Influence of jacket tightness and pressure on raised lung volume forced expiratory maneuvers in infants

Abstract

While the use of the raised volume rapid thoraco-abdominal compression (RVRTC) technique has been shown to provide new insights into airway and pulmonary pathophysiology in infants, and appears to resemble the spirometric techniques used in older subjects, there is as yet no consensus regarding measurement procedures, which are known to vary considerably between laboratories (Gappa [1999] Pediatr Pulmonol 28:391-393). The aims of this study were to assess the effects of tightness of jacket fit, the efficiency with which pressure is transmitted from the jacket to the intrathoracic airways, and the effect of jacket pressure on parameters derived from the RVRTC technique. Paired forced expiratory maneuvers were performed in 20 infants with the jacket snugly or loosely wrapped around the infant's torso, and in a further 21 infants using "optimal" or a higher jacket pressure (P(j)) (1-2 kPa above "optimal" P(j)). When either a loosened jacket or a higher than "optimal" P(j) was used, forced expired flow at low lung volumes (FEF(75)) was significantly reduced by, on average, 8% and 7%, respectively. There were, however, minimal changes in forced vital capacity (FVC) or forced expired volume in 0.4 sec (FEV(0.4)). The observed changes may have been due to the increased pressure transmitted to the intrathoracic structures under these experimental conditions, and emphasize the need to assess optimal jacket pressure within each infant when using the RVRTC technique. In addition, when using a loosened jacket or a higher than "optimal" P(j), chest wall and upper airway reflexes such as glottic closure, peripheral airway closure, and negative flow dependence were more evident.

Comprehensive integrated spirometry using raised volume passive and forced expirations and multiple-breath nitrogen washout in infants

“…However, a true aPao reflective of the extent of lung inflation is crucial and can only be ascertained by occluding the airway for 0.20 sec after terminating the inflating airflow and before activating jacket inflation (Turner et al, 1995; Morris, 1999b). For this reason, the aPao is quite different from maintaining a ‘fixed’ inflating airflow of 12 or 15–20 L/min until a Pao plateau at 30 cm H 2 O and a zero flow are attained via a pressure relief valve before activating jacket inflation as reported in other studies (Feher et al, 1996; Jones et al, 2000; Goldstein et al, 2001; Lum et al, 2002a, 2002b, 2004; Ranganathan et al, 2002a, 2002b; Robin et al, 2004; ATS/ERS Statement, 2005). If the inflating airflow was high relative to the infant’s size, the Pao plateau at V 30 that an investigator observes in real time on the computer monitor screen may not have yet equilibrated with a ‘lower’ distal airways pressure.…”

“…In the FEFV curve, these flow transients often affected the FEF % between PF and FEF 50 and rarely the FEF 50–85 or FEF 90 (personal observations) (Figs. 4 and 9) (Morris, 1999b; Lum et al, 2002b; ATS/ERS Statement, 2005). Meanwhile, maximal expiratory flow was enhanced and flow limitation was achieved in the FEFV curves without startling the sleeping infant (Figs.…”

“…The generated FEFV curves had significant artificial flow transients. These transients would affect the reproducibility of the forced expiratory flows (FEF % ) far more than the volume-time (FEV t ) variables (Feher et al, 1996; Morris, 1999b; Beardsmore et al, 2001; Goldstein et al, 2001; Lum et al, 2002a, 2002b, 2006; Ranganathan et al, 2002b; ATS/ERS Statement, 2005; Merkus et al, 2005; Modl and Eber, 2005; Stocks, 2006). …”

“…Raised volume RTC generates the forced vital capacity (FVC) and forced expiratory flow-volume (FEFV) curves in which flow limitation is most often achieved. The jacket placement and the need to repeat the raised volume RTC using increasing jacket pressures (Pj) until flow limitation is achieved may alter lung mechanics or influence other measurements (Mead, 1980; Turner et al, 1995; Feher et al, 1996; Morris, 1999b; Castile et al, 2000, 2004; Jones et al, 2000; Sly et al, 2000; Beardsmore et al, 2001; Goldstein et al, 2001; Lum et al, 2001, 2002a, 2002b, 2004b, 2006; Hoo et al, 2002, 2004; Ranganathan et al, 2002a, 2002b; ATS/ERS Statement, 2005; Stocks, 2006; Linnane et al, 2008; Loland and Bisgaard, 2008). Attempts were made to assess total lung capacity (TLC) from measurements of crying vital capacity and residual volume (RV) but the (dynamic) (FRC dyn ) functional residual capacity (FRC) has been the lung volume most routinely and reliably measured.…”

Relative Ability of Full and Partial Forced Expiratory Maneuvers to Identify Diminished Airway Function in Infants with Cystic Fibrosis

“…shortly after birth are at increased risk of diminished lung funcAs yet, the RVRTC remains an unstandardized technique tion and subsequent respiratory morbidity in later childhood with respect to equipment, method (24,50), or analysis (23), (58)(59)(60). Thus, early impairment of airway function may have making comparisons of data collected in different centers exlong-term consequences in a disease in which the majority of tremely difficult (49).…”