Voice Reactivity as a Response to Acute Hypobaric Hypoxia at High Altitude

BACKGROUND: Although the understanding of hypobaric hypoxia is increasing, it remains a hazard in aviation medicine. This study examined the feasibility of detecting voice markers sensitive to acute hypobaric hypoxia in an early presymptomatic (PRE-SYMP) stage.METHOD: Eight subjects qualified with hypobaric training completed a series of standardized speech tests in a hypobaric chamber at 20,000 ft and 25,000 ft (6096 and 7620 m) of altitude. Voice response patterns were analyzed in terms of fundamental frequency (F0), F0 range, and voice onset time (VOT). We hypothesized a PRE-SYMP compensatory stage in voice reactivity.RESULTS: There was a different dose-response reactivity course at 20,000 ft vs. 25,000 ft, nonlinear to altitude. At 20,000 ft, our hypothesis was confirmed. In comparison to sea level, a PRE-SYMP compensatory stage could be distinguished, characterized by a decreased F0 range, decreased VOT, and increased F0. During a transitional (TRANS) stage, in comparison with sea level, the F0-range reset, VOT decreased, and F0 increased. During a symptomatic (SYMP) stage, F0 increased, F0 range increased, and VOT decreased. At 25,000 ft, in comparison to sea level, voice reactivity showed increased F0 and F0 range and decreased VOT in a PRE-SYMP stage and increased F0 and F0 range in the SYMP stage.DISCUSSION: The compensatory PRE-SYMP stage is suggested to be the expression of ongoing bottom-up and top-down regulatory mechanisms, whereas the 25,000-ft results are interpreted as a combination of tonic and phasic voice reactivity. This tonic component needs to be foreseen in sea level baseline measures.Van Puyvelde M, Neyt X, Vanderlinden W, Van den Bossche M, Bucovaz T, De Winne T, Pattyn N. Voice reactivity as a response to acute hypobaric hypoxia at high altitude. Aerosp Med Hum Perform. 2020; 91(6):471-478.

Classification Algorithm for Nocturnal Hypoxemia Using Nocturnal Pulse Oximetry

This paper describes an automatic classification algorithm for nocturnal hypoxemia in patients receiving home oxygen therapy (HOT). Nocturnal hypoxemia is a well-known complication in patients with chronic respiratory disease, and the number of patients receiving HOT has increased in recent years. Many studies have reported that 40% of patients receiving HOT have sleep-related oxygen desaturation. To deal with this situation, a nocturnal pulse oximetry is used to measure oxygen saturation (SpO₂) and control the flow rate of highly concentrated oxygen. However, in some cases, the flow rate is not controlled properly and the same flow rate is adopted both during the day and night. There are several types of nocturnal hypoxemia, and it is difficult to classify these types only according to a subjective assessment of a medical doctor. Furthermore, it is difficult to continuously monitor the measurement results of pulse oximetry, although a flexible treatment depending on the state of hypoxemia is desired. To overcome these difficulties, an automatic classification method for SpO₂ measured by the nocturnal pulse oximetry is proposed in this paper. The proposed method uses the time domain waveform and the frequency characteristics of SpO₂. The classification performance of the method is evaluated by using 48 measured SpO₂ values from patients receiving the HOT. The classification results are validated with decisions of ten chest physicians.

[Mechanisms of sympathetic activity in rats exposed to different patterns of hypoxia and the correlation with blood pressure]

OBJECTIVE

To observe the effects of two different hypoxia patterns on blood pressure and the underlying mechanisms.

METHODS

Eighteen male SD rats were randomly divided into three groups: the intermittent hypoxia group (IH group), the continuous hypoxia group (CH group) and the normal control group (NC group). The rats of the IH and CH group were subjected to intermittent hypoxia (7 h/d) and continuous hypoxia (7 h/d) for 42 days respectively. The NC group rats were untreated. The levels of arteria caudilis systolic pressure (ACSP) were measured with noninvasive rats arteria caudilis gauge before the experiment, at the end of 3rd, 6th week of the experiment. The concentrations of norepinephrine (NE) in serum and neuropeptide Y (NPY) in plasma were respectively measured by enzyme-linked-immunosorbent assay (ELISA) and radioimmunoassay. The contents of malondialdehyde (MDA) and the ability of inhibiting hydroxyl free radical in serum were analyzed by thiobarbituric acid colorimetric analysis (TBAR) at the end of 6th week.

RESULTS

At the end of 3rd week, the levels of ACSP were considerably higher than those before the treatment (P<0.05). The concentrations of ACSP, NE, MDA, NPY in the IH group were significantly higher than those in the other two groups at the end of 6th week (all P<0.01). The ability of inhibiting hydroxyl free radical were decreased by the intermittent hypoxia treatment (all P<0.01). However, there was no significant difference in ACSP, NE, MDA, NPY between CH and NC group (all P>0.05). The levels of NE, NPY and MDA were positively related with ACSP (r=0.873, P<0.01; r=0.671, P<0.01; r=0.582, P<0.05). The correlation between the ability of inhibiting hydroxyl free radical and ACSP was negative (r=-0.790, P<0.01). the concentrations of MDA were positively related with NE and NPY respectively (r=0.843, 0.777, P<0.01) and the ability of inhibiting hydroxyl free radical was negatively related with NE and NPY respectively (r=-0.864, -0.717, P<0.01).

CONCLUSION

Intermittent hypoxia can induce high blood pressure, which may be related to the sympathetic over-activity and the oxidative stress.

Mallampati class is not useful in the clinical assessment of sleep clinic patients

STUDY OBJECTIVES

To assess the utility of Mallampati class, a simple grade of oropharyngeal appearance used to assess difficulty of intubation, to predict severe obstructive sleep apnea and absence of OSA (rule in severe OSA and rule out OSA).

METHOD

Retrospective review of consecutive patients undergoing diagnostic polysomnography in a tertiary referral sleep disorders center. Modified Mallampati class and other simple patient characteristics (age, gender, body mass index) were compared to apnea-hypopnea index (AHI). The sensitivity, specificity, and the positive and negative likelihood ratios (LR+ and LR-) were calculated for Mallampati class IV to detect an AHI > 30 (rule in severe OSA) and Mallampati class I to detect an AHI < 5 (rule out OSA).

RESULTS

A total of 953 consecutive patients (619 male) undergoing diagnostic polysomnography were included. The age of the cohort was 50.0 ± 6.4 years, with a BMI of 33.8 ± 8.6 kg/m² and AHI of 26.1 ± 25.1 /h (95% CI 1.4-78.8). Mallampati class was significantly associated with AHI (r = 0.13, p < 0.001), but there were no differences in AHI between Mallampati classes. A Mallampati class IV had a sensitivity of 40%, specificity of 67%, LR+ of 1.21, and LR- of 0.90 for an AHI > 30. A Mallampati class I was only 13% sensitive but 92% specific for an AHI < 5, with LR+ of 1.63 and LR- 0.90.

CONCLUSIONS

Mallampati class is associated with AHI but does not significantly modify likelihood of severe OSA or absence of OSA. As such, it is of limited use to "rule in" severe OSA or "rule out OSA" in the sleep clinic population.

Respiratory responses to acute intermittent hypoxia and hypercapnia in awake rats

This article deals with the recognition of early changes in the breathing pattern, in response to acute intermittent stimuli in awake rats. Two different types of stimuli were given: 9% hypoxia in N(2) and 10% hypercapnia in O(2). Animals were exposed to 3 consecutive cycles consisting of 3-min stimulus period separated by 8-min normoxic recovery intervals. Features of the breathing pattern, such as respiratory frequency, tidal volume, minute ventilation, inspiration and expiration times, peak inspiratory and expiratory flows, were measured by whole body plethysmography. The data were analyzed with the use of pattern recognition methods. We conclude that the overall respiratory changes were rather slight. However, computerized analysis using a k-nearest neighbor decision rule (k-NN) allowed for a good recognition of the respiratory responses to the stimuli. The misclassification rate (E(r)) varied from 5 to 10%. After feature selection, E(r) decreased below 1%. The k-NN classifier differentiated correctly also the type of intermittent stimulus. Our experimental results demonstrate usefulness of pattern recognition algorithms in studying respiratory effects in biological models.

Effects of low and high levels of moderate hypoxia on anaerobic energy release during supramaximal cycle exercise

The purpose of this study was to investigate whether hypoxia can alter anaerobic energy release during supramaximal exercise. Seven male subjects performed 12 submaximal cycling tests to establish the relationship between workload and O2 demand. The subjects also performed 40 s Wingate tests (WT) under normoxia (room air), two levels of moderate hypoxia of 16.4% O2 and 12.7% O2. We measured the power output and oxygen uptake (VO2) during each test and estimated the O2 demand, O2 deficit and percentage of anaerobic energy release (%AnAER). These data were analyzed for each 20 s interval. At all intervals, there were no differences in Pmean per body mass (BM)(-1), O2 demand per BM(-1) or O2 deficit per BM(-1) among the three O2 conditions. However, under hypoxia of 12.7%, VO2 per BM(-1) was significantly decreased and %AnAER was significantly increased in the late phase (20-40 s) of the WT, compared to normoxia (P<0.05). There were no such significant differences between normoxia and hypoxia of 16.4%. Thus, the present results show that the degree of hypoxia affects the magnitude of the hypoxia-induced increase in anaerobic energy release in the late phase of the WT and suggest that certain degrees of hypoxia induce significant increases in the amount of anaerobic energy released, compared to normoxia.

Significance of Hypoxemia Screening in Candidates for Liver Transplantation: Our Experience

Hepatopulmonary syndrome (HPS) is recognized as one of the causes of hypoxemia in patients with chronic liver disease. This complication is responsible for increased mortality and increased perioperative risk in liver transplantation candidates. Recent data from the literature suggest extending the screening for HPS to all candidates for liver transplantation. The aim of this retrospective study was to evaluate the incidence of hypoxemia among a population of patients awaiting liver transplantation. Using pulse oximetry as a screening tool for hypoxemia, 39 of 198 patients (20%) were hypoxemic. The results of this study confirmed the importance of screening for hypoxemia among patients awaiting liver transplantation. In these patients, a more accurate evaluation of respiratory function should be performed to confirm or exclude the diagnosis of HPS.

Exercise training improves lung gas exchange and attenuates acute hypoxic pulmonary hypertension but does not prevent pulmonary hypertension of prolonged hypoxia

Our laboratory has previously shown an attenuation of hypoxic pulmonary hypertension by exercise training (ET) (Henderson KK, Clancy RL, and Gonzalez NC. J Appl Physiol 90: 2057–2062, 2001), although the mechanism was not determined. The present study examined the effect of ET on the pulmonary arterial pressure (Pap) response of rats to short- and long-term hypoxia. After 3 wk of treadmill training, male rats were divided into two groups: one (HT) was placed in hypobaric hypoxia (380 Torr); the second remained in normoxia (NT). Both groups continued to train in normoxia for 10 days, after which they were studied at rest and during hypoxic and normoxic exercise. Sedentary normoxic (NS) and hypoxic (HS) littermates were exposed to the same environments as their trained counterparts. Resting and exercise hypoxic arterial Po2 were higher in NT and HT than in NS and HS, respectively, although alveolar ventilation of trained rats was not higher. Lower alveolar-arterial Po2 difference and higher effective lung diffusing capacity for O2 in NT vs. NS and in HT vs. HS suggest ET improved efficacy of gas exchange. Pap and Pap/cardiac output were lower in NT than NS in hypoxia, indicating that ET attenuates the initial vasoconstriction of hypoxia. However, ET had no effect on chronic hypoxic pulmonary hypertension: Pap and Pap/cardiac output in hypoxia were similar in HS vs HT. However, right ventricular weight was lower in HT than in HS, although Pap was not different. Because ET attenuates the initial pulmonary vasoconstriction of hypoxia, development of pulmonary hypertension may be delayed in HT rats, and the time during which right ventricular afterload is elevated may be shorter in this group. ET effects may improve the response to acute hypoxia by increasing efficacy of gas exchange and lowering right ventricular work.

Nocturnal hypoxia is associated with silent cerebrovascular disease in a high-risk Japanese community-dwelling population

BACKGROUND

Sleep-disordered breathing (SDB) is recognized as a risk factor for cerebrovascular disease. The objective of this study was to investigate the relationship between nocturnal hypoxia and silent cerebral infarct (SCI) in the general population.

METHODS

In the 2001 annual health check in Nishiarita, Japan, 170 individuals at high risk were screened who met more than three of the following criteria: high blood pressure, hypercholesterolemia, left ventricular hypertrophy by electrocardiography, hemoglobinA(1)c >6.5%, proteinuria, central obesity, heavy smoking habit, heavy drinking, and family history of stroke. Overnight pulse oximetry, brain magnetic resonance imaging, and carotid/cardiac ultrasonography were performed in 146 (mean age 67.4 +/- 9.0 years) of the 170 individuals in whom pulse oximetry was successfully performed.

RESULTS

Subjects were classified into a nocturnal hypoxia group (n = 36) and a nonhypoxia group (n = 110) based on a 3% oxygen desaturation index (ODI) 5.6 times per hour during sleep (highest quartile) by pulse oximetry. The presence of silent cerebral infarct (SCI) (57% v 35%, P = .03) was significantly higher in the hypoxia group than in the nonhypoxia group. The number of SCI was positively correlated with age (r = 0.23, P < .01), systolic blood pressure (r = 0.196, P < .05), and 3% ODI (r = 0.318, P < .001). Even after adjustment for confounding factors using logistic regression analysis, nocturnal hypoxia (odds ratio = 2.2, 95% confidence interval = 1.10 to 5.30, P = .026) as well as systolic blood pressure and age (10-year increase: odds ratio = 1.22, 95% confidence interval 1.00 to 1.48, P = .048) were independently associated with SCI in the study subjects.

CONCLUSIONS

Based on the study results, SDB assessed by overnight pulse oximetry was associated with silent cerebral disease in a high-risk, community-dwelling Japanese population.

Markers of endothelial dysfunction and severity of hypoxaemia in the Eisenmenger syndrome

Endothelial dysfunction has been reported in hypoxaemic patients with the Eisenmenger syndrome, but a direct correlation between levels of endothelial markers and the severity of hypoxaemia has not been explored. With this in mind, we compared the levels in the plasma of tissue-type plasminogen activator, thrombomodulin, and von Willebrand factor in 25 patients with the Eisenmenger syndrome. They had a median age of 31 years, and were divided into 2 groups according to their recent clinical history. Thus, 18 patients were stable, being in functional class II or III, seen as outpatients, and having peripheral saturations of oxygen of 89 plus or minus 5 percent. In contrast, 7 patients were unstable, showing episodes of symptoms placing them in functional class IV, requiring care in hospital, and manifesting saturations of oxygen of 77 plus or minus 5 percent. We were able to follow 12 patients, 8 who were stable and 4 unstable, for 24 months. At baseline, levels of von Willebrand factor were higher in the unstable patients when compared to those who were stable, at 142 plus or minus 29 and 110 plus or minus 25 units per decilitre, respectively (p equal to 0.013). This correlated positively with oxygen desaturation (p less than 0.020). The structural abnormalities also correlated positively with the magnitude of hypoxaemia (p less than 0.020). Levels remained higher in the unstable patients throughout the period of follow-up (p equal to 0.006). Tissue-type plasminogen activator was also increased, at 14.3 plus or minus 8.4 versus 6.5 plus or minus 2.7 nanograms per millilitre in controls (p less than 0.001), whereas thrombomodulin was decreased, with values of 14.4 versus 34.6 nanograms per millilitre in controls (p for median values of less than 0.001). There was no correlation with saturations of oxygen. We conclude that measurement of von Willebrand factor, as compared with tissue-type plasminogen activator and thrombomodulin, will prove a better marker of endothelial response to hypoxaemia in patients with the Eisenmenger syndrome.

Tyrosine hydroxylase expression and activity in the rat brain: differential regulation after long-term intermittent or sustained hypoxia

Tyrosine hydroxylase, a hypoxia-regulated gene, may be involved in tissue adaptation to hypoxia. Intermittent hypoxia, a characteristic feature of sleep apnea, leads to significant memory deficits, as well as to cortex and hippocampal apoptosis that are absent after sustained hypoxia. To examine the hypothesis that sustained and intermittent hypoxia induce different catecholaminergic responses, changes in tyrosine hydroxylase mRNA, protein expression, and activity were compared in various brain regions of male rats exposed for 6 h, 1 day, 3 days, and 7 days to sustained hypoxia (10% O2), intermittent hypoxia (alternating room air and 10% O2), or normoxia. Tyrosine hydroxylase activity, measured at 7 days, increased in the cortex as follows: sustained > intermittent > normoxia. Furthermore, activity decreased in the brain stem and was unchanged in other brain regions of sustained hypoxia-exposed rats, as well as in all regions from animals exposed to intermittent hypoxia, suggesting stimulus-specific and heterotopic catecholamine regulation. In the cortex, tyrosine hydroxylase mRNA expression was increased, whereas protein expression remained unchanged. In addition, significant differences in the time course of cortical Ser40tyrosine hydroxylase phosphorylation were present in the cortex, suggesting that intermittent and sustained hypoxia-induced enzymatic activity differences are related to different phosphorylation patterns. We conclude that long-term hypoxia induces site-specific changes in tyrosine hydroxylase activity and that intermittent hypoxia elicits reduced tyrosine hydroxylase recruitment and phosphorylation compared with sustained hypoxia. Such changes may not only account for differences in enzyme activity but also suggest that, with differential regional brain susceptibility to hypoxia, recruitment of different mechanisms in response to hypoxia will elicit region-specific modulation of catecholamine response.

Fructose feeding and intermittent hypoxia affect ventilatory responsiveness to hypoxia and hypercapnia in rats

We hypothesized that, in male rats, 10% fructose in drinking water would depress ventilatory responsiveness to acute hypoxia (10% O2 in N2) and hypercapnia (5% CO2 in O2) that would be depressed further by exposure to intermittent hypoxia. Minute ventilation (V̇e) in air and in response to acute hypoxia and hypercapnia was evaluated in 10 rats before fructose feeding (FF), during 6 wk of FF, and after FF was removed for 2 wk. During FF, five rats were exposed to intermittent air and five to intermittent hypoxia for 13 days. Six rats given tap water acted as control and were exposed to intermittent air and subsequently intermittent hypoxia. In FF rats, plasma insulin levels increased threefold in the rats exposed to intermittent hypoxia and during washout returned to levels observed in rats exposed to intermittent air. During FF, ventilatory responsiveness to acute hypoxia was depressed because of decreased tidal volume (Vt) responsiveness. During washout, V̇e decreased as a result of decreased Vt and frequency of breathing, and the ventilatory responsiveness to hypoxia in intermittent hypoxia rats did not recover. In all rats, the ventilatory responses to hypercapnia were decreased during FF and recovered after washout because of an increased Vt responsiveness. In the control group, hypoxic responsiveness was not depressed after intermittent hypoxia and was augmented after washout. Thus FF attenuated the ventilatory responsiveness of conscious rats to hypoxia and hypercapnia. Intermittent hypoxia interacted with FF to increase insulin levels and depress ventilatory responses to acute hypoxia that remained depressed during washout.

[Classification of hypoxia, hypo-, and hypercapnia]

The new classifications of hypoxical, hypo- and hypercapnical conditions are elaborated. They take into account the ecological factors in the development of various kinds of exogenic hypoxia, hypercapnia. For the first time the positive sides of physiological hypoxia and hypercapnia are brought in. In all classification til the last days hypoxia was considered as pathological process only. However hypoxia can be met in different physiologic conditions of organism: internal period of fetus development, hard physical work, increased sportsmen activity, hypoxia after hearty meal, hypoxia of aged organism. The same it is possible to say about the hypo- and hypercapnical conditions.

Acute and severe hypobaric hypoxia-induced muscle oxidative stress in mice: the role of glutathione against oxidative damage

This study intended to analyze: (1) the effects of acute and severe hypoxia exposure on skeletal muscle oxidative stress and oxidative damage markers; (2) the protective role of the antioxidant glutathione against oxidative damage; and (3) the expression of heat shock protein 70 kDa (HSP70) induced by this hypoxic insult. Forty mice were divided into four groups: control + placebo (C+P), hypoxia + placebo (H+P), control + l-buthionine-[ S, R]-sulfoximine (BSO, a GSH-depleting compound) (C+BSO) and hypoxia + BSO (H+BSO). Hypoxia groups were continuously exposed for 24 h to a hypobaric hypoxic environment equivalent to an altitude of 7000 m and sacrificed immediately after. Control groups were maintained at sea level during the experimental protocol. Analyzed biochemical parameters were: reduced (GSH) and oxidized (GSSG) glutathione, thiobarbituric acid reactive substances (TBARS), sulfhydryl protein groups (SH), N-acetyl-beta- d-glucosaminidase (NAG) and HSP70 protein. Hypoxia (H+P) per se, compared to C+P, induced a significant increase in %GSSG (5.68 vs. 1.14%), TBARS (436.7 vs. 227.9 nM), NAG (4.49 vs. 3.35 U/mg) and HSP70 (178.7 vs. 100%). Compared with H+P, H+BSO showed a significant decrease in total glutathione (19.30 vs. 6.13 nmol/mg) and an additional increase in %GSSG (5.68 vs. 11.33%) and in HSP70 expression (178.7 vs. 202.2%). However, no further oxidative damage was observed in H+BSO. These data suggest that acute hypoxia per se might enhance oxidative stress; however, the glutathione system seems to have a modest role in skeletal muscle protection against hypoxia-induced oxidative stress. Moreover, hypoxia and BSO treatment is a sufficient stimulus to promote HSP70 overexpression.

Serum levels of vascular endothelial growth factor are elevated in patients with obstructive sleep apnea and severe nighttime hypoxia

Obstructive sleep apnea (OSA) is associated with increased cardiovascular morbidity and mortality; however, some patients with OSA do not develop cardiovascular disease even in the presence of severe nocturnal oxygen desaturations. Vascular endothelial growth factor (VEGF) is a hypoxia-sensitive glycoprotein stimulating neoangiogenesis. We hypothesized that VEGF production is increased in OSA because of repetitive nocturnal hypoxia. Three different groups were investigated: 10 OSA patients with severe nighttime hypoxia (Group A), 10 OSA patients with moderate hypoxia (Group B), and 10 healthy volunteers (Group C). Serum levels of VEGF were measured by ELISA from peripheral venous blood samples obtained at 7 AM. Group A had significantly (p < 0.01) increased VEGF serum levels when compared with Group B and Group C (mean +/- SEM: 410 +/- 77 pg/ml versus 224 +/- 38 pg/ml and 245 +/- 61 pg/ml). The degree of nocturnal oxygen desaturation in OSA significantly correlated with the VEGF concentrations (r = 0.67, p < 0.01). In conclusion, serum levels of VEGF are elevated in severely hypoxic patients with OSA and are related to the degree of nocturnal oxygen desaturation. This might constitute an adaptive mechanism to counterbalance the emergence of OSA-related cardiovascular disease.

Time domains of the hypoxic ventilatory response in awake ducks: episodic and continuous hypoxia

Time-dependent ventilatory responses to episodic and continuous isocapnic hypoxia were measured in unidirectionally ventilated, awake ducks. Three protocols were used: (1) ten 3-min episodes of moderate hypoxia (10% O(2)) with 5-min normoxic intervals; (2) three 3-min episodes of severe hypoxia (8% O(2)) with 5-min normoxic intervals; and (3) 30-min of continuous moderate hypoxia. Ventilation (V(I)) increased immediately within a hypoxic episode (acute response), followed by a further slow rise in V(I) (short-term potentiation). The peak V(T) response increased from the first to second moderate hypoxic episode (progressive augmentation), but was unchanged thereafter. During normoxic intervals, V(I) increased progressively (56% following the tenth episode; long term facilitation). Time-dependent changes were not observed during or following 30-min of continuous hypoxia. Although several time-dependent ventilatory responses to episodic hypoxia are observed in awake ducks, they are relatively small and biased towards facilitation versus inhibitory mechanisms.

Fibreoptic bronchoscopy in sedated infants facilitated by an airway endoscopy mask

Fibreoptic bronchoscopy (FB) is frequently associated with a decline in PaO2, whose degree and duration can be substantial especially in infants. The effect of a face mask, which allows the administration of 100% oxygen and continuous positive airway pressure during FB, on the incidence and severity of hypoxaemia was studied in thirty-one consecutive infants. Sedation was provided by intravenous propofol titrated to allow patient comfort. A transient fall in SpO2 <95% was recorded in 6/31 patients during endoscopy of the upper airway (lasting 1.6+/-1.1 min) and in 11/31 patients during endoscopy of the lower airways (lasting 1.4+/-1.1 min). Capillary blood gas analysis before and after endoscopy of the lower airways demonstrated an increase in the PCO2 6.4+/-1.3 to 7.3+/-1.4 kPa (49+/-10 to 56+/-11 mmHg). The risk of hypoxaemia in sedated infants breathing spontaneously is low when 100% oxygen and continuous positive airway pressure are administered during FB

Blast lung injury from an explosion on a civilian bus

OBJECTIVE

To assess clinical signs and management of primary blast lung injury (BLI) from explosions in an enclosed space and to propose a BLI severity scoring system.

DESIGN

Retrospective analysis.

PATIENTS

Fifteen patients with primary BLI resulting from explosions on two civilian buses in 1996.

RESULTS

Ten patients were extremely hypoxemic on admission (PaO2 < 65 mm Hg with oxygen supplementation). Four patients remained severely hypoxemic (PaO2/fraction of inspired oxygen (FIO2) ratio of < 60 mm Hg) after mechanical ventilation was established and pneumothoraces were drained. Initial chest radiographs revealed bilateral lung opacities of various sizes in 12 patients (80%). Seven patients (47%) had bilateral pneumothoraces and two patients had a unilateral pneumothorax. Five (33%) had clinically significant bronchopleural fistulae. After clinical and laboratory data were collected, a BLI severity score was defined based on hypoxemia (PaO2/FIO2 ratio), chest radiographic abnormalities, and barotrauma. Severe BLI was defined as a PaO2/FIO2 ratio of < 60 mm Hg, bilateral lung infiltrates, and bronchopleural fistula; moderate BLI as a PaO2/FIO2 ratio of 60 to 200 mm Hg and diffuse (bilateral/unilateral) lung infiltrates with or without pneumothorax; and mild BLI as a PaO2/FIO2 ratio of > 200, localized lung infiltrates, and no pneumothorax. Five patients developed ARDS with Murray scores > 2.5. Respiratory management included positive pressure ventilation in the majority of the patients and unconventional methods (ie, high-frequency jet ventilation, independent lung ventilation, nitric oxide, and extracorporeal membrane oxygenation) in patients with severe BLI. Of the four patients who had severe BLI, three died. All six patients with moderate BLI survived, and four of five with mild BLI survived (one with head injury died).

CONCLUSIONS

BLI can cause severe hypoxemia, which can be improved significantly with aggressive treatment. The lung damage may be accurately estimated in the early hours after injury. The BLI severity score may be helpful in determining patient management and prediction of final outcome.

Acute hypoxemic respiratory failure in children: case mix and the utility of respiratory severity indices

OBJECTIVE

Acute hypoxemic respiratory failure (AHRF) is a common reason for emergency pediatric intensive care. An objective assessment of disease severity from acute physiological parameters would be of value in clinical practice and in the design of clinical trials. We hypothesised that there was a difference in the best early respiratory indices in those who died compared with those who survived.

DESIGN

A prospective observational study of 118 consecutive AHRF admissions with data analysis incorporating all blood gases.

SETTING

A pediatric intensive care unit in a national children's hospital.

INTERVENTIONS

None.

RESULTS

Mortality was 26/118, 22% (95 % confidence interval 18-26%). There were no significant differences in the best alveolar-arterial oxygen tension gradient (A-aDO2, torr), oxygenation index (OI), ventilation index (VI), or PaO2/FIO2 during the first 2 days of intensive care between the survivors and non-survivors. Only the mean airway pressure (MAP, cm H2O) used for supportive care was significantly different on days 0 and 1 (p < 0.05) with higher pressure being used in non-survivors. Multiple logistic regression analysis did not identify any gas exchange or ventilator parameter independently associated with mortality. Rather, all deaths were associated with coincident pathology or multi-organ system failure, or perceived treatment futility due to pre-existing diagnoses instead of unsupportable respiratory failure. When using previously published predictors of outcome (VI > 40 and OI > 40; A-aDO2 > 450 for 24 h; A-aDO2 > 470 or MAP > 23; or A-aDO2 > 420) the risk of mortality was overestimated significantly in the current population.

CONCLUSION

The original hypothesis was refuted. It appears that the outcome of AHRF in present day pediatric critical care is principally related to the severity of associated pathology and now no longer solely to the severity of respiratory failure. Further studies in larger series are needed to confirm these findings.

The value of a scoring system for hypoxic ischaemic encephalopathy in predicting neurodevelopmental outcome

A numeric scoring system for the assessment of hypoxic ischaemic encephalopathy during the neonatal period was tested. The value of the score in predicting neurodevelopmental outcome at 1 y of age was assessed. Forty-five infants who developed hypoxic ischaemic encephalopathy after birth were studied prospectively. In addition to the hypoxic ischaemic encephalopathy score all but two infants had at least one cranial ultrasound examination. Thirty-five infants were evaluated at 12 months of age by full neurological examination and the Griffiths Scales of Mental Development. Five infants were assessed at an earlier stage, four who died before 6 months of age and one infant who was hospitalized at the time of the 12 month assessment. Twenty-three (58%) of the infants were normal and 17 (42%) were abnormal, 16 with cerebral palsy and one with developmental delay. The hypoxic ischaemic encephalopathy score was highly predictive for outcome. The best correlation with outcome was the peak score; a peak score of 15 or higher had a positive predictive value of 92% and a negative predictive value of 82% for abnormal outcome, with a sensitivity and specificity of 71% and 96%, respectively. For the clinician working in areas where sophisticated technology is unavailable this scoring system will be useful for assessment of infants with hypoxic ischaemic encephalopathy and for prognosis of neurodevelopmental outcome.

Effects of hypobaric-hypoxia on the salivary cortisol levels of aircraft pilots

INTRODUCTION

There has been limited characterization of the endocrine stress reactivity of aircraft pilots under the adverse environmental condition of hypobaric-hypoxia. This seems especially true with respect to using the non-invasive technique of salivary hormonal analysis. Thus, the purpose of this study was to characterize the salivary cortisol response to such an environmental stress.

METHODS

Some 53 pilots were exposed to 30 min of hypobaric-hypoxia (final pressure, 540 hPa). The salivary cortisol levels were measured at baseline (0 min), at 15 and 30 min into exposure (+15 and +30 min) and 30 min after the exposure ended (+60 min). The cortisol response of each pilot was classified according to the difference between the +30 min and 0 min values. Responder categories were: increase (I), decrease (D) or no change (N).

RESULTS

Subjects were not evenly distributed among the three response categories (p < 0.05). The distributions were as follows; D = 5 pilots (9.4%), N = 17 pilots (32.1%), and I = 31 pilots (58.5%). Further, significant (p < 0.05) changes in cortisol levels were noted over the sampling times for the D (+15 min to +60 min < 0 min) and 1 (+15 min to +60 min > 0 min) responders, as well as between the D, N, and I responders at the +15 to +60 min sampling times.

CONCLUSIONS

We conclude that no single consistent change in salivary cortisol level occurred among the different subjects in response to the level and duration of hypobaric-hypoxia studied.

Acute effects of ANP and BNP on hypoxic pulmonary vasoconstriction in humans

1. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) have pulmonary vasorelaxant activity with plasma concentrations being elevated in patients with hypoxaemic pulmonary hypertension. However, their effects on acute hypoxic pulmonary vasoconstriction (HPV), the initiating stimulus for pulmonary hypertension have not to date been investigated. We have therefore studied the effects of ANP and BNP on acute HPV in humans. 2. Eight healthy volunteers were studied on three separate occasions. After reaching a resting haemodynamic state (t0), an infusion of either ANP (10 pmol kg-1 min-1), BNP (10 pmol kg-1 min-1) or placebo (5% dextrose) was commenced. This was given alone for 30 min (t30) before subjects were rendered hypoxaemic (SaO2 75-80%) for a further 30 min (t60), with the initial infusion continuing to t60. Pulsed-wave Doppler analysis of pulmonary artery flow was used to measure mean pulmonary arterial pressure (MPAP) and hence total pulmonary vascular resistance (PVR) was calculated. 3. MPAP and PVR both tended to decrease in response to ANP and BNP infusion, although compared with placebo, the difference at t30 was only statistically significant for PVR. Hypoxaemia increased MPAP and PVR, although values at t60 were significantly lower following both ANP and BNP compared with placebo. 4. In terms of the actual change in PVR (delta PVR) induced by hypoxaemia (from t30 to t60), BNP (146(16) dyn s cm-5), but not ANP (183(21) dyn s cm-5) significantly attenuated delta PVR compared with placebo (194(26) dyns s cm-5): mean difference BNP versus placebo 48 dyn s cm-5, 95% Cl 3-93. An identical pattern was observed for delta MPAP where BNP (15.9(1.1) mmHg), but not ANP (18.0(1.2) mmHg) significantly attenuated delta MPAP compared with placebo (19.0(1.7) mmHg): mean difference BNP versus placebo 3.1 mmHg, 95% Cl 0.7-5.5. 5. Thus, although both ANP and BNP exhibit pulmonary vasorelaxant activity, only BNP significantly attenuated the MPAP and PVR responses to acute hypoxaemia. This suggests that the natriuretic peptides may have a role in attenuating pulmonary hypertension secondary to hypoxaemia.

Classes of tissue hypoxia

We identify eight causes of tissue hypoxia, falling into three classes, A, B, and C, depending upon the effect on the critical mixed venous pO2 and the optimal oxygen consumption rate. The critical mixed venous pO2 is the value above which the oxygen consumption rate is optimal and independent of the mixed venous pO2 and below which the oxygen consumption rate decreases towards zero. Class A hypoxia: primary decrease in mixed venous pO2. Causes: 1) ischaemic hypoxia (decrease in cardiac output), 2) low-extractivity hypoxia (decrease in oxygen extraction tension, px). Class B hypoxia: primary increase in critical mixed venous pO2. Causes: 1) shunt hypoxia (increased a-v shunting), 2) dysperfusion hypoxia (increased diffusion length from erythrocytes to mitochondria and/or decreased total capillary endothelial diffusion area, e.g., tissue oedema, microembolism), 3) histotoxic hypoxia (inhibition of the cytochrome chain). Class C hypoxia: primary increase in optimal oxygen consumption rate. Causes: 1) uncoupling hypoxia (uncoupling of the ATP formation associated with O2 reduction), 2) hypermetabolic hypoxia (increased energy metabolism, e.g., due to hyperthermia).

Plasma levels of atrial natriuretic peptide under acute hypoxia in normal subjects

To investigate whether the acute hypoxia can be a stimulus for atrial natriuretic peptide (ANP) secretion, plasma levels of ANP were determined under three different hypoxic conditions in six normal subjects. During 15% O2 breathing for 10 min, no significant change in plasma ANP level was observed. Severe hypoxia induced by 10% O2 breathing increased the mean pulmonary arterial pressure (Ppa) by 11.6 mm Hg within 10 min (P less than 0.01), accompanying a slight but significant rise in plasma ANP level of pulmonary artery (PA) from 24.3 +/- 5.3 to 28.2 +/- 4.6 pg/ml (P less than 0.05). There was a tendency for the ANP level of PA to rise under hypoxic hypobaria at 515 Torr for 10 min, followed by a decrease of that level during 100% O2 breathing under hypobaric condition. These changes, however, still remained in the normal range. No significant changes were observed both in right atrial pressure and in pulmonary capillary wedge pressure under any of the three hypoxic conditions. From these results we conclude that ANP can be released in response to the elevation of Ppa caused by acute hypoxia in normal subjects, but the changes in plasma ANP level may be too small to play a significant physiological role in hemodynamic responses to acute hypoxia.

[Hypoxia and internal intensive medicine. I. Clinical aspects of acute hypoxia]

The treatment of the topic acute hypoxia and internal intensive medicine with description of the fundaments--classification and definition of hypoxia and its forms, clinic, therapeutic possibilities and oxygen therapy--becomes necessary in order to get in the entity of hypoxia and to find a common language among specialists for intensive medicine. The knowledge of a differentiated treatment of different forms of hypoxia and thus also of clinical pictures seems to be necessary under the aspect of a highly developed respirator technique and the knowledge of anaesthesiology in this field. Application of the first report is the description of the factors of the oxygen transport. Respiratory, stagnation, anaemic and histotoxic hypoxia are defined and possible causes mentioned. The clinically relevant hypoxia will mostly be a mixed form, among which the respiratory insufficiency in shock lung plays an important role in intensive medicine.

On the pathology of chronic mountain sickness

In this report we described the findings in a case of Chronic Mountain Sickness, autopsied at Cerro de Pasco (4,300 feet) and compared with the limited pathologic observations reported by others. It is aparent that in fatal cases of Chronic Mountain Sickness the main changes are located at the level of the pulmonary circulation and are of the type that lead to Chronic Cor Pulmonale. So far histologic studies have been reported only in cases of secondary Chronic Mountain Sickness. The basic pathology in Primary Chronic Mountain Sickness or Monge’s disease remain to be defined.

Vascular and respiratory emergencises

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