The magnitude of increase in the pulmonary blood volume of the postnatal guinea pig.код для вставкиСкачать
THE MAGNITUDE O F INCREASE I N THE PULMONARY BLOOD VOLUME O F T H E POSTNATAL GUINEA P I G NEWTON B. EVERETT AND BARBARA S. SIMMONS Department of Anatomy, University of Washington, School of Medioime, Seattle, Washington ONE FIGURE Through the use of improved methods combining rapid freezing and isotopic tracer techniques, Everett ( '52) demonstrated that after 5 minutes of breathing the blood volume of the newborn guinea pig lung had increased by 25% over that of its nonbreathing littermates. The increase after this time was shown to be more gradual and by 7 hours after delivery the blood volume per-unit-weight of lung had increased by approximately 85%. The studies reported here are a continuation of the former study and cover the period from 7 to 36 hours postpartum, which extends beyond the time of any further increase in the blood volume per-unit-weight of lung. METHODS Sixteen litters of guinea pigs including 42 individual offspring were used for the pulmonary blood volume determinations. The methods used for labeling the blood with radioiron, for freezing the newborn and for comparing the blood volume of the breathing and nonbreathing littermates were the same as in the previous study, Everett ('52). The animals of each litter which were permitted to breathe were kept at This investigation was supported (In part) by a research grant (H-1530) from The National Heart Institute, of the National Institutes of Health, Public Health Service. 429 430 NEWTON B. EVERETT AND BARBARA s. SIMMOKS 37°C. for 16, 24 or 36 hours after delivery. They were fed a mixture of dried milk, dextrose, and water with a medicine dropper a t 2-4 hour intervals until sacrificed. Hemoglobin determinations and radioiron assays of the blood were made on several pigs a t 16, 24 and 36 hours postpartum. These were made to determine if there were any significant changes in the blood during the period of breathing which might influence the distribution of radioiron per unit volume of blood. Electrocardiograms were made on three pigs to determine how long the heart continued to beat after immersing the animals in the freezing mixture of dry ice and ethanol at -75°C. In addition the time required for complete freezing after immersion was determined by recording from thermocouples implanted above the liver near the central point of the diaphragm. RESULTS The comparative radioactivity of lung samples between the breathing and nonbreathing animals is shown in table 1. I n all cases the lung samples from the breathing specimens gave higher counts than the nonbreathing controls. This increase in radioactivity, which is related directly to the increase in blood volume, averaged 100% for the 16 hour group, 126% for the 24 hour group, and 100% for the 36 hour group. In figure 1the percentage increase of lung radioactivity is plotted against time and included with the results of the present series are those of the former study covering the period from 5 minutes to 7 hours postpartum. This scattergram shows that after the initial marked increase within the first 5 minutes of breathing the increase was more gradual and continued so through the 16 hour period. It is further revealed in figure 1 that there was considerable variation amongst the values of the different litters which breathed 24 hours. The increase of 190% for one of the litters in this group is some 46% above the next highest value within any group. Except for this one value the average increase for the 24 hour group and f o r those which breathed 36 hours are 431 POSTNATAL PULMONARY BLOOD VOLUME of the same magnitude as those of the 16 hour series. Thus, the magnitude of increase in the blood volume per-unit-weight of lung was in the range of 100% and this was reached by the 16th hour of breathing. TABLE 1 Radioactimity of lung samples BREATHING TIME LITTER NUMBER AVE. CT.S./MIN. PER EQUAL U N I T WEIGHT ( 5 0 MG) Breathing 16 hr. 218 238 243 24 7 244 197 217 22i 24 hr. P 14 246 245 36 hr. 231 193 190 196 230 (2)' 972 (2) 628 (1) 484 (1) 144 (2) 841 (1) (2) (1) (1) (1) (2) 762 206 381 533 690 893 (1) 903 (1) 676 (2) 1223 (2) 417 (2) 209 % INCREASE AFTER BREATHING Nonbreathing (1)' 592 (1) 33'4 (1) 209 ave. 64 88 131 96 120 100 ( 1 ) 476 60 (1) 71 ave. 190 144 130 129 102 126 ave. 95 103 101 106 95 100 ( 1 ) 73 ( 1 ) 382 (1) (1) (1) (2) (1) (1) (2) (1) (1) 156 232 301 443 462 333 607 202 ioa Number of animals. There were no significant differences in the hemoglobin values for the same animals at 16,24 and 36 hours postpartum, table 2. The greatest difference was 4% in one animal between 16 and 36 hours. A decrease of up to 2% in hemoglobin values could be expected in the second determination due to the withdrawal of 0.1ml of blood used for the first determination. It is noted that where a difference is revealed between the two determinations that the second value was the 432 NEWTON B. EVERETT AND BARBARA S. SIMMONS lower one. There was less than 1%difference in the radioiron assays of blood from the same animals a t 24 and at 36 hours postpartum, table 2. 2 $ 190180170160150140130120110100- INCREASE OF LUNG RADIOACTIVITY WITH BREATHING X X X X X . X X 90- g4 X X X X x x X X :."Ixi 1 ; 40 K K , , , , ; , , , ,,,, , ,,,, , 10 1 2 3 4 5 6 7 16 BREATHING TIME 24 (HOURS) 36 Fig. 1 Increase of lung radiwctivity with breathing TABLE 2 Comparative hemoglobin and radioiron values ANIMAL NUMBER 16 HRS. B-1 B-2 B-3 A-1 A-2 17.3 24 HRS. 36 HRS. % VARIATION Percent Hemoglobin 18.3 19.2 15.6 15.9 17.3 17.8 18.4 15.4 15.6 0 3 4 1.3 1.5 Radioactivity in Counts/min/B~Omm * blood c-1 c-2 243 245 241 246 >I >I POSTNATAL PULMONARY BLOOD VOLUME 433 An electrocardiographic record was obtainable for a variable time after immersion, ranging from 34 to 60 seconds. The average time required for complete freezing was 3* minutes. DISCUSSION The observations presented here show that in the postnatal guinea pig the magnitude of increase in the pulmonary blood volume per-unit-weight of lung is approximately 100%. This increase of 100% over that of the nonbreathing littermate controls is reached by the 16th hour of breathing. It was reported earlier, Everett ('52) that the increase was 85% following 7 hours of breathing. Although the average increase in the pulmonary blood volume for the pigs breathing 24 hours was 126% it is believed that this value is out of line due to the variation within this group. The explanation for the greater variation within this 24 hour group is unknown. The increase of 190% for one of the litters is considerably beyond the individual variations obtained in the other groups after a particular interval of breathing. I n fact, the values obtained for the animals of different litters breathing 36 hours are remarkably uniform. It would appear then that by the 36th hour the blood volume of the lung has become stabilized. The uniform hemoglobin values as well as uniform radioiron values of blood from the same animals at the different time intervals would indicate that no hemal changes have occurred within the experimental period which would influence the results. The 33 minutes required for complete freezing of the newborn pigs was determined by a more accurate method than that used previously, Everett ('52), which indicated that freezing was complete in three minutes. The data obtained from the electrocardiograms would suggest however that there ceases to be a further circulation of blood 30 to 60 seconds after dropping the pigs into the freezing mixtures. The observation that there is an abrupt increase of some 25% in the pulmonary blood volume of the guinea pig by 5 434 NEWTON R. EVERETT AND BARBARA s. SIMMONS minutes postpartum, Everett ( '52), and a more gradual increase thereafter, reaching 100% by 16 hours, is in accord with the recent studies of Ardran et al. ( '52). These investigators observed that in the newborn lamb with the onset of breathing there is a considerable fall in both pulmonary arterial and aortic pressure and that the pulmonary circulation becomes more rapid. It was proposed that the decrease in pulmonary vascular resistance with the onset of ventilation is responsible for these changes. This proposal was later substantiated when it was shown that with ventilation the pulmonary resistance to blood flow decreased from 50 to 90%, Dawes, et al. ('52). Thus it would appear that the initial marked increase in pulmonary blood volume and the subsequent gradual increase is due to the reduction in pulmonary vascular resistance. SUMMARY Comparative blood volumes per-unit-weight of lung have been made between non-breathing and postnatal guinea pigs after 16 to 36 hours of breathing. This has been done by the methods reported previously, Everett ( '52). The increase in blood volume averaged 100% by the 16th hour of breathing. There appears to be no further increase after this time. There were no significant differences in the hemoglobin values or in the radioiron assays of blood from guinea pigs obtained at 16, 24 and 36 hours after birth. LITERATURE CITED ARDRAN, G. M., G . S. DAWES,M. M. L. PRI('IIARD, S. R. M. REYNOLDS A N D D. G. WYATT 1952 The effect of rentilation of the foetal lungs upon the pulmonary circulation. J. Physiol., 218: 12-22. DAWES,G . S.,J. C. Mom, J. G. WIDDICOMBE AND D. G . WYATT 1952 The effect of ventilation on pulmonary blood flow in the newborn lamb. J. Physiol, 118: 45 P. EVERETT, N. B. 1952 Xarly postnatal changes i n pulmonary blood volume of the guinca pig. Am. J. Pliysiol., 1 6 9 : 54-39.