Submitted on October 8, 2002
Accepted on January 4, 2003
Spectral Characteristics of Tidal Flows in Spontaneously Breathing Preterm Infants: Airway Opening versus Chest Wall Measurements
Robert H Habib1*, Kee H Pyon2, Sherry E Courtney2, and Zubair H Aghai2
1 Mercy Children's Hospital at St. Vincent Mercy Medical Center, Toledo, OH, USA; Department of Pediatrics, Medical College of Ohio, Toledo, OH, USA
2 Department of Pediatrics, Cooper Hospital and Robert Wood Johnson Medical School, Camden, NJ, USA
* To whom correspondence should be addressed. E-mail: Robert_Habib{at}mhsnr.org.
We aimed to characterize the harmonic content of tidal flows in spontaneously breathing very low birth weight (VLBW) infants, and to determine if equivalent tidal flow spectral information is available from mouth (proximal) and chest wall (distal) measurements. We measured tidal flows directly at the mouth (facemask and pneumotachograph; P-tach) and indirectly via chest wall tidal excursions (respiratory inductance plethysmography; RIP) in sixteen spontaneously breathing VLBW infants (1,114±230 grams; gestational age: 28±2 weeks). Next, for each, we computed two spectral shape indexes: 1) harmonic distortion (kd) defines the extent to which flows deviated from a single sine wave, and 2) the exponent of the power law (s) describing the spectral energy versus frequency. P-tach and RIP flow spectra exhibited similar power law functional forms consistently in all infants. Also, proximal [SP-tach=3.73 ± 0.23 (95% CI), kd,P-tach=38.8 ± 4.6%] and distal [SRIP=3.51 ± 0.30), kd,RIP = 42.8±4.8%] indexes were of comparable value and were highly correlated [SRIP= 1.17*SP-tach+0.85; r2=0.81; kd,RIP=0.90*kd,P-tach+8.0; r2=0.76]. The corresponding TPTEF/TE were higher than in older infants at 0.62±0.08. The obtained s and kd values are similar to those reported in older/larger chronic lung disease infants, yet appreciably lower than for 1 month old healthy infants of closer age/size. This indicated increased complexity of tidal flows in VLBW babies. Importantly, we demonstrated that equivalent flow spectral information may be obtained from mouth and chest wall tidal measurements. These are desirable since they avoid artificial effects of the facemask and leaks around it, they do not interfere with ventilatory support delivery and hence facilitate longer measurements which are useful in assessment of control of breathing.
