Renal medullary hypoxia during experimental cardiopulmonary bypass: a pilot study

Objectives: To determine the effect of cardiopulmonary bypass (CPB) on renal medullary oxygenation.

Design: Observational.

Setting: Laboratory.

Participants: Pigs ( n=3).

Interventions: Following induction of general anesthesia, a Paratrend™ blood gas probe was placed directly into the left renal medulla. Two animals were subjected to 90 min of CPB, while a third served as a non-CPB control. A probe was also placed in the left renal pelvis of one (CPB) animal to allow direct urine PO2measurements.

Measurements and main results: Medullary hypoxia (PO2B < 65 mmHg) was evident prior to CPB. With the onset of CPB, medullary PO2 further declined to nearly unmeasurable levels; PCO2 and pH were unchanged. Brief circulatory arrest during CPB in one animal resulted in rapid additional PCO2 rise and pH decline that corrected with reperfusion. Following the cessation of CPB, medullary PO2 gradually increased, but remained lower than pre-CPB levels. No changes in medullary PO2 were observed in the sham animal. Renal pelvis urine PO2, but not pH or PCO2, appeared to correlate with medullary values at all times.

Conclusions: Our findings indicate that renal medullary hypoxia is extreme during CPB and may persist following CPB. These data suggest a basis for the vulnerability of the kidney to injury during cardiac surgery. Renal pelvis urine PO2 appears to correlate closely with medullary PO2 and may be a useful tool for studying medullary oxygenation during CPB in humans.

Identifying hypoxia in a newborn piglet model using urinary NMR metabolomic profiling

Establishing the severity of hypoxic insult during the delivery of a neonate is key step in the determining the type of therapy administered. While successful therapy is present, current methods for assessing hypoxic injuries in the neonate are limited. Urine Nuclear Magnetic Resonance (NMR) metabolomics allows for the rapid non-invasive assessment of a multitude breakdown products of physiological processes. In a newborn piglet model of hypoxia, we used NMR spectroscopy to determine the levels of metabolites in urine samples, which were correlated with physiological measurements. Using PLS-DA analysis, we identified 13 urinary metabolites that differentiated hypoxic versus nonhypoxic animals (1-methylnicotinamide, 2-oxoglutarate, alanine, asparagine, betaine, citrate, creatine, fumarate, hippurate, lactate, N-acetylglycine, N-carbamoyl-β-alanine, and valine). Using this metabolomic profile, we then were able to blindly identify hypoxic animals correctly 84% of the time compared to nonhypoxic controls. This was better than using physiologic measures alone. Metabolomic profiling of urine has potential for identifying neonates that have undergone episodes of hypoxia.

Enhanced leukocyte HIF-1alpha and HIF-1 DNA binding in humans after rapid ascent to 4300 m

Hypoxia plays a crucial role in the pathogenesis of a multitude of diseases and clinical conditions such as cancer, diabetes, cardiovascular disease, stroke, pulmonary disease, inflammation, organ transplant, and wound healing. Investigations into the role of hypoxia-inducible transcription factor (HIF) in disease development have been conducted with the basic premise that HIF is activated in vivo during hypoxia in humans, yet this basic physiologic premise has never verified. Thus, we hypothesized that HIF-1 DNA binding would be enhanced in vivo in humans in response to acute global hypoxia. Fourteen human subjects were exposed to normoxia (1600 m) and hypoxia (4300 m, approximately 12% O(2)) in a hypobaric hypoxic chamber (8 h). HIF-1 DNA binding and HIF-1alpha protein were evaluated in circulating leukocytes. Oxidative markers were evaluated by plasma metabolomics using nuclear magnetic resonance and by urinary 15-F(2t)-isoprostane concentrations. Leukocyte HIF-1 DNA binding was increased (p=0.007) and HIF-1alpha was greater during hypoxia compared to normoxia. Circulating total glutathione was reduced by 35% (p=0.001), and lactate and succinate were increased by 29 and 158%, respectively (p=0.007 and 0.001), as were urinary 15-F(2t)-isoprostanes (p=0.037). HIF-1 DNA binding and HIF-1alpha were elevated in vivo in leukocytes of healthy human subjects exposed to 12% oxygen, in association with plasma and urinary markers of hypoxic stress.

Changes in sleep quality of athletes under normobaric hypoxia equivalent to 2,000-m altitude: a polysomnographic study

This study evaluated the sleep quality of athletes in normobaric hypoxia at a simulated altitude of 2,000 m. Eight male athletes slept in normoxic condition (NC) and hypoxic conditions equivalent to those at 2,000-m altitude (HC). Polysomnographic recordings of sleep included the electroencephalogram (EEG), electrooculogram, chin surface electromyogram, and electrocardiogram. Thoracic and abdominal motion, nasal and oral airflow, and arterial blood oxygen saturation (SaO2) were also recorded. Standard visual sleep stage scoring and fast Fourier transformation analyses of the EEG were performed on 30-s epochs. Subjective sleepiness and urinary catecholamines were also monitored. Mean SaO2 decreased and respiratory disturbances increased with HC. The increase in respiratory disturbances was significant, but the increase was small and subclinical. The duration of slow-wave sleep (stage 3 and 4) and total delta power (<3 Hz) of the all-night non-rapid eye movement sleep EEG decreased for HC compared with NC. Subjective sleepiness and amounts of urinary catecholamines did not differ between the conditions. These results indicate that acute exposure to normobaric hypoxia equivalent to that at 2,000-m altitude decreased slow-wave sleep in athletes, but it did not change subjective sleepiness or amounts of urinary catecholamines.

Sleep-disordered breathing and uric acid in overweight and obese children and adolescents

OBJECTIVE

The aim of this study was to determine whether the severity of sleep-disordered breathing (SDB) was associated with increased levels of uric acid (UA), both in serum and in urine, as a marker of tissue hypoxia, in a sample of overweight and obese subjects, irrespective of indexes of adiposity.

METHODS

Consecutive subjects underwent polysomnography, fasting blood sampling, and 24-h urine collection. Outcome parameters were serum UA, UA excretion ([24-h urinary UA x serum creatinine]/urine creatinine) and urinary UA/creatinine ratio.

RESULTS

A total of 93 subjects were included (44% boys; mean [+/- SD] age = 11.1 +/- 2.5; 73% obese). A fasting measurement of serum UA levels was available for 62 patients. The respiratory disturbance index was a significant covariate (beta = 0.09 +/- 0.03; p = 0.01) in the regression model for serum UA, controlling for sex (beta = 0.32 +/- 0.29; p = 0.3), puberty (beta = 0.87 +/- 0.34; p = 0.01), and waist circumference (beta = 0.04 +/- 0.01; p = 0.005). The percentage of total sleep time with arterial oxygen saturation < or = 89% (beta = 0.94 +/- 0.45; p = 0.04) was also significantly associated with serum UA level, controlling for sex (beta = 0.22 +/- 0.30; p = 0.5), puberty (beta = 0.83 +/- 0.35; p = 0.02), and waist circumference (beta = 0.04 +/- 0.02; p = 0.02). None of the SDB variables correlated with UA excretion or with urinary UA/creatinine ratio.

CONCLUSION

This study in overweight children and adolescents demonstrated a relationship between the severity of sleep apnea and increased levels of serum UA, independent of abdominal adiposity. In view of the known associations between UA and cardiovascular risk, this finding may contribute to the mechanisms linking SDB with cardiovascular morbidity.

Sources of amniotic fluid erythropoietin during normoxia and hypoxia in fetal sheep

OBJECTIVE

Erythropoietin is present in human amniotic fluid and has been suggested as a marker of fetal hypoxia. The objectives of the present study were to determine whether erythropoietin is present in ovine amniotic fluid, fetal urine, and/or lung liquid and whether concentrations in these compartments change in parallel with endogenous fetal plasma erythropoietin concentration when the latter is increased experimentally.

STUDY DESIGN

In late gestation chronically catheterized fetal sheep, samples of amniotic fluid and plasma, urine and plasma, lung liquid, amniotic fluid, and plasma were collected before and up to 7 days after induction of 4 types of fetal hypoxia: (1) acute anemic hypoxia that was induced by a single fetal hemorrhage, (2) progressive anemic hypoxia that was induced by daily exchange transfusion, (3) acute hypoxic hypoxia that was induced by the reduction of maternal inspired oxygen content, or (4) chronic placental insufficiency that was induced by daily umbilicoplacental embolization for 4 days. Erythropoietin concentrations were determined by radioimmunoassay. Statistical testing included analysis of variance and least squares regression.

RESULTS

Under basal, nonhypoxic conditions, amniotic fluid erythropoietin concentration averaged 33.2% +/- 1.6% (SE) of fetal plasma erythropoietin concentration, and basal fetal urine and lung liquid erythropoietin concentrations ranged from low (<10% of plasma concentration) to nondetectable. Unlike the strong correlation in humans, basal amniotic fluid and plasma erythropoietin concentrations were correlated only weakly (r = 0.259; r2 = 6.7%; P = .0027; n = 132). Amniotic fluid erythropoietin concentration approximately doubled after 12 hours of severe hypoxic hypoxia or after 24 hours of embolization-induced severe hypoxia but was unchanged after 12 hours of mild-moderate hypoxic hypoxia or 24 hours of anemic hypoxia. Concomitant fetal plasma erythropoietin concentrations increased to 28.1 +/- 5.3, 12.5 +/- 2.7, 10.8 +/- 4.6, and 10.0 +/- 1.3 times basal values, respectively. During progressive fetal anemia, urinary erythropoietin concentration increased almost 10-fold (P = .0023) but remained a small fraction (3.7% +/- 0.4%) of plasma concentration; at 12 hours of hypoxic hypoxia, lung liquid erythropoietin concentration did not vary with the severity of the hypoxia and remained low relative to plasma concentration (4.2% +/- 2.1%).

CONCLUSION

Erythropoietin is present in ovine amniotic fluid, urine, and lung liquid. With only 3 potential sources, the fetal membranes appear to be the primary source of amniotic fluid erythropoietin in the nonhypoxic ovine fetus because basal urine and lung liquid erythropoietin concentrations are much lower than amniotic fluid concentrations. Although unchanged during mild-to-moderate fetal hypoxia, amniotic fluid erythropoietin concentration increases modestly during severe fetal hypoxia. In sheep, fetal urinary erythropoietin may contribute to this rise in amniotic fluid erythropoietin concentration during severe hypoxia, because fetal urinary and plasma concentrations increase in parallel during anemia.

Effects of insulin-like growth factor on nitrogen balance during hypoxic exposure

Acute exacerbations of chronic obstructive pulmonary disease (COPD) accompanied with hypoxaemia may induce net protein catabolism and hypoxaemia could be an important trigger of a systemic catabolic response. The aim of this study was to examine the anabolic effects of recombinant human insulin-like growth factor-I (IGF-1) in rats exposed to hypoxia. Although acute hypoxia is usually accompanied with a decrease in dietary intake, the usual nitrogen intake was maintained in this study. Sprague-Dawley rats were maintained by continuous infusion of solution for total parenteral nutrition for 6 days. The animals were then randomly assigned to a normoxic (N) or a hypoxic (H) group. During the last 3 days of the experiment N and H rats were randomised to receive either IGF-I or vehicle. Exposure to hypoxia caused a decrease in body-weight gain accompanied by a negative nitrogen balance, which was mainly due to increased urinary nitrogen excretion. No effect of recombinant human IGF-I treatment on body weight was observed during exposure to hypoxia, although nitrogen balance normalised. The co-infusion of recombinant human insulin-like growth factor-1 and total parenteral nutrition has a significant net anabolic effect, as demonstrated by nitrogen retention and reduction in urine protein excretion observed in rats. Insulin-like growth factor-1 may help to ameliorate the protein catabolism observed under hypoxic conditions.

Post-mortem urinary myoglobin levels with reference to the causes of death

To evaluate pathophysiological significance of post-mortem urinary myoglobin levels in determining the cause of death, we investigated 210 forensic autopsy cases, partially in comparison with serum levels. Post-mortem serum myoglobin levels were extraordinary high in most cases possibly due to post-mortem change. Urinary myoglobin levels did not correlate with the serum levels, showing possible post-mortem elevation in cases of a prolonged post-mortem period over 48h. A high (>1000 ng/ml), moderate (100-1000 ng/ml), slight (50-100 ng/ml) and not significant (<50 ng/ml) elevation of urinary myoglobin were observed in 26, 43, 31 and 110 cases, respectively. Half the highly elevated cases were those with a survival time over 24h. In cases of minor muscle injury such as head trauma, elevation of urinary myoglobin level was closely related to longer survival. In acute/subacute deaths with a post-mortem interval within 48h, a significant difference was observed in relation to the blood carboxyhemoglobin (COHb) levels of fire victims: myoglobinuria over 100 ng/ml was more frequently and markedly observed in cases with COHb below 60% than over 60%, suggesting muscle damage in fatal burns. Similar elevation was observed in heat stroke victims, and also in some cases of acute and subacute death from polytrauma, asphyxiation, drowning, electricity and spontaneous cerebral bleeding, but not in myocardial infarction. Thus, it was suggested that high post-mortem urinary myoglobin levels in acute and subacute death cases may be a possible indicator of antemortem massive skeletal muscle damage as well as exertional muscle hyperactivity or convulsive disorders associated with hypoxia.

Nitric oxide modulates premature renal circulation in hypoxic newborn piglets

We studied the role of nitric oxide (NO) on the regulation of blood flow in the immature kidney during hypoxia, resuscitation and the recovery period using the NO inhibitor N(omega)-nitro-L-arginine (L-NNA) in a newborn piglet model, and the possibility of urinary cGMP as an index of renal function. After administration of L-NNA, the blood flow in both the cortex and medulla significantly decreased, indicating that NO is constantly released to maintain renal circulation. During hypoxia, the renal blood flow fell remarkably, and there were no differences between the control and L-NNA groups. During the post-resuscitation period, the recovery of renal blood flow was significantly suppressed in L-NNA administration, and it was speculated that NO might be an important factor for recovery of circulation from vasoconstriction due to hypoxemia. Urinary cGMP/cr was significantly increased on recovery from hypoxemia and was suppressed by L-NNA administration. This result suggested that the change in cGMP/cr represents renal blood flow change. We conclude that NO may play an important role in maintaining basal hemodynamics, and may also be a crucial factor for recovery from post-hypoxic vasoconstriction in premature kidneys. Urinary cGMP/cr might serve as one of the indices for assessment of premature renal circulation.

Measurement of purines in urine by capillary electrophoresis for estimating the degree of hypoxia in infants

We describe a simple, rapid and reproducible method for measuring hypoxanthine, xanthine and uric acid in urine samples of infants by capillary electrophoresis with an uncoated fused silica capillary and ultraviolet detection. Conditions were 40 mmol/l borate buffer pH 9.4 with sodium dodecyl sulphate (0.1 mol) 3 s hydrodynamic load and the voltage 20 kV. The calibration curves for hypoxanthine and xanthine were linear to 150 micromol/l and for uric acid to 300 micromol/l. The limits of detection for hypoxanthine, xanthine and uric acid were 0.5, 2.0 and 20 micromol/l, respectively. Analytical recovery of the three purines ranged from 93 to 105%. Overall CVs were < 5.2%. Using this method, we measured purine concentrations in the urine samples of 103 infants, divided into three groups, according to different degrees of hypoxia. There was a significant difference among the three groups only in hypoxanthine concentrations. In 35 urine samples from the control group, 43 urine samples from infants with a history of an apparent life threatening episode and in 25 urine samples from infants with infantile apnoea, the mean concentrations of hypoxanthine (mean +/- SD) were 13.1 +/- 4.0, 25.1 +/- 8.1 and 58.2 +/- 17.4 micromol/mmol creatinine, respectively. The diagnostic accuracy of the purine measurement was evaluated by receiver-operating characteristic curve analysis.

Renal acid-base and sodium handling in hypoxia and subsequent mild metabolic acidosis in foetal sheep

1. To measure the renal contribution to acid-base homeostasis during hypoxia (not associated with hypercapnia) and in response to the subsequent mild metabolic acidosis and to determine the effects of this hypoxia on the renal handling of sodium, studies were performed in six chronically catheterized foetal sheep (129-138 days gestation) before, during and for 1 h after a 2 h period of hypoxia. 2. Hypoxia was induced in the conscious ewe by infusing nitrogen into the trachea. Foetal arterial oxygen tension fell to 12.0 +/- 0.6 mmHg (P < 0.001). Carbon dioxide tension fell during hypoxia (P < 0.001) and was still somewhat reduced in the recovery period (P < 0.005). Arterial pH fell progressively to 7.19 +/- 0.08 in the recovery period (P < 0.05). Plasma bicarbonate concentrations fell (P < 0.001) and lactate rose (P < 0.001). 3. Urinary pH and the excretion rates of bicarbonate, titratable acid, ammonium and net acid did not change during hypoxia. Ammonium excretion and, hence, generation of new bicarbonate increased in the recovery period (P < 0.05). 4. Renal sodium excretion progressively increased and was greatest after normoxia was restored (P < 0.05). This natriuresis was due to a fall in the reabsorption of sodium by the proximal tubule (P < 0.05). Proximal reabsorption of sodium was directly related to foetal pH (P < 0.0001) and bicarbonate reabsorption (P < 0.001). 5. It was concluded that: (i) the foetal kidneys began to contribute to the maintenance of acid-base balance within the first hour of recovery from a 2 h episode of hypocapnic hypoxia, even though the acidosis was relatively mild; and (ii) a reduction in bicarbonate reabsorption was probably the most important factor that limited sodium reabsorption by the renal tubule during this experiment.

Daytime blood pressure elevation after nocturnal hypoxia

The purpose of this study was to investigate whether nocturnal hypoxia causes daytime blood pressure (BP) elevation. We hypothesized that overnight exposure to hypoxia leads the next morning to elevation in BP that outlasts the hypoxia stimulus. We studied the effect on BP of two consecutive night exposures to hypobaric hypoxia in 10 healthy normotensive subjects. During the hypoxia nights, subjects slept for 8 h in a hypobaric chamber at a simulated altitude of 4,000 m (barometric pressure = 462 mmHg). Arterial O(2) saturation and electrocardiogram were monitored throughout the night. For 30 min before the nocturnal simulated ascent and for 4 h after return to baseline altitude the next morning, BP was measured every 5 min while the subject was awake. The same measurements were made before and after 2 normoxic nights of sleep in the hypobaric chamber at ambient barometric pressure (745 mmHg). Principal components analysis was applied to evaluate patterns of BP response after the second night of hypoxia and normoxia. A distinct pattern of diastolic BP (DBP) elevation was observed after the hypoxia night in 9 of the 10 subjects but in none after the normoxia night. This pattern showed a mean increase of 4 mmHg in DBP compared with the presleep-awake baseline in the first 60 min and a return to baseline by 90 min. We conclude that nocturnal hypoxia leads to a carryover elevation of daytime DBP.

Changes in urinary uric acid excretion in obstructive sleep apnea before and after therapy with nasal continuous positive airway pressure

STUDY OBJECTIVE

To assess the utility of urinary uric acid excretion as a marker of nocturnal hypoxia in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS) before and after the institution of nasal continuous positive airway pressure (CPAP).

DESIGN

Prospective, open.

SETTING

Sleep Disorders Laboratory, Veterans Affairs Medical Center.

PARTICIPANTS

Thirty consecutive male subjects, 20 with OSAHS and 10 without OSAHS.

MEASUREMENTS AND METHODS

Spot morning urine and venous blood samples were obtained in all subjects; samples were also obtained after the application of CPAP in those with OSAHS. Uric acid excretion, normalized to creatinine clearance, was calculated as the product of urinary uric acid and serum creatinine concentrations divided by urine creatinine concentration. In patients with OSAHS, uric acid excretion was 0.55+/-0.1 mg/dL before CPAP therapy and decreased to 0.30+/-0.01 mg/dL after CPAP therapy (p < 0.001). The latter value did not differ significantly from the mean value (0.32+/-0.03 mg/dL) in the control group. Uric acid excretion in OSAHS patients correlated significantly with the apnea-hypopnea index (r=0.42; p<0.0003).

CONCLUSION

Uric acid excretion is increased in OSAHS patients and normalizes after CPAP treatment, most likely reflecting differences in tissue oxygenation between the two conditions. Further studies in large number of patients may confirm the usefulness of this simple test for diagnosis and follow-up of patients with OSAHS.

Plasma hypoxanthine reacts more abruptly to changes in oxygenation than base deficit and uric acid in newborn piglets

Previously, high postmortem concentrations of hypoxanthine have been found in vitreous humor of children dying from sudden infant death syndrome (SIDS). We wanted to investigate further the accumulation of hypoxanthine in vitreous humor during hypoxia. Twenty-four piglets aged 9-15 days were exposed to continuous hypoxemia (180 min 11% O2, n = 6), long interval intermittent hypoxemia (60 min 11% O2, 20 min room air, n = 7) or short interval intermittent hypoxemia (10 min 9% O2, 10 min room air with (n = 6) or without (n = 5) superimposed ligation of both carotid arteries). The increase in vitreous humor Hyp was four-fold higher (p < 0.01) with ligation of the carotid arteries (14 +/- 2.4 to 38 +/- 8.9 mumol/l) than without ligation (15 +/- 2.8 to 21 +/- 5.9 mumol/l). During continuous hypoxemia, plasma Hyp (r = 0.85), Xa (r = 0.89) uric acid (UA) (r = 0.85), and base deficit (BD) (r = 0.78) increased almost linearly (p < 0.001). Plasma Hyp responded more abruptly to changes in oxygenation than base deficit (BD) and UA. Ligation of the carotid arteries had a strong impact on Hyp accumulation in vitreous humor, suggesting that vitreous humor Hyp is not merely a filtration product of plasma Hyp, but reflects local hypoxia/ischemia in the eye.

Effects of prolonged hypoxemia on fetal renal function and amniotic fluid volume in sheep

OBJECTIVE

Our purpose was to determine the effects of prolonged hypoxemia on fetal renal function and amniotic fluid volume and composition.

STUDY DESIGN

Twelve pregnant ewes underwent surgery at 115 +/- 2 days after mating (term approximately 147 days) for the implantation of fetal vascular, bladder, and amniotic sac catheters. At 125 +/- 1 days seven fetuses were studied during 6 days of hypoxemia and five control fetuses were studied over six days of normoxemia. Index values of fetal renal function and amniotic fluid volume were measured.

RESULTS

During hypoxemia fetal SaO2 and PaO2 were reduced from 60.9% +/- 1.6% and 21.9 +/- 0.6 mm Hg to 29.6% +/- 3.8% and 14.9 +/- 0.8 mm Hg, respectively. Fetal hypoxemia was associated with a transient acidemia (arterial pH 7.29 +/- 0.02) at 4 hours. There were no sustained alterations in fetal urine production (9.5 +/- 0.8 ml/hr/kg) or glomerular filtration rate (1.3 +/- 0.1 ml/min/kg) during hypoxemia. In control fetuses the amniotic fluid volume increased over 7 days, from 717 +/- 169 ml to 1031 +/- 147 ml, whereas in the hypoxemic fetuses it did not change (741 +/- 68 ml) over the same period.

CONCLUSION

During prolonged fetal hypoxemia in the absence of acidemia, fetal urine production is maintained, whereas the normal gestational increase in amniotic fluid volume is prevented, raising the possibility that intramembranous reabsorption of amniotic fluid is increased by hypoxemia.

Capillary filtration coefficient and urinary albumin leak at altitude

Rapid ascent to altitude risks the development of acute mountain sickness. This study demonstrates changes in peripheral capillary filtration coefficient and renal protein loss in subjects suffering from various degrees of mountain sickness after passive ascent to 4559 m. Capillary filtration coefficient of the calf capillary bed, measured by computer-based multistep strain gauge plethysmography, increased significantly after 23.5 h at altitude when symptoms were most severe: 4.45 (2.76-6.03) to 6.31 (3.86-11.07) ml min(-1) per 100 g of tissue mmHg(-1), median (range) (P < 0.02). Urinary albumin excretion was increased after one night at altitude from 1.1 (0.6-1.5) to 2.45 (1.0-6-8) mg of albumin per mmol of creatinine (P < 0.05). These results demonstrate simultaneous leakage of a peripheral capillary bed to fluid measured by strain gauge plethysmography, and renal albumin leak, and suggest a systemic process of increased capillary leakage for different-sized molecules caused by rapid exposure to hypobaric hypoxia.

Biosynthesis of prostacyclin and thromboxane A2 during chronic hypoxaemia in children with cyanotic congenital heart disease

The high risk of vaso-occlusive events in children younger than 4 years with cyanotic congenital heart disease and polycythaemia has been attributed to increased thromboxane (Tx) A2 formation. In older children with cyanotic congenital heart disease, however, the risk of vaso-occlusive events is much lower. We therefore hypothesized that the formation of TxA2 and prostacyclin is not disturbed in this age group. We measured urinary excretion of stable index metabolites of in vivo TxA2 and prostacyclin formation by gas chromatography-mass spectrometry in nine children (age 5.9-14.4, median 8.7 years) with cyanotic congenital heart disease, and in nine healthy, age-matched control subjects. The patients excreted less 2,3-dinor-TxB2 (systemic TxA2 formation, P = 0.03), 2,3-dinor-6-keto-PGF1 alpha (systemic prostacyclin formation. P = 0.03) and TxB2 (renal TxA2 formation, P = 0.01) than the control subjects. We conclude that in children older than 5 years with cyanotic congenital heart disease, endogenous synthesis of TxA2 and prostacyclin is not stimulated. This result may explain the lower risk of vaso-occlusive events in this age group as compared with younger children. In addition, our results suggest that chronic hypoxaemia may affect the in vivo formation of TxA2 and prostacyclin and the metabolic disposition of TxB2.

Urinary leukotriene E4 levels increase upon exposure to hypobaric hypoxia

STUDY OBJECTIVE

To determine whether urinary leukotriene E4 (uLTE4) levels increase upon exposure to high altitude, and also to ascertain the relationship between uLTE4 levels and symptoms of acute mountain sickness (AMS).

DESIGN

Prospective, unblinded, single-factor (altitude) experimental study.

SETTINGS

US Army research laboratory facilities at sea level ([SL] 50 m), 1,830 m, and 4,300 m.

PARTICIPANTS

Eight healthy male subjects ranging in age from 19 to 24 years.

MEASUREMENTS

uLTE4 levels and symptoms of AMS were measured at just above SL (50 m), 3 1/2 days after being transported from SL to moderate altitude (MA) (1,830 m), and 1 1/2 days after ascent from 1,830 to 4,300 m (high altitude [HA]). Symptoms of AMS were assessed using standard indexes derived from the Environmental Symptoms Questionnaire weighted toward cerebral (AMS-C) and respiratory (AMS-R) manifestations. Oxygen saturation was measured noninvasively by pulse oximetry at SL and HA.

RESULTS

The mean (+/-SEM) uLTE4 levels (pg/mg creatinine) were 67.9 (+/-13.2) at SL; 82.3 (+/-5.5) at MA; and 134.8 (+/-19.4) at HA (p < 0.05 comparing HA with SL and MA).

CONCLUSIONS

We conclude that uLTE4 levels increase shortly after exposure to HA even after staging for 4 days at MA. Although this study does not clearly demonstrate a relationship between uLTE4 levels and symptoms of AMS, it supports the hypothesis that leukotrienes may be involved in the pathophysiologic state of AMS.

Renal kallikrein in chronic hypoxic rats

1. We have studied the role of kallikrein (KK) in the maintenance of renal function in chronic hypoxic rats (high altitude; HA), compared with control rats kept at sea level (SL). Hypoxia was induced by placing female Wistar rats (198-290 g) in an altitude chamber (5500 m) 15 h/day for 4 weeks. Experiments were also conducted to study the interaction of KK with renal nerve activity and endothelin (ET), two parameters previously shown to be altered in this model. 2. It was found that renal cortex tissue KK activity (TKA) was not significantly different in 10 SL and 10 HA rats. However, the urinary KK activity (UKA) was reduced nearly to half (from 35.2 +/- 4.6 to 18.5 +/- 1.7 pkat/min) in HA rats after 4 weeks of chronic hypoxia. 3. Acute renal denervated diuresis was accompanied by a significant increase in UKA (from 9 +/- 2 to 14 +/- 2 pkat/min in HA and denervated HA rats, respectively; P < 0.05) in HA rats. Intrarenal arterial pretreatment of aprotinin reduced the denervated diuresis. 4. Endothelin (600 ng/kg per h) reduced urine flow, sodium and potassium excretion in the ipsilateral kidney in another 10 SL and 10 HA rats. The extent of the drop of these parameters was significantly less in HA rats. Urinary KK activity was correlated significantly with the measured renal functional parameters (r ranging from 0.472 to 0.612) in SL rats, but was insignificant in HA rats (r ranging from 0.032 to 0.192). 5. We have demonstrated that chronic exposure to hypoxia decreases urinary KK excretion and that KK is involved in acute renal denervated diuresis generated in these animals. The present study suggests that KK plays a partial role in the maintenance of renal function in chronic hypoxic rats.

Effects of hypoxia on urinary organic acid and hypoxanthine excretion in fetal sheep

Severe birth asphyxia leads to a transient organic aciduria and increased hypoxanthine excretion. To investigate its origin and timing, we analyzed urine from 12 late gestation fetal sheep in utero subjected to moderately severe isocapnic hypoxia for 1 h. In six fetuses the carotid sinus nerves were cut to determine whether reflex peripheral vasoconstriction contributed to the changes in excretion. After a control period of 1 h, maternal inspired oxygen was reduced for 1 h so that fetal arterial oxygen tension fell significantly from 2.86 +/- 0.12 kPa (mean +/- SEM) to 1.55 +/- 0.04 kPa. The ewes were returned to normoxia, and monitoring was continued for 1 h. Fetal heart rate, arterial blood pressure, and femoral arterial blood flow (intact fetuses only) were recorded, and arterial pH, blood gases, and lactate were measured. Urine collected via a bladder catheter was analyzed for organic acids and hypoxanthine with gas chromatography-mass spectrometry. In intact fetuses, hypoxia increased excretion of hypoxanthine and several organic acids, notably lactic acid and intermediates of valine catabolism. Changes were apparent by 15 min, significant by 45 min, and maximal after reoxygenation. In denervated fetuses, there were small, significant, increases in organic acids and hypoxanthine by 45 min of hypoxia, but there was no surge in excretion posthypoxia. Hypoxia caused a large, significant, fall in femoral arterial blood flow in intact fetuses. We conclude that the extent of the reflex peripheral vasoconstriction, particularly in skeletal muscle, determines the amount of organic acid and hypoxanthine excretion and may explain similar biochemical disturbances after birth asphyxia. Urinary lactic acid measurement has a potential value for grading birth asphyxia.

Phosphate excretion during 24 h of hypoxia in conscious rats

The objective of this study was to investigate renal phosphate excretion during 24 h of hypoxia in conscious rats fed by total parenteral nutrition. Wistar rats weighing 190 g were exposed to hypoxia (inspired oxygen fraction = 0.10) or normoxia (inspired oxygen fraction = 0.21) for 24 h in a normobaric chamber. Renal clearance and hormonal studies were performed. The results showed a greater fractional excretion of phosphate (5.37 +/- 0.07%, P < 0.05) and hypophosphataemia (7.40 +/- 0.12 mg dL-1, P < 0.01) in hypoxic rats (n = 10) than in normoxic rats (n = 13; 3.50 +/- 0.37% and 8.02 +/- 0.16 mg dL-1, respectively). In addition, during hypoxia there was a significant decrease in the excretion of urinary adenosine 3',5'-cyclic monophosphate per glomerular filtrate (2.97 +/- 1.27 nmol dL-1, P < 0.005), a parameter of the renal action of parathyroid hormone, and a stable level of serum parathyroid hormone (10.2 +/- 2.6 ng mL-1) (cf. normoxia: 8.57 +/- 0.70 nmol dL-1 and 8.0 +/- 1.7 ng mL-1, respectively). However, creatinine clearance and the renal adenosine triphosphate level, both of which affect adenosine 3',5'-cyclic monophosphate excretion, were not different between the two groups. These data suggest that exposure of conscious rats to 24 h of hypoxia causes renal hyporesponsiveness to physiological levels of parathyroid hormone, which is manifested as a decrease in adenosine 3',5'-cyclic monophosphate excretion. Phosphaturia is not a direct net effect of hypoxia and secondary hypocapnia on renal phosphate transport, which is known to be regulated by parathyroid hormone through adenosine 3',5'-cyclic monophosphate.

Plasma endogenous digoxin-like substance levels are dependent on blood O2 in man

1. Recently, we have demonstrated that hypoxic breathing is followed by an increase in plasma digoxin-like substance in normal men. 2. This study was undertaken in order to evaluate whether or not a low arterial O2 partial pressure is combined with an increase in plasma digoxin-like substance in chronic pathological conditions also. 3. Sixteen male patients (mean age 53.1 +/- 3.7 years) affected by chronic obstructive pulmonary disease of a mild stage were studied. They were further subdivided according to their arterial O2 partial pressure into 'mild hypoxic' (n = 8, mean age 52.5 +/- 2.7 years), with an arterial O2 partial pressure between 66 and 75 mmHg, and 'severe hypoxic' (n = 8, mean age 54.3 +/- 5.1 years), with an arterial O2 partial pressure < or = 65 mmHg, groups. Seven healthy men (mean age 48.5 +/- 4.8 years) voluntarily participated as the control group. 4. Plasma digoxin-like substance levels were significantly higher in 'severe hypoxic' patients (203.5 +/- 9.9 pg/ml) than in both 'mild hypoxic' patients (169.5 +/- 31.4 pg/ml, P < 0.02) and normal subjects (158.9 +/- 12.4 pg/ml, P < 0.0001) and were directly correlated with urinary Na+ excretion (severe hypoxic group, r = 0.756, P < 0.007; mild hypoxic group, r = 0.789, P < 0.02). Considering the two hypoxic groups together, plasma digoxin-like substance levels were negatively correlated with arterial O2 partial pressure (r = -0.740, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of angiotensin converting enzyme inhibition on sodium excretion in patients with hypoxaemic chronic obstructive pulmonary disease

BACKGROUND

Some patients with hypoxaemic chronic obstructive pulmonary disease (COPD) develop cor pulmonale with sodium and water retention. The sodium retention has been explained as a result of increased plasma levels of aldosterone. If this was true angiotensin converting enzyme (ACE) inhibition would be expected to lower plasma levels of aldosterone and improve the renal excretion of sodium.

METHODS

Six patients with stable hypoxaemic COPD (PaO2 < 8.0 kPa) and a history of an oedematous exacerbation received an intravenous hypertonic saline load (6 ml/kg body weight of 2.7% saline over one hour) before and while taking 4 mg/day perindopril, an ACE inhibitor, for one month. Aldosterone, antidiuretic hormone (ADH), plasma and urine electrolyte levels, osmolality, and volume were measured over four hours. The repeatability of the saline load test was assessed in six patients with a similar severity of hypoxaemic COPD. For comparison the saline load test was also performed in six patients with mild COPD.

RESULTS

The hypertonic saline load test results were repeatable. Perindopril reduced the mean (SD) plasma level of aldosterone from 142 (88) pg/ml to 54 (24) pg/ml at 0 minutes before the saline infusion, and from 64 (35) pg/ml to 30 (17) pg/ml after the infusion without improving the urinary volume or sodium excretion. Before starting treatment with perindopril 43.7 (6.9) mmol (20%) of the sodium load was excreted compared with 49.6 (7.9) mmol (22% of load) when taking perindopril. Patients with mild COPD excreted more sodium (77.6 (21.4) mmol (38.7% of load)) despite having similar plasma aldosterone levels to those in the patients receiving perindopril.

CONCLUSIONS

Patients with stable hypoxaemic COPD have an impaired ability to excrete sodium which is not improved by the administration of an ACE inhibitor. ACE inhibition lowered the plasma level of aldosterone without improving sodium excretion. This suggests that the inability of patients with hypoxaemic COPD to excrete sodium is not caused by their increased plasma levels of aldosterone.

Acute hypoxia and endogenous renal endothelin

Endothelin (ET) is a potent vasoconstrictor peptide of endothelial cell origin. Recent studies have suggested a nonvascular paracrine and/or autocrine role for endothelin in the kidney. This study was designed to elucidate the renal ET response to acute moderate hypoxia, as reflected by urinary ET excretory rate and renal tissue ET immunoreactivity, and to correlate these responses to the hemodynamic and excretory changes during hypoxia. Experiments were conducted in two groups of anesthetized dogs: hypoxic group (10% O2 ventilation: PO2, 44 mm Hg; N = 7) and time control group (room air ventilation: PO2, 111 mm Hg; N = 6). After 60 min of hypoxia or room air ventilation, kidneys were harvested and stained immunohistochemically for ET. Acute moderate hypoxia was associated with significant increases in urinary ET excretion, urine flow, urinary sodium excretion, and fractional excretion of sodium (P < 0.05). There was no significant change in GFR, RBF, renal vascular resistance, or mean arterial pressure. Renal immunohistochemistry for ET revealed increased staining in the proximal and distal tubules in the hypoxic group as compared with controls. This study demonstrates that acute moderate hypoxia results in increased urinary ET excretion and renal tubular ET immunoreactivity, in association with diuresis and natriuresis, and suggests a nonvascular role of endogenously produced renal ET in the regulation of sodium homeostasis during hypoxia.

Effect of acute hypoxia on phosphate excretion in rats

This study evaluated the effect of acute hypoxia on renal handling of phosphate in rats in the presence and absence of parathyroid hormone (PTH). Hypoxia causes respiratory alkalosis in spontaneously breathing humans and animals. Respiratory alkalosis has been reported to induce a blunted phosphaturic response to PTH. In this study, to avoid the confounding effect of hypocapnia accompanying the hypoxia on phosphate excretion, the rats were ventilated mechanically, and arterial PCO2 levels were controlled. Rats were divided into two main groups depending on the arterial PO2 levels: a hypoxic group (n = 16) and a normoxic group (n = 18). Hypoxia was produced by ventilating with 10% oxygen, and hypocapnia was produced by hyperventilation. In response to PTH, the hypoxic rats without hypocapnia showed a greater increase in fractional excretion of phosphate (FEPi; 37.7 +/- 2.6%, mean +/- SE) compared with normoxic rats (27.4 +/- 2.5%, P < 0.02). During hypocapnia, there was no difference in FEPi between hypoxic and normoxic groups (21.2 +/- 1.5 and 19.5 +/- 1.2%, respectively), and both groups showed a significantly blunted phosphaturic response to PTH compared with normocapnia (P < 0.05 and P < 0.01, respectively). Urinary adenosine 3',5'-cyclic monophosphate (cAMP) increased similarly after PTH infusion between each group. To test whether the phosphaturic effect of PTH in hypoxia and the blunted phosphaturic effect of PTH in hypocapnia are due to steps beyond the generation of cAMP, the phosphaturic response to cAMP infusion was evaluated in 1) hypoxic and normocapnic rats (n = 6), 2) normoxic and normocapnic (control) rats (n = 6), and 3) normoxic and hypocapnic rats (n = 7).(ABSTRACT TRUNCATED AT 250 WORDS)

Overnight urinary uric acid: creatinine ratio for detection of sleep hypoxemia. Validation study in chronic obstructive pulmonary disease and obstructive sleep apnea before and after treatment with nasal continuous positive airway pressure

During hypoxia ATP degradation to uric acid is increased in animal models and humans. To assess the reliability of an overnight increase in uric acid excretion as a marker of nocturnal hypoxemia, we selected 10 normal volunteers (7 males and 3 females), 29 COPD patients (26 males and 3 females), and 49 subjects with obstructive sleep apnea (OSA) (43 males and 6 females). The patients underwent standard polysomnography, which was repeated in 14 subjects with nasal continuous positive airway pressure (CPAP), and were subdivided into two groups: Group D included desaturating subjects who spent at least 1 h at SaO2 < 90% and 15 min below 85%, and Group ND were nondesaturating subjects. The overnight change in the uric acid:creatinine ratio (delta UA:Cr) was negative in normal subjects (-27.5 +/- 9.1 [mean +/- SD]) and ND groups: -19.7 +/- 14.3 in COPD, -16.1 +/- 13.0 in OSA. In both COPD and OSA Group D, the ratio was usually positive: delta UA:Cr was 17.9 +/- 31.4 in Group D COPD (p < 0.001 versus ND) and 10.1 +/- 30.7 in Group D OSA (p < 0.001 versus ND and versus normal subjects) despite 4 of 15 false negative results in COPD and 8 of 20 in OSA. CPAP effective treatment induced a marked reduction ((p = 0.0024) in delta UA:Cr, leading to a negative value. We conclude that delta UA:Cr seems to be a promising index of significant nocturnal tissue hypoxia, with good specificity but poor sensitivity (about 30% false negative), which might be useful for the long-term follow-up of outpatients on nasal CPAP with a positive ratio at baseline.

Body fluid alterations during head-down bed rest in men at moderate altitude

To determine the effects of hypoxia on fluid balance responses to simulated zero-gravity, measurements were made in six subjects (acclimatized to 5,400 ft; 1,646 m) before and during -5 degrees continuous head-down bed rest (HDBR) over 8 d at 10,678 ft. The same subjects were studied again at this altitude without HDBR as a control (CON) using a cross-over design. During this time, they maintained normal upright day-time activities, sleeping in the horizontal position at night. Fluid balance changes during HDBR in hypoxia were more pronounced than similar measurements previously reported from HDBR studies at sea level. Plasma volume loss (-19% on day 6) was slightly greater and the diuresis and natriuresis were doubled in magnitude as compared to previous studies in normoxia and sustained for 4 d during hypoxia. These changes were associated with an immediate, but transient rise in plasma atrial natriuretic peptide (ANP) to day 4 of 140% in HDBR and 41% in CON (p < 0.005), followed by a decline towards baseline. Differences were less striking between HDBR and CON for plasma antidiuretic hormone and aldosterone, which were transiently reduced by HDBR. Plasma catecholamines showed a similar pattern to ANP (+122%) in both HDBR and CON, suggesting that elevated ANP and catecholamines together accounted for the enhanced fluid shifts with HDBR during hypoxia.

Effects of hypoxemia at sea level and high altitude on sodium excretion and hormonal levels

Acute hypoxemia at sea level is associated with decreased aldosterone secretion. This inhibition is thought to be mediated through secretion of atrial natriuretic factor (ANF). The interaction of these two hormones should result in enhanced renal salt excretion during hypoxemic conditions. This hypothesis was tested by administration of a standardized salt load to seven normal subjects during normoxemia at sea level (SL), acute hypoxemia (AH) at sea level, and high altitude (HA) (3,000 m). Urine and venous blood samples were collected and analyzed. A natriuresis and diuresis was observed only under AH conditions. It was accompanied by a decrease in plasma aldosterone levels, but did not correlate with changes in plasma aldosterone levels, ANF, or other hormones. Increased plasma renin activity (PRA) and increased norepinephrine levels were encountered at HA, suggesting sympathetic nervous system activation. No change in anti-diuretic hormone (ADH) levels with increased plasma osmolality was seen at HA. We conclude that excretion of a salt load during normobaric hypoxemia is enhanced by a decrease in plasma aldosterone levels, unrelated to changes in ANF or other hormones. The differences observed in norepinephrine, PRA, and ADH levels during HA versus AH conditions suggest that hypobaria or chronic hypoxemia may influence these hormonal responses.

Effects of high altitude exposure on plasma and urinary digoxin-like immunoreactive substance

Six young healthy subjects underwent a 20 day exposure to altitude, at 4930 m (16,174 ft), to evaluate possible plasma and urine digoxin-like immunoreactive substance (DLIS) changes accompanying the altered water and electrolyte balance induced by hypoxia. We studied DLIS, plasma renin activity (PRA), aldosterone, atrial natriuretic peptide (ANP), and arginine vasopressin (ADH) in serial blood and urine samples. An increase in DLIS in plasma (P less than .005) and urine (P less than .01) was found, while aldosterone was decreased (P less than .02). PRA, ADH, and ANP did not change significantly. A trend to a greater loss of sodium through urinary excretion, correlated with urinary DLIS values (r = 0.47, P less than .01), was observed. Data suggest a possible important role of DLIS in adaptive response of human organism to high altitude.

The adenosine receptor blocker aminophylline increases anoxic ethanol excretion in crucian carp

By depressing energy consumption, anoxia-tolerant animals are thought to compensate for a reduced ability to produce energy during anoxia. Adenosine is an inhibitory neuromodulator in vertebrates and, hence, has the potential ability to depress energy consumption. Ethanol is the main metabolic end product in anoxic Carassius, and the present study shows that the rate of ethanol excretion in anoxic crucian carp (Carassius carassius L.) can be increased threefold by treatment with the adenosine receptor antagonist aminophylline (75 mg/kg). By contrast, the same dose of aminophylline did not increase the rate of routine oxygen consumption during normoxia. It is hypothesized that adenosine acts as a metabolic depressant during anoxia in crucian carp.

Influence of endogenous prostaglandins on mTAL injury

We altered renal prostaglandin production by isolated rat kidneys in several ways to see if this would influence the susceptibility of cells lining the medullary thick ascending limb to injury. Rats were fed a diet containing either safflower oil (high in linoleic acid) or fish oil (low in arachidonate precursors) as a source of fat. After 90 min of perfusion, the kidneys of rats fed safflower oil showed only 32.7 +/- 6.7% of medullary thick ascending limb cells near the inner medulla with severe damage, whereas the same zone in perfused kidneys of rats fed fish oil showed 96.6 +/- 1.3% severely damaged cells (P less than 0.01). The protection afforded by safflower oil was accompanied by a doubling of urinary excretion of PGE2 and 6-keto-PGF1 alpha, and was eliminated by indomethacin, which suppressed prostaglandin synthesis. Perfusion with bradykinin also greatly increased prostaglandin excretion and reduced severe medullary thick ascending limb damage in the deepest zone of the outer medulla from 51.3 +/- 6.6% in controls to 28.5 +/- 5.9% (P less than 0.02). The protection provided by bradykinin was also completely reversed by indomethacin. The results suggest that endogenous prostaglandins serve a protective function against hypoxic injury for cells of the medullary thick ascending limb.

[Degradation of purine nucleotides in patients with chronic obstruction to airflow]

The increase in hypoxanthine (Hx), xanthine (X), uric acid (VA) and total purines (TP) that may be found in several clinical conditions associated with tissue hypoxia has been attributed to an increase in adenine nucleotides degradation by a reduced ATP synthesis caused by oxygen deprivation. To test this hypothesis we have investigated the urinary excretion of Hx, X, VA, TP and radioactivity elimination after labeling the adenine nucleotides with adenine (8-14C) in 5 patients with chronic airflow obstruction (CAFO), in the basal state and after oxygen therapy (FiO2, 24%). The results were compared with those from 4 normal individuals. Patients with COFA showed an increase of the renal elimination of Hx, X, VA, TP and radioactivity, which was significantly different from the control group (p less than 0.05). Oxygen administration was associated with a significant reduction in the excretion of purines and radioactivity (p less than 0.01), which decreased to values similar to those found in normal individuals. These findings suggest that in patients with COFA and severe hypoxemia there is a marked increase in the degradation of adenine nucleotides. The normalization of the purine and radioactivity excretion after oxygen therapy points to a basic role of oxygen in the catabolism of adenine nucleotides.

[Effects of hypoxia on plasma concentrations and daily elimination of sodium, potassium and chlorine ions]

Serum concentrations of Na+, K+ and Cl- are studied, as well as the elimination of these ions in urine, in patients suffering from chronic respiratory insufficiency, being classified in two groups according to the level of hypoxemia: group A (PO2 less than 6.66 KPa) and group B (PO2 less than 8 KPa). A third group C of healthy patients with analogous anthropological characteristics has served as a control group. The concentrations of serum of the three ions are noticeably similar in the three groups, but the daily elimination of Na+, K+ and Cl- is less in those suffering from respiratory insufficiency than in those of the control group, with significant statistical differences in all cases except with K+ in those suffering from pronounced hypoxemia. On analysing the correlation between the rates of elimination of ions in urine, with the plasmatic values of PO2, PCO2 and [H+] of all the patients studied, the highest values of the Pearson coefficient are found on correlating the elimination of ions with the partial pressures of oxygen, therefore suggesting that hypoxia could be the main motor inducing metabolic changes.

Nocturnal increase of urinary uric acid:creatinine ratio. A biochemical correlate of sleep-associated hypoxemia

Sleep-associated hypoxemia may result in tissue hypoxia and increased production and excretion of adenosine triphosphate (ATP) degradation intermediates and uric acid. Urinary uric acid:creatinine(UA:Cr) ratio is a convenient method for estimating uric uric acid excretion. We measured the overnight changes in urinary UA:Cr ratio in 17 patients with documented sleep-associated hypoxemia, 13 control patients who remained normoxemic during polysomnography, and 14 normal volunteers. The urinary UA:Cr ratio increased overnight in patients with sleep-associated hypoxemia (+31.2 +/- 10.9%), whereas it decreased in the control patients with negative sleep studies (-13.6 +/- 4.6%; p less than or equal to 0.01) and in the normal volunteers (-23.2 +/- 5.8%). Repeat polysomnography revealed interval resolution of sleep-associated hypoxemia in 2 patients and significant improvement in a third. In every case, this clinical improvement was accompanied by a decrease in the overnight change in UA:Cr ratio. We report that urinary UA:Cr ratio increased overnight in a nonhomogeneous group of patients with sleep-associated hypoxemia.

The combined effects of hypoxemia and mechanical ventilation on renal function

The combined effects of hypoxemia and mechanical ventilation on renal function were investigated in anesthetized dogs. Spontaneously breathing dogs (S) and dogs mechanically ventilated with a volume-ventilator (V) were made hypoxemic by breathing hypoxic gas to achieve PaO2 values of 35 and 22 mm Hg. At a PaO2 of 35 mm Hg, urine output and sodium excretion were increased in both groups. These responses closely followed the blood pressure response, which was greater in the V group. Renal blood flow (RBF), glomerular filtration rate (GFR), and fractional sodium excretion (FNA) were unchanged. At a PaO2 of 22 mm Hg, both groups demonstrated a reduction in urine flow, sodium excretion, FNA, RBF, and GFR. However, the mechanism involved was different and ventilator-dependent. At this low PaO2, arterial blood pressure was reduced in the S group with no change in renal resistance, while blood pressure increased in the V group with a marked increase in renal resistance as a result of the modification of the cardiovascular effects of lung inflation reflexes by mechanical ventilation. These results indicate that renal function is well-maintained at low PaO2 values (35 mm Hg) and reduced at more severe hypoxemia, mainly in response to systemic hemodynamics.

Free, glucuronide, and sulfate catecholamines in the rat: effect of hypoxia

The formation and excretion of conjugated catecholamines (CA) was studied in conscious rats after sympathetic stimulation by hypoxia (5.5-6% O2, 4 h). Hypoxia induced a rapid and intense increase of free epinephrine (E, X 12) and norepinephrine (NE, X 6) but only a limited enhancement of free dopamine (DA, X 2). Sulfate conjugates of E and NE had kinetics similar to the free forms, while glucuronides were only moderately and lately altered. In contrast to free and sulfated DA, DA glucuronide, the major plasma conjugate, was decreased (-25%). This result suggests that DA glucuronide, unlike other CA conjugates, is not related to detoxication but might supply a CA precursor. Urinary conjugates badly reflected plasma conjugates. In normoxic controls, CA conjugates prevailed in the plasma, whereas the free amines prevailed in the urine. Hypoxia increased mainly the excretion of E and NE glucuronide but not of the free amines. Urinary DA, free or conjugated, was decreased (-25%), a result in keeping with plasma DA glucuronide only. The poor relations between plasma and urine catecholamines pinpoint the importance of the kidney in CA handling.

[Alterations in urinary N-Acetyl-beta-D-glucosaminidase (NAG), beta 2-microglobulin (BMG) under acute exposure to simulated 6,000 m altitude]

The changes in NAG and BMG concentration in the urine during sudden exposure to a simulated 6,000 m altitude (354 mmHg) were studied. Subjects were 5 healthy male volunteers before a mountain climbing expedition (20-25 years old). Decompression was commenced at 11:00 and terminated at 17:00 (2-h ascent, 2-h sojourn, 2-h return) for 5 successive days. Urine was discarded at 9:00 and thereafter collected at 11:00 (group I), 14:00 (group II) 17:00 (group III), and 9:00 the next day (group IV) and urinary NAG and BMG was measured. The rate of NAG indicated elevation above 5.0 U/L in 2 cases in group III and elevation which was significantly different from that of the other 3 groups. In the other 3 cases, significant elevation was not observed, but for group III as a whole NAG excretion was significantly elevated compared of the other 3 groups. However, increased excretion of NAG was not observed on all 5 successive days. The change in BMG values was smaller than that of the NAG values and no significant elevation was observed in any of the 4 groups. Increasing urinary excretion of NAG by sudden exposure to a high altitude indicated excessive destroy of epithelium in the proximal tubules, but this change was reversible.

Excretion of vasopressin in the hypoxic lamb: comparison between fetus and newborn

The factors associated with increased renal excretion of vasopressin (VP) were examined in the hypoxic fetus and newborn. Studies were conducted on six chronically instrumented fetal (117-136 days gestation) and seven newborn lambs (2-6-day-old). Hypoxia was produced by administration of 10% oxygen to the ewe or neonate for 30 min. This procedure caused a 50% reduction in PaO2, no significant change in pHa in either fetus or neonate and a slight fall in PaCO2. Hypoxia caused an increase in VP concentrations in plasma from 1.3 +/- 0.53 to 46.4 +/- 4.71 pg/ml in the fetus and from 5.9 +/- 2.80 to 50.2 +/- 26.68 pg/ml in the neonate. After hypoxia there was a fall in urine output from 0.27 +/- 0.045 to 0.17 +/- 0.046 ml/(min X kg) in the fetus and from 0.15 +/- 0.033 to 0.09 +/- 0.022 ml/(min X kg) in the newborn. The corresponding values for urine osmolality were the following: 168 +/- 30.8 to 325 +/- 30.6 mOsm/kg in the fetus and 388 +/- 65.4 to 523 +/- 51.8 mOsm/kg in the newborn. VP concentration in urine increased from 13 +/- 9.4 to a maximum of 176 +/- 32.4 pg/ml after 30 min of recovery in the fetus and 39 +/- 4.6 to 278 +/- 132.5 pg/ml after 1 h of recovery in the newborn. These levels remained high for at least 1 h after the end of hypoxia. There was a good linear correlation between plasma VP levels and the corresponding urine levels and excretion rates in both the fetus and newborn.(ABSTRACT TRUNCATED AT 250 WORDS)

Antidiuretic hormone responses to eucapnic and hypocapnic hypoxia in humans

Urinary excretion rate of antidiuretic hormone (UADHV) was studied in male volunteers in response to hypobaric hypoxia. The first series consisted of three groups. The chamber was decompressed to 465, 495, and 438 Torr during high-altitude (HA) exposure for groups I (n = 5), II (n = 5), and III (n = 4), respectively. In group I, the chamber air contained 3.77% CO2 to prevent alkalosis. The level of hypoxemia was similar in groups I and II. Mean 24-h UADHV was unchanged in group I, but increased 96% (P less than 0.05) and 180% (P less than 0.05) in groups II and III, respectively, on day 1 at HA and was normal during subsequent days at HA regardless of symptoms of acute mountain sickness. Shorter sampling intervals employed in a second series of experiments conducted at 495 Torr revealed a twofold increase in UADHV (P less than 0.05) 8-12 h after ascent in eight asymptomatic subjects; UADHV returned to base line within 9 h and remained low. The symptomatic subjects both had increased UADHV (3- and 8-fold from base line) between 2 and 4 h after ascent. Increased UADHV in asymptomatic subjects may be a result of the concomitant decrease in plasma volume, both of which appeared to be eliminated by CO2 supplementation.

Differential effect of swelling and anoxia on kidney function and its consequences on the mechanism of action of intracellular organ preservation solutions

In order to differentiate the effects of swelling and anoxia on kidney function, a canine experimental model is used. After complete liberation of kidneys and their vessels from adjacent tissues, each kidney is submitted to 10 min of hypotonic flushing, or to 60 min of normothermic anoxia. Swelling resulting from these two procedures are equal and permit the study of the consequences of anoxia independently from swelling. Edema is determined by water content and renal blood flow is measured. Kidney function is studied by time of restoration of urinary flow, creatinine, and inulin clearances and fractional water reabsorption. The results show that nonanoxic edema is much less damaging than anoxic edema and consequently that anoxic injury is not the simple consequence of spatial disruption of cell architecture. Since many works have shown the beneficial effects of intracellular organ preservation solutions and consequently that anoxia is better tolerated in the absence of swelling, it can be deduced that injuries induced by anoxia and by swelling are cumulative and that the efficiency of intracellular solutions cannot be attributed solely to the preventive effect on swelling, considered as lethal for the cell.

The effect of acetazolamide on the proteinuria of altitude

Albumin was measured by dipstick tests and immunologically in 24-h and early morning urine (EMU) samples collected from 20 subjects during a high-altitude trek. Each was given acetazolamide (Diamox sustets) or placebo as part of a double-blind trial on the prophylactic use of acetazolamide in acute mountain sickness (AMS). At the highest altitudes, albuminuria was six times greater in those on placebo (p less than 0.001) and was related to the clinical features of AMS (p less than 0.01) and arterial oxygen tension (p less than 0.001). Urine dipsticks tests for proteinuria were also an index of AMS, but were inaccurate. The proteinuria is probably due to renal hypoxia, which causes increased glomerular permeability, reduced tubular readsorption, or both. The reduction in the clinical features of AMS achieved with acetazolamide therapy is also associate with improved renal function.

Urinary loss of oxypurines in hypoxic premature neonates

The daily urinary excretion of the oxypurines hypoxanthine, xanthine and uric acid during each of the first 3 days of life was determined in premature infants without hypoxia (PI) and in hypoxic premature infants (HPI) with the respiratory distress syndrome. The loss of uric aic was statistically significantly greater in the HPI during days 1, 2, and 3 of life, and so was the loss of xanthine on days 1, and 2, but not on day 3. As to the loss of hypoxanthine, no difference could be shown. In both groups of infants the excretion of hypoxanthine and xanthine together made up about 2% of the total oxypurine loss for each day, the loss of xanthine being the greater of the two. The results did not seem to bear relation to differences between the two groups concerning urinary output, birth weight, gestational age, method of delivery, or administration of exogenic purines. So it appears that the increased loss of oxypurines in HPI is caused by the impact of hypoxia, probably owing to be compromised cellular respiration with a subsequent general displacement of the purine metabolism in the catabolic direction.

[Urinary excretion of hydroxyproline in patients with chronic respiratory insufficiency (author's transl)]

The level of urinary excretion of hydroxyproline is considered as an index of the metabolic activity of the collagen. It increases in situations which include an increase in the osteoblastic activity or in the bone resorption. In respiratory insufficiency a series of conditions occur which are theoretically capable of modyfing this parameter. Twelve patients (9 males and 3 women) with chronic respiratory disease in a situation of respiratory insufficiency (hypoxemia and/or hypercapnia at rest) were studied. The urinary excretion of hydroxyproline in these patients was 15.30 +/- 8.16 mg/day/m2, significantly greater than that of a control group with similar characteristics which was 9.97 +/- 3.07 mg/day/m2 (p less than 0.05; Student's t test). The existence of a significant correlation between the urinary excretion of hydroxyproline and the degree of hypoxemia (r = 0.66; p less than 0.01) was likewise verified; in the same way, although to a lesser degree with the hypercapnia (r = 0.62; p less than 0.05). The different factors capable of influencing the bone metabolism in respiratory insufficiency are discussed, as well as the effects of the medications used by these patients. It is possible, on the other hand, that the increase of the urinary excretion of hydroxyproline does not depend only on alterations in the metabolic condition of the bone, but also on a reduction in the hepatic metabolism of the amino acid in relation with gasometric modifications.

Effects of 6 hours hypoxic and cold exposure on urinary electrolyte and catecholamine excretion

Eleven young male Indian volunteers fasted overnight and were exposed to 6 h to cold at 8 degrees C (I), hypoxia at 4267 m at 28 degrees C (II), and cold plus hypoxia of 4267 m at , degrees C (III), in a walk-in climatic chamber, and excretion of some urinary constituents was measured. Urine output was significantly decreased in (II) and increased in (I) and (III). Urine pH significantly increased only in (II). Catecholamine excretion significantly increased only in (I). Ca++ excretion was significantly raised in (I) and (III) and lowered in (II). Na+ excretion was significantly decreased and K+ excretion remained unchanged in all three stress conditions. Cold seemed to be a greater stressor than hypoxia, under stated experimental conditions.

Erythropoietin excretion in the premature infant

Urinary erythropoietin was determined sequentially in four premature infants throughout their period of physiologic anemia. After the first day of life, no erythropoietin was found, even though there was a marked fall in hematocrit. Among seven premature infants with severe respiratory disease, three excreted elevated amounts of erythropoietin. Premature infants appear able to respond to hypoxia by increasing erythropoietin production. In the absence of hypoxia, however, diminution of erythropoiesis in the early weeks of life is not accompanied by elevated excretion of erythropoietin.

Adrenocortical activity and urinary cyclic AMP levels: effects of hypobaric hypoxia

Six highly motivated and trained military test subjects were exposed to a simulated altitude of 4267 m (477 torr) for 48 hours, prededed and followed by sea level runs lasting 32 hours. During each scenario tests subjects were required to perform their respective military tasks on a continual basis with sporadic rest not exceeding several hours. Extremely high levels of plasma cortisol prior to the start of each session and persistently elevated concentrations of urinary 17-OH corticosteroids at sea level were consistently observed. (This observation probably explains the relatively minor changes in adrenocortical output noted during acute exposure to hypobaric hypoxia. Analogous results were obtained for urinary cyclic AMP, i.e. elevated baseline levels and minimal response to high altitude. The results indicate an attenuated response as well as an association between urinary measures of adrenocortical activity and cyclic AMP excretion.