Inspiratory Changes Research Articles

Loss of ganglioglomerular nerve input to the carotid body impacts the hypoxic ventilatory response in freely-moving rats.

The carotid bodies are the primary sensors of blood pH, pO2 and pCO2. The ganglioglomerular nerve (GGN) provides post-ganglionic sympathetic nerve input to the carotid bodies, however the physiological relevance of this innervation is still unclear. The main objective of this study was to determine how the absence of the GGN influences the hypoxic ventilatory response in juvenile rats. As such, we determined the ventilatory responses that occur during and following five successive episodes of hypoxic gas challenge (HXC, 10% O2, 90% N2), each separated by 15min of room-air, in juvenile (P25) sham-operated (SHAM) male Sprague Dawley rats and in those with bilateral transection of the ganglioglomerular nerves (GGNX). The key findings were that 1) resting ventilatory parameters were similar in SHAM and GGNX rats, 2) the initial changes in frequency of breathing, tidal volume, minute ventilation, inspiratory time, peak inspiratory and expiratory flows, and inspiratory and expiratory drives were markedly different in GGNX rats, 3) the initial changes in expiratory time, relaxation time, end inspiratory or expiratory pauses, apneic pause and non-eupneic breathing index (NEBI) were similar in SHAM and GGNX rats, 4) the plateau phases obtained during each HXC were similar in SHAM and GGNX rats, and 5) the ventilatory responses that occurred upon return to room-air were similar in SHAM and GGNX rats. Overall, these changes in ventilation during and following HXC in GGNX rats raises the possibility the loss of GGN input to the carotid bodies effects how primary glomus cells respond to hypoxia and the return to room-air.

Noninvasive positive pressure ventilation in the assessment of extrinsic tracheal stenosis.

In patients with extrinsic tracheal stenosis caused by a mediastinal mass, an airway stent is a palliative measure to relieve airway obstruction. However, the self-expanding force of the stent may be insufficient to force a rigid stenosis. Our goal was to report a simple strategy to indirectly estimate the rigidity of the stenosis and predict airway patency after inserting the stent. Before the procedure, the inspiratory and expiratory flows and their ratio were evaluated under spontaneous breathing and after positive pressure ventilation generated by a facial mask. In patients with stenosis successfully treated with a stent (n = 11), we found significant changes in expiratory (2.3 ± 0.7 vs 2.8 ± 0.7; p = 0.03) and inspiratory (1.5 ± 0.6 vs 2.5 ± 0.9; p = 0.001) flows and a reduction of their ratio (1.4 ± 0.3 vs 1.1 ± 0.2; p = 0.01) whereas no significant changes were observed in patients (n = 2) whose stent failed to force the stenosis. In these cases, a tracheostomy was performed to assure ventilation. Our simple strategy may help physicians predict airway patency after stenting or plan alternative treatments in patients with rigid stenosis difficult to force by stenting.

Neurons in the Nonhuman Primate Amygdala and Dorsal Anterior Cingulate Cortex Signal Aversive Memory Formation under Sedation.

Anesthetics aim to prevent memory of unpleasant experiences. The amygdala and dorsal anterior cingulate cortex participate in forging emotional and valence-driven memory formation. It was hypothesized that this circuitry maintains its role under sedation. Two nonhuman primates underwent aversive tone-odor conditioning under sedative states induced by ketamine or midazolam (1 to 8 and 0.1 to 0.8 mg/kg, respectively). The primary outcome was behavioral and neural evidence suggesting memory formation. This study simultaneously measured conditioned inspiratory changes and changes in firing rate of single neurons in the amygdala and the dorsal anterior cingulate cortex in response to an expected aversive olfactory stimulus appearing during acquisition and tested their retention after recovery. Aversive memory formation occurred in 26 of 59 sessions under anesthetics (16 of 29 and 10 of 30, 5 of 30 and 21 of 29 for midazolam and ketamine at low and high doses, respectively). Single-neuron responses in the amygdala and dorsal anterior cingulate cortex were positively correlated between acquisition and retention (amygdala, n = 101, r = 0.51, P < 0.001; dorsal anterior cingulate cortex, n = 121, r = 0.32, P < 0.001). Neural responses during acquisition under anesthetics were stronger in sessions exhibiting memory formation than those that did not (amygdala median response ratio, 0.52 versus 0.33, n = 101, P = 0.021; dorsal anterior cingulate cortex median response ratio, 0.48 versus 0.32, n = 121, P = 0.012). The change in firing rate of amygdala neurons during acquisition was correlated with the size of stimuli-conditioned inspiratory response during retention (n = 101, r = 0.22 P = 0.026). Thus, amygdala and dorsal anterior cingulate cortex responses during acquisition under anesthetics predicted retention. Respiratory unconditioned responses to the aversive odor anesthetics did not differ from saline controls. These results suggest that the amygdala-dorsal anterior cingulate cortex circuit maintains its role in acquisition and maintenance of aversive memories in nonhuman primates under sedation with ketamine and midazolam and that the stimulus valence is sufficient to drive memory formation.

High-resolution manometry findings with hiatus hernia

: The esophagogastric junction (EGJ) is comprised of both the intrinsic lower esophageal sphincter (LES) and extrinsic crural diaphragm (CD) such that intraluminal pressure represents a composite of the two. With type I hiatal hernias there is weakening of the pharyngoesophageal ligament attaching the esophagus to the CD such that the distal esophagus, including the LES, becomes displaced cephalad. High-resolution manometry (HRM), can accurately detect an axial hiatal hernia as confirmed by studies comparing HRM to barium esophagram, upper endoscopy, or intraoperative findings. In HRM studies, hiatus hernia becomes evident by a spatial separation between the pressure signature of the LES and that of the CD; the operative confirmation of hiatus hernia correlates with this separation exceeding 1 cm. With LES-CD separation of <2 cm the HRM pressure signatures of the two overlap, but as the LES-CD separation increases beyond that the two become completely separate. The other progression noted in HRM studies is in the location of the respiratory inversion point (RIP), the axial location at which the inspiratory change in pressure transitions from an inspiratory increase, characteristic of intra-abdominal recordings to an inspiratory decrease, characteristic of intrathoracic recordings. In the normal state and with small hiatal hernias, the location of the RIP correlates with where the CD impinges on the esophagus at inspiration. However, with larger hernias the RIP can localize with either the CD or the LES reflective of whether or not the CD has become incompetent, presumably a result of hiatal dilatation. Consequently, there are three distinct EGJ pressure morphologies in HRM: (I) normal with minimal LES-CD separation, (II) hiatus hernia with LES-CD separation >1 cm and the RIP localized at the CD, and (III) hiatus hernia with LES-CD separation >1 cm and the RIP localized at the LES.

Temporary transvenous diaphragm pacing vs. standard of care for weaning from mechanical ventilation: study protocol for a randomized trial

BackgroundMechanical ventilation (MV) is a life-saving technology that restores or assists breathing. Like any treatment, MV has side effects. In some patients it can cause diaphragmatic atrophy, injury, and dysfunction (ventilator-induced diaphragmatic dysfunction, VIDD). Accumulating evidence suggests that VIDD makes weaning from MV difficult, which involves increased morbidity and mortality.Methods and analysisThis paper describes the protocol of a randomized, controlled, open-label, multicenter trial that is designed to investigate the safety and effectiveness of a novel therapy, temporary transvenous diaphragm pacing (TTVDP), to improve weaning from MV in up to 88 mechanically ventilated adult patients who have failed at least two spontaneous breathing trials over at least 7 days. Patients will be randomized (1:1) to TTVDP (treatment) or standard of care (control) groups. The primary efficacy endpoint is time to successful extubation with no reintubation within 48 h. Secondary endpoints include maximal inspiratory pressure and ultrasound-measured changes in diaphragm thickness and diaphragm thickening fraction over time. In addition, observational data will be collected and analyzed, including 30-day mortality and time to discharge from the intensive care unit and from the hospital. The hypothesis to be tested postulates that more TTVDP patients than control patients will be successfully weaned from MV within the 30 days following randomization.DiscussionThis study is the first large-scale clinical trial of a novel technology (TTVDP) aimed at accelerating difficult weaning from MV. The technology tested provides the first therapy directed specifically at VIDD, an important cause of delayed weaning from MV. Its results will help delineate the place of this therapeutic approach in clinical practice and help design future studies aimed at defining the indications and benefits of TTVDP.Trial registrationClinicalTrials.gov, NCT03096639. Registered on 30 March 2017.

Volume-controlled Ventilation Does Not Prevent Injurious Inflation during Spontaneous Effort

Spontaneous breathing during mechanical ventilation increases transpulmonary pressure and Vt, and worsens lung injury. Intuitively, controlling Vt and transpulmonary pressure might limit injury caused by added spontaneous effort. To test the hypothesis that, during spontaneous effort in injured lungs, limitation of Vt and transpulmonary pressure by volume-controlled ventilation results in less injurious patterns of inflation. Dynamic computed tomography was used to determine patterns of regional inflation in rabbits with injured lungs during volume-controlled or pressure-controlled ventilation. Transpulmonary pressure was estimated by using esophageal balloon manometry [Pl(es)] with and without spontaneous effort. Local dependent lung stress was estimated as the swing (inspiratory change) in transpulmonary pressure measured by intrapleural manometry in dependent lung and was compared with the swing in Pl(es). Electrical impedance tomography was performed to evaluate the inflation pattern in a larger animal (pig) and in a patient with acute respiratory distress syndrome. Spontaneous breathing in injured lungs increased Pl(es) during pressure-controlled (but not volume-controlled) ventilation, but the pattern of dependent lung inflation was the same in both modes. In volume-controlled ventilation, spontaneous effort caused greater inflation and tidal recruitment of dorsal regions (greater than twofold) compared with during muscle paralysis, despite the same Vt and Pl(es). This was caused by higher local dependent lung stress (measured by intrapleural manometry). In injured lungs, esophageal manometry underestimated local dependent pleural pressure changes during spontaneous effort. Limitation of Vt and Pl(es) by volume-controlled ventilation could not eliminate harm caused by spontaneous breathing unless the level of spontaneous effort was lowered and local dependent lung stress was reduced.

Does automatic tube compensation change metabolic parameters when added to pressure support mode during weaning?

Artificial airway increases work of breathing (WOB) during weaning [1] which is one of the reasons for weaning failure [2]. Pressure support ventilation (PSV) decreases WOB and oxygen expenditure by decreasing resistance caused by artificial airway. Because inspiratory flow changes with every breath during PSV, it can not constantly compansate the changes in resistance caused by changes due to patient's inspiratory effort. Automatic tube compensation (ATC) compensates the imposed WOB due to artificial airway. ATC adjusts the pressure inside the endotracheal tube therefore we hypothesized that when ATC is added to PSV, this compensation becomes better.

The effect of caffeine citrate on neural breathing pattern in preterm infants

BackgroundCaffeine citrate is widely used to prevent and treat prematurity-associated apnea. AimsThe aim of this study was to characterize the effect of caffeine citrate on the neural control of breathing, especially central apnea, in premature infants. Study designPreterm infants were evaluated for 30min before and 30min after caffeine citrate loading (20mg/kg). A feeding tube including miniaturized sensors was used to measure the diaphragm electrical activity (Edi) waveform. Central apnea was defined as any period where the Edi waveform was flat for >5s. SubjectsSeventeen preterm infants with a mean age of three days and mean birth weight of 900 grams were evaluated. Outcome measuresIn addition to central apnea, several parameters including neural inspiratory time, neural respiratory rate, peak Edi, delta inspiratory change in Edi (phasic Edi) and minimum Edi on exhalation were measured. ResultsThe majority of the apnea were short (5 to 10s) and the number of apnea correlated with birth weight (p=0.039). Caffeine citrate reduced significantly the number of 5-to-10-second-long central apnea during the 30-minute periods (12±11 to 7±7; p=0.02). Caffeine citrate increased both peak and phasic Edi leading to a significant increase in the diaphragm energy expenditure. ConclusionsEdi signal can be reliably measured and processed to study changes in premature infants' neural breathing. The beneficial effect of caffeine citrate on the reduction of the number of apnea is mediated through stimulated neural breathing increasing the diaphragm energy expenditure.

Inspiratory muscle resistance to fatigue during exercise and simulated airway obstruction

Respiratory muscle fatigue can develop during simulated airway obstruction. The aim of this study was to characterize the pattern of inspiratory muscle fatigue and to assess the resistance to fatigue of diaphragm (D), parasternal (PS), sternocleidomastoid (SM) and scalene (SC). 8 healthy untrained subjects participated in this study. To identify signs of inspiratory muscles fatigue development electromyographic activity of D, PS, SCM and SC was recorded during 5-min exercise with loaded breathing (40 cm H2O/L · s(-1)). The before-to-after exercise measurements of maximal inspiratory pressure (MIP) and EMG power spectrum changes were performed. Maximal inspiratory pressure declined about 12% after exercise test compared with control, whereas the peak magnitude of integrated electrical activity of D, PS, SCM and SC during post-exercise Muller's maneuver was significantly greater than in pre-exercise test in all subjects. The extent ofinspiratory muscles fatigue was evaluated by analysis of shift in centroid frequency (fc) of EMG power spectrum. All subjects demonstrated a significant reduction in fc of PS, SCM and SC.fc of D was not changed. Diaphragm is more resistantto fatigue during obstructive breathing compared with PS, SCM and SC. The data suggest that the reduction of maximum inspiratory pressure in chronic obstructive pulmonary disease also caused primarily by the weakening of the accessory muscles, while the weakness of the diaphragm may occur in the later stages of the disease. The functional failure of accessory muscles is an additional factor, which, along with the additional breathing resistance increases the load on the diaphragm, promoting its fatigue and reduced respiratory reserve.

Liquid- and Air-Filled Catheters without Balloon as an Alternative to the Air-Filled Balloon Catheter for Measurement of Esophageal Pressure

BackgroundMeasuring esophageal pressure (Pes) using an air-filled balloon catheter (BC) is the common approach to estimate pleural pressure and related parameters. However, Pes is not routinely measured in mechanically ventilated patients, partly due to technical and practical limitations and difficulties. This study aimed at comparing the conventional BC with two alternative methods for Pes measurement, liquid-filled and air-filled catheters without balloon (LFC and AFC), during mechanical ventilation with and without spontaneous breathing activity. Seven female juvenile pigs (32–42 kg) were anesthetized, orotracheally intubated, and a bundle of an AFC, LFC, and BC was inserted in the esophagus. Controlled and assisted mechanical ventilation were applied with positive end-expiratory pressures of 5 and 15 cmH2O, and driving pressures of 10 and 20 cmH2O, in supine and lateral decubitus.Main ResultsCardiogenic noise in BC tracings was much larger (up to 25% of total power of Pes signal) than in AFC and LFC (<3%). Lung and chest wall elastance, pressure-time product, inspiratory work of breathing, inspiratory change and end-expiratory value of transpulmonary pressure were estimated. The three catheters allowed detecting similar changes in these parameters between different ventilation settings. However, a non-negligible and significant bias between estimates from BC and those from AFC and LFC was observed in several instances.ConclusionsIn anesthetized and mechanically ventilated pigs, the three catheters are equivalent when the aim is to detect changes in Pes and related parameters between different conditions, but possibly not when the absolute value of the estimated parameters is of paramount importance. Due to a better signal-to-noise ratio, and considering its practical advantages in terms of easier calibration and simpler acquisition setup, LFC may prove interesting for clinical use.

Measurement of oxygen concentration delivered via nasal cannulae by tracheal sampling

Oxygen is used in many clinical scenarios, however the variable performance of nasal cannulae makes determining the precise fraction of inspired oxygen (FiO2 ) difficult. We developed a novel method for measurement of the tracheal FiO2 using a catheter placed via bronchoscopy. We investigate the effects of oxygen delivery, respiratory rate, mouth position and estimated minute ventilation (VE ) on the FiO2 delivered by nasal cannulae. The catheter was placed in 20 subjects. Tracheal gas concentrations were analysed during six 5-min treatments controlling for oxygen delivery rate, respiratory rate and mouth position. Ventilation was monitored with respiratory inductive plethysmography (RIP). The FiO2 delivered by nasal cannulae was compared between treatments, and we investigated the relationships among the FiO2 , alveolar partial pressure of oxygen (PA O2 ) and VE . The FiO2 increased by 0.038/L/min of oxygen. Respiratory rate had a significant effect on the FiO2 . A normal respiratory rate of 15 breaths/min and oxygen supplementation via nasal cannula at 2 L/min resulted in an FiO2 of 0.296; however, FiO2 decreased by 0.012 at 20 breaths/min and 0.004 at 10 breaths/min. The mean FiO2 decreased by 0.024 with the mouth open. The FiO2 and PA O2 were observed to decrease with increasing VE . Continuous measurement of the FiO2 using a transtracheal catheter provides detailed insight into inspiratory changes of the FiO2 delivered by nasal cannulae. Our study confirms that respiratory rate, VE and mouth position significantly influence the inspired oxygen concentration. These parameters should be accounted for when prescribing oxygen.

Pathophysiology of Tricuspid Regurgitation

Background— Respiratory dependence of tricuspid regurgitation (TR), a long-held concept suggested by murmur variation, remains unproven and of unclear mechanisms. Methods and Results— In 41 patients with mild or greater TR (median age, 67 years), we performed triple Doppler echocardiographic quantification (TR severity, right ventricular, and right atrial quantification) with simultaneous respirometer recording of respiratory phases. Expiration to inspiration changes (median) affected TR peak velocity (−40 cm/s; 25th to 75th percentile, −60 to −30 cm/s), duration (−12 milliseconds; 25th to 75th percentile, −45 to 2 milliseconds), and time-velocity integral (−17 cm; 25th to 75th percentile, −23.4 to −10 cm; all P &lt;0.001), consistent with decreased TR driving force. Nevertheless, inspiratory TR augmentation was demonstrated by increased effective regurgitant orifice (0.21 cm 2 ; 25th to 75th percentile, 0.09 to 0.34 cm 2 ) and volume (18 mL per beat; 25th to 75th percentile, 10 to 25 mL per beat; all P &lt;0.001) infrequently detected clinically (2 of 41, 5). As a result of reduced TR driving force, regurgitant volume increased less than effective regurgitant orifice (120 [25th to 75th percentile, 78.6 to 169] versus 169 [ 25th to 75th percentile, 12.9 to 226.1]; P &lt;0.001). During inspiration, right ventricular area increased (diastolic, 27.8 [25th to 75th percentile, 22.6 to 36.3] versus 26.5 [21.1 to 31.9]; P &lt;0.0001) with widening of right ventricular shape (length-to-width ratio, 1.6 [ 25th to 75th percentile, 1.37 to 1.95] versus 1.7 [1.46 to 2.1]; P &lt;0.0001), increased systolic annular diameter ( P =0.003), valve tenting height ( P &lt;0.0001) and area ( P &lt;0.0001), and reduced valvular-to-annular ratio ( P =0.006). Effective regurgitant orifice during inspiration was independently determined by inspiratory valvular-to-annular ratio ( P =0.026) and inspiratory change in right ventricular length-to-width ratio ( P =0.008) and valve tenting area ( P =0.015). Conclusions— TR is dynamic with almost universal respiratory changes of large magnitude and complex pathophysiology. During inspiration, a large increase in effective regurgitant orifice causes, despite a decline in regurgitant gradient, a notable increase in regurgitant volume. Effective regurgitant orifice changes are independently linked to inspiratory annular enlargement (decreased valvular coverage) and to inspiratory right ventricular shape widening with increased valvular tenting. These novel physiological insights into TR respiratory dependence underscore right-side heart plasticity and are important for clinical TR severity evaluation.

Primary Cardiac Lymphoma

Human immunodeficiency virus can cause pericarditis, myocarditis, cardiomyopathies, endocarditis, other valvular compromises, cardiac involvement by neoplasm, pulmonary hypertension, arrhythmia, and thromboembolic disease. Myocardial involvement by tumors has been reported in rare cases, with Kaposi sarcoma and non-Hodgkin lymphomas being the most frequent tumor types. In this case, we introduce a 51-year-old man who presented with a febrile syndrome lasting for 30 days. He had just been on a 7-day course of azithromycin prescribed for a respiratory infection. On day 10 after he completed the antibiotic course, fever recurred without evidence of an identifiable infectious focus. Because of the aforementioned clinical presentation and to rule out infectious endocarditis, an echocardiogram was performed on the patient, which showed an image in the right atrium that could correspond to a vegetation. On physical examination, heart rate was 100 bpm, blood pressure 120/75 mm Hg, and jugular distention 3/3 without inspiratory change. Laboratory data were as follows: white blood cells 12 300/mm3, C-reactive protein …

Body mass index is negatively correlated with respiratory muscle weakness and interleukin-6 production after coronary artery bypass grafting

Purpose The present study was performed to clarify the relationships between body mass index (BMI), interleukin-6 (IL-6) production, and respiratory muscle weakness in patients undergoing coronary artery bypass grafting (CABG). Materials and Methods The correlations among BMI, changes in maximum inspiratory and expiratory pressure (ΔMIP, ΔMEP) on postoperative days (POD) 1 and 7, postoperative IL-6, and rapid turnover proteins (retinol-binding protein, prealbumin, and transferrin) on POD1 were assessed in 154 consecutive patients undergoing elective CABG. The patients were divided into quartiles of BMI, Q1 (BMI, <20.8 kg/m 2) to Q4 (BMI, ≥25.25 kg/m 2), and compared among groups. Results There were significant correlations between ΔMIP and BMI (POD1, r = −0.369; POD7, r = −0.285) and IL-6 (POD1, r = 0.423; POD7, r = 0.431), and between ΔMEP and BMI (POD1, r = −0.252; POD7, r = −0.228) and IL-6 (POD1, r = 0.252; POD7, r = 0.384). Interleukin-6 showed a significant negative correlation with BMI ( r = −0.374) and retinol-binding protein ( r = −0.382). Interleukin-6 was highest in Q1 and lowest in Q4. Higher BMI indicated greater respiratory muscle strength than lower BMI. Conclusions Preoperative BMI is correlated with respiratory muscle strength and cytokine production after CABG. The findings of this study suggest that BMI may be a valuable predictor for respiratory management in CABG patients.

How can the response to volume expansion in patients with spontaneous respiratory movements be predicted?

IntroductionThe aim of the study was to evaluate the ability of different static and dynamic measurements of preload to predict fluid responsiveness in patients with spontaneous respiratory movements.MethodsThe subjects were 21 critically ill patients with spontaneous breathing movements receiving mechanical ventilation with pressure support mode (n = 9) or breathing through a face mask (n = 12), and who required a fluid challenge. Complete hemodynamic measurements, including pulmonary artery occluded pressure (PAOP), right atrial pressure (RAP), pulse pressure variation (ΔPP) and inspiratory variation in RAP were obtained before and after fluid challenge. Fluid challenge consisted of boluses of either crystalloid or colloid until cardiac output reached a plateau. Receiver operating characteristics (ROC) curve analysis was used to evaluate the predictive value of the indices to the response to fluids, as defined by an increase in cardiac index of 15% or more.ResultsCardiac index increased from 3.0 (2.3 to 3.5) to 3.5 (3.0 to 3.9) l minute-1 m-2 (medians and 25th and 75th centiles), p < 0.05. At baseline, ΔPP varied between 0% and 49%. There were no significant differences in ΔPP, PAOP, RAP and inspiratory variation in RAP between fluid responders and non-responders. Fluid responsiveness was predicted better with static indices (ROC curve area ± SD: 0.73 ± 0.13 for PAOP, p < 0.05 vs ΔPP and 0.69 ± 0.12 for RAP, p = 0.054 compared with ΔPP) than with dynamic indices of preload (0.40 ± 0.13 for ΔPP and 0.53 ± 0.13 for inspiratory changes in RAP, p not significant compared with ΔPP).ConclusionIn patients with spontaneous respiratory movements, ΔPP and inspiratory changes in RAP failed to predict the response to volume expansion.

Ventilatory response to exercise in simulated obesity by chest loading.

Obesity-related increases of weight on the chest wall are known to decrease lung volume and chest wall compliance, but the effect of this mass loading, independent of other obesity-related complications on the ventilatory response to exercise is unknown. The purpose of this study was to investigate the effect of chest mass loading on the ventilatory response to exercise. External chest loading (CL) was used to simulate the effect of moderate obesity (BMI = 32 kg x m). Eight healthy nonobese subjects performed two incremental exercise tests on a cycle ergometer with work rate increasing 25 W every 3 min once without (control; CON) and once with CL. Expiratory reserve volume (ERV), forced vital capacity (FVC), and forced expiratory volume in 1 s (FEV1) were measured before each test. During exercise, inspiratory capacity (IC), to estimate changes in end-expiratory lung volume, and inspiratory (TI) and expiratory (TE) duration, tidal volume (Vt), breathing frequency (Fb), minute ventilation (VE), mean inspiratory (Vt/TI) and expiratory (Vt/TE) flow rates, and oxygen consumption (VO2) were measured. Baseline ERV, FVC and FEV1 were lower with CL (P < 0.05). Compared with CON, the peak work rate achieved during exercise with CL was lower and VO2, VE, Fb, Vt/TI, and Vt/TE were higher, and Vt was lower at work rates > or = 100 W (P < 0.05). IC increased progressively in CON during exercise but remained unchanged with CL. Obesity-related chest loading decreases lung volumes and increases the mechanical ventilatory constraints during exercise and is likely a critical factor in reducing exercise capacity in obesity.

Diaphragmatic Activity After Laparoscopic Cholecystectomy

SHARMA, RAJIV; AXELSSON, HANS; ÖBERG, ÅKE; JANSSON, ERICA; CLERGUE, FRANCOIS; JOHANSSON, GÖRAN; REIZ, SEBASTIAN Author Information

Heart and lung support interaction — modeling and simulation

Mechanical support of the lungs used to preserve life or during any kind of surgery may have an adverse effect on the cardiovascular system. Usually, positive pressure in alveoli diminishes lung perfusion, venous return and cardiac output. Positive pressure during the respiratory cycle is transfered into the thoracic space. The aim of this study was to assess how synchronization of the respirator with spontaneous breathing influences the distribution of pressure and ventilation in nonhomogeneous lungs and how it should influence hemodynamics. For this purpose a multicompartmental model of respiratory system mechanics was used in the electrical analog of a respirator-lung circuit, which enabled us to simultaneously simulate ventilatory support and spontaneous breathing. Mechanical properties of the respiratory system were modeled by lumped parameters: resistances and capacitances of constant values, independent of lung volume or inspiratory flow changes. A multicompartmental model of the respiratory system enabled us to simulate lung pathology characterized by non-homogeneity of the mechanical properties of the different parts of the lungs. The results of simulations presented in the paper enable us to conclude that lung volume increase, independent of the respirator-patient breathing synchronization, may be modeled as the increase in pulmonary vascular resistance and alveolar pressure increase, dependent on respirator-patient breathing synchronization, may be averaged by esophageous balloon measurements which show intrathoracic pressure changes.

Respiratory responses to preoptic/anterior hypothalamic warming during sleep in kittens.

The preoptic/anterior hypothalamic (POAH) area of 12-48-day-old unanaesthetized, unrestrained kittens was warmed with a diathermic probe to assess respiratory responses to a central thermal challenge during sleep. During quiet sleep (QS), warming of the POAH by 1.4-3.8 degrees C induced periods of tachypnoea (panting) interspersed with periods of slower respiration; the percentage of time spent in panting increased as the kittens matured. During rapid eye movement (REM) sleep, POAH warming induced a much smaller increase in respiratory rate and no sustained panting. Analysis of the dynamics of panting (in QS only, since panting did not occur in REM) revealed several changes from breathing patterns of normal respiration. During panting, the increased respiratory rate did not result from equal changes in inspiratory and expiratory times; inspiratory times accounted for a larger portion of the decline in total respiratory cycle time. Amplitude of diaphragmatic electromyographic activity showed an age-dependent response to thermal panting, which resulted in age-dependent changes in ventilation and inspiratory drive. The interspersion of slower with faster respiratory rates suggests a competition of thermoregulatory and respiratory homeostatic mechanisms. The age-dependent ventilatory responses to thermal panting suggest greater vulnerability to thermal stress at particular ages, and may have implications for the sudden infant death syndrome.

Dynamic Respiratory Responses to Preoptic/Anterior Hypothalamic Warming in the Sleeping Cat

Timing and amplitude characteristics of diaphragmatic muscle activity following bilateral local warming of the preoptic area/anterior hypothalamic region (POAH) were studied during sleep in free-moving, intact adult cats. Warming of the POAH increased local brain temperature by 1.4-3.7 degrees C and elicited thermal tachypnea (panting) during quiet sleep (QS). Following transition to rapid eye movement (REM) sleep, the tachypnea, initially induced by warming during QS, diminished, but respiratory rates remained above baseline REM levels, and an intermittent pattern of faster and slower breathing rates developed. In QS, tachypnea resulted primarily from a decline in inspiratory time (TI), whereas in REM sleep, reduction in expiratory time (TE) was more prominent. Although diaphragmatic electromyographic amplitude decreased by 40% during panting in QS, the much higher respiratory rates (+350%) resulted in apparent increases in relative ventilation and inspiratory drive. A less pronounced respiratory rate change (+46%) emerged during REM sleep, resulting in no significant changes in ventilation and inspiratory drive in response to warming in that state. The results suggest that descending thermal influences on respiratory patterning differ between QS and REM states in both overall respiratory rate and on relative TI and TE, and thus do not affect inspiratory drive exclusively.