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Biomedical subjects

L I Kleinman

Publications and source records attributed to L I Kleinman.

At least 19 recordsLinked to original sources
PubMed1997

Potassium metabolism in extremely low birth weight infants in the first week of life.

OBJECTIVE: Nonoliguric hyperkalemia has been reported to occur in the first week of life in as many as 50% of extremely low birth weight (ELBW) infants. We studied potassium balance and renal function in the first 5 days of life to characterize potassium metabolism during the three phases of fluid and electrolyte homeostasis that we have described in ELBW infants and to elucidate the factors that contribute to the development of nonoliguric hyperkalemia. STUDY DESIGN: Plasma potassium concentration (PK), potassium intake and output, and renal clearances were obtained for the first 6 days of life in 31 infants with a birth weight of 1000 gm or less. Collection periods in which urine flow rate was greater than or equal to 3 ml/kg per hour and weight loss was greater than or equal to 0.8 gm/kg per hour were denoted to be diuretic. Prediuresis includes all collection periods before the first diuretic period; diuresis includes all collection periods between the first and last diuretic periods; postdiuresis includes all collection periods after the last diuretic period. Infants with a PK greater than 6.7 mmol/L on at least one measurement were denoted to have hyperkalemia. RESULTS: PK increased initially after birth--despite the absence of potassium intake- and then decreased and stabilized by the fourth day of life. Diuresis occurred in 27 of 31 infants. The age at which PK peaked was closely related to the onset of diuresis. PK decreased significantly during diuresis as the result of a more negative potassium balance, despite a significant increase in potassium intake. In fact, PK fell to less than 4 mmol/L in 13 of 27 infants during diuresis. After the cessation of diuresis, potassium excretion decreased even though there was a significant increase in potassium intake, potassium balance was zero, and PK stabilized. Hyperkalemia developed in 11 of 31 infants. The pattern of change in PK with age was similar in infants with normokalemia and hyperkalemia: PK initially increased (essentially in the absence of potassium intake) and then decreased and stabilized by the fourth day of life. However, the rise in PK after birth was greater in infants with hyperkalemia than in those with normokalemia: 0.7 +/- 0.2 versus 1.8 +/- 0.2 mmol/L (p < 0.001). No differences in fluid and electrolyte homeostasis or renal function were identified as associated with hyperkalemia. CONCLUSIONS: PK increases in most ELBW infants in the first few days after birth as a result of a shift of potassium from the intracellular to the extracellular compartment. The increase in the glomerular filtration rate and in the fractional excretion of sodium, with the onset of diuresis, facilitates potassium excretion, and PK almost invariably decreases. Hyperkalemia seems to be principally the result of a greater intracellular to extracellular potassium shift immediately after birth in some ELBW infants.

Age Factors↗
PubMed1996

Effects of Carbicarb and sodium bicarbonate on hypoxic lactic acidosis in newborn pigs.

BACKGROUND: Use of sodium bicarbonate (NaHCO3) may result in intracellular acidosis due to the generation of CO2. Carbicarb, has been reported to be superior to sodium bicarbonate (NaHCO3) because of lesser generation of CO2. The present study was designed to investigate whether Carbicarb or NaHCO3 is superior to normal saline in the treatment of hypoxic lactic acidosis. METHODS: Hypoxia was induced by ventilation with 8% O(2) in 30 piglets with fixed ventilation. When the pH fell to < 7.2, hypoxia was reversed by placing the animals in 21% O2 (experiment 1) or 100% O(2) (experiment 2) and either saline, Carbicarb or NaHCO3 were given. Data were collected for 120 minutes after therapy. RESULTS: In both experiment 1 (severe acidosis, pH < or = 7.1) and 2 (moderate acidosis, pH < or = 7.2) use of Carbicarb and NaHCO3 increased the arterial carbon dioxide tension (pCO2) significantly (p < 0.05). With moderate acidosis: 1) use of alkalinizing agents compared to saline resulted in an initial improvement in arterial pH at 1 minute, but thereafter, the differences were not statistically significant; and 2) there were no differences in hemodynamic variables and plasma lactic acid concentration between the three groups. CONCLUSIONS: The data demonstrate that 1) both Carbicarb and NaHCO3 significantly increase arterial pCO2; and 2) use of either alkalinizing agent in moderate acidosis does not alter the course of acidosis.

Acid-Base Equilibrium↗
PubMed1996

Renal bicarbonate excretion in extremely low birth weight infants.

OBJECTIVE: To test the hypothesis that due to the immaturity of their kidneys extremely low birth weight infants lose large amounts of bicarbonate in their urine. METHODS: Urine and blood samples collected every 8 to 12 hours for the first 4 days of life from 22 preterm infants 23 to 29 weeks' gestation weighing 540 to 982 g at birth were prospectively studied. RESULTS: As described previously, three phases of fluid homeostasis were identified. The first phase (prediuresis) was a period of low urine output followed by a period of spontaneous diuresis/natriuresis (diuretic phase) and then by a phase when urine output varied according to fluid intake (postdiuresis). Sodium, potassium, chloride, and bicarbonate excretion rates and bicarbonate balance (bicarbonate or acetate infused minus bicarbonate excreted) were calculated for each of the three phases. Urinary excretion of sodium, potassium, chloride, and bicarbonate increased from the prediuretic to the diuretic phase and decreased from the diuretic to the postdiuretic phase. During the diuretic phase 88% of renal sodium excretion was accompanied by excretion of chloride. Bicarbonate balance was positive in all three fluid phases. Cumulative renal bicarbonate loss over the first 4 days of life was 1.9 +/- 0.5 meq/kg (SD) and the cumulative bicarbonate balance was +4.4 +/- 4.1 meq/kg (SD). The glomerular filtration rate, filtered load of bicarbonate, and absolute tubular reabsorption of bicarbonate significantly increased from the prediuretic to the diuretic phase, while fractional reabsorption of sodium and chloride decreased between these two phases. The fractional reabsorption of bicarbonate did not change from prediuresis to diuresis, but increased from diuresis to postdiuresis and consequently from prediuresis to postdiuresis. CONCLUSIONS: Contrary to our original hypothesis, the total renal bicarbonate excretion of extremely low birth weight infants in the first 4 days of life is low and the net bicarbonate balance is positive. The anion predominantly accompanying the excretion of sodium in all three phases is chloride and not bicarbonate. Bicarbonate excretion appears to be independent of sodium excretion during these phases. The increase in renal tubular bicarbonate reabsorption during the first week of life may be associated with extracellular volume contraction.

Bicarbonates↗
PubMed1995

Phases of fluid and electrolyte homeostasis in the extremely low birth weight infant.

OBJECTIVE: We had shown previously that preterm infants undergo three phases of fluid and electrolyte homeostasis; prediuretic, diuretic, and postdiuretic. The objectives of the present study were: (1) to determine whether infants even more immature and infants cared for under thermal environmental conditions different from those previously studied also undergo these three phases; and (2) to relate these phases to changes in renal function. METHODS: Consecutive, timed urine collections were made during the first 5 days of life in 32 infants with birth weights of 1000 g or less. Infants were cared for in radiant warmers for 24 hours and then transferred to nonhumidified incubators. Diuresis was defined as urine flow rate (V) of 3 mL or more/kg per hour and weight loss of 0.8 g or more/kg per hour. The physiologic relationships among water and sodium balance, insensible water loss, arterial blood pressure, and renal function were made during the three phases. RESULTS: Twenty-eight (87%) of the 32 infants underwent the three homeostatic phases. The median ages of onset and cessation of diuresis were 25 and 96 hours, respectively. There was no correlation between onset of diuresis and change of thermal environment. During the prediuretic phase, V averaged 1.6 mL/kg per hour, and 17 of 28 infants had at least one collection period in which V was less than 1 mL/kg per hour; urinary sodium excretion was 0.1 mEq/kg per hour; the glomerular filtration rate (GFR) was 0.22 mL/kg per hour; fractional excretion of sodium (FENa) was 6.2%; and urine osmolality was dilute (221 mOsm/kg). During the diuretic phase, V and sodium excretion more than tripled; GFR and FENa doubled; and there was no change in urine osmolality. During postdiuresis, V and Na excretion decreased to values intermediate between the prediuretic and diuretic phases, and FENa fell to prediuretic levels, but there was no change in GFR or urine osmolality. There was poor correlation between blood pressure and GFR. Insensible water loss was high and variable during all phases, exceeding 190 mL/kg per day in the smallest infants. CONCLUSIONS: Extremely low birth weight infants manifest three phases of fluid and electrolyte homeostasis, as do more mature infants, independent of thermal environment. Diuresis and natriuresis are the result of abrupt increases in GFR and FENa. We speculate that this may be the result of expansion of the neonatal extracellular space as fetal lung fluid is reabsorbed.

Diuresis↗
PubMed1990

Effects of euvolemic and hypervolemic hyperbicarbonemia on segmental nephron HCO3 reabsorption in the newborn dog.

Studies were undertaken to determine the effect of elevated plasma bicarbonate concentration (PHCO3) with and without volume expansion on segmental nephron HCO3 reabsorption in newborn and adult dogs using the technique of distal blockade. Reabsorption of bicarbonate per mL glomerular filtrate (RHCO3/GFR) in the proximal nephron was more suppressed in euvolemic newborns than euvolemic adults as PHCO3 was increased from baseline to 50-70 mM. Inasmuch as total nephron reabsorption has been shown to be essentially complete under these conditions in both newborns and adults, distal nephron HCO3 delivery and the fraction of the distal HCO3 load reabsorbed must have been greater in euvolemic newborns than adults when PHCO3 was elevated. Total nephron RHCO3/GFR was less suppressed by NaHCO3 volume expansion in the newborn than it was in the adult. However, proximal nephron RHCO3/GFR was similarly suppressed by NaHCO3 volume expansion in newborns and adults. Thus, the NaHCO3-expanded newborn must have reabsorbed a greater proportion of the increased distal HCO3 load than did the NaHCO3-expanded adult. Proximal nephron HCO3 reabsorption is a balance between reabsorption effected by active proton secretion and passive HCO3 back leak. Euvolemic increase in peritubular HCO3 concentration has been shown to suppress proximal tubular proton secretion; volume expansion increases proximal tubule HCO3 permeability and back leak.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1988

Renal function correlates of postnatal diuresis in preterm infants.

A characteristic pattern of fluid homeostasis occurs in the first week of life in many preterm infants. Initially, urine output is low independent of fluid intake, subsequently a diuresis occurs, and finally urine output begins to vary with intake. Renal clearance measurements were made during each of these three phases to elucidate the renal mechanisms involved. Periods during which the ratio of urine output to fluid intake was greater than or equal to 1 and urine output was greater than or equal to 3 mL/kg/h were defined as diuretic. Of 22 preterm infants studied from 12 to 120 hours of age, 17 had at least one period of diuresis. In these infants, urine output, fluid intake rate, output to intake ratio, glomerular filtration rate, and fractional sodium excretion were lowest at 12 to 24 hours of age. During diuresis, urine output tripled without a significant change in fluid intake so that output to intake increased to levels exceeding unity. Diuresis was associated with significant increases in glomerular filtration rate and fractional sodium excretion. By 108 to 120 hours of age, urine output decreased despite an increase in fluid intake. This was accompanied by a decrease in glomerular filtration rate. These results suggest that the initial antidiuretic phase is the result of a low fractional sodium excretion in the face of a low glomerular filtration rate. Subsequently, diuresis and natriuresis occur as a result of abrupt, nonmaturational increases in glomerular filtration rate and fractional sodium excretion. With cessation of diuresis, glomerular filtration rate and fractional sodium excretion decrease and water and electrolyte output begin to vary appropriately with intake.

Age Factors↗
PubMed1986

Renal response of newborn dog to potassium loading.

The renal response to potassium loading was studied in 14 newborn (6-20 days of age) and 14 adult mongrel dogs in order to determine the capacity of the newborn to excrete potassium load. Eight newborn and eight adult dogs were infused with 20 mueq of potassium chloride X min-1 X kg body wt-1 for 240 min. Adults excreted a significantly greater proportion of the potassium load during the 240-min infusion than did newborns (72 +/- 4 vs. 52 +/- 4%, P = 0.003). The infusion resulted in a significantly greater increase in plasma potassium concentration in the newborn (3.9 +/- 0.3 meq/liter) than in the adult (2.8 +/- 0.4 meq/liter), P = 0.05. Average potassium excretion rate per body weight was greater in the adult than newborn during potassium loading (15.0 +/- 1.0 vs. 10.4 +/- 0.7 mu eq X min-1. kg body wt-1, P = 0.003); however, average potassium excretion corrected for glomerular filtration rate was not significantly different between the adult and newborn (3.2 +/- 0.2 vs. 3.0 +/- 0.2 mu eq/ml filtered, P greater than 0.20). In another six newborn and six adult dogs, blockade of distal nephron potassium secretion with amiloride in the potassium-loaded state inhibited more than 90% of potassium excretion in both the newborn and adult.(ABSTRACT TRUNCATED AT 250 WORDS)

Amiloride↗
PubMed1986

Lack of anion effect on volume expansion natriuresis in the developing canine kidney.

The renal response to volume expansion with sodium chloride or sodium bicarbonate was studied in 15 newborn and 13 adult dogs. Proximal and distal nephron function were estimated using the technique of distal nephron blockade. Fractional sodium reabsorption was 99.0 +/- 0.3% in newborn and 96.6 +/- 0.06% in adult during the NaCl expansion (P less than 0.01) and 98.1 +/- 0.7% in the newborn and 93.2 +/- 0.7% in the adult during NaHCO3 expansion (P less than 0.001). With either anion the higher fractional sodium reabsorption in the newborn was due to reabsorption of a greater fraction of the load presented to the distal nephron segment. The percent of the distal sodium load that was reabsorbed was 98.0 +/- 0.6% in the newborn and 92.2 +/- 1.0% in the adult during NaCl expansion, and 96.1 +/- 1.3% in the newborn and 81.5 +/- 2.4% in the adult during NaHCO3 expansion. Differences in distal nephron chloride, potassium and bicarbonate reabsorption among the groups support the hypothesis that the enhanced distal sodium reabsorption in the newborn occurred largely in the ascending loop of Henle with NaCl expansion, while it occurred in the late distal and cortical collecting tubules with NaHCO3 expansion. There was no difference between the natriuretic responses to NaCl or NaHCO3 in the newborn (P greater than 0.20); however, the natriuretic response to NaCl was less than that to NaHCO3 in the adult (P less than 0.001). This suggests that the bulk of the sodium that escaped reabsorption in Henle's loop during NaHCO3 expansion was reabsorbed in the late distal tubule in the newborn, but not in the adult.

Animals↗
PubMed1985

Inulin space studies in fetal sheep.

Extracellular volume was estimated in fetal sheep by measuring the 14C inulin space in 6 in situ unanesthetized fetal lambs at gestational ages ranging from 120 to 145 days (term = 150 days). The total inulin space ranged from 979 to 1,510 ml. A positive correlation between total inulin space and gestational age (r = 0.65) was noted, such that fetal lambs of 120 days gestation had a predicted inulin space of 1,072 ml and fetal lambs near term at 145 days gestation had an inulin space of 1,422 ml. However, since fetal weight increases with gestation, inulin space expressed as a percent of body weight actually decreased with gestational age (r = -0.80), so that at 120 days gestation the fetus would have an estimated inulin space of 59% of body weight and at 145 days the fetus would have an inulin space of only 34% of body weight.

Animals↗
PubMed1985

Cerebrovascular hemodynamics during and after recovery from acute asphyxia in the newborn dog.

Cerebrovascular volume and transmural pressure loads accompanying acute increases in cerebral blood flow are implicated in the pathogenesis of periventricular-intraventricular hemorrhage in preterm infants. An acute increase in cerebral blood flow would be expected during acute recovery from asphyxia. Therefore, cerebrovascular hemodynamics, including flow (microspheres), were studied during and after acute recovery from asphyxia in seven newborn dogs in order to study the determinants of these volume and pressure loads. During the acute recovery phase, cerebral hemispheric blood flow was 69.6 +/- 10 ml/100 g/min (mean +/- SEM) representing a 250% increase from baseline values of 19.9 +/- 1.8 ml/100 g/min (p less than 0.005), while combined cerebellar-brainstem flow was 204.3 +/- 19.3 ml/100 g/min representing a 536% increase from baseline values of 32.0 +/- 1.5 ml/100 g/min (p less than 0.005). Blood flow to both areas had returned to baseline levels 20 min after the onset of recovery. Associated with this cerebral hyperemia was an acute increase in mean arterial pressure from 21.3 +/- 4.5 mm Hg at end asphyxia to 69.5 +/- 6.0 mm Hg at peak recovery (p less than 0.01), and parallel acute increases in sagittal sinus pressure (from 4.0 +/- 0.4 to 14.6 +/- 1.9 mm Hg, p less than 0.01) and cerebrospinal fluid pressure (from 3.8 +/- 0.4 to 14.3 +/- 1.9 mm Hg, p less than 0.01). Central venous pressure fell from 4.3 +/- 0.6 mm Hg at end asphyxia to 1.6 +/- 0.5 mm Hg, and thus is not a determinant of the elevation in sagittal sinus pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1984

The effect of metabolic acidosis upon autoregulation of cerebral blood flow in newborn dogs.

The radioactive microsphere technique was used in 13 newborn dogs to determine the effect of a metabolic (lactic)acidosis upon cardiac output (CO), cerebral blood flow (CBF), and autoregulation of cerebral blood flow. The animals were mechanically ventilated with supplemental oxygen to ensure normocarbia and hyperoxia throughout the experiments. Baseline cardiac output and cerebral blood flow measurements were made, followed by a lactic acid infusion to maintain pH less than 7.25. Metabolic acidosis produced a 27% fall in cardiac output and no change in cerebral blood flow (19 ml/100 g/min). Autoregulation was tested in 6 of the acidemic puppies by acute volume depletion to reduce blood pressure by 30% of baseline, followed by rapid volume re-expansion of the withdrawn blood. With volume depletion, CO decreased by 38%, and with volume re-expansion CO returned to baseline. The CBF remained at baseline levels with volume depletion but was slightly increased after rapid volume re-expansion. Five acidemic controls maintained CO and CBF constant with time. Thus cerebral autoregulation is preserved in the newborn dogs during metabolic acidosis, although cerebral blood flow was slightly increased following volume re-expansion.

Acidosis↗
PubMed1984

Pressure natriuresis during saline expansion in newborn and adult dogs.

Pressure natriuresis was studied in anesthetized saline-expanded adult (n = 10) and neonatal (n = 23) dogs. One group (protocol B) received ethacrynic acid and amiloride to block distal nephron function. Studies in the other group (protocol A) were done without diuretics. Renal arterial blood pressure was raised by bilateral carotid artery occlusion. Renal perfusion pressure was then lowered in steps by partially occluding the aorta proximal to the renal arteries. In protocol B carotid occlusion was associated with an increase in both absolute and fractional sodium excretion by adult and newborn dogs. Moreover, there was significant negative correlation (P less than 0.01) between absolute change in renal arterial pressure and change in tubular reabsorption of sodium per milliliter glomerular filtrate for both age groups. For each mmHg increase in blood pressure there was greater inhibition of sodium reabsorption in the puppy (0.55 mueq/ml glomerular filtrate) than in the adult (0.18 mueq/ml, P less than 0.05). In protocol A puppies, the inhibition of sodium reabsorption due to increases in renal perfusion pressure was less than that occurring in protocol B, indicating that some of the sodium escaping proximal nephron reabsorption was reabsorbed distally. Results of these studies indicate that during saline expansion pressure natriuresis is primarily a proximal tubular event, and the sensitivity of the proximal tubule to changes in renal arterial blood pressure is greater in the newborn than the adult kidney.

Aging↗
PubMed1984

Renal osmotic effect of mannitol in the neonatal and adult dog.

The renal response to mannitol loading was studied in 21 newborn dogs aged 1-19 days and in 12 adult dogs. One group of animals (protocol B) underwent distal nephron blockade with ethacrynic acid and amiloride prior to and during infusion of mannitol to estimate proximal tubule function. The other group of animals (protocol A) received mannitol without the diuretics. Mannitol was infused at progressively increasing dosages, resulting in progressively increasing mannitol excretion rates. For all groups of animals, as mannitol excretion rates increased, urine flow and sodium, potassium, and chloride excretion rates increased. However, there was no correlation between mannitol excretion and bicarbonate excretion. The osmotic effect of mannitol was quantitated from the slope of the plot of mannitol excretion vs. sodium excretion (dNa/dMan). In both pups and adults dNa/dMan was greater in protocol B (1.47 for pups, 0.70 for adults) than in protocol A (0.18 for pups, 0.07 for adults). In addition, in protocol B dNa/dMan was greater in the newborn than in the adult and decreased logarithmically with age in pups. In protocol B, as mannitol excretion increased, the urine-to-plasma sodium ratio declined in adults but did not change in pups. Urine-to-plasma osmolality ratio remained at unity throughout the experiment in both age groups in protocol B. These results indicate that 1) the osmotic effect of mannitol is greater in the immature than in the mature kidney, and 2) the greater osmotic effect in the neonatal kidney is related to inability of the immature proximal tubule to generate and sustain a transtubular sodium gradient.

Animals↗
PubMed1983

Acute cardiovascular effects of indomethacin in anesthetized newborn dogs.

Cardiac output and regional blood flow distribution were measured in 14 newborn dogs before and 90 min following 0.3 mg/kg of indomethacin and in 4 control animals who received buffer alone using the Radioactive Microsphere Reference Organ Technique. Indomethacin produced no significant change in cardiac output or blood flow to the gastrointestinal tract or kidney. There were no changes in cerebral blood flow in animals over 4 days of age. However, in 3 of 8 puppies less than 3 days of age, indomethacin resulted in a 47% fall in cerebral blood flow. In newborn dogs, indomethacin in the dose employed had no deleterious effects on cardiac output and, with the possible exception of the cerebral circulation, on blood flow distribution.

Animals↗
PubMed1983

Segmental nephron sodium and potassium reabsorption in newborn and adult dogs during saline expansion.

Studies were carried out in 23 anesthetized neonatal dogs aged 2 to 20 days and in 16 adult dogs to compare the effects of saline volume expansion on renal tubular Na and K reabsorption between newborn and adult animals. Proximal- and distal-tubule function was estimated by the distal-nephron-blockade technique using ethacrynic acid and amiloride. During saline infusion, which increased extracellular volume by approximately 30% for both age groups, total nephron fractional Na reabsorption was 0.91 for the adult but 0.98 for the puppy (P less than 0.01). However, proximal tubule fractional Na reabsorption was greater in the adult (0.64) than in the puppy (0.48, P less than 0.01) whereas distal nephron fractional Na reabsorption was much greater in the newborn (0.51) than in the adult (0.26, P less than 0.01). Sodium reabsorption normalized to kidney weight was lower in all segments of the neonatal kidney than in the adult kidney. The filtered sodium load was lower in the newborn (27.0 mueq min-1g-1) than in the adult (105.0, P less than 0.01), and the Na load to the distal nephron was also lower in the newborn (14.0 mueq min-1g-1) than in the adult (37.2, P less than 0.01). Fractional K excretion was similar in both age groups even though the fraction of filtered K escaping proximal-tubule reabsorption was greater in the newborn than in the adult, indicating greater net K fractional reabsorption in the distal nephron of the newborn than in the adult kidney. These results indicate that in response to saline expansion there is a greater proximal tubule natriuresis in the neonate than in the adult but overall renal Na excretion is less in the newborn animal due to enhanced fractional Na reabsorption in the neonatal distal nephron, particularly in Henle's Loop. This increase in distal nephron fractional sodium reabsorption may be related in part to the relatively small absolute Na load presented to the distal nephron of the neonatal kidney.

Absorption↗
PubMed1982

Preservation of cerebral autoregulation in the unanesthetized hypoxemic newborn dog.

Studies were conducted to determine the effects of hypoxemia on cerebral blood flow and the influence of hyperoxia and hypoxemia on autoregulation of cerebral blood flow in the unanesthetized newborn dog. Twenty-one newborn dogs less than 2 weeks of age were studied. Cerebral blood flow was measured using radioactive microspheres during successive periods of normotension, hypotension (produced by blood withdrawal) and normotension (produced by infusion of previously withdrawn blood). In the hyperoxic animals, arterial pO2 was maintained above 250 torr by having the animal breathe 100% oxygen, while in the hypoxemic animals arterial pO2 was maintained between 30 and 35 torr by having the animal breathe 12% O2. Cerebral blood flow increased significantly with hypoxemia. In both hypoxemic and hyperoxic animals cerebral blood flow was maintained constant in spite of a large fall in arterial blood pressure and cardiac output, demonstrating the presence of autoregulation. Calculated oxygen transport to the brain was constant during hypoxemia and hypotension in all animals. Thus autoregulation of cerebral blood flow is present in newborn animals and is preserved under conditions of moderate hypoxemia.

Animals↗