Pressure-Controlled Inverse Ratio Ventilation-To the Editor

been shown to significantly increase the distance ambulated during the 6'\VT.ll Furthe rmore, other factors such as psychological and mental health must be considered when evaluating performance during the 6'WT or standard exercise testing. We have recently discovered that psychological status (measured via the SF -36, a 36-item questionnaire measuring eight health profiles) is related to 6'\VT distance ambulated (accounting for 33% of the variability) in patients with emphysema 7 Finally, the relationship of environmental toxins, such as passive smoke and nontobacco sources of carbon monoxide, to exercise performance has not been investigated, to our knowledge, in patients with heart frulure. Although we did not specifically control for exposure to these toxins, the majority of patients in our study were hospitalized b efore testing was initiated. Urine cotinine levels were not drawn in our subjects, but future investigations could easily address the relationship of these toxins to exe rcise performance and reliability of the 6'WT. It is reasonable to conclude that exercise performance would decline with increasing evidence of exposure to these toxins. It is uncertain how this would effect the degree of variability and subsequent reliability of the 6'\Vf. This and other environmental and psychological effects must be carefully evaluated to determine the clinical utility of the 6'\'VT. The clinical utility of the 6'WT and ease of administration make it appealing. However, we agree that reliability and unexplained variability in this test must be further evaluated in future large-scale, prospective studies. Lawrence P. Cahalin, MA Boston University Marc]. Semigran, MD G. William Dec, MD Massachusetts General Hospital Boston REFERENCES l Armstrong PW, Moe GW. Medical advances in the therapy of congestive heart failure. Circulation 1993; 88:2941-52 2 Australian-New Zealand Heart Failure Hesearch Collaborative Group. Effects of carvedilol, a vasodilator-beta-blocker, in patients with congestive heart failure due to ischemic heart disease. Circulation 1995; 92:212-18 3 Sveta CA, Gheorgihiade M, Adams KF, e t a!. Safety and efficacy of epoproste nol in patients \vith severe congestive heatt failure: epopros tenol multicenter research group. Am J Cardiol 1995; 75:34-41 4 Provenier F , Jordoesn S. Evaluation of 6-minute walking test in pati ents with single chamber rate response pacers. Br Hea1t J 1994; 72:192-96 5 Bittner V, Weiner DH , Yusuf S, eta!. Prediction of mortality and morbidity \vith a 6-minute walk test in patients with left ventricular dysfunction. JAMA 1993; 270:1702-07 6 J ette DU, Downing J. The relationship of cardiovascular and psychological impairments to th e health status of patients enrolled in cardiac rehabilitation programs. Phys Ther 1996; 76:130-39 7 Cahalin L, Cannon J, Wright C, et a!. Psychological status is related to six minute walk test p erformance in patients with obstructive lung disease [abstract]. Chest 1996; 110:160S 8 Cahalin LP, Mathier MA, Semigran MJ, eta!. The six-minute walk test predicts peak oxygen uptake and survival in patients with advanced heatt failure. Chest 1996; 110:325-32 9 Carlson DJ. Vo2 max: the gold standard? Chest 1995; 108: 602-03 10 Borg GAY. Psychophysical basis of perceived exertion. Med Sci Sports Exerc 1982; 14:377-81 l l Guyatt GH, Pugsley SO, Sullivan MJ, eta!. Effect of encouragement on walking test performance. Thorax 1984; 39: 818-22

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Pressure-Controlled Inverse Ratio Ventilation To the Editor: Pressure-controlled inverse ratio ventilation (PCIRV) has been proposed as an alternative mode of ventilat01y suppmt in the setting of ARDS. The main idea motivating this ventilat01y support was the heterogeneity of the lung in this disease. PCIH.V would therefore be an interesting mode by creating an intrinsic positive end-expiratOty pressure (PEEPi) and by limiting the barotrauma (but not volotrauma) through pressure control. The difference between th e external PEEP (PEEPe) and the PEEPi is that in the latter, there is a recruitme nt of alveolar units with slow time constants due to the increased inspiratory time, resulting in a more homogenous ventilation of the lung. 1 In the paper by Lud\vigs and colleagues (August 1996), 2 the authors compare two ventilatory modes, PCIRV and volume-controlled ventilation (VCV), \vith PEEP in the normal rabbit lung. Using a normal lung is already a limitation of the use of PCIH.V, which is designed for heterogenous lungs. In PCIRV and VCV, the authors reach the same tidal volume. PCIRV is designed to of hypoventilation, therefore limiting the tidal tolerate a evel l volume compared to VCV. It seems, therefore, difficult to compare these two ventilatory support modes, reaching the goals of the first one at the expense of the second one. Finally, the authors estimate they compare these two modes at equal levels of end-expiratory alveolar pressure. They apply a PEEPe of 5 em of H 2 0 in VCV. In PCIRV, if static PEEP is below 5 em H2 0 , they add an external PEEP of 1 or 2 em H 2 0. ls it really fair to compare the effects of PCIRV, which is supposed to induce an intrinsic PEEP, by adding an external PEEP to reach the same end-expiratory alveolar pressure? Even though the authors do not have m:ygenation goals or ventilatory patterns criteria, they conclude that PCIRV causes an alteration in lung epithelial or membrane function. But a question remains, do we need to meet VCV goals to set PCIRV parameters? Benoit PH Guery, MD Hughes Georges, MD Olivier Leroy, MD Service de Reanimation Medicale Hopital Chatilliez Tourcoing, France Reprint requests: Dr. B. Guery, Service de Reanimation Medicale, 135 Rue du Pdt Coty, 59208 Tourcoing, France REFERENCES 1 Lachmann B, Schairer W, Armbruster S, et al. Improved arterial m:ygenation and C0 2 elimination following changes from volume generated PEEP ventilation with inspiratory/ expiratory ratio of 1:2 to pressure generated ventilation with I/E of 4:1 in patients with severe adult respiratory distress syndrome. Adv Exp Med Bioi 1989; 248:779-86 2 Ludwigs U, Philip A, Robertson B, eta!. Pulmonary epithelial perm eability: an animal study of inverse ratio ventilation and conventional mechanical ventilation. Chest 1996; 110:486-93 To the Editor: We welcome the interest of Dr. Guery and colleagues regarding our article concerning inverse ratio ventilation. vVe also appreciate the opportunity to discuss the issues raised by the authors. vVe agree that pressure-controlled inverse ratio ventilation (PCIRV) is intended for use in patients with severe gas exchange Communications to the Editor

abnormalities. However, it is likely, both from a theoretical point of view and from model studies, that the build-up of intrinsic positive end-expiratory pressure (PEEPi) and increase in regional end-e>-'j)iratory lung volume (EE LV) is greatest in slow lung units (highest compliance andlor highest resistance). 1 Conversely, lung units with low compliance andlor low resistance (fast lung units ) develop the lowest levels ofPEEPi and EELV. Thus, PEEPi may cause overinflation of normal lung and a relative underinflation of fast lung units. This property of PEEPi has been proposed to explain the failure of PCIRV to increase Pa0 2 despite a marked increase in mean airway pressure.2.J Seve ral studies have documented an improved C0 2 clearance with PCIRV,4 and it would be interesting to compare PCIRV with conventional ventilation at equal levels of alveolar ventilation. In the prese nt study, we decided to keep tidal volume and PEEP constant since both these variables are known to influence lung clearance. A study of lung clearance during PCIRV in oleic acid-induced lung injury is underway. Ulf Ludwigs, MD, PhD Anders Philip, MS Sodersjukhuset Stockholm, Sweden Bengt Robertson, MD Karolinska Hospital Solna, Sweden Goran Hedenstiema, MD, FCCP Uppsala University Hospital Uppsala, Sweden

REFERENCES 1 Kacmarek RM , Kirmse M, Nishimura M, e t a!. The effects of applied vs auto-PEEP on local lung unit pressure and volume in a four-unit lung model. Chest 1995; 108:1073-79 2 Mercat A ,Gralni L, Teboul JL, e t a!. Cardiorespiratory effects of pressure-controlled ventilation with and without inverse ratio in the adult respirat01y distress syndrome. Chest 1993; 104:871-75 3 Mang H, Kacmarek RM , Ritz R, et a!. Cardiorespirat01y effects of volume- and pressure-controlled ventilation at various liE ratios in an acute lung injury model. Am J Respir Crit Care Med 1995; 151:731-36 4 Shanholtz C, Brower R. Should inverse ratio ventilation be used in adult respiratory distress syndrome? Am J Respir Crit Care Med 1994; 149:1354-58

Using Corticosteroids to Treat Tuberculous Pleurisy To the Editor:

We read with interes t the report in CHEST by Wyser et al (August 1996)1 concerning the use of corticosteroids in the treatment of tuberculous (TB ) pleurisy. We would like to comment on the article. First of all, we regret to read in th e introduction: " ... to our knowledge, no other placebo-controlled studies that examine this form of treatment have been published. " We have recently published th e results of a large prospective, doubl e-blind, placebo-controlled, and randomized trial of corticosteroids in the treatment of this disease. 2 The ove rall design of both studies is similar, but with some relevant diffe rences in the methodology: (1) we use needle biopsy

for obtaining specimens of pleura (instead of thoracoscopy), with simultaneous pa1tial drainage of the effusion by needle thoracocentesis (no tube drainage); (2) we use a two-drug regimen for 6 months as treatment of the pleurisy, and (3) we use a steroid treatment starting with a dose of 1 mg/kglday, gradually tapered until completing 1 month of corticosteroids; Wyser and colleagues start with 0.75 mglday for 1 month and th en taper off, completing 8 weeks of treatment. Our aim in draining the pleural cavity was to equalize, in both groups-placebo and steroids, the volume of liquid to be reabsorbed as a result of drug therapy. In both studies, the evolution of the clinical, radiologic, and functional parameters showed similar comparative results in both groups of patients, with no statistically significant differences . The rapidly favorabl e clinical changes observed after th e complete drainage of the ple ural cavity in both groups even b efore randomization in the study of Wyser and colleagues are to be expected (particularly concerning dyspnea, chest pain); but we would not normally submit our patients with TB pleurisy to a thoracoscopy followed b y a2-day tube drainage. Furthermore, in co mpmison \'lith the control group, the patients treated with steroids by Wyser and colleagues showed a more rapid clinical recovery according to the visual analog scale (VAS ) score. We believe that this statistically significant difference may be related to the effect of steroids in three of the seven parameters selected in the VAS: tiredness, appetite, and well being. We have also observed that those patients treated with steroids showed a more rapid decline of fever, but the difference was not statistically significant. At the same time in the study of Wyser and colleagues, 44% of the patients in the placebo group and 21.2% in th e steroid group showed pulmonary involve ment. This difference could also determine a more slowly clinical evolution in the placebo group, because as the authors remark, pulmona1y changes resolve more slowly than the pleural ones. The authors state that the factor responsible for symptomatic improve ment in all patients was the complete early drainage of the effusion at the time of the thoracoscopy. The good results that we have observed in our study in all the patients, treated \vith steroids or not, support the view that a complete drainage of the effusion is not a sin e qua non for a good res ult in the treatment of TB pleurisy. According to our results, we suppo1t the view that: ( 1)the good outcome of TB pleurisy is mainly due to the effect of an effective (two- or three-drug regimen) antituberculous therapy, and that (2) a complete drainage of the pleural cavity is not necessary. Finally, we would like to confirm that after a 1-year follow-up neither fibrothorax nor recurrence of pulmonary TB have occurred in our seri es, so that we can answer to the last statement of the mticle of Wyser and colleagues that early drainage is not superior to no (or minimal ) drainage in the long-term outcome of TB pleurisy. Federico Manresa, MD Itziar Galarza, MD Concepcion Caiiete, MD Servei de Pneumologia Hospital d e Belluitge Universitat de Barcelona Barcelona, Spain

REFERENCES Wyser C, Walzl G, Smedema JP, et al. Corticosteroids in the treatment of tuberculous pleurisy: a double-blind, placebocontrolled, randomized study. Chest 1996; 110:333-38 2 Galarza I, Cafiete C, Granados A, et al. Randomized trial of corticosteroids in the treatment of tuberculous pleurisy. Thorax 1995; 50:1305-07 CHEST I 112 I 1 I JULY, 1997

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