Pulmonary function testing. What is 'normal'?

For many years, confusion has existed concerning the normal range for pulmonary function test results. Using statistical guidelines that have been traditionally applied to the interpretation of measured forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1), we have redefined normal limits for the most common pulmonary function test values, including those for FVC, FEV1, mean forced expiratory flow during the middle half of the FVC, FEV1 as a proportion of FVC, residual volume, functional residual capacity, total lung capacity, diffusion capacity, maximum voluntary ventilation, and peak expiratory flow. Our goal is to provide a simple and consistent scheme for interpretation of pulmonary function test data. We consider the assumptions used to achieve this simplification to be reasonable, as long as their limitations are understood.

Noninvasive nasal mask ventilation for acute respiratory failure. Institution of a new therapeutic technology for routine use.

OBJECTIVE: We successfully implemented the delivery of noninvasive mechanical ventilation for patients with acute respiratory failure, a previously controversial use of this technique, using a simplified ventilator (BiPAP) with nasal mask. Pilot work showed this mode of support to be effective when administered by the members of a research team, and in the current study we were able to transfer this responsibility to usual care providers. SETTING: Almost 90 percent of the patients in this study were in either the 16-bed medical or 31-bed surgical intensive care units at our hospital. SUBJECTS: One hundred ten hemodynamically stable patients with acute respiratory failure being considered for intubation and mechanical ventilation participated in this study. Eighty percent were surgical patients, most of whom had hypercapnic failure. INTERVENTION: Patients were administered noninvasive ventilatory support using a ventilatory support system (BiPAP) applied with a nasal mask. This intervention was administered by a research team in the initial 31 patients (special care, phase 1). The administration was transferred to usual care personnel in the next 45 patients (transition, phase 2). Usual care personnel almost exclusively administered care in the final 34 patients (usual care, phase 3). RESULTS: Withdrawal of ventilatory support for greater than 48 h (successful outcome) was about the same during usual care (phase 3, 80 percent) as it was during special care (phase 1, 76 percent).

A simplified computer report. Towards an understandable pulmonary function test.

We have developed a graphic format for the display of pulmonary function test results. Patient test results appear as a series of horizontal bar graphs. Each bar length is proportional to the test result and is printed over the normal ranges. This format allows rapid recognition of individually abnormal values. We have also grouped bars to create distinctive patterns characteristic of obstructive or restrictive lung disease. A computer program generates a custom form for each patient, displaying the results and ranges only for the specific test performed on that individual. No preprinting of forms is required. Written in the BASIC computer language, this program was designed to be flexible. A change of program parameters requires only minor program modification. In addition, because of its simplicity, our program can be implemented on almost any computer printer.

Experimental studies on heterotopic lung transplantation during temporary pulmonary insufficiency.

Survival from reversible forms of severe pulmonary insufficiency remains dismal despite the development of artificial oxygenators. We hypothesized that an intraabdominal heterotopic lung could help maintain adequate oxygenation during acute pulmonary insufficiency. Five mongrel dogs underwent an acute heterotopic lung transplant (HLT). The left atrial cuff was anastomosed to the inferior vena cava, and the left pulmonary artery was anastomosed to the abdominal aorta. The trachea was exteriorized, intubated, and ventilated with a volume-controlled ventilator. Ventilation to the native lungs was discontinued. The heterotopic lung was then ventilated at a rate of 20/min, tidal volume of 15 ml/kg, and inspired concentration (FIO2) of 50 percent. Partial pressure of oxygen (PO2) and mixed venous oxygen saturation (SvO2) were maintained at 53 +/- 5.2 mm Hg and 71 +/- 12 percent, respectively. Flow through the HLT was approximately 20 percent of the systemic cardiac output and did not vary with changes in FIO2, respiratory rate, or positive end-expiratory pressure (PEEP). Four separate animals underwent HLT and were studied 2 to 3 days later. The FIO2 was reduced in the native lungs to 10 percent until SaO2 was less than 90 percent. The HLT was then ventilated at a tidal volume of 300 ml, an FIO2 of 50 percent, and a respiratory rate of 10. Arterial PO2 increased from 62 +/- 4 mm Hg to 75 +/- 2 mm Hg, and SvO2 increased from 75 +/- 2 percent to 82 +/- 3 percent (p < 0.05). Flow through the HLT increased slightly to 27 percent of the systemic cardiac output. We conclude that a HLT can augment oxygenation after induction of moderate hypoxemia, but cannot serve as the sole source for gas exchange because flow through the HLT is limited to less than 30 percent of the cardiac output.

Pressure support ventilation with a simplified ventilatory support system administered with a nasal mask in patients with respiratory failure.

Thirty-one consecutive patients with respiratory failure in whom treatment with intubation and mechanical ventilation was being strongly considered received alternative ventilatory support by means of a BiPAP ventilatory support system and nasal mask. Laboratory measurements and physical findings were documented before and 1 h after initiation of support. This support improved patient comfort, slowed respiratory rate, and improved oxygenation. Support lasted from 2 h to six days. Seventy-six percent (22/29) of patients recovered from this episode of respiratory failure, avoiding alternative mechanical ventilatory support. There were no complications associated with aspiration, gastric distention, or acute separation from support.

Aerosol administration of fenoterol hydrobromide (Th 1165a) in subjects with reversible obstructive airway disease.

Bronchodilatory and side effects of fenoterol hydrobromide (Th1165a; hydroxyphenylorciprenaline; Berotec) and isoproterenol given by inhalation were compared in a double-blind crossover study involving 20 volunteer subjects with reversible obstructive disease of the airways. Subjects inhaled medications from aerosol canisters containing fenoterol hydrobromide (0.1 mg, 0.2 mg, or 0.4 mg) or isoproterenol (0.15 mg) or an inert placebo propellant in a random sequence of five testing days. All active drugs substantially increased the forced expiratory volume in one second, the mean forced expiratory flow during the middle half of the forced vital capacity, and the specific conductance. The onset of bronchodilation after both fenoterol and isoproterenol was rapid, but the effect from fenoterol lasted much longer, up to eight hours. None of the medications cuased significant tachycardia or hypertension. After inhalation of 0.1 mg of fenoterol hydrobromide, none of the subjects reported nervousness, headache, tremor, or nausea, incontrast with results reported for isoproterenol, higher aerosol doses fo fenoterol, or oral administration of fenoterol. No additional therapeutic benefit was found in the administration of higher doses of fenoterol.

Nutritional status and lung function in patients with emphysema and chronic bronchitis.

This study compared the nutritional status of patients with emphysema and chronic bronchitis and examined the relationship between lung dysfunction and nutritional depletion in patients with emphysema. There was no evidence of nutritional depletion in patients with chronic bronchitis (n = 4). In contrast, patients with emphysema (n = 14) were somatically depleted. They exhibited lower values for percent ideal body weight (%IBW), arm muscle circumference (AMC), and triceps skin fold thickness (TSF) (p less than 0.05) than did patients with chronic bronchitis. The creatinine height index (CHI) was also lower in this group, but the difference was not significant (p = 0.08). In patients with emphysema, there was a good correlation between the degree of airflow obstruction and of somatic depletion (FEV1 vs %IBW, r = 0.699, p less than 0.001). The single-breath diffusing capacity (DCO) also correlated well with %IBW (r = 0.6052, p less than 0.019). These results confirm that patients with emphysema are frequently nutritionally depleted and suggest that nutritional depletion contributes to lung dysfunction in emphysema.

Pulmonary function in progressive systemic sclerosis. Comparison of CREST syndrome variant with diffuse scleroderma.

The pulmonary function and chest roentgenograms were evaluated in 88 patients with the CREST syndrome variant of progressive systemic sclerosis (PSS or scleroderma). Seventy-two percent of the patients had abnormal pulmonary function. An isolated decrease in diffusing capacity was the most common abnormality noted, followed by restrictive abnormalities and airway obstruction. Chest roentgenograms revealed interstitial infiltrates consistent with pulmonary fibrosis in 33 percent. When compared to a contemporaneous group of 77 patients with PSS and diffuse scleroderma, patients with the CREST syndrome had similar abnormalities on pulmonary function testing and chest roentgenogram. However, patients with the CREST syndrome had a lower mean diffusing capacity despite a higher mean vital capacity; this combination of findings suggests primary pulmonary vascular disease. Calcified granulomata were identified significantly more often in PSS-CREST patients, while superior rib notching occurred exclusively in patients with PSS and diffuse scleroderma. The CREST variant of PSS is associated with frequent roentgenographic and pulmonary function abnormalities similar to those seen in PSS with diffuse scleroderma.

Heterotopic lung transplantation: temporary biologic support for reversible pulmonary insufficiency.

BACKGROUND: The mortality rate resulting from adult respiratory distress syndrome in patients awaiting orthotopic lung transplantation remains high. Providing an "extra" lung may provide a potential solution to support a failing pulmonary system. We hypothesized that using a heterotopic lung transplant can correct hypoxemia and hypercarbia in both the short term and the long term. METHODS: Seven mongrel dogs underwent transplantation of a left lung into the abdomen. Anastomosis between the left atrial cuff and the pulmonary artery of the donor lungs was accomplished to systemic venous and arterial circulations, respectively. The main stem bronchus was exteriorized, intubated, and ventilated. Immunosuppression consisted of prednisone and azathioprine both preoperatively and postoperatively. Progressive levels of systemic hypoxemia and hypercarbia were induced. The heterotopic lung transplant augmented oxygenation with a tidal volume of 300 cc, a fraction of inspired oxygen of 50%, and a respiratory rate of 10 and then 20 breaths/min. Four animals were studied again at 48 hours. Flow through the heterotopic lung transplant ranged from 25% to 33% of the cardiac output. RESULTS: Statistically significant improvements were seen in both systemic oxygenation and ventilation in the short-term experiment. The systemic oxygen pressure improved from 37 +/- 3 mm Hg to 67 +/- 5 mm Hg after ventilation of the heterotopic lung transplant, and the carbon dioxide pressure improved from 56 +/- 1 mm Hg to 43 +/- 2 mm Hg. At 48 hours an improvement in oxygen pressure was noted after ventilation of the heterotopic lung transplant, from 42 +/- 3 mm Hg to 56 +/- 2 mm Hg and an improvement in systemic carbon dioxide pressure was noted after ventilation of the heterotopic lung transplant from 57 +/- 7 mm Hg to 46 +/- 4 mm Hg. CONCLUSIONS: The heterotopic lung transplant was able to provide effective gas exchange and support both oxygenation and ventilation after the induction of acute hypoxemia or hypercarbia, both immediately and at 48 hours after implantation. The heterotopic lung transplant may serve as an alternative mode of temporary support for those with acute respiratory insufficiency or as a bridge for those awaiting orthotopic lung transplantation.

Indirect calorimetry with a hood: flow requirements, accuracy, and minute ventilation measurement.

Flow-dilution-based hood systems for indirect calorimetry eliminate the conventional mouthpiece or mask of sealed-circuit systems allow measurements with improved patient comfort. This feature is particularly relevant when measurements are made over long periods of time or are repeated often. The flow of air pulled through the hood into the calorimeter in these systems is necessary to clear CO2 from inside the hood. The errors in these systems are greater than those in the sealed-circuit systems and are proportional to the flow. We show that the CO2 concentration within the hood at steady state does not depend on hood size. We describe the accuracy in determination of O2 consumption (VO2), CO2 production, and respiratory exchange ratio with a hood system as a function of the accuracy of the O2 and CO2 analyzers and the water vapor in collected gas. For example, we show that if there is a 1% error in O2 concentration, the percent error in VO2 changes from 5% in a sealed circuit to 51% when a cleansing flow of 50 l/min is introduced. The error in VO2 caused by a 5% error in CO2 determination is 10.6% at this cleansing flow. Removal of 90% of the water vapor (instead of 100%) before analysis of the expired gas introduces a 15.8% error in VO2. By use of the equations described, the accuracy of any measurement system can be determined. In addition, we demonstrate that the measurement of ventilation, usually lost in a hood system, can be preserved using dual pneumotachographs and a sealed hood.

Metabolic rate and weight loss in chronic obstructive lung disease.

Although weight loss is a common problem in chronic obstructive pulmonary disease (COPD), the precise cause of malnutrition in COPD patients is not known. The purpose of this study was to measure and compare resting energy expenditure (REE) in stable undernourished and adequately nourished COPD. REE was measured in normal, adequately nourished, and undernourished COPD patients by indirect calorimetry and then compared to predicted basal metabolic rate (BMR) calculated from the Harris-Benedict equation. We found that measured REE, compared to predicted, was significantly higher in the undernourished group, (1.15 +/- 0.02) and compared to the adequately nourished COPD (0.99 +/- 0.03) and normal groups (0.93 +/- 0.02) (p less than 0.0001). We conclude that there is a hypermetabolic state in stable malnourished COPD patients which may be a factor in weight loss. This elevated REE also needs to be taken into account when determining caloric requirements for COPD patients.

Distressful events in the ICU as perceived by patients recovering from coronary artery bypass surgery.

OBJECTIVE: To determine what events are perceived as most stressful to patients in the surgical intensive care unit (SICU). DESIGN: Descriptive cross-sectional survey. PATIENTS: One hundred twenty-seven patients who had undergone coronary artery bypass graft (CABG) at 48 hours after their transfer from the SICU. OUTCOME MEASURE: Stressful events as perceived by patients while in the SICU determined by 25 specific items on a questionnaire rated on a Likert scale ranging from 1 (no distress) to 4 (extremely distressful). RESULTS: Two stressors, being intubated and not being able to talk, were significantly more stressful, by Newman-Keuls multiple range test, than all the other stressors. The mean stressfulness score for all other stressors was between no distress and mild distress. CONCLUSION: Overall stress associated with specific events during a short stay in the SICU was minimal. Intubation and inability to communicate were the most stressful experiences.

Noninvasive ventilation for postoperative support and facilitation of weaning.

Noninvasive ventilation includes continuous positive airway pressure with mask, positive pressure ventilation with mask, and negative pressure body ventilation. Noninvasive ventilation is a ventilatory support mode intermediate in both effectiveness and potential complications between oxygen administration and intubation with mechanical ventilation. The advantages, disadvantages, and experimental results of the use of noninvasive ventilation in patients who have been extubated following recovery from surgery and subsequently experience respiratory difficulties are discussed. In general, noninvasive ventilation seems to provide useful ventilatory support in about three of four patients in whom it is tried. In addition, the use of noninvasive ventilation as an aid to weaning of patients from mechanical ventilation is discussed. This use of noninvasive ventilation has not yet been extensively reported, although it appears to be potentially useful.

Quantitative measurement of ventilation at the mouth and nose with heat sensors.

Airflow at the nose and mouth is routinely measured during polysomnography for the evaluation of respiratory disturbances during sleep. The usual monitoring device is a small thermocouple placed in front of the nose and mouth that qualitatively detects airflows in or out. A more accurate pneumotachometer on a tight-fitting mask is less frequently used because of the discomfort that is introduced and its potential interference with sleep. The authors tested ten heat-sensing devices modified to increase accuracy without increasing discomfort. The designs of these ventilation monitors differed in choices of specific heat detector, techniques of mounting on the face, and types of heat-trapping covers employed. The goal was to find a comfortable oronasal monitor and to define a procedure that could identify those units that generate signals approaching quantitative ventilatory flow. The signal from each device was compared with a "standard" signal derived from respiratory belts during contrived respiratory maneuvers that assessed specific potential sensing problems. The devices behaved differently, and design perturbations could be controlled to construct flow detectors to closely match actual flow. The more accurate devices could be as comfortable as commonly used monitors that do not have the enhanced accuracy. The principles and techniques described for improving the measurement of oronasal ventilation by heat sensor can be invoked to develop monitors that can closely measure actual quantitative ventilatory flow.