A method for noninvasive determination of inspiratory resistance during proportional assist ventilation

Currently available noninvasive methods for measuring inspiratory resistance (RI) are difficult to implement or interpret during assisted mechanical ventilation on account of the confounding effect of respiratory efforts (Pmus). We propose a simple method consisting of brief reductions in airway pressure (Paw) in the early part of the inflation phase (pulse). Paw, flow (V), and volume (V) are measured at the beginning of the pulse (T (0)), at the trough of the pulse (TI) and at a point 0.1 s before T(0) (T(-1)). Equations of motion of the form [Pmus + Paw = V. K(1) + V (2). K(2) +V. E] are generated for the data at the three time points (E = elastance, K(1) and K(2) are Rohrer's constants). These three equations can be solved for K(1) and K(2) if it is arranged that the pulse has appropriate configuration and timing, and if it is assumed that DeltaPmus/Deltat is constant over the brief pulse period. The method was tested in 67 patients ventilated with proportional assist ventilation (PAV). The results were compared with those obtained using the interrupter technique during a period of controlled mechanical ventilation (CMV). RI, expressed at a standard flow of 1 L. s(-)(1), was slightly higher during PAV (16.4 +/- 4.9 versus 15.5 +/- 4.5 cm H(2)O. L(-1). s, p < 0.001). The average difference was 0.9 +/- 2.0 cm H(2)O. L(-1). s, corresponding to 5.4 +/- 12.6% of the average of RCMV and RPAV. The correlation coefficient was 0.92 (p = 8E-28) with a slope (1.01) and intercept (0.8) not significantly different from 1.0 and 0, respectively. We conclude that brief negative pulses applied early during the inflation phase can be used to provide reliable estimates of inspiratory resistance during PAV.     

无创正压通气治疗慢性阻塞性肺疾病高碳酸血症的疗效观察

目的探讨无创正压通气治疗慢性阻塞性肺疾病（COPD）高碳酸血症的价值.方法58例COPD二氧化碳潴留患者随机分入治疗组及对照组,对照组仅行常规药物治疗,治疗组在常规药物治疗的基础上加用无创正压通气治疗.比较治疗开始2小时、24小时、7天两组同期血气、血压、心率、呼吸频率等改善情况.结果治疗组同期血气、血压、心率、呼吸频率等较对照组明显改善（P均＜0.05）.结论应用无创通气可明显改善COPD患者症状,提高PO2降低PCO2,对COPD高碳酸血症患者有确切疗效.     

Effects of noninvasive proportional assist vs pressure support ventilation on respiratory work in chronic obstructive pulmonary disease patients with hypercapnia

正Objective To investigate the effect of noninvasive proportional assist ventilation(PAV)on respiratory work in chronic obstructive pulmonary disease(COPD)patients,in comparison with noninvasive pressure support ventilation(PSV).Methods Ten severe COPD patients     

Mask proportional assist vs pressure support ventilation in patients in clinically stable condition with chronic ventilatory failure

OBJECTIVE: To compare the short-term physiologic effects of mask pressure support ventilation (PSV) and proportional assist ventilation (PAV) in patients in clinically stable condition with chronic ventilatory failure (CVF). DESIGN: Randomized, controlled physiologic study. SETTING: Lung function units of two pulmonary rehabilitation centers. PATIENTS: Eighteen patients with CVF caused by COPD (11 patients) and restrictive chest wall diseases (RCWDs) [7 patients]. METHODS: Assessment of breathing pattern and minute ventilation (E), respiratory muscles and lung mechanics, and patient/ventilator interaction during both unassisted and assisted ventilation. After baseline assessment during spontaneous breathing (SB), mask PSV and PAV were randomly applied at the patient's comfort, with the addition of the same level of continuous positive airway pressure (2 cm H2O or 4 cm H2O in all patients), for 30 min each, with a 20-min interval of SB between periods of assisted ventilation. RESULTS: A longer time was spent to set PAV than PSV (663 +/- 179 s and 246 +/- 58 s, respectively; p < 0.001). Mean airway opening pressure (Pao) computed over a period of 1 min, but not peak Pao, was significantly lower with PAV than with PSV (151 +/- 45 cm H2O/s/min and 207 +/- 73 cm H2O/s/min, respectively; p < 0.002). Tidal volume (VT) exhibited a greater variability with PAV than with PSV (variation coefficient, 16.3% +/- 10.5% vs 11.6% +/- 7.7%, respectively; p < 0.05). Compared with SB, both modalities resulted in a significant increase in VT (by 40% and 36% with PAV and PSV, respectively, on average) and E (by 37% and 35%) with unchanged breathing frequency and duty cycle. Both modalities significantly reduced esophageal (by 39% and 51%) and diaphragmatic (by 42% and 63%) pressure-time products, respectively. Ineffective efforts were observed with neither modes of assistance in any patient. CONCLUSIONS: In resting, awake patients in clinically stable condition with CVF caused by either COPD or RCWD, noninvasive application of PAV, set at the patient's comfort, was not superior to PSV either in increasing VT and E or in unloading the inspiratory muscles. We failed to find any difference in patient/ventilator interaction between ventilatory modes.     

Effects of nasal pressure support on ventilation and inspiratory work in normocapnic and hypercapnic patients with stable COPD

OBJECTIVES: To assess and compare the effect of nasal continuous positive airway pressure (nCPAP), inspiratory pressure support (PSV), and bilevel positive airway pressure (biPAP) on ventilatory parameters and inspiratory work (WOB) in normocapnic and hypercapnic patients with stable COPD. METHODS: While administering nasal pressure support to 10 normocapnic and 10 hypercapnic patients with COPD, we measured airflow and volume with a pneumotachograph as well as esophageal and gastric pressures under nCPAP, PSV, and biPAP conditions. RESULTS: nCPAP had no influence on ventilatory parameters but decreased WOB and transdiaphragmatic work (Wdi) at 10 cm H(2)O of pressure in both groups. With PSV and biPAP, ventilatory parameters increased proportionally to the inspiratory applied pressure. WOB and Wdi decreased significantly in both groups while increasing the pressure support. A similar decrease was observed during biPAP proportionally to the level of pressure support. The diaphragmatic pressure-time product decreased similarly in both groups during PSV and biPAP. CONCLUSION: The ventilatory response under nCPAP, PSV, and biPAP conditions is similar in hypercapnic and normocapnic patients with stable COPD; PSV and biPAP increase ventilatory parameters and improve Wdi. On the contrary, nCPAP improves WOB but does not increase ventilatory parameters.     

Noninvasive mechanical ventilation in patients with stable severe COPD

Noninvasive positive pressure ventilation in patients with stable chronic obstructive pulmonary disease. The role of non-invasive positive pressure ventilation (NIPPV) is well documented in patients with restrictive thoracic diseases like kyphoscoliosis, tuberculosis sequelae or neuromuscular disease. There is also a good evidence for the use of NIPPV in acute respiratory failure in patients with an exacerbation of COPD. The application of NIPPV in patients with chronic respiratory failure is growing, but there is less evidence than in restrictive disorders. NIPPV can unload the respiratory muscles in patients with chronic hypercapnic COPD and so alleviates fatigue of the respiratory pump, but improvement in the maximal inspiratory pressure (Pi (max)) is small or even absent. An improvement of sleep quality has also postulated, there was an increase in total sleep time and sleep effectiveness when using higher inspiratory pressure. An increase of the walking distance was shown in short term studies, only. In most studies, there was an increase in quality of life as a main topic. Mortality was unchanged in the two long-term randomised controlled studies. Current data suggest a possible role of NIPPV in patients with severe hypercapnia. A high effective inspiratory pressure and a ventilator mode with a significant reduction in the work of breathing should be choosen. NIPPV should be started in hospital, a close reassessment must be performed. Patients who accepted NIPPV in the first weeks had a good compliance for long-term use.     

Oscillatory resistance measured during noninvasive proportional assist ventilation.

Setting proportional assist ventilation (PAV) requires the measurement of patient resistance and elastance. To avoid patient sedation/paralysis or the use of an esophageal balloon, noninvasive PAV is indirectly set by the "runaway" method or in accordance with patient comfort. The aim of this study was to ascertain whether the forced oscillation technique (FOT) applied by the ventilator during noninvasive PAV is useful in assessing patient respiratory resistance. Nasal PAV was applied to 14 patients with severe chronic obstructive pulmonary disease. During PAV a modified ventilator applied a 5-Hz pressure oscillation to noninvasively assess FOT resistance (Rrs). Lung resistance (RL) was measured in seven of the patients by using an esophageal balloon. Moreover, measurements were also performed in five of the patients when PAV was applied through the mouth. Rrs was close to RL both during nasal (Rrs = 8.9 +/- 3.1, RL = 9.0 +/- 2.6; cm H(2)O x s/L; n = 7, p > 0.05) and mouth (Rrs = 5.6 +/- 2.1, RL = 5.8 +/- 1.4; cm H(2)O x s/L; n = 5, p > 0.05) breathing. Rrs was slightly greater than the maximum value of flow assistance applied during the setting of PAV (FAmax): 11.1 +/- 5.4 and 9.5 +/- 2.9 cm H(2)O x s/L, respectively (n = 14, p > 0.05), both variables being significantly correlated (r = 0.72, p < 0.05). FOT applied by the PAV ventilator allowed the assessment of patient resistance. These results suggest that FOT could be useful in setting PAV flow assistance and in automatically and continuously updating this setting in accordance with patient resistance.     

Noninvasive proportional assist ventilation for acute respiratory insufficiency. Comparison with pressure support ventilation.

Noninvasive positive pressure ventilation (NPPV) is usually applied using pressure support ventilation (PSV). Proportional assist ventilation (PAV) is a newer mode that delivers assisted ventilation in proportion to patient effort. We hypothesized that PAV for NPPV would support gas exchange and avoid intubation as well as PSV and be more comfortable and tolerable for patients. Adult patients with acute respiratory insufficiency were randomized to receive NPPV with PAV delivered using the Respironics Vision ventilator or PSV using a Puritan-Bennett 7200ae critical care ventilator. Each mode was adjusted to relieve dyspnea and improve gas exchange until patients met weaning or intubation criteria, died, or refused to continue. Twenty-one and 23 patients were entered into the PAV and PSV groups, respectively, and had similar diagnoses and baseline characteristics, although pH was slightly lower in the PAV group (7.30 versus 7.35, p = 0.02). Mortality and intubation rates were similar, but refusal rate was lower, reduction in respiratory rate was more rapid, and there were fewer complications in the PAV group. We conclude that use of the PAV mode is feasible for noninvasive therapy of acute respiratory insufficiency. Compared with PSV delivered with the Puritan-Bennett 7200ae, PAV is associated with more rapid improvements in some physiologic variables and is better tolerated.     

比例辅助通气临床应用的方法学及疗效评价

目的建立比例辅助通气（PAV）临床应用的方法,评价其治疗慢性阻塞性肺疾病（COPD）急性发作期患者的疗效,并与压力辅助通气（PSV）比较。方法选取10例COPD插管机械通气患者,分别采用吸气阻断法和脱逸法设定参数。每例随机先后采用PAV或PSV,PAV辅助比例分别设为80％、60％和40％。同时监测主观感受、血流动力学、氧动力学和呼吸力学指标。结果吸气阻断法与脱逸法设定的参数有很好的相关性r＝0．928（P＜0．01）。PAV不同的辅助比例只影响吸气峰压、呼吸机及患者做功,对通气指标无显著影响（P＞0．05）。对循环功能稳定者,PAV组与PSV组的血流动力学指标差异无显著性（P＞0．05）,氧合均保持在满意水平。PAV组比PSV组潮气量有减小趋势（P＞0．05）,动脉血二氧化碳分压（PaCO2）显著增高（P＜0．05）,吸气峰压显著减低（P＜0．05）。结论采用脱逸法设定参数简单可靠。PAV是安全有效的通气模式,人机协调性好。在做功相同时,PAV比PSV吸气峰压降低,并根据患者的需要保持相应的通气量。     

无创正压通气治疗慢性阻塞性肺疾病合并Ⅱ型呼吸衰竭近期疗效观察

目的探讨无创正压机械通气(NIPPV)在慢性阻塞性肺疾病(COPD)急性发作期合并Ⅱ型呼吸衰竭中的应用价值。方法64例COPD急性发作期合并呼吸衰竭患者随机分为对照组和治疗组。对照组给予常规治疗;治疗组除常规治疗外,加用NIPPV,通气时间5~7 d。比较两组同期血气分析及临床症状变化。结果治疗组血气、心率、呼吸频率等较对照组明显改善(P<0.01)。结论应用NIPPV可明显改善COPD急性发作期患者症状,提高PaO2,降低PaCO2,值得推广应用。     

Physiological response to intrapulmonary percussive ventilation in stable COPD patients

Intrapulmonary percussive ventilation (IPV) is a ventilatory technique that delivers bursts of high-flow respiratory gas into the lung at high rates, intended for treating acute respiratory failure and for mobilization of secretions. We performed a study, aimed at assessing the physiological response to IPV, on patients' breathing pattern, inspiratory effort, lung mechanics and tolerance to ventilation. Ten COPD patients underwent randomized trials of IPV through a face mask at different pressure/frequency combinations (1.2 bar/250 cycles/min; 1.8/250; 1.2/350; 1.8/350), separated by return to baseline (SB), using the IMP2 ventilator. In 5 patients we have also compared the physiological changes of IPV with those obtained during pressure support ventilation (PSV). Minute ventilation did not vary among the trials, but tidal volumes (VT) were significantly greater during 1.2/250, 1.2/350 and 1.8/350 compared to SB. The pressure time product of the diaphragm per minute (PTPdi/min) estimate of the diaphragm oxygen expenditure was also significantly reduced during 1.2/250 and 1.8/250 (209 cmH2O x s/min for SB vs. 143 and 125 for 1.2/250 and 1.8/250, respectively P < 0.05), as well as dynamic intrinsic end-expiratory pressure (PEEPi,dyn). Similar reduction in PTPdi/min were obtained also during PSV. Tolerance to ventilation and oxygen saturation were satisfactory and did not change during the different trials. In 5 normal subjects a prolonged apnea trial lasting > 2 min was also performed, without any significant decrease in SaO2 or subjective discomfort. In conclusion, IPV was able to guarantee an adequate ventilation, while inducing a significant unloading of the diaphragm during the "low-frequency" trials.     

慢性阻塞性肺疾病急性发作期患者对比例辅助通气的生理反应

目的　探讨比例辅助通气 (PAV)不同辅助水平对慢性阻塞性肺疾病 (COPD)急性发作期患者生理反应的影响。方法　 9例COPD急性发作期患者接受三个不同比例辅助水平的PAV通气 ,观察患者吸气肌肉用力情况和呼吸方式的变化。结果　 (1)与自主呼吸 (SB)相比 ,PAV各辅助水平时的潮气量 (VT)、分钟通气量 (V·E)和呼吸频率 (RR)均稍增高 (P >0 0 5 )。各比例辅助水平之间的VT、V·E 和RR比较差异无显著性 (P >0 0 5 )。 (2 )与SB相比 ,各比例辅助水平时的跨膈压 (Pdi)、压力时间乘积 (PTP)和患者呼吸做功均明显减少 (P >0 0 1) ,Pdi、PTP和患者呼吸做功分别平均减少 8 36cmH2 O、11 4 9cmH2 O·s-1·L-1和 0 5 3J/L。随比例辅助水平的升高 ,Pdi、PTP和患者呼吸功无明显变化(P >0 0 5 )。 (3)PAV可减轻患者呼吸困难 (P <0 0 5 )。结论　本试验证实了无创PAV在COPD急性发作期患者中应用的可行性。患者感觉最舒适的PAV辅助比例水平是 (5 7± 11) %。根据患者感觉舒适情况而设定比例辅助水平的无创PAV可减轻患者的呼吸肌肉负担 ,最舒适水平时呼吸功减少5 7% ,Pdi减少 72 % ,PTP减少 6 5 % ;并改善患者的呼吸方式和呼吸困难     

Current status of noninvasive ventilation in stable COPD patients

Noninvasive ventilation (NIV) has been one of the major advances in respiratory medicine in the last decade. NIV improves quality of life, prolongs survival, and improves gas exchange and sleep quality in restrictive patients, but evidence available now does not allow us to establish clear criteria for prescribing NIV in patients with chronic respiratory failure due to COPD. On the basis of the available studies, NIV should not be used as a treatment of choice for all patients with COPD, even when disease is severe. However, there is more evidence that NIV has an important effect in these patients. In fact, a selected group of patients may well benefit from domiciliary mechanical ventilation, and we need to be able to identify who they are. Moreover, NIV can be a new strategy to improve exercise tolerance in COPD patients.     

Steady-state breathing pattern responses to small inspiratory resistive loads in COPD patients. Application to weaning from mechanical ventilation

We investigated the effect of small inspiratory resistive loads on the breathing patterns of patients with COPD admitted to the ICU for acute respiratory failure. Patients were in stable clinical condition three days after weaning from the acute-phase ventilation. Healthy nonsmokers served as controls. Breathing patterns were recorded for 20-min periods during unloaded breathing (R0), then with small inspiratory resistive loads (R1 = 2.5 cmH2O L/s and R2 = 5.2 cmH2O L/s) applied in random order. Respiratory parameters were memorized in real time and blood gases measured continuously with a transcutaneous PO2/PCO2 monitor and compared periodically with arterial blood gases. Minute volume (VE) and respiratory rate decreased with no modification in blood gas values. In the COPD patients, R1 was too small to be perceived; when R2 was applied, no increase in TI was observed, and VT and VT/TI decreased. The VE could not be maintained despite a shortening of expiratory time. The COPD patients did not have significant increase of occlusion pressure (P0.1). Mean blood gas values did not change during the testing, but the coefficient of variation of tcPCO2 increased. During the critical period following weaning from artificial ventilation, COPD patients did not respond in the same manner as normal subjects to inspiratory resistive loads, but did not have modified gas exchange during the 20-min period.     

Physiologic evaluation of pressure support ventilation by nasal mask in patients with stable COPD.

We evaluated the physiologic effects of pressure support ventilation by nasal route (NPSV) in eight patients with severe stable COPD and chronic hypercapnia who were randomly submitted to 2-h sessions of NPSV both with a portable ventilator (Respironics BIPAP device) and with a standard ventilator (Bird 6400ST device) at an inspiratory airway pressure of 22 cm H2O. Two sessions with each ventilator were performed using an FIO2 of 0.21 in each patient on two consecutive days. One patient did not tolerate either form of ventilation. Comparison of spontaneous with BIPAP ventilation showed a significant improvement in pH, PaCO2, and PaO2. Ventilatory pattern assessed by a respiratory inductive plethysmograph showed a significant increase in minute ventilation (VE), VT, and Ttot. Integrated surface diaphragmatic EMG activity measured only during BIPAP device ventilation decreased from that measured during spontaneous breathing. Similar changes in blood gases and ventilatory pattern were observed during ventilation by the Bird 6400ST except for VT/Ti ratio, which significantly increased. Comparison of baseline with measurements performed 12 h after the whole cycle of treatment showed a significant increase in pH and VE and a decrease in PaCO2. We conclude that short-term NPSV may be useful in improving respiratory pattern and blood gases in stable COPD patients with chronic hypercapnia.     

Haemodynamic effects of proportional assist ventilation during high-intensity exercise in patients with chronic obstructive pulmonary disease

Background and objective: Proportional assist ventilation (PAV) has been proposed as a more physiological modality of non‐invasive ventilation, thereby reducing the potential for deleterious cardio‐circulatory effects during exercise, in patients with COPD. We therefore evaluated whether PAV modulates the kinetic and ‘steady‐state’ haemodynamic responses to exercise in patients with moderate‐to‐severe COPD. Methods: Twenty patients underwent constant‐load (75–80% peak work rate) cycle ergometer exercise testing to the limit of tolerance (T_lim), while receiving PAV or breathing spontaneously. Stroke volume (SV), heart rate (HR) and cardiac output (CO) were monitored by impedance cardiography. Results: Compared with unassisted breathing, PAV increased T_lim in 8/20 patients (median improvement 113% (range 8 to 212) vs −20% (range −40 to −9)). PAV had no significant effects on ‘steady‐state’ haemodynamic responses either in patients with or those without increased T_lim (P > 0.05). However, at the onset of exercise, SV kinetics were slowed with PAV, in 13/15 patients with analysable data. HR dynamics remained unaltered or failed to accelerate sufficiently in nine of these patients, thereby slowing CO kinetics (T_1/2 61 s (range 81–30) vs 89 s (range 100–47)). These deleterious effects were not, however, associated with PAV‐induced changes in T_lim (P > 0.05). Conclusions: PAV slowed the SV and CO kinetics at the onset of high‐intensity exercise in selected patients with moderate‐to‐severe COPD. However, these adverse effects of PAV disappeared during the stable phase of exercise, and were not related to the ergogenic potential of PAV in this patient population.     

Training with inspiratory pressure support in patients with severe COPD.

This study evaluates the effects of training with noninvasive ventilatory support in patients with chronic obstructive pulmonary disease in a randomised, controlled, observer-blinded trial. Twenty-nine patients with chronic obstructive pulmonary disease and with a ventilatory limited exercise capacity (forced expiratory volume in one second < 60% predicted, breathing reserve at maximal exercise < 20% of maximally voluntary ventilation, resting arterial oxygen tension > or = 8 kPa (60 mmHg), end-exercise arterial oxygen saturation measured by pulse oximetry > or = 85%) completed an 8-week supervised outpatient cycle exercise programme. Fourteen patients were randomised to training with inspiratory pressure support of 10 cmH2O and 15 patients to training with control (sham) inspiratory pressure support of 5 cmH2O. Outcome measures were the incremental shuttle walking test and a constant-load cycle endurance test at 75% of peak work rate including the measurement of physiological responses, and health status measured using the St. George's Respiratory Questionnaire. Statistically significant between-group differences were found in favour of the inspiratory pressure support of 10 cmH2O group for improvement in shuttle walking distance (16+/-17 versus 3+/-13%), cycle endurance (164+/-124 versus 88+/-128%), and the reduction in minute ventilation during exercise (-11+/-10 versus -2+/-9%). It was concluded that exercise training with inspiratory pressure support of 10 cmH2O resulted in statistically significantly larger improvements in exercise performance than training with inspiratory pressure support of 5 cmH2O in patients with chronic obstructive pulmonary disease suffering from a ventilatory limited exercise capacity. Inspiratory pressure support of 10 cmH2O may be considered as adjunct during high-intensity exercise training.     

A meta-analysis of nocturnal noninvasive positive pressure ventilation in patients with stable COPD

STUDY OBJECTIVES: The potential benefits of noninvasive positive pressure ventilation (NIPPV) for patients with COPD remains inconclusive, as most studies have included only a small number of patients. We therefore undertook a meta-analysis of randomized controlled trials (RCTs) that compared nocturnal NIPPV with conventional management in patients with COPD and stable respiratory failure. DESIGN: RCTs were identified from several sources, such as MEDLINE, EMBASE, and CINAHL. In addition, records were identified through hand searching of abstracts from meetings of the American Thoracic Society, the American College of Chest Physicians, and the European Respiratory Society. PATIENTS: Patients with COPD according to the definition of the American Thoracic Society. INTERVENTIONS: NIPPV applied via a nasal or facemask for at least 5 h/d for at least 3 weeks. Patients in the actively treated group continued to receive the usual management for COPD. The control group received the same management as the study group but did not receive NIPPV. Measurements and results: PaCO(2), PaO(2), 6-min walking distance (6MWD), respiratory muscle function, FEV(1), vital capacity, and sleep efficiency (time asleep as a percentage of total time in bed) were used as outcome measures. The publications were reduced to 10 potentially eligible articles from 164 publications retrieved from computer searches and 8 further abstracts. Four trials were finally included in the meta-analysis. The only outcome for which the confidence intervals excluded zero was maximal inspiratory pressure (PImax). The confidence intervals for the other outcomes included zero. The mean treatment effects for FEV(1) and PImax were small, whereas it was moderate for the 6MWD. Small negative effects were found for the outcomes of vital capacity, PaCO(2), and sleep efficiency. CONCLUSIONS: This meta-analysis of 3 months of NIPPV in patients with stable COPD showed that ventilatory support did not improve lung function, gas exchange, or sleep efficiency. The high upper limit of the confidence interval for the 6MWD suggested that some people do improve their walking distance. The small overall sample size precluded a clear clinical direction regarding the effects of NIPPV in patients with COPD.     

Noninvasive proportional assist ventilation and pressure support ventilation during arm elevation in patients with chronic respiratory failure. A preliminary, physiologic study

BACKGROUND: It has been shown that upper limbs activity increases the respiratory workload in patients with chronic respiratory failure (CRF). The object of the present study was to investigate whether, in these patients: (i) noninvasive positive pressure ventilation (NPPV) could sustain the inspiratory muscles to meet the greater ventilatory demand during upper limbs activity with the arm elevation test (AE); (ii) proportional assist ventilation (PAV) might be superior to pressure support ventilation (PSV) during AE, because of its potential more adaptable response to sudden changes in the ventilatory pattern. METHODS: The study was performed in the pulmonary function laboratory of the Pulmonary Division in Verona General Hospital, Verona, Italy. We studied 8 male patients with CRF due to chronic obstructive pulmonary disease (COPD). Each patient received 2 treatment in random order with a crossover design: spontaneous breathing (SB), SB with AE, either PSV or PAV without and with AE, SB without and with AE, either PSV or PAV without and with AE. We measured: lung function tests, lung mechanics, ventilatory pattern and diaphragmatic effort (pressure time product, PTP(di)). RESULTS: (i) AE increases minute ventilation (+14%) and PTP(di) (+64%); (ii) ventilatory support, both with PSV and PAV unloads the diaphragm both at rest (PTP(di) -77% and -54%, respectively) and during arm elevation (PTP(di) -54% and -44%, respectively). CONCLUSIONS: PAV and PSV unloads the diaphragm in patients with CRF due to COPD both during SB and AE; PAV can be more efficient than PSV in assisting the diaphragm during AE in producing a greater level of minute ventilation for a similar rise in PTP(di) compared to PSV. Noninvasive ventilatory support should be considered in rehabilitation programs for training of upper limbs activity.     

Renal response to mechanical ventilation in patients with chronic hypercapnia

Alkalosis in hypercapneic patients caused by abrupt respirator-induced reduction of the partial pressure of carbon dioxide leads to bicarbonate diuresis. Potassium is the predominant cation accompanying bicarbonate loss in the urine.The determining variable for induction of proportional changes in renal bicarbonate and potassium excretion is the partial pressure of carbon dioxide. The reduction of the partial pressure of carbon dioxide modifies bicarbonate regeneration directly by limiting the hydration reaction and facilitates potassium loss indirectly by reducing extracellular, and by inference intracellular, hydrogen ion activity.