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PubMed1998

Cardiorespiratory responses to acute hypoxemia in the chronically catheterized fetal llama at 0.7-0.9 of gestation.

The adult llama (Lama glama) has several compensatory mechanisms that allow it to successfully survive at high altitude. Llama fetuses at 0.6-0.7 of gestation, and near-term llama fetuses studied close to surgery, did not increase cerebral blood flow and decreased cerebral oxygen delivery during acute hypoxemia. It is not known whether these responses were the result of immaturity or surgical stress. The aim of this study was to determine whether the lack of increase in cerebral blood flow and the decrease in cerebral oxygen delivery during hypoxemia in the fetal llama is characteristic of this high-altitude species near term, and under nonstressed conditions. We chronically catheterized 7 llamas and their fetuses near to term, at 0.7-0.9 of gestation. Fetal cardiac output, cerebral and regional blood flows, systemic blood pressure, heart rate, pH, and blood gases, organ vascular resistances and organ oxygen deliveries were determined at least 4 days after surgery, both during the basal state and after 1 hr of acute fetal hypoxemia. During hypoxemia the llama fetus did not increase cerebral blood flow and markedly decreased its cerebral oxygen delivery. There was also a marked decrease in kidney blood flow and oxygen delivery. These results indicate that, in contrast to fetuses of lowland species, the fetal llama does not increase the cerebral blood flow during hypoxemia, suggesting specific cellular mechanisms to preserve brain integrity during oxygen limitation.

Acclimatization↗

PubMed1991

The effect of combined hypoxemia and cephalic hypotension on fetal cerebral blood flow and metabolism.

The effect of hypoxemia and cephalic hypotension, alone and in combination, on hemispherical CBF and metabolism was examined in seven chronically catheterized fetal sheep. Hypoxemia was induced by lowering the maternal inspired oxygen fraction and cephalic hypotension was generated by partial occlusion of the fetal brachiocephalic artery. CBF was measured with radionuclide-labeled microspheres. During control, the arterial blood oxygen content (CaO2) was 3.2 +/- 1.0 (SD) mM and CBF averaged 131 +/- 21 (SD) ml min-1 100 g-1. The cephalic perfusion pressure (PP, mean cephalic arterial-sagittal venous) was 40 +/- 4 mm Hg and cerebral vascular resistance (CVR, PP/CBF) was 0.31 +/- 0.06 mm Hg ml-1 min 100 g. During induced hypoxemia, CaO2 was 1.4 +/- 0.7 mM and CBF was elevated to 223 +/- 60 ml min-1 100 g-1. PP was not different from control and CVR was lower at 0.19 +/- 0.04 mm Hg ml-1 min 100 g, reflecting cerebral vasodilation. With cephalic hypotension alone (PP = 21 +/- 4 mm Hg; CaO2 = 3.4 +/- 0.9 mM), CBF fell to 83 +/- 23 ml min-1 100 g-1 and there was no significant change in CVR (0.26 +/- 0.05 mm Hg ml-1 min 100 g). During combined hypoxemia and hypotension (CaO2 = 1.5 +/- 0.8 mM and PP = 18 +/- 4 mm Hg), CBF was significantly greater than during hypotension alone (100 +/- 6 ml min-1 100 g). CVR was 0.19 +/- 0.05 mm Hg ml-1 min 100 g, identical to that measured in normotensive hypoxemia and significantly less than found during hypotension alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1998

Doppler ultrasound evaluation of ductus venosus blood flow during acute hypoxemia in fetal lambs.

It has been demonstrated with invasive techniques in fetal lambs that the ratio of ductus venosus to umbilical vein blood flow rate (DV/UV ratio) increases during hypoxemia and infusion of catecholamines. Recently it was found in human fetuses using pulsed wave Doppler ultrasound equipment that the DV/UV ratio in fetuses with intrauterine growth restriction was significantly increased. The aim of the present study was to show in fetal lambs whether routine Doppler ultrasound devices were capable of determining the DV/UV ratio with sufficient reliability. The experiments were performed on seven near-term instrumented fetal lambs using pulsed wave Doppler ultrasound to measure flow rates (derived, in milliliters per min, from the intensity-weighted mean velocity (Vmean) and the vessel's cross-sectional area) in the ductus venosus and intra-abdominal umbilical vein. Fetal hypoxemia was induced by administering a low-oxygen gas to the ewe (5-7% oxygen, 2% carbon dioxide). Fetal arterial pO2 and heart rate decreased significantly during maternal hypoxia. The proportion of umbilical venous return passing through the ductus venous in controls was 36 +/- 5% (mean +/- SD). This increased to 53 +/- 6% (p < 0.001) because the umbilical venous blood flow fell during late hypoxemia when the heart rate had decreased by 20%. Severe hypoxemia tended to reduce the mean velocity (Vmean) and the minimum velocity (Vmin) (based on the maximum velocity envelope curve) in the ductus venosus, descending aorta and inferior vena cava. The pulsatility index of the umbilical artery significantly increased at the end of hypoxemia. We conclude that determination of the proportion of umbilical vein blood flow entering the ductus venosus by Doppler ultrasound in a clinical setting may contribute to the detection and evaluation of fetal distress.

Acute Disease↗

PubMed2000

Postcardiopulmonary bypass hypoxemia: a prospective study on incidence, risk factors, and clinical significance.

OBJECTIVE: To evaluate the clinical significance of low arterial oxygen tension-inspired oxygen concentration (PaO2-FIO2) ratio, as a measure of hypoxemia, in the early period after cardiac surgery with cardiopulmonary bypass (CPB); and to evaluate the preoperative, intraoperative, and postoperative factors contributing to the development of hypoxemia within the first 24 hours after cardiac surgery with CPB. DESIGN: Prospective observational study. SETTING: University hospital. PARTICIPANTS: Patients who underwent elective or emergency cardiac surgery with CPB (n = 466). INTERVENTIONS: Preoperative clinical and laboratory data were recorded, as were intraoperative and postoperative data regarding the PaO2-FIO2 ratio, fluid and drug therapy, and chest radiograph. Data analysis evaluated hypoxemia as depicted by the PaO2-FIO2 ratios at 1, 6, and 12 hours after surgery. Thereafter, the effect of the PaO2-FIO2 ratios on time to extubation, lung injury, and length of hospital stay was evaluated. The risk factors were analyzed in 3 separate periods: preoperative, intraoperative, and postoperative. Univariate and multivariate analyses were performed on each period separately. All data were analyzed in 2 consecutive steps: univariate analysis and multivariate analysis. MEASUREMENTS AND MAIN RESULTS: PaO2-FIO2 ratios after CPB were significantly lower compared with baseline values. Six patients (1.32%) met the clinical criteria compatible with acute lung injury. All 6 patients had prompt recovery. Significant risk factors for hypoxemia were age, obesity, reduced cardiac function, previous myocardial infarction, emergency surgery, baseline chest radiograph with alveolar edema, high creatinine level, prolonged CPB time, decreased baseline PaO2-FIO2, use of dopamine after discontinuation of CPB, coronary artery bypass grafting, use of left internal mammary artery, higher pump flow requirement during CPB, increased level of hemoglobin or total protein content, persistent hypothermia 2 and 6 hours after surgery, requirement for reexploration, event requiring reintubation, and chest radiograph with alveolar edema 1 hour after surgery. Six hours after surgery, a lower PaO2-FIO2 ratio correlated significantly with time to extubation and lung injury. CONCLUSIONS: This study shows that despite improvements in the technique of CPB, hypoxemia depicted by low PaO2-FIO2 ratios is common in patients after CPB. It is short lived, however, and has minimal effect on the postoperative clinical course of these patients.

Adolescent↗

PubMed2001

Plasma endothelin-1 and atrial natriuretic peptide levels during prolonged (24-h) non-acidemic hypoxemia in fetal goats.

OBJECTIVE: The purpose of this study was to investigate the effects of prolonged (24-h) non-acidemic hypoxemia on plasma endothelin-1 and atrial natriuretic peptide (ANP) in fetal goats. METHODS: During continuous infusion of nitrogen into the maternal trachea, fetal plasma endothelin-1 and ANP levels were measured in nine chronically instrumented goat fetuses at 117-129 days' gestation. Endothelin-1 and ANP were measured by radioimmunoassay. RESULTS: Fetal arterial pO(2) decreased significantly from 23.1 +/- 1.0 mmHg (control) to 15.2 +/- 0.9 mmHg during the first 2 h of hypoxemia and to 15.7 +/- 1.1 mmHg at the end of the experimental period of hypoxemia. The plasma endothelin-1 concentration increased from 10.6 +/- 1.9 pg/ml to 20.4 +/- 4.3 pg/ml (p < 0.05) during the first 2 h and was 19.7 +/- 2.4 pg/ml (p < 0.01) at the end of the experimental period. The plasma ANP concentration also increased, from 20.3 +/- 5.5 pg/ml to 23.0 +/- 4.7 pg/ml in the first 2 h and then to 58.0 +/- 8.8 pg/ml (p < 0.05) at the end of the experimental period. There was a significant negative correlation between fetal plasma endothelin-1 and pO(2), but no significant correlation was found between fetal plasma ANP and pO(2). CONCLUSIONS: Prolonged non-acidemic hypoxemia induces a continuous increase in fetal plasma endothelin-1 and ANP levels. Fetal plasma ANP increases time-dependently but endothelin-1 remains constant during hypoxemia.

Animals↗

PubMed1998

The hemodynamic effects of hypoxemia in anesthetized pigs: a comparison between right heart catheter and echocardiography.

UNLABELLED: During hypoxemia, hypoxic pulmonary vasoconstriction and tachycardia are often observed in association with increases in pulmonary artery pressure and cardiac output. Nevertheless, the hemodynamic consequences of hypoxemia have never been evaluated by echocardiography and simultaneously compared with invasive hemodynamic variables. Fourteen open-chest, anesthetized piglets (weight 29-36 kg) were submitted to progressive hypoxemia and reoxygenation. Usual invasive hemodynamic variables were obtained from peripheral and central heart catheters. Direct epicardial echocardiography was used to measure right and left ventricular areas on a short-axis view at mid-papillary level. The mean pulmonary artery pressure (MPAP) increased with pulmonary vascular resistance in a dose-related manner as the fraction of inspired oxygen (FIO2) declined from 0.5 to 0.12. The MPAP correlated with right ventricular end-diastolic area (RVEDA) only at FIO2 0.08. There was a 49% reduction in left ventricular end systolic wall stress (LVESWS) between FIO2 0.5 and 0.08. Left ventricular ejection fraction area (LVEFA) increased by 33% above baseline and correlated with the decrease in LVESWS. No correlation was observed between left ventricular end-diastolic area and pulmonary artery occlusion pressure or left atrial pressure and between cardiac output and LVEFA. Systemic vascular resistance underestimates the magnitude of changes in LVESWS but overestimates the afterload compared with LVESWS. This study demonstrates that, for the lowest FIO2 (0.08), changes in MPAP correlated with changes in RVEDA but not in pulmonary vascular resistance. Moreover, LVESWS decreases significantly in a dose-related manner under progressive hypoxemia and normalizes immediately after reoxygenation. This study also shows that, under hypoxemic conditions, echocardiography enhances understanding of hemodynamic changes compared with right heart catheterization alone. IMPLICATIONS: Acute hypoxemia in pigs is responsible for pulmonary vasoconstriction-induced pulmonary hypertension (which is restricted by the right ventricular failure), as well as a PaO2-dependent decrease in left ventricular afterload. These changes are better displayed by echocardiography than by right heart catheter.

Anesthesia↗

PubMed1990

Hypoxemia in the postanesthesia care unit: an observer study.

To determine the incidence and duration of hypoxemia in the postanesthesia care unit (PACU), 200 patients were investigated in a single-blind observer study. The number of unrecognized hypoxemic episodes, as well as risk factors and possible association between hypoxemia and postoperative morbidity, were studied. Oxygenation was monitored continuously with a pulse oximeter. One or more hypoxemic episodes (SpO2 less than or equal to 90%) were noted in 55% of the patients. SpO2 values less than or equal to 80% were noted in 13% of the patients. Supplementary oxygen was given during 55% of the 447 hypoxemic episodes registered. The hypoxemic episodes were unrecognized by the staff in 95% of the cases. With stepwise multiple logistic regression analyses, risk factors associated with a higher incidence of hypoxemia were: duration of anesthesia (P less than 0.0001), age (P less than 0.002) and a history of smoking (P less than 0.01). Patients who had undergone regional anesthesia had a lower risk of hypoxemia (P less than 0.0002). The occurrence of hypoxemia in the PACU could not be correlated to postoperative morbidity. We conclude that hypoxemic episodes in our PACU are common and that the routine use of supplemental oxygen combined with normal clinical surveillance did not prevent hypoxemic episodes.

Adolescent↗

PubMed1997

Variability of indices of hypoxemia in adult respiratory distress syndrome.

OBJECTIVE: To determine the usefulness of indices of hypoxemia in assessing patients with the adult respiratory distress syndrome (ARDS). DESIGN: Retrospective analysis of previously published data that describe the distributions of ventilation and pulmonary blood flow in ARDS. SETTING: University research laboratory. PATIENTS: Sixteen patients with ARDS. INTERVENTIONS: The FIO2 was varied between 0.21 and 1.0 in a computer model of gas exchange, based on a 50-compartment model of ventilation/perfusion inhomogeneity plus true shunt and deadspace. The indices of hypoxemia that were calculated as a function of inspired oxygen concentration included PaO2/FIO2, arterial/alveolar ratio (PaO2/alveolar PO2), the alveolar-arterial PO2 difference (P[A-a]O2), respiratory index (P[A-a]O2/PaO2), and venous admixture. MEASUREMENTS AND MAIN RESULTS: The PaO2/FIO2 ratio in patients with moderate shunts (< 30%) varied considerably with alteration in FIO2. At both extremes of FIO2, the PaO2/FIO2 in these patients was substantially greater than at intermediate FIO2. Patients with larger shunts (> 30%) had greater PaO2/FIO2 ratios at low FIO2, but the PaO2/FIO2 ratios decreased to relatively stable values at FIO2 values of > 0.5. In all patients, PaO2/FIO2 remained relatively stable at FIO2 values of > or = 0.5 and PaO2 values of < or = 100 torr (< or = 13.3 kPa). Other PO2-based indices exhibited less stability as FIO2 was varied. If hypoxemia resulted from true shunting, venous admixture was found to be stable at all FIO2 values. However, approximately one half of patients had clinically important hypoxemia resulting from mismatching of ventilation and blood flow. In these patients, venous admixture varied substantially with change in FIO2, and the degree of variation was proportional to the fraction of cardiac output perfusing gas exchange units with ventilation/perfusion ratios of < 0.1. CONCLUSIONS: All indices of hypoxemia are affected by changes in FIO2 in patients with ARDS. PaO2/FIO2 ratio exhibits the most stability at FIO2 values of > or = 0.5 and PaO2 values of < or = 100 torr (< or = 13.3 kPa), and is a useful estimation of the degree of gas exchange abnormality under usual clinical conditions. Venous admixture varies substantially with alteration of FIO2 in patients who have clinically important ventilation/perfusion abnormalities. Under these circumstances, venous admixture is a poor indicator of the efficiency of pulmonary oxygen exchange, even if venous admixture is calculated from measured arterial and venous oxygen content values. Estimated venous admixture, based on an assumed arterial-venous oxygen content difference, is even more unreliable.

Computer Simulation↗

PubMed2001

Left ventricular hypertrophy and nocturnal hypoxemia in hemodialysis patients.

OBJECTIVE: Nocturnal hypoxemia has recently been proposed as a cardiovascular risk factor in patients with chronic renal failure. In this study we have tested the hypothesis that this disturbance is associated with left ventricular hypertrophy (LVH) in dialysis patients. METHODS: During a mid-week non-dialysis day, 38 hemodialysis patients underwent continuous monitoring of arterial O2 saturation (SaO2) during night-time as well as 24 h ambulatory blood pressure monitoring and echocardiography. RESULTS: Eighteen patients had one or more episodes of O2 desaturation during night-time (average: 21 episodes; range 1 to 120) while the other 20 had no episode. Neither day-time arterial pressure nor heart rate were significantly associated with nocturnal hypoxemia. However there was a significant correlation between the night/day systolic ratio and the severity of hypoxemia during night-time (r = 0.36, P = 0.03). On multivariate analysis, nocturnal hypoxemia proved to be the stronger independent predictor of relative wall thickness, mean wall thickness and left ventricular mass index, suggesting that nocturnal O2 desaturation is linked to concentric hypertrophy and to concentric geometry of the left ventricle. Accordingly, the proportion of patients with such geometric alteration was higher (chi2 = 4.1, P = 0.04) in patients with a pulse oximetry severity score > 50th percentile [15 of 19 (79%)] than in those below this threshold [nine of 19 (47%)]. CONCLUSIONS: Nocturnal hypoxemia is an important correlate of LVH in hemodialysis patients. Such an association is largely independent of arterial pressure. These data further underscore the importance of disturbed respiratory control as a cardiovascular risk factor in dialysis patients.

Adult↗

PubMed1999

Hypoxemia near mid-gestation has long-term effects on fetal brain development.

We tested the hypotheses that an episode of hypoxemia near mid-gestation in fetal sheep has long-term effects on brain development and that the extent and type of damage is related to the stage of development within a particular brain structure at the time of the hypoxemia. Fetal sheep (n = 8) were made hypoxemic at 90 +/- 2 days (term approximately 147 days) by restricting the maternal blood supply to the placenta for 12 hours (h) using a vascular clamp so as to reduce fetal arterial O2 saturation by 50%-60%. Fetuses were killed 35 days later and the brains analysed histologically and immunohistochemically. Age-matched fetuses (n = 8) were used as controls. Gross brain damage was observed in only 1 fetus, the most acidemic during the period of hypoxemia. There was a reduction of 12% (p < 0.05) in the cross-sectional area of the cerebral cortex in hypoxemic fetuses compared with controls. In lobule 6 of the cerebella of hypoxemic fetuses, significant reductions were seen in (a) the volume density of Purkinje cells (33%), (b) the width of the molecular layer (13%), (c) the area of the inner granule cell layer (13%), (d) the area of the white matter (18%), and (e) the total cross-sectional area (15%). There were also significant reductions in the area of arborization of Purkinje cell dendritic trees (50%), in the branching density (25%), and in the number of dendritic spines (31%). In the ventral hippocampi of hypoxemic fetuses, there was a 36% reduction (p < 0.05) in the volume density of CA1 pyramidal cells and a 50% increase (p < 0.05%) in the number of astrocytes. We conclude that an episode of hypoxemia near mid-gestation reduces neuronal numbers in the hippocampus and cerebellum and probably also in the cerebral cortex. The growth of neural processes in a particular region will be significantly retarded if the hypoxemia occurs at an early stage of the growth of neural processes (e.g. cerebellum) but not if development is well advanced at the time of the insult (e.g. hippocampus). Damage is sustained in the white matter of the cerebral hemispheres if the insult is particularly severe. Together, these deficits could affect neural connectivity and impair postnatal brain function.

Animals↗

PubMed2005

Spurious hypoxemia.

OBJECTIVE: To discuss the pathophysiology and clinical implications of spurious hypoxemia in the setting of hyperleukocytosis. DESIGN: Case report and review of the literature. SETTING: A 22-bed, adult neurosciences critical care unit at a tertiary care hospital. PATIENT: A 49-yr-old male with chronic myelogenous leukemia. INTERVENTIONS: Administration of hydroxyurea and imatinib mesylate. MEASUREMENTS AND MAIN RESULTS: The patient was admitted to the neurosciences critical care unit with an acute nontraumatic subdural hematoma that required emergent surgical evacuation. His clinical course was notable for neurologic deterioration, sepsis, hyperleukocytosis, severe hypoxemia, and prolonged mechanical ventilation. An inverse relationship was observed between arterial oxygen tension and the magnitude of hyperleukocytosis. Hypoxemia resolved after the institution of chemotherapy and normalization of white cell count. Pulse oximeter saturation was normal throughout. CONCLUSIONS: Patients with hyperleukocytosis are at risk for severe hypoxemia, which may be real or spurious. Failure to recognize spurious hypoxemia can lead to unnecessary diagnostic tests and therapeutic interventions, exposing patients to avoidable risk. A diagnostic algorithm is proposed.

Algorithms↗

PubMed1998

Nocturnal hypoxemia, night-day arterial pressure changes and left ventricular geometry in dialysis patients.

It is well established that nocturnal hypoxemia in sleep apnea causes an inversion of the circadian arterial pressure rhythm and triggers nocturnal hypertension. Since sleep apnea is very frequent in dialysis patients, we hypothesized that nocturnal hypoxemia may be a factor that contributes to alter the 24-hour arterial pressure profile in these patients. To test the hypothesis 32 dialysis patients underwent 24-hour blood pressure (BP) monitoring and continuous monitoring of arterial O2 saturation during the night-time. Hemodialysis patients were studied during the non-dialysis day. All patients underwent an echocardiographic study. Thirteen patients had no episode of nocturnal hypoxemia (group I), 7 had at least one episode overnight but less than 2 episodes/hr (group II) and 12 had > or = 2 episodes/hr (group III). The average daytime systolic pressure was similar in the three groups. However, the average nocturnal systolic pressure fell in the first group (-2.5 +/- 4.2%) and rose in the second (+2.0 +/- 3.6%) and in the third (+3.9 +/- 2.2%) group (one way ANOVA, P < 0.005). The relative wall thickness of the left ventricle (RWT) was significantly (P < 0.05) higher in group III than in group I, and in the aggregate (N = 32) there was an inverse relationship between average nocturnal SaO2 and RWT (r = -0.43, P = 0.015). The proportion of patients with concentric remodeling or concentric hypertrophy was higher (P = 0.05) in the group with a more severe degree of nocturnal hypoxemia (group III, 8 of 12) than in the other two groups (group I, 3 of 13; group II, 2 of 7). Nocturnal hypoxemia is associated with the "non-dipping" arterial pressure profile in dialysis patients. Disturbed respiratory control during the night may represent an important cardiovascular risk factor in dialysis patients.

Adolescent↗

PubMed1999

Prevalence of hypoxemia in 102 Japanese patients with alcoholic and nonalcoholic cirrhosis.

OBJECTIVE: Liver cirrhosis is often accompanied by arterial hypoxemia in the absence of cardiopulmonary disease. The aim of this study was to investigate the relationship between various clinicopathological conditions and the hypoxemia seen in Japanese patients with liver cirrhosis. METHODS: In 102 consecutive patients with alcoholic (N = 45) and nonalcoholic (N = 57) cirrhosis not associated with cardiopulmonary disease, we performed lung perfusion scintigraphy, contrast echocardiography, and arterial blood gas analysis and measured oxygen consumption. RESULTS: No abnormality was seen in pulmonary blood flow in cirrhotic patients, but 38 (38%) of them had a decreased partial pressure of oxygen (PaO2). The hypoxemic patients did not show any pulmonary signs or symptoms. The hypoxemia was not associated with the Child-Pugh grade, and was observed in 32 (71%) of the 45 alcoholic patients but in only six (11%) of the 57 nonalcoholic patients (p < 0.001). Oxygen consumption was significantly higher in the alcoholic group than in the nonalcoholic group (p < 0.0001), and a high incidence of oxygen consumption was seen in all 45 (100%) of the alcoholic patients and in 34 (60%) of the nonalcoholic subjects, the difference being significant (p < 0.01). The relationship between oxygen consumption and PaO2 in the 102 cirrhotic patients showed an inverse correlation (r = -0.85, p < 0.0001). Among the alcoholic patients, the incidence of hypoxemia did not differ between the 33 smokers and the 12 nonsmokers. After 1 wk of abstinence from alcohol a significant increase (p < 0.0001) in the PaO2 was seen in 14 of 19 patients with alcoholic cirrhosis. CONCLUSIONS: We conclude that the hypoxemia in Japanese patients with liver cirrhosis occurs mainly in drinking alcoholic patients, presumably due to an increased oxygen consumption by alcohol.

Aged↗

PubMed1993

The association between preterm newborn hypotension and hypoxemia and outcome during the first year.

Ninety-eight newborn infants, less than 34 weeks at birth, were studied to examine the relationship between newborn hypotension and hypoxemia and brain damage. Heart rate, blood pressure and oxygen tension were recorded continuously during the 96 h following delivery. Outcome measures included neuropathology in children who died, and motor and cognitive development at one year corrected age in children who survived. There were 22 children with a minor and 27 with a major abnormal outcome. There was a relationship between newborn hypotension, newborn hypoxemia and low birth weight, and a major abnormal outcome. The probability of a major abnormal outcome increased from 8% in newborns with no hypotension or hypoxemia, to 53% in children with both hypotension and hypoxemia. These findings support the contention that combinations of sustained newborn hypotension and hypoxemia are important factors in the development of brain damage, accounting for a major abnormal outcome.

Acidosis↗

PubMed1997

Influence of carotid denervation on the body-core temperature and metabolic responses to changes in ambient temperature during normoxemia and acute hypoxemia in guinea pigs during postnatal maturation.

Acute hypoxemia produces a decrease in body-core temperature (Tbc) in guinea pigs during postnatal maturation, although the factors mediating the response remain unknown. Experiments were therefore carried out to test the hypothesis that the carotid chemoreceptors and (or) baroreceptors mediate the decrease in Tbc during acute hypoxemia. Twelve guinea pigs, six carotid intact and six carotid denervated, were studied in a metabolic chamber to determine the influence of carotid denervation on the Tbc and metabolic (i.e., oxygen consumption) responses to changes in ambient temperature during normoxemia and during acute hypoxemia at 2, 3, and 4 weeks of age. Carotid denervation accentuated the decrease in Tbc in response to a decrease in ambient temperature during normoxemia at 2 and 3 weeks of age but not at 4 weeks of age without altering the metabolic response. This suggests that carotid denervation disrupted heat conservation mechanisms rather than heat production mechanisms in an age-specific manner. Furthermore, carotid denervation accentuated the decrease in Tbc and oxygen consumption in response to acute hypoxemia at all ages studied. This provides evidence that the carotid chemoreceptors and (or) baroreceptors do not mediate the decrease in Tbc that occurs in response to acute hypoxemia in guinea pigs during postnatal maturation.

Animals↗

PubMed1976

Differences in the altered energy metabolism of hemorrhagic shock and hypoxemia.

The effect of hemorrhagic shock, hypoxemia, and anoxia on the levels of adenine and pyridine nucleotides of liver and kidney was assessed. ATP levels in liver and kidney of animals in shock or animals subjected to 7 min of anoxia decreased by 85 and 73%, respectively. Under hypoxic conditions (arterial PO2 AT 18 MMHg), the decrease was only 62 and 48% in liver and kidney, respectively. Tissue NAD levels decreased and NADH levels increased during shock but were found to be essentially unaltered during experimental hypoxemia. Thus, shock produced greater alterations in adenine and pyridine nucleotides than did hypoxemia alone, indicating that stagnant hypoxemia due to shock is more deleterious to energy metabolism than is severe hypoxemia with an otherwise normal circulation. The results also suggest that if an anterial PO2 OF 18 MMHg represents the initial stages of tissue hypoxia, then tissue ATP levels are a more sensitive indicator of this than NAD levels.

Adenine Nucleotides↗

PubMed1985

Influence of hypoxemia and respiratory acidosis on the plasma kinetics and tissue distribution of digoxin in the conscious dog.

The aim of the present study was to investigate the influence of hypoxemia combined with respiratory acidosis on the kinetics of digoxin in conscious dogs. One group of three beagles was exposed to air and 7 days later to 10% O2, 10% CO2, and 80% N2. In a second group of three dogs, the order of exposure to the two atmospheric conditions was reversed. The dogs received 25 micrograms/kg digoxin and blood and urine samples were collected over the next 29 h. At the conclusion of the second treatment, the dogs were sacrificed to determine digoxin concentrations in the left ventricle, liver, renal cortex, and skeletal muscle. Digoxin total body clearance increased from 6.2 +/- 0.9 in control to 9.0 +/- 1.0 mL X min-1 X kg-1 in hypoxemic and hypercapnic dogs (p less than 0.05). The digoxin apparent volume of distribution at steady state (Vss) was increased in the dogs with hypoxemia and hypercapnia (11.63 +/- 1.11 vs. 8.62 +/- 0.41 L/kg in the controls, p less than 0.05). As a consequence the digoxin plasma half-life remained unchanged (18.6 +/- 1.5 h in hypoxemic and hypercapnic dogs versus 20.1 +/- 2.8 h in the controls). In dogs with hypoxemia and hypercapnia, the ratio of tissue to plasma digoxin concentrations tended to increase in the liver, in the renal cortex, and in the left ventricle and remained unchanged in the left hind leg muscle. In vitro studies showed that the digoxin total binding to erythrocyte membranes was slightly increased in the dogs with hypoxemia and hypercapnia, resulting from an increase in the apparent intrinsic association constant for digoxin (p less than 0.003). It is concluded that hypoxemia combined with respiratory acidosis changes digoxin disposition in the conscious dog and is the cause of a digoxin redistribution into the tissues.

Acidosis, Respiratory↗

PubMed1988

Acute hypoxemia stimulates atrial natriuretic factor secretion in vivo.

The hypothesis was tested that acute hypoxemia may be a physiological stimulus for atrial natriuretic factor (ANF) secretion in anesthetized, spontaneously breathing rabbits. Base-line plasma ANF (range from 29.8 to 219 pg/ml; mean +/- SE = 87.0 +/- 14.1 pg/ml; n = 16 rabbits) was negatively correlated with base-line arterial PO2 (r = -0.759; P less than 0.01) but not with PCO2, pH, mean arterial blood pressure, central venous pressure (CVP), minute ventilation, heart rate, or type of anesthetics used. Acute hypoxemia (arterial PO2 22.3-44.3 mmHg) lasting 10 min increased plasma ANF levels over base line by 69.2 +/- 47.7 (SE) pg/ml at 6 min and 87.5 +/- 46.8 (SE) pg/ml at 9 min (P less than 0.01; n = 9). The increase in arterial pH and minute ventilation and the decrease of arterial PCO2 paralleled the changes in plasma ANF. Mean arterial blood pressure, CVP, and heart rate did not change significantly. ANF responses to hypoxemia (range from 4.4 to 423 pg/ml) correlated with base-line CVP (r = 0.761; P less than 0.01) and base-line ANF (r = 0.523; P less than 0.05) but with no other measured variable. Although the mediators of hypoxemia-induced release of ANF need to be explored further, this study raises the possibility that ANF might be involved in the adaptation to hypoxemia.

Animals↗