Hypoxemic Subjects Research Articles

Hemodynamic Effects of Awake Prone Positioning With COVID-19 Acute Respiratory Failure.

Awake prone positioning (PP) reduces need for intubation for patients with COVID-19 with acute respiratory failure. We investigated the hemodynamic effects of awake PP in non-ventilated subjects with COVID-19 acute respiratory failure. We conducted a single-center prospective cohort study. Adult hypoxemic subjects with COVID-19 not requiring invasive mechanical ventilation receiving at least one PP session were included. Hemodynamic assessment was done with transthoracic echocardiography before, during, and after a PP session. Twenty-six subjects were included. We observed a significant and reversible increase in cardiac index (CI) during PP compared to supine position (SP): 3.0 ± 0.8 L/min/m2 in PP, 2.5 ± 0.6 L/min/m2 before PP (SP1), and 2.6 ± 0.5 L/min/m2 after PP (SP2, P < .001). A significant improvement in right ventricular (RV) systolic function was also evidenced during PP: The RV fractional area change was 36 ± 10% in SP1, 46 ± 10% during PP, and 35 ± 8% in SP2 (P < .001). There was no significant difference in PaO2 /FIO2 and breathing frequency. CI and RV systolic function are improved by awake PP in non-ventilated subjects with COVID-19 with acute respiratory failure.

Acute Effects of Sitting Out of Bed and Exercise on Lung Aeration and Oxygenation in Critically Ill Subjects.

Early mobilization during critical illness is safe and has beneficial effects on functional outcomes. However, its impact on pulmonary function has not been thoroughly explored. We hypothesized that a sitting position out of bed coupled with exercise could result in an improvement in oxygenation and lung aeration. The study was conducted on a cohort of adult subjects within a week of their admission to an ICU. Subjects were transferred to a chair and undertook a 15-min session of exercise, either active or passive. Subjects in the control group were only transferred to a chair. Electrical impedance tomography, a reliable bedside technique monitoring regional lung aeration and the distribution of ventilation, was continuously performed, and blood gases were assessed at baseline and 20 min post-exercise. The cohort included 40 subjects, 17 of whom were mechanically ventilated and 23 spontaneously breathing. The control group for each modality consisted of 5 mechanically ventilated or 5 spontaneously breathing subjects. Mild hypoxemia was present in 45% of the spontaneously breathing cohort, whereas the mechanically ventilated subjects demonstrated moderate (50%) or severe (12%) hypoxemia. Compared with the control group, early mobilization induced a significant increase in lung aeration. In mechanically ventilated subjects, lung aeration increased, especially in the anterior lung regions (mean impedance [95% CI]: T1 (baseline in bed) = 1,265 [691-1,839]; T2 (chair sitting) = 2,003 [1,042-2,963]; T3 (exercise) = 1,619 [810 2,427]; T4 (post exercise in chair) = 2,320 [1,186-3,455]). In spontaneously breathing subjects, lung aeration increased mainly in the posterior lung regions (mean impedance [95% CI]: T1 = 380 [124-637]; T2 = 655 [226-1,084]; T3 = 621 [335-906]; T4 = 600 [340-860]). [Formula: see text] increased, especially in subjects with lower [Formula: see text] at baseline (< 200) (133 ± 31 to 158 ± 48, P = .041). For critically ill subjects, a sitting position and exercise increased lung aeration and were associated with an improvement in [Formula: see text] in the more severely hypoxemic subjects.

The Impact of High-Flow Nasal Cannula on Olfactory Function.

Oxygen therapy provided via high-flow nasal cannula (HFNC) improves gas exchange lung compliance and results in increased lung expiratory volumes. Previous data indicate that hyperbaric and humid states improve the olfactory thresholds compared to hypobaric and dry conditions. This prospective, observational study aimed to determine the impact of oxygen delivery through HFNC on olfactory function in subjects admitted to the ICU for acute respiratory failure (ARF). 30 subjects who were admitted to the ICU for ARF underwent an olfactory sniff test before and after oxygen therapy with HFNC. Baseline olfactory function of subjects with ARF was also compared against 30 healthy controls. Odor threshold (OT), odor discrimination (OD), odor identification (OI) and global olfactory score (TDI) were recorded for all subjects. The OT, OD, OI, and TDI scores were significantly higher in the control group compared to the baseline scores of the subjects with ARF (P < .001 for all comparisons). In subjects with ARF, administration of oxygen with HFNC led to significant improvements in OT (P = .02), OD (P = .001), OI (P = .02), and TDI (25.5 ± 3.8 vs 27.1 ± 3.5, P < .001) scores. Our results indicate that subjects with ARF had relative olfactory dysfunction compared to healthy controls. These results also suggest that implementation of HFNC to relieve hypoxemia in subjects presenting with ARF can lead to a significant improvement in olfactory function.

Oxygen Conservation Methods With Automated Titration.

Oxygen titration is recommended to avoid hyperoxemia and hypoxemia. Automated titration, as well as the [Formula: see text] target, may have an impact on oxygen utilization, with potential logistical effects in emergency and military transportation. We sought to assess the oxygen flow required for different [Formula: see text] targets in spontaneously breathing subjects, and to evaluate individualized automated oxygen titration to maintain stable oxygenation in subjects with COPD and healthy subjects with induced hypoxemia. In the first part of the study, oxygen flow was evaluated in hospitalized subjects for different [Formula: see text] targets from 90% to 98%. Oxygen requirements to reach these targets were determined using a device that automatically adjusts oxygen flow every second on the basis of the [Formula: see text] target. In the second part of the study, the same automated oxygen titration method was used to correct hypoxemia in subjects with COPD and in healthy subjects with induced hypoxemia while the subjects wore a gas mask. Oxygen flow, [Formula: see text], and heart rate were continuously recorded. Thirty-six spontaneously breathing hospitalized subjects were included in the first part of the study. Oxygen flow was reduced more than 6-fold when the [Formula: see text] target was decreased from 98% to 90%. The second part of the study included 15 healthy and 9 subjects with stable COPD. In healthy subjects, heterogeneous oxygen flows were required to correct induced hypoxemia (0.2-2.5 L/min). In subjects with COPD, oxygen flow varied from 0 L/min (in 9 of 18 tested conditions) to 2.9 L/min. Significant reductions in the amount of oxygen delivered could be obtained with optimized [Formula: see text] targets. Oxygen delivery through a gas mask to correct hypoxemia is feasible, and automated oxygen titration may help individualize oxygen administration and reduce oxygen utilization. (ClinicalTrials.gov registration: NCT02782936, NCT02809807.).

The novel combination of theophylline and bambuterol as a potential treatment of hypoxemia in humans.

Hypoxemia can be life-threatening, both acutely and chronically. Because hypoxemia causes vascular dysregulation that further restricts oxygen availability to tissue, it can be pharmacologically addressed. We hypothesized that theophylline can be safely combined with the β2-adrenergic vasodilator bambuterol to improve oxygen availability in hypoxemic patients. Ergogenicity and hemodynamic effects of bambuterol and theophylline were measured in rats under hypobaric and normobaric hypoxia (12% O2). Feasibility in humans was assessed using randomized, double-blind testing of the influence of combined slow-release theophylline (300 mg) and bambuterol (20 mg) on adverse events (AEs), plasma K+, pulse, blood pressure, and drug interaction. Both drugs and their combination significantly improved hypoxic endurance in rats. In humans, common AEs were low K+ (<3.5 mmol/L; bambuterol: 12, theophylline: 4, combination: 13 episodes) and tremors (10, 0, 14 episodes). No exacerbation or serious AE occurred when drugs were combined. A drop in plasma K+ coincided with peak bambuterol plasma concentrations. Bambuterol increased heart rate by approximately 13 bpm. Drug interaction was present but small. We report promise, feasibility, and relative safety of combined theophylline and bambuterol as a treatment of hypoxemia in humans. Cardiac safety and blood K+ will be important safety endpoints when testing these drugs in hypoxemic subjects.

Resting arterial hypoxaemia in subjects with chronic heart failure, pulmonary hypertension and patent foramen ovale.

What is the central question of this study? Does a patent foramen ovale contribute to resting arterial hypoxaemia, defined as arterial oxygen saturation <95%, in subjects with chronic heart failure with or without pulmonary arterial hypertension? What is the main finding and its importance? The presence of a patent foramen ovale contributed to resting arterial hypoxaemia only in subjects with chronic heart failure with pulmonary arterial hypertension. These data suggest that the presence of a patent foramen ovale should be considered in chronic heart failure patients with arterial hypoxaemia and pulmonary hypertension. The roles of intrapulmonary and intracardiac shunt in contributing to arterial hypoxaemia at rest in subjects with chronic heart failure (CHF) have not been well investigated. We hypothesized that blood flow through intrapulmonary arteriovenous anastomoses (Q̇ IPAVA ) and/or patent foramen ovale (Q̇ PFO ) could potentially contribute to arterial hypoxaemia and, with pulmonary hypertension (PH) secondary to CHF, this contribution may be exacerbated. Fifty-six subjects with CHF (New York Heart Association Classes I-III), with (+) or without (-) PH [defined as peak tricuspid regurgitation velocity ≥2.9ms(-1) (CHF PH+, n=32) and peak tricuspid regurgitation velocity ≤2.8ms(-1) (CHF PH-, n=24)], underwent arterial blood gas analysis and transthoracic saline contrast echocardiography concomitant with transcranial Doppler to detect Q̇ IPAVA and Q̇ PFO . Seventeen of 56 subjects with CHF (30%) had Q̇ PFO , but only four of 56 subjects with CHF had Q̇ IPAVA (7%), both similar to age- and sex-matched control subjects. Mean arterial oxygen saturation (SaO2) was lower in subjects with Q̇ PFO . Only CHF PH+ subjects with Q̇ PFO had arterial hypoxaemia (mean SaO2 <95%). Bubble scores assessed using transthoracic saline contrast echocardiography were correlated with microembolic signals detected with transcranial Doppler in subjects with Q̇ PFO . Significant Q̇ IPAVA was not present in either CHF PH+ or PH- subjects, suggesting that Q̇ IPAVA is not dependent on increased pulmonary pressure and does not contribute significantly to arterial hypoxaemia in older subjects with CHF. Given that SaO2 was lower in all subjects with CHF who had Q̇ PFO compared with those without Q̇ PFO , a patent foramen ovale should be considered when determining potential causes of arterial hypoxaemia, because Q̇ PFO was present in 30% of these subjects.

Long-Term Oxygen Therapy: In a Perfect World

This issue of Respiratory Care contains 2 papers of interest that deal with long-term oxygen therapy (LTOT). In the first, Marti et al investigated the efficacy of 2 oxygen-conserving devices in correcting exercise-induced hypoxemia in subjects with either COPD or interstitial lung disease (ILD).

Experimental Pain and Opioid Analgesia in Volunteers at High Risk for Obstructive Sleep Apnea

BackgroundObstructive sleep apnea (OSA) is characterized by recurrent nocturnal hypoxia and sleep disruption. Sleep fragmentation caused hyperalgesia in volunteers, while nocturnal hypoxemia enhanced morphine analgesic potency in children with OSA. This evidence directly relates to surgical OSA patients who are at risk for airway compromise due to postoperative use of opioids. Using accepted experimental pain models, we characterized pain processing and opioid analgesia in male volunteers recruited based on their risk for OSA.MethodsAfter approval from the Intitutional Review Board and informed consent, we assessed heat and cold pain thresholds and tolerances in volunteers after overnight polysomnography (PSG). Three pro-inflammatory and 3 hypoxia markers were determined in the serum. Pain tests were performed at baseline, placebo, and two effect site concentrations of remifentanil (1 and 2 µg/ml), an μ-opioid agonist. Linear mixed effects regression models were employed to evaluate the association of 3 PSG descriptors [wake after sleep onset, number of sleep stage shifts, and lowest oxyhemoglobin saturation (SaO2) during sleep] and all serum markers with pain thresholds and tolerances at baseline, as well as their changes under remifentanil.ResultsForty-three volunteers (12 normal and 31 with a PSG-based diagnosis of OSA) were included in the analysis. The lower nadir SaO2 and higher insulin growth factor binding protein-1 (IGFBP-1) were associated with higher analgesic sensitivity to remifentanil (SaO2, P = 0.0440; IGFBP-1, P = 0.0013). Other pro-inflammatory mediators like interleukin-1β and tumor necrosis factor-α (TNF-α) were associated with an enhanced sensitivity to the opioid analgesic effect (IL-1β, P = 0.0218; TNF-α, P = 0.0276).ConclusionsNocturnal hypoxemia in subjects at high risk for OSA was associated with an increased potency of opioid analgesia. A serum hypoxia marker (IGFBP-1) was associated with hypoalgesia and increased potency to opioid analgesia; other pro-inflammatory mediators also predicted an enhanced opioid potency.Trial Registration: ClinicalTrials.gov NCT00672737.

Bronchoscopic Lung Biopsy Using Noninvasive Ventilatory Support: Case Series and Review of Literature of NIV-Assisted Bronchoscopy

Fiberoptic bronchoscopy and lung biopsy are important diagnostic tools in patients with diffuse pulmonary infiltrates. However, these patients often have hypoxemic respiratory failure that makes this procedure hazardous. Noninvasive ventilation (NIV) has been shown to improve oxygenation in hypoxemic patients. To report the efficacy and safety of an innovative technique of NIV-assisted bronchoscopic lung biopsy in a small case-series of hypoxemic subjects with diffuse parenchymal infiltrates; also to systematically review the literature on NIV-assisted bronchoscopy. Subjects with bilateral diffuse parenchymal infiltrates and P(aO(2))/F(IO(2)) < 200 mm Hg underwent bronchoscopic lung biopsy under NIV support. NIV was initiated 10 min before the procedure and continued for 30 min after the procedure. The primary outcomes were performance of successful procedure and episodes of decline in S(pO(2)) < 90%. Secondary end points were the change in the respiratory and hemodynamic parameters during the procedure and occurrence of complications such as pneumothorax, hemorrhage, and endotracheal intubation. Six subjects, with a mean ± SD age of 44.5 ± 11.6 years, were included in the study. The median (interquartile range [IQR]) P(aO(2))/F(IO(2)) prior to lung biopsy was 164.5 mm Hg (146.3-176.3 mm Hg), and the median (IQR) inspiratory and expiratory positive airway pressures were 14 cm H(2)O (12-15 cm H(2)O) and 5 cm H(2)O. Fiberoptic bronchoscopy was well tolerated and all subjects maintained S(pO(2)) > 92% during the procedure. One subject required endotracheal intubation due to hemoptysis. A definite diagnosis was obtained in 5 of the 6 subjects. A repeat procedure was performed in one subject, which again yielded no diagnosis. No other periprocedural complications were encountered. NIV-assisted bronchoscopic lung biopsy is a novel method for obtaining diagnosis in hypoxemic patients with diffuse lung infiltrates. However, this approach should be reserved for centers with extensive experience in NIV. More studies are required to define the utility of this approach.

A career in cardiothoracic surgery

BACKGROUND: High-flow nasal cannula (HFNC) oxygen therapy is used to deliver an FIO2 from 0.21 to 1.0. The double-trunk mask (DTM) is a device designed to increase the FIO2 in patients with a high inspiratory flow demand. The aim of our study was to evaluate the effect of DTM in hypoxemic subjects already receiving HFNC. METHODS: We report a prospective multi-center crossover pilot study including 15 subjects treated with HFNC for acute hypoxemic respiratory failure. Measurements were performed at the end of 30-min periods with HFNC only, with HFNC + DTM, and again with HFNC only. RESULTS: Compared with HFNC alone, HFNC + DTM increased PaO2 from 68 ± 14 mm Hg to 85 ± 22 mm Hg (P CONCLUSIONS: In subjects receiving oxygen via HFNC, the addition of the DTM over the HFNC increased PaO2 without changing the PaCO2.

Is it possible to predict which patients with mild pneumonias will develop hypoxemia?

Usually, mortality due to mild community-acquired pneumonias (CAP) (Pneumonia severity index (PSI) classes I-III) is low (<3%), but the appearance of hypoxemia significantly increases mortality. Our aim was to determine the clinical parameters associated with risk factors of developing hypoxemia in subjects with mild CAP (PSI I-III) and the clinical outcomes of the hypoxemic group. We analyzed clinical characteristics and the outcomes of patients with mild CAP and hypoxemia (PaO2/FiO2<300), in a prospective, multicenter cohort study of 1195 patients. Mild pneumonias (PSI I-III) were found in 645 cases (53.9%), of which 217 (33.6%) presented hypoxemia according to a PaO2/FiO2<300. Patients with PaO2/FiO2<300 required more ICU admissions, mechanical ventilation, and developed septic shock than other PSI I-III patients. The clinical parameters associated with hypoxemia were: COPD, bilateral chest X-ray involvement, and hypoalbuminemia. We conclude that patients with COPD, those with bilateral chest X-ray involvement, or hypoalbuminemia were significantly more likely to have hypoxemia in mild CAP. Hypoxemic patients with low-risk pneumonia have worse clinical outcomes, including more ICU admission, need for mechanical ventilation and presence of septic shock than non-hypoxemic low-risk patients.

Mécanismes intégrés de la dyspnée et du handicap au cours de la bronchopneumopathie chronique obstructive

Today, dyspnea in chronic obstructive pulmonary disease (COPD) is attributed to thoracic distention secondary to bronchial obstruction and hyperventilation. It inevitably occurs during exercise, even in patients with little obstruction, when they are capable of the elevated and prolonged power output that necessitates substantial hyperventilation. Exercise intolerance is due mainly to dyspnea, but muscle fatigue is also involved, especially in COPD patients who are malnourished. Deterioration of muscle function follows a substantial reduction in daily physical activity. In malnourished and hypoxemic subjects, however, responsibility for this is attributed to diverse aggravating biological processes related to chronic low-grade inflammation and to accentuated oxidative stress. The drastic diminution of physical activity results from ventilatory and muscle impairment and from symptoms that make movement painful. Improvement of ventilatory and muscle function, however, does not lead to recovery that allows sufficient physical activity. The spiral of disengagement, a morbid, psychodynamic process, accompanies chronic diseases and has the strongest effect in patients who were not highly physically active before becoming ill. Improvement of this handicap therefore requires a comprehensive management of patients, not confined to the prescription of physical activity under medical supervision. The aim is to offer diverse treatment propositions that can produce sustainable behavioral change.

Role of Oxygen Availability in CFTR Expression and Function

The cystic fibrosis transmembrane conductance regulator (CFTR) serves a pivotal role in normal epithelial homeostasis; its absence leads to destruction of exocrine tissues, including those of the gastrointestinal tract and lung. Acute regulation of CFTR protein in response to environmental stimuli occurs at several levels (e.g., ion channel phosphorylation, ATP hydrolysis, apical membrane recycling). However, less information is available concerning the regulatory pathways that control levels of CFTR mRNA. In the present study, we investigated regulation of CFTR mRNA during oxygen restriction, examined effects of hypoxic signaling on chloride transport across cell monolayers, and related these findings to a possible role in the pathogenesis of chronic hypoxic lung disease. CFTR mRNA, protein, and function were robustly and reversibly altered in human cells in relation to hypoxia. In mice subjected to low oxygen in vivo, CFTR mRNA expression in airways, gastrointestinal tissues, and liver was repressed. CFTR mRNA expression was also diminished in pulmonary tissues taken from hypoxemic subjects at the time of lung transplantation. Environmental factors that induce hypoxic signaling regulate CFTR mRNA and epithelial Cl(-) transport in vitro and in vivo.

‘Oxygen uptake efficiency slope’ in trained and untrained subjects exposed to hypoxia

We assessed the ability of the oxygen uptake efficiency slope, whether calculated on 100 and 80% of maximal exercise test duration (OUES(100) and OUES(80)), to identify the change in cardiorespiratory capacities in response to hypoxia in subjects with a broad range of V(O2 peak). Four maximal exercise tests were performed in trained (T) and untrained subjects (UT) in normoxia and at 1000, 2500 and 4500 m. The mean reductions in maximal exercise capacities at 4500 m were the same in T subjects for V(O2 peak) (-30%), OUES(80) (-26%) and OUES(100) (-26%) whereas in UT subjects only OUES(100) (-14%), but not OUES(80) (-20%), was lower compared with V(O2 peak) (-21%, p<0.05). OUES(100) and OUES(80) were correlated with V(O2 peak) and the ventilatory anaerobic threshold in both groups. Multiple regression analyses showed that V(O2 peak), OUES(100) and OUES(80) were significantly linked to O(2) arterial-venous difference. The OUES(80) could be considered as an interesting sub-maximal index of cardiorespiratory fitness in normal or hypoxemic subjects unable to reach V(O2 peak).

Evidence of Decrease in Peak Heart Rate in Acute Hypoxia: Effect of Exercise-Induced Arterial Hypoxemia

This study focuses on the influence of the arterial oxygen saturation level at exhaustion on peak heart rate under acute moderate hypoxia, in endurance-trained subjects. Nineteen competing male cyclists performed exhaustive ramp exercise (cycle ergometer) under normoxia and normobaric hypoxia (15 % O (2)). After the normoxic trial, the subjects were divided into those demonstrating exercise-induced arterial hypoxemia during exercise (> 5 % decrease in SaO (2) between rest and the end of exercise, n = 10) and those who did not (n = 9). O (2) uptake, heart rate and arterial O (2) saturation (ear-oximeter) levels were measured. Under hypoxia, peak heart rate decreased for both groups (p < 0.001) and to a greater extent for hypoxemic subjects (p < 0.01). Arterial O (2) saturation under hypoxia was lower for the hypoxemic than for the non-hypoxemic subjects (p < 0.001) and it was correlated to the fall in peak heart rate between normoxia and hypoxia for all subjects (p < 0.01; r = 0.65). Hypoxemic subjects presented greater decrease in maximal O (2) uptake than non-hypoxemic ones (19.6 vs. 15.6 %; p < 0.05). The results confirm the greater decrement in arterial O (2) saturation under hypoxia in hypoxemic subjects and demonstrates a more pronounced reduction in peak heart rate in those subjects compared with non-hypoxemic ones. These data confirm the possible influence of arterial oxygenation on the decrease in peak heart rate in acute hypoxia.

Prevalence of oxygen desaturation and use of oxygen at home in adults at sea level and at moderate altitude

The aim of this study was to determine the prevalence of oxygen desaturation in adults aged>or=40 yrs as altitude above sea level increases. A population-based, cross-sectional study with a multistage cluster sampling of 1,063 subjects from metropolitan Mexico City (Mexico; 2,240 m above sea level), 1,357 from Caracas (Venezuela; 950 m) and 943 from Montevideo (Uruguay; 35 m). The mean of six measurements of arterial oxygen saturation (SP,O2) was estimated using a pulse oximeter. Mean SP,O2 decreased with altitude. No subject from Montevideo had a mean SP,O2<or=88%. Prevalence of subjects with SP,O2<or=88%, a common criterion used for oxygen prescription, was 1.0% in Caracas and 6.0% in Mexico City. Additional predicting factors for hypoxaemia in multiple regression models were age, body mass index and a low forced expiratory volume in one second as a percentage of the predicted value. In Mexico City and Caracas, <10% of the hypoxaemic subjects reported use of domiciliary oxygen, whereas at least half of the subjects reporting use of oxygen at home had a resting SP,O2>88%. In conclusion, the prevalence of hypoxaemia was closely related to altitude. Priorities for oxygen prescription must be defined in moderate altitudes because it is unfeasible to provide it to all subjects fulfilling the criteria commonly used.

Effect of hyperoxia on maximal O2 uptake in exercise-induced arterial hypoxaemic subjects

This study focuses on the effect of hyperoxia on maximal oxygen uptake VO2max and maximal power (Pmax) in subjects exhibiting exercise-induced arterial hypoxemia (EIH) at sea level. Sixteen competing male cyclists VO2max > 60 ml.min(-1).kg(-1)) performed exhaustive ramp exercise (cycle-ergometer) under normoxia and moderate hyperoxia (FIO2 = 30%). After the normoxic trial, the subjects were divided into those demonstrating EIH during exercise [arterial O2 desaturation (delta SaO2) >5%; n = 9] and those who did not (n = 7). Under hyperoxia, SaO2 raised and the increase was greater for the EIH than for the non-EIH group (P<0.001). VO2max improved for both groups and to a greater extent for EIH (12.8 +/- 5.7% vs. 4.2 +/- 4.6%, P<0.01; mean+/-SD) and the increase was correlated to the gain in SaO2 for all subjects (r = 0.71, P<0.01). Pmax improved by 3.3 +/- 3.3% (P<0.01) regardless of the group. These data suggest that pulmonary gas exchange contributes to a limitation in VO2max and power for especially EIH subjects.

Effects of chronic hypoxemia on the afferent nerve activities from skeletal muscle.

An acute reduction of the oxygen supply to contracting muscles not only affects their metabolism but also modifies their sensorimotor control through changes in afferent discharge of the group I and group III-IV nerve fibers, the latter playing a pivotal role in the protective mechanisms against muscle fatigue. The effects of chronic hypoxemia on the muscle sensitivity are totally unknown. In the present study, group I fibers (mechanosensory afferents) and group III-IV fibers (mechanosensory and chemosensory afferents) from the anterior tibial muscle were recorded in normoxemic and chronic hypoxemic rats. Hypoxemic rats breathed for 45 d a gas mixture containing 9.5 to 10% O(2) in N(2). The data were compared with those obtained in normoxemic animals of the same age. To activate the different muscle afferents, we used different test agents, including electrically induced fatigue (EIF), KCl, lactic acid injections, as well as tendon vibrations. The conduction velocity of all nerve fibers was significantly (p < 0.01) higher in hypoxemic rats than in the normoxemic group. Chronic hypoxemia significantly depressed the response of the group III-IV muscle afferents to KCl injections and even abolished their response to lactic acid and EIF. However, the response to tendon vibrations of the group I afferents was similar in hypoxemic and normoxemic rats. These results suggest that chronic hypoxemia markedly alters the chemosensitivity of the group III-IV muscle afferents, which may explain the higher fatigability of hypoxemic subjects.

Screening patients in general practice with COPD for long term domiciliary oxygen requirement using pulse oximetry

Epidemiological data suggest long term oxygen therapy (LTOT) delivered by oxygen concentrators in patients with severe hypoxic chronic obstructive pulmonary disease (COPD) is under-prescribed by General Practitioners (GPs) in England and Wales. One reason for this may be the unavailability to GPs of a measure of arterial oxygenation needed to fulfil the defined prescription criteria. Provision of a non-invasive measure of oxygenation may improve detection of hypoxic subjects and increase appropriate prescribing. This study aimed to evaluate pulse oximetry in a general practice setting and to screen for severe undetected hypoxaemia fulfilling the LTOT prescription criteria in patients with COPD. All COPD patients attending surgery in two practices were screened with oximeters for hypoxaemia. Those with an oxygen saturation of ≤92% were referred to hospital for formal arterial blood gas analysis and an oxygen concentrator assessment. GPs were asked to evaluate their experience in the ease of use and application of oximetry. The number of patients receiving oxygen by concentrator before the study was compared with the national rate and the number after the study with the estimated need suggested by epidemiological studies. Over a 12-month period a total of 114 patients were screened in the two practices with a combined list size of 15 742. Thirteen patients had saturations of ≤92%. Two refused and 11 underwent formal arterial gas analysis. Three had PaO 2 <7·3 kPa and new prescriptions for oxygen concentrators were made in these previously unsuspected severely hypoxaemic subjects as a result. One other hypoxaemic subject was referred and found to have another treatable medical condition. The initial prevalence of concentrator prescription (0·013% CI 0·003, 0·047) was similar to the national rate (0·024%) and the prevalence observed after screening (0·031%, CI 0·013, 0·073) fell within the lower suggested prescription need of previous epidemiological data (0·02–0·10%). All practitioners found the oximeters simple to use and helpful in assisting with assessment of the severity of their patients' condition. Oximetry provides a readily usable non-invasive method of screening and when applied to all COPD patients seen in general practice can reveal those fulfilling the criteria for long term oxygen who would otherwise not be identified as needing this treatment.

Use of macroaggregated albumin lung perfusion scan to diagnose hepatopulmonary syndrome: A new approach

Background & Aims: We have reported that contrast echocardiography is a sensitive screening test for the hepatopulmonary syndrome (HPS). However, contrast echocardiography lacks specificity because many cirrhotic patients have positive study results with normal arterial blood gases and therefore do not fulfill criteria for HPS. The aim of this study was to assess the role of macroaggregated albumin lung perfusion scans (MAA scans) in the diagnosis of HPS. Methods: MAA scans were performed in 25 patients with HPS, 25 cirrhotic patients without HPS, and 15 hypoxemic subjects with intrinsic lung disease alone. An MAA shunt fraction was calculated from brain and lung counts. Results: MAA scan results were positive in 21 of 25 patients with HPS and negative in all controls. All 21 patients with positive MAA scans had P O 2 values of <60 mm Hg. There was a strong inverse correlation between the degree of the MAA shunt fraction and arterial hypoxemia ( r = −0.726). Conclusions: A positive MAA scan result in cirrhosis is specific for the presence of moderate to severe HPS. We speculate that MAA scans may be particularly useful in evaluating the contribution of HPS to the hypoxemia in cirrhotic patients with intrinsic lung disesase. GASTROENTEROLOGY 1998;114:305-310