected to the depressions, extend 0.25 inch beyond the acrylic plates. These tubes are connected to the flowmeter (pneumotachygraph) pre ssure ports with polyvinyl chloride tubing (0 .238 inch O.D., 0.188 inch J.D ., and 1.5 inches long) . The acrylic plastic support arm, holding the
Volume 66 Number 4
Valve assembly for studying pulmonary function
609
October, 1973
------r----
---/06· 4/·
4/·
Handle
Fig. 2. Top view (top) and end view (bottom) of valve, AI, Patient port. A2 and A3, Ports for attachments. B, Spring assembly which helps hold sliding plates together. C, Central axis with compression spring. Clamp is used to connect valve to support rod.
transducer, is bolted to the flowmeter (pneumotachygraph). The flowmeter/transducer unit is attached to the rotating valve at port A2 with a conical acrylic. plastic fitting. Air flow, transpulmonary pressure, and tidal volume are simultaneously recorded on a Model DR12 recorder (Electronics for Medicine, Inc., White Plains, N. Y.). The output of the shutter and flowmeter/ transducer assembly (Fig. 5) is a linear function of flow up to the maximum flow tested (5 L. per second). The response of the flowmeter/transducer system was tested
by step function analysis' (damped natural frequency = 160 Hz; damping ratio = 0.15). The frequency response of the system was also tested with a constant sinusoidal volume signal of varying frequency. * A mechanical piston pump (stroke volume = 20 ml.) was used as the volume generator. The output (RMS voltage) of the Model DP45 transducer was proportional to frequency at all volume generator frequencies ·Courtesy of Dr. Edward Michaelson, Biodynamics Branch, U. S. Air Force School of Aerospace Medicine, Brooks Air Force Base, San Antonio, Texas.
The Journal 0/
6 10
Spitzer, Morris, Arnhold
Thoracic and Cardiovascular Surgery
Fig. 3. Valve with Otis-McKerrow valve attached for collection of expired air. Sliders (51 and 52) are used to adjust the angle of the apparatus. as required by the patient's position . SUPPORT ARM
TRANSDUCER
-" ',- ""- 7 --;: ~
\ ~ --
I -r/ ',
/ I
I
, \
,
,
:"~
ATTACHMENT I\ \. POINT FOR ARM '\, ,, ~ . ~
/
TRANSDUCER
:
I
-: :;_= '- - ~=-":'"'- : "~ " /" , Ii
0 \
'i
~,
RUBBER O-RING
r:
Yi':' ~
~ .--/
ACRYLIC PLASTIC. \; thick
,
~
'
/ FLOWMETER PORT FLOWMETER
:
I- "L~I
.~od.
\ 'id
CONCAVE DEPRESSION.O.27"deep METAL TUBE. O.202'oo.O.169"id.O.625"long
, I O.238"od.O.l89"id,1.50"long 'l .
POLYVINVLCHLORIDE TUBING.
,j _ ~-l
FLOWMETER
Fig. 4. Front view (left) and side view (right) of the flowmeter (pneumotachygraph) and transducer showing assembly details and dimensions of the transducer to flowmeter connectors.
up to 14 Hz, the highest frequency tested. The apparatus (shutter and flowmeter/ transducer assembly) can therefore accurately record, without amplitude distortion, respiratory events with frequency contents up to at least 14 Hz and probably up to 25 or 30 Hz. The esophageal balloon signal and the flow signal were found to be in phase at all respiratory rates up to 120 breaths per minute, the highest respiratory frequency with which we tested the apparatus. Using this apparatus, we have recorded approximately 200 individual static lung deflation pressure-volume curves in 11 normal and 15 burned pati ents. We have also performed, in the same number
of subjects , approximately 200 measurements of dynamic lung compliance (breathing spontaneously and at about 60 breaths per minute), inspiratory pulmonary pressure-volume work of breathing (at two respiratory frequencies) , and total pulmonary resistance. Nitrogen washout. In this arrangement (Fig. 6) , the breathe-through sample head of a nitrogen meter (Model 700, Ohio Medical Products, Madison, Wis.) is attached to the patient port Al of the valve and the Otis-McKerrow valve to port A3 (Fig. 1) . The flowmeter is attached to port A2 . The subjects breathe humidified 99.5 to 100 per cent oxygen through the Otis-
Volume 66 Number 4 October, 1973
Valve assembly for studying pulmonary function
Fig. S. Valve with shutter, flowmeter, and transducer connected, as used for pulmonary mechanics studies.
611
Fig. 6. Valve with nitrogen meter sample head, flowmeter, and Otis-McKerrow valve attached, as used for nitrogen washout studies.
Fig. 7. Valve with rebreathing bag and flowmeter in place, as used far carbon monoxide diffusing capacity studies.
McKerrow valve, and the expired gas is collected in a Douglas bag for the calculation of functional residual capacity or residual volume. Tidal volume and end-tidal nitrogen are recorded (Electronics for
Medicine, Model DR 12 recorder). An arterial blood sample drawn for POz analysis at the end of the washout permits an estimation of right-to-left shunting. Rebreathing DLco. The use of the valve
The Journal 0/
6 I 2
Spitzer, Morris, Arnhold
Thoracic and Cardiovascular Surgery
for measurement of OLeo by the rebreathing technique" is illustrated in Fig. 7. The contents of the 6 L. rubber rebreathing bag are continuously circulated through an infrared carbon monoxide analyzer (Model 215A, Beckman Instruments, Inc., Fullerton, Calif.), through inlet and outlet tubes. The bag is attached to the valve with an acrylic plastic cylinder (1.375 inches 0.0., 1.125 inches 1.0., and 2.50 inches long). The patient breathes room air through the flowmeter at port A2. After exhaling to residual volume, the subject is quickly switched to the rebreathing bag. We have made 83 measurements of OLc(I on 14 burned patients and 7 normal subjects with this apparatus. A proposed additional test. The rebreathing carbon dioxide response test described by Read" could be carried out with this valve assembly without the need for a bagbox system. Attachment of the rebreathing bag to the end of the flowmeter would allow measurement of the minute ventilation. The applications of this system are not limited to the tests described above. Modifications of this apparatus should prove useful in the study of lung function in severely ill patients.
tient manipulation. The apparatus has been used to perform numerous measurements of pulmonary mechanics, ventilation, oxygen consumption, carbon monoxide diffusing capacity, and nitrogen washouts in severely burned patients.
Summary
5
A valve assembly which facilitates pulmonary function testing in trauma patients is described. By providing the support and central location for a number of interchangeable parts, it eliminates excessive pa-
We thank Julius V. George, Specialist Sixth Class, for his valuable technical assistance in constructing this apparatus, Drs. B. A. Pruitt, Jr., A. D. Mason, Jr., W. McManus, F. D. Foley, and D. W. Wilmore for reviewing the manuscript, Miss C. Chalkley for the drawn illustrations, and J. A. Kafka and F. T. Rodriguez for the photographs.
REFERENCES
2
3
4
6
Svanberg, L.: Influence of Posture on the Lung Volumes, Ventilation and Circulation in Normals: A Spirometric-Bronchospirometric Investigation, Scand. J. Clin. Lab. Invest. 9: I, 1957 (Suppl. 25). Mead, J., and Whittenberger, J.: Evaluation of Airway Interruption Technique as a Method for Measuring Pulmonary Air-Flow Resistance. J. Appl, Physiol. 6: 408, 1954. Milic-Emili, 1., Mead, J., Turner, J. M., and Glauser. E. M.: Improved Technique for Estimating Pleural Pressure From Esophageal Balloons, J. Appl. PhysioI. 19: 207. 1964. Fry, D. F.: Physiologic Recording by Modern Instruments With Particular Reference to Pressure Recording, Physiol. Rev. 40: 753, 1960. Lewis, B. M., Lin, T. H., Noe, F. E., and Hayford-Welsing, E. J.: The Measurement of Pulmonary Diffusing Capacity for Carbon Monoxide by a Rebreathing Method, J. Clin. Invest. 38: 2073, 1959. Read, D. J. C.: A Clinical Method for Assessing the Ventilatory Response to Carbon Dioxide, Aust. Ann. Med. 16: 20, 1967.
Introductory abstracts Beginning in January, 1974, it is requested that each article begin with a brief abstract. Authors submitting articles on or after September I, 1973, should supply an abstract of ISO words or less.