American journal of respiratory and critical care medicine
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Am. J. Respir. Crit. Care Med. · Jan 1997
Qualitative aspects of exertional breathlessness in chronic airflow limitation: pathophysiologic mechanisms.
We compared qualitative aspects of the sensory experience of exertional breathlessness in normal subjects and in patients with chronic airflow limitation (CAL) and sought a physiologic rationale for these. Twelve patients (66 +/- 2 yr of age, mean +/- SEM) with severe CAL (FEV1 = 37 +/- 5% predicted) and 12 age-matched normal subjects (FEV1 = 103 +/- 5% predicted) were studied. Perceived inspiratory difficulty (BorgIN), inspiratory effort (esophageal pressure expressed as a fraction of maximal esophageal pressure at isovolume [Pes/PImax]), breathing pattern, and operational lung volumes (end-expiratory/inspiratory lung volumes [EELV/EILV]) were measured during symptom-limited incremental cycle exercise testing and compared at a standard VO2 of 50% predicted maximum in normal subjects and in patients with CAL. ⋯ Stepwise regression analysis identified the ratio of Pes/PImax to VT/predicted VC as the strongest correlate of standardized BorgIN (n = 24, r = 0.86, p < 0.001). This latter measurement, which reflects the relationship between effort and ventilatory output, correlated strongly with dynamic EELV/TLC at isotime (r = 0.78, p < 0.001). In conclusion, the qualitatively discrete respiratory sensations of exertional inspiratory difficulty peculiar to patients with CAL may have their origins in thoracic hyperinflation and the resultant disparity between inspiratory effort and ventilatory output.
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Am. J. Respir. Crit. Care Med. · Jan 1997
Comparative StudyBroxaterol increases force output of fatigued canine diaphragm more than salbutamol.
We previously demonstrated that broxaterol enhanced recovery of fatigued canine diaphragm. The aim of this study was to compare the inotropic effects of salbutamol and broxaterol on fatigued canine diaphragm. Low-frequency fatigue was induced in 14 mongrel dogs by electrophrenic stimulation, which was continued until transdiaphragmatic pressure (Pdi) at 20 Hz was reduced by 50% or for 1 h. ⋯ In contrast, salbutamol did not alter Pdi at 20 Hz. Neither drug affected Pdi at 100 Hz. We conclude that broxaterol promoted recovery of low-frequency fatigue of the canine diaphragm in vivo in a dose-dependent manner, whereas salbutamol only minimally improved force production by the fatigued diaphragm.
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Am. J. Respir. Crit. Care Med. · Jan 1997
Comparative StudyRacial differences in sleep-disordered breathing in African-Americans and Caucasians.
In this case-control family study of sleep-disordered breathing (SDB), we describe the distributions of SDB and SDB risk factors in African-Americans and Caucasians. A total of 225 African-Americans and 622 Caucasians, ages 2 to 86 yr, recruited as members of families with an individual with known sleep apnea (85 index families) or as members of neighborhood control families (63 families) were studied with an overnight home sleep-study, questionnaires, and physical measurements. A subsample underwent cephalometry. ⋯ In subjects < or = 25 yr, RDI level and IAA prevalence were higher in African-Americans (odds ratio, adjusted for obesity, sex, proband sampling, and familial clustering, 1.88, 1.03 to 3.52, 95% CI). In this age group, racial differences also were observed in the relationship between RDI and age (p < 0.001 for the RDI-age interaction). This suggests that young African-Americans may be at increased risk for sleep apnea.
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Am. J. Respir. Crit. Care Med. · Jan 1997
Chronic, episodic, reversible airway obstruction after viral bronchiolitis in rats.
Viral bronchiolitis in human infants has been associated with persistent airway abnormalities, but not proven as a cause. Previously we observed some adult rats had airway obstruction and hyperresponsiveness following bronchiolitis at an early age. The purpose of this study was to determine, via serial measurements of lung mechanics, whether the postbronchiolitis airway obstruction was episodic or continuous, and to determine the magnitude and duration of glucocorticoid effects. ⋯ The virus group had higher lung resistance (p = 0.03) and lower dynamic compliance (p = 0.005) than control rats, with airway obstruction occurring in an episodic pattern. Dexamethasone treatment had a transient effect in postbronchiolitis rats; lung resistance normalized in Week 15 (p = 0.006), then returned to pretreatment levels by Weeks 16-18. We conclude that viral bronchiolitis in rats can result in a chronic syndrome of intermittent, reversible airway obstruction which has multiple parallels with human asthma over a prolonged time period.