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The relationship of age to canine cerebral metabolic rate
THE
JOHN
RELATIONSHIP
D.
OF AGE METABOLIC -. -___
MICHENFELDER,
M.D.,
PREVIOUS STUDIES in man have demonstrated a relationship between age and cerebral metabolic rate (CMR). Kennedy and Sokoloff [5] found that the CMRo, of children (up to age II years) was 25% greater than that of young adults. Lassen and associates [6] reported the CMR,,, of elderly adults (more than 66 years old) to be 9% lower than that of young adults. No such relationship has been established for the dog. In earlier canine studies done in this laboratory, a wide variation in individual CMR,,, control values was noted although group mean values were similar [S, 9, 12, 131. The suspicion that at least a part of the observed variation was based on age differences was confirmed in the present study.
MATERIALS
AND
METHODS
Fifteen clipped, unpremeditated dogs more than 6 months old and weighing 12 to 16 kg. were studied in the prone position. Anesthesia was induced and maintained with halothane (1.0%) in nitrogen (60%) and oxygen. After administration of 30 mg. of succinylcholine, From the Mayo Clinic and Mayo Foundation: Section of Anesthesiology, Rochester, Minnesota. This investigation was supported in part by Research Grants NB-7507 and HE-4881 from the National Institutes of Health, Public Health Service. Submitted for publication May 28, 1969.
TO CANINE RATE AND
RICHARD
CEREBRAL
A.
THEYE,
M.D.
the trachea was intubated with a cuffed tube and ventilation was controlled with a Harvard pump. Catheters were inserted into a femoral vein (for drug and blood infusion) and a femoral artery (for sampling and arterial pressure). Muscle paralysis was maintained with intravenously administered succinylcholine ( 150 mg./hr. ) . Temperature was maintained with a water bath. Preparations for direct measurement of blood flow from the isolated sagittal sinus were carried out as previously described [7]. Essential features of the technique include interruption of the extracerebral vessels draining into the sagittal sinus, exposure and cannulation of the posterior portion of the sagittal sinus, and occlusion of the sinus posterior to the cannula. Blood flow was measured by automatic, timed collection in a 23-ml. reservoir maintained at the level of the sagittal sinus. With this technique, 43% of the total brain weight, as determined at autopsy ( primarily cerebral hemispheres), is drained by the cannulated sagittal sinus [7]. This factor (43%) is used in converting units of flow from ml./min. to ml./100 gm./min. Oxygen contents of arterial and sagittal sinus blood were calculated from measured oxygen tension (IL electrode), oxygen satJration, and hemoglobin concentration (IL 182 CO-oximeter) using a factor of 1.34 ml. 0, per gram of saturated hemoglobin. This
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
9,
NO.
11,
NOVEMBER
1969
method had been previously validated by comparison with Van Slyke determinations of 0, content (Goldstein modification) [ 111. Blood glucose determinations were by an enzymatic method. Additional measurements included arterial pH and Pco2 (IL electrodes ) , arterial pressure ( strain-gauge), esophageal and parietal epidural temperatures ( thermistors ) , and inspired halothane concentrations (gas chromatography), Because the exact ages of the dogs studied were unknown and the methods for estimation of age are relatively crude, a specific age could not be assigned to each dog. Instead, the dogs were divided into three age groups based on the degree of wearing of the teeth, the quality of the bone encountered in the skull, and the development of the teeth. The teeth development only permitted confirmation that the dogs were more than 6 months old, as evidenced by the presence of all adult teeth [lo]. Assignments to age groups were made prior to the study by three investigators, including a doctor of veterinary medicine. Mature dogs (more than 3 years old) were identified by the smoothness and wearing of the teeth and the compact bone of the skull. Immature dogs (less than 1.5 years old) showed little or no wearing of the teeth and the bone of the skull was relatively soft and cancellous. Dogs in whom these characteristics were not clearly defined were assigned to a middle-age group (approximately 1.5 to 3 years). There were five dogs in each age group.
in the usual manner. The oxygen-glucose index (O.G.I.) was calculated as described by Cohen and associates [ 11. The data were analyzed by use of the Student t test for independent data.
Studies were initiated only after multiple determinations had established a steady inspired concentration of halothane (l.O%)), a mean arterial pressure above 80 mm. Hg, a between 35 and 45 mm. Hg, and an ho, epidural temperature of 37.O”C. In each dog, 15 to 20 successive determinations of blood flow and arterial-sagittal sinus blood oxygen content differences were made. Blood for glucose analysis was only taken during periods of steady blood flow; a minimum of three arterial and venous samples were analyzed. The CMRO,, CMR glucose, and cerebral vascular resistance (CVR) were calculated
Table 1. Individual CMRo2 Values (ml./ 100 gm./min.) of 15 Dogs in Three Age Groups
646
RESULTS The largest individual CMRo, values were observed in the youngest dogs, and the smallest values in dogs estimated to be more than 3 years of age (Table 1). Mean CMRo, values for the two groups of young dogs were significantly greater than that value of the mature dogs (more than 3 years old). The difference between immature dogs (0.5 to 1.5 years old) and dogs estimated to be 1.5 to 3 years of age was not significant. The least variability in individual CMRo, values was observed in the mature dogs. The differences in the mean values for CMR glucose, cerebral blood flow, and CVR between the mature and immature dogs were not significant (Table 2) but were compatible with the observed differences in CMRo, values. The calculated values of O.G.I. for the three groups were not significantly different, and no age-related trend is suggested.
DISCUSSION In four previous studies [8, 9, 12, 131, average CMRO, control values in random
Age group, years 0.5 to 1.5
1.5 to 3.0
More than 3.0
4.45
5.10 4.55 4.69 5.57 4.32
4.38 4.52 4.28 4.21 3.70
4.85f 0.22
4.22 0.14
5.91
4.81 5.88 5.32 Mean 5.27’ SE 0.28 *Signifbntly than 3 years ~Significantly than 3 years
different from (P < 0.02). different from old ( P < 0.05).
mean
of
goup
more
mean
of
group
more
old
MICHENFELDER
Table
2.
Cerebral
Metabolism.
AND
THEYE:
ACE
and Circulation
AND
in Three
CEREBRAL
METABOLIC
RATE
Age Groups
Age group, yr. Measurement CMR glucose, mg./lOO gm./min. Oxygen-glucoseindex Cerebral blood flow, ml./100 gm./min. Cerebral vascular resistance, mm. of Hg/ml./lOO gm./min.
0.5 to 1.5 Mean SE 8.3 0.87
89 1.1
groups of 10 or more dogs were similar (4.48 to 4.78 ml./100 gm./min.) despite a wide range in individual values (3.5 to 6.0 ml./100 gm./min. ). In the present study, the mean CMRo, for 15 dogs was 4.78 ml./100 gm./ min., and the range was 3.70 to 5.91 ml./100 gm./min. In these dogs, the variation in individual CMRo, values could be accounted for in part by differences in age. The possibility of a linear relationship between age and CMRo, could not be examined, since the exact ages of the dogs were unknown. In man, Kennedy and Sokoloff [5] were unable to demonstrate a linear relationship over an age range of 3 to 11 years. The magnitude of the effect of age on CMRo, in man and in dogs is similar for approximately similar age groups (assuming a 1:7-year ratio). In both the children studied by Kennedy and Sokoloff and the immature dogs (0.5 to 1.5 years old) of this study, the mean CMRo, was approximately 25% greater than that observed in adults of the species. The basis for high values for CMRo, in the young has not been established, although in man an effect of steroid hormone levels has been postulated [2]. There was no evidence in this study to indicate a difference in the metabolic pathways of the young and adult dog brains. The calculated values of O.G.I. for all dogs were similar, and the group mean values were within the normal range reported for man [I]. In vitro metabolic studies are not available for comparison with the present data. Such metabolic studies have been limited to
0.8 0.04 8 0.2
1.5 to 3.0
Mean 6.9 0.94 72 1.4
SE
More than 3.0 Mean SE
0.4
6.6
0.3
0.02
0.86
0.04
6 0.2
75
1.5
12 0.2
developing dog or rat brain taken from newborn animals [3, 4, 141. In both the children studied by Kennedy and Sokoloff and the dogs of this study, the age range was such that near full development of the brain could be assumed. The findings of this study emphasize the importance of obtaining meaningful individual control values in the experimental animal and the potential for error in comparing individual values in animals of unknown or different ages. SUMMARY In 15 unpremeditated dogs, an inverse relationship between age and cerebral metabolic rate ( CMRo2) was observed. In dogs estimated to be 0.5 to 1.5 and 1.5 to 3 years of age, the mean CMRo, values (5.27 and 4.85 ml./100 gm./min.) were significantly greater than that value of dogs more than 3 years old (4.22 ml./100 gm./min.). No difference in metabolic pathways between the groups was observed. The relative magnitude of the effect of age on CMRo, is similar to that reported for man (assuming a 1:7-year ratio). Such an effect provides a significant potential source of error when comparing individual cerebral metabolic studies in animals of a different or an unknown age. REFERENCES 1. Cohen, P. J., Alexander, S. C., Smith, T. C., Reivich, M., and Wollman, H. Effects of hy647
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
9,
NO.
poxia and normocarbia on cerebral blood flow and metabolism in conscious man. I. AppZ. Physiol. 23: 183, 1967. 2.
Gordan, G. S., Guadagni, N., Pi&i, J., and Adams, J. E. Steroid anesthesia in man: Clinical and cerebral metabolic effects. J. Int. CoZZ. Surg. 25:9, 1956.
3.
Himwich, H. E., Baker, Zelma, and Fazekas, J. F. The respiratory metabolism of infant brain. Amer. J. Physiol. 125:601, 1939.
4.
Himwich, H. E., and Fazekas, J. F. Comparative studies of the metabolism of the brain of infant and adult dogs. Amer. J. Physiol. 132:454, 1941.
5.
6.
648
Kennedy, C., and Sokoloff, L. An adaptation of the nitrous oxide method to the study of the cerebral circulation in children: Normal values for cerebral blood flow and cerebral metabolic rate in childhood. J. Clin. Inuest. 36:1130, 1957. Lassen, N. A., Feinberg, I., and Lane, M. H. Bilateral studies of cerebral oxygen uptake in young and aged normal subjects and in patients with organic dementia. J. CZin. Inueyt. 39:491, 1960.
11,
NOVEMBER
7.
8.
9.
10. 11.
12.
13.
14.
1969
Michenfelder, J. D., Messick, J. M., Jr., and Theye, R. A. Simultaneous cerebral blood flow measured by direct and indirect methods. J. Surg. Rex 8~475, 1968. Michenfelder, J. D., and Theye, R. A. The effects of profound hypocapnia and dilutional anemia on canine cerebral metabolism and blood flow. Anesthesiology. ( In press. ) Michenfelder, J. D., and Theye, R. A. Hypothermia: Effect on canine brain and whole-body metabolism. Anesthesiology 29:1107, 1968. Anatomy of the Dog. PhiladelMiller, M. E. phia: W. B. Saunders Company, 1964, p. 652. Theye, R. A. The determination of 0, and CO, content in blood containing halothane. Anesthesiology 30:325, 1969. Theye, R. A., and Michenfe!der, J. 1). The effect of halothane on canine cerebral metaboljsm. Anesthesiology 29:1113, 1968. Theye, R. A., and Michenfelder, J. D. The effect of nitrous oxide on canine cerebral metabolism. Anesthesiology 29:1119, 1968. Tyler, D. B., and Van Harreveld, A. The respiration of the developing brain. Amer. J. Physiol. 136:600, 1942.
JOHN
RELATIONSHIP
D.
OF AGE METABOLIC -. -___
MICHENFELDER,
M.D.,
PREVIOUS STUDIES in man have demonstrated a relationship between age and cerebral metabolic rate (CMR). Kennedy and Sokoloff [5] found that the CMRo, of children (up to age II years) was 25% greater than that of young adults. Lassen and associates [6] reported the CMR,,, of elderly adults (more than 66 years old) to be 9% lower than that of young adults. No such relationship has been established for the dog. In earlier canine studies done in this laboratory, a wide variation in individual CMR,,, control values was noted although group mean values were similar [S, 9, 12, 131. The suspicion that at least a part of the observed variation was based on age differences was confirmed in the present study.
MATERIALS
AND
METHODS
Fifteen clipped, unpremeditated dogs more than 6 months old and weighing 12 to 16 kg. were studied in the prone position. Anesthesia was induced and maintained with halothane (1.0%) in nitrogen (60%) and oxygen. After administration of 30 mg. of succinylcholine, From the Mayo Clinic and Mayo Foundation: Section of Anesthesiology, Rochester, Minnesota. This investigation was supported in part by Research Grants NB-7507 and HE-4881 from the National Institutes of Health, Public Health Service. Submitted for publication May 28, 1969.
TO CANINE RATE AND
RICHARD
CEREBRAL
A.
THEYE,
M.D.
the trachea was intubated with a cuffed tube and ventilation was controlled with a Harvard pump. Catheters were inserted into a femoral vein (for drug and blood infusion) and a femoral artery (for sampling and arterial pressure). Muscle paralysis was maintained with intravenously administered succinylcholine ( 150 mg./hr. ) . Temperature was maintained with a water bath. Preparations for direct measurement of blood flow from the isolated sagittal sinus were carried out as previously described [7]. Essential features of the technique include interruption of the extracerebral vessels draining into the sagittal sinus, exposure and cannulation of the posterior portion of the sagittal sinus, and occlusion of the sinus posterior to the cannula. Blood flow was measured by automatic, timed collection in a 23-ml. reservoir maintained at the level of the sagittal sinus. With this technique, 43% of the total brain weight, as determined at autopsy ( primarily cerebral hemispheres), is drained by the cannulated sagittal sinus [7]. This factor (43%) is used in converting units of flow from ml./min. to ml./100 gm./min. Oxygen contents of arterial and sagittal sinus blood were calculated from measured oxygen tension (IL electrode), oxygen satJration, and hemoglobin concentration (IL 182 CO-oximeter) using a factor of 1.34 ml. 0, per gram of saturated hemoglobin. This
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
9,
NO.
11,
NOVEMBER
1969
method had been previously validated by comparison with Van Slyke determinations of 0, content (Goldstein modification) [ 111. Blood glucose determinations were by an enzymatic method. Additional measurements included arterial pH and Pco2 (IL electrodes ) , arterial pressure ( strain-gauge), esophageal and parietal epidural temperatures ( thermistors ) , and inspired halothane concentrations (gas chromatography), Because the exact ages of the dogs studied were unknown and the methods for estimation of age are relatively crude, a specific age could not be assigned to each dog. Instead, the dogs were divided into three age groups based on the degree of wearing of the teeth, the quality of the bone encountered in the skull, and the development of the teeth. The teeth development only permitted confirmation that the dogs were more than 6 months old, as evidenced by the presence of all adult teeth [lo]. Assignments to age groups were made prior to the study by three investigators, including a doctor of veterinary medicine. Mature dogs (more than 3 years old) were identified by the smoothness and wearing of the teeth and the compact bone of the skull. Immature dogs (less than 1.5 years old) showed little or no wearing of the teeth and the bone of the skull was relatively soft and cancellous. Dogs in whom these characteristics were not clearly defined were assigned to a middle-age group (approximately 1.5 to 3 years). There were five dogs in each age group.
in the usual manner. The oxygen-glucose index (O.G.I.) was calculated as described by Cohen and associates [ 11. The data were analyzed by use of the Student t test for independent data.
Studies were initiated only after multiple determinations had established a steady inspired concentration of halothane (l.O%)), a mean arterial pressure above 80 mm. Hg, a between 35 and 45 mm. Hg, and an ho, epidural temperature of 37.O”C. In each dog, 15 to 20 successive determinations of blood flow and arterial-sagittal sinus blood oxygen content differences were made. Blood for glucose analysis was only taken during periods of steady blood flow; a minimum of three arterial and venous samples were analyzed. The CMRO,, CMR glucose, and cerebral vascular resistance (CVR) were calculated
Table 1. Individual CMRo2 Values (ml./ 100 gm./min.) of 15 Dogs in Three Age Groups
646
RESULTS The largest individual CMRo, values were observed in the youngest dogs, and the smallest values in dogs estimated to be more than 3 years of age (Table 1). Mean CMRo, values for the two groups of young dogs were significantly greater than that value of the mature dogs (more than 3 years old). The difference between immature dogs (0.5 to 1.5 years old) and dogs estimated to be 1.5 to 3 years of age was not significant. The least variability in individual CMRo, values was observed in the mature dogs. The differences in the mean values for CMR glucose, cerebral blood flow, and CVR between the mature and immature dogs were not significant (Table 2) but were compatible with the observed differences in CMRo, values. The calculated values of O.G.I. for the three groups were not significantly different, and no age-related trend is suggested.
DISCUSSION In four previous studies [8, 9, 12, 131, average CMRO, control values in random
Age group, years 0.5 to 1.5
1.5 to 3.0
More than 3.0
4.45
5.10 4.55 4.69 5.57 4.32
4.38 4.52 4.28 4.21 3.70
4.85f 0.22
4.22 0.14
5.91
4.81 5.88 5.32 Mean 5.27’ SE 0.28 *Signifbntly than 3 years ~Significantly than 3 years
different from (P < 0.02). different from old ( P < 0.05).
mean
of
goup
more
mean
of
group
more
old
MICHENFELDER
Table
2.
Cerebral
Metabolism.
AND
THEYE:
ACE
and Circulation
AND
in Three
CEREBRAL
METABOLIC
RATE
Age Groups
Age group, yr. Measurement CMR glucose, mg./lOO gm./min. Oxygen-glucoseindex Cerebral blood flow, ml./100 gm./min. Cerebral vascular resistance, mm. of Hg/ml./lOO gm./min.
0.5 to 1.5 Mean SE 8.3 0.87
89 1.1
groups of 10 or more dogs were similar (4.48 to 4.78 ml./100 gm./min.) despite a wide range in individual values (3.5 to 6.0 ml./100 gm./min. ). In the present study, the mean CMRo, for 15 dogs was 4.78 ml./100 gm./ min., and the range was 3.70 to 5.91 ml./100 gm./min. In these dogs, the variation in individual CMRo, values could be accounted for in part by differences in age. The possibility of a linear relationship between age and CMRo, could not be examined, since the exact ages of the dogs were unknown. In man, Kennedy and Sokoloff [5] were unable to demonstrate a linear relationship over an age range of 3 to 11 years. The magnitude of the effect of age on CMRo, in man and in dogs is similar for approximately similar age groups (assuming a 1:7-year ratio). In both the children studied by Kennedy and Sokoloff and the immature dogs (0.5 to 1.5 years old) of this study, the mean CMRo, was approximately 25% greater than that observed in adults of the species. The basis for high values for CMRo, in the young has not been established, although in man an effect of steroid hormone levels has been postulated [2]. There was no evidence in this study to indicate a difference in the metabolic pathways of the young and adult dog brains. The calculated values of O.G.I. for all dogs were similar, and the group mean values were within the normal range reported for man [I]. In vitro metabolic studies are not available for comparison with the present data. Such metabolic studies have been limited to
0.8 0.04 8 0.2
1.5 to 3.0
Mean 6.9 0.94 72 1.4
SE
More than 3.0 Mean SE
0.4
6.6
0.3
0.02
0.86
0.04
6 0.2
75
1.5
12 0.2
developing dog or rat brain taken from newborn animals [3, 4, 141. In both the children studied by Kennedy and Sokoloff and the dogs of this study, the age range was such that near full development of the brain could be assumed. The findings of this study emphasize the importance of obtaining meaningful individual control values in the experimental animal and the potential for error in comparing individual values in animals of unknown or different ages. SUMMARY In 15 unpremeditated dogs, an inverse relationship between age and cerebral metabolic rate ( CMRo2) was observed. In dogs estimated to be 0.5 to 1.5 and 1.5 to 3 years of age, the mean CMRo, values (5.27 and 4.85 ml./100 gm./min.) were significantly greater than that value of dogs more than 3 years old (4.22 ml./100 gm./min.). No difference in metabolic pathways between the groups was observed. The relative magnitude of the effect of age on CMRo, is similar to that reported for man (assuming a 1:7-year ratio). Such an effect provides a significant potential source of error when comparing individual cerebral metabolic studies in animals of a different or an unknown age. REFERENCES 1. Cohen, P. J., Alexander, S. C., Smith, T. C., Reivich, M., and Wollman, H. Effects of hy647
JOURNAL
OF
SURGICAL
RESEARCH
VOL.
9,
NO.
poxia and normocarbia on cerebral blood flow and metabolism in conscious man. I. AppZ. Physiol. 23: 183, 1967. 2.
Gordan, G. S., Guadagni, N., Pi&i, J., and Adams, J. E. Steroid anesthesia in man: Clinical and cerebral metabolic effects. J. Int. CoZZ. Surg. 25:9, 1956.
3.
Himwich, H. E., Baker, Zelma, and Fazekas, J. F. The respiratory metabolism of infant brain. Amer. J. Physiol. 125:601, 1939.
4.
Himwich, H. E., and Fazekas, J. F. Comparative studies of the metabolism of the brain of infant and adult dogs. Amer. J. Physiol. 132:454, 1941.
5.
6.
648
Kennedy, C., and Sokoloff, L. An adaptation of the nitrous oxide method to the study of the cerebral circulation in children: Normal values for cerebral blood flow and cerebral metabolic rate in childhood. J. Clin. Inuest. 36:1130, 1957. Lassen, N. A., Feinberg, I., and Lane, M. H. Bilateral studies of cerebral oxygen uptake in young and aged normal subjects and in patients with organic dementia. J. CZin. Inueyt. 39:491, 1960.
11,
NOVEMBER
7.
8.
9.
10. 11.
12.
13.
14.
1969
Michenfelder, J. D., Messick, J. M., Jr., and Theye, R. A. Simultaneous cerebral blood flow measured by direct and indirect methods. J. Surg. Rex 8~475, 1968. Michenfelder, J. D., and Theye, R. A. The effects of profound hypocapnia and dilutional anemia on canine cerebral metabolism and blood flow. Anesthesiology. ( In press. ) Michenfelder, J. D., and Theye, R. A. Hypothermia: Effect on canine brain and whole-body metabolism. Anesthesiology 29:1107, 1968. Anatomy of the Dog. PhiladelMiller, M. E. phia: W. B. Saunders Company, 1964, p. 652. Theye, R. A. The determination of 0, and CO, content in blood containing halothane. Anesthesiology 30:325, 1969. Theye, R. A., and Michenfe!der, J. 1). The effect of halothane on canine cerebral metaboljsm. Anesthesiology 29:1113, 1968. Theye, R. A., and Michenfelder, J. D. The effect of nitrous oxide on canine cerebral metabolism. Anesthesiology 29:1119, 1968. Tyler, D. B., and Van Harreveld, A. The respiration of the developing brain. Amer. J. Physiol. 136:600, 1942.