Efectos beneficiosos de la respiración manejada a voluntad sobre la frecuencia cardíaca y temperatura periférica / Beneficial effects of controlled breathing on cardiac frecuency and peripheral temperature

Este estudio trató de mostrar los efectos que tenía la respiración manejada a voluntad en forma de inspiraciones cortas y espiraciones largas. El estudio se realizó con 14 sujetos, empleando 8 sesiones de tratamiento. Los resultados mostraron diferencias significativas en el descenso de la frecuencia cardíaca y en el aumento de la temperatura periférica a la finalización del tratamiento, en relación con los valores previos al tratamiento (AU)

Efecto del diámetro interno del tubo endotraqueal sobre el consumo de oxígeno durante la respiración espontánea / Effect of the inner diameter of the endotracheal tube on oxygen consumption during spontaneous respiration

Objetivo. Valorar, en pacientes con respiración espontánea, el efecto de la reducción simulada del diámetro interno del tubo endotraqueal (TET) desde 8 a 7 mm sobre el consumo de oxígeno (V.O2) y la frecuencia respiratoria. Métodos. Durante la desconexión de la ventilación mecánica, en doce pacientes que mantenían una correcta respiración espontánea a través de un TET, medimos el V.O2 y la producción de CO2 (V.CO2) en dos ocasiones, una con un TET de 8 mm de diámetro interno ( ) y otra con un conector de un TET de 6 mm de , que simula la resistencia al flujo de aire de un TET de 7 mm de . Medimos el V.O2 y la V.CO2 con el método del circuito abierto mediante un espirómetro Wright y un analizador de gases IL-1312 (Izasa, España). Se ha utilizado la prueba de la "t" de Student para datos pareados. Se consideró significativo un valor de p < 0,05.Resultados. La reducción del del TET de 8 a 7 mm se acompañó de un incremento en el V.O2 de 8 (DE 13) ml/min (límites de -12 a 27 ml/min, 95 por ciento IC de -1 a 16 ml/min; p = 0,07) y en la V.CO2 de 9 (DE 8) ml/min (límites de -6 a 16 ml/min, 95 por ciento IC de 4 a 14 ml/min; p = 0,002). La frecuencia respiratoria disminuyó de 26 a 25 rpm (p = 0,07). Conclusión. Durante la desconexión de la ventilación mecánica, en pacientes con buena tolerancia a la respiración espontánea en "tubo en T", la reducción del diámetro interno del tubo endotraqueal de 8 a 7 mm no modifica el consumo de O2, ni la frecuencia respiratoria, de forma clínicamente relevante. (AU)

Venipuncture in the medical physiology laboratory.

Medical physiology laboratories, traditionally devoted to animal experimentation, face unprecedented difficulties linked to cost, staffing, instrumentation, and the use of animals. At the same time, laboratory experiences with living creatures play a unique role in medical education. In this article we describe the use of venipuncture and subsequent blood analysis, with medical students serving as both subjects and experimenters, in a sequence of first-year physiology laboratories. These experiments are safe, robust, inexpensive, and time efficient, and they teach the principles of cardiovascular, respiratory, renal, nutritional, and gastrointestinal physiology. In addition, they enhance medical education in several other important dimensions. First, they teach safe venous blood collection and handling, a training appropriate for students at this level. Second, by serving each week as subjects as well as experimenters, students experience aspects of both sides of the doctor-patient relationship. Third, the laboratories can be used to teach fundamentals of research design and analysis. Finally, because blood analysis is central to medicine, and because the student's own blood data are discussed, students are enthusiastic and cooperative, and the clinical relevance of the data is clear.

Students' misconceptions about perceived physiological responses.

Students' misconceptions about scientific phenomena can arise from at least two possible sources, the students' personal experience with those phenomena and things learned in the classroom. Misconceptions have been studied in a variety of science disciplines, but little attention has been given to the faulty models that students have for physiological processes. In this study 393 undergraduates in three different research universities were asked to predict the changes in heart rate and strength of cardiac contraction and breathing frequency and depth of breathing (physiological parameters that can be directly and personally perceived) under conditions that result in predicted that heart rate would increase but that the strength of contraction would decrease or stay unchanged. Approximately one-half of the students predicted that breathing frequency would increase but depth of breathing would decrease (also erroneous). Explanations for these erroneous predictions were elicited, and the reasons offered revealed significant misconceptions about cardiac and respiratory mechanics. The persistence of such misconceptions was demonstrated in a small group of first-year medical students. A general approach to detecting and remediating misconceptions is discussed.

Changing central nervous system control following intercostal nerve transfer.

OBJECT: The goal of this study was to find which central nervous system (CNS) pathways are involved in volitional control over reinnervated biceps or pectoral muscles. METHODS: Intercostal nerves (ICNs) were coapted to the musculocutaneous nerve (MCN) or the medial pectoral nerve (MPN) in 23 patients with root avulsions of the brachial plexus to restore biceps or pectoral muscle function. The facilitatory effects of respiration and voluntary contraction on cortical motor-evoked potentials of biceps or pectoral muscles were used to study CNS control over the reinnervated muscles. The time course of the facilitatory effect of respiration and voluntary contraction differed significantly. In the end stage of nerve regeneration, the facilitatory effect of voluntary contraction was significantly larger than that of respiration, indicating that the CNS control network over the muscle comes to resemble that of the recipient nerve (MCN or MPN) rather than that of the donor nerve (ICN). CONCLUSIONS: The strengthening of previously subthreshold synaptic connections in a CNS network connecting ICN to MCN or MPN neurons may underlie changing excitability.

Clinical reliability of single-lead VDD pacing from evaluation of P-wave sensing under dynamic conditions.

In a group of 20 patients implanted with a single-lead VDD pacing system, a wide interindividual variability was found in P-wave amplitude changes occurring under dynamic conditions, even though they were of minor clinical relevance because constant atrial tracking was maintained.

Activity of the delta-opioid receptor is partially reduced, whereas activity of the kappa-receptor is maintained in mice lacking the mu-receptor.

Previous pharmacological studies have indicated the possible existence of functional interactions between mu-, delta- and kappa-opioid receptors in the CNS. We have investigated this issue using a genetic approach. Here we describe in vitro and in vivo functional activity of delta- and kappa-opioid receptors in mice lacking the mu-opioid receptor (MOR). Measurements of agonist-induced [35S]GTPgammaS binding and adenylyl cyclase inhibition showed that functional coupling of delta- and kappa-receptors to G-proteins is preserved in the brain of mutant mice. In the mouse vas deferens bioassay, deltorphin II and cyclic[D-penicillamine2, D-penicillamine5] enkephalin exhibited similar potency to inhibit smooth muscle contraction in both wild-type and MOR -/- mice. delta-Analgesia induced by deltorphin II was slightly diminished in mutant mice, when the tail flick test was used. Deltorphin II strongly reduced the respiratory frequency in wild-type mice but not in MOR -/- mice. Analgesic and respiratory responses produced by the selective kappa-agonist U-50,488H were unchanged in MOR-deficient mice. In conclusion, the preservation of delta- and kappa-receptor signaling properties in mice lacking mu-receptors provides no evidence for opioid receptor cross-talk at the cellular level. Intact antinociceptive and respiratory responses to the kappa-agonist further suggest that the kappa-receptor mainly acts independently from the mu-receptor in vivo. Reduced delta-analgesia and the absence of delta-respiratory depression in MOR-deficient mice together indicate that functional interactions may take place between mu-receptors and central delta-receptors in specific neuronal pathways.

Recording from afferents in the intact recurrent laryngeal nerve during respiration and vocalization.

The goal of this study was to determine whether sensory fibers in an intact recurrent laryngeal nerve (RLN) are influenced by respiration or vocalization. Patterns of RLN afferent activity were examined during respiration and evoked vocalization by means of midbrain electrical stimulation in cats anesthetized with alpha-chloralose. Nerve bundles were dissected from an intact RLN, with motor function preserved. The bundles were cut and the laryngeal end was placed on floating bipolar electrodes. Fifteen right RLNs were examined. A total of 9 single and multiunit afferent fibers from 4 cats were isolated and examined during respiration. Four units, analyzed from 3 fibers, showed respiratory phase modulation. Eight units, analyzed from 4 fibers in 1 cat, were observed during vocalization and showed no vocalization phase modulation. The RLN afferents could contribute to reflex modulation of the respiratory cycle, but more extensive sampling would be necessary to preclude effects from vocalization.

Long-term within-subject variability of inspiratory neural drive response to hypoxia.

STUDY OBJECTIVE: We analyze the within-subject variation of mouth occlusion pressure (P0.1) response to progressive isocapnic hypoxic stimulation over long time periods in normal subjects. PATIENTS AND INTERVENTIONS: We studied 21 healthy subjects (14 male and 7 female; aged 40+/-12 yrs) (mean+/-SD). Lung volumes, basal P0.1, and P0.1 response to hypoxia were measured on two separate occasions 2 months apart, under similar ambient and clinical conditions. RESULTS: There was no significant change in clinical condition, FVC, FEV1, arterial oxygenation saturation, end-tidal and mixed venous PCO2 levels, or P0.1 between the two visits. The mean P0.1 responses to hypoxia in the two explorations were 0.032+/-0.022 and 0.034+/-0.022 kPa/%, respectively. There was a moderate intrasubject variability of P0.1 response to hypoxia, with a coefficient of reproducibility of 0.01 kPa/%. Power calculations to establish the optimal sample size required for hypoxic stimulation are presented. CONCLUSION: Long term within-subject variability of P0.1 response to hypoxia is moderate. This intrinsic variability needs to be emphasized when interpreting the effects of experimental interventions on hypoxic sensitivity.

Influence of mechanical stretch on thrombin regulation by fetal mixed lung cells.

Respiratory distress syndrome (RDS) is characterized by intrapulmonary fibrin deposition, which can adversely affect surfactant function, and stimulate fibroblast proliferation, which may contribute to the development of bronchopulmonary dysplasia (BPD). We speculated that the premature lung may have impaired regulation of thrombin, thus making preterm infants susceptible to fibrin formation within the lung. Therefore, we studied the effect of stretch, which simulates fetal breathing movements (FBMs), on the generation and inhibition of a key hemostatic enzyme-thrombin-by rat fetal mixed lung cells (FMLCs). Our results showed that stretch induced glycosaminoglycan production with increased antithrombin activity due to an increase in the concentration of active chondroitin sulfate. Stretch downregulated secretion of tissue factor procoagulant activity, which may lead to decreased thrombin generation on the surface of FMLCs. Overall, stretch enhanced the local control of thrombin by FMLCs. These results suggest that premature infants, who will have experienced less FBM, may have impaired thrombin regulation. Impaired thrombin regulation likely contributes to increased fibrin deposition and, potentially, the development of BPD.

Respiratory function among preterm infants whose mothers smoked during pregnancy.

We examined whether the adverse effects of prenatal exposure to tobacco on lung development are limited to the last weeks of gestation by comparing respiratory function in preterm infants whose mothers had and had not smoked during pregnancy. Maximal forced expiratory flow (Vmax FRC) and time to peak tidal expiratory flow as a proportion of total expiratory time (TPTEF:TE) were measured prior to discharge from hospital in 108 preterm infants (mean [SD] gestational age, 33.5 [1.8] wk), 40 of whose mothers had smoked during pregnancy. Infant urinary cotinine was less than 4 ng/ml in those born to nonsmokers, but it was as high as 458 ng/ml in exposed infants (p < 0.0001). TPTEF:TE was significantly lower in infants exposed to tobacco in utero (mean [SD], 0.369 [0.109]) when compared with those who were not (0.426 [0.135]) (p <= 0.02). Vmax FRC was also reduced in exposed infants (mean [SD], 85.2 [41.7] ml/s versus 103.8 [49.7] ml/s) (p = 0.07). After allowing for sex, ethnic group, body size, postnatal age, and socioeconomic status, TPTEF:TE remained significantly diminished in infants exposed prenatally to tobacco (p < 0.05). Thus, impaired respiratory function is evident in infants born on average 7 wk prior to the expected delivery date, suggesting that the adverse effects of prenatal exposure to tobacco are not limited to the last weeks of pregnancy.

Effects of changes in fresh fruit consumption on ventilatory function in healthy British adults.

Cross-sectional studies have shown frequent fresh fruit consumption to be associated with higher lung function in both children and adults. This relationship is investigated longitudinally in a national sample of 2,171 British adults age 18 to 73 initially examined in 1984, who were reexamined 7 yr later, and had no reported history of chronic respiratory disease throughout. Outcome was assessed by change in forced expiratory volume in one second (FEV1) between the two examinations, standardized for age, height, and sex and related to fresh fruit consumption estimated by food frequency questionnaires at both examinations. After adjustment for region, social class, and smoking, changes in fresh fruit consumption levels were positively associated with changes in FEV1 (p = 0.002), highlighted by a more marked fall in FEV1 (107 ml; 95% confidence interval, 36 to 178 ml) in subjects who reduced their fresh fruit consumption the greatest compared with those with no change. In contrast, average levels of fruit intake were not associated with change in FEV1 (p = 0.695). The implication is that the cross-sectional effects of fresh fruit consumption on ventilatory function appear to be reversible and not progressive, such that consistently low levels of fresh fruit intake do not appear to increase lung function decline.

Control of ventilation during lung volume changes and permissive hypercapnia in dogs.

We investigated the effect changes in end-expiratory lung volume (EEVL) had on the response to progressive hypercapnia (CO2-response curve) in eight open-chest, anesthetized dogs, in order to clarify the role that vagal lung mechanoreceptors have in altered respiratory drive during permissive hypercapnia. The dogs were ventilated using a positive-pressure ventilator driven by phrenic neural activity. Systemic arterial CO2 tension (PaCO2) was elevated by increasing the fraction of CO2 delivered to the ventilator. EEVL was altered from approximated functional residual capacity ("FRC") to 1.5 and 0.5 "FRC" by changing positive end-expiratory pressure. Although the tidal volume (VT)-PaCO2 and inspiratory time (TI)-PaCO2 relationships were not affected, decreasing EEVL from 1.5 "FRC" to "FRC" and then to 0.5 "FRC" caused a significant (p < 0.01) upward shift in the CO2-response curves for minute ventilation (V I) and frequency (f ), and a significant (p < 0.01) downward shift in the CO2- response curve for expiratory time (TE). We conclude that these shifts were explained by a decrease in the inhibitory activity of slowly adapting pulmonary stretch receptors (PSRs) as EEVL was lowered. In addition, increases in EEVL from 0.5 "FRC" to 1.5 "FRC" caused a significant (p < 0.05) increase in the apneic threshold, which we attribute to an inhibitory effect on central drive caused by increased PSR activity.

Language of dyspnea in assessment of patients with acute asthma treated with nebulized albuterol.

To investigate whether the language of dyspnea provides relevant clinical information in addition to that provided by ratings of overall dyspnea intensity when assessing subjective response to therapy, we conducted a prospective study in a cohort of 25 patients with acute asthma presenting to the emergency department of a tertiary care hospital. Patients received nebulized albuterol treatments every 20 min with a maximum of three doses. At presentation and after each treatment, patients completed spirometry, rated overall dyspnea intensity on a modified Borg scale, and selected phrases that described qualities of breathlessness from a 15-item questionnaire. Paired Student's t tests revealed significant improvements in FEV1 (from 1.39 +/- 0.66 L to 1.80 +/- 0.76 L, p < 0. 001) and reductions in dyspnea intensity (from 5.12 +/- 2.08 to 2.82 +/- 1.59, p < 0.001) after the first albuterol treatment. Dyspnea intensity continued to decrease significantly in response to the second treatment, modified Borg rating 2.26 +/- 1.52, although there was no positive bronchodilator response. The results from Cochran Q tests revealed that the frequency of the experience of "chest tightness" decreased significantly across the phases of treatment. However, the sensations of "work" or "breathing effort" persisted at the same time that the FEV1 revealed ongoing airways obstruction. We conclude that attention to the language of dyspnea would alert health care providers to residual air flow obstruction despite decreases in overall dyspnea intensity.

Prognostic indicators for blood and marrow transplant patients admitted to an intensive care unit.

Although hematopoietic stem cell transplantation (HSCT) can be curative in patients with certain malignancies, survival is poor if the recipient becomes critically ill. This prospective study examined the outcomes of 115 consecutive HSCT patients admitted to the medical intensive care unit (MICU) of a tertiary cancer center and identified variables associated with survival. The need for endotracheal intubation and mechanical ventilation ("intubation") had a profound adverse effect on survival. Overall, 9 of 48 (18.8%) intubated patients survived compared with a survival rate of 44 of 67 (65.7%) among patients not intubated (p < 0.001). This pattern persisted for nearly all patient subgroups. Among intubated patients, those receiving peripheral blood stem cell transplant (PBSCT) had significantly better survival than bone marrow transplant (BMT) patients (8 of 26, 31% versus 1 of 22, 4%; p = 0.028). Multiple logistic regression analyses indicated that the probability a patient admitted to the MICU survived decreased significantly if the patient was intubated, had an allogeneic rather than autologous transplant, had an infection or gastrointestinal bleeding, and also decreased with higher respiratory rate, higher heart rate, longer time from transplant to MICU admission or higher bilirubin. These results may be of value in deciding which critically ill patients will benefit from intubation following major complications after HSCT transplantation.

Exhaled nitric oxide is higher both at day and night in subjects with nocturnal asthma.

Nitric oxide in exhaled air is thought to reflect airway inflammation. No data have been reported so far on circadian changes in NO in subjects with nocturnal asthma. To determine whether exhaled NO shows a circadian rhythm inverse to the circadian rhythm in airway obstruction in subjects with nocturnal asthma, we conducted a study involving six healthy controls, eight individuals without nocturnal asthma (4-h to 16-h variation in peak expiratory flow [PEF] <= 15%), and six individuals with nocturnal asthma (4-h to 16-h PEF variation > 15%). Smoking, use of corticosteroids, and recent respiratory infections were excluded. NO concentrations were measured at 12, 16, 20, and 24 h, and at 4, 8, and 12 h of the next day, using the single-breath method. At the same times, FEV1 and PEF were also measured. Mean NO concentrations were significantly higher in subjects with nocturnal asthma than in subjects without nocturnal asthma, and higher in both groups than in healthy controls at all time points. Mean exhaled NO levels over 24 h correlated with the 4-h to 16-h variation in PEF (r = 0.61, p < 0.01). Exhaled NO did not show a significant circadian variation in any of the three groups as assessed with cosinor analysis, in contrast to the FEV1 in both asthma groups (p < 0.05). At 4 h, mean +/- SD NO levels were higher than at 16 h in subjects with nocturnal asthma; at 50 +/- 20 ppb versus 42 +/- 15 ppb (p < 0.05); other measurements at all time points were similar. Differences in NO and FEV1 from 4 h to 16 h did not correlate with one another. We conclude that subjects with nocturnal asthma exhale NO at higher levels both at night and during the day, which may reflect more severe diurnal airway-wall inflammation. A circadian rhythm in exhaled NO was not observed. NO levels did not correspond to the circadian rhythm in airway obstruction. The small increase in NO at 4 h may indicate an aspect of inflammation, but it is not associated with increased nocturnal airway obstruction.

Gastric ulcer presenting as gastroesophageal reflux and apnea in a term neonate.

Apnea in the neonatal period frequently is associated with prematurity. Full-term infants who develop apnea usually have associated clinical conditions such as infection, shock, metabolic disorders, neonatal abstinence syndrome, intracranial pathology, and gastroesophageal reflux. Gastric ulcer also is a rare phenomenon in the neonatal period. We describe a full-term infant presenting with apnea. Upon investigation, a 6-channel pneumocardiogram revealed central apnea and multiple episodes of low esophageal pH (< 4), which is suggestive of gastroesophageal reflux. This was confirmed by an upper gastrointestinal series. A small antral ulcer crater also was demonstrated. When assessing the etiology of apnea in a full-term infant, gastroesophageal reflux and gastric ulcer should be considered.