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The application of pneumotachography on small unrestrained animals
Comp. Bxrkem
Pkyaiol., 1978 Vol 5%
pp. 425 IO 427 Perpmon
Press. Primed m Great Britain
SHORT COMMUNICATION
THE
APPLICATION ON
SMALL
OF
PNEUMOTAC~OGRAP~Y
UNRESTRAINED
ANIMALS
MOGENS L. GLASS, STEPHENC. WOOD* and KJELL JOHANSEN Department of Zoophysiology. University of Aarhus. DK-8000 Aarhus C., Denmark lRrcriued
14 June
1977)
Abstract-l. Pneumotachography, as a method of measuring ventilation is common in human physiology. 2. In contrast. comparative physiology has not taken advantage of the method due to difficulties in applying the conventional version of the method on small animals. 3. These difficulties have been solved by combining a close-fitting face mask with a built-on. lightweight flow transducer head. This modification of the method is inexpensive and permits measurement on unrestrained animals,
INTRODUCTION Pn~umotachography, as a method of measuring gas flow, was introduced by Fleisch (1925). The measurement is based on the principle that laminar flow of a gas of constant viscocity is proportional to the pressure gradient along a tube system of constant bore and length (Poiseuille, 1840). Measurement of the pressure gradient permits calculation of air flow, and volumes are derived by integration of the flow signals. Tube systems and a sensitive differential pressure transducer are commercially available as a unit [Godart, Hewlett-Packard (H.P.)]. The tube systems (Fleisch flow transducer heads) are interchangeable as each transducer head is dimensioned for use in a limited flow range. The flow signals are integrated electronically (e.g. by the Godart model) and outputs provided for the display of volumes by a recorder. The HP model provides the same information when delivered with signal conditioners. The advantage of pneumotachography for measurement of gas flow are low resistance, minimum of rebreathing of the expired gas, and very fast response characteristics. Although this method is widely employed in clinical studies of respiration it has rarely been applied in comparative physiology. One reason for this may be that commercial transducer heads are often too large and heavy and the sensitivity too low for use in small animals, The present paper describes the construction and use of light weight Fleisch transducer heads as employed in studies of amphibians. reptiies and birds. Construction
of
the face
mask and the Fleisch
head
The success of this method depends on the use of a light-weight, close-fitting face mask with a minimum of dead space between the nostrils of the animal and
* Present address: Department versity of New Mexico. School New Mexico 87131, U.S.A.
of
of
Physiology,
The Uni-
Medicine. Albuquerque, 425
the flow transducer head. A mold of the head of each animal is made using dental impression material (Zelgan, De Trey, Ziirich). The head of each animal is submerged in a gel (37 g Zelgan/lOO ml H20). Within two minutes the gel hardens into a rubbery consistency and the head can be pulled out without distorting the mold. If the species in question is unable to tolerate a 2-min breath holding period, tracheal intubation may be used during the period needed for the setting of the gel. Once the mold is prepared. it is filled with a 1s; solution of KAl (SO,), . 12H20 which prevents formation of air bubbles in the gypsum used for the cast. The mold is then emptied. flushed dry with air, and filled with the gypsum solution. After the gypsum dries, the impression material is easily peeled off and a detailed cast of the head is available for construction of the mask. The face mask is made from a flexible polymer called Drufosoft (Dreve Dentamid. Unna. Germany) which is supplied in flat sheets of 1.5 or 2mm thickness. When heated, the material becomes very pliable and forms a close fit when pressed against the gypsum cast. Once the basic mask is formed it may be sculptured using a heated scalpel blade. The flow transducer heads are constructed from plastic syringe barrels. A 2-3 cm length of the syringe barrel is packed with small diameter polyethylene tubing. The combination of syringe volume. length and size of tubing selected will depend on the expected flow range. The strain gauge systems of the commercial pneumotachographs are constructed to monitor pressure differentials of a few mm H,O. To keep the pressure drop along the transducer head in this range, the resistance has to be low if flow is rapid. Holes are drilled at each end of the syringe barrel and 13-gauge steel tubes are glued into place. Thickwalled. flexible tubing is used to connect the steel tubes with the connections of the differential pressure transducer. It is important to use tubing which does not easily kink or compress to avoid interference with
MOGENS t,. GLASS, STEPHEN C. Wtxm
426
the pressure measurement. Neophrene tubing is recommended. These self-made Bow transducer heads can be constructed at a very low cost and are also much lighter than those commercially available (3 g compared with 166 g for an equally sensitive commercial model). For a given Fleisch Row transducer head the flow/ pressure relationship is linear only within a certain range, i.e. if flow becomes turbulent. the pressure drop becomes proportional to the square of the air Row. The linear range may be determined by emptying a known volume from a spirometer through the transducer head at different rates. Volume calibration is achieved using a syringe. The syringe volume is changed at a rate which produces flow signals within the linearity range of the transducer head. Detailed discussions of calibration are given by Hobbes (1966) and Grenvik rt al. (1967). The transducer head can be firmly fixed to the face mask by wrapping Drufosoft around the syringe barrel. Face mask and the
and
KJELL
.~MAYSI
*.
It is necessary to check that the glue forms an alrtlghr seal during the period of measurement. This can hc done by sucking a known amount of air through 3 catheter terminating in a hypodermic needle that penetrates the face mask close to the nostrils. If a fraction
Fieisrh
Head
transducer head can be melted together when heated. This may be important. since a compact single unit will stand the mechanical hazards of using the technique on unrestrained animab ~r~~ar~iio?~.~ ,for ~e~~u~~~n~rli The mask can be glued to the head of the animaI using a rapidly setting epoxy glue (Araidite. rapid).
Vf
lOOmi
P,o,
V,
1OOmmHg
Fig. 1. Sckmatic drawmg which illustrates the application of the face mask technique as used by Wood YI crl. (1977) in a study of respiration in varanid lizards. Notice that the mask and the transducer head form a single compact unit.
!
Flamingo
~~
2mt
Nile Flow
cracadile
20Oml+ set-f
M
Time mark
20 sec.
Fig. 2. Pen tracings of gas Aows, tidal volumes and expired gases from the app~i~at~on of the mask technique on a bird, a frog and a crocodile. The two upper tracings show inspired tidal volume and expired POz of a flamingo (Phoenicopterus nrber). The tracings in the middle show inspired and expired gas flow and inspired tidal volume in a bullfrog (Ram cotesbeiana). The four bottom tracings show expired dry gas contents of O2 and CO,, inspired and expired gas flow and inspired tidal volume of a nile crocodile (Crocadylus niloticus). Notice the intermittent breathing in the frog and the crocodile in contrast to the continuous pattern of the bird. The drift on the inspired volume reading of the bottom tracing is due to continuous sampling of expired gases to a respiratory mass spectrometer [Medspect 2). This drift can be electron&&y removed. but may provide a check that ieaks or plugs do not occur in the mask or the sampie tine.
Short communicatjon of the volume does not pass through the transducer head, then the volume signal will be lower than expected from the preceeding calibration. The catheter can serve purposes other than calibration, as it can be used as a probe for continuous sampling of expired air to fast gas analyzers. The simultaneous measurement of expired air flow by a pneumotach and of gas concentrations by mass spectrometers or other fast gas analyzers permits detailed analysis of pulmonary function (Muysers & Smidt, 1969). Extensive information on respiratory characteristics during rest or activity can thus be obtained by combining the face mask technique with various other methods. Figure 1 shows the head of a varanid lizard with face mask and flow transducer schematically drawn in. Figure 2 shows representative tracings obtained from application of the method on a bird, a bullfrog and a crocodile.
427 REFERENCES
FLEISCHA.
(1925) Der Pneumotachograph-ein Apparat zur Geschwindigkeitsregistrierung der Atemluft. Pfliigers
Arch. ges. Physiol. 209, 713-122. GRENVIK A.. HEDSTRANDU. & SJ&REN H. (1966) Problems in pneumota~hography. Acta anaestk. stand. 10, 147-155.
HOBOESA. F. T. (1967) A comparison of methods of calibrating the pneumotachograph. Br. J. Anaesth. 39, 899-907. MUYSERSK. & SMIDT U.
(1969) Respirations-Massenspekrrometrie. Schattauer. Stuttgart. POISEUILLE .J. L. M. (1840) Recherches experimentales sur les mouvements des liquides dans les tubes des tres petits diamitres. C.r. hehd. Stfanc. Acad. Sci. Paris XI. 961-967. 104-1048.
Wool S. C.. GLASSM. L. & JOHANSENK. (1977) Effects of temperature on respiration and acid-base balance in a monitor lizard. J. camp. Physiol. 116 (3). 287-296.
Pkyaiol., 1978 Vol 5%
pp. 425 IO 427 Perpmon
Press. Primed m Great Britain
SHORT COMMUNICATION
THE
APPLICATION ON
SMALL
OF
PNEUMOTAC~OGRAP~Y
UNRESTRAINED
ANIMALS
MOGENS L. GLASS, STEPHENC. WOOD* and KJELL JOHANSEN Department of Zoophysiology. University of Aarhus. DK-8000 Aarhus C., Denmark lRrcriued
14 June
1977)
Abstract-l. Pneumotachography, as a method of measuring ventilation is common in human physiology. 2. In contrast. comparative physiology has not taken advantage of the method due to difficulties in applying the conventional version of the method on small animals. 3. These difficulties have been solved by combining a close-fitting face mask with a built-on. lightweight flow transducer head. This modification of the method is inexpensive and permits measurement on unrestrained animals,
INTRODUCTION Pn~umotachography, as a method of measuring gas flow, was introduced by Fleisch (1925). The measurement is based on the principle that laminar flow of a gas of constant viscocity is proportional to the pressure gradient along a tube system of constant bore and length (Poiseuille, 1840). Measurement of the pressure gradient permits calculation of air flow, and volumes are derived by integration of the flow signals. Tube systems and a sensitive differential pressure transducer are commercially available as a unit [Godart, Hewlett-Packard (H.P.)]. The tube systems (Fleisch flow transducer heads) are interchangeable as each transducer head is dimensioned for use in a limited flow range. The flow signals are integrated electronically (e.g. by the Godart model) and outputs provided for the display of volumes by a recorder. The HP model provides the same information when delivered with signal conditioners. The advantage of pneumotachography for measurement of gas flow are low resistance, minimum of rebreathing of the expired gas, and very fast response characteristics. Although this method is widely employed in clinical studies of respiration it has rarely been applied in comparative physiology. One reason for this may be that commercial transducer heads are often too large and heavy and the sensitivity too low for use in small animals, The present paper describes the construction and use of light weight Fleisch transducer heads as employed in studies of amphibians. reptiies and birds. Construction
of
the face
mask and the Fleisch
head
The success of this method depends on the use of a light-weight, close-fitting face mask with a minimum of dead space between the nostrils of the animal and
* Present address: Department versity of New Mexico. School New Mexico 87131, U.S.A.
of
of
Physiology,
The Uni-
Medicine. Albuquerque, 425
the flow transducer head. A mold of the head of each animal is made using dental impression material (Zelgan, De Trey, Ziirich). The head of each animal is submerged in a gel (37 g Zelgan/lOO ml H20). Within two minutes the gel hardens into a rubbery consistency and the head can be pulled out without distorting the mold. If the species in question is unable to tolerate a 2-min breath holding period, tracheal intubation may be used during the period needed for the setting of the gel. Once the mold is prepared. it is filled with a 1s; solution of KAl (SO,), . 12H20 which prevents formation of air bubbles in the gypsum used for the cast. The mold is then emptied. flushed dry with air, and filled with the gypsum solution. After the gypsum dries, the impression material is easily peeled off and a detailed cast of the head is available for construction of the mask. The face mask is made from a flexible polymer called Drufosoft (Dreve Dentamid. Unna. Germany) which is supplied in flat sheets of 1.5 or 2mm thickness. When heated, the material becomes very pliable and forms a close fit when pressed against the gypsum cast. Once the basic mask is formed it may be sculptured using a heated scalpel blade. The flow transducer heads are constructed from plastic syringe barrels. A 2-3 cm length of the syringe barrel is packed with small diameter polyethylene tubing. The combination of syringe volume. length and size of tubing selected will depend on the expected flow range. The strain gauge systems of the commercial pneumotachographs are constructed to monitor pressure differentials of a few mm H,O. To keep the pressure drop along the transducer head in this range, the resistance has to be low if flow is rapid. Holes are drilled at each end of the syringe barrel and 13-gauge steel tubes are glued into place. Thickwalled. flexible tubing is used to connect the steel tubes with the connections of the differential pressure transducer. It is important to use tubing which does not easily kink or compress to avoid interference with
MOGENS t,. GLASS, STEPHEN C. Wtxm
426
the pressure measurement. Neophrene tubing is recommended. These self-made Bow transducer heads can be constructed at a very low cost and are also much lighter than those commercially available (3 g compared with 166 g for an equally sensitive commercial model). For a given Fleisch Row transducer head the flow/ pressure relationship is linear only within a certain range, i.e. if flow becomes turbulent. the pressure drop becomes proportional to the square of the air Row. The linear range may be determined by emptying a known volume from a spirometer through the transducer head at different rates. Volume calibration is achieved using a syringe. The syringe volume is changed at a rate which produces flow signals within the linearity range of the transducer head. Detailed discussions of calibration are given by Hobbes (1966) and Grenvik rt al. (1967). The transducer head can be firmly fixed to the face mask by wrapping Drufosoft around the syringe barrel. Face mask and the
and
KJELL
.~MAYSI
*.
It is necessary to check that the glue forms an alrtlghr seal during the period of measurement. This can hc done by sucking a known amount of air through 3 catheter terminating in a hypodermic needle that penetrates the face mask close to the nostrils. If a fraction
Fieisrh
Head
transducer head can be melted together when heated. This may be important. since a compact single unit will stand the mechanical hazards of using the technique on unrestrained animab ~r~~ar~iio?~.~ ,for ~e~~u~~~n~rli The mask can be glued to the head of the animaI using a rapidly setting epoxy glue (Araidite. rapid).
Vf
lOOmi
P,o,
V,
1OOmmHg
Fig. 1. Sckmatic drawmg which illustrates the application of the face mask technique as used by Wood YI crl. (1977) in a study of respiration in varanid lizards. Notice that the mask and the transducer head form a single compact unit.
!
Flamingo
~~
2mt
Nile Flow
cracadile
20Oml+ set-f
M
Time mark
20 sec.
Fig. 2. Pen tracings of gas Aows, tidal volumes and expired gases from the app~i~at~on of the mask technique on a bird, a frog and a crocodile. The two upper tracings show inspired tidal volume and expired POz of a flamingo (Phoenicopterus nrber). The tracings in the middle show inspired and expired gas flow and inspired tidal volume in a bullfrog (Ram cotesbeiana). The four bottom tracings show expired dry gas contents of O2 and CO,, inspired and expired gas flow and inspired tidal volume of a nile crocodile (Crocadylus niloticus). Notice the intermittent breathing in the frog and the crocodile in contrast to the continuous pattern of the bird. The drift on the inspired volume reading of the bottom tracing is due to continuous sampling of expired gases to a respiratory mass spectrometer [Medspect 2). This drift can be electron&&y removed. but may provide a check that ieaks or plugs do not occur in the mask or the sampie tine.
Short communicatjon of the volume does not pass through the transducer head, then the volume signal will be lower than expected from the preceeding calibration. The catheter can serve purposes other than calibration, as it can be used as a probe for continuous sampling of expired air to fast gas analyzers. The simultaneous measurement of expired air flow by a pneumotach and of gas concentrations by mass spectrometers or other fast gas analyzers permits detailed analysis of pulmonary function (Muysers & Smidt, 1969). Extensive information on respiratory characteristics during rest or activity can thus be obtained by combining the face mask technique with various other methods. Figure 1 shows the head of a varanid lizard with face mask and flow transducer schematically drawn in. Figure 2 shows representative tracings obtained from application of the method on a bird, a bullfrog and a crocodile.
427 REFERENCES
FLEISCHA.
(1925) Der Pneumotachograph-ein Apparat zur Geschwindigkeitsregistrierung der Atemluft. Pfliigers
Arch. ges. Physiol. 209, 713-122. GRENVIK A.. HEDSTRANDU. & SJ&REN H. (1966) Problems in pneumota~hography. Acta anaestk. stand. 10, 147-155.
HOBOESA. F. T. (1967) A comparison of methods of calibrating the pneumotachograph. Br. J. Anaesth. 39, 899-907. MUYSERSK. & SMIDT U.
(1969) Respirations-Massenspekrrometrie. Schattauer. Stuttgart. POISEUILLE .J. L. M. (1840) Recherches experimentales sur les mouvements des liquides dans les tubes des tres petits diamitres. C.r. hehd. Stfanc. Acad. Sci. Paris XI. 961-967. 104-1048.
Wool S. C.. GLASSM. L. & JOHANSENK. (1977) Effects of temperature on respiration and acid-base balance in a monitor lizard. J. camp. Physiol. 116 (3). 287-296.