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.

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.

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.

Complex demodulation of cardiorespiratory dynamics preceding vasovagal syncope.

BACKGROUND: The dynamic autonomic processes leading to vasovagal syncope are poorly understood. METHODS AND RESULTS: We used complex demodulation to continuously assess changes in respiration, R-R interval, and arterial pressure (blood pressure) variability during 60 degree head-up tilt in 25 healthy subjects with tilt-induced vasovagal syncope and 25 age-matched nonsyncopal control subjects. Coherence and transfer function analyses were used to examine the relation between respiration and R-R interval variability before syncope. Baseline blood pressure, R-R, and ventilation were similar between syncope subjects and control subjects. Syncope subjects experienced an increase in tidal volume and decrease in BP beginning 3 minutes before impending syncope (systolic blood pressure <80 mm Hg) necessitated termination of tilt. Approximately 90 seconds before syncope there was a sudden prolongation of R-R interval and increase in amplitude of high and low frequency R-R interval variability, indicating an abrupt enhancement of vagal tone. The increase in respiratory amplitude between 180 and 90 seconds before syncope was not accompanied by changes in R-R interval or R-R variability, suggesting a dissociation between respiration and the respiratory sinus arrhythmia. The coherence analysis showed fewer syncope subjects with coherence between respiratory and R-R interval variabilities and lower transfer magnitudes in syncope subjects compared with control subjects. Nonsyncopal subjects had no change in respiratory, R-R interval, or blood pressure dynamics during matched time periods before the time of syncope. CONCLUSIONS: Vasovagal syncope is preceded by a period of hyperpnea and cardiorespiratory decoupling followed by an abrupt increase in cardiovagal tone. Respiratory pumping without inspiratory cardiac slowing may partially counteract preload reduction until sudden bradycardia precipitates syncope.

[Participation of rostral ventral medullary neuron structures in the regulation of the respiratory rhythm mechanism in rats]. / Uchastie rostral'nykh ventromedulliarnykh neironnykh struktur v reguliatsii mekhanizma formirovaniia dykhatel'nogo ritma u krys.

The role of neuronal structures of the rostral ventromedullary area in regulation of central inspiratory activity, was studied. The data obtained suggests that the structures of subretrofacial area are important for the respiratory rhythm generation due to regulation of excitability of the inspiratory neurons.

[Pre-Bötzinger complex participates in respiratory effects of thyroliberin]. / Kompleks pre-Betzingera uchastvuet v realizatsii respiratornykh éffektov tiroliberina.

Responses of the TRH microinjections into the pre-Bötzinger complex of adult anesthetised rats involved a dose-dependent increase in respiratory rate as well as shortening of inspiratory and expiratory duration. The tidal volume and inspiratory muscles' activity decreased following high concentrations of the TRH. The heart rate did not change. The findings suggest that the pre-Bötzinger complex is at least partly responsible for the TRH tachypnoic effect.

[Participation of reticular neurons of the cat medulla oblongata in the integration of the respiration center activity]. / Uchastie retikuliarnykh neironov prodolgovatogo mozga koshki v integrativnoi deiatel'nosti dykhatel'nogo tsentra.

Reticular neurons of the respiratory centre are divided into three groups. The 1st one is located in the medial areas and accepts afferents from chemoreceptors. The 2nd one is located in inspiratory and expiratory areas of the centre and take part in integration of afferent signals and activation of the effector mechanism. The 3rd group is present in both areas and organizes the effector activity of the centre. Electrical stimulation of the brain stem nuclei can modify reticular neurons in lateral areas.

[Comparative analysis of changes in respiration and systemic hemodynamics during activation of GABA receptors in cats and rats]. / Sravnitel'nyi analiz izmenenii dykhaniia i sistemnogo krovoobrashcheniia u koshek i krys pri aktivirovanii GAMK-retseptorov.

Effects of alpha-hydroxybutyrate (GHB) involved a decrease in the respiration rate and subsequent periodic breathing in anesthetised cats and rats. No considerable changes occurred in systemic circulation. There were, however, some differences between the species in the patterns of respiratory arrest. Possible mechanisms of the similarity and difference are discussed.

[The role of pharyngeal muscles in the regulation of airway resistance during inspiration resistive load in rabbits]. / Rol' faringeal'nykh myshts v reguliatsii soprotivleniia dykhatel'nykh putei pri intspiratornoi rezistivnoi nagruzke u krolikov.

In anesthetised spontaneously breathing rabbits, an increase in the inspiratoryactivity m.genioglossus was greater than a simultaneous increase in the respiratory activity of the diaphragm cluring loaded breathing. A bypass of the air flow via tracheostoma did not affect the response of the m.genioglossus to a resistive load. The difference seems to be due to different functional inputs from the lung mechanoreceptors to phrenic and hypoglossal neuronal pools.