Mouth Occlusion Pressure Research Articles

Respiratory Muscle Weakness and Respiratory Failure in Pediatric Neuromuscular Disorders: The Value of Noninvasive Determined Tension-Time Index.

Background In pediatric neuromuscular disorders (NMD), respiratory muscle weakness parallels respiratory failure. The objectives of this study are (1) to evaluate respiratory muscle capacity in neuromuscular children and (2) to assess the relationship between vital capacity, respiratory muscle performance, and alveolar ventilation during sleep and wakefulness. Methods Inspiratory vital capacity (IVC), peak inspiratory pressure (PIP), mouth occlusion pressure (P0.1), and noninvasive tension-time index of the respiratory muscles (TTImus) were studied in 80 NMD subjects (12.1 ± 3.3 years) and 80 healthy children (11.1 ± 2.2 years). Subjects' results were compared with arterial blood gases and polysomnography. Results In 15 NMD subjects with normal ventilation IVC and PIP were reduced to 70% predicted but TTImus was normal. In 50 NMD subjects with nocturnal hypoventilation IVC and PIP were lower than 50% predicted, TTImus was doubled compared with the control group. In 15 NMD subjects with diurnal and nocturnal hypoventilation IVC and PIP were below 30% predicted, TTImus was increased fourfold, and thus the main determinant of respiratory failure. Conclusions In NMD children, reduced IVC and PIP result in increased respiratory muscle load and disturbed ventilation. TTImus is an important noninvasive determinant of disturbed ventilation in children with NMD.

Performances of domiciliary ventilators compared by using a parametric procedure

Noninvasive mechanical ventilation is sufficiently widely used to motivate bench studies for evaluating and comparing performances of the domiciliary ventilators. In most (if not in all) of the previous studies, ventilators were tested in a single (or a very few) conditions, chosen to avoid asynchrony events. Such a practice does not reflect how the ventilator is able to answer the demand from a large cohort of patients with their inherent inter-patient variability. We thus developed a new procedure according which each ventilator was tested with more than 1200 “simulated” patients. Three lung mechanics (obstructive, restrictive and normal) were simulated using a mechanical lung (ASL 5000) driven by a realistic muscular pressure. 420 different dynamics for each of these three lung mechanics were considered by varying the breathing frequency and the mouth occlusion pressure. For each of the nine ventilators tested, five different parameter settings were investigated. The results are synthesized in colored maps where each color represents the ventilator (in)ability to synchronize with a given muscular pressure dynamics. A synchronizability e is then computed for each map. The lung model, the breathing frequency and the mouth occlusion pressure strongly affect the synchronizability of ventilators. The Vivo 50 (Breas) and the SomnoVENT autoST (Weinmann) are well synchronized with the restrictive model ( $\overline {\varepsilon }=86$ and 78 %, respectively), whereas the Elisee 150 (ResMed), the BiPAP A40 and the Trilogy 100 (Philips Respironics) better fit with an obstructive lung mechanics ( $\overline {\varepsilon }=87$ , 86 and 86 %, respectively). Triggering and pressurization performances of the nine ventilators present heterogeneities due to their different settings and operating strategies. Performances of domiciliary ventilators strongly depend not only on the breathing dynamics but also on the ventilator strategy. One given ventilator may be more adequate than another one for a given patient.

Inspiratory muscle performance in endurance-trained elderly males during incremental exercise

The aim of this study was to compare the inspiratory muscle performance during an incremental exercise of twelve fit old endurance-trained athletes (OT) with that of fit young athletes (YT) and healthy age-matched controls (OC). The tension-time index (TT0.1) was determined according to the equation TT0.1=P0.1/PImax×ti/ttot, where P0.1 is the mouth occlusion pressure, PImax the maximal inspiratory pressure and ti/ttot the duty cycle. For a given VCO2, OT group displayed P0.1, P0.1/PImax ratio, TT0.1 and effective impedance of the respiratory muscle values which were lower than OC group and higher than YT group. At maximal exercise, P0.1/PImax ratio and TT0.1 was still lower in the OT group than OC group and higher than YT group. This study showed lower inspiratory muscle performance attested by a higher (TT0.1) during exercise in the OT group than YT group, but appeared to be less marked in elderly men having performed lifelong endurance training compared with sedentary elderly subjects.

Diffference between mouth and esophageal occlusion pressure during CO2 rebreathing in chronic obstructive pulmonary disease.

During CO2 rebreathing, we measured the pressures generated at the mouth and in the esophagus during the first 0.1 sec of inspiratory effort against a closed airway in 6 normal subjects and 6 patients with chronic obstructive lung disease. Normal subjects showed similar reponses to CO2 in terms of both mouth pressure and esophageal pressure. Patients' responses at the mouth to CO2 were decreased compared to those of normal subjects, but the responses in the esophagus were not significantly different. The patients demonstrated a greater response of occlusion pressure measured in the esophagus than at the mouth. In patients with altered mechanical properties of the lung, the change in mouth occlusion pressure might be influenced by problems of equalization of pressure within the airways due to unequal time constants, by problems of regional differences in pressure gradients over the pleural surface, or both. Esophageal pressure during airway occlusion 100 msec after the onset of inspiration may be better measure of respiratory drive than mouth pressure in patients with intrinsic increase of airway resistance.

Impairment of respiratory function in late-onset distal myopathy due to MATR3 Mutation.

Recently, mutations in the MATR3 gene were found to cause late-onset distal myopathy. The frequency and impact of respiratory involvement are not clear. Respiratory parameters [maximum vital capacity (VCmax); forced expiratory volume (FEV1 ); peak expiratory flow (PEF), postural drop of VCmax from sitting to supine, maximum inspiratory muscle pressure (PImax), mouth occlusion pressure after 100 ms (P 0.1), peak cough flow, and blood-gas analysis] were monitored prospectively at baseline, and then 6 months and 12 months later in 8 patients with genetically confirmed MATR3 myopathy. All patients showed involvement of respiratory function. Six of 8 reported exertional dyspnea. At the end of follow-up, 5 of 8 had decreased VC, 7 of 8 had reduced PImax, and 5 of 7 had decreased partial pressure of oxygen (PO2 ). Within 12 months, respiratory parameters deteriorated non-significantly. No patient required non-invasive ventilation. There is a high risk of abnormal respiratory function with progressive worsening in MATR3 myopathy.

Mouth Occlusion Pressure (P0.1) Provides Valuable Information in the Clinical Assessment and Follow‐up of Ventilatory Drive in Obstructive and Restrictive Lung Disease

Ventilatory acclimatization to hypoxia (VAH) includes a time‐dependent increase in minute ventilation with re‐setting of the arterial partial pressure of CO2 “set point” that results in persistent hyperventilation with concomitant changes in arterial oxygen levels. One of the methods used to evaluate the neuromuscular drive to breathe is the airway occlusion pressure (P0.1), which is the pressure generated at the airway opening 100 ms after the onset of occluded inspiratory effort. We hypothesized that P0.1 is a marker of disease that should be follow as a part of the treatment in patients with lung disease, we studied the correlation between P0.1 with FEV1, FVC, FEV1/FVC in patients with lung disease. We retrospectively studied 100 subjects that had PFTs and P0.1 done between September and October 2014. Mean age was 59.3 (range, 19‐89 years). In restrictive lung disease (39/100, 39%) P0.1 was correlated with the FVC and FEV1/FVC, in obstructive lung disease (61/100, 61%) P0.1 was correlated with FEV1 and FEV1/FVC. In subjects with diagnosis of obstructive lung disease P0.1 had a significant correlation with FEV1 and FEV1/FVC (p=0.001 and 0.003), in restrictive lung disease, P0.1 had a significant correlation with FVC (p=0.001) but no significant correlation with FEV1/FVC (p=0.2). Our results showed that P0.1 has a significant correlation with disease severity in lung disease. Previous studies showed that ventilatory drive decreases as a consequence of treatment, and hypoxia correction, is likely that P0.1 is a good marker of disease progression and can help diagnose and guide treatment in both obstructive and restrictive pulmonary disease, more studies are necessary to further evaluate the limitations of the P0.1 in different lung mechanics.

Normal values for inspiratory muscle function in children

Assessment of inspiratory muscle function (IMF) is limited in children with neuromuscular disorders, because respiratory muscle tests are poorly standardized and valid normative data are unavailable. We investigated maximum inspiratory pressure after exhalation to residual volume (MIP), mouth occlusion pressure (P0.1) and time of inspiration during quiet breathing and derived inspiratory muscle load (P0.1/MIP), and tension time index (TTI) in 301 healthy schoolchildren 6–16 years old. Gender-specific and age-dependent percentile curves for MIP were drawn with the median, 5%, 10%, 25%, 75% and 95% percentile. P0.1 was equal in boys and girls (0.23 ± 0.11 kPa), while MIP was significantly higher in boys (6.8 ± 2.2 versus 5.8 ± 2.4 kPa). Consequently, P0.1/MIP (4.8% ± 3.2% versus 4.0% ± 3.1%) and TTI (0.2 ± 0.14 versus 0.16 ± 0.14) were significantly higher in girls. MIP was 2.90 + 0.36 × age (kPa) and 3.19 + 0.24 × age (kPa) in boys and girls, respectively. The 95% confidence intervals for boys and girls, respectively, were MIP, 6.3–7.3 kPA and 5.4–6.2 kPa; P0.1/MIP, 3.5%–4.5% and 4.3%–5.3%; TTI, 0.14–0.18 and 0.18–0.22; and P0.1, 0.20–0.24 kPa for both. IMF in children has a wide interindividual variability; however percentile curves facilitate a longitudinal assessment of individual patients. Furthermore, narrow confidence intervals allow for comparisons of study populations, making IMF an appropriate endpoint for clinical trials.

Realistic human muscle pressure for driving a mechanical lung

An important issue in noninvasive mechanical ventilation consists in understanding the origins of patient-ventilator asynchrony for reducing their incidence by adjusting ventilator settings to the intrinsic ventilatory dynamics of each patient. One of the possible ways for doing this is to evaluate the performances of the domiciliary mechanical ventilators using a test bench. Such a procedure requires to model the evolution of the pressure imposed by respiratory muscles, but for which there is no standard recommendations. In this paper we propose a mathematical model for simulating the muscular pressure developed by the inspiratory muscles and corresponding to different patient ventilatory dynamics to drive the ASL 5000 mechanical lung. Our model is based on the charge and discharge of a capacitor through a resistor, simulating contraction and relaxation phases of the inspiratory muscles. Our resulting equations were used to produce 420 time series of the muscle pressure with various contraction velocities, amplitudes and shapes, in order to represent the inter-patient variability clinically observed. All these dynamics depend on two parameters, the ventilatory frequency and the mouth occlusion pressure. Based on the equation of the respiratory movement and its electrical analogy, the respiratory muscle pressure was simulated with more consistency in regards of physiological evidences than those provided by the ASL 5000 software. The great variability in the so-produced inspiratory efforts can cover most of realistic patho-physiological conditions.

Increased respiratory drive relates to severity of dyspnea in systemic sclerosis

BackgroundDyspnea may be a presenting symptom in progressive systemic sclerosis (SSc). Respiratory drive (mouth occlusion pressure, MOP, at rest and during CO2 rebreathing, 7% CO2, 93% O2) is a major determinant of dyspnea and may relate to the magnitude of dyspnea.MethodsIn a prospective design, MOP at 0.1 sec (P0.1) was measured in 73 SSc patients while breathing room air and during CO2 rebreathing. An abnormal V’E/P0.1 is defined as < 8 L/min/cm H2O. Dyspnea scores were assessed by a shortness of breath questionnaire (UCSD dyspnea scale).ResultsMean P0.1 in patients with normal V’E/P0.1 (n = 45) was 1.1 ± 0.04 and 1.6 ± 0.08 cm H2O in patients with abnormal V’E/P0.1 (n = 28), p <0.001. ∆P0.1/∆PetCO2 differed significantly between these groups (0.45 versus 0.75 cm H2O/mmHg, P < 0.001), but no significant difference was present in ∆V’E/∆PetCO2. V’E/P0.1 showed the highest significant correlation with the UCSD dyspnea score (r = -0.76, p <0.001). UCSD cut-off value for abnormal V’E/P0.1 was 8.5 (sensitivity 93%, specificity 96%, area under the curve 0.98).ConclusionsIn SSc patients an abnormal V’E/P0.1 better relates to the severity of dyspnea than traditional lung function parameters and can easily be assessed at first outpatient consultation.

Impact of hemodialysis on dyspnea and lung function in end stage kidney disease patients.

Background. Respiratory symptoms are usually underestimated in patients with chronic kidney disease undergoing maintenance hemodialysis. Therefore, we set out to investigate the prevalence of patients chronic dyspnea and the relationship of the symptom to lung function indices. Methods. Twenty-five clinically stable hemodialysis patients were included. The mMRC dyspnea scale was applied before and after hemodialysis. Spirometry, single breath nitrogen test, arterial blood gases, static maximum inspiratory (P imax⁡) and expiratory (P emax⁡) muscle pressures, and mouth occlusion pressure (P 0.1) were also measured. Results. Despite normal spirometry, all patients (100%) reported mild to moderate degree of chronic dyspnea pre which was reduced after hemodialysis. The sole predictor of (Δ) mMRC was the (Δ) P 0.1 (r = 0.71, P < 0.001). The P imax⁡ was reduced before and correlated with the duration of hemodialysis (r = 0.614, P < 0.001), whilst after the session it was significantly increased (P < 0.001). Finally (Δ) weight was correlated with the (Δ) P imax⁡ %pred (r = 0.533, P = 0,006) and with the (Δ) CV (%pred) (r = 0.65, P < 0.001). Conclusion. We conclude that dyspnea is the major symptom among the CKD patients that improves after hemodialysis. The neuromechanical dissociation observed probably is one of the major pathophysiologic mechanisms of dyspnea.

Respiratory drive and breathing pattern abnormalities are related to exercise intolerance in chronic heart failure patients

BackgroundPatients with chronic heart failure (CHF) are characterized by exercise intolerance and ventilatory abnormalities that are related to poor prognosis. We hypothesized that CHF patients have increased respiratory drive and abnormal breathing pattern during exercise in relation to disease severity. Materials and methodsThe study population consisted of 219 stable CHF patients and 30 healthy control subjects. All subjects underwent a symptom-limited cardiopulmonary exercise testing (CPET), pulmonary function tests, measurement of the maximal inspiratory pressure (PImax) and respiratory drive (P0.1).Measurements included peak oxygen uptake (VO2 peak, ml/kg/min). Respiratory drive was measured by mouth occlusion pressure P0.1 and P0.1/PImax ratio at rest, and by mean inspiratory flow (VT/TI) at rest and during exercise. CHF patients were divided into 3 groups according to VO2 peak (Group A: >20, Group B: 20–16 and Group C: <16ml/kg/min). ResultsCHF patients presented higher P0.1/PImax (4.1±3.6 vs 3.0±1.5, p=0.007) and VT/TI at rest (0.48±0.14 vs 0.41±0.10, L/s respectively, p=0.004) and lower VT/TI at peak exercise (2.17±0.66 vs 2.56±0.73, L/s, p=0.009) compared to controls. P0.1/PImax was higher in CHF Group C vs B vs A (4.9±2.9 vs 3.6±1.8 vs 3.1±1.8, respectively, p<0.001), while VT/TI at peak exercise was lower (1.71±0.43 vs 2.15±0.52 vs 2.65±0.64, L/s, respectively, p<0.001). ConclusionsCHF patients present increased respiratory drive at rest and abnormal breathing pattern during exercise in relation to CHF severity.

Prediction of Extubation Success in Myasthenic Crisis Using Bedside Functional Residual Capacity Measurement: A Prospective Feasibility Study

Address for Correspondence / Yaz›flma Adresi: Mehmet Akif Topcuoglu, MD, Department of Neurology, Faculty of Medicine, Hacettepe University, Ankara, Turkey Phone: +90 312 305 18 06 e.mail: mat@hacettepe.edu.tr doi:10.5152/dcbybd.2012.09 Aim: Extubation failure often complicates the recovery phase of a myasthenic crisis (MC). Bedside functional residual capacity (FRC) is a relatively new technique shown to be promising in the improvement of ventilation management in the intensive care unit (ICU), and may have a role in the estimation of extubation success. Since the prediction of extubation success is difficult due to the absence of formally evaluated disease-specific criteria, the appropriateness of any strategy described for non-neuromuscular conditions should be validated for specific neuromuscular diseases such as MC. In accordance, we designed a pilot study to determine the feasibility of bedside FRC measurement in the prediction of extubation success in MC and to determine its yield when added to the conventional parameters. Material and Methods: We prospectively studied the additive value of bedside FRC measurements to predict extubation outcome in 11 MC episodes. The area under the receiver operating characteristic curve (ROC AUC), sensitivity and specificity of all weaning and extubation indices that passed exploratory analysis were determined. Results: The frequency of extubation failure, defined as the need for reinstitution of ventilatory support within 72 hours of planned endotracheal tube removal, was 55% in this study population, in which all patients met the standard weaning indices indicating safety of extubation. The risk of extubation failure was connected to higher airway pressures (peak inspiratory and plato pressures; PIP and Pplato; ROC AUCs: 0.933 and 0.917), increased gradient of end-tidal CO2 to arterial CO2 (CO2 gradient; ROC AUC:0.900) and total airway care score (ACS; ROC AUC:0.983), but not to FRC, the simplified acute physiology score (SAPS-II) and the traditional weaning criteria such as the rapid shallow breathing index (RSBI) and mouth occlusion pressure (P0.1). Although perhaps useful when measurable, the utility of maximal inspiratory/expiratory mouth pressures (MIP and MEP) was also low due to the inability of MC patients to perform the maneuvers required to obtain these parameters. In contrast, FRC measurement was easily attainable at the bedside, with zero risk to the patient and correlated well to the aerated lung volume measured by chest CT (r=0.717). Conclusion: This preliminary study suggests that bedside FRC measurement is safe and feasible for long-term monitoring of intubated myasthenic patients. Its utility in determining weaning and extubation outcomes requires further studies with larger samples. Standard weaning parameters may not be accurate enough in the prediction of extubation outcome in MC, probably reflecting differences in the pathophysiology of failure of extubation and weaning. As a new semi-objective measurement of pulmonary secretion status, ACS can be helpful in the identification of the risk of extubation failure. (Yogun Bakim Derg 2012; 3: 36-42)

Cross-Sectional Assessment of the Relationships between Dyspnea Domains and Lung Function in Diffuse Parenchymal Lung Disease

Background: Activity-related dyspnea is the main contributor to the altered quality of life in diffuse parenchymal lung diseases (DPLD). Instruments pertaining to dyspnea are classified as pertaining to domains of sensory-perceptual experience, affective distress or symptom/disease impact; whether these domains are equally related to lung function impairments remains to be established. Objectives: They were to assess the relationships between two domains of dyspnea (sensory-perceptual experience and symptom impact) and pulmonary function tests according to their evaluation of ventilatory demand, capacity and drive in patients suffering from DPLD. Methods: Fifty patients were prospectively enrolled (median age, 58 years; 25 women) and underwent spirometry, body plethysmography, measurements of lung diffusion for carbon monoxide (DL<smlcap>CO</smlcap>) and nitric oxide, maximal airway pressures (capacity and demand assessments), mouth occlusion pressure at 0.1 s (P_0.1: respiratory drive assessment) and a 6-min walk test with Borg score assessment (dyspnea: sensory domain). The impact domain of dyspnea was evaluated using the baseline dyspnea index. Results: The sensory domain of dyspnea was linked to demand (CO transfer coefficient, k<smlcap>CO</smlcap>) only, while the impact domain was independently linked to demand and capacity (k<smlcap>CO</smlcap> and forced vital capacity, respectively). Among resting pulmonary function tests, both P_0.1 and DL<smlcap>CO</smlcap> allowed the assessment of these two domains of dyspnea. Conclusions: In DPLD, the sensory-perceptual domain of dyspnea is mainly linked to alterations in ventilatory demand while the impact domain is related to both demand and capacity. DL<smlcap>CO</smlcap> that assesses both demand and capacity and P_0.1 were the strongest correlates of dyspnea.

Relation of respiratory muscle strength, cachexia and survival in severe chronic heart failure

BackgroundRespiratory muscle (RM) function predicts prognosis in non-cachectic patients with chronic heart failure (CHF). We hypothesized that weakness of RM (maximum inspiratory mouth occlusion pressure, Pimax) is a function of body mass index, and that outcome is more a function of BMI than of Pimax or ventilatory drive (P0.1).Subjects and methodsWe enrolled 249 CHF patients (11.2 % female, median age 54.2 years) at the German Heart Institute Berlin. Patients were in NYHA classes I/II/III/IV by n = 16/90/108/35. All patients underwent tests of pulmonary function, RM (Pimax, P0.1), cardiopulmonary exercise testing (peakVO2, VE/VCO2-slope), and right heart catheterization.ResultsMean follow-up time was 18 (1–36) months, 47 patients (18.9 %) died or underwent cardiac assist implantation. Pimax correlated weakly with BMI (r = 0.19), peakVO2 (r = 0.15), and FEV1 (r = 0.34, all p < 0.02), and was lower in females compared to males (3.9 ± 1.7 vs. 6.6 ± 2.7 kPa; p < 0.001). P0.1 correlated with pulmonary pressure (rho = 0.2; p < 0.01) and peakVO2 (rho = −0.14; p < 0.02). Neither Pimax [hazard ratio (HR) 0.98; confidence interval (CI) 0.88–1.08] nor P0.1 (HR 0.52; 0.06–4.6) predicted survival. Multivariate regression analysis revealed gender, BMI, and FEV1 as cofactors of Pimax, with only BMI (HR 0.87; CI 0.80–0.95) predicting survival independently. The lowest quintile in BMI had the worst outcome (log-rank χ² = 13.5, p = 0.009).SummaryIn CHF patients including cachexia and NYHA IV, Pimax does not predict survival. Pimax depends on gender, BMI, FEV1, and peakVO2, with only BMI and peakVO2 predicting survival. The impaired Pimax in CHF might be a result of catabolism and weight loss and is not a predictive factor in itself.

Respiratory muscle function in interstitial lung disease

Interstitial lung diseases limit daily activities, impair quality of life and result in (exertional) dyspnoea. This has mainly been attributed to a decline in lung function and impaired gas exchange. However, the contribution of respiratory muscle dysfunction to these limitations remains to be conclusively investigated. Interstitial lung disease patients and matched controls performed body plethysmography, a standardised 6-min walk test, volitional tests (respiratory drive (P0.1), global maximal inspiratory mouth occlusion pressure (PImax), sniff nasal pressure (SnPna) and inspiratory muscle load) and nonvolitional tests on respiratory muscle function and strength (twitch mouth and transdiaphragmatic pressure during bilateral magnetic phrenic nerve stimulation (TwPmo and TwPdi)). 25 patients and 24 controls were included in the study. PImax and SnPna remained unaltered (both p>0.05), whereas P0.1 and the load on the inspiratory muscles were higher (both p<0.05) in interstitial lung disease patients compared with controls. TwPmo and TwPdi were lower in interstitial lung disease patients (mean±sd TwPmo 0.86±0.4 versus 1.32±0.4, p<0.001; TwPdi 1.34±0.6 versus 1.88±0.5, p=0.022). Diaphragmatic force generation seems to be impaired in this cohort of interstitial lung disease patients while global respiratory muscle strength remains preserved. Central respiratory drive and the load imposed on the inspiratory muscles are increased. Whether impaired respiratory muscle function impacts morbidity and mortality in interstitial lung disease patients needs to be investigated in future studies.

Respiratory function in late-onset Pompe disease patients receiving long-term enzyme replacement therapy for more than 48 months

Respiratory impairment is the most important prognostic factor in patients with adult-onset Pompe disease. The effect of long-term enzyme replacement therapy (ERT) on pulmonary function remains unclear.Respiratory parameters (vital capacity (VCmax); forced expiratory volume (FEV1); peak expiratory flow (PEF); and blood gas analysis) were monitored every 6 months during a treatment period of 48-77 months of ERT in six patients with genetically and biochemically confirmed adult-onset Pompe disease. Postural drop of VCmax from sitting to supine position, maximal inspiratory muscle pressure (PImax), mouth occlusion pressure after 100 ms (P0.1), and peak cough flow (PCF) were measured over a period of 12 months. Mean change to baseline were +8.8 % points for ΔVCmax, +6.2 % points for ΔFEV1, and +6.6 % points for ΔPEF after 48 months of ERT. In one patient, a decrease of respiratory parameters with later stabilization was observed under ERT until month 42, but noninvasive ventilation (NIV) had to be initiated due to nocturnal desaturation. In the final 12 months period, progressive diaphragm weakness was detected in 3/6 patients (median change in VC% drop +8 %).ERT seems to stabilize pulmonary function and may delay the requirement for ventilation in patients with late-onset Pompe disease.

Pulmonary Function and Expiratory Flow Limitation in Acute Cervical Spinal Cord Injury

Alvisi V, Marangoni E, Zannoli S, Uneddu M, Uggento R, Farabegoli L, Ragazzi R, Milic-Emili J, Belloni GP, Alvisi R, Volta CA. Pulmonary function and expiratory flow limitation in acute cervical spinal cord injury. ObjectiveTo identify the nature of the changes of respiratory mechanics in patients with middle cervical spinal cord injury (SCI) and their correlation with posture. DesignClinical trial. SettingAcute SCI unit. ParticipantsPatients with SCI (N=34) at C4-5 level studied within 6 months of injury. InterventionsPatients were assessed by the negative expiratory pressure test, maximal static respiratory pressure test, and standard spirometry. Main Outcome MeasuresThe following respiratory variables were recorded in both the semirecumbent and supine positions: (1) tidal expiratory flow limitation (TEFL); (2) airway resistances; (3) mouth occlusion pressure developed 0.1 seconds after occluded inspiration at functional residual capacity (P0.1); (4) maximal static inspiratory pressure (MIP) and maximal static expiratory pressure (MEP); and (5) spirometric data. ResultsTEFL was detected in 32% of the patients in the supine position and in 9% in the semirecumbent position. Airway resistances and P0.1 were much higher compared with normative values, while MIP and MEP were markedly reduced. The ratio of forced expiratory volume in 1 second to forced vital capacity was less than 70%, while the other spirometric data were reduced up to 30% of predicted values. ConclusionsPatients with middle cervical SCI can develop TEFL. The presence of TEFL, associated with increased airway resistance, could increase the work of breathing in the presence of a reduced capacity of the respiratory muscles to respond to the increased load. The semirecumbent position and the use of continuous positive airway pressure can be helpful to (1) reduce the extent of TEFL and avoid the opening/closure of the small airways; (2) decrease airway resistance; and (3) maintain the expiratory flow as high as possible, which aids in the removal of secretions.

Breath-Hold Diving

Extensive breath-hold (BH) diving imposes high pulmonary stress by performing voluntary lung hyperinflation maneuvers (glossopharyngeal insufflation, GI), hyperinflating the lung up to 50% of total lung capacity. Breath-hold durations of up to 10 min without oxygen support may also presume cerebral alterations of respiratory drive. Little is known about the long-term effects of GI onto the pulmonary parenchyma and respiratory adaptation processes in this popular extreme sport. Lung function assessments and subsequent measures of pulmonary static compliance were obtained for 5 min after GI in 12 elite competitive breath-hold divers (BHD) with a mean apnea diving performance of 6.6 yr. Three-year follow-up measurements were performed in 4 BHD. Respiratory drive was assessed in steady-state measurements for 6% and 9% CO2 in ambient air. Short-term pulmonary stress effects for static compliance during GI (13.75 L·kPa) could be confirmed in these 12 divers without exhibiting permanent changes to the lungs' distensibility (7.41 L·kPa) or lung function parameters as confirmed by the follow-up measurements and for 4 BHD after 3 yr (P>0.05). Respiratory drive was significantly reduced in these BHD revealing a characteristic breathing pattern with a significant increase in VE and mouth occlusion pressure (P0.1) between free breathing and 6% CO2, as well as between 6% CO2 and 9% CO2 (all P<0.001). BH diving with performance of GI does not permanently alter pulmonary distensibility or impair ventilatory flows and volumes. A blunted response to elevated CO2 concentrations could be demonstrated, which was supportive of the hypothesis that CO2 tolerance is a training effect due to BH diving rather than being an inherited phenomenon.

A Decision-Tree Model for Predicting Extubation Outcome in Elderly Patients After a Successful Spontaneous Breathing Trial

The commonly used single tests, based on a 1-time measurement of a physiologic variable, are often poorly predictive of tracheal extubation outcome because they examine only a single aspect of physiological function that affects the extubation outcome. We hypothesized that the construction of a decision-tree model, which includes multiple variables and considers the changes of these variables, may more accurately predict successful extubation. This was a prospective observational study. From 2007 to 2008, 113 elderly patients in the medical intensive care unit on ventilation for >48 hours were enrolled. All patients underwent a 60-minute spontaneous breathing trial (SBT) [positive end-expiratory pressure of 5 cm H(2)O; automatic tube compensation, 100%]. Patients tolerating the trial were extubated immediately. The mouth occlusion pressure (P(0.1)), rapid shallow breathing index (RSBI,) and their combination (P(0.1) × RSBI) were recorded at the first, 30th, and 60th minute of the SBT. The changes in RSBI, which were determined at the 30th and 60th minute of the SBT (ΔRSBI30, ΔRSBI60), were assessed as the ratio (of RSBI30 or RSBI60) to RSBI at the first minute of the SBT. Twenty-two patients (19.5%) failed the SBT and were not included in the analysis, and 91 tolerated the trial and were extubated. At 48 hours, 73 (80.2%) remained extubated (successful extubation), and 18 (19.8%) required reintubation (extubation failure). Although theΔRSBI(30) was significantly higher in the extubation failure patients (118% ± 34%) than that in the successful extubation patients (93% ± 35%, P = 0.01), the receiver operating characteristic (ROC) analysis demonstrated that this index, with the threshold of <98%, presented poor performance in predicting successful extubation with area under the ROC curve (AUC) of only 0.76. The classification and regression-tree analysis selected 3 variables (P(0.1) × RSBI(30), RSBI(1), ΔRSBI(30)) and began with P(0.1) × RSBI(30). For patients with P(0.1) × RSBI-(30) >474 cmH(2)O*breaths/min/L, ΔRSBI(30) >98% defined a group including all failure patients but no success patients, whereas ΔRSBI(30) ≤98% included all success patients with no failure patients. For patients with P(0.1) × RSBI(30) ≤474 cm H(2)O*breaths/min/L, the combination of both a P(0.1) × RSBI(30) >328 cm H(2)O*breaths/min/L and RSBI(1) >112 breaths/min/L also defined a group including all success patients but no failure patients. Indeed, the diagnostic accuracy (DA) of the tree model, which was 89.1% with only the P(0.1) × RSBI(30) included, increased to 94.5% when both the P(0.1) × RSBI(30) and ▵RSBI(30) were included. The final tree model with the inclusion of all 3 discriminators could capture the successful extubation with diagnostic accuracy of 96.7%, AUC of 0.94 (95% confidence interval [CI], 0.87 to 0.98). If the current tree model is confirmed by a prospective study with a larger sample size, it would be useful in guiding physicians making extubation decisions in elderly medical intensive care unit patients.

Effects of interval exercise training on respiratory drive in patients with chronic heart failure

Patients with chronic heart failure (CHF) suffer from ventilatory abnormalities. This study examined the effects of interval exercise training on the respiratory drive in CHF patients. Forty-six clinically stable CHF patients (38 males/8 women, mean age = 53 +/- 11 years) participated in an exercise rehabilitation program (ERP) 3 times/week, for 12 weeks by interval training modality with or without the addition of resistance training. All patients underwent symptom-limited cardiopulmonary exercise testing (CPET), and measurements of mouth occlusion pressure at 100 ms (P(0.1)) and maximum inspiratory muscle strength (P(Imax)) before and after ERP. Respiratory drive was estimated by mouth occlusion pressure P(0.1) and P(0.1)/P(Imax) ratio at rest, and the ventilatory pattern by resting mean inspiratory flow (V(T)/T(I)) and by V(T)/T(I) at identical CPET workloads, before and after ERP. We also studied a control non exercising group of 11 patients (8 men and 3 women). P(0.1) at rest decreased from 3.04 +/- 1.52 to 2.62 +/- 0.9 cmH(2)O (p = 0.015), P(0.1)/P(Imax) % at rest from 4.56 +/- 3.73 to 3.69 +/- 2.03 (p = 0.006), resting V(T)/T(I) from 0.44 +/- 0.10 to 0.41 +/- 0.10 l/s (p = 0.014), and V(T)/T(I) at identical work rate from 2.13 +/- 0.59 to 1.93 +/- 0.58 l/s (p = 0.001) after ERP. VO(2) at peak exercise increased from 16.3 +/- 4.8 to 18.5 +/- 5.3 ml/kg/min (p < 0.001) in the exercise group. No improvement was noted in the control group. ERP by interval training improves the respiratory drive and ventilatory pattern at rest and during exercise in CHF patients.