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PubMed1997

Three-dimensional reconstruction of human diaphragm with the use of spiral computed tomography.

We developed a technique of diaphragm imaging by using spiral computed tomography, and we studied four normal subjects who had been previously investigated with magnetic resonance imaging (A. P. Gauthier, S. Verbanck, M. Estenne, C. Segebarth, P. T. Macklem, and M. Paiva. J. Appl. Physiol. 76: 495-506, 1994). One acquisition of 15- to 25-s duration was performed at residual volume, functional residual capacity, functional residual capacity plus one-half inspiratory capacity, and total lung capacity with the subject holding his breath and relaxing. From these acquisitions, 20 coronal and 30 sagittal images were reconstructed at each lung volume; on each image, diaphragm contour in the zone of apposition and in the dome was digitized with the software Osiris, and the digitized silhouettes were used for three-dimensional reconstruction with Matlab. Values of length and surface area for the diaphragm, the dome, and the zone of apposition were very similar to those obtained with magnetic resonance imaging. We conclude that satisfactory three-dimensional reconstruction of the in vivo diaphragm may be obtained with spiral computed tomography, allowing accurate measurements of muscle length, surface area, and shape.

Adult↗
PubMed2002

Breath-by-breath measurement of the volume displaced by diaphragm motion.

To develop an accurate method to measure the volume displaced by diaphragm motion (DeltaVdi) breath by breath, we compared DeltaVdi measured by a previously evaluated biplanar radiographic method (Singh B, Eastwood PR, and Finucane KE. J Appl Physiol 91: 1913-1923, 2001) at several lung volumes during vital capacity inspirations in 10 healthy and nine hyperinflated subjects with 1) DeltaVdi measured from the same chest X-rays by two previously described uniplanar methods (Petroll WM, Knight H, and Rochester DF. J Appl Physiol 69: 2175-2182, 1990; Verschakelen JA, Deschepper K, and Demendts M. J Appl Physiol 72: 1536-1540, 1992) and a proposed method that considered actual cross-sectional shape of the rib cage and spinal volume (DeltaVdi(S)); and 2) DeltaVdi(S) measured by lateral fluoroscopy in the same 10 healthy subjects. Relative to biplanar DeltaVdi, DeltaVdi(S) values from lateral chest X-rays and fluoroscopy were not different, whereas DeltaVdi values of Petroll et al. and Verschakelen et al. were increased by (means +/- SD) 1.98 +/- 1.59 and 1.16 +/- 0.82 liters, respectively (both P < 0.001). During quiet breathing, DeltaVdi(S) by lateral fluoroscopy was 66 +/- 16% of tidal volume and similar to that between functional residual capacity and one-half inspiratory capacity by the biplanar radiographic method. We conclude that accurate breath-by-breath measurements of DeltaVdi can be made by using lateral fluoroscopy.

Adult↗
PubMed1999

Static lung volumes: reference values from a Latin population of Spanish descent.

BACKGROUND AND OBJECTIVES: The aim of this study was to develop a set of prediction equations and 90% confidence intervals for static lung volumes using the multibreath helium equilibration method from a sample of asymptomatic Caucasian subjects of Spanish descent. Moreover, these equations were compared with those of previous studies. METHODS: Measurements of static lung volumes using techniques recommended by the American Thoracic Society and the European Community for Steel and Coal were carried out on a selected sample of 591 healthy nonsmoking volunteers (305 men and 286 women) aged 18-88 years, living in the metropolitan area of Valencia, on the east coast of Spain. Multiple regression analysis using height, age and weight as independent variables were used to provide predicted values for both sexes. These reference values were compared with other sets of prediction equations reported in the literature using an independent sample of 69 subjects (32 men and 37 women). RESULTS: Simple linear regression equations using age, height and body weight predicted all the subdivisions of lung volumes (vital capacity, expiratory reserve volume (ERV), inspiratory capacity, functional residual capacity (FRC), residual volume (RV), total lung capacity (TLC), FRC/TLC and RV/TLC) as well as more complex equational models. The distribution of residuals fulfilled the assumptions of multiple regression analysis (independence, homoscedasticity and Gaussian distribution of residuals), except for ERV, using simple linear models. The derived equations did not differ significantly from most of the previously reported equations and were usually superior in their ability to predict the lung volumes. CONCLUSIONS: The use of the present prediction equations is recommended in the Latin population of Spanish descent and in populations with similar Caucasian characteristics.

Adolescent↗
PubMed2000

Flow limitation and dynamic hyperinflation during exercise in COPD patients after single lung transplantation.

STUDY OBJECTIVE: Using the negative expiratory pressure (NEP) method, we have previously shown that patients receiving single lung transplantation (SLT) for COPD do not exhibit expiratory flow limitation and have little dyspnea at rest. In the present study, we assessed whether SLT patients exhibit flow limitation, overall hyperinflation, and dyspnea during exercise. METHODS: Expiratory flow limitation assessed by the NEP method and inspiratory capacity maneuvers used to determine end-expiratory lung volume (EELV) and end-inspiratory lung volume (EILV) were performed at rest and during symptom-limited incremental cycle exercise in eight SLT patients. RESULTS: At the time of the study, the mean (+/- SD) FEV(1), FVC, functional residual capacity, and total lung capacity (TLC) amounted to 55 +/- 14%, 67 +/- 12%, 137 +/- 16%, and 110 +/- 11% of predicted, respectively. At rest, all patients did not experience expiratory flow limitation and were without dyspnea. At peak exercise, the maximal mechanical power output and maximal oxygen consumption amounted to 72 +/- 20% and 65 +/- 8% of predicted, respectively, with a maximal dyspnea Borg score of 6 +/- 3. All but one patient exhibited flow limitation and dynamic hyperinflation; the EELV and EILV amounted to 74 +/- 5% and 95 +/- 9% TLC, respectively. The patient who did not exhibit flow limitation during exercise had the lowest dyspnea score. CONCLUSION: Most SLT patients for COPD exhibit expiratory flow limitation and dynamic hyperinflation during exercise, whereas maximal dyspnea is variable.

Aged↗
PubMed1978

Effect of curare on maximum static PV relationships of the respiratory system.

The effect of respiratory muscle weakness on the maximum static pressure-volume (PV) characteristics of the respiratory system was studied in four healthy males infused slowly with d-tubocurarine (dtc). Inspiratory capacity (IC), expiratory reserve volume (ERV), maximum static inspiratory and expiratory mouth pressures at four lung volumes, and handgrip were measured during induction of, and recovery from muscle weakness. The maximum effect of dtc varied among the muscle groups tested; peripheral muscles were most severely affected, expiratory muscles moderately, and inspiratory muscles least affected. At each level of weakness studied, decreases of IC and ERV were proportional to decreases of maximum static mouth pressures. Vital capacity, measured at each level of weakness was much less than values predicted from the static mechanical properties of the respiratory system. Our findings suggest that the marked change in the extremes of lung volume during submaximal neuromuscular blockade (SMNB) is due, in part, to unequal distribution of muscle weakness, reflected by decreased ability to change ribcage dimensions even at modest levels of SMNB.

Abdomen↗
PubMed2006

Longitudinal changes in hyperinflation parameters and exercise capacity after giant bullous emphysema surgery.

OBJECTIVE: Although resection of giant bullae for the purpose of improving the function of underlying compressed lung is an accepted form of surgery for emphysema, there is only limited information regarding long-term improvement in dynamic hyperinflation and exercise tolerance. Our major goal was to investigate the effects of lung resection for giant bullae on pulmonary function, dynamic hyperinflation, and exercise capacity in patients with chronic obstructive pulmonary disease characterized by emphysema. METHODS: Pulmonary function and exercise testing were assessed prospectively before and 3, 6, 12, 24, and 48 months after surgery in 12 patients who had chronic obstructive pulmonary disease with emphysema who underwent lung resection of giant bullae. RESULTS: Forced expiratory volume, diffusing capacity for carbon monoxide, arterial partial pressure of oxygen, and exercise capacity were significantly increased after resection of surgical bullae. Dynamic hyperinflation, as assessed by reduction in inspiratory capacity and dyspnea Borg scale, were significantly decreased during exercise. Improvement in baseline and exercise functional capacity slightly decreased over time, remaining, however, far above the value before surgery. CONCLUSION: Altogether, these findings suggest that surgery for resection of giant bullae is an effective procedure for improving airflow, limiting gas exchange, and limiting exercise dynamic hyperinflation over time.

Aged↗
PubMed1998

Total lung capacity by N2 washout from high and low lung volumes in ventilated infants and children.

Although there is a strong rationale for the assessment of the subdivisions of lung volume, lung function testing has focused on the measurement of FRC alone in ventilated infants and children. To assess the feasibility, reproducibility, and accuracy of measurements of total lung capacity (TLC), FRC, and their ratio, we determined both lung volumes in 50 critically ill, intubated, and paralyzed infants (mean age [SEM]), 19.9 [4.6] mo) with a variety of lung diseases, by a modified N2 washout technique from end-exhalation and from +40 cm H2O inspiratory pressure, respectively. In the same infants, we also defined TLC by adding inspiratory capacity, measured by pneumotachograph during a passive exhalation from +40 cm H2O to FRC measured by N2 washout. Respiratory mechanics were measured by single-breath occlusion, and the patients were classified according to clinical picture and lung function into groups without lung disease or with restrictive or obstructive disease. The TLC data obtained by both methods showed good agreement for the infants without lung disease or restrictive disease (limits of agreement [LOA]: -3.8/4.6 and -2.9/3.2 ml/kg, respectively). The agreement was less in the infants with airflow obstruction where the N2 washout gave slightly higher values (LOA: -7.1/11.3 ml/kg). Mean FRC/TLC was significantly elevated in the obstructive group, whereas mean FRC alone did not differ from the group without lung disease. Our results suggest that TLC can be measured by both methods in intubated infants, but with limited agreement in obstructive disease. FRC/TLC ratios allow an estimation of the degree of pulmonary hyperinflation.

Child, Preschool↗
PubMed2001

The diaphragm and dyspnea during chemically stimulated breathing in a subset of patients with diabetes.

In patients with insulin-dependent diabetes mellitus (IDDM) isolated peripheral airway involvement may give rise to inspiratory threshold load (ITL) contributing to dyspnea. Based on the reported evidence of a greater increase in end-expiratory lung volume (EELV) with hypoxia than with hypercapnia in IDDM, we wondered whether, and to what extent in the two conditions, EELV contribute to perception of dyspnea (PD). We studied five nonsmokers aged between 19 and 45, with IDDM under good metabolic control and five normal control subjects matched for age. In each patient, we evaluated the electromyographic activity of the diaphragm (Edi), the swings of esophageal (Pessw), gastric (Pgsw), and transdiaphragmatic (Pdisw = Pgsw-Pessw) pressures; PD was assessed by a modified Borg scale during hypercapnic-hyperoxic (HCH) and hypoxic-isocapnic (HIC) stimulation. Change in inspiratory capacity (IC) was considered the mirror image of increase in EELV, that is, dynamic hyperinflation (DH), while intrinsic positive end inspiratory pressure (PEEPi) was measured as an index of inspiratory threshold load (ITL). In controls, Edi and Pdi but not their ratio (Edi/Pdi) related to Borg. In patients the following was found: (1) with each of the two stimuli, for any given Edi, Pdi, and Edi/Pdi ratio, there was greater Borg than in controls, (2) a similar increase in ITL and DH with HCH and HIC, (3) Edi/Pdi related to Borg similarly with HCH as with HIC. In conclusion, in controls, Edi and Pdi were associated with the perception of dyspnea similarly with the two chemical stimuli. In this subset of patients with IDDM, Edi/Pdi ratio throughout increase in EELV and ITL was found to affect the perception of dyspnea in hypoxia to a similar extent as in hypercapnia.

Adult↗
PubMed1980

Methods of intermittent positive pressure breathing.

Inspiratory capacity (IC) was evaluated in 60 patients during the following four respiratory maneuvers: (1) coached unassisted inspiration; (2) inspiratory positive-pressure breathing (IPPB) at 15 cm H2O with the patient passively inspiring; (3) IPPB at 15 cm H2O with the patient coached to actively inspire; and (4) IPPB at a peak pressure adjusted according to the judgment of the respiratory therapist, with the patient coached to actively inspire. The IC attained with these maneuvers were, respectively, as follows: (1) 1.29 +/- 0.75 L; (2) 1.13 +/- 0.52 L; (3) 1.77 +/- 0.11 L; and (4) 2.27 +/- 0.11 L (mean +/- SE). The peak ventilator pressure for maneuver 4 averaged 30 +/- 7 cm H2O (mean +/- SD), and no patient experienced harmful side effects from these peak pressures. These data indicate that the method of treatment with IPPB has profound effects upon the degree of pulmonary expansion. All research on therapy with IPPB should be carefully controlled for the method of administering IPPB, and the volumes obtained during the treatment should be carefully documented before general conclusions are drawn concerning the effects of IPPB on morbidity. For the present, we suggest that IPPB, when administered clinically, be given as described in method 4.

Adult↗
PubMed1990

Breathing pattern in chronic quadriplegia.

The resting breathing pattern in 14 chronic C6 and C7 traumatic quadriplegics was compared with six age-matched healthy controls. All quadriplegics had complete motor loss below the lesion level and were at least two years postinjury. Tests were performed with subjects seated. Forced vital capacity (FVC), forced expiratory volume in one second (FEV1.0), inspiratory capacity (IC), and maximum inspiratory mouth pressure (Pimax) were measured. Resting breathing pattern was assessed for 20 minutes using mercury in rubber strain gauges and a computer-assisted data acquisition and analysis program. Inspiratory time (Ti), expiratory time (Te), and tidal volume (Vt) were measured, and the remaining timing components were calculated from these values. The variability of breathing was assessed by comparing the coefficients of variation of each variable. The FVC, IC, and Pimax were significantly reduced; Vt was significantly lower (p less than 0.01) and frequency significantly elevated (p less than 0.05) in quadriplegics. The decreased Vt in quadriplegics was due entirely to a significantly decreased mean inspiratory flow (p less than 0.01); Ti was the same in quadriplegics as in controls. The ratio of mean Ti to total cycle time (Ti/Ttot) was significantly longer in quadriplegics (p less than 0.005). There was no difference in variability of breathing between the two groups for any timing component of ventilation. There was no significant difference in sighing frequency between groups for either breaths greater than 2x mean Vt or breaths greater than 3x mean Vt. Chronic quadriplegics demonstrated a rapid, shallow breathing pattern, probably due to the mechanical restrictions resulting from paralysis of the thorax musculature. They retained the ability to sigh, suggesting that chest wall afferents may not be required in this process.

Adult↗
PubMed2003

Resting lung function and hemodynamic parameters as predictors of exercise capacity in patients with chronic heart failure.

STUDY OBJECTIVES: The aim of this study was to examine the role of resting pulmonary function and hemodynamic parameters as predictors of exercise capacity in patients with chronic heart failure. MEASUREMENTS AND RESULTS: Fifty-one patients with chronic heart failure underwent resting pulmonary function testing, including inspiratory capacity (IC) and symptom-limited, treadmill cardiopulmonary exercise testing (CPET). Right-heart catheterization and radionuclide ventriculography were performed within 2 days of CPET. Mean (+/- SD) left ventricular ejection fraction was 31 +/- 12% and cardiac index was 2.34 +/- 0.77 L/min/m(2). Percentage of predicted FEV(1) was 92 +/- 14%, percentage of predicted FVC was 94 +/- 15%, FEV(1)/FVC was 81 +/- 4%, and percentage of predicted IC was 84 +/- 18%. Mean peak oxygen uptake (peak O(2)) was 17.9 +/- 5.4 mL/kg/min. Analysis of variance among the three functional Weber classes showed statistically significant differences for pulmonary capillary wedge pressure (PCWP) and IC. Specifically, the more severe the exercise intolerance, the lower was IC and the higher was PCWP. In a multivariate stepwise regression analysis, using peak O(2) (liters per minute) as the dependent variable and the pulmonary function test measurements as independent variables, the only significant predictor selected was IC (r = 0.71, p < 0.0001). In a final stepwise regression analysis including all the independent variables of the resting pulmonary function tests and hemodynamic measurements, the two predictors selected were IC and PCWP (r(2) = 0.58). CONCLUSIONS: In patients with chronic heart failure, IC is inversely related to PCWP and is a strong independent predictor of functional capacity.

Cardiac Output↗
PubMed2005

Effects of imposed pursed-lips breathing on respiratory mechanics and dyspnea at rest and during exercise in COPD.

STUDY OBJECTIVES: To investigate the effect of volitional pursed-lips breathing (PLB) on breathing pattern, respiratory mechanics, operational lung volumes, and dyspnea in patients with COPD. SUBJECTS: Eight COPD patients (6 male and 2 female) with a mean (+/-SD) age of 58 +/- 11 years and a mean FEV1 of 1.34 +/- 0.44 L (50 +/- 21% predicted). METHODS: Wearing a tight-fitting transparent facemask, patients breathed for 8 min each, with and without PLB at rest and during constant-work-rate bicycle exercise (60% of maximum). RESULTS: PLB promoted a slower and deeper breathing pattern both at rest and during exercise. Whereas patients had no dyspnea with or without PLB at rest, during exercise dyspnea was variably affected by PLB across patients. Changes in the individual dyspnea scores with PLB during exercise were significantly correlated with changes in the end-expiratory lung volume (EELV) values estimated from inspiratory capacity maneuvers (as a percentage of total lung capacity; r2 = 0.82, p = 0.002) and with changes in the mean inspiratory ratio of pleural pressure to the maximal static inspiratory pressure-generating capacity (PcapI) [r2 = 0.84; p = 0.001], measured using an esophageal balloon, where PcapI was determined over the range of inspiratory lung volumes and adjusted for flow. CONCLUSION: PLB can have a variable effect on dyspnea when performed volitionally during exercise by patients with COPD. The effect of PLB on dyspnea is related to the combined change that it promotes in the tidal volume and EELV and their impact on the available capacity of the respiratory muscles to meet the demands placed on them in terms of pressure generation.

Adult↗
PubMed1996

Inhaled bronchodilators reduce dynamic hyperinflation during exercise in patients with chronic obstructive pulmonary disease.

Dynamic hyperinflation (DH) is a major pathophysiologic consequence of airflow limitation during exercise in patients with chronic obstructive pulmonary disease (COPD) and an important contributing factor to breathlessness. In this study we aimed to examine the effect of inhaled beta agonist therapy on DH during exercise in these patients and the relationship between changes in DH and breathlessness. In 13 COPD patients (mean age 65.1 +/- 2.0, FEV1 1.20 +/- 0.17, FEV1/FVC 40 +/- 3) we measured pulmonary function tests, exercise breathlessness by Borg score, and exercise flow volume and pressure volume loops on two separate days. Prior to testing, patients randomly received inhaled placebo or albuterol on the first test day and the alternative medication on the second test day. From measurements of exercise inspiratory capacity (IC), we calculated the end-expiratory and end-inspiratory lung volumes (EELV, EILV). We used esophageal pressure recordings to measure peak inspiratory esophageal pressure (Pesins) during exercise and this was related to the maximal capacity for pressure generation taking into account lung volume and airflow changes (Pcapi). Bronchodilator caused significant increase in both FEV1 and FVC (+0.23 and +0.51, p<0.01). Comparisons of breathlessness, exercise volumes, and pressures were made at the highest equivalent work load. There was a significant reduction in the peak exercise EELV/TLC (80 +/- 0.02% to 76 +/- 0.02%, p<0.05) while the peak EILV/TLC decreased by 2% (97 +/- 1% to 95 +/- 1%, p<0.05). The peak Pesins/Pcapi decreased (0.79 +/- 0.10 to 0.57 +/- 0.05, p<0.05), and the Pcapi - Pesins increased (7.4 +/- 3 to 13.0 +/- 3 cm H2O, p<0.05). There was significant improvement in neuroventilatory coupling for volume change (Pesins/Pcapi/VT/TLC 5.45 +/- 0.5 to 3.25 +/- 1.0, p<0.05). There was a significant reduction in breathlessness as measured by Borg score (4.5 +/- 0.7 to 3.1 +/- 0.5, p<0.05) and there was a significant correlation between delta Borg and delta EILV/TLC (r=0.771, p<0.01) with a trend for Pesins/Pcapi/VT/TLC (r=0.544, p=0.067). There was also a significant correlation between delta EELV/TLC and delta Pesins/Pcapi/VT/TLC (r=0.772, p<0.01). The relationships between delta Borg, delta resting volumes, and flow rates were not significant. We conclude that in patients with COPD, inhaled bronchodilator reduces exercise DH and improves inspiratory pressure reserve and neuroventilatory coupling. Changes in DH and neuroventilatory coupling were the main determinants of reduced breathlessness.

Administration, Inhalation↗
PubMed1979

The pattern of breathing in patients with chronic airflow obstruction.

1. The pattern of breathing in 12 patients with severe irreversible airflow obstruction has been studied during ventilatory stimulation by rebreathing CO2. Mean maximum tidal volume response was only 1.23 +/- 0.30 litres (mean +/- SD); this represented 65% of mean measured vital capacity and 82% of mean measured inspiratory capacity. During the course of rebreathing mean total breath duration was reduced from 3.48 +/- 0.93 to 2.44 +/- 0.48 s. 2. End-expiratory thoracic gas volume (FRC) was elevated at rest in all subjects and increased significantly by a further 0.50 +/- 1.90 litres during ventilatory stimulation in 10 of the 12 subjects. The maximum increase in FRC was proportional to the degree of airflow obstruction afforded by the airways in each subject. 3. It is suggested that the increase in FRC during ventilatory stimulation is responsible for the diminished tidal volume response and is an important determinant of breathing pattern and symptomatology in patients with airflow obstruction.

Adult↗
PubMed1999

Sensation of inspiratory difficulty during inspiratory threshold and hyperinflationary loadings. Effect of inspiratory muscle strength.

Dynamic hyperinflation loads the inspiratory muscles by increasing end-expiratory lung volume (EELV) and imposing intrinsic positive end-expiratory pressure (PEEPi), the latter behaving as an inspiratory threshold load (ITL). The aim of the current study was to examine how induced-inspiratory muscle fatigue affects the independent effects of the imposed ITL and increasing operating lung volume on the perceived inspiratory difficulty. Dynamic hyperinflation in healthy subjects was induced by positive end-expiratory pressure (PEEP). Increasing operating lung volume alone (without PEEPi) and increasing ITL alone (without change in EELV) were induced by continuous positive airway pressure (CPAP) and external ITL, respectively. Inspiratory difficulty was quantified by the modified Borg scale and analyzed by step forward multiple regression, using the imposed ITL, EELV, and end-inspiratory lung volume (EILV) as independent variables. When fresh, the first entered variable was the imposed ITL (r(2), 0.38). Adding EILV into the model increased r(2) to 0.67. After fatigue, the first entered variable became EILV (r(2), 0.50) and the second selected variable was the imposed ITL, which increased r(2) to 0.66. EELV was insignificant under both conditions. The coefficient of EILV increased significantly from 0.039 +/- 0.005 to 0.092 +/- 0.012 (% inspiratory capacity(-)(1)) after fatigue run (p < 0.001), whereas that of the imposed ITL did not change. It is concluded that in the experimental conditions studied, inspiratory muscle fatigue increased the importance of lung volume over that of inspiratory threshold load in determining the perceived inspiratory difficulty.

Humans↗
PubMed1995

Pulmonary function testing in spinal cord injury: correlation with vital capacity.

Spinal cord injury (SCI) causes restrictive ventilatory changes, with reductions in vital capacity, functional residual capacity, and expiratory reserve volume. Vital capacity (VC) often is used as an indicator of overall pulmonary function in these patients. In an effort to determine the extent to which VC correlates with other pulmonary function tests, 52 patients with recent acute traumatic SCI underwent complete pulmonary function testing. Statistical relationships were determined between VC and nine other tests. VC was found to be significantly correlated with forced expiratory volume in 1 s, inspiratory capacity, expiratory reserve volume, functional residual capacity, residual volume (RV), total lung capacity (TLC), and RV/TLC ratio, but not with maximum positive expiratory pressure nor with maximum negative inspiratory pressure. The excellent correlations between vital capacity and nearly all of the other pulmonary function tests support the use of VC as a single global measure of overall ventilatory status in SCI patients.

Adolescent↗
PubMed2004

Effect of heliox on lung dynamic hyperinflation, dyspnea, and exercise endurance capacity in COPD patients.

We tested the hypothesis that heliox breathing, by reducing lung dynamic hyperinflation (DH) and dyspnea (Dys) sensation, may significantly improve exercise endurance capacity in patients with chronic obstructive pulmonary disease [n = 12, forced expiratory volume in 1 s = 1.15 (SD 0.32) liters]. Each subject underwent two cycle ergometer high-intensity constant work rate exercises to exhaustion, one on room air and one on heliox (79% He-21% O2). Minute ventilation (VE), carbon dioxide output, heart rate, inspiratory capacity (IC), Dys, and arterial partial pressure of CO2 were measured. Exercise endurance time increased significantly with heliox [9.0 (SD 4.5) vs. 4.2 (SD 2.0) min; P < 0.001]. This was associated with a significant reduction in lung DH at isotime (Iso), as reflected by the increase in IC [1.97 (SD 0.40) vs. 1.77 (SD 0.41) liters; P < 0.001] and a decrease in Dys [6 (SD 1) vs. 8 (SD 1) score; P < 0.001]. Heliox induced a state of relative hyperventilation, as reflected by the increase in VE [38.3 (SD 7.7) vs. 35.5 (SD 8.8) l/min; P < 0.01] and VE/carbon dioxide output [36.3 (SD 6.0) vs. 33.9 (SD 5.6); P < 0.01] at peak exercise and by the reduction in arterial partial pressure of CO2 at Iso [44 (SD 6) vs. 48 (SD 6) Torr; P < 0.05] and at peak exercise [46 (SD 6) vs. 48 (SD 6) Torr; P < 0.05]. The reduction in Dys at Iso correlated significantly (R = -0.75; P < 0.01) with the increase in IC induced by heliox. The increment induced by heliox in exercise endurance time correlated significantly with resting increment in resting forced expiratory in 1 s (R = 0.88; P < 0.01), increase in IC at Iso (R = 0.70; P < 0.02), and reduction in Dys at Iso (R = -0.71; P < 0.01). In chronic obstructive pulmonary disease, heliox breathing improves high-intensity exercise endurance capacity by increasing maximal ventilatory capacity and by reducing lung DH and Dys.

Administration, Inhalation↗
PubMed1997

[The etiology of chronic hypercapnia].

BACKGROUND: The ventilatory and the pressure response to CO2 in patients with advanced thoracic disorders are critically dependent on the mechanics of the lung and the respiratory muscles. Changes in drive, therefore, can not be directly assessed with that method. However during changes as a result of intermittent mechanical ventilation, changes in drive can be assessed, if lung and muscle mechanics remain unaffected. In addition, to study changes in ventilatory drive independently in patients successfully treated by intermittent mechanical ventilation, we determined the recruitment threshold, pCO2RT, of the unloaded ventilatory pump to CO2. PATIENTS: 16 patients with various disorders (4 COPD, 4 COPD and sleep apnoea, 7 scoliosis, 1 fibrothorax) were studied, 14 during nasal IPPV and 2 during mechanical ventilation via tracheostomy. RESULTS: After they had been successfully adapted to the ventilator, they were entered into the study. The apnoea threshold in all cases had already been reached during the adaptation period. pCO2AT was determined 32 +/- 5 mm Hg. While the patients were passively ventilated, the inspiratory CO2 was increased every 5 minutes, resulting in a stepwise increase in arterial pCO2 by 3 mm Hg. The recruitment threshold pCO2RT was then defined as the lowest pCO2, which resulted in a deformation of the inspiratory pressure curve by the patients own inspiratory efforts. pCO2RT was reproducible within trials and in different trials with a standard error of 1.2 mm Hg. It was found 6 +/- 4 mm Hg above the pCO2 during spontaneous breathing (p < 0.01) in all patients. pCO2RT decreased from 58 +/- 10 to 47 +/- 4 mm Hg during intermittent IPPV and so did the threshold during CO2 rebreathing, while spontaneous pCO2 decreased from 53 +/- 12 to 42 +/- 5 mm Hg. The slope, reflecting drive was decreased to 0.28 compared to normals but remained unchanged 0.32 (n. s.) during the study. Lung function did not change. A highly significant increase in the indices of maximal inspiratory force was observed (p < 0.002) and as a result a decrease in the inspiratory demand (p < 0.008). CONCLUSION: Intermittent IPPV does efficiently suppress phasic respiratory drive via thoracic afferent inhibition and therefore effectively unloads the ventilatory pump. The CO2 threshold is increased in patients with hypercapnic ventilatory failure, probably to minimise the load to the ventilatory muscles. With the increase in inspiratory capacity the pCO2 threshold can be restored to normal by intermittent noninvasive or invasive IPPV.

Adult↗