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The breathing of newborns is destabilized by warm temperatures. We hypothesized that in unanesthetized, intact newborn rats, body temperature ([T.sub.B]) influences the peripheral chemoreflex response (PCR response) to hypercapnia. To test this, we delivered square-wave challenges of 8% C[O.sub.2] in air to postnatal day 4-5 (P4-P5) rats held at a [T.sub.B] of 30[degrees]C (Cold group, n = 11), 33[degrees]C (Cool group, n = 10), and 35[degrees]C thermoneutral zone group [thermoneutral zone (TNZ) group, n = 11], while measuring ventilation ([??]) directly with a pneumotach and mask. Cool animals were challenged with 8% C[O.sub.2] balanced in either air or hyperoxia (n = 10) to identify the PCR response. Breath-to-breath analysis was performed on 30 room air breaths and every breath of the 1-min C[O.sub.2] challenge. As expected, warmer [T.sub.B] was associated with an unstable breathing pattern in room air: TNZ animals had a coefficient of variation in [??] ([??] CV%) that was double that of animals held at cooler [T.sub.B] (P < 0.001). Hyperoxia markedly suppressed the hypercapnic ventilatory response over the first 10 breaths (or ~4 s), suggesting that this domain is dominated by the PCR response. The PCR response (P = 0.03) and total response (P = 0.04) were significantly greater in TNZ animals compared with hypothermic animals. The total response had a significant, negative relationship with [??]C[O.sub.2] ([R.sup.2] = 0.53; P < 0.001). Breathing stability was positively related to the total response ([R.sup.2] = 0.36; P < 0.001) and to a lesser extent, the PCR response ([R.sup.2] = 0.19; P - 0.01) and was negatively related to [??]C[O.sub.2] ([R.sup.2] = 0.34; P < 0.001). ANCOVA confirmed a significant effect of [T.sub.B] alone on breathing stability (P < 0.01), with no independent effects of [??]C[O.sub.2] (P = 0.41), the PCR response (P = 0.82), or the total VE response (P = 0.08). Our data suggest that in early postnatal life, the chemoreflex responses to C[O.sub.2] are highly influenced by [T.sub.B], and while related to breathing stability, are not predictors of stability after accounting for the independent effect of [T.sub.B]. ventilation; carotid body; newborn; apnea; C[O.sub.2] response

Byline: Rebeca Paiva (1,3,4), Uros Krivec (2,3,4), Guillaume Aubertin (3), Emmanuelle Cohen (4), Annick Clement (3,4), Brigitte Fauroux (3,4) Keywords: Carbon dioxide; Noninvasive positive pressure ventilation; Child; Arterial blood gases Abstract: Introduction Routine monitoring of noninvasive respiratory support relies on nocturnal pulse oximetry and daytime arterial blood gases, without systematic nocturnal carbon dioxide recording. The aim of the study was to assess if overnight pulse oximetry and daytime blood gases are sufficiently accurate to detect nocturnal hypoventilation in children receiving long-term noninvasive respiratory support. Materials and methods Pulse oximetry and carbon dioxide pressure measured by capillary arterialized blood gases and a combined transcutaneous carbon dioxide and pulse oximetry (PtcCO.sub.2/SpO.sub.2) monitor were compared in 65 patients (asthma, n = 16, recurrent bronchitis, n = 8, lung infection, n = 8, cystic fibrosis, n = 15, interstitial lung disease, n = 6, neuromuscular disease, n = 12). Daytime capillary arterialized blood gases and nocturnal recording of pulse oximetry and carbon dioxide by means of a combined PtcCO.sub.2/SpO.sub.2 monitor were performed in 50 other patients receiving nocturnal noninvasive respiratory support at home. Results A correlation was observed between pulse oximetry (r = 0.832, P < 0.0001) and carbon dioxide pressure (r = 0.644, P < 0.0001) measured by capillary arterialized blood gases and the combined PtcCO.sub.2/SpO.sub.2 monitor. Twenty-one of the 50 patients (42%) on long-term noninvasive respiratory support presented nocturnal hypercapnia, defined by a PtcCO.sub.2 value >50 mmHg, without nocturnal hypoxemia. Daytime capillary arterialized carbon dioxide levels were normal in 18 of these 21 patients. Conclusions Nocturnal hypercapnia may occur in children receiving nocturnal noninvasive respiratory support at home. Nocturnal pulse oximetry and daytime arterial blood gases are not sufficiently accurate to diagnose nocturnal hypercapnia, underlying the importance of a systematic carbon dioxide monitoring in children receiving noninvasive respiratory support. Author Affiliation: (1) Pediatric Pulmonary Department, Exequiel Gonzalez Cortes Hospital, Santiago, Chili (2) Unit for Pulmonary Diseases, Division of Pediatrics, University Medical Center, Ljubljana, Slovenia (3) Pediatric Pulmonary Department, AP-HP, Hopital Armand Trousseau, Research Unit INSERM UMR-S 893 Equipe 12, Universite Pierre et Marie Curie-Paris6, 28 avenue du Docteur Arnold Netter, 75012, Paris, France (4) INSERM UMR S-893 Equipe 12, Universite Pierre et Marie Curie-Paris6, Paris, France Article History: Registration Date: 13/01/2009 Received Date: 08/09/2008 Accepted Date: 06/01/2009 Online Date: 27/01/2009

We compared the integrated cardiovascular and autonomic responses to hypercapnia and hypoxia to test the hypothesis that these stimuli differentially affect muscle sympathetic nerve activity (MSNA) discharge patterns and cardiovagal and sympathetic baroreflex function in a manner related to ventilatory chemoreflex sensitivity. Six males and six females underwent 5 rain of hypoxia (end-tidal [Po.sub.2] = 45 Tort) and 5 min of hypercapnia (end-tidal [Pco.sub.2] = +8 Tort from baseline), causing similar ventilatory responses. A downward right shift in cardiovagal set point was observed during both conditions, which was strongly related to the change in inspiratory time (Ti) from baseline to hypercapnia ([r.sup.2] = 0.67, P = 0.007) and hypoxia ([r.sup.2] = 0.79, P < 0.001). Cardiovagal baroreflex gain was decreased during hypoxia (20.1 [+ or -] 6.9 vs. 8.9 [+ or -] 5.1 ms/mmHg, P < 0.001) but not hypercapnia (26.7 [+ or -] 12.7 vs. 23.0 [+ or -] 9.1 ms/mmHg). Both hypoxia and hypercapnia increased MSNA burst amplitude, whereas hypoxia, but not hypercapnia, also increased in MSNA burst frequency (21 [+ or -] 9 vs. 28 -4- 7 bursts/rain, P = 0.03) and total MSNA (4.56 [+ or -] 3.07 vs. 7.37 [+ or -] 3.26 mV/min, P = 0.002). However, neither hypereapnia nor hypoxia affected sympathetic burst probability or baroreflex gain. Hypoxia also caused a greater reduction in total peripheral resistance (P = 0.04), a greater increase in heart rate (P = 0.002), and a trend for a greater cardiac output response (P = 0.06) compared with hypercapnia. Nonetheless, central venous pressure remained unchanged during either condition. These results suggest that hypercapnia and hypoxia exert differential effects on cardiovagal, but not sympathetic, baroreflex gain and set point in a manner not related to ventilatory chemoreflex sensitivity. Furthermore, the data suggest that the individual's respiratory pattern to hypoxia or hypercapnia, as reflected in the inspiratory time, was a strong determinant of cardiovagal baroreflex set-point rather than the total ventilatory chemoreflex gain per se. respiration; autonomic nervous system; sympathetic nerve activity; baroreflex

Byline: Raffaele Scala (1), Sandra Bartolucci (2), Mario Naldi (1), Marcello Rossi (3), Mark W. Elliott (4) Keywords: Co-morbidities; Chronic obstructive pulmonary disease; Acute hypercapnic respiratory failure; Non-invasive positive pressure ventilation; Charlson index Abstract: Objective To assess the prevalence and the impact of chronic and/or acute non-respiratory co-morbidity on short and longer-term outcome of non-invasive positive pressure ventilation (NIPPV) in acute decompensations of chronic obstructive pulmonary disease (COPD) with acute hypercapnic respiratory failure (AHRF). Design and setting An observational study in a three-bed respiratory monitoring unit in a respiratory ward of a non-university hospital. Patients We grouped 120 consecutive COPD patients requiring NIPPV for AHRF (pH 7.28+-0.05, PaO.sub.2/FIO.sub.2 ratio 192+-63, PaCO.sub.2 78.3+-12.3 mmHg) according to whether NIPPV succeeded (n=98) or failed (n=22) in avoiding the need for endotracheal intubation and whether alive (n=77) or dead (n=42) at 6 months. Measurements and results The prevalence of chronic and acute co-morbidity was, respectively, 20% and 41.7% most of the cases were cardiovascular. In-hospital NIPPV failure was greater in patients with than in those without chronic (33.3% vs. 14.6%) or acute co-morbidity (32% vs. 8.6%). Six-month mortality was worse in patients with than in those without chronic (54.2% vs. 30.5%) or more than one acute co-morbidity (66.7% vs. 30.8%). Multiple regression analysis predicted in-hospital NIPPV failure by acute co-morbidity and forced expiratory volume in 1 s, while death at 6 months was predicted by having more than one acute co-morbidity, non-cardiovascular chronic co-morbidity and Activities of Daily Living score. Conclusions Chronic and acute co-morbidities are common in COPD patients with AHRF needing NIPPV and their presence influences short and longer-term outcome. Author Affiliation: (1) U.O. Pneumologia, USL8, Ospedale S. Donato, Via Nenni 20, 52100, Arezzo, Italy (2) U.O. Sistema Informativo, Via Fonte Veneziana 16, 52100, Arezzo, Italy (3) U.O. Fisiopatologia e Riabilitazione Respiratoria, Azienda Ospedaliera Senese, Siena, Italy (4) Department of Respiratory Medicine, St. James's University Hospital, Beckett Street, Leeds, LS9 7TF, UK Article History: Registration Date: 11/06/2004 Received Date: 13/02/2004 Accepted Date: 01/06/2004 Online Date: 17/07/2004

Byline: S. Lethvall (1), S. Sondergaard (1), S. Karason (1), S. Lundin (1), O. Stenqvist (1) Keywords: Dead-space Tracheal pressure Carbon dioxide Hypercapnia Acute respiratory distress syndrome Double lumen tube Abstract: Abstract Objective. To evaluate the effects on CO.sub.2 washout of the coaxial double lumen tube (DLT) as compared to a standard endotracheal tube (ETT) and tracheal gas insufflation (TGI). Precision of tracheal pressure monitoring through the DLT and safety issues, including intrinsic PEEP (PEEPi) formation during DLT ventilation, were also evaluated. Design. Lung model study. Setting. University research laboratory. Measurements and results. CO.sub.2 washout was analysed in a lung model by measuring single alveolar CO.sub.2 concentration during DLT ventilation as compared to standard ETT ventilation, at different minute ventilation (6--14 l/min) and different CO.sub.2-output levels (180 ml/min, 240 ml/min, and 300 ml/min). At a CO.sub.2 output level of 240 ml/min the CO.sub.2 washout was also compared to tidal volume-adjusted continuous TGI and expiratory synchronised TGI. Precision of tracheal pressure monitoring and PEEPi formation during DLT ventilation was evaluated by comparing pressure in each limb above the tube to reference tracheal pressure, varying I:E ratios (1:2, 1:1, and 2:1), tidal volumes (300--700 ml), breathing frequencies (15--25), and compliance (20--50 ml/cm[H.sub.2]O). DLT ventilation had the same efficacy in removing CO.sub.2 as continuous and expiratory synchronised TGI, reducing single alveolar CO.sub.2 concentration by 9--21% compared to normal ventilation. Tracheal pressure could be measured through the DLT with high precision. There was only marginal formation of PEEPi at tidal volumes a$?600 ml, I:E ratio a$?1:1, and compliance a$?35 ml/cm[H.sub.2]O. Conclusions. The double lumen tube is as effective as tracheal gas insufflation in reducing CO.sub.2 tension. Tracheal pressure and formation of PEEPi can be monitored with high precision without interrupting ventilation. Author Affiliation: (1) Department of Anaesthesia and Intensive Care, Sahlgrenska University Hospital, 413 45 Goteborg, Sweden Article History: Received Date: 13/06/2001 Accepted Date: 14/04/2002 Article note: Electronic Publication

Byline: P. Sitbon (1), J. Teboul (2), J. Duranteau (1), N. Anguel (2), C. Richard (2), K. Samii (1) Keywords: Gastric mucosa Hypercapnia Acute respiratory distress syndrome (ARDS) Laser-Doppler flowmetry Abstract: Objective: This study was conducted with the aim of testing the effects of a reduction in tidal volume (V.sub.T) on gastric mucosal perfusion using laser-Doppler flowmetry in patients with acute respiratory distress syndrome (ARDS). Design: It was designed as a prospective study. Patients: Seventeen patients with ARDS were enrolled in the study. All patients were mechanically ventilated in volume-controlled mode. Before the start of the protocol, V.sub.T was set at 9 ml/kg body weight. Intervention: V.sub.T was reduced to 6 ml/kg body weight. Measurements and results: Measurements of systemic hemodynamic parameters and gastric mucosal blood flow (GMBF) were obtained before and after reduction of V.sub.T. Cardiac index, heaart rate and pulmonary arterial pressure increased significantly after V.sub.T reduction. The increase in cardiac output was observed in all patients. However, despite a mean 25% increase in cardiac output after V.sub.T reduction, no significant increase in mean GMBF was observed, and individual GMBF responses were heterogeneous. Conclusion: V.sub.T reduction in patients with ARDS, despite resulting in an increase in cardiac output, did not change gastric mucosal perfusion. The heterogeneity in the individual response of GMBF to V.sub.T reduction could be due to opposite direct (i.e., local vasodilatory effect) and indirect (i.e., global sympathetic stimulation) effects of hypercapnia on gut vessels. Author Affiliation: (1) Service d'Anesthesie-Reanimation, Hopital de Bicetre, Assistance Publique des Hopitaux de Paris, 78 rue du General Leclerc, 94275 Le Kremlin-Bicetre Cedex, France (2) Service de Reanimation Medicale, Hopital de Bicetre, Assistance Publique des Hopitaux de Paris, 78 rue du General Leclerc, 94275 Le Kremlin-Bicetre Cedex, France Article History: Received Date: 31/08/1999 Article note: Final revision received: 3 November 2000 Electronic Publication