Spleen Volume and Contraction During Apnea in Mt. Everest Climbers and Everest Base Camp Trekkers.

The human spleen can contract and transiently boost the blood with stored erythrocytes. We measured spleen volume and contraction during apneas in two groups, each containing 12 Caucasian participants (each 3 women): one group planning to summit Mt. Everest (8848 m; "Climbers") and another trekking to Everest Base Camp (5300 m; "Trekkers"). Tests were done in Kathmandu (1370 m) 1-3 days after arrival, before the Climb/Trek. Age, height, weight, vital capacity, resting heart rate, and arterial oxygen saturation were similar between groups (not significant). After 15 minutes of sitting rest, all participants performed a 1-minute apnea and, after 2 minutes of rest, 1 maximal duration apnea was performed. Six of the climbers did a third apnea and hemoglobin concentration (Hb) was measured. Three axial spleen diameters were measured by ultrasonic imaging before and after the apneas for spleen volume calculation. Mean (standard deviation) baseline spleen volume was larger in Climbers [367 (181) mL] than in Trekkers [228 (70) mL; p = 0.022]. Spleen contraction occurred during apneas in both groups, with about twice the magnitude in Climbers. Three apneas in six of the Climbers resulted in a spleen volume reduction from 348 (145) to 202 (91) mL (p = 0.005) and an Hb elevation from 147.9 (13.1) to 153.3 (11.3) g/L (p = 0.024). Maximal apneic duration was longer in Climbers [88 (23) seconds vs. 67 (18) seconds in Trekkers; p = 0.023]. We concluded that a large spleen characterizes Climbers, suggesting that spleen function may be important for high-altitude climbing performance.

Early therapeutic effects of adaptive servo-ventilation on cardiac sympathetic nervous function in patients with heart failure evaluated using a combination of 11C-HED PET and 123I-MIBG SPECT.

RATIONALE: Adaptive servo-ventilation (ASV), a novel respiratory support therapy for sleep disorders, may improve cardiac function in heart failure (HF). However, the reasons that ASV improves cardiac function have not been fully studied especially in sympathetic nervous function (SNF). The purpose of the present study was to investigate the effects of ASV therapy on cardiac SNF in patients with HF. METHODS: We evaluated ASV therapeutic effects before and 6 months after ASV therapy in 9 HF patients [57.3 ± 17.3 years old, left ventricular ejection fraction (LVEF) 36.1 ± 16.7%]. We performed echocardiography, polysomnography, biomarkers, 11C-hydroxyephedrine (HED) PET as a presynaptic function marker and planar 123I-metaiodobenzylguanidine (MIBG) to evaluate washout rate. RESULTS: ASV therapy reduced apnea-hypopnea index (AHI) and improved plasma brain natriuretic peptide (BNP) concentration. In 123I-MIBG imaging, the early heart/mediastinum (H/M) ratio increased after ASV therapy (2.19 ± 0.58 to 2.40 ± 0.67; P = 0.045). Washout rate did not change (23.8 ± 7.3% to 23.8 ± 8.8%; P = 0.122). Global 11C-HED retention index (RI) improved from 0.068 ± 0.033/s to 0.075 ± 0.034/s (P = 0.029). CONCLUSIONS: ASV reduced AHI and improved BNP. ASV might initially improve presynaptic cardiac sympathetic nervous function in HF patients after 6 months of treatment.

Poincaré plot analysis of cerebral blood flow signals: Feature extraction and classification methods for apnea detection.

OBJECTIVE: Rheoencephalography is a simple and inexpensive technique for cerebral blood flow assessment, however, it is not used in clinical practice since its correlation to clinical conditions has not yet been extensively proved. The present study investigates the ability of Poincaré Plot descriptors from rheoencephalography signals to detect apneas in volunteers. METHODS: A group of 16 subjects participated in the study. Rheoencephalography data from baseline and apnea periods were recorded and Poincaré Plot descriptors were extracted from the reconstructed attractors with different time lags (τ). Among the set of extracted features, those presenting significant differences between baseline and apnea recordings were used as inputs to four different classifiers to optimize the apnea detection. RESULTS: Three features showed significant differences between apnea and baseline signals: the Poincaré Plot ratio (SDratio), its correlation (R) and the Complex Correlation Measure (CCM). Those differences were optimized for time lags smaller than those recommended in previous works for other biomedical signals, all of them being lower than the threshold established by the position of the inflection point in the CCM curves. The classifier showing the best performance was the classification tree, with 81% accuracy and an area under the curve of the receiver operating characteristic of 0.927. This performance was obtained using a single input parameter, either SDratio or R. CONCLUSIONS: Poincaré Plot features extracted from the attractors of rheoencephalographic signals were able to track cerebral blood flow changes provoked by breath holding. Even though further validation with independent datasets is needed, those results suggest that nonlinear analysis of rheoencephalography might be a useful approach to assess the correlation of cerebral impedance with clinical changes.

A Case Series of Parechovirus Encephalopathy: Apnea and Autonomic Dysregulation in Critically Ill Infants.

This article aims to describe a rare cause of severe encephalitis in 2 cases of infants with signs of intracranial hypertension and severe autonomic dysregulation. The authors conclude that human parechoviruses are becoming a more recognized cause of encephalitis because of the increasing use of rapid detection methods. With early recognition of this clinical entity, improved care can be administered.

Cardiovascular magnetic resonance assessment of acute cardiovascular effects of voluntary apnoea in elite divers.

BACKGROUND: Prolonged breath holding results in hypoxemia and hypercapnia. Compensatory mechanisms help maintain adequate oxygen supply to hypoxia sensitive organs, but burden the cardiovascular system. The aim was to investigate human compensatory mechanisms and their effects on the cardiovascular system with regard to cardiac function and morphology, blood flow redistribution, serum biomarkers of the adrenergic system and myocardial injury markers following prolonged apnoea. METHODS: Seventeen elite apnoea divers performed maximal breath-hold during cardiovascular magnetic resonance imaging (CMR). Two breath-hold sessions were performed to assess (1) cardiac function, myocardial tissue properties and (2) blood flow. In between CMR sessions, a head MRI was performed for the assessment of signs of silent brain ischemia. Urine and blood samples were analysed prior to and up to 4 h after the first breath-hold. RESULTS: Mean breath-hold time was 297 ± 52 s. Left ventricular (LV) end-systolic, end-diastolic, and stroke volume increased significantly (p < 0.05). Peripheral oxygen saturation, LV ejection fraction, LV fractional shortening, and heart rate decreased significantly (p < 0.05). Blood distribution was diverted to cerebral regions with no significant changes in the descending aorta. Catecholamine levels, high-sensitivity cardiac troponin, and NT-pro-BNP levels increased significantly, but did not reach pathological levels. CONCLUSION: Compensatory effects of prolonged apnoea substantially burden the cardiovascular system. CMR tissue characterisation did not reveal acute myocardial injury, indicating that the resulting cardiovascular stress does not exceed compensatory physiological limits in healthy subjects. However, these compensatory mechanisms could overly tax those limits in subjects with pre-existing cardiac disease. For divers interested in competetive apnoea diving, a comprehensive medical exam with a special focus on the cardiovascular system may be warranted. TRIAL REGISTRATION: This prospective single-centre study was approved by the institutional ethics committee review board. It was retrospectively registered under ClinicalTrials.gov (Trial registration: NCT02280226 . Registered 29 October 2014).

Identifying sleep apnoea and hypopnoea episodes from respiratory polygraphy signals / Identificación automática de episodios de SAHS utilizando seriales de poligrafía respiratoria

Abstract Objective: To design a diagnostic support system for sleep apnoea and hypopnoea syndrome (SAHS) using moving average based on knowledge, able to identify SAHS episodes from a respiratory polygraphy (RP) database. Methods: An analysis was made of data obtained from a public database, that included the RP signals, nasobucal airflow, thoracoabdominal movement, and pulse oximetry of 23 patients between 28 and 68 years with suspected SAHS, and with a body mass index (BMI) from 25.1 to 42.5. Results: The identification and classification of episodes of apnoea and hypopnoea was obtained. Conclusions: The algorithm designed identified episodes of SAHS using polygraphy signals, which by implementating in a graphical interface allows visualisation of onset, duration, type, oxygen saturation, and pulse oximetry of each episode, and can be used as a support tool for the diagnosis of sleep disorders.

Resumen Objetivo: Diseñar un sistema de apoyo diagnóstico para el síndrome de apneas-hipopneas del sueño (SAHS) utilizando conocimientos basados en media móvil, capaz de identificar episodios de SAHS a partir de una base de datos de poligrafía respiratoria (PR). Métodos: Se analizaron las señales de poligrafía respiratoria (flujo aéreo nasobucal, movimiento toracoabdominal y pulsioximetría) de 23 pacientes con sospecha de SAHS (edad, 28-68 años; índice de masa corporal, 25,1-42,5), obtenidas de una base de datos pública. Resultados : Se identificaron y se clasificaron episodios de apnea y hipopnea. Conclusiones: Se detectaron los episodios de SAHS utilizando señales de poligrafía respiratoria cuya implementación en una interfaz gráfica permite la visualización del inicio, la duración, el tipo, la saturación de oxígeno y la pulsioximetría de cada episodio, y se puede emplear como herramienta de apoyo al diagnóstico del trastorno del sueño.

Reduction of Respiratory Motion During PET/CT by Pulsatile-Flow Ventilation: A First Clinical Evaluation.

UNLABELLED: Respiratory motion negatively affects PET/CT image quality and quantitation. A novel Pulsatile-Flow Ventilation (PFV) system reducing respiratory motion was applied in spontaneously breathing patients to induce sustained apnea during PET/CT. METHODS: Four patients (aged 65 ± 14 y) underwent PET/CT for pulmonary nodule staging (mean, 11 ± 7 mm; range, 5-18 mm) at 63 ± 3 min after (18)F-FDG injection and then at 47 ± 7 min afterward, during PFV-induced apnea (with imaging lasting ≥8.5 min). Anterior-posterior thoracic amplitude, SUVmax, and SUVpeak (SUVmean in a 1-cm-diameter sphere) were compared. RESULTS: PFV PET/CT reduced thoracic amplitude (80%), increased mean lesion SUVmax (29%) and SUVpeak (11%), decreased lung background SUVpeak (25%), improved lesion detectability, and increased SUVpeak lesion-to-background ratio (54%). On linear regressions, SUVmax and SUVpeak significantly improved (by 35% and 23%, respectively; P ≤ 0.02). CONCLUSION: PFV-induced apnea reduces thoracic organ motion and increases lesion SUV, detectability, and delineation, thus potentially affecting patient management by improving diagnosis, prognostication, monitoring, and external-radiation therapy planning.

Online apnea-bradycardia detection based on hidden semi-Markov models.

In this paper, we propose a new online apnea-bradycardia detection scheme that takes into account not only the instantaneous values of time series, but also their temporal evolution. The detector is based on a set of hidden semi-Markov models, representing the temporal evolution of beat-to-beat interval (RR interval) time series. A preprocessing step, including quantization and delayed version of the observation vector, is also proposed to maximize detection performance. This approach is quantitatively evaluated through simulated and real signals, the latter being acquired in neonatal intensive care units (NICU). Compared to two conventional detectors used in NICU, our best detector shows an improvement on average of around 15 % in sensitivity and 7 % in specificity. Furthermore, a reduced detection delay of approximately 2 s is also observed with respect to conventional detectors.

Simple, almost anywhere, with almost anyone: remote low-cost telementored resuscitative lung ultrasound.

BACKGROUND: Apnea (APN) and pneumothorax (PTX) are common immediately life-threatening conditions. Ultrasound is a portable tool that captures anatomy and physiology as digital information allowing it to be readily transferred by electronic means. Both APN and PTX are simply ruled out by visualizing respiratory motion at the visceral-parietal pleural interface known as lung sliding (LS), corroborated by either the M-mode or color-power Doppler depiction of LS. We thus assessed how economically and practically this information could be obtained remotely over a cellular network. METHODS: Ultrasound images were obtained on handheld ultrasound machines streamed to a standard free internet service (Skype) using an iPhone. Remote expert sonographers directed remote providers (with variable to no ultrasound experience) to obtain images by viewing the transmitted ultrasound signal and by viewing the remote examiner over a head-mounted webcam. Examinations were conducted between a series of remote sites and a base station. Remote sites included two remote on-mountain sites, a small airplane in flight, and a Calgary household, with base sites located in Pisa, Rome, Philadelphia, and Calgary. RESULTS: In all lung fields (20/20) on all occasions, LS could easily and quickly be seen. LS was easily corroborated and documented through capture of color-power Doppler and M-mode images. Other ultrasound applications such as the Focused Assessment with Sonography for Trauma examination, vascular anatomy, and a fetal wellness assessment were also demonstrated. CONCLUSION: The emergent exclusion of APN-PTX can be immediately accomplished by a remote expert economically linked to almost any responder over cellular networks. Further work should explore the range of other physiologic functions and anatomy that could be so remotely assessed.

Computed tomography assessment of lung structure in patients undergoing cardiac surgery with cardiopulmonary bypass.

Hypoxemia is a frequent complication after coronary artery bypass graft (CABG) with cardiopulmonary bypass (CPB), usually attributed to atelectasis. Using computed tomography (CT), we investigated postoperative pulmonary alterations and their impact on blood oxygenation. Eighteen non-hypoxemic patients (15 men and 3 women) with normal cardiac function scheduled for CABG under CPB were studied. Hemodynamic measurements and blood samples were obtained before surgery, after intubation, after CPB, at admission to the intensive care unit, and 12, 24, and 48 h after surgery. Pre- and postoperative volumetric thoracic CT scans were acquired under apnea conditions after a spontaneous expiration. Data were analyzed by the paired Student t-test and one-way repeated measures analysis of variance. Mean age was 63 ± 9 years. The PaO2/FiO2 ratio was significantly reduced after anesthesia induction, reaching its nadir after CPB and partially improving 12 h after surgery. Compared to preoperative CT, there was a 31% postoperative reduction in pulmonary gas volume (P < 0.001) while tissue volume increased by 19% (P < 0.001). Non-aerated lung increased by 253 ± 97 g (P < 0.001), from 3 to 27%, after surgery and poorly aerated lung by 72 ± 68 g (P < 0.001), from 24 to 27%, while normally aerated lung was reduced by 147 ± 119 g (P < 0.001), from 72 to 46%. No correlations (Pearson) were observed between PaO2/FiO2 ratio or shunt fraction at 24 h postoperatively and postoperative lung alterations. The data show that lung structure is profoundly modified after CABG with CPB. Taken together, multiple changes occurring in the lungs contribute to postoperative hypoxemia rather than atelectasis alone.

Might asphyxia cause respiratory inhibition after crying in mature infants?

BACKGROUND: To clarify the timing of injury in utero causing respiratory inhibition after crying (RIAC), the relationship between asphyxia and RIAC was investigated in infants whose gestational age was ≥ 36 weeks. METHODS: RIAC and cranial ultrasound abnormalities were examined for retrospectively in infants treated in the neonatal intensive care unit from April 2004 through March 2009. All included infants were gestational age ≥ 36 weeks and had an Apgar score <4 points at 1 min. The relationship between RIAC and perinatal factors was also examined. RESULTS: Twenty-six infants were included. Three infants had RIAC, seven infants had poor prognosis, and nine infants had ultrasound abnormalities in the ganglionic eminence (GE). There was a significant relationship between RIAC and ultrasound abnormalities in the GE (P= 0.032). Poor prognosis was significantly associated with low Apgar score at 5 min (P ≤ 0.001), disseminated intravascular coagulation (P= 0.047), hypoxic ischemic encephalopathy (P= 0.028), and brain hypothermia therapy (P= 0.028). There was no significant relationship between RIAC and poor prognosis. All infants had ultrasound abnormalities in the GE on the day of birth. CONCLUSION: Damage occurring in utero prior to 36 weeks gestation might cause increased echogenicity or cyst formation in the GE, potentially disturbing maturation of the respiratory center with the development of RIAC.

Chest sonography detects lung water accumulation in healthy elite apnea divers.

BACKGROUND: Ultrasound lung comets (ULCs) detected by chest sonography are a simple, noninvasive, semiquantitative sign of increased extravascular lung water. Pulmonary edema may occur in elite apnea divers, possibly triggered by centralization of blood flow from the periphery to pulmonary vessels. We assessed the prevalence of ULCs in top-level breath-hold divers after immersion. METHODS: We evaluated 31 consecutive healthy, top-level, breath-hold divers (10 female, 21 male; age 31 +/- 5 years) participating in a yearly international apnea diving contest in Sharm-el-Sheik, Egypt, November 1 to 3, 2007. We performed chest and cardiac sonography with a transthoracic probe (2.5-3.5 MHz, Esaote Mylab) in all divers, both on the day before and 10 +/- 9 minutes after immersion. In a subset of 4 divers, chest scan was also repeated at 24 hours after immersion. ULCs were evaluated on the anterior and posterior chest at 61 predefined scanning sites. An independent sonographer, blind to both patient identity and status (pre- or post-diving), scored ULCs. RESULTS: Diving depth ranged from 31 to 112 m. Duration of immersion ranged from 120 to 225 seconds. The ULC score was 0.5 +/- 1.5 at baseline and 13 +/- 21 after diving (P = .012). At individual patient analysis, ULCs appeared in 14 athletes (45%) after diving. Of these 14 athletes, 4 were asymptomatic, 6 showed aspecific symptoms with transient loss of motor control ("Samba"), 2 had palpitations with frequent premature ventricular contractions, and 2 had persistent cough with hemoptysis and pulmonary crackles. In a subset of 4 athletes with post-diving ULCs in whom late follow-up study also was available, chest sonography findings fully normalized at 24 hours of follow-up. CONCLUSION: In top-level breath-hold divers, chest sonography frequently reveals an increased number of ULCs after immersion, indicating a relatively high prevalence of (often subclinical) reversible extravascular lung water accumulation.

Nasal continuous positive airway pressure (n-CPAP) does not change cardiac output in preterm infants.

Our objective was to study how invasive mechanical ventilation impairs cardiac output (CO) in children and adults. Although the application of continuous positive airway pressure (CPAP) is widely practiced in neonatal intensive care, its hemodynamic consequences have not yet been investigated. A prospective study to assess the hemodynamic effects was conducted in 21 preterm infants < 1500 g using two-dimensional M-mode and pulsed Doppler echocardiography during and 1 hour after discontinuation of nasal CPAP (n-CPAP). Gestational age was 28.0 +/- 1.9 weeks (mean +/- standard deviation); birthweight, 1000 +/- 238 g; age at study entry, 200 +/- 155 hours; total maintenance fluid, 154 +/- 42 mL/kg/day; and n-CPAP level, 4.4 +/- 0.9 cm H(2)O. None of the infants received inotropic support, and n-CPAP did not cause any significant difference in the parameters measured: stroke volume, 3.1 +/- 1.0 mL (with n-CPAP) versus 3.1 +/- 1.0 mL (without n-CPAP); cardiac output, 487 +/- 156 mL/minute versus 500 +/- 176 mL/minute; left ventricular diastolic diameter, 1.22 +/- 0.15 cm versus 1.24 +/- 0.14 cm; fractional shortening, 0.30 +/- 0.05% versus 0.29 +/- 0.04%; and aortic velocity-time integral, 8.64 +/- 1.80 cm versus 8.70 +/- 1.65 cm. The n-CPAP level did not influence CO; n-CPAP (up to 7 cm H (2)O) has no echocardiographically detectable hemodynamic effect in preterm infants. Our data imply there is no need to withhold n-CPAP support to prevent circulatory compromise in these infants.

End-expiratory and tidal volumes measured in conscious mice using single projection x-ray images.

The evaluation of airway resistance (R(aw)) in conscious mice requires both end-expiratory (V(e)) and tidal volumes (V(t)) (Lai-Fook SJ and Lai YL. J Appl Physiol 98: 2204-2218, 2005). In anesthetized BALB/c mice we measured lung area (A(L)) from ventral-to-dorsal x-ray images taken at FRC (V(e)) and after air inflation with 0.25 and 0.50 ml (DeltaV(L)). Total lung volume (V(L)) described by equation: V(L) = DeltaV(L) + V(FRC) = KA(L)(1.5) assumed uniform (isotropic) inflation. Total V(FRC) averaged 0.55 ml, consisting of 0.10 ml tissue, 0.21 ml blood and 0.24 ml air. K averaged 1.84. In conscious mice in a sealed box, we measured the peak-to-peak box pressure excursions (DeltaP(b)) and x-rays during several cycles. K was used to convert measured A(L)(1.5) to V(L) values. We calculated V(e) and V(t) from the plot of V(L) vs. cos(alpha - phi). Phase angle alpha was the minimum point of the P(b) cycle to the x-ray exposure. Phase difference between the P(b) and V(L) cycles (phi) was measured from DeltaP(b) values using both room- and body-temperature humidified box air. A similar analysis was used after aerosol exposures to bronchoconstrictor methacholine (Mch), except that phi depended also on increased R(aw). In conscious mice, V(e) (0.24 ml) doubled after Mch (50-125 mg/ml) aerosol exposure with constant V(t), frequency (f), DeltaP(b), and R(aw). In anesthetized mice, in addition to an increased V(e), repeated 100 mg/ml Mch exposures increased both DeltaP(b) and R(aw) and decreased f to apnea in 10 min. Thus conscious mice adapted to Mch by limiting R(aw), while anesthesia resulted in airway closure followed by diaphragm fatigue and failure.

Spleen and cardiovascular function during short apneas in divers.

We investigated the spleen volume changes as related to the cardiovascular responses during short-duration apneas at rest. We used dynamic ultrasound splenic imaging and noninvasive photoplethysmographic cardiovascular measurements before, during, and after 15-20 s apneas in seven trained divers. The role of baroreflex was studied by intravenous bolus of vasodilating drug trinitrosan during tidal breathing. The role of lung volume was studied by comparing the apneas at near-maximal lung volume with apneas after inhaling tidal volume, with and without cold forehead stimulation. In apneas at near maximal lung volume, a 20% reduction in splenic volume (P = 0.03) was observed as early as 3 s after the onset of breath holding. Around that time the heart rate increased, the mean arterial pressure abruptly decreased from 89.6 to 66.7 mmHg (P = 0.02), and cardiac output decreased, on account of reduction in stroke volume. Intravenous application of trinitrosan resulted in approximately 6-mmHg decrement in mean arterial pressure, while the splenic volume decreased for approximately 13%. In apneas at low lung volume, the early splenic contraction was also observed, 10% without and 12% with cold forehead stimulation, although the mean arterial pressure did not change or even increased, respectively. In conclusion, the spleen contraction is present at the beginning of apnea, accentuated by cold forehead stimulation. At large, but not small, lung volume, this initial contraction is probably facilitated by downloaded baroreflex in conditions of decreased blood pressure and cardiac output.

Total haemoglobin mass and spleen contraction: a study on competitive apnea divers, non-diving athletes and untrained control subjects.

In diving mammals splenic contraction increases circulating red cell volume, whereas in humans increased haemoglobin concentrations have been reported. It is unknown, however, whether repetitive apnea diving also comprises an adaptive increase in total red cell volume as reported in endurance athletes. The first aim of the study therefore was to investigate the effect of repeated apnea dives on splenic size and putative red cell release in trained apnea divers (n = 10) and control subjects (SCUBA divers performing apneas without long-term apnea training, n = 7). Long-term effects of repetitive apnea diving may elevate the oxygen transport capacity by an adaptive increase in total haemoglobin mass as reported in endurance athletes. The second goal, therefore, was to compare the trained apnea divers' and the control divers' total haemoglobin mass (tHb-mass) with that of endurance-trained (n = 9) and untrained (n = 10) non-divers. Before and immediately after a series of five dives to a depth of 4 m in a heated pool, spleen volume was assessed with ultrasound tomography. tHb-mass and plasma volume were measured using the CO-rebreathing method. In the trained apnea divers, repeated apnea dives resulted in a 25% reduction of spleen size (P < 0.001), whereas no significant effect was observed in the control subjects. While tHb-mass did not differ between trained apnea divers, untrained SCUBA divers performing apneas and untrained non-divers, it was 30% lower than in endurance-trained non-divers. We conclude that prolonged apnea training causes marked apnea-induced splenic contraction. In contrast to athletes in endurance sports, the trained apnea divers did not present with increased total haemoglobin mass and, hence, no increase in blood oxygen stores.

Respiratory inhibition after crying in infants.

BACKGROUND: Among full-term neonates, the authors discovered infants who showed respiratory inhibition after crying which involved a marked decrease in SpO2. The infants were found to present increased echogenicity or a cyst in a cranial region termed the ganglionic eminence, or to have a subependymal cyst. The authors prospectively examined the relationship between respiratory inhibition after crying and these changes to examine the prevention and treatment of the episode. METHODS: The authors conducted cranial ultrasonography to screen 381 full-term neonates who showed no abnormalities at birth and whose parents requested ultrasonographic screening of the head, followed by polygraphy of infants who showed increased echogenicity or a cyst in ganglionic eminence, or had a subependymal cyst. The authors similarly conducted polygraphy for 50 neonates without cranial ultrasound abnormalities; the former constituted the control group. Respiratory inhibition was defined to be central apnea immediately after crying with a decrease in SpO2 to <60%. RESULTS: Among 381 neonates examined, 104 showed cranial ultrasound abnormalities; 60 of the 104 neonates indicated respiratory inhibition after crying. Oxygenation failed to improve the episode in 17 neonates with severe respiratory inhibition. However, theophylline alleviated the episode, and SpO2 no longer decreased to <60%. Theophylline was discontinued successfully by 6 months after birth, while 50 neonates in the control group showed no respiratory inhibition after crying. CONCLUSION: Respiratory inhibition after crying which involved a marked decrease in SpO2 was observed in full-term neonates who showed no abnormalities after birth. These neonates could be screened by cranial ultrasonography.

Low-flow transtracheal rescue insufflation of oxygen after profound desaturation.

BACKGROUND: The objective of this study was to determine whether low-flow transtracheal insufflation of oxygen (TRIO) could rescue an animal from profound desaturation. This temporizing maneuver could be useful during cannot-intubate or -ventilate scenarios by resolving hypoxia without the morbidity associated with more invasive procedures. METHODS: Seven swine for a total of 12 runs were studied. Animals were pharmacologically anesthetized, paralyzed, and mechanically ventilated with room air. After disconnection from the ventilator and desaturation to an Spo2 < 50%, low-flow TRIO (2 L/min) was administered for 1 hour. RESULTS: All animals survived and Spo2 increased to greater than 90% in 23 seconds on average. Pao2 (mean, 183 mm Hg) remained elevated throughout the study. Hemodynamic stability was maintained for at least 15 minutes. CONCLUSION: Low-flow TRIO rescued animals from profound hypoxia and maintained oxygenation for at least 1 hour. Low-flow TRIO did not prevent hypercarbia with its subsequent sympathetic activation.

Speed of spleen volume changes evoked by serial apneas.

Diving mammals may enhance dive duration by injecting extra erythrocytes into the circulation by spleen contraction. This mechanism may also be important for apneic duration in humans. We studied the speed and magnitude of spleen volume changes evoked by serial apneas, and the associated changes in hematocrit (Hct) and hemoglobin (Hb) concentration, diving response and apneic duration. Three maximal apneas separated by 2 min rest elicited spleen contraction in all ten subjects, by a mean of 49 (27) ml (18%; P<0.001). During the same period, Hct and Hb rose by 2.2 and 2.4% respectively (P<0.01 and P<0.001), and apneic duration rose by 20 s (22% P<0.05). The mean heart rate reduction of the diving response was 15%, which remained the same throughout the apnea series. While the diving response was completely reversed between the apneas, spleen size was not recovered until 8-9 min after the final apnea corresponding with recovery of Hct and Hb. Thus, although the spleen contraction may be associated with the cardiovascular diving response, it is likely to be triggered by different mechanisms, and it may remain activated between dives spaced by short pauses. The two adjustments may provide a fast, quickly reversed, and a slow, but long-lasting, way of shifting to a diving mode in humans.