Exercise Effects on Maternal Vascular Health and Blood Pressure during Pregnancy and Postpartum: A Systematic Review and Meta-Analysis.

AIM: This systematic review aimed to assess the effects of exercise training during pregnancy and the postpartum period on maternal vascular health and blood pressure (BP). METHODS: The outcome of interest were pulse wave velocity (PWV), flow-mediated dilation (FMD), and BP from pregnancy until 1-year postpartum. Five databases, including Ovid MEDLINE, EMBASE, CINAHL, Web of Science, and Cochrane Library, were systematically searched from inception to August 2023. Studies of randomized controlled trials (RCTs) comparing the effects of prenatal or postpartum exercise to a non-exercise control group were included. The risk of bias and the certainty of evidence were assessed. Random-effects meta-analyses and sensitivity analyses were conducted. RESULTS: In total, 20 RCTs involving 1,221 women were included. Exercise training, initiated from week 8 during gestation or between 6-14 weeks after delivery, with the program lasting for a minimum of 4 weeks up to 6 months, showed no significant impact on PWV and FMD. However, it resulted in a significant reduction in systolic BP (SBP) (MD: -4.37 mmHg; 95% CI: -7.48 to -1.26; p = 0.006) and diastolic BP (DBP) (MD: -2.94 mmHg; 95% CI: -5.17 to -0.71; p = 0.01) with very low certainty. Subgroup analyses revealed consistent trends across different gestational stages, types of exercise, weekly exercise times, and training periods. CONCLUSION: Exercise training during pregnancy and the postpartum period demonstrates a favorable effect on reducing maternal BP. However, further investigations with rigorous methodologies and larger sample sizes are needed to strengthen these conclusions.

This systematic review of the literature demonstrates that exercise training during pregnancy and postpartum can reduce blood pressure in women. Key findings: Exercise training significantly decreased both systolic and diastolic blood pressure values in pregnant and postpartum women.The positive exercise effects on maternal blood pressure were consistently observed regardless of the specific stage of pregnancy, type of exercise, frequency of weekly exercise sessions, or duration of the training programs.

Inclusion of Exercise Prescription in Solid Organ Transplant in Physical Therapy Curricula Across Canadian Universities: A National Survey.

Purpose: This study evaluated the extent of education about exercise prescription for patients with solid organ transplant (SOT) provided in physical therapy (PT) entry-level programmes across Canadian universities. The nature (content being taught), delivery (modes used to disseminate information), time dedicated to the topic, and opinions of educators were explored. Method: A cross-sectional survey was emailed to 36 educators at Canadian universities. The survey questions related to the nature, delivery, and time dedicated to SOT exercise prescription, and the opinions of educators. Results: The response rate was 93%. Educators reported that lung and heart transplantation were taught the most, followed by kidney and liver, with little to no emphasis on pancreas transplants. This material was mainly taught at the graduate level and as part of cardiopulmonary courses with minimal emphasis on practical skills. Aerobic exercise is the main exercise prescription being taught. The main barrier to offering more SOT prescription education experienced by educators was the lack of available class time. Conclusions: SOT exercise prescription is not extensively covered in PT curricula and does not include all organ groups to the same extent. Students have few practical opportunities, which are important to gain the abilities and confidence to treat this population. The development of a continuing education course could promote greater knowledge.

Objectif : évaluer la portée de l'éducation fournie par les programmes de physiothérapie des universités canadiennes pour l'entrée en pratique à l'égard des prescriptions d'exercices aux patients ayant une transplantation d'organe plein (TOP). Les auteurs ont exploré la nature (matière enseignée), la prestation (modes de diffusion de l'information), le temps consacré au sujet et les avis des éducateurs sur la question. Méthodologie : les auteurs ont envoyé un sondage transversal par courriel à 36 éducateurs d'universités canadiennes. Les questions du sondage portaient sur la nature, la prestation, le temps consacré aux prescriptions d'exercices aux TOP et les avis des éducateurs. Résultats : le taux de réponse s'est élevé à 93 %. Les éducateurs ont indiqué que les transplantations des poumons et du cœur étaient les plus enseignées, suivies des reins et du foie, et que celles du pancréas étaient très peu abordées, sinon pas du tout. Cette matière était surtout enseignée aux cycles supérieurs, dans le cadre de cours cardiorespiratoires qui s'attardaient très peu aux habiletés pratiques. L'exercice aérobique était la principale prescription d'exercices enseignée. Selon les éducateurs, le manque de temps en classe était le principal obstacle à l'offre d'une période d'éducation plus prolongée sur les prescriptions aux TOP. Conclusions : les prescriptions d'exercices aux TOP ne sont pas approfondies dans les programmes de physiothérapie et n'accordent pas la même importance à tous les groupes d'organes. Les étudiants ont peu de possibilités d'exercice pratique, ce qui est toutefois important pour acquérir les habiletés et la confiance nécessaires pour traiter cette population. La création d'une formation continue pourrait favoriser l'accroissement des connaissances.

Intensive care unit clinicians identify many barriers to, and facilitators of, early mobilisation: a qualitative study using the Theoretical Domains Framework.

QUESTION: From the perspective of intensive care unit (ICU) clinicians, what are the barriers to and facilitators of implementing early mobilisation? DESIGN: A qualitative study using focus groups, with analysis using the Theoretical Domains Framework. PARTICIPANTS: Physicians, nurses, respiratory therapists and physiotherapists from the ICUs of three university-affiliated hospitals in Montreal, Canada. METHODS: Four focus group meetings were conducted with 33 participating ICU clinicians. Two researchers independently performed thematic content analysis on verbatim transcriptions of the audio recordings using the Theoretical Domains Framework. RESULTS: Data saturation was reached after the third focus group. Thirty-six barriers were categorised in 13 domains of the Theoretical Domains Framework. The key barriers to early mobilisation were: lack of conviction and knowledge regarding the available evidence about early mobilisation; lack of attention to the provision of optimal care; poor communication; the unpredictable nature of the ICU; and limited staffing, equipment, time and clinical knowledge. Twenty-five facilitators categorised in ten TDF domains were also identified. These included individual-level facilitators (intrinsic motivation, positive outcome expectations, conscious effort to mobilise early, good planning/coordination, the presence of ICU champions, and expert support by a physiotherapist) and organisational-level facilitators (reminder system, pro-early mobilisation culture, implementation of an early mobilisation protocol, and improved ICU organisation). CONCLUSIONS: A broad array of barriers to and facilitators of early mobilisation in the ICU were identified in this study. Clinicians can consider whether these barriers and facilitators are operating in their ICU. These may inform the design of tailored knowledge translation interventions to promote early mobilisation in the ICU.

Early rehabilitation reduces the likelihood of developing intensive care unit-acquired weakness: a systematic review and meta-analysis.

BACKGROUND: Intensive care unit-acquired weakness (ICUAW) is associated with significant impairments in body structure and function, activity limitation, and participation restriction. The etiology and management of ICUAW remain uncertain. OBJECTIVE: To estimate the extent to which early rehabilitation interventions (early mobilization [EM] and/or neuromuscular electrical stimulation [NMES]) compared to usual care reduce the incidence of ICUAW in critically ill patients. DATA SOURCES: We searched MEDLINE, EMBASE, CINAHL, Cochrane Central and Physiotherapy Evidence Database databases from inception to May 1st, 2017. ELIGIBILITY CRITERIA: Randomized controlled trials of EM and/or NMES interventions in critically ill adults. DATA EXTRACTION AND DATA SYNTHESIS: Data on the incidence of ICUAW and secondary outcomes were extracted. Both odds and risk ratios for ICUAW were pooled using the random-effects model. RESULTS: We identified 1421 reports after duplicate removal. Nine studies including 841 patients (419 intervention and 422 usual care) were included in the final analysis. The interventions involved EM in five trials, NMES in three trials, and both EM and NMES in one trial. Early rehabilitation decreased the likelihood of developing ICUAW: odds ratio of 0.63 (95% CI: 0.43 to 0.92) in the screened population, and 0.71 (95% CI: 0.53 to 0.95) in the randomized population. CONCLUSION, IMPLICATIONS OF KEY FINDINGS: Early rehabilitation was associated with a decreased likelihood of developing ICUAW. Our findings support early rehabilitation in the ICU. While results were consistent in both the screened and randomized populations, the wide confidence intervals suggest that well-conducted trials are needed to validate our findings. SYSTEMATIC REVIEW REGISTRATION NUMBER: PROSPERO registration ID: CRD42017065031.

Interprofessional Survey of Perceived Barriers and Facilitators to Early Mobilization of Critically Ill Patients in Montreal, Canada.

OBJECTIVE: Early mobilization is safe, feasible, and associated with better outcomes in patients with critical illness. However, barriers to mobilization in clinical practice still exist. The objective of this study was to assess the knowledge and practice patterns of intensive care unit (ICU) clinicians, as well as the barriers and facilitators to early mobilization. DESIGN: Cross-sectional survey. SETTING: Intensive care units of 3 university-affiliated hospitals in Montreal, Canada. PARTICIPANTS: One hundred and thirty-eight ICU clinicians, including nurses, physicians, respiratory therapists, and physiotherapists. INTERVENTIONS: None. MEASUREMENTS: Perceived barriers, facilitators, knowledge, and practice patterns of early mobilization were assessed using a previously validated mobility survey tool. MAIN RESULTS: The overall response rate was 50.0% (138 of 274). Early mobilization was not perceived as a top priority in 49% of respondents. Results showed that clinicians were not fully aware of the benefits of early mobilization as per the current literature. About 58% of clinicians did not feel well trained and informed to mobilize mechanically ventilated patients. Perceptions on patient-level barriers varied with clinicians' professional training, but there was a high degree of interprofessional and intraprofessional disagreement on the permissible maximal level activity in different scenarios of critically ill patients. CONCLUSIONS: Our survey shows limited awareness, among our respondents, of the clinical benefits of early mobilization and high level of disagreement on the permissible maximal level of activity in the critically ill patients. Future studies should evaluate the role of knowledge translation in modifying these barriers and improving early mobilization.

Mechanical ventilation modulates pro-inflammatory cytokine expression in spinal cord tissue after injury in rats.

RATIONALE: Spinal cord injury (SCI) may induce significant respiratory muscle weakness and paralysis, which in turn may cause a patient to require ventilator support. Central nervous system alterations can also exacerbate local inflammatory responses with immune cell infiltration leading to additional risk of inflammation at the injury site. Although mechanical ventilation is the traditional treatment for respiratory insufficiency, evidence has shown that it may directly affect distant organs through systemic inflammation. OBJECTIVES: This study aimed to better understand the impact of invasive mechanical ventilation on local spinal cord inflammatory responses following cervical or thoracic SCI. METHODS: Five groups of female Sprague-Dawley rats were anesthetised for 24 h. Three groups received mechanical ventilation: seven rats without SCI, seven rats with cervical injury (C4-C5), and seven rats with thoracic injury (T10); whereas, two groups were non-ventilated: six rats without SCI; and six rats with thoracic injury (T10). Changes in inflammatory responses were determined in the spinal cord tissues collected at the local site of injury. Cytokines were measured using ELISA. MAIN RESULTS: SCI induced local pro-inflammatory cytokine IL-6 expression for all groups. Mechanical ventilation also had effects on pro-inflammatory cytokines and independently increased TNF-α and decreased IL-1ß levels in the spinal cords of anesthetized rats. CONCLUSION: These data provide the first evidence that mechanical ventilation contributes to local inflammation after SCI and in the absence of direct tissue injury.

Effects of Pressure Support Ventilation May Be Lost at High Exercise Intensities in People with COPD.

Pressure support ventilation (PSV) may be used for exercise training in chronic obstructive pulmonary disease (COPD), but its acute effect on maximum exercise capacity is not fully known. The objective of this study was to evaluate the effect of 10 cm H2O PSV and a fixed PSV level titrated to patient comfort at rest on maximum exercise workload (WLmax), breathing pattern and metabolic parameters during a symptom-limited incremental bicycle test in individuals with COPD. Eleven individuals with COPD (forced expiratory volume in one second: 49 ± 16%; age: 64 ± 7 years) performed three exercise tests: without a ventilator, with 10 cm H2O of PSV and with a fixed level titrated to comfort at rest, using a SERVO-i ventilator. Tests were performed in randomized order and at least 48 hours apart. The WLmax, breathing pattern, metabolic parameters, and mouth pressure (Pmo) were compared using repeated measures analysis of variance. Mean PSV during titration was 8.2 ± 4.5 cm H2O. There was no difference in the WLmax achieved during the three tests. At rest, PSV increased the tidal volume, minute ventilation, and mean inspiratory flow with a lower end-tidal CO2; this was not sustained at peak exercise. Pmo decreased progressively (decreased unloading) with PSV at workloads close to peak, suggesting the ventilator was unable to keep up with the increased ventilatory demand at high workloads. In conclusion, with a Servo-i ventilator, 10 cm H2O of PSV and a fixed level of PSV established by titration to comfort at rest, is ineffective for the purpose of achieving higher exercise workloads as the acute physiological effects may not be sustained at peak exercise.

Quality of life, symptom status and physical performance in patients with advanced non-small cell lung cancer undergoing chemotherapy: an exploratory analysis of secondary data.

OBJECTIVES: Our objectives were: (a) to identify predictors of change in health-related quality of life (HRQOL) in patients with advanced non-small cell lung cancer (NSCLC) undergoing chemotherapy; and (b) to characterize symptom status, nutritional status, physical performance and HRQOL in this population and to estimate the extent to which these variables change following two cycles of chemotherapy. METHODS: A secondary analysis of a longitudinal observational study of 47 patients (24 men and 23 women) with newly diagnosed advanced NSCLC receiving two cycles of first-line chemotherapy was performed. Primary outcomes were changes in HRQOL (physical and mental component summaries (PCS and MCS) of the 36-item Short-Form Health Survey (SF-36)). Predictors in the models included pre-chemotherapy patient-reported symptoms (Schwartz Cancer Fatigue Scale (SCFS) and Lung Cancer Subscale), nutritional screening (Patient-Generated Subjective Global Assessment) and physical performance measures (6-min Walk Test (6MWT), one-minute chair rise test and grip strength). RESULTS: Mean SF-36 PCS score, 6MWT distance and grip strength declined following two cycles of chemotherapy (p<0.05). Multiple linear regression modelling revealed pre-chemotherapy SCFS score and 6MWT distance as the strongest predictors of change in the mental component of HRQOL accounting for 13% and 9% of the variance, respectively. No significant predictors were found for change in the physical component of HRQOL. CONCLUSIONS: Pre-chemotherapy 6MWT distance and fatigue severity predicted change in the mental component of HRQOL in patients with advanced NSCLC undergoing chemotherapy, while physical performance declined during treatment. Clinical management of these factors may be useful for HRQOL optimization in this population.

Spinal cord injury modulates the lung inflammatory response in mechanically ventilated rats: a comparative animal study.

Mechanical ventilation (MV) is widely used in spinal injury patients to compensate for respiratory muscle failure. MV is known to induce lung inflammation, while spinal cord injury (SCI) is known to contribute to local inflammatory response. Interaction between MV and SCI was evaluated in order to assess the impact it may have on the pulmonary inflammatory profile. Sprague Dawley rats were anesthetized for 24 h and randomized to receive either MV or not. The MV group included C4-C5 SCI, T10 SCI and uninjured animals. The nonventilated (NV) group included T10 SCI and uninjured animals. Inflammatory cytokine profile, inflammation related to the SCI level, and oxidative stress mediators were measured in the bronchoalveolar lavage (BAL). The cytokine profile in BAL of MV animals showed increased levels of TNF-α, IL-1ß, IL-6 and a decrease in IL-10 (P = 0.007) compared to the NV group. SCI did not modify IL-6 and IL-10 levels either in the MV or the NV groups, but cervical injury induced a decrease in IL-1ß levels in MV animals. Cervical injury also reduced MV-induced pulmonary oxidative stress responses by decreasing isoprostane levels while increasing heme oxygenase-1 level. The thoracic SCI in NV animals increased M-CSF expression and promoted antioxidant pulmonary responses with low isoprostane and high heme oxygenase-1 levels. SCI shows a positive impact on MV-induced pulmonary inflammation, modulating specific lung immune and oxidative stress responses. Inflammation induced by MV and SCI interact closely and may have strong clinical implications since effective treatment of ventilated SCI patients may amplify pulmonary biotrauma.

Bi-level Positive Airway Pressure (BiPAP) with standard exhalation valve does not improve maximum exercise capacity in patients with COPD.

BACKGROUND: Although BiPAP has been used as an adjunct to exercise, little is know about its effect on exercise in COPD. We aimed to evaluate the acute effect of BiPAP delivered with a standard valve (Vision, Respironics), compared to no assist, on exercise capacity in individuals with COPD. METHODS: Peak exercise workload (WLpeak), dyspnea (Borg), end-expiratory lung volume (EELV), tidal volume (VT), minute ventilation (VE), O2 uptake (VO2), and CO2 production (VCO2) were assessed in 10 COPD patients (FEV1 53 ± 22% pred) during three symptom-limited bicycle exercise tests while breathing i) without a ventilator (noPS), ii) with a pressure support (PS) of 0 cm H2O (PS0; IPAP & EPAP 4 cm H2O) and iii) PS of 10 cm H2O (PS10; IPAP 14 & EPAP 4 cm H2O) on separate days using a randomized crossover design. RESULTS: WLpeak was significantly lower with PS10 (33 ± 16) and PS0 (30.5 ± 13) than noPS (43 ± 19) (p < 0.001). Dyspnea at peak exercise was similar with noPS, PS0 and PS10; at isoload it was lower with noPS compared to PS10 and PS0 (p < 0.01). VT and VE were highest with PS10 and lowest with noPS both at peak exercise and isoload (p < 0.001). EELV was similar at peak exercise with all three conditions. VO2 and VCO2 were greater with PS10 and PS0 than noPS (p < 0.001), both at peak exercise and isoload. CONCLUSION: Use of BiPAP with a standard exhalation valve during exercise increases VT and VE at the expense of augmenting VCO2 and dyspnea, which in turns reduces WLpeak in COPD patients.

Combining both generic and disease-specific properties: development of the McGill COPD quality of life questionnaire.

UNLABELLED: Presently, a generic and a disease-specific questionnaire are often co-administered to capture the different domains of quality of life in chronic obstructive pulmonary disease (COPD) subjects. A health-related-quality of life (HRQL) questionnaire in COPD combining both generic and disease-specific properties is needed. OBJECTIVE: To develop a new, hybrid-HRQL questionnaire, the McGill-COPD-questionnaire, with qualities of both generic and disease-specific instruments. Using pre-defined criteria, we selected items from the SF-36 to complement the items from a COPD-specific-module to create the new hybrid-HRQL-questionnaire. Domains were identified via confirmatory factor analysis. The McGill COPD questionnaire is available in English and French; it assesses three domains: symptoms, physical-function and feelings, has 29 items: 17 from the COPD-specific-module and 12 from the SF-36. The symptom sub-scale has 6 items, all from the COPD-specific-module; the feelings sub-scale has 10 items, 5 each from COPD-specific-module and SF-36 and the physical-function sub-scale has 13 items, 6 from COPD-specific-module and 7 from SF-36. The McGill COPD questionnaire was developed using a novel method of combining items from the SF-36 and a COPD-specific-module. Thus, this new questionnaire has items from a generic-questionnaire and a disease-specific-module and, hence, is promising to be a stand alone quality-of-life questionnaire for COPD subjects.

Factors discriminating spontaneous pursed-lips breathing use in patients with COPD.

Pursed-lips breathing (PLB) is often spontaneously performed by chronic obstructive pulmonary disease (COPD) patients. The aim of this study was to evaluate spontaneous PLB prevalence and to identify factors discriminating its use. Fifty-seven patients with COPD (FEV(1) = 44.3 +/- 17.4%pred) underwent pulmonary function testing and two incremental bicycle exercise tests. Peak workload (Wpeak), oxygen uptake (VO(2)peak), breathing pattern, and dyspnea (Borg scale) were measured in the first exercise test and spontaneous PLB performance in the second. Six patients spontaneously performed pursed-lips breathing during rest (PLBrest), exercise and recovery, 18 during exercise and recovery (PLBex), 7 during recovery only (PLBrec), 20 not at all (PLBno), and 6 performed other expiratory resistive maneuvers. PLBrest and PLBex patients exhibited a lower Wpeak, O(2) uptake, and minute ventilation (V(E)), greater expiratory flow limitation and higher slopes relating dyspnea to V(E) or W (%predicted). PLBrest patients were more hypercapnic, had a lower exercise tolerance and diffusion capacity, and greater flow limitation and hyperinflation. PLBrec and PLBno patients were indistinguishable with regard to pulmonary function, dyspnea, and exercise performance. The most significant independent predictors of spontaneous PLB use during exercise were FEV(1)/FVC and the slope relating dyspnea to V(E). Spontaneous PLB is most often performed by COPD subjects when ventilation is stimulated by exercise, and during recovery from exercise. Severity of airflow obstruction and the dyspnea experienced during exercise play an important role in determining whether or not PLB is spontaneously performed by COPD patients.

Patient-ventilator interaction during pressure support ventilation and neurally adjusted ventilatory assist.

OBJECTIVE: To compare the effect of pressure support ventilation and neurally adjusted ventilatory assist on breathing pattern, patient-ventilator synchrony, diaphragm unloading, and gas exchange. Increasing the level of pressure support ventilation can increase tidal volume, reduce respiratory rate, and lead to delayed ventilator triggering and cycling. Neurally adjusted ventilatory assist uses diaphragm electrical activity to control the timing and pressure of assist delivery and is expected to enhance patient-ventilator synchrony. DESIGN: Prospective, comparative, crossover study. SETTING: Adult critical care unit in a tertiary university hospital. PATIENTS: Fourteen nonsedated mechanically ventilated patients (n = 12 with chronic obstructive pulmonary disease). INTERVENTIONS: Patients were ventilated for 10-min periods, using two pressure support ventilation levels (lowest tolerable and +7 cm H2O higher) and two neurally adjusted ventilatory assist levels (same peak pressures and external positive end-expiratory pressure as with pressure support ventilation), delivered in a randomized order. MEASUREMENTS AND MAIN RESULTS: Diaphragm electrical activity, respiratory pressures, air flow, volume, neural and ventilator respiratory rates, and arterial blood gases were measured. Peak pressures were 17 +/- 6 cm H2O and 24 +/- 6 cm H2O and 19 +/- 5 cm H2O and 24 +/- 6 cm H2O with high and low pressure support ventilation and neurally adjusted ventilatory assist, respectively. The breathing pattern was comparable with pressure support ventilation and neurally adjusted ventilatory assist during low assist; during higher assist, larger tidal volumes (p = .003) and lower breathing frequencies (p = .008) were observed with pressure support ventilation. Increasing the assist increased cycling delays only with pressure support ventilation (p = .003). Compared with pressure support ventilation, neurally adjusted ventilatory assist reduced delays of ventilator triggering (p < .001 for low and high assist) and cycling (high assist: p = .004; low assist: p = .04), and abolished wasted inspiratory efforts observed with pressure support ventilation in six subjects. The diaphragm electrical activity and pressure-time product for ventilator triggering were lower with neurally adjusted ventilatory assist (p = .005 and p = .02, respectively; analysis of variance). Arterial blood gases were similar with both modes. CONCLUSIONS: Neurally adjusted ventilatory assist can improve patient-ventilator synchrony by reducing the triggering and cycling delays, especially at higher levels of assist, at the same time preserving breathing and maintaining blood gases.

Inspiratory muscle unloading by neurally adjusted ventilatory assist during maximal inspiratory efforts in healthy subjects.

BACKGROUND: Neurally adjusted ventilatory assist (NAVA) is a mode of mechanical ventilation in which the ventilator is controlled by the electrical activity of the diaphragm (EAdi). During maximal inspirations, the pressure delivered can theoretically reach extreme levels that may cause harm to the lungs. The aims of this study were to evaluate whether NAVA could efficiently unload the respiratory muscles during maximal inspiratory efforts, and if a high level of NAVA would suppress EAdi without increasing lung-distending pressures. METHOD: In awake healthy subjects (n = 9), NAVA was applied at increasing levels in a stepwise fashion during quiet breathing and maximal inspirations. EAdi and airway pressure (Paw), esophageal pressure (Pes), and gastric pressure, flow, and volume were measured. RESULTS: During maximal inspirations with a high NAVA level, peak Paw was 37.1 +/- 11.0 cm H(2)O (mean +/- SD). This reduced Pes deflections from - 14.2 +/- 2.7 to 2.3 +/- 2.3 cm H(2)O (p < 0.001) and EAdi to 43 +/- 7% (p < 0.001), compared to maximal inspirations with no assist. At high NAVA levels, inspiratory capacity showed a modest increase of 11 +/- 11% (p = 0.024). CONCLUSION: In healthy subjects, NAVA can safely and efficiently unload the respiratory muscles during maximal inspiratory maneuvers, without failing to cycle-off ventilatory assist and without causing excessive lung distention. Despite maximal unloading of the diaphragm at high levels of NAVA, EAdi is still present and able to control the ventilator.

Diaphragmatic function in advanced Duchenne muscular dystrophy.

The aim of this study was to assess diaphragm electrical activation and diaphragm strength in patients with advanced Duchenne muscular dystrophy during resting conditions. Eight patients with advanced Duchenne muscular dystrophy (age of 25 +/- 2 years) were studied during tidal breathing, maximal inspiratory capacity, maximal sniff inhalations, and magnetic stimulation of the phrenic nerves. Six patients were prescribed home mechanical ventilation (five non-invasive and one tracheotomy). Transdiaphragmatic pressure and diaphragm electrical activation were measured using an esophageal catheter. During tidal breathing (tidal volume 198 +/- 83 ml, breathing frequency 25 +/- 7), inspiratory diaphragm electrical activation was clearly detectable in seven out of eight patients and was 12 +/- 7 times above the noise level, and represented 45 +/- 19% of the maximum diaphragm electrical activation. Mean inspiratory transdiaphragmatic pressure during tidal breathing was 1.5 +/- 1.2 cmH2O, and during maximal sniff was 7.6 +/- 3.6 cmH2O. Twitch transdiaphragmatic pressure deflections could not be detected. This study shows that despite near complete loss of diaphragm strength in advanced Duchenne muscular dystrophy, diaphragm electrical activation measured with an esophageal electrode array remains clearly detectable in all but one patient.

Effects of imposed pursed-lips breathing on respiratory mechanics and dyspnea at rest and during exercise in COPD.

STUDY OBJECTIVES: To investigate the effect of volitional pursed-lips breathing (PLB) on breathing pattern, respiratory mechanics, operational lung volumes, and dyspnea in patients with COPD. SUBJECTS: Eight COPD patients (6 male and 2 female) with a mean (+/-SD) age of 58 +/- 11 years and a mean FEV1 of 1.34 +/- 0.44 L (50 +/- 21% predicted). METHODS: Wearing a tight-fitting transparent facemask, patients breathed for 8 min each, with and without PLB at rest and during constant-work-rate bicycle exercise (60% of maximum). RESULTS: PLB promoted a slower and deeper breathing pattern both at rest and during exercise. Whereas patients had no dyspnea with or without PLB at rest, during exercise dyspnea was variably affected by PLB across patients. Changes in the individual dyspnea scores with PLB during exercise were significantly correlated with changes in the end-expiratory lung volume (EELV) values estimated from inspiratory capacity maneuvers (as a percentage of total lung capacity; r2 = 0.82, p = 0.002) and with changes in the mean inspiratory ratio of pleural pressure to the maximal static inspiratory pressure-generating capacity (PcapI) [r2 = 0.84; p = 0.001], measured using an esophageal balloon, where PcapI was determined over the range of inspiratory lung volumes and adjusted for flow. CONCLUSION: PLB can have a variable effect on dyspnea when performed volitionally during exercise by patients with COPD. The effect of PLB on dyspnea is related to the combined change that it promotes in the tidal volume and EELV and their impact on the available capacity of the respiratory muscles to meet the demands placed on them in terms of pressure generation.

Effect of increased diaphragm activation on diaphragm power spectrum center frequency.

Increased transdiaphragmatic pressure, reduced muscle blood flow, and increased duty cycle have all been associated with a reduction in the center frequency (CFdi) of the diaphragm's electrical activity (EAdi). However, the specific influence of diaphragm activation on CFdi is unknown. We evaluated whether increased diaphragm activation would result in a greater decline in the CFdi when pressure-time product (PTPdi) was kept constant. Five healthy subjects performed periods of intermittent quasi-static diaphragmatic contractions with a fixed duty cycle. In separate runs, subjects targeted transdiaphragmatic pressures (Pdi) by performing end-inspiratory holds with the glottis open and expulsive maneuvers at end-expiratory lung volume (EELV). Diaphragm activation and pressures were measured with an electrode array and balloons mounted on an esophago-gastric catheter, respectively. The EAdi, which was 25+/-8%(S.D.) of maximum at EELV, increased to 61+/-8% (P<0.001) when an identical Pdi (averaging 31+/-13 cmH2O) was generated at a higher lung volume (77% of inspiratory capacity). The latter was associated with a 17% greater decline in CFdi (P=0.012). In order to reproduce at EELV, the decrease in CFdi observed at the increased lung volume, a two-fold increase in PTPdi was required. We conclude that CFdi responds specifically to increased diaphragm activation when pressure-time product remains constant.

Closed-loop control of respiratory drive using pressure-support ventilation: target drive ventilation.

By using diaphragm electrical activity (multiple-array esophageal electrode) as an index of respiratory drive, and allowing such activity above or below a preset target range to indicate an increased or reduced demand for ventilatory assistance (target drive ventilation), we evaluated whether the level of pressure-support ventilation can be automatically adjusted in response to exercise-induced changes in ventilatory demand. Eleven healthy individuals breathed through a circuit (18 cm H2O/L/second inspiratory resistance at 1 L/second flow; 0.5-1.0 L/second expiratory flow limitation) connected to a modified ventilator. Subjects breathed for 6-minute periods at rest and during 20 and 40 W of bicycle exercise, with and without target drive ventilation (the target was set to 60% of the increase in diaphragm electrical activity observed between rest and 20 W of unassisted exercise). With target drive ventilation during exercise, the level of pressure-support ventilation was automatically increased, reaching 13.3 +/- 4.0 and 20.3 +/- 2.8 cm H2O during 20- and 40-W exercise, respectively, whereas diaphragm electrical activity was reduced to a level within the target range. Both diaphragmatic pressure-time product and end-tidal CO2 were significantly reduced with target drive ventilation at the end of the 20- (p < 0.01) and 40-W (p < 0.001) exercise periods. Minute ventilation was not altered. These results demonstrate that target drive ventilation can automatically adjust pressure-support ventilation, maintaining a constant neural drive and compensating for changes in respiratory demand.