Biomedical subjects

R H Habib

Publications and source records attributed to R H Habib.

21 records · Page 2Linked to original sources

PubMed1991

Moment analysis of a multibreath nitrogen washout based on an alveolar gas dilution number.

A common method for analyzing a multibreath nitrogen washout (MBNW) is to perform moment analysis and derive the mean dilution number (MDN). A homogeneously mixed alveolar space with zero series dead space (VD = 0) will always result in a MDN = 1, regardless of breathing pattern. A higher MDN implies more inhomogeneity. But, if VD greater than 0, the MDN can become sensitive (artificially high) to VD/VT ratios. We present an alveolar-based mean dilution number (AMDN) that uses the cumulative expired alveolar volume. Unlike the MDN, the AMDN for a homogeneously mixed alveolar space is unity, regardless of VD or VT, and hence should be a more appropriate index of inhomogeneity at the alveolar level. Two sets of experiments were used to compare the AMDN with the MDN. First, a MBNW was performed by five healthy subjects at spontaneous VD/VT and at a low VD/VT achieved by a controlled increase in VT. Here, the MDN decreased from 1.98 +/- 0.1 to 1.79 +/- 0.06, whereas the AMDN was essentially unchanged (1.42 +/- 0.04 to 1.38 +/- 0.06). Second, MBNW values from seven healthy subjects, five with cystic fibrosis, and 10 asthmatic subjects (before and after bronchodilation) were analyzed. Compared with the MDN, the AMDN showed a significantly wider separation between clinical groups. Also, the AMDN demonstrated an increased variability within both sick groups versus a decrease in the healthy group. We conclude that the AMDN is superior to the MDN because of its decreased sensitivity to breathing pattern but increased sensitivity to degree of disease.

Adolescent↗

PubMed1990

Respiratory impedance and multibreath N2 washout in healthy, asthmatic, and cystic fibrosis subjects.

We measured forced expiratory volume in 1 s (FEV1), respiratory impedance (Zrs) from 4 to 60 Hz, and a multibreath N2 washout (MBNW) in 6 normal, 10 asthmatic, and 5 cystic fibrosis (CF) subjects. The MBNW were characterized by the mean dilution number (MDN) derived by a moment analysis. The Zrs spectra were characterized by the minimum resistance (Rmin), the drop in resistance (Rdrop) from 4 Hz to Rmin, and the first resonance frequency (Fr1). Measurements were repeated after bronchodilation in three normal and all asthmatic subjects. Before bronchodilation, six of the asthmatic subjects showed close to normal FEV1. The Zrs in the normal subjects showed low Rmin (1.9 +/- 0.7 cmH2O.l-1.s), Rdrop (0.4 +/- 0.4), and Fr1 (10 +/- 2 Hz). Four of the mildly obstructed asthmatic subjects had normal Zrs but elevated MDNs (i.e., abnormal ventilation distribution). The other six asthmatic subjects had significantly elevated Rmin (4.1 +/- 0.8), Rdrop (6.3 +/- 5.8), and Fr1 (34 +/- 0.4 Hz) and elevated MDNs. The CF patients had elevated Zrs features and MDNs. After bronchodilation, no changes in FEV1, MDN, or Zrs occurred in the normal subjects. All asthmatic subjects showed increased FEV1 and decreased MDN, but the Zrs was unaltered in the four asthmatic subjects whose base-line Zrs was normal. For the other six asthmatic subjects, there were large decreases in the Rmin, Rdrop, and Fr1. Finally, there was a poor correlation between the MDN and the Zrs features but high correlation between the Zrs features alone. These results imply that significant nonuniform peripheral airway obstruction can exist such that ventilation distribution is abnormal but Zrs from 4 to 60 Hz is not. Abnormalities in Zrs from 4 to 60 Hz occur only after significant overall obstruction in the peripheral and more central airways. Combining Zrs and the MBNW may permit us to infer whether the disease is predominantly in the lung periphery or in the more central airways.

Adolescent↗

PubMedDate not supplied

Serial distribution of airway diameters from input impedance and computed tomography.

Indirect measures of airway diameter such as respiratory system input impedance (Zin) have been widely used to infer or quantify bronchoconstriction, or bronchodilation. One such measure, Zin above 100 Hz has been shown to be primarily influenced by airway geometry and airway walls but not by lung and chest wall tissues. We used a recently developed method based on a complex asymmetrically branched network of tubes with nonrigid walls to analyze Zin from 100 to 2,000 Hz in control and bronchoconstricted (histamine injection) dogs. The resulting estimates of airway diameters indicated that peripheral airways were constricted far more (approximately 30% of their control diameters) than central airways (i.e., 0% in the trachea). Separate measurements of changes in airway diameters were made in an excised dog lung using high resolution computed tomography. The observed changes in airway diameter between lung volumes of total lung capacity (TLC) and functional residual capacity (FRC) were quantitatively consistent with those obtained from Zin data in our control dogs at FRC. We conclude that this systems identification method can be used to estimate the distribution of airway diameters from Zin.

Airway Resistance↗