Respiratory sensation and pattern of respiratory muscle activation during diaphragm fatigue.

We have examined the relationship between respiratory effort sensation (modified Borg scale) and amplitude of the integrated surface electromyogram of the diaphragm (Edi, esophageal electrode), rib cage muscles (Erc), and sternomastoid muscle (Esm) during the development of diaphragm fatigue in five normal subjects. Three conditions were studied: run A: transdiaphragmatic pressure (Pdi), 65% Pdimax; esophageal pressure (Pes), 60% Pesmax; run B: Pdi, 50% Pdimax; Pes, 60% Pesmax; and run C: Pdi, 50% Pdimax; Pes, 20% Pesmax. During all runs there was a progressive rise in sensation, which was greater in runs A and B than in run C (P less than 0.05, analysis of variance). There was no difference between runs A and B. At the end of run C subjects did not report a maximal Borg score despite their inability to generate the target Pdi. The increase in sensory score with fatigue correlated highly with Esm/Esmmax and with Erc/Ercmax. There was no correlation between sensory score and Edi/Edimax. We conclude that the increase in respiratory effort sensation that accompanies diaphragm fatigue is not due to perception of increased diaphragmatic activation. It may reflect increased overall respiratory motor output not directed to the diaphragm.

Effect of chronic lung disease on the perception of added inspiratory loads.

The perceived magnitude of externally added loads to breathing was estimated in 10 normal subjects and 10 patients with chronic lung disease (5 obstructive, 5 interstitial disorders) to determine if chronic mechanical abnormalities of the respiratory system are accompanied by changes in the perception of dyspnea. Flow rates and tidal volumes were varied to assess the effect of altered patterns of breathing. With added resistive loads, the perceived magnitude increased as both resistance and the flow rate increased. With elastic loads the perceived magnitude increased as both elastance and tidal volume increased. In all subjects, perceived magnitude of added loads was most directly related to the inspiratory pressure used to overcome the load. Although the exponent for the power function relationship between perceived magnitude and the physical magnitude of the load was affected by the subject's age, there was no difference between the patients studied and the age-matched normal subjects. The results indicate that the sensation associated with added loads to breathing is the same in patients with chronic lung disease as in normal subjects. Also, they suggest that the altered pattern of breathing in patients with chronic lung disease is a behavioral adaptation to minimize respiratory distress.

Prurigo nodularis and gluten enteropathy.

Two cases of prurigo nodularis are described. Each is considered to have a gluten sensitive enteropathy. This association may be one facet of prurigo nodularis.

Effect of a walking aid on disability, oxygenation, and breathlessness in patients with chronic airflow limitation.

PURPOSE: This study assessed the effect of a wheeled walking aid on disability, oxygenation, and breathlessness in patients with severe disability secondary to chronic irreversible airflow limitation. METHODS: Eleven subjects with chronic irreversible airflow limitation, mean forced expired volume in 1 second (FEV1) 0.71 L +/- .33 L, were studied. Subjects performed four 6-minute walk tests, two on each of two study days, twice unaided and twice with the assistance of a wheeled walking aid. A randomized cross-over design was used. All subjects were oriented to 6-minute walk tests, use of bronchodilators was controlled, and standard encouragement was given during each walk test. Outcome measures were the distance walked in 6 minutes, change in oxyhemoglobin saturation during the walk, and breathlessness using a modified Borg Scale. RESULTS: The use of a wheeled walker resulted in a significant increase in 6-minute walking distance, a significant reduction in hypoxemia with walking and a significant reduction in breathlessness during the walk test. CONCLUSIONS: The use of a wheeled walker resulted in significant decreases in disability, hypoxemia, and breathlessness during a 6-minute walk test. By reducing disability and breathlessness, a wheeled walker may improve quality of life in individuals with severe impairment in lung function.

Comparison of the Psychosocial Adjustment to Illness Scale-Self Report and clinical judgment in patients with chronic lung disease.

BACKGROUND: The study assessed the value of the Psychosocial Adjustment to Illness Scale-Self Report (PAIS-SR) in determining the psychosocial impact of impairment and disability in patients with chronic irreversible airflow limitation. METHODS: Fifty-six consecutive patients admitted to respiratory rehabilitation were studied. Psychosocial adjustment was measured with the PAIS-SR and was judged separately by two health-care workers on the rehabilitation team. Agreement between the PAIS-SR and the health-care workers was determined using the Kappa statistic. RESULTS: Four subjects did not complete the questionnaire. The data from 52 subjects were analyzed. The mean forced expired volume in one second (FEV1) was 1.2 +/- 0.4 L. The mean age was 66.4 +/- 9.0 years. There was good agreement between the individual assessment of each health-care worker (P < 0.001). There was good agreement between the score on the PAIS-SR and the clinical assessment by each of the health-care workers (P < 0.001). However, there were 10 subjects who identified severe adjustment difficulties that were not recognized by the health-care professionals. CONCLUSION: Although there was agreement between the PAIS-SR and clinical judgment in assessing the psychosocial impact impairment and disability in chronic airflow limitation, the PAIS-SR may identify individuals with adjustment difficulties not recognized by members of the health-care team. The results support the routine use of objective measures to assess the psychosocial impact of chronic airflow limitation.

Weber's law and resistive load detection.

The threshold of detection for added resistive loads to breathing (delta R50) was measured in 4 normal subjects at 4 different background resistances (Ro). Under normal conditions (Ro = 2.26 +/- 0.16 (SEM) cm H2O/L/s), the mean delta R50 was 0.53 +/- 0.17 cm H2O/L/s and the Weber fraction (delta R50/Ro) was 0.24 +/- 0.07. When the background resistance was increased, the threshold of detection increased proportionately, so that the Weber fraction did not change significantly. The background resistance was also decreased by having the subject breathe heliox. Although this did not result in a change in delta R50 (0.68 +/- 0.1 cm H2O/L/s), the Weber fraction increased to 0.49 +/- 0.08. These results show that although the Weber fraction is relatively constant over a wide range of background resistances, it rises sharply at low levels of background resistance, a finding that is similar to other sensory modalities.

The quantification of respiratory sensations by normal subjects.

The technique of open magnitude scaling was used in normal subjects to define the exponent (n) of Stevens; psychophysical power law for four respiratory variables: tidal volume (VT), inspiratory flow (V), ventilation (Ve), and frequency (f). Stevens' psychophysical law states that the perceived magnitude (psi) of a stimulus is related to the physical magnitude (phi) by a constant (k) and an exponent (n): psi = kappaphin. The mean value of n was for VT 1.14 plus or minus 0.08 (SEM), V 1.13 plus or minus 0.15, for Ve 1.28 plus or minus 0.11 and for f 1.04 plus or minus 0.15. These results show that these respiratory variables are judged with an expanded sensory scale. The similarity of exponents for VT and V leaves open the possibility tht both are sensed by the same neurophysiological mechanism. Further experiments on VT showed that both passive ventilation and chest vibration impaired the ability of subjects to accurately judge tidal volumes. Our results indicate that the sensation of volume is mediated by afferent information generated by receptors affected by respiratory muscle concentration.

Pulmonary mechanics during exercise in normal males.

A body plethysmograph adapted to contain the pedals of an electrically braked cycle ergometer was used to measure pulmonary mechanics during steady-state exercise in 12 normal male subjects aged 22-65 yr. During exercise there was a progressive increase in residual volume to 119% of the value at rest (P less than 0.01), but functional residual capacity and total lung capacity did not change. The maximum expiratory flow-volume (MEFV) curves did not change and flow rates during tidal breathing did not exceed the MEFV curve. Dynamic pulmonary compliance fell to 91.3% of the control value and static expiratory pulmonary compliance fell to 76.9% of the control value (P less than 0.05). Pulmonary resistance did not change during exercise. Transpulmonary pressure during tidal breathing was negative even at the highest power outputs. The fall in compliance may be due to an increase in pulmonary capillary blood volume. These results demonstrate the importance of measuring absolute thoracic gas volume and the elastic properties of the lung when comparing pulmonary mechanics at rest and during exercise.

Pulmonary mechanics during exercise in subjects with chronic airflow obstruction.

A body plethysmograph was used to measure pulmonary mechanics in six subjects with chronic airflow obstruction during steady states at rest and during exercise at 200 and 400 kpm . min-1. The mean forced expired volume in 1 s was 1.32 liters (39.2% predicted). The flow rates during tidal breathing reached the maximum expiratory flow-volume (MEFV) curve in all but one subject, and on exercise they all reached the MEFV curve. Total lung capacity did not change significantly, but functional residual capacity increased to 104% of the control value (P less than 0.05) and residual volume increased to 113.3% of the control value (P less than 0.02). The MEFV curves did not change and tidal flow rates in excess of th MEFV curve were not seen. Dynamic compliance fell with increasing exercise to 52.8% (P less than 0.01) and static expiratory pulmonary compliance to 90.2% of the control value. Transpulmonary pressures during tidal breathing when expiratory flow reached the MEFV curve increased to progressively higher values as the work load increased. At low work loads there were several subjects with negative transpulmonary pressure when maximum flow rates were present. In patients with chronic airflow obstruction, little change occurs during exercise in pulmonary mechanics; the tidal flow patterns are dominated by the expired flow-volume curve, which is not changed by exercise; maximum flow occurs in some patients when transpulmonary pressure is still negative.

Randomised controlled trial of weightlifting exercise in patients with chronic airflow limitation.

UNLABELLED: BACKGROUND PATIENTS: with chronic airflow obstruction are often limited by muscle fatigue and weakness. As exercise rehabilitation programmes have produced modest improvements at best a study was designed to determine whether specific muscle training techniques are helpful. METHODS: Thirty four patients with chronic airflow limitation (forced expiratory volume in one second (FEV1) 38% of predicted values) were stratified for FEV1 to vital capacity (VC) ratio less than 40% and arterial oxygen desaturation during exercise and randomised to a control or weightlifting training group. In the experimental group training was prescribed for upper and lower limb muscles as a percentage of the maximum weight that could be lifted once only. It was carried out three times a week for eight weeks. RESULTS: Three subjects dropped out of each group; results in the remaining 14 patients in each group were analysed. Adherence in the training group was 90%. In the trained subjects muscle strength and endurance time during cycling at 80% of maximum power output increased by 73% from 518 (SE69) to 898 (95) s, with control subjects showing no change (506 (86) s before training and 479 (89) s after training). No significant changes in maximum cycle ergometer exercise capacity or distance walked in six minutes were found in either group. Responses to a chronic respiratory questionnaire showed significant improvements in dyspnoea and mastery of daily living activities in the trained group. CONCLUSIONS: Weightlifting training may be successfully used in patients with chronic airflow limitation, with benefits in muscle strength, exercise endurance, and subjective responses to some of the demands of daily living.

Psychophysics of inspiratory muscle force.

The perceived magnitude of static inspiratory muscle pressure was studied in normal subjects using psychophysical techniques. The sensory magnitude of a range of inspiratory pressures increased as the magnitude of the pressure increased. When the duration of the inspiratory pressure was controlled, the sensory magnitude also increased as duration increased. The relationship can be described by a single psychophysical function, psi = k x P1.234 x t0.62, where psi is perceived magnitude, P is inspiratory pressure, t is duration, and k is a constant. Use of different muscle groups and changes in lung volume altered the perceived magnitude of static inspiratory pressures. When static inspiratory pressures were generated by the abdomen-diaphragm, the perceived magnitude was significantly greater (P less than 0.01) than when they were generated by the rib cage. When lung volume was increased, the perceived magnitude of pressure was reduced. The results show that the perceived magnitude of static inspiratory pressures is affected by the pressure itself, pressure duration, the muscles used, and the lung volume at which the pressure is generated.

Lung volume, closing volume, and gas exchange.

The effect of a voluntary reduction in lung volume on arterial O2 saturation (SaO2) was studied in 10 normal subjects aged 19-63 yr. SaO2 was measured by ear oximetry first during tidal breathing at functional residual capacity, and then during tidal breathing at 380 ml above residual volume. Tidal volume and breathing frequency were kept constant, and end-tidal CO2 partial pressure remained stable or fell in 9 out of 10 subjects. When lung volume was reduced, SaO2 fell by a mean of 1.5% (range 0-3%). Closing volume (CV) was measured by the N2-washout method (mean 0.89 liter, range 0.41-1.44). There was a close correlation between CV and the fall in SaO2 (r = 0.867, P = 0.001). Arterial and mixed venous CO2 were measured in one subject; the results indicated some fall in cardiac output following the lung volume change, but this accounted for less than half of the fall in SaO2. The relationship between CV and the lung volume at which tidal breathing occurs is an important determinant of pulmonary gas exchange through its effect on the matching of ventilation to perfusion.

Some physical signs in patients with chronic airflow obstruction.

Forty subjects with chronic airflow obstruction were examined independently by 2 observers, and their assessment of several physical signs was recorded. Spirometry and lung volumes were measured. Most of the signs studied correlated closely with the degree of airflow obstruction as assessed by the forced expiratory volume in one second. Certain signs also correlated closely with the degree of hyperinflation, the duration of symptoms, or the age of the subject. The agreement between observes in this study was good. Although all the signs are related in one way or another to the severity of airflow obstruction, some are due to large variations in intrathoracic pressure, some to hyperinflation and some, possibly, to changes in the shape of the chest and the action of the respiratory muscles. Hence, we suggest that these signs should not be regarded as inferior to tests of pulmonary function; physical examination and spirometry should be complementary.

Effect of background loads on the perception of added loads to breathing.

Using open-magnitude scaling, we compared the perceived magnitude of externally added resistive and elastic loads to breathing in normal subjects with that perceived when the background load (i.e., the minimum load of the circuit) was increased by the addition of either resistive or elastic loads of increasing magnitude. The study was carried out over four experimental sessions. After a control experiment (no added background load), the background load was increased by the addition of either a resistive or an elastic load for a duration of 3 min. The perceived magnitude of a further series of loads, proportionately increased, was then ascertained. This sequence was then repeated after a further increase in background. The results showed that the perceived magnitude of the load was closely related [mean r = 0.96 +/- 0.01 (SE)] to the magnitude of the physical stimulus expressed as the peak inspiratory pressure by a power function relationship in keeping with Stevens' law. After the increases in background resistance or elastance, there were no significant differences in either exponents or intercepts compared with basal conditions. There was no significant difference in the perceived magnitude of the loads after adaptation. At the smallest load, the perceived magnitude was less than expected from the control experiment. However, this reduction did not reach statistical significance. In the special senses, moderate-to-large stimuli show little change after adaptation, whereas small stimuli are reduced. Although not conclusive, we suggest that the relationship is similar with loaded breathing.