Effects of diaphragm plication for phrenic nerve paralysis on respiratory mechanics and diaphragm function

The purpose of this study is to examine the effects of unilateral diaphragm plication for phrenic nerve paralysis on the respiratory mechanics and diaphragm function. Study 1: We performed thoracotomy (BASELINE), left phrenicotomy (INJURY) and left diaphragm plication (PLICATION) in ten dogs. After chest was closed in each condition, measured were the tidal volume (TV), respiratory rate (f), esophageal and gastric pressure swing (delta Pes, delta Pga), dynamic compliance (Cdyn) the ratio of gastric to esophageal pressure swing (delta Pga/delta Pes) and the work of breathing per liter (WOB/L) under stable spontaneous breathing. Study 2: In eight other left-phrenicotomized dogs, Pdi and fractional shortening of the costal diaphragm during contralateral electrophrenic stimulation were measured before and after plication. After plication TV, delta Pga/delta Pes, Cdyn, Pdi and fractional shortening during stimulation increased significantly, whereas Pes and WOB/L decreased significantly compared with INJURY condition. In conclusion unilateral diaphragm plication after paralysis improves the intact hemidiaphragm contractility and diaphragmatic contribution to breathing.     

Effect of CPAP on intrinsic PEEP,inspiratory effort,and lung volume in severe stable COPD

BACKGROUND: Intrinsic positive end expiratory pressure (PEEPi) constitutes an inspiratory threshold load on the respiratory muscles, increasing work of breathing. The role of continuous positive airway pressure (CPAP) in alleviating PEEPi in patients with severe stable chronic obstructive pulmonary disease is uncertain. This study examined the effect of CPAP on the inspiratory threshold load, muscle effort, and lung volume in this patient group. METHODS: Nine patients were studied at baseline and with CPAP increasing in increments of 1 cm H(2)O to a maximum of 10 cm H(2)O. Breathing pattern and minute ventilation (I), dynamic PEEPi, expiratory muscle activity, diaphragmatic (PTPdi/min) and oesophageal (PTPoes/min) pressure-time product per minute, integrated diaphragmatic (EMGdi) and intercostal EMG (EMGic) and end expiratory lung volume (EELV) were measured. RESULTS: Expiratory muscle activity was present at baseline in one subject. In the remaining eight, PEEPi was reduced from a mean (SE) of 2.9 (0.6) cm H(2)O to 0.9 (0.1) cm H(2)O (p<0.05). In two subjects expiratory muscle activity contributed to PEEPi at higher pressures. There were no changes in respiratory pattern but I increased from 9.2 (0.6) l/min to 10.7 (1.1) l/min (p<0.05). EMGdi remained stable while EMGic increased significantly. PTPoes/min decreased, although this did not reach statistical significance. PTPdi/min decreased significantly from 242.1 (32.1) cm H(2)O.s/min to 112.9 (21.7) cm H(2)O.s/min). EELV increased by 1.1 (0.3) l (p<0.01). CONCLUSION: High levels of CPAP reduce PEEPi and indices of muscle effort in patients with severe stable COPD, but only at the expense of substantial increases in lung volume.     

Effects of aminophylline on diaphragmatic dysfunction after upper abdominal surgery

The effects of upper abdominal surgery on diaphragmatic function were studied in eight supine patients before and after administration of aminophylline. Changes in pleural (delta Ppl) and gastric pressure (delta Pga) swings were measured with balloon catheter systems. Transdiaphragmatic pressure change (delta Pdi) was calculated as the difference delta Pga-delta Ppl. The ratio delta Pga/delta Pdi, used as an index of the diaphragmatic contribution to the quiet breathing process, decreased significantly as early as 1 h after operation without any further change throughout the 6-h period studied. Administration of aminophylline (6 mg/kg), six hours postoperatively, produced a significant increase in this diaphragmatic index. These data indicate that the early reduced diaphragmatic activity, after upper abdominal surgery, partially may be reversed by administration of aminophylline. The mechanism of its action may involve central nervous stimulation and/or a direct inotropic effect on diaphragmatic muscle. Further studies are needed to evaluate if the correction of altered diaphragmatic motion by aminophylline improves postoperative lung function.     

Physiological effects and optimisation of nasal assist-control ventilation for patients with chronic obstructive pulmonary disease in respiratory failure

BACKGROUND: A study was undertaken to investigate the effects of non- invasive assist-control ventilation (ACV) by nasal mask on respiratory physiological parameters and comfort in acute on chronic respiratory failure (ACRF). METHODS: Fifteen patients with chronic obstructive pulmonary disease (COPD) were prospectively and randomly assigned to two non-invasive ventilation (NIV) sequences in spontaneous breathing (SB) and ACV mode. ACV settings were always optimised and therefore subsequently adjusted according to patient's tolerance and air leaks. RESULTS: ACV significantly decreased all the total inspiratory work of breathing (WOBinsp) parameters, pressure time product, and oesophageal pressure variation in comparison with SB mode. The ACV mode also resulted in a significant reduction in surface diaphragmatic electromyographic activity to 36% of the control values and significantly improved the breathing pattern. SB did not change the arterial blood gas tensions from baseline values whereas ACV significantly improved both the PaO2 from a mean (SD) of 8.45 (2.95) kPa to 13.31 (2.15) kPa, PaCO2 from 9.52 (1.61) kPa to 7.39 (1.39) kPa, and the pH from 7.32 (0.03) to 7.40 (0.07). The respiratory comfort was significantly lower with ACV than with SB. CONCLUSIONS: This study shows that the clinical benefit of non-invasive ACV in the management of ACRF in patients with COPD results in a reduced inspiratory muscle activity providing an improvement in breathing pattern and gas exchange. Despite respiratory discomfort, the muscle rest provided appears sufficient when ACV settings are optimised.


     

Surgical and functional results after surgical lung volume reduction in 94 patients with severe emphysema

Lung volume reduction (LVR) is a new surgical approach designed to relieve shortness of breath and improve exercise tolerance in patients with severe lung emphysema. The aim of this study was to analyse surgical results and changes in the lung function, gas exchange, exercise tolerance and degree of dyspnoea until two years after LVR. From June 1994 to September 1997 ninety-four patients (31 women and 63 men, mean age 64 [35-79] years) with severe emphysema (12 with alpha 1-Pi-deficiency) underwent unilateral (n = 24) or bilateral (n = 70) LVR. 92 from 94 patients were extubated immediately after surgery. 30 days mortality was 2.2% (2/94), 90 days 3.3% (3/94) respectively. Most common postoperative complications were pneumonia (n = 15, 16%) and air leakage longer than 7 days (n = 22, 23.4%). One month after surgery there was a significant increase in forced expiratory vital capacity after one second (FEV1 59%) and significant decrease in total lung capacity (TLC 19%) and residual volume (RV 28%). Also significant changes were observed in paO2, paCO2, 6-minute walking distance, dyspnoea score and respiratory muscle function. Two years after LVR lung function tests in patients with smokers emphysema showed the benefit to be maintained (high responders). Patients with alpha 1-Pi-deficiency showed 6 to 12 months after surgery a remarkable deterioration of functional data (low responders). In selected patients with severe emphysema surgical LVR shows significant improved pulmonary function, gas exchange, dyspnoea and walking distance. The results are better after bilateral operation. Patients selection, rehabilitation program and interdisciplinary care resulted in a low operative morbidity and mortality.     

Renal functional reserve in patients with severe chronic obstructive pulmonary disease

BACKGROUND: Renal functional reserve is the normal increase in renal blood flow after a protein load, and reduced or absent renal functional reserve is an early index of renal impairment. Renal blood flow is frequently reduced during acute oedematous exacerbations of chronic obstructive pulmonary disease (COPD). It is possible that patients with severe COPD in the stable state may have a reduced or absent renal functional reserve which could be a factor in oedema formation. METHODS: Sixteen stable patients with severe COPD and five normal controls were studied. The mean (SD) arterial oxygen and carbon dioxide tensions (PaO2, PaCO2) and forced expiratory volume in one second (FEV1) of patients with COPD were 8.1 (1.04) kPa, 6.3 (0.69) kPa, and 0.74 (0.27) 1, respectively. The pulsatility index (PI), an index of renovascular resistance, was measured non-invasively by Doppler ultrasonography at baseline and at intervals after a protein load of 250 g steak. RESULTS: The PI fell after the protein load in the normal subjects from 1.04 (0.19) to 0.84 (0.17), mean difference 0.20, 95% confidence interval of difference (CI) 0.14 to 0.27, p < 0.001. In the COPD group there was no change; baseline PI = 1.04 (0.16), PI after protein load = 1.08 (0.19), mean difference = -0.04, 95% CI-0.11 to 0.04, p = NS. Six of the patients with COPD were normocapnic and 10 were hypercapnic (PaCO2 > or = 6.0 kPa). The normocapnic patients had no significant change in PI (baseline PI = 1.07 (0.15), PI after protein load = 1.01 (0.16), mean difference = 0.06, 95% CI -0.03 to 0.15) while in the hypercapnic patients the PI tended to rise (baseline PI = 1.03 (0.17), PI after protein load = 1.12 (0.21), mean difference = -0.09, 95% CI 0.18 to 0.007, p = 0.06). CONCLUSIONS: Renal haemodynamics were unchanged after a protein load in patients with severe COPD, suggesting that they had no renal functional reserve. This may be a factor in the development of oedema frequently seen in patients with severe COPD, particularly in hypercapnic patients.


     

小潮气量肺保护性通气策略与压力通气模式对妇科腹腔镜手术患者氧合功能的影响

目的:评价小潮气量肺保护性通气策略(protective lung ventilation mode,PLV)与压力通气模式(pressure con-trolled ventilation,PCV)在妇科腹腔镜手术中应用的有效性及安全性。方法:拟于我院择期行妇科腹腔镜手术的患者共计144例,按随机序列号分为PLV组和PCV组,每组72例。PLV组潮气量6 ml/kg,吸呼比1∶2,呼吸频率16次/min,呼气末正压5 cmH 2O(1 cmH 2O=0.098 kPa);PCV组设定通气压力维持潮气量8 ml/kg,吸呼比1∶2,呼吸频率12~16次/min。分别于气管插管后5 min(T1)、气腹后10 min(T2)、气腹后20 min(T3)、撤除气腹后10 min(T4)记录患者气道峰压(airway peak pressure,Ppeak)、平均气道压(mean airway pressure,Pmean),并计算动态肺顺应性(dynamic lung compliance,Cdyn)。于T3、T4时点行血气分析记录PaO 2、PaCO 2、肺泡-动脉氧分压差(alveoli-arterial oxygen partial pressure,A-aDO 2),并计算氧合指数(oxygenation index,OI)。结果:PLV组T3时点Ppeak、Pmean显著高于PCV组,但Cdyn低于PCV组,差异有统计学意义(P<0.05)。PLV组T4时点Ppeak显著高于PCV组,差异有统计学意义(P<0.05)。两组T2、T3时点Ppeak、Pmean较T1时点显著升高,而Cdyn显著低于T1时点,差异有统计学意义(P<0.05)。PLV组T3时点Ppeak、Pmean显著高于T2时点,Cdyn显著低于T2时点,差异有统计学意义(P<0.05)。PLV组T3时点PaO 2、OI显著高于PCV组,而PaCO 2、A-aDO 2显著低于PCV组,差异有统计学意义(P<0.05)。两组T4时点PaO 2、OI较T3时点显著升高,而PaCO 2、A-aDO 2较T3时点显著降低,差异有统计学意义(P<0.05)。两组T4时点PaO 2、PaCO 2、A-aDO 2、OI差异无统计学意义(P>0.05)。两组间各呼吸系统并发症发生情况及住院天数差异均无统计学意义(P>0.05)。结论:对妇科腹腔镜手术患者而言,PCV有助于维持患者呼吸动力学稳定,而小潮气量PLV有助于维持患者术中氧合功能,二者安全性差异无统计学意义。     

Physiological effects of flow and pressure triggering during non- invasive mechanical ventilation in patients with chronic obstructive pulmonary disease

BACKGROUND: The effect of the type of trigger system on inspiratory effort has been studied in intubated patients, but no data are available in non-invasive mechanical ventilation where the "trigger variable" may be even more important since assisted modes of ventilation are often employed from the beginning of mechanical ventilation. METHODS: The effect of flow triggering (1 and 5 1/min) and pressure triggering (-1 cm H2O) on inspiratory effort during pressure support ventilation (PSV) and assisted controlled mode (A/C) delivered non-invasively with a full face mask were compared in patients with chronic obstructive pulmonary disease (COPD) recovering from an acute exacerbation. The patients were studied during randomised 15 minute runs at zero positive end expiratory pressure (ZEEP). The oesophageal pressure time product (PTPoes), dynamic intrinsic PEEP (PEEPi,dyn), fall in maximal airway pressure (delta Paw) during inspiration, and ventilatory variables were measured. RESULTS: Minute ventilation, respiratory pattern, dynamic lung compliance and resistances, and changes in end expiratory lung volume (delta EELV) were the same with the two triggering systems. The total PTPoes and its pre-triggering phase (PTP due to PEEPi and PTP due to valve opening) were significantly higher during both PSV and A/C with pressure triggering than with flow triggering at both levels of sensitivity. delta Paw was larger during pressure triggering, and PEEPi,dyn was significantly reduced during flow triggering in the A/C mode only. CONCLUSIONS: In patients with COPD flow triggering reduces the inspiratory effort during both PSV and A/C modes compared with pressure triggering. These findings are likely to be due to a reduction in PEEPi,dyn and in the time of valve opening with a flow trigger.


     

Diaphragmatic function during sevoflurane anaesthesia in dogs

The effect of increasing the concentration of sevoflurane anaesthesia on diaphragmatic function was investigated in six mechanically ventilated dogs. Diaphragmatic function was assessed by measuring the transdiaphragmatic pressure (Pdi) generated during bilateral supramaximal stimulation of the cervical phrenic nerves at frequencies of 0.5, 10, 20, 50, and 100 Hz under quasi-isometric conditions. Measurements were performed at 1, 1.5 and 2 MAC concentrations after maintaining stable conditions for one hour. The Pdi-stimulus frequency relationship was compared at each anaesthetic concentration. The sequence of changing anaesthetic depth was altered in random fashion among animals. The Pdi amplitude generated by single twitch (0.5 Hz) was unchanged at the three concentrations. In addition, no change in Pdi during 10, 20, 50 Hz stimulation was noted at any of the three levels of anaesthesia. By contrast, Pdi with 100 Hz stimulation during 2 MAC sevoflurane exposure (28.1 +/- 5.0 cmH2O) decreased below Pdi levels seen at 1 and 1.5 MAC (35.3 +/- 4.3 cmH2O and 31.5 +/- 4.3 cmH2O, respectively) (P less than 0.05). From these results, we conclude that sevoflurane impairs diaphragmatic function in deep anaesthesia.     

Wasting as an independent predictor of mortality in patients with cystic fibrosis

BACKGROUND: Cystic fibrosis (CF) is the most common life threatening autosomal recessive disorder in the white population. Wasting has long been recognised as a poor prognostic marker in CF. Whether it predicts survival independently of lung function and arterial blood gas tensions has not previously been reported. METHODS: 584 patients with CF (261 women) of mean (SD) age 21 (7) years were studied between 1985 and 1996, all of whom were being followed up in a tertiary referral centre. Lung function tests, body weight, arterial blood oxygen (PaO(2)) and carbon dioxide (PaCO(2)) tensions were measured. The weight was calculated as a percentage of the ideal body weight for age, height, and sex. RESULTS: Forced expiratory volume in one second (FEV(1)) recorded at the start of the study was 1.8 (1.0) l (52 (26)% predicted FEV(1)), PaO(2) 9.8 (1.9) kPa, PaCO(2) 5.0 (0.9) kPa, and % ideal weight 92 (18)%. During the follow up period (45 (27) months) 137 patients died (5 year survival 72%, 95% CI 67 to 73). FEV(1), % predicted FEV(1), PaO(2), % ideal weight (all p<0.0001), and PaCO(2) (p=0.04) predicted survival. In multivariate analysis, % predicted FEV(1) (p<0.0001), % ideal weight (p=0.004), and PaCO(2) (p=0.02) were independent predictors of outcome. Patients with >85% ideal body weight had a better prognosis at 5 years (cumulative survival 84%, 95% CI 79 to 89) than those with < or =85% ideal weight (survival 53%, 95% CI 45 to 62), p<0.0001. Percentage predicted FEV(1) (area under curve 0.83; 95% CI 0.78 to 0.87) and % ideal weight (area under curve 0.74; 95% CI 0.68 to 0.79) were accurate predictors of survival at 5 years follow up (receiver-operating characteristic analysis). CONCLUSIONS: Body wasting is a significant predictor of survival in patients with CF independent of lung function, arterial blood oxygen and carbon dioxide tensions.     

无创正压机械的通气对慢性阻塞性肺疾病患者膈肌功能影响

目的：探索与评估膈肌功能测定对重度慢性阻塞性肺疾病（COPD）急性加重期患者无创正压机械通气（NPPV）疗效的意义。方法：选择住院的急性加重期COPD患者28例,施行常规治疗＋NPPV。分别记录无创通气前,通气后48小时、终止无创通气前的跨膈压（Pdi）,肺功能、动脉血气,同时综合评估通气前、后的支气管-肺部感染情况。结果：1、无创通气治疗成功组：通气后Pdi,第一秒用力呼气容积（FEV1）．动脉血二氧化碳分压（PaCO2）、动脉血氧分压（PaO2）、pH值分别为（14．04±2．40）cmH2O、（0．70±0.24）L、（48．2±4．2）mmHg．（70．0±6．3）mmHg、（7．37±0．05）,与通气前（（10．98±0．45）cmH20、（0．59±0．11）L、（68．2±10．2）mmHg、（52．5±6．1）mmHg、（7．34±0．06））比较差异均有统计学意义（P均〈0．05）。2、开创通气治疗失败者：2例。1例其Pdi在通气前为8．74cmH2O,通气48小时为9．24cmH2O;另1势9Pdi,通气前为7,56cmH2O,结论：在NPPV治疗过程中,Pdi和EIIFEV1．PaCO2、PaO2、pH值的变化有高度一致性,Pdi的动态变化．可以客观地反映膈肌的功能状态;NPPV有助手改善AECOPD患者的膈肌功能。     

Sequential VATS lung volume reduction surgery: prolongation of benefits derived after the initial operation.

OBJECTIVE: Sequential lung volume reduction (LVR) is thought to provide additional and prolonged benefit compared with unilateral LVR. We tested this hypothesis by reviewing physiological, subjective and survival outcome data on patients who underwent sequential or unilateral LVR. METHODS: LVR was performed as a unilateral video-assisted thoracoscopic surgery (VATS) procedure, with bilateral reduction being undertaken in a staged manner. Pulmonary function data were collected prospectively. A telephone survey of patients and general practitioners was used to determine quality of life and survival. RESULTS: Fifty patients underwent LVR. Twenty-one patients had staged reduction of the contra-lateral lung at a median interval of 9 months. Pre-operatively, patients undergoing sequential LVR were not significantly different from patients undergoing unilateral LVR: forced expiratory volume in 1 s (FEV1) 23% predicted vs. 27% predicted, KCO 40% vs. 45%, total lung capacity (TLC) 124% vs. 121%, residual volume (RV) 217% vs. 214%, health score 34.5 vs. 30.8. After single-side LVR, both groups demonstrated equivalent and significant improvement in spirometric and subjective health scores: FEV1 +15% predicted (P<0.01), TLC -5% (P=0.03), health score +80% (P<0.01). Patients undergoing sequential reduction demonstrated no further significant improvements using either an intragroup comparison with their pre-second operation values or an intergroup comparison with the unilateral LVR patients. However, sequential LVR appeared to prolong the benefits experienced after the initial surgery by 1 year. Overall, 12 patients (24%) died during follow-up with no survival difference between the two groups (P=0.65). CONCLUSION: Sequential LVR is a safe strategy. Undertaking LVR to the second side does not further improve spirometric or subjective performance but does prolong the benefits achieved with the initial reduction.     

Abdominal muscle recruitment and PEEPi during bronchoconstriction in chronic obstructive pulmonary disease

BACKGROUND: It has been recently shown that, when breathing at rest, many patients with severe chronic obstructive pulmonary disease (COPD) contract abdominal muscles during expiration, and that this contraction is an important determinant of positive end expiratory alveolar pressure (PEEPi). In this study the effects of acute bronchoconstriction on abdominal muscle recruitment in patients with severe COPD were studied, together with the consequence of abdominal muscle action on chest wall mechanics. METHODS: Breathing pattern, pleural (PPL) and gastric (PGA) pressures, and changes in abdomen anteroposterior (AP) diameter were studied in 14 patients with COPD (mean forced expiratory volume in one second (FEV1) 1.06 (0.08) 1) under control conditions and during histamine-induced bronchoconstriction. RESULTS: The analysis of plots of PGA versus the AP diameter of the abdomen revealed that during maximal broncho- constriction (decrease in FEV1 of 34.8% (95% confidence intervals (CI) 29.9 to 39.7)) the expiratory rise in PGA increased significantly whereas end expiratory abdomen AP diameter decreased, indicating marked abdominal muscle recruitment. As a consequence, the rib cage compartment accounted for all of the volume of hyperinflation during bronchoconstriction (mean value 0.66 I, 95% CI 0.49 to 0.83). Positive end expiratory alveolar pressure during progressive bronchoconstriction was related directly to the expiratory rise in PGA and inversely to the expiratory time. CONCLUSIONS: The results indicate that, in patients with severe COPD, the abdominal muscles are recruited during acute bronchoconstriction. This recruitment probably preserves diaphragm length at the beginning of inspiratory muscle contraction despite the hyperinflation, and contributes significantly to positive end expiratory alveolar pressure. The degree of dynamic pulmonary hyperinflation during bronchoconstriction can be overestimated if abdominal muscle contraction is not assessed.


     

Effects of aminophylline on regional diaphragmatic shortening after thoracotomy in the awake lamb.

Aminophylline has been reported to augment diaphragmatic contraction, although this remains a controversial finding. We studied the effect of aminophylline on regional diaphragmatic shortening, changes in transdiaphragmatic pressure (delta Pdi), and integrated regional electromyographic (EMG) activity of the diaphragm (Edi) after a right thoracotomy in nine lambs using sonomicrometry, esophageal and gastric balloons, and EMG. Sonomicrometer crystals and EMG leads were implanted into the costal and crural regions of the diaphragm through a right thoracotomy, and a tracheostomy was performed. The animals were studied while awake within 4 days after surgery. Fractional costal and crural diaphragmatic shortening was measured using the sonomicrometer; delta Pdi was calculated from esophageal and gastric pressures. Respiratory variables were measured through the tracheostomy. Data were collected during quiet breathing and during CO2 rebreathing. After control measurements, aminophylline (10 mg/kg) was administered intravenously, producing a serum concentration of 17.7 +/- 1.5 micrograms/ml. Aminophylline did not augment shortening, increase delta Pdi, or overcome postoperative diaphragmatic inhibition acutely in the awake sheep after a right lateral thoracotomy. A small decrease of end-tidal CO2, from 5.2% to 4.9%, was measured at rest during aminophylline infusion, but Edi was unchanged. Although during CO2 rebreathing diaphragmatic shortening increased, the addition of aminophylline did not further augment shortening. Our data in awake lambs suggest that aminophylline does not improve diaphragmatic contraction in the acute postoperative period.     

Ventilation, dynamic compliance and ventilatory response to CO2

Age dependent variations in minute ventilation (VE), tidal volume (Vr), respiratory rate and dynamic compliance (Cdyn) as well as ventilatory response to inhalation of carbon dioxide (CO2) were investigated in 20 spontaneously breathing intubated infants and children during halothane anaesthesia. Ages ranged from 6 days to 5 years. Seven patients were younger than 6 months of age. Ventilation volumes were measured by pneumotachography and end tidal carbon dioxide concentration by an in-line capnograph. Fluid-filled oesophageal catheters were used for pressure recordings. Measurements were made before surgery (with and without 2.22 and 3.71% of CO2 in inspired gas) and during surgery. Regression analysis of the relationship between VE and body weight revealed no direct proportionality. On a weight basis, VE was significantly higher in younger than in older patients. Tidal volume was directly proportional to body weight. The mean (SEM) value of tidal volume was 4.3 (0.2) ml/kg. Dynamic compliance showed a direct proportionality with weight. The mean (SEM) value of Cdyn was 10 (1.1) ml/kPa/kg. There was no ventilatory response in any patient to inhalation of 2.22% CO2. In the older group of children (greater than 6 months of age) VE increased by 34% during inhalation of 3.71% CO2 (p less than 0.025). In the younger patients (less than 6 months of age) no ventilatory response to inhalation of 3.71% of CO2 was found, indicating a more pronounced depression of ventilation in these infants.     

Limitations of measurement of transdiaphragmatic pressure in detecting diaphragmatic weakness.

Intrathoracic (oesophageal), intra-abdominal (gastric), and transdiaphragmatic (Pdi) pressures were studied in 20 untrained, healthy subjects during a full inspiration and repeated maximal static inspiratory efforts. The pattern of pressure generation during these two types of respiratory manoeuvre was highly reproducible in each subject. By contrast, it varied over a wide range among individuals. In particular a substantial number of subjects naturally had a strong recruitment of their intercostal and accessory muscles and thus, low Pdi values, during both slowly performed and forceful inspiratory manoeuvres. These observations make it clear that Pdi values, as usually obtained, are commonly open to misinterpretation. For this approach to ensure a reliable assessment of diaphragmatic function and detect diaphragm weakness adequately, it appears essential either to monitor the abdominothoracic configuration or to standardise the pattern of respiratory muscle contraction.     

Respiratory muscle weakness in the Lambert-Eaton myasthenic syndrome.

Respiratory muscle function was assessed in six patients with the Lambert-Eaton myasthenic syndrome. Five had histologically proved small cell carcinoma of the lung; the sixth later developed metastases from an unknown primary site. Two patients had ventilatory failure, one without respiratory symptoms; another, who had emphysema, had dyspnoea and orthopnoea. The remaining three patients had no respiratory symptoms. Four patients had limb muscle weakness as judged by the maximal voluntary contraction of the quadriceps muscle (range for all subjects 32-100% predicted). Transdiaphragmatic pressure (Pdi) was measured during a maximal unoccluded sniff (Pdi: sniff), a maximal sustained inspiratory effort against a closed airway (Pdi: Pimax), and phrenic nerve stimulation (Pdi: twitch). Mild to moderate diaphragmatic weakness was present in all six patients in proportion to the degree of leg weakness (Pdi: sniff 30-64% predicted; r = 0.6; Pdi:Pimax 6-69% predicted, r = 0.8); this was associated with very low or absent Pdi:twitch during phrenic nerve stimulation. Four patients had weakness of the expiratory muscles. Improvement in muscle strength was documented in two patients after tumour chemotherapy and specific treatment with 3,4-diaminopyridine and prednisolone; one patient was still alive five years from first diagnosis. It is concluded that the respiratory muscles may be implicated in this condition more often than has previously been recognised. As the lack of mobility may cause respiratory symptoms to be minimised, the presence of respiratory muscle weakness may remain undiagnosed unless formal measurement of respiratory muscle function is made.     

Diaphragmatic activity during isoflurane anaesthesia in dogs

The effect of isoflurane administration on diaphragmatic activity was investigated in six anaesthetized mechanically ventilated dogs. Diaphragmatic strength was assessed by measuring the transdiaphragmatic pressure (Pdi) generated during supramaximal stimulation of both cervical phrenic nerves at frequencies of 0.5, 10, 20, 50 and 100 Hz under partially isometric conditions at 1, 1.5 and 2 minimum alveolar anaesthetic concentrations (MAC), after maintaining 1 h of stable conditions. Pdi measurements were made at the start of the stimulation (initial) and at the end of a 2-s period (2-s). The force-frequency relationship was compared at each anaesthetic level. For single twitch (0.5 Hz) stimulation, the time constant of diaphragmatic relaxation was also assessed. The sequence of changing anaesthetic depth was altered in random fashion between animals. Pdi amplitude at single twitch stimulation was unchanged at the three anaesthetic concentrations. There was no significant difference in initial Pdi at various stimulus frequencies with increasing depth of isoflurane anaesthesia. In addition, no change in 2-s Pdi during low frequency stimulation (10 and 20 Hz) was noted during any of the three levels of anaesthesia. By contrast, 2-s Pdi with 50 Hz stimulation during 2 MAC isoflurane exposure decreased significantly below Pdi levels seen at 1 and 1.5 MAC (P<O.O1). Furthermore, 2-s Pdi at 100 Hz stimulation decreased significantly in a dose-dependent fashion. From these results, we conclude that isoflurane reduces diaphragmatic activity at higher stimulation frequencies of 50 and 100 Hz.     

RETRACTED ARTICLE: Effect of xenon on diaphragmatic contractility in dogs

PURPOSE: This study was undertaken to examine the effect of xenon on diaphragmatic contractility in pentobarbitone- anesthetized, mechanically ventilated dogs. METHODS: Twenty-one dogs were randomly allocated to three groups (n=7 of each): Group I received oxygen 100%; Group II received xenon 30% in oxygen; Group III received xenon 60% in oxygen. Diaphragmatic contractility was assessed by measuring transdiaphragmatic pressure (Pdi) generated during supramaximal stimulation of phrenic nerves at the neck at low-frequency (20-Hz) and high-frequency (100-Hz) stimulation, after maintaining 60 min of stable condition. RESULTS: With inhalation of xenon at two different concentration (30% and 60%), no changes were observed in Pdi at either concentration. There was no difference in Pdi among the three groups. CONCLUSION: Increasing the concentration of xenon to 60% has no effect on diaphragmatic contractility in dogs. This suggests that xenon may be used safely as an anesthetic with respect to respiratory muscle function.     

Breathing pattern and carbon dioxide retention in severe chronic obstructive pulmonary disease.

BACKGROUND: The factors leading to chronic hypercapnia and rapid shallow breathing in patients with severe chronic obstructive pulmonary disease (COPD) are not completely understood. In this study the interrelations between chronic carbon dioxide retention, breathing pattern, dyspnoea, and the pressure required for breathing relative to inspiratory muscle strength in stable COPD patients with severe airflow obstruction were studied. METHODS: Thirty patients with COPD in a clinically stable condition with forced expiratory volume in one second (FEV1) of < 1 litre were studied. In each patient the following parameters were assessed: (1) dyspnoea scale rating, (2) inspiratory muscle strength by measuring minimal pleural pressure (PPLmin), and (3) tidal volume (VT), flow, pleural pressure swing (PPLsw), total lung resistance (RL), dynamic lung elastance (ELdyn), and positive end expiratory alveolar pressure (PEEPi) during resting breathing. RESULTS: Arterial carbon dioxide tension (PaCO2) related directly to RL/PPLmin, and ELdyn/PPLmin, and inversely to VT and PPLmin. There was no relationship between PaCO2 and functional residual capacity (FRC), total lung capacity (TLC), or minute ventilation. PEEPi was similar in eucapnic and hypercapnic patients. Expressing PaCO2 as a combined function of VT and PPLmin (stepwise multiple regression analysis) explained 71% of the variance in PaCO2. Tidal volume was directly related to inspiratory time (TI), and TI was inversely related to the pressure required for breathing relative to inspiratory muscle strength (PPLsw, %PPLmin). There was an association between the severity of dyspnoea and both the increase in PPLsw (%PPLmin) and the shortening in TI. CONCLUSIONS: The results indicate that, in stable patients with COPD with severe airflow obstruction, hypercapnia is associated with shallow breathing and inspiratory muscle weakness, and rapid and shallow breathing appears to be linked to both a marked increase in the pressure required for breathing relative to inspiratory muscle strength and to the severity of the breathlessness.