Lung volumes, chest wall configuration, and pattern of breathing in microgravity

We studied the changes in functional residual capacity (FRC), thoracoabdominal volume (Vw), and chest wall configuration in five normal subjects seated in an aircraft flying parabolic trajectories resulting in 20-s periods of microgravity. We measured vital capacity (VC), inspiratory capacity, and tidal volume by integrating airflow at the mouth and changes in rib cage and abdominal volume (delta Vrc and delta Vab, respectively, where delta Vrc + delta Vab = delta Vw) using induction plethysmography. During microgravity (0 Gz) FRC decreased by 413 +/- 70 (SE) ml and VC by 0.37 liter. The decrease in Vw did not differ from that in FRC and was entirely the result of reduction of Vab, the Vrc showing no significant change. During tidal breathing the abdominal contribution (delta Vab/delta Vw) increased from 0.39 +/- 0.08 at 1 Gz to 0.57 +/- 0.08 at 0 Gz. During brief periods of hypergravity (approximately 1.8 Gz) all changes were opposite in sign and relatively smaller. Limited data during "roller coaster" flight patterns suggested that, in contrast to configurational changes, the temporal pattern of breathing was uninfluenced by changes in Gz. We conclude that at the onset of weightlessness there are substantial changes in lung volume and thoracoabdominal configuration. Abdominal contribution to tidal excursions increases but the temporal pattern of breathing is unchanged.     

Lung volumes during +Gz acceleration and the effects of positive pressure breathing and chest counter-pressure

The advent of agile fast jet aircraft has initiated the research and development of enhanced systems to protect man against high +Gz acceleration. As part of such an enhanced system, the breathing of a pressurised gas mixture under +Gz is likely to become routine during the next decade in many of the world's air forces. This procedure, termed positive pressure breathing for G protection (PBG), typically uses breathing pressures of up to 65 mmHg in order to elevate intra-thoracic arterial blood pressure. In this way the fall in head level arterial blood pressure under +Gz acceleration is minimised. Consciousness is therefore preserved, with the aim of reducing the incidence of G Induced Loss of Consciousness (G-LOC). The aim of the research reported here is to assess the viability of the experimental technique and to gather preliminary data on the changes in lung volume subdivisions under PBG (specifically VC, ERV and the VC/ERV ratio).     

Sensation of inspired volumes and pressures in professional wind instrument players

Previous studies have failed to show consistent differences in pulmonary function between wind instrument musicians and normal controls. In this study, respiratory sensation was assessed in 13 professional wind instrument players and 13 age-matched controls. Psychophysical techniques were used to assess magnitude estimation and reproduction of lung volumes and inspiratory pressures. The exponent for volume magnitude estimation was not different in musicians and controls (1.17 +/- 0.11 vs. 1.16 +/- 0.11), but volume reproduction was more accurate in musicians. The mean exponent for pressure magnitude estimation was 1.34 +/- 0.14 and 1.06 +/- 0.09 (P = 0.057) in musicians and controls, respectively. There was no difference between groups for absolute or constant error for pressure reproduction. Professional wind instrument players appear to have some inherent or acquired differences in respiratory perception and ventilatory neuromuscular control compared with other normal subjects.     

Control of breathing at elevated lung volumes in anesthetized cats

We monitored the steady-state ventilatory responses of anesthetized cats to increases in lung volume produced by expiratory threshold loads (ETL) to study the roles of peripheral and central neural mechanisms in controlling respiration at elevated lung volumes. Application of an ETL of 5 cmH2O produced a significant decrease in respiratory frequency (-18%) but no change in minute ventilation (VE) due to a significant increase in tidal volume (VT) (19.3%). The drop in frequency was due solely to an increase in expiratory duration. ETL of 10 cmH2O significantly reduced VE (-17.5%) for the same reason. VT was maintained or increased at elevated lung volumes due to both an increase in the rate of rise of phrenic activity and a maintenance of inspiratory duration (TI) despite increases in both chemical drive and pulmonary stretch receptor (PSR) activity. No PSR adapted completely to the maintained change in lung volume. The sensitivity of the inspiratory off-switch mechanism to increases in lung volume, given by the reciprocal of the VT-TI relationship, decreased significantly during breathing on ETL. The results are consistent with the hypothesis that central habituation, not just peripheral adaptation of PSR, determines breathing pattern at elevated lung volumes.     

Lung volumes during low-intensity steady-state cycling

The use of inspiratory capacity (IC) to estimate end-expiratory lung volume (EELV) during exercise has been questioned because of the assumption of constant total lung capacity (TLC). To investigate lung volumes during low-intensity steady-state cycling, we measured EELV by the open-circuit N2 washout method (MR-1, currently Sensormedics 2100) in eight healthy men while at rest and during unloaded and 60-W cycling. TLC was calculated by adding EELV and IC. Measurement variation of TLC was 142 ml at rest, 121 ml during unloaded cycling, and 158 ml during 60-W cycling. TLC did not differ significantly among the three conditions studied. EELV decreased during unloaded (P less than 0.002) and 60-W cycling (P less than 0.001) compared with rest. End-inspiratory lung volume increased only during 60-W cycling (P = 0.03). The decrease in EELV accounted for 100% of the increase in tidal volume during unloaded cycling. Although minute ventilation was similar in the subjects during unloaded cycling, we noted that breathing patterns varied among the subjects. The increase in respiratory frequency was negatively correlated to the change in tidal volume (R2 = 0.54, P = 0.038) and to the change in end-inspiratory lung volume (R2 = 0.68, P = 0.012). We conclude that TLC does not differ significantly during low-intensity steady-state cycling and that use of IC to estimate changes in EELV is appropriate.     

Lung volumes and respiratory mechanics in elastase-induced emphysema in mice

Absolute lung volumes such as functional residual capacity, residual volume (RV), and total lung capacity (TLC) are used to characterize emphysema in patients, whereas in animal models of emphysema, the mechanical parameters are invariably obtained as a function of transrespiratory pressure (Prs). The aim of the present study was to establish a link between the mechanical parameters including tissue elastance (H) and airway resistance (Raw), and thoracic gas volume (TGV) in addition to Prs in a mouse model of emphysema. Using low-frequency forced oscillations during slow deep inflation, we tracked H and Raw as functions of TGV and Prs in normal mice and mice treated with porcine pancreatic elastase. The presence of emphysema was confirmed by morphometric analysis of histological slices. The treatment resulted in an increase in TGV by 51 and 44% and a decrease in H by 57 and 27%, respectively, at 0 and 20 cmH(2)O of Prs. The Raw did not differ between the groups at any value of Prs, but it was significantly higher in the treated mice at comparable TGV values. In further groups of mice, tracheal sounds were recorded during inflations from RV to TLC. All lung volumes but RV were significantly elevated in the treated mice, whereas the numbers and size distributions of inspiratory crackles were not different, suggesting that the airways were not affected by the elastase treatment. These findings emphasize the importance of absolute lung volumes and indicate that tissue destruction was not associated with airway dysfunction in this mouse model of emphysema.     

Lung resistance and elastance in spontaneously breathing preterm infants: effects of breathing pattern and demographics

Reported values of lung resistance(RL) and elastance (EL) in spontaneouslybreathing preterm neonates vary widely. We hypothesized that thisvariability in lung properties can be largely explained by both inter-and intrasubject variability in breathing pattern and demographics.Thirty-three neonates receiving nasal continuous positive airwaypressure [weight 606-1,792 g, gestational age (GA) of25-33 wk, 2-49 days old] were studied. Transpulmonary pressure was measured by esophageal manometry and airway flow by facemask pneumotachography. Breath-to-breath changes in RL andEL in each infant were estimated by Fourier analysis ofimpedance (Z) and by multiple linear regression (MLR).RL_MLR (RL_MLR = 0.85 × RL_Z 0.43; r² = 0.95) and EL_MLR(EL_MLR = 0.97 × EL_Z + 8.4; r² = 0.98) werehighly correlated to RL_Z andEL_Z, respectively. Both RL(mean ± SD; RL_Z = 70 ± 38, RL_MLR = 59 ± 36 cmH₂O · s · l¹)and EL (EL_Z = 434 ± 212, EL_MLR = 436 ± 210 cmH₂O/l)exhibited wide intra- and intersubject variability.Regardless of computation method, RL was found to decreaseas a function of weight, age, respiratory rate (RR), and tidal volume(VT) whereas it increased as a function ofRR · VT and inspiratory-to-expiratorytime ratio (TI/TE). EL decreasedwith increasing weight, age, VT and female gender andincreased as RR and TI/TE increased. Weconclude that accounting for the effects of breathing patternvariability and demographic parameters on estimates of RLand EL is essential if they are to be of clinical value.Multivariate statistical models of RL and ELmay facilitate the interpretation of lung mechanics measurements inspontaneously breathing infants.

     

Sprint patterns in rugby union players during competition

The purpose of this study was to characterize sprint patterns of rugby union players during competition. Velocity profiles (60 m) of 28 rugby players were initially established in testing from standing, walking, jogging, and striding starts. During competition, the individual sprinting patterns of 17 rugby players were determined from video by using the individual velocity profiles. Forwards commenced sprints from a standing start most frequently (41%), whereas backs sprinted from standing (29%), walking (29%), jogging (29%), and occasionally striding (13%) starts. Forwards and backs achieved speeds in excess of 90% maximal velocity (Vmax) on 5 +/- 4 and 9 +/- 4 occasions ( approximately 50% of the sprints performed), respectively, during competition. The higher frequency of sprinting for the backs compared with the forwards highlights the importance of speed training for this positional group. The similar relative distribution of velocities achieved during competition for forwards and backs suggests both positional groups should train acceleration and Vmax qualities. The backs should have a higher total volume of sprint training. Sprinting efforts should be performed from a variety of starting speeds to mimic the movement patterns of competition.