Maximal Respiratory Pressures Research Articles

Nocturnal oxygenation and prognosis in Duchenne muscular dystrophy.

REM-related oxygen desaturation occurs in advanced Duchenne muscular dystrophy (DMD) and might be an independent predictor of disease progression. We have followed 18 patients for 10 yr after an initial respiratory sleep study or until death or onset of nasal ventilation. We measured baseline spirometry, blood gas tensions, maximal respiratory pressures, and body mass index. In 11 cases, VC was recorded serially. Median survival was 50 (range, 13 to 89) mo from initial study and unrelated to age at time of study, BMI, or mouth pressures but correlated with PaCO2 (r = -0.72, p < 0.005, n = 17), minimal nocturnal SaO2 (r = 0.62, p < 0.007, n = 18) and VC (r = 0. 65, p < 0.005, n = 17). Cox regression analysis showed a VC of less than 1 L at the time of study to be the best single predictor of subsequent survival. The only measure associated with age of death was the age at which the VC fell below 1 L (r = 0.79, p < 0.004). These data suggest measurement of PaCO2 or serial assessment of VC should be studied further as valid methods of assessing prognosis in DMD.

Reliability of Maximal Respiratory Pressures in Multiple Sclerosis

To assess the reliability of maximal inspiratory pressure (P(I)max) and maximal expiratory pressure (P(E)max) in subjects with multiple sclerosis (MS) and healthy control subjects by identifying the number of testing sessions and the number of measurements needed in a single testing session to obtain consistent, reproducible results. A descriptive, comparative design with repeated measures was used. Four sets of 10 P(I)max and 10 P(E)max measurements were obtained over a 4-week period from MS subjects in their homes. The same measurements were obtained from healthy control subjects in a private setting. Seventy-two MS patients and 61 healthy control subjects participated in the study. P(I)max and P(E)max values were obtained by using previously published methods. Mean P(E)max and P(I)max values for MS patients differed over the first three of the four testing sessions. By contrast, mean P(E)max and P(I)max values for healthy control subjects differed only when the first session values were compared with values from the last three sessions. For MS patients, P(E)max and P(I)max increased between the first and 10th trial during the first testing session, but not during the subsequent three sessions. The results of this study suggest that several practice sessions should be provided in order to obtain reliable P(E)max and P(I)max values in persons with MS. At least one practice session should be provided for healthy control subjects before identifying a baseline.

A simplified method for separate measurements of lung and chest wall mechanics in ventilator-treated patients.

Airway pressure measurements above the endotracheal tube will be distorted because of endotracheal tube resistance. To separate lung and chest wall compliance, esophageal pressure is conventionally measured with an air-filled balloon catheter, which is difficult to insert in unconscious patients. We have developed a methodology with fluid-filled catheters for intratracheal and esophageal pressure measurements. Twelve anesthetized patients were studied. Tidal volumes were measured by side-stream spirometry. Airway pressures were measured at the Y-piece and in the trachea with fluid-filled pressure lines. Esophageal pressure was measured via the narrow lumen in a fluid-filled Salem double-lumen stomach tube, which was slowly retracted from the stomach up through the esophagus until maximal respiratory pressure readings and minimal cardiac artifacts were obtained. Lung mechanics were measured at different tidal volumes (TV) and positive end-expiratory pressure (PEEP). There was a significant difference between airway pressures at the Y-piece and in the trachea. Total compliance significantly increased with increasing TV and decreased with increasing PEEP. Chest wall compliance increased significantly with increasing TV, while lung compliance did not change significantly. Two patients showed repeatedly marked increase in lung compliance at one specific ventilatory setting, an increase the proportion of which was not reflected by changes in total compliance. Y-piece pressures are not representative of intratracheal pressures, which can be measured by inserting a fluid-filled pressure line through the tube. Esophageal pressure is easily recorded with a fluid-filled Salem double-lumen catheter. Large changes in lung compliance may pass unnoticed when only total compliance is monitored. Monitoring of lung compliance may offer an improved basis for decisions about ventilator settings.

Dyspnea in Obese Healthy Men

To determine whether obese, apparently healthy individuals experience dyspnea at rest and, if so, whether their pulmonary function test (PFT) profile and maximal respiratory pressures are different from obese, healthy subjects without dyspnea. Prospective, open. Pulmonary function test laboratory, Veterans Administration Medical Center. Twenty-three obese male subjects (each with a body mass index [BMI] of > 28 kg/m2) with an FEV1 level and an FEV1/FVC ratio > or = 80% of predicted and no coexisting conditions. Fifteen complained of dyspnea, where eight denied having it, at rest. Standard PFT parameters and maximum static inspiratory (P(Imax)) and expiratory (P(Emax)) mouth pressures were determined. Subjects with dyspnea had similar age and height but larger body weight (113.9+/-5.0 vs 97.4+/-2.6 kg, p = 0.03) and BMI (37.4+/-1.6 vs 31.8+/-0.7 kg/m2, p = 0.02) than subjects without dyspnea, and a greater number of them were current or previous smokers. Forced expiratory flow at 75% vital capacity (54.9+/-6 vs 75.5+/-7% predicted, p = 0.05), maximum voluntary ventilation (MVV; 90.2+/-3.8 vs 107.8+/-9.3% predicted, p = 0.05), and P(Emax) (77+/-2 vs 97.8% predicted, p = 0.007) were significantly reduced in the group of subjects with dyspnea. Large airway function (FVC, FEV1, and FEV1/FVC ratio), lung volumes, and gas exchange parameters were similar between the two groups. Some obese, but otherwise healthy, individuals experience dyspnea at rest. Reduced P(Emax) and MVV combined with greater body mass and peripheral airway disease are most likely responsible for the sensation of dyspnea in these individuals.

Association between self-reported leisure-time physical activity and measures of cardiorespiratory fitness in an elderly population.

Leisure-time physical activity enhances health and functioning in older populations. However, few data are available on the correlation between self-reported leisure-time physical activity and cardiorespiratory fitness in the elderly. Treadmill exercise testing results were obtained for 1,006 members (median age 67 years) of a community-based sample. Subjects completed a standardized evaluation of medical/social history and measures of physical function. Leisure-time physical activity in the 12 months and 7 days before interview and over subjects' lifetimes was summarized as total and activity-specific METs/week and [METs * (hours/week)]. Multiple linear regression was used to investigate the cross-sectional, sex-specific associations between peak oxygen consumption (VO2) and exercise duration. After adjustment for age, body mass index, smoking history, medical morbidity, direct measures of physical functioning, forced expiratory volumes, and maximum respiratory muscle pressure, leisure-time physical activity accounted for < or = 5% of the variance of VO2 and exercise duration. Results were unchanged when analyses were restricted to subjects who achieved high levels of exercise. These data indicate that measures of aerobic capacity cannot be used to "validate" self-reported leisure-time physical activity in older subjects, and they further suggest that beneficial effects of physical activity in the elderly are the result of metabolic effects that are not reflected well by maximal aerobic capacity during exercise testing.

“Postpolio” Sequelae and Sleep-Related Disordered Breathing

To analyze the clinical manifestations and various types of sleep-related disordered breathing (SRDB) in patients with a history of poliomyelitis and with current "postpolio" sequelae (PPS). We retrospectively reviewed the medical records of 108 consecutive patients with PPS and sleep disturbances encountered during an 11-year period at Mayo Clinic Rochester and abstracted the features of acute polio, PPS, and results of sleep evaluation (overnight oximetry or polysomnography). Only those patients who were not receiving ventilatory support were included in the study. The features of PPS were dyspnea, fatigue, new weakness, and musculoskeletal pain. Of the 108 patients, 35 fulfilled the inclusion criteria. Sleep evaluations revealed three general types of disturbances: obstructive sleep apnea (group O, N = 19); hypoventilation (group H, N = 7); and both (group OH, N = 9). The mean apnea/hypopnea index was 37, 4, and 16 per hour in patients in groups O, H, and OH, respectively (P < 0.05), and the mean arterial carbon dioxide tension was 39, 60, and 55 mm Hg in these respective study groups (P < 0.05). The overall mean age at onset of symptoms of SRDB was 47 years, and the mean latent period after acute polio was 37 years. Hypersomnolence was the commonest SRDB symptom, present in 32 of the 35 patients. Snoring was noted in 100% of patients in group O, 0% in group H, and 67% in group OH. Patients in group O were obese and had normal lung function. Patients in group H tended to have normal weights and a history of diffuse neurologic deficits involving the trunk during the acute episode of polio. Scoliosis, restricted lung function, cor pulmonale, and decreased maximal respiratory pressures were common in patients in group H. Patients in group OH had overlapping features of those in groups O and H. In patients with PPS, we identified three patterns of sleep disturbances--obstructive sleep apnea, hypoventilation, and a combination of both. These groups are characterized by clinical features and by results of arterial blood gas determinations, overnight oximetry, and polysomnography. SRDB is a late sequela of poliomyelitis, and clinical evaluation should include information about sleep.

Entrenamiento de los músculos inspiratorios en la enfermedad pulmonar obstructiva crónica. Su impacto sobre las alteraciones funcionales y sobre la tolerancia al ejercicio

The aim of this study was to evaluate the impact of inspiratory muscle training on lung function and exercise tolerance in patients with chronic obstructive pulmonary disease (COPD). Thirty-five patients with stable COPD were enrolled. We measured lung function variables and peak inspiratory and expiratory pressures (PImax and PEmax). Tests of progressive maximal exercise tolerance and stable submaximal exercise tolerance were administered. Two study groups were formed. Group A patients (n = 20) were enrolled in a respiratory muscle training program lasting four months. Group B (n = 15) was the control group. At the end of the study period the patients underwent testing similar to the first battery of tests. All showed moderate to severe obstruction with no significant differences between groups (FEV1: group A 37.6 +/- 13%, group B 36.6 +/- 12%; FVC: group A 80.4 +/- 15%, group B 80 +/- 12%). Nor were there any significant differences between the two groups in initial results of either maximal respiratory pressures or exercise tolerance. No lung function changes were observed in either group. PImax in group A increased significantly at the end of the study (from 54 +/- 9 to 78 +/- 16 cmH2O; p < 0.001); there were no changes in group B. No changes were seen in VO2max or ventilatory response and/or gasometry during exercise in any of the groups. The trained group, on the other hand, experienced a significant decrease in dyspnea evaluated on the Borg scale exercise in maximal (5.7 +/- 1.1 versus 4.7 +/- 1.2, p < 0.005) and submaximal (5.9 +/- 0.9 versus 4.9 +/- 1.3, p < 0.005) and an increase in time of submaximal exercise tolerance (5.5 +/- 2 versus 7 +/- 3 min, p < 0.05), changes that were not observed in the control group. Based on these results, and although specific training of inspiratory muscles does not appear to improve lung function in patients with COPD, it is accompanied by a decreased sense of dyspnea during exercise and greater tolerance.

Indices of Respiratory Muscle Endurance in Healthy Subjects

Background: The evaluation of respiratory muscle performance can be described in terms of strength and endurance, the latter usually being measured by means of resistive or threshold inspiratory loads, using devices that are also used for respiratory muscle training. Few authors, however, have published endurance reference values for healthy subjects. To that end, we studied two indices of respiratory muscle endurance in a population of 99 healthy volunteers (50 men, 49 women) divided into five age groups (20–70 years old) applying a modification of the methods of Martyn et al. and Nickerson and Keens. Inspiratory muscle endurance (T_lim) was defined as the time the subject was able to sustain breathing against an inspiratory pressure load equivalent to 80% of the maximum tolerated load (C_max). C_max was calculated using a 2-min incremental threshold load. Results: We found that the heaviest inspiratory threshold load tolerated for 2 min and the time a load equivalent to 80% of C_max (T_lim) could be sustained were not significantly different for male and female subjects. T_lim correlated with C_max, age, height, and maximum respiratory pressures.

Comparison of the functional results of single lung transplantation for pulmonary fibrosis and chronic airway obstruction.

BACKGROUND: Single lung transplantation (SLT) is now a treatment option for patients with both pulmonary fibrosis and advanced chronic airway obstruction. Lung function after transplantation might be expected to be...

Pulmonary dysfunction and reduced exercise capacity in patients with myelomeningocele

To evaluate pulmonary function and exercise capacity in children with myelomeningocele. Prospective evaluation in a randomly selected cohort of 12 subjects (10 to 17 years of age) with myelomeningocele and 12 control subjects matched for age, sex, and arm span. Spirometry, lung volumes, maximum respiratory pressures, maximum oxygen expenditure during arm ergometry, and anaerobic threshold were measured. Mean total lung capacity and fractional lung volumes were significantly lower in case subjects than control subjects. Eleven subjects (92%) had a reduced forced vital capacity; seven (58%) had restrictive disease as evidenced by reductions in total lung capacity with normal or increased forced expiratory volume in 1 second/forced vital capacity ratio. Nine subjects (75%) had respiratory muscle weakness as evidenced by reduced maximum respiratory pressures or a low maximum voluntary ventilation. Exercise capacity was reduced as evidenced by a lower maximum oxygen consumption at peak exercise (13.8 +/- 4.8 vs 21.3 +/- 7.5 ml/min per kilogram of body weight; p < 0.02) and a lower anaerobic threshold (12.4 +/- 5.1 vs 17.3 +/- 4.2 ml/min per kilogram; p < 0.01) than the control group. Though the majority of subjects with myelomeningocele had a significant degree of restrictive disease, respiratory muscle weakness, or both, only one subject had pulmonary symptoms during exercise. Though most subjects with myelomeningocele had a significant degree of restrictive lung disease, respiratory muscle weakness, or both, exercise capacity was mostly limited by arm weakness. Skeletal muscle weakness may mask the symptoms of an underlying pulmonary abnormality, which may not be evident unless a pathologic cause of increased ventilation is present. Pulmonary function testing is suggested to screen for these abnormalities.

Respiratory mechanics after heart-lung and bilateral lung transplantation.

BACKGROUND: The factors determining respiratory mechanics following heart-lung transplantation (HLT) and bilateral lung transplantation (BLT) are incompletely understood. METHODS: The dynamic and static lung volumes of 15 patients after HLT...

Clinical implications of maximal respiratory pressure determinations for individuals with Duchenne muscular dystrophy.

To analyze the relationship between disease progression, pulmonary volumes, respiratory muscle strength (maximum inspiratory [MIP] and expiratory [MEP] pressure), and arterial blood gases for patients with Duchenne muscular dystrophy (DMD). An inception cohort study of pulmonary volumes, MIPs, and MEPs, correlated with age and PaCO2 levels and with each other using linear and nonlinear regression analyses. Outpatient clinic. Fifty-two consecutive DMD patients who presented for regular evaluations at a regional DMD center. Maximum expiratory pressures were 47.7% +/- 10.9% of normal in the 167- to 14-year-old patients and decreased linearly thereafter (MEP% = -2.7 x age +73.8; p < .001). Declines in MEP also correlated linearly with expiratory reserve volume (p < .001) and inversely with residual volume (p < .001). By contrast, MIP was 66.3% +/- 19.0% in the 357- to 14-year-old patients and then declined to 30.2% +/- 19.5% after age 14. No linear relationships were found with age but declines did correlate linearly with inspiratory reserve volume (p < .001) and total lung capacity (p < .001). PaCO2 elevations correlated best with decreases in MIP (p < .0001) and appeared when MIP was below 30cmH2O. Lung volume changes in DMD patients correlate with respiratory muscle weakness, and although inspiratory muscle dysfunction plays a key role in the development of chronic ventilatory insufficiency, reductions in expiratory muscle strength are the first signs of dysfunction and lead to the first episodes of respiratory failure.

Lung volumes and respiratory muscle strength in adult patients with childhood- or adult-onset growth hormone deficiency: effect of 12 months' growth hormone replacement therapy.

We have described impairment of the respiratory function in adult patients with childhood-onset growth hormone (GH) deficiency. The aim of the present study was to evaluate lung volumes and respiratory muscle strength in patients diagnosed as GH deficient before and after 6 and 12 months of recombinant GH treatment. Ten adults diagnosed as GH deficient in childhood, ten adults diagnosed as GH deficient in adulthood and ten healthy subjects entered the study. For each subject, evaluation of respiratory function followed the same standard approach, consisting of respiratory muscle strength assessment, record of flow-volume curves, measurement of static lung volumes and lung diffusing capacity. Childhood-onset GH-deficient patients had a significant reduction of maximal inspiratory (p < 0.01) and maximal expiratory (p < 0.05) mouth pressures. Total lung capacity, vital capacity and functional residual capacity were significantly reduced compared to healthy subjects (p < 0.05). Conversely, residual volume and diffusing lung capacity did not show any significant change. No significant change of the ratio between the percentage forced expiratory volume in 1 s and the forced vital capacity was observed. The decrease of respiratory mouth pressures was not correlated to the decrease of lung volumes. Adult-onset GH-deficient patients had only a significant reduction of maximal expiratory pressure compared to healthy subjects (p < 0.05). After 6 months of treatment no significant differences in any of the evaluated parameters were found. After 12 months of treatment patients with childhood-onset GH deficiency show a significant improvement of lung volumes (p < 0.01) and maximal respiratory mouth pressures (p < 0.005), whereas adult-onset GH-deficient patients show a significant improvement of maximal expiratory pressure (p < 0.05). In conclusion, the results of this study showed that adult patients affected with childhood-onset GH deficiency suffer from an impairment of the ventilatory function due to a reduction of lung volumes and a decrease of respiratory pressures probably due to a reduction of respiratory muscle strength. This impairment was reversed after 12 months of treatment with recombinant GH. Conversely, adult-onset GH-deficient patients had only an impairment of the maximal expiratory pressure, probably due to respiratory muscle weakness re-established after 12 months of GH therapy.

Long‐term pulmonary toxicity of multiagent chemotherapy including bleomycin and cyclophosphamide in osteosarcoma survivors

Purpose To assess long-term pulmonary effects of multiagent chemotherapy, we studied serial pulmonary function tests (PFTs) of 35 children with osteosarcoma up to 12 years after diagnosis. Patients and Methods We analyzed 84 sets of PFTs from 35 patients diagnosed with osteosarcoma between 1981 and 1991. They received bleomycin, cyclophosphamide, methotrexate, doxorubicin, cisplatin, and actinomycin D over 9–12 months and we performed PFTs from 3 days to 152 months after diagnosis. Time period I included 36 PFTs (43%) performed between 1 and 5 months from diagnosis, time period II included 20 PFTs (24%) performed between 8 and 12 months from diagnosis, and time period III included 28 PFTs (33%) performed between 12 and 119 months from diagnosis. Total lung capacity (TLC), forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), and carbon monoxide diffusing capacity (DLCO) were analyzed. Maximal respiratory pressures and arterial blood gases were measured to assess muscle weakness and gas exchange, respectively. Mean differences in PFTs were compared among the three time periods and between time period pairs. Results All mean PFT values showed significant differences among time periods. Significant decline in DLCO; (P = .012), TLC (P = .020), and FEV1 (P = .028) between time periods I and II were noted followed by a trend towards recovery between time periods II and III. Time periods I and III were not significantly different from one another. Mean PFTs performed after 2 years of diagnosis were not different from mean PFTs performed from diagnosis to 2 years. Conclusion This dosage regimen of multiagent chemotherapy for osteosarcoma patients caused a transient, but significant, decline in PFTs within 8–12 months after administration but appears to cause no significant long-term pulmonary function abnormalities. © 1996 Wiley-Liss, Inc.

Regulation of Breathing and Perception of Dyspnea in Healthy Pregnant Women

To examine if the perception of dyspnea during normal pregnancy may be related to an inappropriate ventilatory response to the increased metabolic rate, due to a higher chemosensitivity. At weeks 12, 24, and 36 of gestation and 4 months after delivery, 11 healthy pregnant women with dyspnea and 12 asymptomatic pregnant women were studied. Progesterone plasma levels, lung volumes, diffusion capacity, maximal respiratory pressures, rest oxygen uptake, breathing pattern, and mouth occlusion pressure (P0.1) were measured. Progressive isocapnic hypoxic stimulation and progressive hyperoxic hypercapnic stimulation were performed. Oxygen ventilation equivalent during pregnancy was significantly higher for the dyspneic group than for nondyspneic pregnant women. Dyspneic patients exhibited greater minute ventilation, tidal volume, and P0.1 than the nondyspneic group. The mean values of ventilatory and P0.1 slopes to hypoxia and CO2 during pregnancy were significantly greater in the patients with dyspnea than in asymptomatic subjects. These changes were not due to differences in progesterone plasma levels. A significant relation among the Borg score, inspiratory drive, and chemosensitivity was found. In some pregnant women, a higher sensitivity to CO2 and hypoxia may induce excessive ventilation to metabolic demand, which would contribute to dyspnea.

Long-term pulmonary toxicity of multiagent chemotherapy including bleomycin and cyclophosphamide in osteosarcoma survivors.

To assess long-term pulmonary effects of multiagent chemotherapy, we studied serial pulmonary function tests (PFTs) of 35 children with osteosarcoma up to 12 years after diagnosis. We analyzed 84 sets of PFTs from 35 patients diagnosed with osteosarcoma between 1981 and 1991. They received bleomycin, cyclophosphamide, methotrexate, doxorubicin, cisplatin, and actinomycin D over 9-12 months and we performed PFTs from 3 days to 152 months after diagnosis. Time period I included 36 PFTs (43%) performed between 1 and 5 months from diagnosis, time period II included 20 PFTs (24%) performed between 8 and 12 months from diagnosis, and time period III included 28 PFTs (33%) performed between 12 and 119 months from diagnosis. Total lung capacity (TLC), forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), and carbon monoxide diffusing capacity (DLCO) were analyzed. Maximal respiratory pressures and arterial blood gases were measured to assess muscle weakness and gas exchange, respectively. Mean differences in PFTs were compared among the three time periods and between time period pairs. All mean PFT values showed significant differences among time periods. Significant decline in DLCO; (P=.012), TLC (P=.020), and FEV1 (P=.028) between time periods I and II were noted followed by a trend towards recovery between time periods II and III. Time periods I and III were not significantly different from one another. Mean PFTs performed after 2 years of diagnosis were not different from mean PFTs performed from diagnosis at 2 years. This dosage regimen of multi-agent chemotherapy for osteosarcoma patients caused a transient, but significant, decline in PFTs within 8-12 months after administration but appears to cause no significant long-term pulmonary function abnormalities.

Maximum inspiratory and expiratory pressures have no daytime variation in healthy men

The variation of maximal respiratory pressures ( P imax and P emax) in healthy subjects were studied on the same day in 16 non-smoking healthy men (age 26·2 ± 3·2 years). The P imax and P emax were obtained on three occasions (8 a.m., 2 p.m. and 9 p.m.) within the same day. There were no differences between readings for P imax and P emax values.

Spirometry and Maximal Respiratory Pressure References From Healthy Minnesota 65- to 85-Year-Old Women and Men

To obtain spirometry and maximal respiratory pressure (MRP) reference values for elderly persons. Survey. General community. Four hundred seventy-one healthy ambulatory white women and men age 65+ years. A stringent spirometry quality assurance program exceeded American Thoracic Society recommendations. A "healthy" subgroup of 176 women and 112 men between the ages of 65- and 85 years were identified by excluding those with conditions that negatively influenced FEV1 in a multiple regression analysis. Reference equations and normal ranges for FEV1, FVC, FEF25-75%, peak flow, and maximal inspiratory and expiratory pressures (MRPs) were determined from the healthy group with good quality maneuvers. Less than 10% of the subjects were unable to perform three acceptable spirometry maneuvers and ten MRP maneuvers. When the age and height corrected FEV1s from this group were compared with other spirometry reference studies, mean values from the women were nearly identical to those from Morris, while these men had substantially lower FEV1 values (by 0.3- to 0.5L) than elderly men in Crapo's study. Mean peak flow was over 20% higher when compared with previous studies, suggesting greater initial expiratory effort by our subjects. The maximal inspiratory pressure (MIP) values were about 20% higher than those reported by the Cardiovascular Health Study, perhaps because five MIP maneuvers were always performed. Spirometry and MRP reference values used for elderly patients should come from population studies using similar techniques and with large numbers of subjects over age 65 years.

Nocturnal saturation and respiratory muscle function in patients with chronic obstructive pulmonary disease.

Nocturnal desaturations, mainly caused by hypoventilation, occur frequently in patients with chronic obstructive pulmonary disease (COPD). Daytime arterial oxygen and carbon dioxide tensions (PaO2 and PaCO2) appear to predict which patients will desaturate at night. It is unknown if respiratory muscle strength, which may be decreased in these patients, plays an additional part. Polysomnography, maximal respiratory pressures, lung function, and arterial blood gas tensions were measured in 34 patients with COPD (mean (SD) forced expiratory volume in one second (FEV1) 41.7 (19.9)% pred). Significant correlations were found between the mean nocturnal arterial oxygen saturation and maximal inspiratory mouth pressure (r = 0.65), maximal inspiratory transdiaphragmatic pressure (r = 0.53), FEV1 (r = 0.61), transfer coefficient (KCO) (r = 0.38), arterial oxygen saturation (SaO2) (r = 0.75), and PaCO2 (r = -0.44). Multiple regression analysis showed that 75% of the variance in nocturnal SaO2 (70%) and FEV1 (5%). Inspiratory muscle strength and nocturnal saturation data are correlated, but daytime SaO2 and FEV1 remain the most important predictors of nocturnal saturation.

Effects of Body Position, Hyperinflation, and Blood Gas Tensions on Maximal Respiratory Pressures in Patients with Chronic Obstructive Pulmonary Disease

BACKGROUND--Inspiratory muscle strength in patients with chronic obstructive pulmonary disease (COPD) can be affected by mechanical factors which influence the length of the diaphragm, and by non-mechanical factors. The aim of the present study was to evaluate firstly the effects of body position on respiratory pressures and, secondly, to determine the relative contribution of age, body mass index (BMI), lung volumes, and arterial blood gas tensions to respiratory muscle strength. METHODS--Thirty male patients with stable COPD (mean FEV1 40.4% predicted) participated in the study. Maximal inspiratory and expiratory mouth pressures (PImax, PEmax) and maximal inspiratory transdiaphragmatic pressures (PDI) in the sitting and supine position, lung function, and arterial blood gas tensions were measured. RESULTS--Mean (SD) PImax in the sitting position was higher than in the supine position (7.1(2.3)kPa v 6.4(2.2)kPa respectively). In contrast, PDI in the sitting position was lower than in the supine position (10.0(3.5)kPa v 10.8(3.7)kPa respectively). PEmax was higher in the sitting position (9.3(3.0)kPa) than in the supine position (8.7(2.8)kPa). Significant correlations were found between inspiratory muscle strength on the one hand, and lung function parameters, BMI, and arterial blood gas tensions on the other. CONCLUSIONS--Inspiratory muscle strength in patients with COPD is influenced by mechanical factors (body position, lung volumes) and non-mechanical factors (BMI, FEV1, and blood gases). PImax and PEmax are lower in the supine position while, in contrast to healthy subjects, PDI is higher in the supine position than in the sitting position.